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Sample records for water splitting cycle

  1. Solar High Temperature Water-Splitting Cycle with Quantum Boost

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Robin [SAIC; Davenport, Roger [SAIC; Talbot, Jan [UCSD; Herz, Richard [UCSD; Genders, David [Electrosynthesis Co.; Symons, Peter [Electrosynthesis Co.; Brown, Lloyd [TChemE

    2014-04-25

    A sulfur family chemical cycle having ammonia as the working fluid and reagent was developed as a cost-effective and efficient hydrogen production technology based on a solar thermochemical water-splitting cycle. The sulfur ammonia (SA) cycle is a renewable and sustainable process that is unique in that it is an all-fluid cycle (i.e., with no solids handling). It uses a moderate temperature solar plant with the solar receiver operating at 800°C. All electricity needed is generated internally from recovered heat. The plant would operate continuously with low cost storage and it is a good potential solar thermochemical hydrogen production cycle for reaching the DOE cost goals. Two approaches were considered for the hydrogen production step of the SA cycle: (1) photocatalytic, and (2) electrolytic oxidation of ammonium sulfite to ammonium sulfate in aqueous solutions. Also, two sub-cycles were evaluated for the oxygen evolution side of the SA cycle: (1) zinc sulfate/zinc oxide, and (2) potassium sulfate/potassium pyrosulfate. The laboratory testing and optimization of all the process steps for each version of the SA cycle were proven in the laboratory or have been fully demonstrated by others, but further optimization is still possible and needed. The solar configuration evolved to a 50 MW(thermal) central receiver system with a North heliostat field, a cavity receiver, and NaCl molten salt storage to allow continuous operation. The H2A economic model was used to optimize and trade-off SA cycle configurations. Parametric studies of chemical plant performance have indicated process efficiencies of ~20%. Although the current process efficiency is technically acceptable, an increased efficiency is needed if the DOE cost targets are to be reached. There are two interrelated areas in which there is the potential for significant efficiency improvements: electrolysis cell voltage and excessive water vaporization. Methods to significantly reduce water evaporation are

  2. Entropy Analysis of Solar Two-Step Thermochemical Cycles for Water and Carbon Dioxide Splitting

    Directory of Open Access Journals (Sweden)

    Matthias Lange

    2016-01-01

    Full Text Available The present study provides a thermodynamic analysis of solar thermochemical cycles for splitting of H2O or CO2. Such cycles, powered by concentrated solar energy, have the potential to produce fuels in a sustainable way. We extend a previous study on the thermodynamics of water splitting by also taking into account CO2 splitting and the influence of the solar absorption efficiency. Based on this purely thermodynamic approach, efficiency trends are discussed. The comprehensive and vivid representation in T-S diagrams provides researchers in this field with the required theoretical background to improve process development. Furthermore, results about the required entropy change in the used redox materials can be used as a guideline for material developers. The results show that CO2 splitting is advantageous at higher temperature levels, while water splitting is more feasible at lower temperature levels, as it benefits from a great entropy change during the splitting step.

  3. Solar Hydrogen Production via a Samarium Oxide-Based Thermochemical Water Splitting Cycle

    Directory of Open Access Journals (Sweden)

    Rahul Bhosale

    2016-04-01

    Full Text Available The computational thermodynamic analysis of a samarium oxide-based two-step solar thermochemical water splitting cycle is reported. The analysis is performed using HSC chemistry software and databases. The first (solar-based step drives the thermal reduction of Sm2O3 into Sm and O2. The second (non-solar step corresponds to the production of H2 via a water splitting reaction and the oxidation of Sm to Sm2O3. The equilibrium thermodynamic compositions related to the thermal reduction and water splitting steps are determined. The effect of oxygen partial pressure in the inert flushing gas on the thermal reduction temperature (TH is examined. An analysis based on the second law of thermodynamics is performed to determine the cycle efficiency (ηcycle and solar-to-fuel energy conversion efficiency (ηsolar−to−fuel attainable with and without heat recuperation. The results indicate that ηcycle and ηsolar−to−fuel both increase with decreasing TH, due to the reduction in oxygen partial pressure in the inert flushing gas. Furthermore, the recuperation of heat for the operation of the cycle significantly improves the solar reactor efficiency. For instance, in the case where TH = 2280 K, ηcycle = 24.4% and ηsolar−to−fuel = 29.5% (without heat recuperation, while ηcycle = 31.3% and ηsolar−to−fuel = 37.8% (with 40% heat recuperation.

  4. Solar Hydrogen Production via a Samarium Oxide-Based Thermochemical Water Splitting Cycle

    OpenAIRE

    Rahul Bhosale; Anand Kumar; Fares AlMomani; Ujjal Ghosh; Mohammad Saad Anis; Konstantinos Kakosimos; Rajesh Shende; Marc A. Rosen

    2016-01-01

    The computational thermodynamic analysis of a samarium oxide-based two-step solar thermochemical water splitting cycle is reported. The analysis is performed using HSC chemistry software and databases. The first (solar-based) step drives the thermal reduction of Sm2O3 into Sm and O2. The second (non-solar) step corresponds to the production of H2 via a water splitting reaction and the oxidation of Sm to Sm2O3. The equilibrium thermodynamic compositions related to the thermal reduction and wat...

  5. Spinel Metal Oxide-Alkali Carbonate-Based, Low-Temperature Thermochemical Cycles for Water Splitting and CO_2 Reduction

    OpenAIRE

    Xu, Bingjun; Bhawe, Yashodhan; Davis, Mark E.

    2013-01-01

    A manganese oxide-based, thermochemical cycle for water splitting below 1000 °C has recently been reported. The cycle involves the shuttling of Na+ into and out of manganese oxides via the consumption and formation of sodium carbonate, respectively. Here, we explore the combinations of three spinel metal oxides and three alkali carbonates in thermochemical cycles for water splitting and CO_2 reduction. Hydrogen evolution and CO_2 reduction reactions of metal oxides with a given alkali carbona...

  6. A hybrid water-splitting cycle using copper sulfate and mixed copper oxides

    Science.gov (United States)

    Schreiber, J. D.; Remick, R. J.; Foh, S. E.; Mazumder, M. M.

    1980-01-01

    The Institute of Gas Technology has derived and developed a hybrid thermochemical water-splitting cycle based on mixed copper oxides and copper sulfate. Similar to other metal oxide-metal sulfate cycles that use a metal oxide to 'concentrate' electrolytically produced sulfuric acid, this cycle offers the advantage of producing oxygen (to be vented) and sulfur dioxide (to be recycled) in separate steps, thereby eliminating the need of another step to separate these gases. The conceptual process flow-sheet efficiency of the cycle promises to exceed 50%. It has been completely demonstrated in the laboratory with recycled materials. Research in the electrochemical oxidation of sulfur dioxide to produce sulfuric acid and hydrogen performed at IGT indicates that the cell performance goals of 200 mA/sq cm at 0.5 V will be attainable using relatively inexpensive electrode materials.

  7. Vapor compression CuCl heat pump integrated with a thermochemical water splitting cycle

    Energy Technology Data Exchange (ETDEWEB)

    Zamfirescu, C., E-mail: Calin.Zamfirescu@uoit.ca [Faculty of Engineering and Applied Science, University of Ontario Institute of Technology (UOIT), 2000 Simcoe Street North, Oshawa, ON, Canada L1H 74K (Canada); Naterer, G.F., E-mail: Greg.Naterer@uoit.ca [Faculty of Engineering and Applied Science, University of Ontario Institute of Technology (UOIT), 2000 Simcoe Street North, Oshawa, ON, Canada L1H 74K (Canada); Dincer, I., E-mail: Ibrahim.Dincer@uoit.ca [Faculty of Engineering and Applied Science, University of Ontario Institute of Technology (UOIT), 2000 Simcoe Street North, Oshawa, ON, Canada L1H 74K (Canada)

    2011-01-10

    In this paper, the feasibility of using cuprous chloride (CuCl) as a working fluid in a new high temperature heat pump with vapor compression is analyzed. The heat pump is integrated with a copper-chlorine (Cu-Cl) thermochemical water splitting cycle for internal heat recovery, temperature upgrades and hydrogen production. The minimum temperature of heat supply necessary for driving the water splitting cycle can be lowered because the heat pump increases the working fluid temperature from 755 K up to {approx}950 K, at a high COP of {approx}6.5. Based on measured data available in past literature, the authors have determined the T-s diagram of CuCl, which is then used for the thermodynamic modeling of the cycle. In the heat pump cycle, molten CuCl is flashed in a vacuum where the vapor quality reaches {approx}2.5%, and then it is boiled to produce saturated vapor. The vapor is then compressed in stages (with inter-cooling and heat recovery), and condensed in a direct contact heat exchanger to transfer heat at a higher temperature. The heat pump is then integrated with a copper-chlorine water splitting plant. The heat pump evaporator is connected thermally with the hydrogen production reactor of the water splitting plant, which performs an exothermic reaction that generates heat at 760 K. Additional source heat is obtained from heat recovery from the hot reaction products of the oxy-decomposer. The heat pump transfers heat at {approx}950 K to the oxy-decomposer to drive its endothermic chemical reaction. It is shown that the heat required at the heat pump source can be obtained completely from internal heat recovery within the plant. First and second law analyses and a parametric study are performed for the proposed system to study the influence of the compressor's isentropic efficiency and temperature levels on the heat pump's COP. Two new indicators are presented: one represents the heat recovery ratio (the ratio between the thermal energy obtained by

  8. Solar Metal Sulfate-Ammonia Based Thermochemical Water Splitting Cycle for Hydrogen Production

    Science.gov (United States)

    Huang, Cunping (Inventor); T-Raissi, Ali (Inventor); Muradov, Nazim (Inventor)

    2014-01-01

    Two classes of hybrid/thermochemical water splitting processes for the production of hydrogen and oxygen have been proposed based on (1) metal sulfate-ammonia cycles (2) metal pyrosulfate-ammonia cycles. Methods and systems for a metal sulfate MSO.sub.4--NH3 cycle for producing H2 and O2 from a closed system including feeding an aqueous (NH3)(4)SO3 solution into a photoctalytic reactor to oxidize the aqueous (NH3)(4)SO3 into aqueous (NH3)(2)SO4 and reduce water to hydrogen, mixing the resulting aqueous (NH3)(2)SO4 with metal oxide (e.g. ZnO) to form a slurry, heating the slurry of aqueous (NH4)(2)SO4 and ZnO(s) in the low temperature reactor to produce a gaseous mixture of NH3 and H2O and solid ZnSO4(s), heating solid ZnSO4 at a high temperature reactor to produce a gaseous mixture of SO2 and O2 and solid product ZnO, mixing the gaseous mixture of SO2 and O2 with an NH3 and H2O stream in an absorber to form aqueous (NH4)(2)SO3 solution and separate O2 for aqueous solution, recycling the resultant solution back to the photoreactor and sending ZnO to mix with aqueous (NH4)(2)SO4 solution to close the water splitting cycle wherein gaseous H2 and O2 are the only products output from the closed ZnSO4--NH3 cycle.

  9. Thermochemical water-splitting cycle, bench-scale investigations and process engineering. Annual report, October 1, 1978-September 30, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Caprioglio, G.; McCorkle, K.H.; Besenbruch, G.E.; Rode, J.S.

    1980-03-01

    A program to investigate thermochemical water splitting has been under way at General Atomic Company (GA) since October 1972. This document is an annual progress report of Department of Energy (DOE) sponsored process development work on the GA sulfur-iodine thermochemical water splitting cycle. The work consisted of laboratory bench-scale investigations, demonstration of the process in a closed-loop cycle demonstrator, and process engineering design studies. A bench-scale system, consisting of three subunits, has been designed to study the cycle under continuous flow conditions. The designs of subunit I, which models the main solution reaction and product separation, and subunit II, which models the concentration and decomposition of sulfuric acid, were presented in an earlier annual report. The design of subunit III, which models the purification and decomposition of hydrogen iodide, is given in this report. Progress on the installation and operation of subunits I and II is described. A closed-loop cycle demonstrator was installed and operated based on a DOE request. Operation of the GA sulfur-iodine cycle was demonstrated in this system under recycle conditions. The process engineering addresses the flowsheet design of a large-scale production process consisting of four chemical sections (I through IV) and one helium heat supply section (V). The completed designs for sections I through V are presented. The thermal efficiency of the process calculated from the present flowsheet is 47%.

  10. Initial Screening of Thermochemical Water-Splitting Cycles for High Efficiency Generation of Hydrogen Fuels Using Nuclear Power

    Energy Technology Data Exchange (ETDEWEB)

    Brown, L.C.; Funk, J.F.; Showalter, S.K.

    1999-12-15

    OAK B188 Initial Screening of Thermochemical Water-Splitting Cycles for High Efficiency Generation of Hydrogen Fuels Using Nuclear Power There is currently no large scale, cost-effective, environmentally attractive hydrogen production process, nor is such a process available for commercialization. Hydrogen is a promising energy carrier, which potentially could replace the fossil fuels used in the transportation sector of our economy. Fossil fuels are polluting and carbon dioxide emissions from their combustion are thought to be responsible for global warming. The purpose of this work is to determine the potential for efficient, cost-effective, large-scale production of hydrogen utilizing high temperature heat from an advanced nuclear power station. Almost 800 literature references were located which pertain to thermochemical production of hydrogen from water and over 100 thermochemical watersplitting cycles were examined. Using defined criteria and quantifiable metrics, 25 cycles have been selected for more detailed study.

  11. Thermodynamic Analysis of the Use a Chemical Heat Pump to Link a Supercritical Water-Cooled Nuclear Reactor and a Thermochemical Water-Splitting Cycle for Hydrogen Production

    Science.gov (United States)

    Granovskii, Mikhail; Dincer, Ibrahim; Rosen, Marc A.; Pioro, Igor

    Increases in the power generation efficiency of nuclear power plants (NPPs) are mainly limited by the permissible temperatures in nuclear reactors and the corresponding temperatures and pressures of the coolants in reactors. Coolant parameters are limited by the corrosion rates of materials and nuclear-reactor safety constraints. The advanced construction materials for the next generation of CANDU reactors, which employ supercritical water (SCW) as a coolant and heat carrier, permit improved “steam” parameters (outlet temperatures up to 625°C and pressures of about 25 MPa). An increase in the temperature of steam allows it to be utilized in thermochemical water splitting cycles to produce hydrogen. These methods are considered by many to be among the most efficient ways to produce hydrogen from water and to have advantages over traditional low-temperature water electrolysis. However, even lower temperature water splitting cycles (Cu-Cl, UT-3, etc.) require an intensive heat supply at temperatures higher than 550-600°C. A sufficient increase in the heat transfer from the nuclear reactor to a thermochemical water splitting cycle, without jeopardizing nuclear reactor safety, might be effectively achieved by application of a heat pump, which increases the temperature of the heat supplied by virtue of a cyclic process driven by mechanical or electrical work. Here, a high-temperature chemical heat pump, which employs the reversible catalytic methane conversion reaction, is proposed. The reaction shift from exothermic to endothermic and back is achieved by a change of the steam concentration in the reaction mixture. This heat pump, coupled with the second steam cycle of a SCW nuclear power generation plant on one side and a thermochemical water splitting cycle on the other, increases the temperature of the “nuclear” heat and, consequently, the intensity of heat transfer into the water splitting cycle. A comparative preliminary thermodynamic analysis is conducted

  12. HYDRGN - a computerized technique for the analysis of thermochemical water-splitting cycles

    Energy Technology Data Exchange (ETDEWEB)

    Carty, R. H.; Conger, W. L.; Funk, J. E.; Barker, R.

    1977-06-01

    The HYDRGN computer program was designed to analyze closed thermochemical cycles for the production of hydrogen from water. This report includes the basic theory, assumptions, and methods of calculation used in this analysis along with a description of the program and its use. The source program and necessary data bank are available from the University of Kentucky. These may be obtained by sending a magnetic tape (minimum length 1200 ft) and a written request specifying the type of computer and recording characteristics of the tape. A small fee is charged for the recording and handling of the tape.

  13. Life cycle assessment of nuclear-based hydrogen production via thermochemical water splitting using a copper-chlorine (Cu-Cl) cycle

    Science.gov (United States)

    Ozbilen, Ahmet Ziyaettin

    The energy carrier hydrogen is expected to solve some energy challenges. Since its oxidation does not emit greenhouse gases (GHGs), its use does not contribute to climate change, provided that it is derived from clean energy sources. Thermochemical water splitting using a Cu-Cl cycle, linked with a nuclear super-critical water cooled reactor (SCWR), which is being considered as a Generation IV nuclear reactor, is a promising option for hydrogen production. In this thesis, a comparative environmental study is reported of the three-, four- and five-step Cu-Cl thermochemical water splitting cycles with various other hydrogen production methods. The investigation uses life cycle assessment (LCA), which is an analytical tool to identify and quantify environmentally critical phases during the life cycle of a system or a product and/or to evaluate and decrease the overall environmental impact of the system or product. The LCA results for the hydrogen production processes indicate that the four-step Cu-Cl cycle has lower environmental impacts than the three- and five-step Cu-Cl cycles due to its lower thermal energy requirement. Parametric studies show that acidification potentials (APs) and global warming potentials (GWPs) for the four-step Cu-Cl cycle can be reduced from 0.0031 to 0.0028 kg SO2-eq and from 0.63 to 0.55 kg CO2-eq, respectively, if the lifetime of the system increases from 10 to 100 years. Moreover, the comparative study shows that the nuclear-based S-I and the four-step Cu-Cl cycles are the most environmentally benign hydrogen production methods in terms of AP and GWP. GWPs of the S-I and the four-step Cu-Cl cycles are 0.412 and 0.559 kg CO2-eq for reference case which has a lifetime of 60 years. Also, the corresponding APs of these cycles are 0.00241 and 0.00284 kg SO2-eq. It is also found that an increase in hydrogen plant efficiency from 0.36 to 0.65 decreases the GWP from 0.902 to 0.412 kg CO 2-eq and the AP from 0.00459 to 0.00209 kg SO2-eq for the

  14. Development of a laboratory cycle for a thermochemical water-splitting process (Me/MeH cycle)

    Energy Technology Data Exchange (ETDEWEB)

    Weirich, W.; Biallas, B.; Kuegler, B.; Oertel, M.; Pietsch, M.; Winkelmann, U.

    1986-01-01

    Metal-metal hydride (Me/MeH) processes for water splitting using HTR heat are being developed at the Institute for Nuclear Reactor Technology. The research work is concentrated on setting up a laboratory facility and developing metal membranes. It is planned to perform the first experiments as from the beginning of 1986. These will be investigations in the transport of Me/MeH suspensions and long-term tests with the metal membranes. TiNi-base alloys and coated materials will be used as membranes. TiNi-alloys did not exhibit any loss of weight due to corrosion in electrolytic experiments lasting more than 500 h. The permeation rates were constant and amounted to approximately 500 A m/sup -2/ (s = 50 ..mu..m, rhosub(H2) = 1 bar). Pd/Cu-coatings on Ta or Nb, in contrast to pure Pd-coatings are resistant for long duration. Annealing tests at 500/sup 0/C lasting 4000 h verify this behaviour.

  15. Thermochemical water-splitting cycle, bench-scale investigations, and process engineering. Final report, February 1977-December 31, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Norman, J.H.; Besenbruch, G.E.; Brown, L.C.; O' Keefe, D.R.; Allen, C.L.

    1982-05-01

    The sulfur-iodine water-splitting cycle is characterized by the following three reactions: 2H/sub 2/O + SO/sub 2/ + I/sub 2/ ..-->.. H/sub 2/SO/sub 4/ + 2HI; H/sub 2/SO/sub 4/ ..-->.. H/sub 2/O + SO/sub 2/ + 1/2 O/sub 2/; and 2HI ..-->.. H/sub 2/ + I/sub 2/. This cycle was developed at General Atomic after several critical features in the above reactions were discovered. These involved phase separations, catalytic reactions, etc. Estimates of the energy efficiency of this economically reasonable advanced state-of-the-art processing unit produced sufficiently high values (to approx.47%) to warrant cycle development effort. The DOE contract was largely directed toward the engineering development of this cycle, including a small demonstration unit (CLCD), a bench-scale unit, engineering design, and costing. The work has resulted in a design that is projected to produce H/sub 2/ at prices not yet generally competitive with fossil-fuel-produced H/sub 2/ but are projected to be favorably competitive with respect to H/sub 2/ from fossil fuels in the future.

  16. Stoichiometry of Reducing Equivalents and Splitting of Water in the Citric Acid Cycle.

    Science.gov (United States)

    Madeira, Vitor M. C.

    1988-01-01

    Presents a solution to the problem of finding the source of extra reducing equivalents, and accomplishing the stoichiometry of glucose oxidation reactions. Discusses the citric acid cycle and glycolysis. (CW)

  17. Stoichiometry of Reducing Equivalents and Splitting of Water in the Citric Acid Cycle.

    Science.gov (United States)

    Madeira, Vitor M. C.

    1988-01-01

    Presents a solution to the problem of finding the source of extra reducing equivalents, and accomplishing the stoichiometry of glucose oxidation reactions. Discusses the citric acid cycle and glycolysis. (CW)

  18. Activated Carbon Catalysts for the Production of Hydrogen for the Sulfur-Iodine Thermochemical Water Splitting Cycle

    Energy Technology Data Exchange (ETDEWEB)

    Lucia M. Petkovic; Daniel M. Ginosar; Harry W. Rollins; Kyle C Burch; Cristina Deiana; Hugo S. Silva; Maria F. Sardella; Dolly Granados

    2009-05-01

    Seven activated carbon catalysts obtained from a variety of raw material sources and preparation methods were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. Within the group of ligno-cellulosic steam-activated carbon catalysts, activity increased with surface area. However, both a mineral-based steam-activated carbon and a ligno-cellulosic chemically-activated carbon displayed activities lower than expected based on their higher surface areas. In general, ash content was detrimental to catalytic activity while total acid sites, as determined by Bohem’s titrations, seemed to favor higher catalytic activity within the group of steam-activated carbons. These results suggest, one more time, that activated carbon raw materials and preparation methods may have played a significant role in the development of surface characteristics that eventually dictated catalyst activity and stability as well.

  19. Activated carbon catalysts for the production of hydrogen via the sulfur-iodine thermochemical water splitting cycle

    Energy Technology Data Exchange (ETDEWEB)

    Petkovic, Lucia M.; Ginosar, Daniel M.; Rollins, Harry W.; Burch, Kyle C. [Idaho National Laboratory, Interfacial Chemistry, P.O. Box 1625, Idaho Falls, ID 83415-2208 (United States); Deiana, Cristina; Silva, Hugo S.; Sardella, Maria F.; Granados, Dolly [Instituto de Ingenieria Quimica, Facultad de Ingenieria, Universidad Nacional de San Juan, Libertador 1109 (oeste) 5400 San Juan (Argentina)

    2009-05-15

    Seven activated carbon catalysts obtained from a variety of raw material sources and preparation methods were examined for their catalytic activity to decompose hydrogen iodide (HI) to produce hydrogen, a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. Within the group of lignocellulosic steam-activated carbon catalysts, activity increased with surface area. However, both a mineral-based steam-activated carbon and a lignocellulosic chemically activated carbon displayed activities lower than expected based on their higher surface areas. In general, ash content was detrimental to catalytic activity while total acid sites, as determined by Boehm's titrations, seemed to favor higher catalytic activity within the group of steam-activated carbons. These results suggest that activated carbon raw materials and preparation methods may have played a significant role in the development of surface characteristics that eventually dictated catalyst activity and stability as well. (author)

  20. Preliminary results from bench-scale testing of a sulfur-iodine thermochemical water-splitting cycle

    Energy Technology Data Exchange (ETDEWEB)

    O' Keefe, D.; Allen, C.; Besenbruch, G.; McCorkle, K.; Norman, J.; Sharp, R.

    1980-07-01

    Portions of a bench-scale model of a sulfur-iodine thermochemical water-splitting cycle have been operated at General Atomic Company as part of a comprehensive program to demonstrate the technology for hydrogen production from nonfossil sources. The hydrogen program is funded by the US Department of Energy, the Gas Research Institute, and General Atomic Company. The bench-scale model consists of three subunits which can be operated separately or together and is capable of producing as much as 4 std liters/min (6.7 x 10/sup -5/ m/sup 3//s at standard conditions) of gaseous hydrogen. One subunit (main solution reaction) reacts liquid water, liquid iodine (I/sub 2/) and gaseous sulfur dioxide (SO/sub 2/) to form two separable liquid phases: 50 wt % sulfuric acid (H/sub 2/SO/sub 4/) and a solution of iodine in hydriodic acid (HI/sub x/). Another subunit (H/sub 2/SO/sub 4/ concentration and decomposition) concentrates the H/sub 2/SO/sub 4/ phase to the azeotropic composition, then decomposes it at high temperature over a catalyst to form gaseous SO/sub 2/ and oxygen. The third subunit (HI separation and decomposition) separates the HI from water and I/sub 2/ by extractive distillation with phosphoric acid (H/sub 3/PO/sub 4/) and decomposes the HI in the vapor phase over a catalyst to form I/sub 2/ and product hydrogen. This paper presents the results of on-going parametric studies to determine the operating characteristics, performance, and capacity limitations of major components.

  1. Solar water splitting: efficiency discussion

    OpenAIRE

    Juodkazyte, Jurga; Seniutinas, Gediminas; Sebeka, Benjaminas; Savickaja, Irena; Malinauskas, Tadas; Badokas, Kazimieras; Juodkazis, Kestutis; Juodkazis, Saulius

    2016-01-01

    The current state of the art in direct water splitting in photo-electrochemical cells (PECs) is presented together with: (i) a case study of water splitting using a simple solar cell with the most efficient water splitting electrodes and (ii) a detailed mechanism analysis. Detailed analysis of the energy balance and efficiency of solar hydrogen production are presented. The role of hydrogen peroxide formation as an intermediate in oxygen evolution reaction is newly revealed and explains why a...

  2. Ispra Mark-10 water splitting process

    Science.gov (United States)

    1975-01-01

    A thermochemical water splitting process, the Ispra Mark-10 chemical reaction cycle, was chosen for examining the possibility of using water to produce hydrogen on a large scale for fuel and major industrial chemical uses. The assumed energy source for the process is an HTGR (helium cooled). A process flow diagram, a material balance, and an energy balance were developed for the thermochemical reaction cycle. Principal reactions which constitute the cycle are included.

  3. Helioseismic Solar Cycle Changes and Splitting Coefficients

    Indian Academy of Sciences (India)

    S. C. Tripathy; Kiran Jain; A. Bhatnagar

    2000-09-01

    Using the GONG data for a period over four years, we have studied the variation of frequencies and splitting coefficients with solar cycle. Frequencies and even-order coefficients are found to change significantly with rising phase of the solar cycle. We also find temporal variations in the rotation rate near the solar surface.

  4. Innovative solar thermochemical water splitting.

    Energy Technology Data Exchange (ETDEWEB)

    Hogan, Roy E. Jr.; Siegel, Nathan P.; Evans, Lindsey R.; Moss, Timothy A.; Stuecker, John Nicholas (Robocasting Enterprises, Albuquerque, NM); Diver, Richard B., Jr.; Miller, James Edward; Allendorf, Mark D. (Sandia National Laboratories, Livermore, CA); James, Darryl L. (Texas Tech University, Lubbock, TX)

    2008-02-01

    Sandia National Laboratories (SNL) is evaluating the potential of an innovative approach for splitting water into hydrogen and oxygen using two-step thermochemical cycles. Thermochemical cycles are heat engines that utilize high-temperature heat to produce chemical work. Like their mechanical work-producing counterparts, their efficiency depends on operating temperature and on the irreversibility of their internal processes. With this in mind, we have invented innovative design concepts for two-step solar-driven thermochemical heat engines based on iron oxide and iron oxide mixed with other metal oxides (ferrites). The design concepts utilize two sets of moving beds of ferrite reactant material in close proximity and moving in opposite directions to overcome a major impediment to achieving high efficiency--thermal recuperation between solids in efficient counter-current arrangements. They also provide inherent separation of the product hydrogen and oxygen and are an excellent match with high-concentration solar flux. However, they also impose unique requirements on the ferrite reactants and materials of construction as well as an understanding of the chemical and cycle thermodynamics. In this report the Counter-Rotating-Ring Receiver/Reactor/Recuperator (CR5) solar thermochemical heat engine and its basic operating principals are described. Preliminary thermal efficiency estimates are presented and discussed. Our ferrite reactant material development activities, thermodynamic studies, test results, and prototype hardware development are also presented.

  5. Solar water splitting: efficiency discussion

    CERN Document Server

    Juodkazyte, Jurga; Sebeka, Benjaminas; Savickaja, Irena; Malinauskas, Tadas; Badokas, Kazimieras; Juodkazis, Kestutis; Juodkazis, Saulius

    2016-01-01

    The current state of the art in direct water splitting in photo-electrochemical cells (PECs) is presented together with: (i) a case study of water splitting using a simple solar cell with the most efficient water splitting electrodes and (ii) a detailed mechanism analysis. Detailed analysis of the energy balance and efficiency of solar hydrogen production are presented. The role of hydrogen peroxide formation as an intermediate in oxygen evolution reaction is newly revealed and explains why an oxygen evolution is not taking place at the thermodynamically expected 1.23 V potential. Solar hydrogen production with electrical-to-hydrogen conversion efficiency of 52% is demonstrated using a simple ~0.7%-efficient n-Si/Ni Schottky solar cell connected to a water electrolysis cell. This case study shows that separation of the processes of solar harvesting and electrolysis avoids photo-electrode corrosion and utilizes optimal electrodes for hydrogen and oxygen evolution reactions and achieves ~10% efficiency in light...

  6. Thermochemical reactivity of 5–15 mol% Fe, Co, Ni, Mn-doped cerium oxides in two-step water-splitting cycle for solar hydrogen production

    Energy Technology Data Exchange (ETDEWEB)

    Gokon, Nobuyuki, E-mail: ngokon@eng.niigata-u.ac.jp [Center for Transdisciplinary Research, Niigata University, 8050 Ikarashi 2-nocho, Nishi-ku, Niigata 950-2181 (Japan); Suda, Toshinori [Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181 (Japan); Kodama, Tatsuya [Department of Chemistry & Chemical Engineering, Faculty of Engineering, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181 (Japan)

    2015-10-10

    Highlights: • 5–15 mol% M-doped ceria are examined for thermochemical two-step water-splitting. • 5 mol% Fe- and Co-doped ceria have stoichiometric production of oxygen and hydrogen. • 10–15 mol% Fe- and Mn-doped ceria showed near-stoichiometric production. - Abstract: The thermochemical two-step water-splitting cycle using transition element-doped cerium oxide (M–CeO{sub 2−δ}; M = Fe, Co, Ni, Mn) powders was studied for hydrogen production from water. The oxygen/hydrogen productivity and repeatability of M–CeO{sub 2−δ} materials with M doping contents in the 5–15 mol% range were examined using a thermal reduction (TR) temperature of 1500 °C and water decomposition (WD) temperatures in the 800–1150 °C range. The temperature, steam partial pressure, and steam flow rate in the WD step had an impact on the hydrogen productivity and production rate. 5 mol% Fe- and Co-doped CeO{sub 2−δ} enhances hydrogen productivity by up to 25% on average compared to undoped CeO{sub 2}, and shows stable repeatability of stoichiometric oxygen and hydrogen production for the cyclic thermochemical two-step water-splitting reaction. In addition, 5 mol% Mn-doped CeO{sub 2−δ}, 10 and 15 mol% Fe- and Mn-doped CeO{sub 2−δ} show near stoichiometric reactivities.

  7. Water splitting by cooperative catalysis

    NARCIS (Netherlands)

    D.G.H. Hetterscheid; J.I. van der Vlugt; B. de Bruin; J.N.H. Reek

    2009-01-01

    A mononuclear Ru complex is shown to efficiently split water into H2 and O2 in consecutive steps through a heat- and light-driven process (see picture). Thermally driven H2 formation involves the aid of a non-innocent ligand scaffold, while dioxygen is generated by initial photochemically induced re

  8. 2-Photon tandem device for water splitting

    DEFF Research Database (Denmark)

    Seger, Brian; Castelli, Ivano Eligio; Vesborg, Peter Christian Kjærgaard;

    2014-01-01

    Within the field Of photocatalytic water splitting there are several strategies to achieve the goal of efficient and cheap photocatalytic water splitting. This work examines one particular strategy by focusing on monolithically stacked, two-photon photoelectrochemical cells. The overall aim of th...

  9. Electrocatalytic water splitting to produce fuel hydrogen

    Science.gov (United States)

    Yuan, Hao

    Solar energy is regarded as a promising source for clean and sustainable energy. However, it is not a continuous energy source, thus certain strategies have to be developed to effectively convert and store it. Solar-driven electrocatalytic water splitting, which converts solar energy into chemical energy for storage as fuel hydrogen, can effectively mitigate the intermittence of solar radiation. Water splitting consists of two half reactions: water oxidation and hydrogen evolution. Both reactions rely on highly effective electrocatalysts. This dissertation is an account of four detailed studies on developing highly effective low-cost electrocatalysts for both reactions, and includes a preliminary attempt at system integration to build a functional photoanode for solar-driven water oxidation. For the water oxidation reaction, we have developed an electrochemical method to immobilize a cobalt-based (Co-OXO) water oxidation catalyst on a conductive surface to promote recyclability and reusability without affecting functionality. We have also developed a method to synthesize a manganese-based (MnOx) catalytic film in situ, generating a nanoscale fibrous morphology that provides steady and excellent water oxidation performance. The new method involves two series of cyclic voltammetry (CV) over different potential ranges, followed by calcination to increase crystallinity. The research has the potential to open avenues for synthesizing and optimizing other manganese-based water oxidation catalysts. For the hydrogen evolution reaction, we have developed a new electrodeposition method to synthesize Ni/Ni(OH)2 catalysts in situ on conductive surfaces. The new method involves only two cycles of CV over a single potential range. The resulting catalytic film has a morphology of packed walnut-shaped particles. It has superior catalytic activity and good stability over long periods. We have investigated the feasibility of incorporating manganese-based water oxidation catalysts

  10. Inorganic photocatalysts for overall water splitting.

    Science.gov (United States)

    Xing, Jun; Fang, Wen Qi; Zhao, Hui Jun; Yang, Hua Gui

    2012-04-01

    Photocatalytic water splitting using semiconductor photocatalysts has been considered as a "green" process for converting solar energy into hydrogen. The pioneering work on electrochemical photolysis of water at TiO(2) electrode, reported by Fujishima and Honda in 1972, ushered in the area of solar fuel. As the real ultimate solution for solar fuel-generation, overall water splitting has attracted interest from researchers for some time, and a variety of inorganic photocatalysts have been developed to meet the challenge of this dream reaction. To date, high-efficiency hydrogen production from pure water without the assistance of sacrificial reagents remains an open challenge. In this Focus Review, we aim to provide a whole picture of overall water splitting and give an outlook for future research.

  11. Comparing Electrochemical and Biological Water Splitting

    DEFF Research Database (Denmark)

    Rossmeisl, Jan; Dimitrievski, Kristian; Siegbahn, P.

    2007-01-01

    On the basis of density functional theory calculations, we compare the free energies of key intermediates in the water splitting reaction over transition metal oxide surfaces to those of the Mn cluster in photo system II. In spite of the very different environments in the enzyme system...

  12. Artificial photosynthesis for solar water-splitting

    Science.gov (United States)

    Tachibana, Yasuhiro; Vayssieres, Lionel; Durrant, James R.

    2012-08-01

    Hydrogen generated from solar-driven water-splitting has the potential to be a clean, sustainable and abundant energy source. Inspired by natural photosynthesis, artificial solar water-splitting devices are now being designed and tested. Recent developments based on molecular and/or nanostructure designs have led to advances in our understanding of light-induced charge separation and subsequent catalytic water oxidation and reduction reactions. Here we review some of the recent progress towards developing artificial photosynthetic devices, together with their analogies to biological photosynthesis, including technologies that focus on the development of visible-light active hetero-nanostructures and require an understanding of the underlying interfacial carrier dynamics. Finally, we propose a vision for a future sustainable hydrogen fuel community based on artificial photosynthesis.

  13. Modelling heterogeneous interfaces for solar water splitting

    Science.gov (United States)

    Pham, Tuan Anh; Ping, Yuan; Galli, Giulia

    2017-04-01

    The generation of hydrogen from water and sunlight offers a promising approach for producing scalable and sustainable carbon-free energy. The key of a successful solar-to-fuel technology is the design of efficient, long-lasting and low-cost photoelectrochemical cells, which are responsible for absorbing sunlight and driving water splitting reactions. To this end, a detailed understanding and control of heterogeneous interfaces between photoabsorbers, electrolytes and catalysts present in photoelectrochemical cells is essential. Here we review recent progress and open challenges in predicting physicochemical properties of heterogeneous interfaces for solar water splitting applications using first-principles-based approaches, and highlights the key role of these calculations in interpreting increasingly complex experiments.

  14. Modelling heterogeneous interfaces for solar water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Pham, Tuan Anh; Ping, Yuan; Galli, Giulia

    2017-01-09

    The generation of hydrogen from water and sunlight others a promising approach for producing scalable and sustainable carbon-free energy. The key of a successful solar-to-fuel technology is the design of efficient, long-lasting and low-cost photoelectrochemical cells, which are responsible for absorbing sunlight and driving water splitting reactions. To this end, a detailed understanding and control of heterogeneous interfaces between photoabsorbers, electrolytes and catalysts present in photoelectrochemical cells is essential. Here we review recent progress and open challenges in predicting physicochemical properties of heterogeneous interfaces for solar water splitting applications using first-principles-based approaches, and highlights the key role of these calculations in interpreting increasingly complex experiments.

  15. Photoelectrochemical water splitting: optimizing interfaces and light absorption

    NARCIS (Netherlands)

    Park, S.

    2015-01-01

    In this thesis several photoelectrochemical water splitting devices based on semiconductor materials were investigated. The aim was the design, characterization, and fabrication of solar-to-fuel devices which can absorb solar light and split water to produce hydrogen.

  16. Solar Water Splitting Using Semiconductor Photocatalyst Powders

    KAUST Repository

    Takanabe, Kazuhiro

    2015-07-01

    Solar energy conversion is essential to address the gap between energy production and increasing demand. Large scale energy generation from solar energy can only be achieved through equally large scale collection of the solar spectrum. Overall water splitting using heterogeneous photocatalysts with a single semiconductor enables the direct generation of H from photoreactors and is one of the most economical technologies for large-scale production of solar fuels. Efficient photocatalyst materials are essential to make this process feasible for future technologies. To achieve efficient photocatalysis for overall water splitting, all of the parameters involved at different time scales should be improved because the overall efficiency is obtained by the multiplication of all these fundamental efficiencies. Accumulation of knowledge ranging from solid-state physics to electrochemistry and a multidisciplinary approach to conduct various measurements are inevitable to be able to understand photocatalysis fully and to improve its efficiency.

  17. Thermodynamic evaluation of the Kalina split-cycle concepts for waste heat recovery applications

    OpenAIRE

    2014-01-01

    The Kalina split-cycle is a thermodynamic process for converting thermal energy into electrical power. It uses an ammonia–water mixture as a working fluid (like a conventional Kalina cycle) and has a varying ammonia concentration during the pre-heating and evaporation steps. This second feature results in an improved match between the heat source and working fluid temperature profiles, decreasing the entropy generation in the heat recovery system. The present work compares the thermodynamic p...

  18. Development of a multi-level approach to model and optimise the Kalina Split Cycle

    DEFF Research Database (Denmark)

    Larsen, Ulrik; Nguyen, Tuong-Van; Haglind, Fredrik

    2012-01-01

    efficiencies than conventional power cycles and could be suitable for this purpose. The Split Cycle technique provides a method to further increase the thermal efficiency, by reducing the thermodynamic losses in the heat recovery system. This is achieved by having two separate streams of different ammonia...... cycle. Results suggest a 9% net power output increase and 7% higher thermal efficiency compared to the baseline case.......In the marine sector there is a strong motivation for increasing the propulsion system energy efficiency, mainly because of increasing fuel prices and stricter upcoming emission regulations. The Kalina cycle, based on a mixture of ammonia and water as working fluid, exhibits higher conversion...

  19. The global water cycle

    Science.gov (United States)

    Oki, Taikan; Entekhabi, Dara; Harrold, Timothy Ives

    The global water cycle consists of the oceans, water in the atmosphere, and water in the landscape. The cycle is closed by the fluxes between these reservoirs. Although the amounts of water in the atmosphere and river channels are relatively small, the fluxes are high, and this water plays a critical role in society, which is dependent on water as a renewable resource. On a global scale, the meridional component of river runoff is shown to be about 10% of the corresponding atmospheric and oceanic meridional fluxes. Artificial storages and water withdrawals for irrigation have significant impacts on river runoff and hence on the overall global water cycle. Fully coupled atmosphere-land-river-ocean models of the world's climate are essential to assess the future water resources and scarcities in relation to climate change. An assessment of future water scarcity suggests that water shortages will worsen, with a very significant increase in water stress in Africa. The impact of population growth on water stress is shown to be higher than that of climate change. The virtual water trade, which should be taken into account when discussing the global water cycle and water scarcity, is also considered. The movement of virtual water from North America, Oceania, and Europe to the Middle East, North West Africa, and East Asia represents significant global savings of water. The anticipated world water crisis widens the opportunities for the study of the global water cycle to contribute to the development of sustainability within society and to the solution of practical social problems.

  20. Large Bandgap Semiconductors for Solar Water Splitting

    DEFF Research Database (Denmark)

    Malizia, Mauro

    water splitting devices having tandem design. The increase of the photovoltage produced by GaP under illumination was the main goal of this work. GaP has a bandgap of 2.25 eV and could in theory produce a photovoltage of approximately 1.7 V. Instead, the photovoltage produced by the semiconductor...... density generated by GaP was increased by more than 60% by electrochemical etching of the surface. The etching process produces a rough microstructured surface that increases the optical path length of the incident photons and the collection of photogenerated electrons.Furthermore, the synthesis of BiVO4...

  1. Solar hydrogen production on some water splitting photocatalysts

    Science.gov (United States)

    Takata, Tsuyoshi; Hisatomi, Takashi; Domen, Kazunari

    2016-09-01

    Photocatalytic overall water splitting into H2 and O2 is expected to be a promising method for the efficient utilization of solar energy. The design of optimal photocatalyst structures is a key to efficient overall water splitting, and the development of photocatalysts which can efficiently convert large portion of visible light spectrum has been required. Recently, a series of complex perovskite type transition metal oxynitrides, LaMgxT 1-xO1+3xN2-3x, was developed as photocatalysts for direct water splitting operable at wide wavelength of visible light. In addition two-step excitation water splitting via a novel photocatalytic device termed as photocatalyst sheet was developed. This consists of two types of semiconductors (hydrogen evolution photocatalyst and oxygen evolution photocatalyst) particles embedded in a conductive layer, and showed high efficiency for overall water splitting. These recent advances in photocatalytic water splitting were introduced.

  2. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting.

    Science.gov (United States)

    Hisatomi, Takashi; Kubota, Jun; Domen, Kazunari

    2014-11-21

    Photocatalytic and photoelectrochemical water splitting under irradiation by sunlight has received much attention for production of renewable hydrogen from water on a large scale. Many challenges still remain in improving energy conversion efficiency, such as utilizing longer-wavelength photons for hydrogen production, enhancing the reaction efficiency at any given wavelength, and increasing the lifetime of the semiconductor materials. This introductory review covers the fundamental aspects of photocatalytic and photoelectrochemical water splitting. Controlling the semiconducting properties of photocatalysts and photoelectrode materials is the primary concern in developing materials for solar water splitting, because they determine how much photoexcitation occurs in a semiconductor under solar illumination and how many photoexcited carriers reach the surface where water splitting takes place. Given a specific semiconductor material, surface modifications are important not only to activate the semiconductor for water splitting but also to facilitate charge separation and to upgrade the stability of the material under photoexcitation. In addition, reducing resistance loss and forming p-n junction have a significant impact on the efficiency of photoelectrochemical water splitting. Correct evaluation of the photocatalytic and photoelectrochemical activity for water splitting is becoming more important in enabling an accurate comparison of a number of studies based on different systems. In the latter part, recent advances in the water splitting reaction under visible light will be presented with a focus on non-oxide semiconductor materials to give an overview of the various problems and solutions.

  3. Possibilities of improving the efficiency of power generation with regard to electrolytic water splitting

    Science.gov (United States)

    Knoche, K. F.; Hasberg, W.; Roth, M.

    The efficiency of power generation has a considerable influence on the upper limit of the total efficiency of electrolytic water splitting. This paper deals with the energetic potential of power generation processes and therefore with the water electrolysis processes. In the investigations reported here, it was assumed that the heat source is always the same (high-temperature nuclear reactor). For comparing thermochemical or hybrid water splitting cycles and water electrolysis, the upper limit of process temperatures must be comparable, too. Therefore, high-temperature processes for power generation have been investigated. A detailed energy and exergy balance is presented for the following cycles: (1) steam turbine cycles; (2) helium gas turbine cycles; (3) combined gas/steam turbine cycles. For these different processes an exergy analysis was performed in order to localize the process units, which make a considerable contribution to the decrease in total efficiency.

  4. Forests and water cycle

    Directory of Open Access Journals (Sweden)

    Iovino F

    2009-06-01

    Full Text Available Based on a comprehensive literature analysis, a review on factors that control water cycle and water use in Mediterranean forest ecosystems is presented, including environmental variables and silvicultural treatments. This important issue is considered in the perspective of sustainable forest management of Mediterranean forests, with special regard to crucial environmental hazards such as forest fires and desertification risks related to climate change.

  5. Towards Highly Efficient Bias-Free Solar Water Splitting

    NARCIS (Netherlands)

    Abdi, F.F.

    2013-01-01

    Solar water splitting has attracted significant attention due to its potential of converting solar to chemical energy. It uses semiconductor to convert sunlight into electron-hole pairs, which then split water into hydrogen and oxygen. The hydrogen can be used as a renewable fuel, or it can serve as

  6. Towards Highly Efficient Bias-Free Solar Water Splitting

    NARCIS (Netherlands)

    Abdi, F.F.

    2013-01-01

    Solar water splitting has attracted significant attention due to its potential of converting solar to chemical energy. It uses semiconductor to convert sunlight into electron-hole pairs, which then split water into hydrogen and oxygen. The hydrogen can be used as a renewable fuel, or it can serve as

  7. Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

    KAUST Repository

    Hisatomi, Takashi

    2014-10-16

    Abstract: Some particulate semiconductors loaded with nanoparticulate catalysts exhibit photocatalytic activity for the water-splitting reaction. The photocatalysis is distinct from the thermal catalysis because photocatalysis involves photophysical processes in particulate semiconductors. This review article presents a brief introduction to photocatalysis, followed by kinetic aspects of the photocatalytic water-splitting reaction.Graphical Abstract: [Figure not available: see fulltext.

  8. Thermochemical processes for water splitting - status and outlook

    Energy Technology Data Exchange (ETDEWEB)

    Weirich, W.; Behr, F. (Technische Hochschule Aachen (Germany, F.R.). Lehrstuhl fuer Reaktortechnik); Knoche, K.F. (Technische Hochschule Aachen (Germany, F.R.). Lehrstuhl fuer Technische Thermodynamik und Inst. fuer Thermodynamik); Barnert, H. (Kernforschungsanlage Juelich G.m.b.H. (Germany, F.R.). Inst. fuer Reaktorentwicklung)

    1984-04-01

    In this paper we discuss the proposals for processes which have already been realised in form of bench scale units or which have been planned, as well as those which have a high degree of development potential. A part of these cycles have in common the splitting of sulfuric acids which causes corrosion problems unsolved up to now. The essential part of the metal/metal hydride-processes is a hydrogen permeable membrane which separates the hydrogen acceptor from the water containing electrolyte melt. Actually we are intending to build up a lab cycle using a TiNi-basis membrane. The metal membranes offer a number of further interesting applications, such as (1) hydrogen production from gas mixtures at high temperatures, and (2) tritium separation from the helium of the HTR primary cooling circuit. A further promising process is the hydrocarbon hybrid cycle, in which the reduction of methanol to methane and oxygen is the key reaction. Till now we can detect a methane yield of up to 50%. An interesting combined procedure for the production of hydrogen and electricity is proposed, where sulphuric acid is decomposed by means of coal. The detailed mass and energy balance shows an efficiency of up to 57%. Thermodynamic analysis for the watersplitting cycles indicates efficiencies up to 50%. Further research and development work is necessary in order to solve material problems and to demonstrate the suitability and availability of the techniques using larger scale laboratory and prototype units.

  9. Nano-architecture and material designs for water splitting photoelectrodes.

    Science.gov (United States)

    Chen, Hao Ming; Chen, Chih Kai; Liu, Ru-Shi; Zhang, Lei; Zhang, Jiujun; Wilkinson, David P

    2012-09-07

    This review concerns the efficient conversion of sunlight into chemical fuels through the photoelectrochemical splitting of water, which has the potential to generate sustainable hydrogen fuel. In this review, we discuss various photoelectrode materials and relative design strategies with their associated fabrication for solar water splitting. Factors affecting photoelectrochemical performance of these materials and designs are also described. The most recent progress in the research and development of new materials as well as their corresponding photoelectrodes is also summarized in this review. Finally, the research strategies and future directions for water splitting are discussed with recommendations to facilitate the further exploration of new photoelectrode materials and their associated technologies.

  10. Recent Progress in Energy-Driven Water Splitting.

    Science.gov (United States)

    Tee, Si Yin; Win, Khin Yin; Teo, Wee Siang; Koh, Leng-Duei; Liu, Shuhua; Teng, Choon Peng; Han, Ming-Yong

    2017-05-01

    Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

  11. Recent developments in solar H2 generation from water splitting

    Indian Academy of Sciences (India)

    Sivaraman Rajaambal; Kumarsrinivasan Sivaranjani; Chinnakonda S Gopinath

    2015-01-01

    Hydrogen production from water and sunlight through photocatalysis could become one of the channels, in the not-so-distant future, to meet a part of ever growing energy demands. However, accomplishing solar water splitting through semiconductor particulate photocatalysis seems to be the ‘Holy Grail’ problem of science. In the present mini-review, some of the critical strategies of semiconductor photocatalysis are focused with the aim of enumerating underlying critical factors such as visible light harvesting, charge carrier separation, conduction and their utilization that determine the quantum efficiency. We attempted to bring out the essential requirements expected in a material for facile water splitting by explaining important and new designs contributed in the last decade. The newly emerged designs in semiconductor architecture employing nanoscience towards meeting the critical factors of facile photocatalysis are elucidated. The importance of band gap engineering is emphasized to utilize potential wide band gap semiconductors. Assistance of metal nanostructures and quantum dots to semiconductors attains vital importance as they are exuberant visible light harvesters and charge carrier amplifiers. Benevolent use of quantum dots in solar water splitting and photoelectrochemical water splitting provides scope to revolutionize the quantum efficiency by its multiple exciton generation features. A list of drawbacks and issues that hamper the much needed breakthrough in photocatalysis of water splitting is provided to invite attention to address them and move towards sustainable water splitting.

  12. Hydrogen Production from Semiconductor-based Photocatalysis via Water Splitting

    Directory of Open Access Journals (Sweden)

    Jeffrey C. S. Wu

    2012-10-01

    Full Text Available Hydrogen is the ideal fuel for the future because it is clean, energy efficient, and abundant in nature. While various technologies can be used to generate hydrogen, only some of them can be considered environmentally friendly. Recently, solar hydrogen generated via photocatalytic water splitting has attracted tremendous attention and has been extensively studied because of its great potential for low-cost and clean hydrogen production. This paper gives a comprehensive review of the development of photocatalytic water splitting for generating hydrogen, particularly under visible-light irradiation. The topics covered include an introduction of hydrogen production technologies, a review of photocatalytic water splitting over titania and non-titania based photocatalysts, a discussion of the types of photocatalytic water-splitting approaches, and a conclusion for the current challenges and future prospects of photocatalytic water splitting. Based on the literatures reported here, the development of highly stable visible–light-active photocatalytic materials, and the design of efficient, low-cost photoreactor systems are the key for the advancement of solar-hydrogen production via photocatalytic water splitting in the future.

  13. Hydrogen production from a chemical cycle of H{sub 2}S splitting

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hui [Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan (Canada)

    2007-11-15

    The sulphur-iodine thermochemical water-splitting cycle (S-I cycle) developed for hydrogen production from water is fundamentally based on the following three chemical reactions: H{sub 2}SO{sub 4}{yields}H{sub 2}O+SO{sub 2}+0.5O{sub 2},2H{sub 2}O+SO{sub 2}+I{sub 2}{yields}H{sub 2}SO{sub 4}+2HI,2HI{yields}H{sub 2}+I{sub 2}.This paper proposes to replace the H{sub 2}SO{sub 4} decomposition with a reaction between H{sub 2}S and H{sub 2}SO{sub 4} and the replacement gives rise to a H{sub 2}S-splitting cycle that produces H{sub 2} and elemental S from H{sub 2}S, shown as follows: H{sub 2}S+H{sub 2}SO{sub 4}{yields} S+SO{sub 2}+2H{sub 2}O,2H{sub 2}O+I{sub 2}+SO{sub 2}{yields}H{sub 2}SO{sub 4}+2HI,2HI{yields}H{sub 2}+I{sub 2}.Combined with the reactions such as O{sub 2}+S{yields}SO{sub 2},SO{sub 2}+0.5O{sub 2}{yields}SO{sub 3},SO{sub 3}+H{sub 2}O{yields}H{sub 2}SO{sub 4},this new cycle cannot only produce more H{sub 2} and extra H{sub 2}SO{sub 4} but also facilitate flexible H{sub 2} to H{sub 2}SO{sub 4} production ratio. Thermodynamic analysis shows that the new cycle is more energy-efficient than the S-I cycle of water-splitting because a series of endothermic reactions in H{sub 2}SO{sub 4} decomposition have been replaced with an exothermic reaction between H{sub 2}S and H{sub 2}SO{sub 4}. Technologies to be developed from this chemistry will be able to convert H{sub 2}S from sour or acid gas into H{sub 2} and elemental S or H{sub 2}SO{sub 4}, which are more valuable than elemental S only, the product of the Claus process. In upgrading and refinery, the H{sub 2} produced can be returned to use in hydrotreating; and in gas plants, H{sub 2} from H{sub 2}S splitting is an alternative clean fuel. Environmentally, H{sub 2} production based on this H{sub 2}S-splitting cycle is carbon free. (author)

  14. Guidelines to Develop Efficient Photocatalysts for Water Splitting

    KAUST Repository

    Garcia Esparza, Angel T.

    2016-04-03

    Photocatalytic overall water splitting is the only viable solar-to-fuel conversion technology. The research discloses an investigation process wherein by dissecting the photocatalytic water splitting device, electrocatalysts, and semiconductor photocatalysts can be independently studied, developed and optimized. The assumption of perfect catalysts leads to the realization that semiconductors are the limiting factor in photocatalysis. This dissertation presents a guideline for efficient photocatalysis using semiconductor particles developed from idealized theoretical simulations. No perfect catalysts exist; then the discussion focus on the development of efficient non-noble metal electrocatalysts for hydrogen evolution from water reduction. Tungsten carbide (WC) is selective for the catalysis of hydrogen without the introduction of the reverse reaction of water formation, which is critical to achieving photocatalytic overall water splitting as demonstrated in this work. Finally, photoelectrochemistry is used to characterize thoroughly Cu-based p-type semiconductors with potential for large-scale manufacture. Artificial photosynthesis may be achieved by following the recommendations herein presented.

  15. Poly 3-Hexylthiophene as a photocathode for solar water splitting

    OpenAIRE

    Suppes, Graeme McCallum

    2015-01-01

    The focus of this research is to determine the extent to which poly 3-hexylthiophene (P3HT) can be used as a photoelectrode for solar water splitting. Research in the area of solar water splitting mostly focuses on inorganic materials but conjugated polymers, such as P3HT, offer several advantages. Most metal oxides used as photoelectrodes are only able to carry out water oxidation, require thick films to absorb significant amounts of light, and absorb light mainly in the ultraviolet part of ...

  16. Thermochemical production of hydrogen via multistage water splitting processes

    Science.gov (United States)

    Funk, J. E.

    1975-01-01

    This paper presents and reviews the fundamental thermodynamic principles underlying thermochemical water splitting processes. The overall system is considered first and the temperature limitation in process thermal efficiency is developed. The relationship to an ideal water electrolysis cell is described and the nature of efficient multistage reaction processes is discussed. The importance of the reaction entropy change and the relation of the reaction free energy change to the work of separation is described. A procedure for analyzing thermochemical water splitting processes is presented and its use to calculate individual stage efficiency is demonstrated. A number of processes are used to illustrate the concepts and procedures.

  17. Self-powered water splitting using flowing kinetic energy.

    Science.gov (United States)

    Tang, Wei; Han, Yu; Han, Chang Bao; Gao, Cai Zhen; Cao, Xia; Wang, Zhong Lin

    2015-01-14

    By utilizing a water-flow-driven triboelectric nanogenerator, a fully self-powered water-splitting process is demonstrated using the electricity converted from a water flow without additional energy costs. Considering the extremely low costs, the demonstrated approach is universally applicable and practically usable for future water electrolysis, which may initiate a research direction in the field of triboelectrolysis and possibly impacts energy science in general. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Tantalum nitride for photocatalytic water splitting: concept and applications

    KAUST Repository

    Nurlaela, Ela

    2016-10-12

    Along with many other solar energy conversion processes, research on photocatalytic water splitting to generate hydrogen and oxygen has experienced rapid major development over the past years. Developing an efficient visible-light-responsive photocatalyst has been one of the targets of such research efforts. In this regard, nitride materials, particularly Ta3N5, have been the subject of investigation due to their promising properties. This review focuses on the fundamental parameters involved in the photocatalytic processes targeting overall water splitting using Ta3N5 as a model photocatalyst. The discussion primarily focuses on relevant parameters that are involved in photon absorption, exciton separation, carrier diffusion, carrier transport, catalytic efficiency, and mass transfer of the reactants. An overview of collaborative experimental and theoretical approaches to achieve efficient photocatalytic water splitting using Ta3N5 is discussed.

  19. Enabling unassisted solar water splitting by iron oxide and silicon

    Science.gov (United States)

    Jang, Ji-Wook; Du, Chun; Ye, Yifan; Lin, Yongjing; Yao, Xiahui; Thorne, James; Liu, Erik; McMahon, Gregory; Zhu, Junfa; Javey, Ali; Guo, Jinghua; Wang, Dunwei

    2015-06-01

    Photoelectrochemical (PEC) water splitting promises a solution to the problem of large-scale solar energy storage. However, its development has been impeded by the poor performance of photoanodes, particularly in their capability for photovoltage generation. Many examples employing photovoltaic modules to correct the deficiency for unassisted solar water splitting have been reported to-date. Here we show that, by using the prototypical photoanode material of haematite as a study tool, structural disorders on or near the surfaces are important causes of the low photovoltages. We develop a facile re-growth strategy to reduce surface disorders and as a consequence, a turn-on voltage of 0.45 V (versus reversible hydrogen electrode) is achieved. This result permits us to construct a photoelectrochemical device with a haematite photoanode and Si photocathode to split water at an overall efficiency of 0.91%, with NiFeOx and TiO2/Pt overlayers, respectively.

  20. Tantalum-based semiconductors for solar water splitting.

    Science.gov (United States)

    Zhang, Peng; Zhang, Jijie; Gong, Jinlong

    2014-07-07

    Solar energy utilization is one of the most promising solutions for the energy crises. Among all the possible means to make use of solar energy, solar water splitting is remarkable since it can accomplish the conversion of solar energy into chemical energy. The produced hydrogen is clean and sustainable which could be used in various areas. For the past decades, numerous efforts have been put into this research area with many important achievements. Improving the overall efficiency and stability of semiconductor photocatalysts are the research focuses for the solar water splitting. Tantalum-based semiconductors, including tantalum oxide, tantalate and tantalum (oxy)nitride, are among the most important photocatalysts. Tantalum oxide has the band gap energy that is suitable for the overall solar water splitting. The more negative conduction band minimum of tantalum oxide provides photogenerated electrons with higher potential for the hydrogen generation reaction. Tantalates, with tunable compositions, show high activities owning to their layered perovskite structure. (Oxy)nitrides, especially TaON and Ta3N5, have small band gaps to respond to visible-light, whereas they can still realize overall solar water splitting with the proper positions of conduction band minimum and valence band maximum. This review describes recent progress regarding the improvement of photocatalytic activities of tantalum-based semiconductors. Basic concepts and principles of solar water splitting will be discussed in the introduction section, followed by the three main categories regarding to the different types of tantalum-based semiconductors. In each category, synthetic methodologies, influencing factors on the photocatalytic activities, strategies to enhance the efficiencies of photocatalysts and morphology control of tantalum-based materials will be discussed in detail. Future directions to further explore the research area of tantalum-based semiconductors for solar water splitting

  1. Water splitting and electricity with semiconducting silicides in sunlight

    Energy Technology Data Exchange (ETDEWEB)

    Demuth, Martin [Max-Planck-Institut fuer Bioanorganische Chemie, Muelheim an der Ruhr (Germany); H2 Solar GmbH, Loerrach (Germany); Kerpen, Klaus; Kuklya, Andriy; Wuestkamp, Marc-Andre [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany)

    2010-07-01

    Generation of hydrogen and oxygen from water is described using mainly the semiconductor titanium disilicide as catalyst and halogen light which closely mimics solar radiation. The reactions are carried out under non-aerobic conditions, i.e., under nitrogen. High efficiencies are reached at 1.1-1.2 bar pressure. In the first phase of these reactions the catalytically active centers are built up. During this phase of reaction the kinetics of the water splitting process is growing in and leads to a linear dependence in the further course of the reactions which consists of >96% water splitting to yield hydrogen and oxygen in a 2:1 ratio. Hydrogen is partially and reversibly stored physically, depending on temperature. Oxygen behaves differently since it is stored entirely under the applied reaction conditions (50-80 C and light) and can be liberated from storage upon heating the slurries in the dark. This allows convenient separation of hydrogen and oxygen. The stability of titanium disilicide has been positively tested over several months. This material is abundant and inexpensive besides that it absorbs most of the solar radiation. Further, XRD and XPS studies show that titanium disilicide is 80% crystalline and the oxide formation is limited to a few molecular layers in depth. By using labeled water it was shown that labeled dioxygen appears in the gas phase of such reactions, this showing definitively that hydrogen evolution occuring here stems from photochemical splitting of water. Further, water splitting is part of a project which involves photoelectrochemistry and in which the silicides are used as light-receiving electrode and transition metal-coated anodes serve to split water. (orig.)

  2. Visible-light-induced water splitting on a chip

    NARCIS (Netherlands)

    Zoontjes, Michel Gerardus Cornelis

    2015-01-01

    In this thesis, a photoelectrochemical water splitting cell concept is discussed, based on a combination of semiconductors comprising a Z-scheme. The motivation for the development of the cell is that in the future a transition will take place from a fossil fuel-based economy, to an economy based on

  3. Visible light water splitting using dye-sensitized oxide semiconductors.

    Science.gov (United States)

    Youngblood, W Justin; Lee, Seung-Hyun Anna; Maeda, Kazuhiko; Mallouk, Thomas E

    2009-12-21

    Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO(2) to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process. This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy)(3)](2+) derivatives, catalyze the photoproduction of hydrogen from sacrificial

  4. The potential versus current state of water splitting with hematite.

    Science.gov (United States)

    Zandi, Omid; Hamann, Thomas W

    2015-09-21

    This review describes the potential of hematite as a photoanode material for photoelectrochemical (PEC) water splitting. The current understanding of key loss-mechanisms of hematite are introduced and correlated to performance enhancement strategies. The significant voltage loss associated with overcoming the competitive water oxidation and surface state recombination has recently been surmounted through a combination of high temperature annealing and surface modification with water oxidation catalysts. Substantial efforts have been made at nanostructuring electrodes to increase the charge separation efficiency without sacrificing light absorption. Even in optimized nanostructured electrodes, however, charge separation continues to be the primary barrier to achieving efficient water splitting with hematite. Specifically, significant depletion region recombination results in voltage dependant photocurrent which constrains the fill factor. Thus, future directions to enhance the efficiency of hematite electrodes are discussed with an emphasis on circumventing depletion region recombination.

  5. The NEWS Water Cycle Climatology

    Science.gov (United States)

    Rodell, Matthew; Beaudoing, Hiroko Kato; L'Ecuyer, Tristan; William, Olson

    2012-01-01

    NASA's Energy and Water Cycle Study (NEWS) program fosters collaborative research towards improved quantification and prediction of water and energy cycle consequences of climate change. In order to measure change, it is first necessary to describe current conditions. The goal of the first phase of the NEWS Water and Energy Cycle Climatology project was to develop "state of the global water cycle" and "state of the global energy cycle" assessments based on data from modern ground and space based observing systems and data integrating models. The project was a multi-institutional collaboration with more than 20 active contributors. This presentation will describe the results of the water cycle component of the first phase of the project, which include seasonal (monthly) climatologies of water fluxes over land, ocean, and atmosphere at continental and ocean basin scales. The requirement of closure of the water budget (i.e., mass conservation) at various scales was exploited to constrain the flux estimates via an optimization approach that will also be described. Further, error assessments were included with the input datasets, and we examine these in relation to inferred uncertainty in the optimized flux estimates in order to gauge our current ability to close the water budget within an expected uncertainty range.

  6. The Water Cycle Solutions Network

    Science.gov (United States)

    Houser, P.; Belvedere, D.; Imam, B.; Schiffer, R.; Schlosser, C.; Gupta, H.; Welty, C.; Vörösmarty, C.; Matthews, D.; Lawford, R.

    2006-12-01

    The goal of the Water cycle Solutions Network is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend research results to augment decision support tools and meet national needs. WaterNet will engage relevant NASA water cycle research resources and community-of-practice organizations, to develop what we term an "actionable database" that can be used to communicate and connect water cycle research results (WCRs) towards the improvement of water-related Decision Support Tools (DSTs). An actionable database includes enough sufficient knowledge about its nodes and their heritage so that connections between these nodes are identifiable and robust. Recognizing the many existing highly valuable water-related science and application networks, we will focus the balance of our efforts on enabling their interoperability in a solutions network context. We will initially focus on identification, collection, and analysis of the two end points, these being the WCRs and water related DSTs. We will then develop strategies to connect these two end points via innovative communication strategies, improved user access to NASA resources, improved water cycle research community appreciation for DST requirements, improved policymaker, management and stakeholder knowledge of NASA research and application products, and improved identification of pathways for progress. Finally, we will develop relevant benchmarking and metrics, to understand the network's characteristics, to optimize its performance, and to establish sustainability. The WaterNet will deliver numerous pre-evaluation reports that will identify the pathways for improving the collective ability of the water cycle community to routinely harness WCRs that address crosscutting water cycle challenges.

  7. Silicon and tungsten oxide nanostructures for water splitting

    Science.gov (United States)

    Reyes Gil, Karla R.; Spurgeon, Joshua M.; Lewis, Nathan S.

    2009-08-01

    Inorganic semiconductors are promising materials for driving photoelectrochemical water-splitting reactions. However, there is not a single semiconductor material that can sustain the unassisted splitting of water into H2 and O2. Instead, we are developing a three part cell design where individual catalysts for water reduction and oxidation will be attached to the ends of a membrane. The job of splitting water is therefore divided into separate reduction and oxidation reactions, and each catalyst can be optimized independently for a single reaction. Silicon might be suitable to drive the water reduction. Inexpensive highly ordered Si wire arrays were grown on a single crystal wafer and transferred into a transparent, flexible polymer matrix. In this array, light would be absorbed along the longer axial dimension while the resulting electrons or holes would be collected along the much shorter radial dimension in a massively parallel array resembling carpet fibers on a microscale, hence the term "solar carpet". Tungsten oxide is a good candidate to drive the water oxidation. Self-organized porous tungsten oxide was successfully synthesized on the tungsten foil by anodization. This sponge-like structure absorbs light efficiently due to its high surface area; hence we called it "solar sponge".

  8. Photochemical water splitting mediated by a C1 shuttle

    KAUST Repository

    Alderman, N. P.

    2016-10-31

    The possibility of performing photochemical water splitting in a two-stage system, separately releasing the H and O components, has been probed with two separate catalysts and in combination with a formaldehyde/formate shuttling redox couple. In the first stage, formaldehyde releases hydrogen vigorously in the presence of an Na[Fe(CN)]·10HO catalyst, selectively affording the formate anion. In the second stage, the formate anion is hydro-genated back to formaldehyde by water and in the presence of a BiWO photocatalyst whilst releasing oxygen. Both stages operate at room temperature and under visible light irradiation. The two separate photocatalysts are compatible since water splitting can also be obtained in one-pot experiments with simultaneous H/O evolution.

  9. Photoelectrochemical water splitting in separate oxygen and hydrogen cells.

    Science.gov (United States)

    Landman, Avigail; Dotan, Hen; Shter, Gennady E; Wullenkord, Michael; Houaijia, Anis; Maljusch, Artjom; Grader, Gideon S; Rothschild, Avner

    2017-06-01

    Solar water splitting provides a promising path for sustainable hydrogen production and solar energy storage. One of the greatest challenges towards large-scale utilization of this technology is reducing the hydrogen production cost. The conventional electrolyser architecture, where hydrogen and oxygen are co-produced in the same cell, gives rise to critical challenges in photoelectrochemical water splitting cells that directly convert solar energy and water to hydrogen. Here we overcome these challenges by separating the hydrogen and oxygen cells. The ion exchange in our cells is mediated by auxiliary electrodes, and the cells are connected to each other only by metal wires, enabling centralized hydrogen production. We demonstrate hydrogen generation in separate cells with solar-to-hydrogen conversion efficiency of 7.5%, which can readily surpass 10% using standard commercial components. A basic cost comparison shows that our approach is competitive with conventional photoelectrochemical systems, enabling safe and potentially affordable solar hydrogen production.

  10. Computational Screening of Materials for Water Splitting Applications

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio

    Design new materials for energy production in a photoelectrochemical cell, where water is split into hydrogen and oxygen by solar light, is one possible solution to the problem of increasing energy demand and storage. A screening procedure based on ab-initio density functional theory calculations...... has been applied to guide the search for new materials. The main descriptors of the properties relevant for the screening are: heat of formation, electronic bandgap, and positions of the band edges with respect to the red-ox levels of water. A recently implemented exchange-correlation functional...... for visible light harvesting, 20 for the one-photon and 12 for the two-photon water splitting process. In addition, 16 candidates were suggested for the transparent shielding of the photocatalyst. The problem of corrosion has been addressed for the candidates for the one-photon scheme using Pourbaix diagrams...

  11. Evaluation of selected information on splitting devices for water samples

    Science.gov (United States)

    Capel, P.D.; Larson, S.J.

    1996-01-01

    Four devices for splitting water samples into representative aliquots are used by the U.S. Geological Survey's Water Resources Division. A thorough evaluation of these devices (14-liter churn, 8-liter churn, plastic cone, and Teflon cone) encompasses a wide variety of concerns, based on both chemical and physical considerations. This report surveys the existing data (as of April 1994) on cleaning efficiency and splitting capability of these devices and presents the data in a systematic framework for evaluation. From the existing data, some of these concerns are adequately or partially addressed, but the majority of concerns could not be addressed because of the lack of data. In general, the existing cleaning and transport protocols are adequate at the milligram per liter level, but the adequacy is largely unknown for trace elements and organic chemicals at lower concen- trations. The existing data indicate that better results are obtained when the splitters are cleaned in the laboratory rather than in the field. Two conclusions that can be reached on the splitting capability of solids are that more work must be done with all four devices to characterize and quantify their limitations and range of usefulness, and that the 14-liter churn (and by association, the 8-liter churn) is not useful in obtaining representative splits of sand-sized particles.

  12. Efficient solar-to-fuels production from a hybrid microbial-water-splitting catalyst system.

    Science.gov (United States)

    Torella, Joseph P; Gagliardi, Christopher J; Chen, Janice S; Bediako, D Kwabena; Colón, Brendan; Way, Jeffery C; Silver, Pamela A; Nocera, Daniel G

    2015-02-24

    Photovoltaic cells have considerable potential to satisfy future renewable-energy needs, but efficient and scalable methods of storing the intermittent electricity they produce are required for the large-scale implementation of solar energy. Current solar-to-fuels storage cycles based on water splitting produce hydrogen and oxygen, which are attractive fuels in principle but confront practical limitations from the current energy infrastructure that is based on liquid fuels. In this work, we report the development of a scalable, integrated bioelectrochemical system in which the bacterium Ralstonia eutropha is used to efficiently convert CO2, along with H2 and O2 produced from water splitting, into biomass and fusel alcohols. Water-splitting catalysis was performed using catalysts that are made of earth-abundant metals and enable low overpotential water splitting. In this integrated setup, equivalent solar-to-biomass yields of up to 3.2% of the thermodynamic maximum exceed that of most terrestrial plants. Moreover, engineering of R. eutropha enabled production of the fusel alcohol isopropanol at up to 216 mg/L, the highest bioelectrochemical fuel yield yet reported by >300%. This work demonstrates that catalysts of biotic and abiotic origin can be interfaced to achieve challenging chemical energy-to-fuels transformations.

  13. To Split or Not to Split, That Is the Question in Some Shallow Water Equations

    CERN Document Server

    Martínez, Vicente

    2012-01-01

    In this paper we analyze the use of time splitting techniques for solving shallow water equation. We discuss some properties that these schemes should satisfy so that interactions between the source term and the shock waves are controlled. This paper shows that these schemes must be well balanced in the meaning expressed by Greenberg and Leroux [5]. More speci?cally, we analyze in what cases it is enough to verify an Approximate C-property and in which cases it is required to verify an Exact C-property (see [1], [2]). We also include some numerical tests in order to justify our reasoning.

  14. Photocatalytic and Photoelectrochemical Water Splitting by Inorganic Materials

    KAUST Repository

    Deng, Xiaohui

    2012-12-01

    Hydrogen has been identified as a potential energy carrier due to its high energy capacity and environmental harmlessness. Compared with hydrogen production from hydrocarbons such as methane and naphtha in a conventional hydrogen energy system, photocatalytic hydrogen evolution from water splitting offers a more economic approach since it utilizes the abundant solar irradiation as energy source and water as initial reactant. Powder photocatalyst, which generates electrons and holes under illumination, is the origin where the overall reaction happens. High solar energy conversion efficiency especially from visible range is commonly the target. Besides, cocatalyst for hydrogen and oxygen evolution is also playing an essential role in facilitating the charge separation and enhancing the kinetics. In this thesis, the objective is to achieve high energy conversion efficiency towards water splitting from diverse aspects. The third chapter focuses on a controllable method to fabricate metal pattern, which is candidate for hydrogen evolution cocatalyst while chapter 4 is on the combination of strontium titanium oxide (SrTiO3) with graphene oxide (GO) for a better photocatalytic performance. In the last chapter, photoelectrochemical water splitting by Ta3N5 photoanode and FeOOH as a novel oxygen evolution cocatalyst has been investigated.

  15. Noble metal-free hydrogen evolution catalysts for water splitting.

    Science.gov (United States)

    Zou, Xiaoxin; Zhang, Yu

    2015-08-07

    Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

  16. Toward visible light response: Overall water splitting using heterogeneous photocatalysts

    KAUST Repository

    Takanabe, Kazuhiro

    2011-01-01

    Extensive energy conversion of solar energy can only be achieved by large-scale collection of solar flux. The technology that satisfies this requirement must be as simple as possible to reduce capital cost. Overall water splitting by powder-form photocatalysts directly produces a mixture of H 2 and O2 (chemical energy) in a single reactor, which does not require any complicated parabolic mirrors and electronic devices. Because of its simplicity and low capital cost, it has tremendous potential to become the major technology of solar energy conversion. Development of highly efficient photocatalysts is desired. This review addresses why visible light responsive photocatalysts are essential to be developed. The state of the art for the photocatalysts for overall water splitting is briefly described. Moreover, various fundamental aspects for developing efficient photocatalysts, such as particle size of photocatalysts, cocatalysts, and reaction kinetics are discussed. Copyright © 2011 De Gruyter.

  17. Ti-doped hematite thin films for efficient water splitting

    Science.gov (United States)

    Atabaev, Timur Sh.; Ajmal, Muhammad; Hong, Nguyen Hoa; Kim, Hyung-Kook; Hwang, Yoon-Hwae

    2015-03-01

    Uniform Ti-doped hematite thin films were deposited on transparent fluorine-doped tin oxide FTO coated glasses using a pulsed laser deposition method. An influence of dopant concentration on the photoelectrochemical characteristics was examined under water splitting. Photocurrent measurements indicated that 3 mol% of Ti atoms was optimal dopant concentration in hematite films produced by this method. The maximum photocurrent density of un-doped and 3 mol% Ti-doped Fe2O3 photoelectrodes was 0.67 and 1.64 mA/cm2 at 1.23 V versus RHE, respectively. The incorporation of Ti atoms into hematite photoelectrodes was found to drastically enhance the water splitting performance.

  18. A Review of ABO3 Perovskite Photocatalysts for Water Splitting

    Institute of Scientific and Technical Information of China (English)

    Zhang Hongjie; Chen Gang; Li Zhonghua; Liu Jiangwen

    2007-01-01

    Photocatalysts with perovskites for hydrogen production from aqueous solution were reviewed. Among the most of metal oxide photocatalysts, the family of ABO3 Perovskite-type oxide shows higher photocatalytie activity, especially alkaline earth titanate and alkali tantalate. Therein, sodium tantalate showed the highest activity for water splitting. The reasons for the high photocatalytic activity of ABO3 perovskties are considered to the diverse and flexible crystal structure. The photocatalytic activity of ABO3 perovskties can be improved by doping other element at A site, B site or O site and loading CO-catalysts such as NiO and Pt. In this paper, the mechanism of photocatalytic water splitting, the structure of ABO3 perovsktie, and Perovskite-type photocatalysts were reviewed.

  19. Photoelectrochemical water splitting standards, experimental methods, and protocols

    CERN Document Server

    Chen, Zhebo; Miller, Eric

    2014-01-01

    This book outlines many of the techniques involved in materials development and characterization for photoelectrochemical (PEC) - for example, proper metrics for describing material performance, how to assemble testing cells and prepare materials for assessment of their properties, and how to perform the experimental measurements needed to achieve reliable results towards better scientific understanding. For each technique, proper procedure, benefits, limitations, and data interpretation are discussed. Consolidating this information in a short, accessible, and easy to read reference guide will allow researchers to more rapidly immerse themselves into PEC research and also better compare their results against those of other researchers to better advance materials development. This book serves as a "how-to" guide for researchers engaged in or interested in engaging in the field of photoelectrochemical (PEC) water splitting. PEC water splitting is a rapidly growing field of research in which the goal is to deve...

  20. Rational design of semiconductors for photoelectrochemical water splitting

    Science.gov (United States)

    Wei, Su-Huai

    2013-12-01

    Using first-principles method as a tool, we discuss the general strategies for the rational design of semiconductors to simultaneously meet all of requirements for high-efficiency, solar-driven photoelectrochemical (PEC) water-splitting devices. Our studies demonstrate that theoretical calculations, which provided deep understanding of the underlying physics behind these PEC materials, can greatly accelerate scientific discovery of new PEC materials in this exciting field.

  1. Thermodynamic evaluation of the Kalina split-cycle concepts for waste heat recovery applications

    DEFF Research Database (Denmark)

    Nguyen, Tuong-Van; Knudsen, Thomas; Larsen, Ulrik

    2014-01-01

    of varying boundary conditions by conducting an exergy analysis. The design parameters of each configuration were determined by performing a multi-variable optimisation. The results indicate that the Kalina split-cycle with reheat presents an exergetic efficiency by 2.8% points higher than a reference Kalina...... and condenser, and indicates a reduction of the exergy destruction by about 23% in the heat recovery system compared to the baseline cycle....

  2. Water Splitting with Series-Connected Polymer Solar Cells.

    Science.gov (United States)

    Esiner, Serkan; van Eersel, Harm; van Pruissen, Gijs W P; Turbiez, Mathieu; Wienk, Martijn M; Janssen, René A J

    2016-10-12

    We investigate light-driven electrochemical water splitting with series-connected polymer solar cells using a combined experimental and modeling approach. The expected maximum solar-to-hydrogen conversion efficiency (ηSTH) for light-driven water splitting is modeled for two, three, and four series-connected polymer solar cells. In the modeling, we assume an electrochemical water splitting potential of 1.50 V and a polymer solar cell for which the external quantum efficiency and fill factor are both 0.65. The minimum photon energy loss (Eloss), defined as the energy difference between the optical band gap (Eg) and the open-circuit voltage (Voc), is set to 0.8 eV, which we consider a realistic value for polymer solar cells. Within these approximations, two series-connected single junction cells with Eg = 1.73 eV or three series-connected cells with Eg = 1.44 eV are both expected to give an ηSTH of 6.9%. For four series-connected cells, the maximum ηSTH is slightly less at 6.2% at an optimal Eg = 1.33 eV. Water splitting was performed with series-connected polymer solar cells using polymers with different band gaps. PTPTIBDT-OD (Eg = 1.89 eV), PTB7-Th (Eg = 1.56 eV), and PDPP5T-2 (Eg = 1.44 eV) were blended with [70]PCBM as absorber layer for two, three, and four series-connected configurations, respectively, and provide ηSTH values of 4.1, 6.1, and 4.9% when using a retroreflective foil on top of the cell to enhance light absorption. The reasons for deviations with experiments are analyzed and found to be due to differences in Eg and Eloss. Light-driven electrochemical water splitting was also modeled for multijunction polymer solar cells with vertically stacked photoactive layers. Under identical assumptions, an ηSTH of 10.0% is predicted for multijunction cells.

  3. Solar Water Splitting and Nitrogen Fixation with Layered Bismuth Oxyhalides.

    Science.gov (United States)

    Li, Jie; Li, Hao; Zhan, Guangming; Zhang, Lizhi

    2017-01-17

    Hydrogen and ammonia are the chemical molecules that are vital to Earth's energy, environmental, and biological processes. Hydrogen with renewable, carbon-free, and high combustion-enthalpy hallmarks lays the foundation of next-generation energy source, while ammonia furnishes the building blocks of fertilizers and proteins to sustain the lives of plants and organisms. Such merits fascinate worldwide scientists in developing viable strategies to produce hydrogen and ammonia. Currently, at the forefronts of hydrogen and ammonia syntheses are solar water splitting and nitrogen fixation, because they go beyond the high temperature and pressure requirements of methane stream reforming and Haber-Bosch reaction, respectively, as the commercialized hydrogen and ammonia production routes, and inherit the natural photosynthesis virtues that are green and sustainable and operate at room temperature and atmospheric pressure. The key to propelling such photochemical reactions lies in searching photocatalysts that enable water splitting into hydrogen and nitrogen fixation to make ammonia efficiently. Although the past 40 years have witnessed significant breakthroughs using the most widely studied TiO2, SrTiO3, (Ga1-xZnx)(N1-xOx), CdS, and g-C3N4 for solar chemical synthesis, two crucial yet still unsolved issues challenge their further progress toward robust solar water splitting and nitrogen fixation, including the inefficient steering of electron transportation from the bulk to the surface and the difficulty of activating the N≡N triple bond of N2. This Account details our endeavors that leverage layered bismuth oxyhalides as photocatalysts for efficient solar water splitting and nitrogen fixation, with a focus on addressing the above two problems. We first demonstrate that the layered structures of bismuth oxyhalides can stimulate an internal electric field (IEF) that is capable of efficiently separating electrons and holes after their formation and of precisely channeling

  4. Round and Round the Water Cycle

    Science.gov (United States)

    Bradley, Barbara A.

    2017-01-01

    Children enjoy water play, and kindergarten children can learn about the water cycle. Teachers are already introducing elements of the water cycle when discussing weather and bodies of water. The water cycle also can be a springboard for teaching children about plants and animals and the importance of water for sustaining life and shaping our…

  5. Photocatalytic water splitting with acridine dyes: Guidelines from computational chemistry

    Science.gov (United States)

    Liu, Xiaojun; Karsili, Tolga N. V.; Sobolewski, Andrzej L.; Domcke, Wolfgang

    2016-01-01

    The photocatalytic splitting of water into Hrad and OHrad radicals in hydrogen-bonded chromophore-water complexes has been explored with computational methods for the chromophores acridine orange (AO) and benzacridine (BA). These dyes are strong absorbers within the range of the solar spectrum. It is shown that low-lying charge-transfer excited states exist in the hydrogen-bonded AOsbnd H2O and BAsbnd H2O complexes which drive the transfer of a proton from water to the chromophore, which results in AOHradsbnd OHrad or BAHradsbnd OHrad biradicals. The AOHrad and BAHrad radicals possess bright ππ∗ excited states with vertical excitation energies near 3.0 eV which are predissociated by a low-lying repulsive πσ∗ state. The conical intersections of the πσ∗ state with the ππ∗ excited states and the ground state provide a mechanism for the photodetachment of the H-atom by a second photon. Our results indicate that AO and BA are promising chromophores for water splitting with visible light.

  6. Comparative studies on different nanofiber photocatalysts for water splitting

    Science.gov (United States)

    Alharbi, Abdulaziz; Alarifi, Ibrahim M.; Khan, Waseem S.; Asmatulu, Ramazan

    2016-04-01

    Water splitting using photocatalyst has become a topic of recent investigation since it has the potential of producing hydrogen for clean energy from sunlight. An extensive number of solid photocatalysts have been studied for overall water splitting in recent years. In this study, two methods were employed to synthesize two different photocatalysts for water splitting. The first method describes the synthesis of nickel oxide-loaded strontium titanate (NiO-SrTiO3) particles on electrospun polyacrylonitrile (PAN) nanofibers incorporated with graphene nanoplatelets for water splitting. The electrospun PAN fibers were first oxidized at 270°C for two hours and subsequently immersed in a solution containing ethanol, titanium (IV)-isopropoxide [C12H28O4Ti] and strontium nitrate [Sr(NO3)2]. This solution was then treated with NiO nanoparticles dispersed in toluene. The surface treated PAN fibers were annealed at 600°C in air for 1 hour to transform fibers into a crystalline form for improved photocatalyst performance. In the second method, coaxial electrospinning process was used to produce core/shell strontium titanate/nickel oxide (SrTiO3-NiO) nanofibers. In coaxial method, poly (vinyl pyrrolidone) (PVP) was dissolved in deionized (DI) water, and then titanium (IV) isopropoxide [C12H28O4Ti] and strontium nitrate [Sr(NO3)2] were added into the solution to form the inner (core) layer. For outer (shell) solution, polyacrylonitrile (PAN) polymer was dissolved in dimethylformamide (DMF) at a weight ratio of 10:90 and then nickel oxide was mixed with the solution. Ultraviolet (UV) spectrophotometry and static contact angle measurement techniques were employed to characterize the structural properties of photocatalysts produced by both methods and a comparison was made between the two photocatalysts. The morphology and diameter of the nanofibers were observed by scanning electron microscopy (SEM). The structure and crystallinity of the calcined nanofibers were also observed

  7. Transtion metal oxides for solar water splitting devices

    Science.gov (United States)

    Smith, Adam M.

    Although the terrestrial flux of solar energy is enough to support human endeavors, storage of solar energy remains a significant challenge to large-scale implementation of solar energy production. One route to energy storage involves the capture and conversion of sunlight to chemical species such as molecular hydrogen and oxygen via water splitting devices. The oxygen evolution half-reaction particularly suffers from large kinetic overpotentials. Additionally, a photoactive material that exhibits stability in oxidizing conditions present during oxygen evolution represents a unique challenge for devices. These concerns can be potentially addressed with a metal oxide photoanode coupled with efficient water oxidation electrocatalysts. Despite decades of research, structure-composition to property relationships are still needed for the design of metal oxide oxygen evolution materials. This dissertation investigates transition metal oxide materials for the oxygen evolution portion of water splitting devices. Chapter I introduces key challenges for solar driven water splitting. Chapter II elucidates the growth mechanism of tungsten oxide (WOX) nanowires (NWs), a proposed photoanode material for water splitting. Key findings include (1) a planar defect-driven pseudo-one-dimensional growth mechanism and (2) morphological control through the supersaturation of vapor precursors. Result 1 is significant as it illustrates that common vapor-phase syntheses of WOX NWs depend on the formation of planar defects through NWs, which necessitates reconsideration of WOX as a photoanode. Chapter III presents work towards (1) single crystal WOX synthesis and characterization and (2) WOX NW device fabrication. Chapter IV makes use of the key result that WOX NWs are defect rich and therefore conductive in order to utilize them as a catalyst scaffold for oxygen evolution in acidic media. Work towards utilizing NW scaffolds include key results such as stability under anodic potentials and

  8. Silicon/Carbon Nanotube Photocathode for Splitting Water

    Science.gov (United States)

    Amashukeli, Xenia; Manohara, Harish; Greer, Harold F.; Hall, Lee J.; Gray, Harry B.; Subbert, Bryan

    2013-01-01

    A proof-of-concept device is being developed for hydrogen gas production based on water-splitting redox reactions facilitated by cobalt tetra-aryl porphyrins (Co[TArP]) catalysts stacked on carbon nanotubes (CNTs) that are grown on n-doped silicon substrates. The operational principle of the proposed device is based on conversion of photoelectron energy from sunlight into chemical energy, which at a later point, can be turned into electrical and mechanical power. The proposed device will consist of a degenerately n-doped silicon substrate with Si posts covering the surface of a 4-in. (approximately equal to 10cm) wafer. The substrate will absorb radiation, and electrons will move radially out of Si to CNT. Si posts are designed such that the diameters are small enough to allow considerable numbers of electrons to transport across to the CNT layer. CNTs will be grown on top of Si using conformal catalyst (Fe/Ni) deposition over a thin alumina barrier layer. Both metallic and semiconducting CNT will be used in this investigation, thus allowing for additional charge generation from CNT in the IR region. Si post top surfaces will be masked from catalyst deposition so as to prevent CNT growth on the top surface. A typical unit cell will then consist of a Si post covered with CNT, providing enhanced surface area for the catalyst. The device will then be dipped into a solution of Co[TArP] to enable coating of CNT with Co(P). The Si/CNT/Co [TArP] assembly then will provide electrons for water splitting and hydrogen gas production. A potential of 1.23 V is needed to split water, and near ideal band gap is approximately 1.4 eV. The combination of doped Si/CNT/Co [TArP] will enable this redox reaction to be more efficient.

  9. Development of metal tungstate alloys for photoelectrochemical water splitting

    Science.gov (United States)

    Prasher, D.; Chong, M.; Chang, Y.; Sarker, P.; Huda, M. N.; Gaillard, N.

    2013-09-01

    In the present paper, we report our efforts on the development of metal tungstate alloys for efficient and economical photoelectrochemical water splitting. As suggested by density functional theory (DFT), the addition of copper to the host tungsten trioxide improves the visible light absorption. Past studies at the Hawaii Natural Energy Institute have demonstrated that water splitting with co-sputtered and spray-deposited CuWO4 with 2.2 eV band gap was feasible, although the efficiency of the process was severely limited by charge carrier recombination. Density functional theory calculation showed that CuWO4 contains unfilled mid-gap states and high electron effective mass. To improve transport properties of CuWO4, we hypothesized that copper tungstate (CuWO4) hollow nanospheres could improve holes transfer to the electrolyte and reduce recombination, improving the water splitting efficiency. Nanospheres were synthesized by sonochemical technique in which the precursors used were copper acetate, ammonium meta-tungstate and thiourea (used as a fuel to complete the reaction). All chemicals undergo a high-energy sonication by using ethylene glycol as a solvent. Preliminary linear scan voltammetry (LSV) performed for annealed CuWO4 under front side and back side simulated AM-1.5 illumination demonstrated that the CuWO4 hollow nanospheres were photoactive. Subsequent scanning (SEM) and transmission (TEM) electron microscopy studies revealed the clear formation of nano sized hollow spherical shaped CuWO4 particles. X-ray diffraction analysis showed a clear formation of triclinic CuWO4 structure during the sonochemical process.

  10. All inorganic semiconductor nanowire mesh for direct solar water splitting.

    Science.gov (United States)

    Liu, Bin; Wu, Cheng-Hao; Miao, Jianwei; Yang, Peidong

    2014-11-25

    The generation of chemical fuels via direct solar-to-fuel conversion from a fully integrated artificial photosynthetic system is an attractive approach for clean and sustainable energy, but so far there has yet to be a system that would have the acceptable efficiency, durability and can be manufactured at a reasonable cost. Here, we show that a semiconductor mesh made from all inorganic nanowires can achieve unassisted solar-driven, overall water-splitting without using any electron mediators. Free-standing nanowire mesh networks could be made in large scales using solution synthesis and vacuum filtration, making this approach attractive for low cost implementation.

  11. Wiring of Photosystem II to Hydrogenase for Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Mersch, Dirk; Lee, Chong-Yong; Zhang, Jenny Zhenqi; Brinkert, Katharina; Fontecilla-Camps, Juan C; Rutherford, A William; Reisner, Erwin

    2015-07-08

    In natural photosynthesis, light is used for the production of chemical energy carriers to fuel biological activity. The re-engineering of natural photosynthetic pathways can provide inspiration for sustainable fuel production and insights for understanding the process itself. Here, we employ a semiartificial approach to study photobiological water splitting via a pathway unavailable to nature: the direct coupling of the water oxidation enzyme, photosystem II, to the H2 evolving enzyme, hydrogenase. Essential to this approach is the integration of the isolated enzymes into the artificial circuit of a photoelectrochemical cell. We therefore developed a tailor-made hierarchically structured indium-tin oxide electrode that gives rise to the excellent integration of both photosystem II and hydrogenase for performing the anodic and cathodic half-reactions, respectively. When connected together with the aid of an applied bias, the semiartificial cell demonstrated quantitative electron flow from photosystem II to the hydrogenase with the production of H2 and O2 being in the expected two-to-one ratio and a light-to-hydrogen conversion efficiency of 5.4% under low-intensity red-light irradiation. We thereby demonstrate efficient light-driven water splitting using a pathway inaccessible to biology and report on a widely applicable in vitro platform for the controlled coupling of enzymatic redox processes to meaningfully study photocatalytic reactions.

  12. Solar water splitting in a molecular photoelectrochemical cell.

    Science.gov (United States)

    Alibabaei, Leila; Brennaman, M Kyle; Norris, Michael R; Kalanyan, Berç; Song, Wenjing; Losego, Mark D; Concepcion, Javier J; Binstead, Robert A; Parsons, Gregory N; Meyer, Thomas J

    2013-12-10

    Artificial photosynthesis and the production of solar fuels could be a key element in a future renewable energy economy providing a solution to the energy storage problem in solar energy conversion. We describe a hybrid strategy for solar water splitting based on a dye sensitized photoelectrosynthesis cell. It uses a derivatized, core-shell nanostructured photoanode with the core a high surface area conductive metal oxide film--indium tin oxide or antimony tin oxide--coated with a thin outer shell of TiO2 formed by atomic layer deposition. A "chromophore-catalyst assembly" 1, [(PO3H2)2bpy)2Ru(4-Mebpy-4-bimpy)Rub(tpy)(OH2)](4+), which combines both light absorber and water oxidation catalyst in a single molecule, was attached to the TiO2 shell. Visible photolysis of the resulting core-shell assembly structure with a Pt cathode resulted in water splitting into hydrogen and oxygen with an absorbed photon conversion efficiency of 4.4% at peak photocurrent.

  13. Ultrasonic splitting of oil-in-water emulsions

    DEFF Research Database (Denmark)

    Hald, Jens; König, Ralf; Benes, Ewald

    1999-01-01

    Standing resonant ultrasonic wave fields can be utilized for liquid–liquid separation of the dispersed particles and the fluid caused by the acoustic radiation pressure and the induced particle agglomeration or coagulation/coalescence process. For the splitting of oil-in-water emulsions...... emulsion samples have been investigated. The quality of the ultrasonic-induced particle separation/coagulation process is characterized by physical–chemical analysis of the separated oil- and water phase and by determining the change of the particle size distribution of the initial emulsion due...... of up to 24 W/cm2 into the sonication volume. The chosen resonance frequency is kept stable by automatic frequency control utilizing the maximum true power criterion. Physically and chemically well-defined low and high density pure laboratory and also industrially used cooling-lubricating oil-in-water...

  14. Hydrogen production via thermochemical water-splitting by lithium redox reaction

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Naoya [Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530 (Japan); Miyaoka, Hiroki, E-mail: miyaoka@h2.hiroshima-u.ac.jp [Institute for Sustainable Sciences and Development, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530 (Japan); Ichikawa, Takayuki; Kojima, Yoshitsugu [Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530 (Japan); Institute for Advanced Materials Research, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530 (Japan)

    2013-12-15

    Highlights: •Hydrogen production via water-splitting by lithium redox reactions possibly proceeds below 800 °C. •Entropy control by using nonequilibrium technique successfully reduces the reaction temperature. •The operating temperature should be further reduced by optimizing the nonequilibrium condition to control the cycle. -- Abstracts: Hydrogen production via thermochemical water-splitting by lithium redox reactions was investigated as energy conversion technique. The reaction system consists of three reactions, which are hydrogen generation by the reaction of lithium and lithium hydroxide, metal separation by thermolysis of lithium oxide, and oxygen generation by hydrolysis of lithium peroxide. The hydrogen generation reaction completed at 500 °C. The metal separation reaction is thermodynamically difficult because it requires about 3400 °C in equilibrium condition. However, it was indicated from experimental results that the reaction temperature was drastically reduced to 800 °C by using nonequilibrium technique. The hydrolysis reaction was exothermic reaction, and completed by heating up to 300 °C. Therefore, it was expected that the water-splitting by lithium redox reactions was possibly operated below 800 °C under nonequilibrium condition.

  15. The GA sulfur-iodine water-splitting process - A status report

    Science.gov (United States)

    Besenbruch, G. E.; Chiger, H. D.; Mccorkle, K. H.; Norman, J. H.; Rode, J. S.; Schuster, J. R.; Trester, P. W.

    1981-01-01

    The development of a sulfur-iodine thermal water splitting cycle is described. The process features a 50% thermal efficiency, plus all liquid and gas handling. Basic chemical investigations comprised the development of multitemperature and multistage sulfuric acid boost reactors, defining the phase behavior of the HI/I2/H2O/H3PO4 mixtures, and development of a decomposition process for hydrogen iodide in the liquid phase. Initial process engineering studies have led to a 47% efficiency, improvements of 2% projected, followed by coupling high-temperature solar concentrators to the splitting processes to reduce power requirements. Conceptual flowsheets developed from bench models are provided; materials investigations have concentrated on candidates which can withstand corrosive mixtures at temperatures up to 400 deg K, with Hastelloy C-276 exhibiting the best properties for containment and heat exchange to I2.

  16. The GA sulfur-iodine water-splitting process - A status report

    Science.gov (United States)

    Besenbruch, G. E.; Chiger, H. D.; Mccorkle, K. H.; Norman, J. H.; Rode, J. S.; Schuster, J. R.; Trester, P. W.

    1981-01-01

    The development of a sulfur-iodine thermal water splitting cycle is described. The process features a 50% thermal efficiency, plus all liquid and gas handling. Basic chemical investigations comprised the development of multitemperature and multistage sulfuric acid boost reactors, defining the phase behavior of the HI/I2/H2O/H3PO4 mixtures, and development of a decomposition process for hydrogen iodide in the liquid phase. Initial process engineering studies have led to a 47% efficiency, improvements of 2% projected, followed by coupling high-temperature solar concentrators to the splitting processes to reduce power requirements. Conceptual flowsheets developed from bench models are provided; materials investigations have concentrated on candidates which can withstand corrosive mixtures at temperatures up to 400 deg K, with Hastelloy C-276 exhibiting the best properties for containment and heat exchange to I2.

  17. Colloidal nanocrystals for photoelectrochemical and photocatalytic water splitting

    Science.gov (United States)

    Gadiyar, Chethana; Loiudice, Anna; Buonsanti, Raffaella

    2017-02-01

    Colloidal nanocrystals (NCs) are among the most modular and versatile nanomaterial platforms for studying emerging phenomena in different fields thanks to their superb compositional and morphological tunability. A promising, yet challenging, application involves the use of colloidal NCs as light absorbers and electrocatalysts for water splitting. In this review we discuss how the tunability of these materials is ideal to understand the complex phenomena behind storing energy in chemical bonds and to optimize performance through structural and compositional modification. First, we describe the colloidal synthesis method as a means to achieve a high degree of control over single material NCs and NC heterostructures, including examples of the role of the ligands in modulating size and shape. Next, we focus on the use of NCs as light absorbers and catalysts to drive both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), together with some of the challenges related to the use of colloidal NCs as model systems and/or technological solution in water splitting. We conclude with a broader prospective on the use of colloidal chemistry for new material discovery.

  18. Facile Growth of Porous Hematite Films for Photoelectrochemical Water Splitting

    Directory of Open Access Journals (Sweden)

    Shaohua Shen

    2013-01-01

    Full Text Available We introduced a simple fabrication method of porous hematite films with tunable thickness in an aqueous solution containing FeCl3 as the single precursor. We demonstrated that the optimized thickness was necessary for high performance photoelectrochemical water splitting, by balancing photon absorption and charge carrier transport. The highest photocurrent of ca. 0.15 mA cm−2 at 1.0 V versus Ag/AgCl was achieved on the 300 nm thick porous hematite film as photoanode, with IPCE at 370 nm and 0.65 V versus Ag/AgCl to be 9.0%. This simple method allows the facile fabrication of hematite films with porous nanostructure for enabling high photon harvesting efficiency and maximized interfacial charge transfer. These porous hematite films fabricated by this simple solution-based method could be easily modified by metal doping for further enhanced photoelectrochemical activity for water splitting.

  19. Nanonet-based hematite heteronanostructures for efficient solar water splitting.

    Science.gov (United States)

    Lin, Yongjing; Zhou, Sa; Sheehan, Stafford W; Wang, Dunwei

    2011-03-02

    We report the highest external quantum efficiency measured on hematite (α-Fe(2)O(3)) without intentional doping in a water-splitting environment: 46% at λ = 400 nm. This result was enabled by the introduction of TiSi(2) nanonets, which are highly conductive and have suitably high surface areas. The nanonets serve a dual role as a structural support and an efficient charge collector, allowing for maximum photon-to-charge conversion. Without the addition of any oxygen-evolving catalysts, we obtained photocurrents of 1.6 and 2.7 mA/cm(2) at 1.23 and 1.53 V vs RHE, respectively. These results highlight the importance of charge transport in semiconductor-based water splitting, particularly for materials whose performance is limited by poor charge diffusion. Our design introduces material components to provide a dedicated charge-transport pathway, alleviating the reliance on the materials' intrinsic properties, and therefore has the potential to greatly broaden where and how various existing materials can be used in energy-related applications.

  20. Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting

    Science.gov (United States)

    Tee, Si Yin; Lee, Coryl Jing Jun; Safari Dinachali, Saman; Lai, Szu Cheng; Williams, Evan Laurence; Luo, He-Kuan; Chi, Dongzhi; Hor, T. S. Andy; Han, Ming-Yong

    2015-10-01

    This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.

  1. Nanocrystals and Nanoclusters as Cocatalysts for Photocatalytic Water Splitting

    KAUST Repository

    Sinatra, Lutfan

    2016-12-04

    The energy consumptions worldwide have increased simultaneously with the growth of the population and of the economy. Nowadays, finding an alternative way to satisfy the energy demand is one of the great challenges for the future of humanity, especially due to the limitation of fossil fuels and their effect on global warming. Hydrogen, as an alternative fuel for the future, is very attractive. Compared to traditional methods, such as the steam reforming of natural gas or coal gasification, photocatalytic water splitting (PWS) is considered to be the most sustainable alternative for producing hydrogen as a future fuel. PWS usually relies on semiconductor material that can transform the absorbed solar photon into photogenerated electrons and holes, creating a photopotential which can drive the electrochemical production of molecular hydrogen from the reduction of water. Despite its promising application, semiconductor-based PWS usually suffers from low carrier mobility and short diffusion length. Furthermore, the recombination of photogenerated electrons and holes might occur, especially if there are no suitable reaction sites available on the surface of the semiconductor. In order to facilitate the catalytic reactions on the surface of the semiconductor, the presence of a cocatalyst is necessary in order to obtain more efficient PWS processes. To this day, noble metals such as Pt, Pd, RuO2 and IrO2 are still the benchmark cocatalysts for PWS. Nevertheless, due to their high cost and limited supply, it is mandatory to develop a suitable strategy and to identify more efficient materials. Therefore, within the framework of this dissertation, novel cocatalysts and strategies that can improve the efficiency of the photocatalytic water splitting processes have been developed. Firstly, we developed a cocatalyst combining noble metals and semiconductors by means of partial galvanic replacement of the Cu2O nanocrystal with Au. The deposition of this cocatalyst on TiO2 was

  2. Transferring Knowledge of Electrocatalysis to Photocatalysis: Photocatalytic Water Splitting

    KAUST Repository

    Takanabe, Kazuhiro

    2017-06-24

    One of the most attractive features of photocatalytic reactions is the ability to achieve energetically uphill (photosynthetic) reactions. In many photocatalytic reactions, the reactions involve multielectron transfers with the adsorbed intermediates. In this case, photocatalysis is nothing but electrocatalysis initiated and driven by the electron potential shift caused by the photocatalyst (photon absorber). This condition is indeed true for photocatalysts for water splitting, which are also electrocatalysts because both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) require multiple electron transfers at the active surfaces. This chapter deals with the product-side in the six-gear concept. It shows the electrocatalytic performance when using an electrocatalyst on the surface. The chapter further shows the current-potential curve for an electrocatalytic process isolated from the photocatalyst process. For an electrocatalyst to achieve electrochemical reactions, the potential of the catalyst must be shifted at the interface of the semiconductor, providing electromotive force or overpotential for redox reactions.

  3. Layered Perovskite Nanofibers via Electrospinning for Overall Water Splitting.

    Science.gov (United States)

    Hildebrandt, Nils C; Soldat, Julia; Marschall, Roland

    2015-05-06

    The (111)-layered perovskite materials Ba5 Ta4 O15 , Ba5 Ta2 Nb2 O15 and Ba5 Nb4 O15 are prepared with nanofiber morphology via electrospinning for the first time. The nanofibers are built up from small single crystals, with up to several micrometers length even after calcination. The formation mechanism is investigated in detail, revealing an intermediate formation of amorphous barium carbonate strengthening the nanofiber morphology for high temperature treatment. All nanofiber compounds are able to generate hydrogen without any co-catalyst in photocatalytic reformation of methanol. After photodeposition of Rh-Cr2 O3 co-catalysts, the nanofibers show better activity in overall water splitting compared to sol-gel-derived powders.

  4. Focussing the view on Nature's water-splitting catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Messinger, Johannes; Yano, Junko

    2008-01-01

    About 3 billion years ago Nature invented a catalyst that splits water with highefficiency into molecular oxygen and hydrogen equivalents (protons and electrons). This reaction is energetically driven by sun light and the active centre contains relatively cheap and abundant metals: manganese and calcium. This biological system therefore forms the paradigm for all man made attempts for direct solar fuel production and several studies are underway to determine the electronic and geometric structures of this catalyst. In this report we briefly summarize the problems and the current status of these efforts, and propose a DFT-based strategy for obtaining a reliable high resolution structure of this unique catalyst that includes both the inorganic core and the first ligand sphere.

  5. Design of Compact Photoelectrochemical Cells for Water Splitting

    Directory of Open Access Journals (Sweden)

    Bosserez Tom

    2015-09-01

    Full Text Available Solar driven water splitting can be achieved by coupling electrolyzers with PhotoVoltaics (PV. Integration of both functions in a compact PhotoElectroChemical (PEC cell is an attractive option but presents significant scientific challenges. In this work, the design of single- and dual-compartment PEC cells for research purposes is discussed. The fabrication of separator-electrode assemblies is an important aspect, and upscaling of these architectures even to centimeter scale is not trivial. The layout of a new dual-compartment compact PEC cell with in-situ monitoring of pH, temperatures, and oxygen and hydrogen evolution for research purposes is presented. Finally, a prospect of future PEC cells for practical applications is presented.

  6. Black Phosphorus: Critical Review and Potential for Water Splitting Photocatalyst

    Directory of Open Access Journals (Sweden)

    Tae Hyung Lee

    2016-10-01

    Full Text Available A century after its first synthesis in 1914, black phosphorus has been attracting significant attention as a promising two-dimensional material in recent years due to its unique properties. Nowadays, with the development of its exfoliation method, there are extensive applications of black phosphorus in transistors, batteries and optoelectronics. Though, because of its hardship in mass production and stability problems, the potential of the black phosphorus in various fields is left unexplored. Here, we provide a comprehensive review of crystal structure, electronic, optical properties and synthesis of black phosphorus. Recent research works about the applications of black phosphorus is summarized. Among them, the possibility of black phosphorous as a solar water splitting photocatalyst is mainly discussed and the feasible novel structure of photocatalysts based on black phosphorous is proposed.

  7. Molecular concepts of water splitting. Nature's approach

    Energy Technology Data Exchange (ETDEWEB)

    Cox, Nicholas; Lubitz, Wolfgang [Max-Planck-Institut fuer Chemische Energiekonversion, Muelheim an der Ruhr (Germany)

    2013-07-01

    Based on studies of natural systems, much has also been learned concerning the design principles required for biomimetic catalysis of water splitting and hydrogen evolution. In summary, these include use of abundant and inexpensive metals, the effective protection of the active sites in functional environments, repair/replacement of active components in case of damage, and the optimization of reaction rates. Biomimetic chemistry aims to mimic all these features; many labs are working toward this goal by developing new approaches in the design and synthesis of such systems, encompassing not only the catalytic center, but also smart matrices and assembly via self-organization. More stable catalysts that do not require self-repair may be obtained from fully artificial (inorganic) catalytic systems that are totally different from the biological ones and only apply some basic principles learned from nature. Metals other than Mn/Ca, Fe, and Ni could be used (e.g. Co) in new ligand spheres and other matrices. For light harvesting, charge separation/stabilization, and the effective coupling of the oxidizing/reducing equivalents to the redox catalysts, different methods have been proposed - for example, covalently linked molecular donor-acceptor systems, photo-voltaic devices, semiconductor-based systems, and photoactive metal complexes. The aim of all these approaches is to develop catalytic systems that split water with sunlight into hydrogen and oxygen while displaying high efficiency and long-term stability. Such a system - either biological, biomimetic, or bioinspired - has the potential to be used on a large scale to produce 'solar fuels' (e.g. hydrogen or secondary products thereof). (orig.)

  8. Solar energy conversion by photocatalytic overall water splitting

    KAUST Repository

    Takanabe, Kazuhiro

    2015-07-04

    Summary: Solar energy is abundant and renewable energy: however, extensive conversion of the solar energy can only be achieved by large-scale collection of solar flux. The technology that satisfies this requirement must be as simple as possible to reduce capital cost. Overall water splitting (OWS) by powder-form photocatalysts directly produces H2 as a chemical energy in a single reactor, which does not require any complicated parabolic mirrors and electronic devices. Because of its simplicity and low capital cost, it has tremendous potential to become the major technology of solar energy conversion. To achieve the OWS efficiently, the development of efficient photocatalysts is mandatory. The OWS hotocatalysis involves the electrocatalys is for both water reduction and oxidation on the surafce of photocatalysts, which is driven by particular semiconductors that absorb photons to generate excited carriers. Such photocatalysts must be designed to maximize the charge separation efficiency at the catalyst-semiconductor and semiconductor-electrolyte interface. In addition the low-overpotential electrocatalyts towards water redox reactions should be insensitive to the back-reaction of the produced H2 and O2 that produces H2O. In this presentation, some recent progress on the topic of the OWS in our group will be discussed.

  9. An Optically Transparent Iron Nickel Oxide Catalyst for Solar Water Splitting.

    Science.gov (United States)

    Morales-Guio, Carlos G; Mayer, Matthew T; Yella, Aswani; Tilley, S David; Grätzel, Michael; Hu, Xile

    2015-08-12

    Sunlight-driven water splitting to produce hydrogen fuel is an attractive method for renewable energy conversion. Tandem photoelectrochemical water splitting devices utilize two photoabsorbers to harvest the sunlight and drive the water splitting reaction. The absorption of sunlight by electrocatalysts is a severe problem for tandem water splitting devices where light needs to be transmitted through the larger bandgap component to illuminate the smaller bandgap component. Herein, we describe a novel method for the deposition of an optically transparent amorphous iron nickel oxide oxygen evolution electrocatalyst. The catalyst was deposited on both thin film and high-aspect ratio nanostructured hematite photoanodes. The low catalyst loading combined with its high activity at low overpotential results in significant improvement on the onset potential for photoelectrochemical water oxidation. This transparent catalyst further enables the preparation of a stable hematite/perovskite solar cell tandem device, which performs unassisted water splitting.

  10. Discovery of Novel Perovskites for Solar Thermochemical Water Splitting from High-Throughput First-Principles Calculations

    Science.gov (United States)

    Emery, Antoine; Wolverton, Chris

    Among the several possible routes of hydrogen synthesis, thermochemical water splitting (TWS) cycles is a promising method for large scale production of hydrogen. The choice of metal oxide used in a TWS cycle is critical since it governs the rate and efficiency of the gas splitting process. In this work, we present a high-throughput density functional theory (HT-DFT) study of ABO3 perovskite compounds to screen for thermodynamically favorable two-step thermochemical water splitting materials. We demonstrate the use of two screens, based on thermodynamic stability and oxygen vacancy formation energy, on 5,329 different compositions to predict 139 stable potential candidate materials for water splitting applications. Several of these compounds have not been experimentally explored yet and present promising avenues for further research. Additionally, the large dataset of compounds and stability in our possession allowed us to revisit the structural maps for perovskites. This study shows the benefit of using first-principles calculations to efficiently screen an exhaustively large number of compounds at once. It provides a baseline for further studies involving more detailed exploration of a restricted number of those compounds.

  11. Recent Progress in Metal-Organic Frameworks for Applications in Electrocatalytic and Photocatalytic Water Splitting.

    Science.gov (United States)

    Wang, Wei; Xu, Xiaomin; Zhou, Wei; Shao, Zongping

    2017-04-01

    The development of clean and renewable energy materials as alternatives to fossil fuels is foreseen as a potential solution to the crucial problems of environmental pollution and energy shortages. Hydrogen is an ideal energy material for the future, and water splitting using solar/electrical energy is one way to generate hydrogen. Metal-organic frameworks (MOFs) are a class of porous materials with unique properties that have received rapidly growing attention in recent years for applications in water splitting due to their remarkable design flexibility, ultra-large surface-to-volume ratios and tunable pore channels. This review focuses on recent progress in the application of MOFs in electrocatalytic and photocatalytic water splitting for hydrogen generation, including both oxygen and hydrogen evolution. It starts with the fundamentals of electrocatalytic and photocatalytic water splitting and the related factors to determine the catalytic activity. The recent progress in the exploitation of MOFs for water splitting is then summarized, and strategies for designing MOF-based catalysts for electrocatalytic and photocatalytic water splitting are presented. Finally, major challenges in the field of water splitting are highlighted, and some perspectives of MOF-based catalysts for water splitting are proposed.

  12. Effect of Installation of Solar Collector on Performance of Balcony Split Type Solar Water Heaters

    Directory of Open Access Journals (Sweden)

    Xu Ji

    2015-01-01

    Full Text Available The influences of surface orientation and slope of solar collectors on solar radiation collection of balcony split type solar water heaters for six cities in China were analyzed by employing software TRNSYS. The surface azimuth had greater effect on solar radiation collection in high latitude regions. For deviation of the surface slope angle within ±20° around the optimized angle, the variation of the total annual collecting solar radiation was less than 5%. However, with deviation of 70° to 90°, the variation was up to 20%. The effects of water cycle mode, reverse slope placement of solar collector, and water tank installation height on system efficiency were experimentally studied. The thermal efficiencies of solar water heater with single row horizontal arrangement all-glass evacuated tubular collector were higher than those with vertical arrangement at the fixed surface slope angle of 90°. Compared with solar water heaters with flat-plate collector under natural circulation, the system thermal efficiency was raised up to 63% under forced circulation. For collector at reverse slope placement, the temperature-based water stratification in water tank deteriorated, and thus the thermal efficiency became low. For improving the system efficiency, an appropriate installation height of the water tank was suggested.

  13. Substitutional Doping for Aluminosilicate Mineral and Superior Water Splitting Performance

    Science.gov (United States)

    Zhang, Yi; Fu, Liangjie; Shu, Zhan; Yang, Huaming; Tang, Aidong; Jiang, Tao

    2017-07-01

    Substitutional doping is a strategy in which atomic impurities are optionally added to a host material to promote its properties, while the geometric and electronic structure evolution of natural nanoclay mineral upon substitutional metal doping is still ambiguous. This paper first designed an efficient lanthanum (La) doping strategy for nanotubular clay (halloysite nanotube, HNT) through the dynamic equilibrium of a substitutional atom in the presence of saturated AlCl3 solution, and systematic characterization of the samples was performed. Further density functional theory (DFT) calculations were carried out to reveal the geometric and electronic structure evolution upon metal doping, as well as to verify the atom-level effect of the La doping. The CdS loading and its corresponding water splitting performance could demonstrate the effect of La doping. CdS nanoparticles (11 wt.%) were uniformly deposited on the surface of La-doped halloysite nanotube (La-HNT) with the average size of 5 nm, and the notable photocatalytic hydrogen evolution rate of CdS/La-HNT reached up to 47.5 μmol/h. The results could provide a new strategy for metal ion doping and constructive insight into the substitutional doping mechanism.

  14. Hydrogen evolution from water splitting on nanocomposite photocatalysts

    Directory of Open Access Journals (Sweden)

    Wenfeng Shangguan

    2007-01-01

    Full Text Available The photocatalytic production of H2 in one step is potentially one of the most promising ways for the conversion and storage of solar energy. The paper overviews our recent studies on the photocatalysts splitting water into hydrogen under irradiation. The attention was mainly focused on the promotion effects of nanosized modifications in the interlayer and surface of photocatalysts for hydrogen evolution with visible light. The photocatalytic activity depended significantly on modification techniques, such as loading, proton exchange, and intercalation. The formation of a "nest" on the particle surface promoted a uniform distribution and strong combination of the nanosized particles on the surface of catalysts. By the methods of intercalation and pillaring as well as by selecting both host and guest, a large variety of molecular designed host–guest systems were obtained. Cadmium sulfide (CdS-intercalated composites showed higher activity and stability. This activity of K4Ce2M10O30 (M=Ta, Nb evolving H2 under visible light irradiation was enhanced by the incorporation of Pt, RuO2 and NiO as co-catalysts. Especially, the nanosized NiOx (Ni–NiO double-layer structure greatly prompted the photocatalytic H2 evolution significantly.

  15. Method for controlling start-up and steady state performance of a closed split flow recompression brayton cycle

    Energy Technology Data Exchange (ETDEWEB)

    Pasch, James Jay

    2017-02-07

    A method of resolving a balanced condition that generates control parameters for start-up and steady state operating points and various component and cycle performances for a closed split flow recompression cycle system. The method provides for improved control of a Brayton cycle thermal to electrical power conversion system. The method may also be used for system design, operational simulation and/or parameter prediction.

  16. Sn-doped hematite nanostructures for photoelectrochemical water splitting.

    Science.gov (United States)

    Ling, Yichuan; Wang, Gongming; Wheeler, Damon A; Zhang, Jin Z; Li, Yat

    2011-05-11

    We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn(4+) substitution at Fe(3+) sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm(2) at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm(2) at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron-hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.

  17. Solar-thermal Water Splitting Using the Sodium Manganese Oxide Process & Preliminary H2A Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Francis, Todd M; Lichty, Paul R; Perkins, Christopher; Tucker, Melinda; Kreider, Peter B; Funke, Hans H; Lewandowski, A; Weimer, Alan W

    2012-10-24

    There are three primary reactions in the sodium manganese oxide high temperature water splitting cycle. In the first reaction, Mn2O3 is decomposed to MnO at 1,500°C and 50 psig. This reaction occurs in a high temperature solar reactor and has a heat of reaction of 173,212 J/mol. Hydrogen is produced in the next step of this cycle. This step occurs at 700°C and 1 atm in the presence of sodium hydroxide. Finally, water is added in the hydrolysis step, which removes NaOH and regenerates the original reactant, Mn2O3. The high temperature solar-driven step for decomposing Mn2O3 to MnO can be carried out to high conversion without major complication in an inert environment. The second step to produce H2 in the presence of sodium hydroxide is also straightforward and can be completed. The third step, the low temperature step to recover the sodium hydroxide is the most difficult. The amount of energy required to essentially distill water to recover sodium hydroxide is prohibitive and too costly. Methods must be found for lower cost recovery. This report provides information on the use of ZnO as an additive to improve the recovery of sodium hydroxide.

  18. Studies on the preparation of active oxygen-deficient copper ferrite and its application for hydrogen production through thermal chemical water splitting

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Hydrogen generation through thermal chemical water splitting technology has recently received in- creasingly international interest in the nuclear hydrogen production field. Besides the main known sulfur-iodine (S-I) cycle developed by the General Atomics Company and the UT3 cycle (iron, calcium, and bromine) developed at the University of Tokyo, the thermal cycle based on metal oxide two-step water splitting methods is also receiving research and development attention worldwide. In this work, copper ferrite was prepared by the co-precipitation method and oxygen-deficient copper ferrite was synthesized through first and second calcination steps for the application of hydrogen production by a two-step water splitting process. The crystal structure, properties, chemical composition and δ were investigated in detail by utilizing X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), atomic absorption spectrometer (AAS), ultraviolet spectrophotometry (UV), gas chro- matography (GC), and so on. The experimental two-step thermal chemical cycle reactor for hydrogen generation was designed and developed in this lab. The hydrogen generation process of water splitting through CuFe2O4-δ and the cycle performance of copper ferrite regeneration were firstly studied and discussed.

  19. Studies on the preparation of active oxygen-deficient copper ferrite and its application for hydrogen production through thermal chemical water splitting

    Institute of Scientific and Technical Information of China (English)

    YU Bo; ZHANG Ping; ZHANG Lei; CHEN Jing; XU JingMing

    2008-01-01

    Hydrogen generation through thermal chemical water splitting technology has recently received in-creasingly international interest in the nuclear hydrogen production field. Besides the main known sulfur-iodine (S-I) cycle developed by the General Atomics Company and the UT3 cycle (iron, calcium, and bromine) developed at the University of Tokyo, the thermal cycle based on metal oxide two-step water splitting methods is also receiving research and development attention worldwide. In this work, copper ferrite was prepared by the co-precipitation method and oxygen-deficient copper ferrite was synthesized through first and second calcination steps for the application of hydrogen production by a two-step water splitting process. The crystal structure, properties, chemical composition and δwere investigated in detail by utilizing X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), atomic absorption spectrometer (AAS), ultraviolet spectrophotometry (UV), gas chro-matography (GC), and so on. The experimental two-step thermal chemical cycle reactor for hydrogen generation was designed and developed in this lab. The hydrogen generation process of water splitting through CuFe2O4-δ and the cycle performance of copper ferrite regeneration were firstly studied and discussed.

  20. Water Cycle Missions for the Next Decade

    Science.gov (United States)

    Houser, P. R.

    2013-12-01

    The global water cycle describes the circulation of water as a vital and dynamic substance in its liquid, solid, and vapor phases as it moves through the atmosphere, oceans and land. Life in its many forms exists because of water, and modern civilization depends on learning how to live within the constraints imposed by the availability of water. The scientific challenge posed by the need to observe the global water cycle is to integrate in situ and space-borne observations to quantify the key water-cycle state variables and fluxes. The vision to address that challenge is a series of Earth observation missions that will measure the states, stocks, flows, and residence times of water on regional to global scales followed by a series of coordinated missions that will address the processes, on a global scale, that underlie variability and changes in water in all its three phases. The accompanying societal challenge is to foster the improved use of water data and information as a basis for enlightened management of water resources, to protect life and property from effects of extremes in the water cycle. A major change in thinking about water science that goes beyond its physics to include its role in ecosystems and society is also required. Better water-cycle observations, especially on the continental and global scales, will be essential. Water-cycle predictions need to be readily available globally to reduce loss of life and property caused by water-related natural hazards. Building on the 2007 Earth Science Decadal Survey, NASA's Plan for a Climate-Centric Architecture for Earth Observations and Applications from Space , and the 2012 Chapman Conference on Remote Sensing of the Terrestrial Water Cycle, a workshop was held in April 2013 to gather wisdom and determine how to prepare for the next generation of water cycle missions in support of the second Earth Science Decadal Survey. This talk will present the outcomes of the workshop including the intersection between

  1. Investigation of Iron Oxide Morphology in a Cyclic Redox Water Splitting Process for Hydrogen Generation

    Directory of Open Access Journals (Sweden)

    Michael M. Bobek

    2012-10-01

    Full Text Available A solar fuels generation research program is focused on hydrogen production by means of reactive metal water splitting in a cyclic iron-based redox process. Iron-based oxides are explored as an intermediary reactive material to dissociate water molecules at significantly reduced thermal energies. With a goal of studying the resulting oxide chemistry and morphology, chemical assistance via CO is used to complete the redox cycle. In order to exploit the unique characteristics of highly reactive materials at the solar reactor scale, a monolithic laboratory scale reactor has been designed to explore the redox cycle at temperatures ranging from 675 to 875 K. Using high resolution scanning electron microscope (SEM and electron dispersive X-ray spectroscopy (EDS, the oxide morphology and the oxide state are quantified, including spatial distributions. These images show the change of the oxide layers directly after oxidation and after reduction. The findings show a significant non-stoichiometric O/Fe gradient in the atomic ratio following oxidation, which is consistent with a previous kinetics model, and a relatively constant, non-stoichiometric O/Fe atomic ratio following reduction.

  2. Water Splitting by Thin Film Metal-Oxo Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Nocera, Daniel [Harvard Univ., Cambridge, MA (United States)

    2013-03-15

    The dropping price of silicon photovoltaics in the United States is causing load defection to solar supply at an accelerated pace. This conversion to solar and, more generally, other renewable energy sources has accordingly turned the energy research focus from generation to one of storage. Truly disruptive improvements in energy storage technologies are limited by energy density. This limitation, however, does not apply to fuels, which possess the energy density needed for large-scale energy storage. The first step of the basic science needed to drive such historic restructuring of the U.S. energy infrastructure begins with the solar-driven generation of hydrogen and oxygen from water. The solar-produced hydrogen may then be combined with carbon dioxide to deliver any number of fuels. Obviously, light does not directly act on water to engender its splitting into its elemental components. Hence, catalysts are needed to drive the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Of these two reactions, the four-electron, four-proton oxidation of OER is the more kinetically challenging reaction, and therefore the development of energy efficient solar fuels processes demands that OER be accomplished at a minimal overpotential. The research completed in this program developed catalysts that drive OER and at the same time meet the important criteria of (1) using non-critical materials that (2) are easy to assemble and (3) accomplish OER under simple conditions. Research was designed to uncover the chemical principles that underlie the self-assembly of metal oxide oxygen evolving catalysts (M-OEC) from the metals of M = Mn, Co, and Ni. For example, a dogma of heterogeneous catalysis of any sort is that “edges” matter in promoting catalytic transformations. We provided a rationale for such dogma by showing that the OER in Co-OEC occurred at a dimensionally reduced dicobalt edge site. Edge site reactivity was clearly revealed analyzing 18O labeled

  3. Controlled synthesis of GaN-based nanowires for photoelectrochemical water splitting applications

    Science.gov (United States)

    Ebaid, Mohamed; Kang, Jin-Ho; Ryu, Sang-Wan

    2017-01-01

    Photoelectrochemical (PEC) water splitting using semiconductor materials as light absorbers have been extensively studied. Several semiconducting materials have been proposed, such as TiO2, ZnO, and GaN. Because the efficiency of PEC water splitting is dependent on visible light absorption, the ability to tune the bandgap of GaN by alloying with In makes it advantageous over other wide bandgap semiconductors. The fabrication of GaN-based materials with nanoscale geometry offers more merit for their use in PEC water splitting. In this review, we provide an overview of the recent progress made in the synthesis and application of GaN-based nanomaterials in PEC water splitting. The outstanding challenges and the future prospects of this field will also be addressed.

  4. Two-Step Water Splitting with Concentrated Solar Heat Using Rotary-Type Solar Furnace

    Energy Technology Data Exchange (ETDEWEB)

    Kaneko, H.; Fuse, A.; Miura, T.; Ishihara, H.; Tamara, Y.

    2006-07-01

    The rotary-type solar furnace has been developed and fabricated for solar hydrogen production by a two-step water splitting reaction using the special reactive ceramic. The rotary-type solar furnace is the dual cell solar reactor, which has two different type reaction rooms, one is for discharging oxygen and another is for water splitting reaction. The detailed specification and the efficiency of the rotary-type solar furnace were examined. Successive evolutions of oxygen and hydrogen were observed in the discharging oxygen and water splitting reaction cells, respectively. Two-step water splitting process using newly developed rotary type solar furnace was achieved. The optimum reaction temperatures of the oxygen releasing reaction and hydrogen generation reaction with Ni,Mn-ferrite were 1173 K and 1473 K, respectively. (Author)

  5. 10-fold enhancement in light-driven water splitting using niobium oxynitride microcone array films

    KAUST Repository

    Shaheen, Basamat

    2016-03-26

    We demonstrate, for the first time, the synthesis of highly ordered niobium oxynitride microcones as an attractive class of materials for visible-light-driven water splitting. As revealed by the ultraviolet photoelectron spectroscopy (UPS), photoelectrochemical and transient photocurrent measurements, the microcones showed enhanced performance (~1000% compared to mesoporous niobium oxide) as photoanodes for water splitting with remarkable stability and visible light activity. © 2016 Elsevier B.V. All rights reserved.

  6. What can density functional theory tell us about artificial catalytic water splitting?

    Science.gov (United States)

    Mavros, Michael G; Tsuchimochi, Takashi; Kowalczyk, Tim; McIsaac, Alexandra; Wang, Lee-Ping; Voorhis, Troy Van

    2014-07-07

    Water splitting by artificial catalysts is a critical process in the production of hydrogen gas as an alternative fuel. In this paper, we examine the essential role of theoretical calculations, with particular focus on density functional theory (DFT), in understanding the water-splitting reaction on these catalysts. First, we present an overview of DFT thermochemical calculations on water-splitting catalysts, addressing how these calculations are adapted to condensed phases and room temperature. We show how DFT-derived chemical descriptors of reactivity can be surprisingly good estimators for reactive trends in water-splitting catalysts. Using this concept, we recover trends for bulk catalysts using simple model complexes for at least the first-row transition-metal oxides. Then, using the CoPi cobalt oxide catalyst as a case study, we examine the usefulness of simulation for predicting the kinetics of water splitting. We demonstrate that the appropriate treatment of solvent effects is critical for computing accurate redox potentials with DFT, which, in turn, determine the rate-limiting steps and electrochemical overpotentials. Finally, we examine the ability of DFT to predict mechanism, using ruthenium complexes as a focal point for discussion. Our discussion is intended to provide an overview of the current strengths and weaknesses of the state-of-the-art DFT methodologies for condensed-phase molecular simulation involving transition metals and also to guide future experiments and computations toward the understanding and development of novel water-splitting catalysts.

  7. Spin State as a Marker for the Structural Evolution of Nature's Water-Splitting Catalyst.

    Science.gov (United States)

    Krewald, Vera; Retegan, Marius; Neese, Frank; Lubitz, Wolfgang; Pantazis, Dimitrios A; Cox, Nicholas

    2016-01-19

    In transition-metal complexes, the geometric structure is intimately connected with the spin state arising from magnetic coupling between the paramagnetic ions. The tetramanganese-calcium cofactor that catalyzes biological water oxidation in photosystem II cycles through five catalytic intermediates, each of which adopts a specific geometric and electronic structure and is thus characterized by a specific spin state. Here, we review spin-structure correlations in Nature's water-splitting catalyst. The catalytic cycle of the Mn4O5Ca cofactor can be described in terms of spin-dependent reactivity. The lower "inactive" S states of the catalyst, S0 and S1, are characterized by low-spin ground states, SGS = 1/2 and SGS = 0. This is connected to the "open cubane" topology of the inorganic core in these states. The S2 state exhibits structural and spin heterogeneity in the form of two interconvertible isomers and is identified as the spin-switching point of the catalytic cycle. The first S2 state form is an open cubane structure with a low-spin SGS = 1/2 ground state, whereas the other represents the first appearance of a closed cubane topology in the catalytic cycle that is associated with a higher-spin ground state of SGS = 5/2. It is only this higher-spin form of the S2 state that progresses to the "activated" S3 state of the catalyst. The structure of this final metastable catalytic state was resolved in a recent report, showing that all manganese ions are six-coordinate. The magnetic coupling is dominantly ferromagnetic, leading to a high-spin ground state of SGS = 3. The ability of the Mn4O5Ca cofactor to adopt two distinct structural and spin-state forms in the S2 state is critical for water binding in the S3 state, allowing spin-state crossing from the inactive, low-spin configuration of the catalyst to the activated, high-spin configuration. Here we describe how an understanding of the magnetic properties of the catalyst in all S states has allowed conclusions on

  8. Kinetic Flux Vector Splitting Method for the Shallow Water Wave Equations

    Institute of Scientific and Technical Information of China (English)

    施卫平; WeiShyy

    2003-01-01

    Based on the analogy to gas dynamics,the kinetic flux flux vector splitting (KFVS) method is used to stimulate the shallow water wave equations,The flus vectors of the equations are split on the basis of the local equilibrium Maxwell-Boltzmann distribution One dimensional examples including a dam breaking wave and flows over a ridge are calcualted.The solutions exhibit second-order accuracy with no spurious oscillation.

  9. Global water cycle and solar activity variations

    Science.gov (United States)

    Al-Tameemi, Muthanna A.; Chukin, Vladimir V.

    2016-05-01

    The water cycle is the most active and most important component in the circulation of global mass and energy in the Earth system. Furthermore, water cycle parameters such as evaporation, precipitation, and precipitable water vapour play a major role in global climate change. In this work, we attempt to determine the impact of solar activity on the global water cycle by analyzing the global monthly values of precipitable water vapour, precipitation, and the Solar Modulation Potential in 1983-2008. The first object of this study was to calculate global evaporation for the period 1983-2008. For this purpose, we determined the water cycle rate from satellite data, and precipitation/evaporation relationship from 10 years of Planet Simulator model data. The second object of our study was to investigate the relationship between the Solar Modulation Potential (solar activity index) and the evaporation for the period 1983-2008. The results showed that there is a relationship between the solar modulation potential and the evaporation values for the period of study. Therefore, we can assume that the solar activity has an impact on the global water cycle.

  10. Formation mechanism of TiO2 nanotubes and their applications in photoelectrochemical water splitting and supercapacitors.

    Science.gov (United States)

    Chen, Bo; Hou, Junbo; Lu, Kathy

    2013-05-14

    Structural observations of the transition of TiO2 nanopores into nanotubes by increasing the OH(-) concentration in the electrolyte challenge the validity of existing formation mechanisms of anodic TiO2 nanotubes. In this study, dehydration of titanium hydroxide in the cell wall is proposed as the mechanism that leads to the separation of neighboring nanotubes. Based on this understanding, bamboo-type TiO2 nanotubes with large surface area and excellent interconnectivity are achieved by cycling high and low applied potentials. After thermal treatment in a H2 atmosphere, the bamboo-type TiO2 nanotubes show large photoelectrochemical water splitting efficiency and supercapacitors performace.

  11. Towards versatile and sustainable hydrogen production via electrocatalytic water splitting: Electrolyte engineering

    KAUST Repository

    Shinagawa, Tatsuya

    2016-12-17

    Recent advances in power generation from renewable resources necessitate conversion of electricity to chemicals and fuels in an efficient manner. The electrocatalytic water splitting is one of the most powerful and widespread technologies. The development of highly efficient, inexpensive, flexible and versatile water electrolysis devices is desired. This review discusses the significance and impact of the electrolyte on electrocatalytic performance. Depending on the circumstances where water splitting reaction is conducted, required solution conditions such as the identity and molarity of ions may significantly differ. Quantitative understanding of such electrolyte properties on electrolysis performance is effective to facilitate developing efficient electrocatalytic systems. The electrolyte can directly participate in reaction schemes (kinetics), electrode stability, and/or indirectly impacts the performance by influencing concentration overpotential (mass transport). This review aims to guide fine-tuning of the electrolyte properties, or electrolyte engineering, for (photo)electrochemical water splitting reactions.

  12. Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects

    Directory of Open Access Journals (Sweden)

    Pankaj Chowdhury

    2017-05-01

    Full Text Available Today, global warming and green energy are important topics of discussion for every intellectual gathering all over the world. The only sustainable solution to these problems is the use of solar energy and storing it as hydrogen fuel. Photocatalytic and photo-electrochemical water splitting and sacrificial hydrogen generation show a promise for future energy generation from renewable water and sunlight. This article mainly reviews the current research progress on photocatalytic and photo-electrochemical systems focusing on dye-sensitized overall water splitting and sacrificial hydrogen generation. An overview of significant parameters including dyes, sacrificial agents, modified photocatalysts and co-catalysts are provided. Also, the significance of statistical analysis as an effective tool for a systematic investigation of the effects of different factors and their interactions are explained. Finally, different photocatalytic reactor configurations that are currently in use for water splitting application in laboratory and large scale are discussed.

  13. Charge carrier separation in nanostructured TiO2 photoelectrodes for water splitting.

    Science.gov (United States)

    Cowan, Alexander J; Leng, Wenhua; Barnes, Piers R F; Klug, David R; Durrant, James R

    2013-06-14

    There is intense interest in developing new novel nanostructured photoanodes for water splitting. It is therefore important that methods to analyze the effect of nanostructuring on water splitting yields are developed in order to rationalize the relative merits of this approach for different materials. In this study the dependence of charge separation efficiency (η(sep)) on potential during photoelectrochemical water splitting at pH 2 has been quantified in a model electrode system (nanocrystalline, mesoporous TiO2) using two independent methods. These are (i) analysis of incident photon conversion efficiency (IPCE) measurements and (ii) transient absorption (TA) spectroscopy measurements. The techniques provide good agreement with each other and show that a low maximum value of η(sep) (~0.18) is the primary cause of the low IPCE for water oxidation on these nc-TiO2 electrodes.

  14. Comparison of clinical outcomes between in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in IVF-ICSI split insemination cycles.

    Science.gov (United States)

    Lee, Sun Hee; Lee, Jae Hyun; Park, Yong-Seog; Yang, Kwang Moon; Lim, Chun Kyu

    2017-06-01

    This study aimed to compare the clinical outcomes between in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in sibling oocytes. Additionally, we evaluated whether the implementation of split insemination contributed to an increase in the number of ICSI procedures. A total of 571 cycles in 555 couples undergoing split insemination cycles were included in this study. Among them, 512 cycles (89.7%) were a couple's first IVF cycle. The patients were under 40 years of age and at least 10 oocytes were retrieved in all cycles. Sibling oocytes were randomly allocated to IVF or ICSI. Total fertilization failure was significantly more common in IVF cycles than in ICSI cycles (4.0% vs. 1.4%, p<0.05), but the low fertilization rate among retrieved oocytes (as defined by fertilization rates greater than 0% but <30%) was significantly higher in ICSI cycles than in IVF cycles (17.2% vs. 11.4%, p<0.05). The fertilization rate of ICSI among injected oocytes was significantly higher than for IVF (72.3%±24.3% vs. 59.2%±25.9%, p<0.001), but the fertilization rate among retrieved oocytes was significantly higher in IVF than in ICSI (59.2%±25.9% vs. 52.1%±22.5%, p<0.001). Embryo quality before embryo transfer was not different between IVF and ICSI. Although the sperm parameters were not different between the first cycle and the second cycle, split insemination or ICSI was performed in 18 of the 95 cycles in which a second IVF cycle was performed. The clinical outcomes did not differ between IVF and ICSI in split insemination cycles. Split insemination can decrease the risk of total fertilization failure. However, unnecessary ICSI is carried out in most split insemination cycles and the use of split insemination might make ICSI more common.

  15. One‐dimensional TiO2 Nanotube Photocatalysts for Solar Water Splitting

    Science.gov (United States)

    Ge, Mingzheng; Li, Qingsong; Cao, Chunyan; Huang, Jianying; Li, Shuhui; Zhang, Songnan; Chen, Zhong; Zhang, Keqin; Al‐Deyab, Salem S.

    2016-01-01

    Hydrogen production from water splitting by photo/photoelectron‐catalytic process is a promising route to solve both fossil fuel depletion and environmental pollution at the same time. Titanium dioxide (TiO2) nanotubes have attracted much interest due to their large specific surface area and highly ordered structure, which has led to promising potential applications in photocatalytic degradation, photoreduction of CO2, water splitting, supercapacitors, dye‐sensitized solar cells, lithium‐ion batteries and biomedical devices. Nanotubes can be fabricated via facile hydrothermal method, solvothermal method, template technique and electrochemical anodic oxidation. In this report, we provide a comprehensive review on recent progress of the synthesis and modification of TiO2 nanotubes to be used for photo/photoelectro‐catalytic water splitting. The future development of TiO2 nanotubes is also discussed. PMID:28105391

  16. One-Dimensional Metal-Oxide Nanostructures for Solar Photocatalytic Water-Splitting

    Science.gov (United States)

    Wang, Fengyun; Song, Longfei; Zhang, Hongchao; Luo, Linqu; Wang, Dong; Tang, Jie

    2017-08-01

    Because of their unique physical and chemical properties, one-dimensional (1-D) metal-oxide nanostructures have been extensively applied in the areas of gas sensors, electrochromic devices, nanogenerators, and so on. Solar water-splitting has attracted extensive research interest because hydrogen generated from solar-driven water splitting is a clean, sustainable, and abundant energy source that not only solves the energy crisis, but also protects the environment. In this comprehensive review, the main synthesis methods, properties, and especially prominent applications in solar water splitting of 1-D metal-oxides, including titanium dioxide (TiO2), zinc oxide (ZnO), tungsten trioxide (WO3), iron oxide (Fe2O3), and copper oxide (CuO) are fully discussed.

  17. Efficient Overall Water-Splitting Electrocatalysis Using Lepidocrocite VOOH Hollow Nanospheres

    KAUST Repository

    Shi, Huanhuan

    2016-11-29

    Herein we report the control synthesis of lepidocrocite VOOH hollow nanospheres and further their applications in electrocatalytic water splitting for the first time. By tuning the surface area of the nanospheres, the optimal performance can be achieved with low overpotentials of 270 mV for the oxygen evolution reaction (OER) and 164 mV for the hydrogen evolution reaction (HER) at 10 mA cm-2 in 1 m KOH, respectively. Furthermore, when used as both the anode and cathode for overall water splitting, a low cell voltage of 1.62 V is required to reach the current density of 10 mA cm-2 , making the VOOH hollow nanospheres an efficient alternative to water splitting.

  18. One-dimensional TiO2 Nanotube Photocatalysts for Solar Water Splitting.

    Science.gov (United States)

    Ge, Mingzheng; Li, Qingsong; Cao, Chunyan; Huang, Jianying; Li, Shuhui; Zhang, Songnan; Chen, Zhong; Zhang, Keqin; Al-Deyab, Salem S; Lai, Yuekun

    2017-01-01

    Hydrogen production from water splitting by photo/photoelectron-catalytic process is a promising route to solve both fossil fuel depletion and environmental pollution at the same time. Titanium dioxide (TiO2) nanotubes have attracted much interest due to their large specific surface area and highly ordered structure, which has led to promising potential applications in photocatalytic degradation, photoreduction of CO2, water splitting, supercapacitors, dye-sensitized solar cells, lithium-ion batteries and biomedical devices. Nanotubes can be fabricated via facile hydrothermal method, solvothermal method, template technique and electrochemical anodic oxidation. In this report, we provide a comprehensive review on recent progress of the synthesis and modification of TiO2 nanotubes to be used for photo/photoelectro-catalytic water splitting. The future development of TiO2 nanotubes is also discussed.

  19. Modern Estimates of Global Water Cycle Fluxes

    Science.gov (United States)

    Rodell, M.; Beaudoing, H. K.; L'Ecuyer, T. S.; Olson, W. S.

    2014-12-01

    The goal of the first phase of the NASA Energy and Water Cycle Study (NEWS) Water and Energy Cycle Climatology project was to develop "state of the global water cycle" and "state of the global energy cycle" assessments based on data from modern ground and space based observing systems and data integrating models. Here we describe results of the water cycle assessment, including mean annual and monthly fluxes over continents and ocean basins during the first decade of the millennium. To the extent possible, the water flux estimates are based on (1) satellite measurements and (2) data-integrating models. A careful accounting of uncertainty in each flux was applied within a routine that enforced multiple water and energy budget constraints simultaneously in a variational framework, in order to produce objectively-determined, optimized estimates. Simultaneous closure of the water and energy budgets caused the ocean evaporation and precipitation terms to increase by about 10% and 5% relative to the original estimates, mainly because the energy budget required turbulent heat fluxes to be substantially larger in order to balance net radiation. In the majority of cases, the observed annual, surface and atmospheric water budgets over the continents and oceans close with much less than 10% residual. Observed residuals and optimized uncertainty estimates are considerably larger for monthly surface and atmospheric water budget closure, often nearing or exceeding 20% in North America, Eurasia, Australia and neighboring islands, and the Arctic and South Atlantic Oceans. The residuals in South America and Africa tend to be smaller, possibly because cold land processes are a non-issue. Fluxes are poorly observed over the Arctic Ocean, certain seas, Antarctica, and the Australasian and Indonesian Islands, leading to reliance on atmospheric analysis estimates. Other details of the study and future directions will be discussed.

  20. An efficient bifunctional electrocatalyst for water splitting based on cobalt phosphide

    Science.gov (United States)

    Yang, Libin; Qi, Honglan; Zhang, Chengxiao; Sun, Xuping

    2016-06-01

    The development of highly efficient electrocatalysts for water splitting is critical for various renewable-energy technologies. In this letter, we demonstrate a cobalt phosphide nanowire array grown on a Ti mesh (CoP/TM) behaving as a bifunctional electrocatalyst for water splitting. The CoP/TM electrode delivers 10 mA cm-2 at an overpotential of 72 mV for the hydrogen evolution reaction (HER) and 310 mV for the oxygen evolution reaction (OER) in 1.0 M KOH. Furthermore, its corresponding two-electrode alkaline electrolyzer displays 10 mA cm-2 at 1.64 V.

  1. THERMODYNAMIC CONSIDERATIONS FOR THERMAL WATER SPLITTING PROCESSES AND HIGH TEMPERATURE ELECTROLYSIS

    Energy Technology Data Exchange (ETDEWEB)

    J. E. O' Brien

    2008-11-01

    A general thermodynamic analysis of hydrogen production based on thermal water splitting processes is presented. Results of the analysis show that the overall efficiency of any thermal water splitting process operating between two temperature limits is proportional to the Carnot efficiency. Implications of thermodynamic efficiency limits and the impacts of loss mechanisms and operating conditions are discussed as they pertain specifically to hydrogen production based on high-temperature electrolysis. Overall system performance predictions are also presented for high-temperature electrolysis plants powered by three different advanced nuclear reactor types, over their respective operating temperature ranges.

  2. Single-Crystal Semiconductors with Narrow Band Gaps for Solar Water Splitting.

    Science.gov (United States)

    Wang, Tuo; Gong, Jinlong

    2015-09-07

    Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single-crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.

  3. Evaluation method for regional water cycle health based on nature-society water cycle theory

    Science.gov (United States)

    Zhang, Shanghong; Fan, Weiwei; Yi, Yujun; Zhao, Yong; Liu, Jiahong

    2017-08-01

    Regional water cycles increasingly reflect the dual influences of natural and social processes, and are affected by global climate change and expanding human activities. Understanding how to maintain a healthy state of the water cycle has become an important proposition for sustainable development of human society. In this paper, natural-social attributes of the water cycle are synthesized and 19 evaluation indices are selected from four dimensions, i.e., water-based ecosystem integrity, water quality, water resource abundance and water resource use. A hierarchical water-cycle health evaluation system is established. An analytic hierarchy process is used to set the weight of the criteria layer and index layer, and the health threshold for each index is defined. Finally, a water-cycle health composite-index assessment model and fuzzy recognition model are constructed based on the comprehensive index method and fuzzy mathematics theory. The model is used to evaluate the state of health of the water cycle in Beijing during 2010-2014 and in the planning year (late 2014), considering the transfer of 1 billion m3 of water by the South-to-North Water Diversion Project (SNWDP). The results show health scores for Beijing of 2.87, 3.10, 3.38, 3.11 and 3.02 during 2010-2014. The results of fuzzy recognition show that the sub-healthy grade accounted for 54%, 49%, 61% and 49% of the total score, and all years had a sub-healthy state. Results of the criteria layer analysis show that water ecosystem function, water quality and water use were all at the sub-healthy level and that water abundance was at the lowest, or sick, level. With the water transfer from the SNWDP, the health score of the water cycle in Beijing reached 4.04. The healthy grade accounted for 60% of the total score, and the water cycle system was generally in a healthy state. Beijing's water cycle health level is expected to further improve with increasing water diversion from the SNWDP and industrial

  4. Strategies for stable water splitting via protected photoelectrodes

    DEFF Research Database (Denmark)

    Bae, Dowon; Seger, Brian; Vesborg, Peter Christian Kjærgaard

    2017-01-01

    Photoelectrochemical (PEC) solar-fuel conversion is a promising approach to provide clean and storable fuel (e.g., hydrogen and methanol) directly from sunlight, water and CO2. However, major challenges still have to be overcome before commercialization can be achieved. One of the largest barriers...

  5. Performance of genetic algorithms in search for water splitting perovskites

    DEFF Research Database (Denmark)

    Jain, A.; Castelli, Ivano Eligio; Hautier, G.

    2013-01-01

    We examine the performance of genetic algorithms (GAs) in uncovering solar water light splitters over a space of almost 19,000 perovskite materials. The entire search space was previously calculated using density functional theory to determine solutions that fulfill constraints on stability, band...

  6. WaterNet: The NASA Water Cycle Solutions Network

    Science.gov (United States)

    Belvedere, D. R.; Houser, P. R.; Imam, B.; Schiffer, R.; Schlosser, C. A.; Gupta, H. V.; Welty, C.; Vorosmarty, C.; Matthews, D.; Lawford, R.

    2006-05-01

    The water cycle is continuously being transformed by climate change, erosion, pollution, salinization, and engineering practices, and is central to drought, flood, and disease hazards. Therefore, it is a national priority is to use advancements in scientific observations and knowledge to develop solutions to society's water challenges. NASA's unique role in this national priority is to exploit its unique view from space to improve water and energy cycle monitoring and prediction. As such, NASA's Earth science programs have collected substantial water cycle information and knowledge that must be integrated and shared to develop solutions in all twelve national priority application areas. However, NASA alone cannot achieve the ultimate goal of improved operational environmental assessments, predictions and applications and therefore must establish collaborations and interoperability with existing networks and nodes of research organizations, operational agencies, the scientific community, and private industry. Therefore, we propose to develop WaterNet: The NASA Water Cycle Solutions Network whose goal is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend NASA research results to augment decision support tools and meet national needs. We will develop WaterNet by engaging relevant NASA water and energy cycle resources and community-of-practice organizations to develop what we term an "actionable database" that can be used to communicate and connect NASA Water and energy cycle focus area research Results (NWRs) towards the improvement of water-related Decision Support Tools (DSTs). Recognizing the many existing highly valuable water-related science and application networks, we will focus a balance of our efforts to enable their interoperability in a solutions network context. We will initially focus on identifying, collecting information about, and analyzing the

  7. Solution transformation of Cu₂O into CuInS₂ for solar water splitting.

    Science.gov (United States)

    Luo, Jingshan; Tilley, S David; Steier, Ludmilla; Schreier, Marcel; Mayer, Matthew T; Fan, Hong Jin; Grätzel, Michael

    2015-02-11

    Though Cu2O has demonstrated high performance as a photocathode for solar water splitting, its band gap is too large for efficient use as the bottom cell in tandem configurations. Accordingly, copper chalcopyrites have recently attracted much attention for solar water splitting due to their smaller and tunable band gaps. However, their fabrication is mainly based on vacuum evaporation, which is an expensive and energy consuming process. Here, we have developed a novel and low-cost solution fabrication method, and CuInS2 was chosen as a model material due to its smaller band gap compared to Cu2O and relatively simple composition. The nanostructured CuInS2 electrodes were synthesized at low temperature in crystalline form by solvothermal treatment of electrochemically deposited Cu2O films. Following the coating of overlayers and decoration with Pt catalyst, the as-fabricated CuInS2 electrode demonstrated water splitting photocurrents of 3.5 mA cm(-2) under simulated solar illumination. To the best of our knowledge, this is the highest performance yet reported for a solution-processed copper chalcopyrite electrode for solar water splitting. Furthermore, the electrode showed good stability and had a broad incident photon-to-current efficiency (IPCE) response to wavelengths beyond 800 nm, consistent with the smaller bandgap of this material.

  8. Nanoscaled Components for Improved Efficiency in a Multiplanel Photocatalytic Water-Splitting System

    Energy Technology Data Exchange (ETDEWEB)

    Fox, Marye Anne [Univ. of California, San Diego, CA (United States); Whitesell, James [Univ. of California, San Diego, CA (United States)

    2014-04-30

    The goal of this program was to construct a multicell photochemical device for the direct conversion of solar energy directly to hydrogen by water splitting. We have fabricated a practical photolytic system for quantum efficient production of hydrogen. Our approach is based on the assembly of a multi-component integrated system for direct photocatalytic splitting of water for the efficient production of hydrogen. We propose to produce hydrogen as an energy source that is cost competitive with fossil fuels and without the concomitant production of greenhouse gases. The concept is quite straightforward. In order to achieve the over potential required for direct water splitting, the device is composed of multiple dye-sensitized cells directly linked in series, as illustrated in the figure below. The advantage of this concept is that each cell need contribute only a fraction of the overall potential required for water splitting, thus permitting device engineering to maximized efficiently without regard to electric potential. Progress and barriers to practical application will be described.

  9. Enhanced Electrocatalytic Activity for Water Splitting on NiO/Ni/Carbon Fiber Paper

    Directory of Open Access Journals (Sweden)

    Ruoyu Zhang

    2016-12-01

    Full Text Available Large-scale growth of low-cost, efficient, and durable non-noble metal-based electrocatalysts for water splitting is crucial for future renewable energy systems. Atomic layer deposition (ALD provides a promising route for depositing uniform thin coatings of electrocatalysts, which are useful in many technologies, including the splitting of water. In this communication, we report the growth of a NiO/Ni catalyst directly on carbon fiber paper by atomic layer deposition and report subsequent reduction and oxidation annealing treatments. The 10–20 nm NiO/Ni nanoparticle catalysts can reach a current density of 10 mA·cm−2 at an overpotential of 189 mV for hydrogen evolution reactions and 257 mV for oxygen evolution reactions with high stability. We further successfully achieved a water splitting current density of 10 mA·cm−2 at 1.78 V using a typical NiO/Ni coated carbon fiber paper two-electrode setup. The results suggest that nanoparticulate NiO/Ni is an active, stable, and noble-metal-free electrocatalyst, which facilitates a method for future water splitting applications.

  10. Photocharged BiVO4 photoanodes for improved solar water splitting

    NARCIS (Netherlands)

    Trześniewski, B.J.; Smith, W.A.

    2015-01-01

    Bismuth vanadate (BiVO4) is a promising semiconductor material for the production of solar fuels via photoelectrochemical water splitting, however, it suffers from substantial recombination losses that limit its performance to well below its theoretical maximum. Here we demonstrate for the first tim

  11. Foliar boron and nickel applications reduce water-stage fruit-split of pecan

    Science.gov (United States)

    Water-stage fruit-split (WSFS) is a relatively common and often major problem of certain pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. This study evaluates the possibility that the malady can be influenced by improving tree micronutrient nutrition. Foliar sprays of boron (B) and nickel...

  12. New cubic perovskites for one- and two-photon water splitting using the computational materials repository

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Landis, David; Thygesen, Kristian Sommer

    2012-01-01

    screening of around 19 000 oxides, oxynitrides, oxysulfides, oxyfluorides, and oxyfluoronitrides in the cubic perovskite structure with PEC applications in mind. We address three main applications: light absorbers for one- and two-photon water splitting and high-stability transparent shields to protect...

  13. Calculated Pourbaix Diagrams of Cubic Perovskites for Water Splitting: Stability Against Corrosion

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2014-01-01

    We use density functional theory calculations to investigate the stability of cubic perovskites for photo-electrochemical water splitting taking both materials in their bulk crystal structure and dissolved phases into account. The method is validated through a detailed comparison of the calculated...

  14. Solar Water Splitting: Photocatalyst Materials Discovery and Systems Development

    Energy Technology Data Exchange (ETDEWEB)

    McNulty, Thomas F.

    2008-05-02

    Hydrogen promises to be an attractive transportation fuel in the post-fossil fuel era. Relatively abundant and clean burning (water being the principal byproduct), hydrogen offers the potential to significantly reduce greenhouse gas emissions. However, there are significant technical barriers that require solutions before hydrogen can be implemented in large scale. These are: · Sources (e.g. hydrocarbon, water) · Transportation · Storage Each of the aforementioned barriers carries with it important considerations. First, would a hydrocarbon-based hydrogen source be of any benefit compared to conventional fossil fuels? Second, will a system based on centralized generation and distribution be viable? Finally, methods of on-board storage, whether they are liquefaction, adsorption, or intercalation, are far from optimized. The scope of this program is limited to hydrogen generation, specifically generation using solarinitiated water electrolysis. Though concept of making hydrogen using water and sunlight may sound somewhat far-fetched, in reality the concept is very real. Since the discovery of solar-generated hydrogen, termed photoelectrochemical hydrogen, nearly 30 years ago by Fujishima and Honda, significant advances in both fundamental understanding and technological capability have been made. Using solar radiation to generate hydrogen in a fashion akin to using solar to generate electricity offers many advantages. First, hydrogen can be generated at the point of use, reducing the importance of transportation. Second, using water as the hydrogen source eliminates greenhouse gas evolution and the consequences that come with it. Finally, because the process uses very little electricity (pumps and compressors predominantly), the quantity of chemical fuel produced far exceeds the amount of electricity consumed. Consequently, there is some level of truth to the notion that photoelectrochemically-derived hydrogen offers the potential to nearly eliminate greenhouse

  15. Vapor-liquid phase behavior of the iodine-sulfur water-splitting process : LDRD final report for FY03.

    Energy Technology Data Exchange (ETDEWEB)

    Bradshaw, Robert W.; Larson, Richard S.; Lutz, Andrew E.

    2004-01-01

    This report summarizes the results of a one-year LDRD project that was undertaken to better understand the equilibrium behavior of the iodine-water-hydriodic acid system at elevated temperature and pressure. We attempted to extend the phase equilibrium database for this system in order to facilitate development of the iodine-sulfur water-splitting process to produce hydrogen to a commercial scale. The iodine-sulfur cycle for thermochemical splitting of water is recognized as the most efficient such process and is particularly well suited to coupling to a high-temperature source of process heat. This study intended to combine experimental measurements of vapor-liquid-liquid equilibrium and equation-of-state modeling of equilibrium solutions using Sandia's Chernkin software. Vapor-liquid equilibrium experiments were conducted to a limited extent. The Liquid Chernkin software that was developed as part of an earlier LDRD project was enhanced and applied to model the non-ideal behavior of the liquid phases.

  16. Nanosized TiO[subscript 2] for Photocatalytic Water Splitting Studied by Oxygen Sensor and Data Logger

    Science.gov (United States)

    Zhang, Ruinan; Liu, Song; Yuan, Hongyan; Xiao, Dan; Choi, Martin M. F.

    2012-01-01

    Photocatalytic water splitting by semiconductor photocatalysts has attracted considerable attention in the past few decades. In this experiment, nanosized titanium dioxide (nano-TiO[subscript 2]) particles are used to photocatalytically split water, which is then monitored by an oxygen sensor. Sacrificial reagents such as organics (EDTA) and metal…

  17. Nanosized TiO[subscript 2] for Photocatalytic Water Splitting Studied by Oxygen Sensor and Data Logger

    Science.gov (United States)

    Zhang, Ruinan; Liu, Song; Yuan, Hongyan; Xiao, Dan; Choi, Martin M. F.

    2012-01-01

    Photocatalytic water splitting by semiconductor photocatalysts has attracted considerable attention in the past few decades. In this experiment, nanosized titanium dioxide (nano-TiO[subscript 2]) particles are used to photocatalytically split water, which is then monitored by an oxygen sensor. Sacrificial reagents such as organics (EDTA) and metal…

  18. Conceptual design model of the sulfur-iodine S-I thermochemical water splitting process for hydrogen production using nuclear heat source

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez Rodriguez, Daniel; Parra, Lazaro Garcia, E-mail: dgr@instec.cu, E-mail: lgarcia@instec.cu [Departamento de Ingenieria Nuclear, Instituto Superior de Ciencias y Tecnologias Aplicadas, La Habana (Cuba)

    2011-07-01

    Hydrogen is the most indicated candidate for its implementation as energy carrier in a future sustainable scenario. The current hydrogen production is based on fossils fuels; they have a huge contribution to the atmosphere pollution. Thermochemical water-splitting cycles do not have this issue because they use solar or nuclear heat; their environment impact is smaller than conventional fuels. The software based on chemical process simulation (CPS) can be used to simulate the thermochemical water splitting cycle Sulfur-Iodine for hydrogen production. In the paper is developed a model for Sulfur-Iodine process in order to analyze his sensibility and calculate the efficiency and the influence of many parameters on this value. (author)

  19. Following the Water Cycle to Sustainability

    Science.gov (United States)

    Lutz, T. M.

    2012-12-01

    systems learning model based on feedback and limits to perception. I focus on a part of the course that builds on connections that start in the hydrosphere and that includes some basic experiential learning about the water cycle and students' reliance on it. We measure and visualize aspects of the water cycle in nearby areas of campus (designated as an outdoor classroom and demonstration garden). The evapotranspiration flow is used to introduce notions of what can happen when flows are not sensed (e.g., invisible to us). Students use an online water footprint calculator to discover how large their water reliance is, particularly through energy generation, food consumption and food waste; and how far their water reach extends (virtual water trade). They consider the ethical implications of their water use in a world in which it is becoming a more rare resource and in some cases a valued commodity. They learn about non-utilitarian values of water based on an activity on the values of nature. They look at local, community-based efforts to improve water quality and to re-localize water dependence. A reading from Aldo Leopold puts the water cycle in a historical and cultural perspective. The water cycle is strongly interwoven with natural and human energy systems, the climate system, the carbon cycle, nutrient cycles, the rock cycle, and serves as a starting point to reach many other topics.

  20. Light illuminated α-Fe2O3/Pt nanoparticles as water activation agent for photoelectrochemical water splitting.

    Science.gov (United States)

    Li, Xiaodong; Wang, Zhi; Zhang, Zemin; Chen, Lulu; Cheng, Jianli; Ni, Wei; Wang, Bin; Xie, Erqing

    2015-03-16

    The photoelectrochemical (PEC) water splitting is hampered by strong bonds of H2O molecules and low ionic conductivity of pure water. The photocatalysts dispersed in pure water can serve as a water activation agent, which provides an alternative pathway to overcome such limitations. Here we report that the light illuminated α-Fe2O3/Pt nanoparticles may produce a reservoir of reactive intermediates including H2O2, ·OH, OH(-) and H(+) capable of promoting the pure water reduction/oxidation half-reactions at cathode and highly photocatalytic-active TiO2/In2S3/AgInS2 photoanode, respectively. Remarkable photocurrent enhancement has been obtained with α-Fe2O3/Pt as water activation agent. The use of α-Fe2O3/Pt to promote the reactivity of pure water represents a new paradigm for reproducible hydrogen fuel provision by PEC water splitting, allowing efficient splitting of pure water without adding of corrosive chemicals or sacrificial agent.

  1. The artificial water cycle: emergy analysis of waste water treatment.

    Science.gov (United States)

    Bastianoni, Simone; Fugaro, Laura; Principi, Ilaria; Rosini, Marco

    2003-04-01

    The artificial water cycle can be divided into the phases of water capture from the environment, potabilisation, distribution, waste water collection, waste water treatment and discharge back into the environment. The terminal phase of this cycle, from waste water collection to discharge into the environment, was assessed by emergy analysis. Emergy is the quantity of solar energy needed directly or indirectly to provide a product or energy flow in a given process. The emergy flow attributed to a process is therefore an index of the past and present environmental cost to support it. Six municipalities on the western side of the province of Bologna were analysed. Waste water collection is managed by the municipal councils and treatment is carried out in plants managed by a service company. Waste water collection was analysed by compiling a mass balance of the sewer system serving the six municipalities, including construction materials and sand for laying the pipelines. Emergy analysis of the water treatment plants was also carried out. The results show that the great quantity of emergy required to treat a gram of water is largely due to input of non renewable fossil fuels. As found in our previous analysis of the first part of the cycle, treatment is likewise characterised by high expenditure of non renewable resources, indicating a correlation with energy flows.

  2. Materials-Related Aspects of Thermochemical Water and Carbon Dioxide Splitting: A Review

    Directory of Open Access Journals (Sweden)

    Robert Pitz-Paal

    2012-10-01

    Full Text Available Thermochemical multistep water- and CO2-splitting processes are promising options to face future energy problems. Particularly, the possible incorporation of solar power makes these processes sustainable and environmentally attractive since only water, CO2 and solar power are used; the concentrated solar energy is converted into storable and transportable fuels. One of the major barriers to technological success is the identification of suitable active materials like catalysts and redox materials exhibiting satisfactory durability, reactivity and efficiencies. Moreover, materials play an important role in the construction of key components and for the implementation in commercial solar plants. The most promising thermochemical water- and CO2-splitting processes are being described and discussed with respect to further development and future potential. The main materials-related challenges of those processes are being analyzed. Technical approaches and development progress in terms of solving them are addressed and assessed in this review.

  3. Photocatalytic and Photoelectrochemical Water Splitting on TiO2 via Photosensitization

    Directory of Open Access Journals (Sweden)

    Saji Thomas Kochuveedu

    2016-01-01

    Full Text Available The search for an alternative to replace conventional fuel has been going on for years due to the limited storage of fossil fuel and excess CO2 emission from the fuel. Using H2 as fuel has gained wide attention recently, as well as consequently splitting of water into hydrogen and oxygen. Seminal semiconductors such as TiO2 and ZnO have their position of CB and VB in alignment with water reduction and oxidation potential, respectively, but their wide bandgap allows them to absorb only UV light of the solar spectrum. Combining narrow bandgap semiconductors or other visible light active sensitizers with TiO2/ZnO is a facile route to exploit the visible light region of the solar spectrum. In this review, I make an attempt to summarize the various photosensitizers used in combination with TiO2 for water splitting with recent reports as examples.

  4. Sunlight driven photocatalytic water splitting using nanostructured bismuth tungstate (Bi2WO6)

    Science.gov (United States)

    Radha, R.; Sakar, M.; Bharathkumar, S.; Balakumar, S.

    2017-05-01

    Sunlight driven photocatalytic water splitting properties of nanosized Bi2WO6 have been demonstrated. Upon the structural confirmation using XRD and Raman studies, the band edge offset deduced from UV-DRS spectra showed that the energy band structure of Bi2WO6 is manifested due to electronic transition in the hybridized orbital of Bi6s and O2p to the W5d orbital. The observed Bi2WO6 nanoparticulates-assisted H2 generation from glycerol-water mixture may be attributed to the following two competitive phenomena: (i) the photocatalytic degradation of glycerol and (ii) photocatalytic splitting of water molecules, where glycerol acts as a sacrificial agent. This study sheds lights on the photocatalytic reformation of contaminated aqueous ecosystems as a green resource to produce hydrogen energy.

  5. The DOE Water Cycle Pilot Study

    Energy Technology Data Exchange (ETDEWEB)

    Miller, N.L.; King, A.W.; Miller, M.A.; Springer, E.P.; Wesely, M.L.; Bashford, K.E.; Conrad, M.E.; Costigan, K.; Foster, P.N.; Gibbs, H.K.; Jin, J.; Klazura, J.; Lesht, B.M.; Machavaram, M.V.; Pan, F.; Song, J.; Troyan, D.; Washington-Allen, R.A.

    2003-09-20

    A Department of Energy (DOE) multi-laboratory Water Cycle Pilot Study (WCPS) investigated components of the local water budget at the Walnut River Watershed in Kansas to study the relative importance of various processes and to determine the feasibility of observational water budget closure. An extensive database of local meteorological time series and land surface characteristics was compiled. Numerical simulations of water budget components were generated and, to the extent possible, validated for three nested domains within the Southern Great Plains; the DOE Atmospheric Radiation Measurement/Cloud Atmospheric Radiation Testbed (ARM/CART), the Walnut River Watershed (WRW), and the Whitewater Watershed (WW), Kansas A 2-month Intensive Observation Period (IOP) was conducted to gather detailed observations relevant to specific details of the water budget, including fine-scale precipitation, streamflow, and soil moisture measurements not made routinely by other programs. Event and season al water isotope (delta 18O, delta D) sampling in rainwater, streams, soils, lakes, and wells provided a means of tracing sources and sinks within and external to the WW, WRW, and the ARM/CART domains. The WCPS measured changes in leaf area index for several vegetation types, deep groundwater variations at two wells, and meteorological variables at a number of sites in the WRW. Additional activities of the WCPS include code development toward a regional climate model with water isotope processes, soil moisture transect measurements, and water level measurements in ground water wells.

  6. Hybrid bio-photo-electro-chemical cells for solar water splitting

    Science.gov (United States)

    Pinhassi, Roy I.; Kallmann, Dan; Saper, Gadiel; Dotan, Hen; Linkov, Artyom; Kay, Asaf; Liveanu, Varda; Schuster, Gadi; Adir, Noam; Rothschild, Avner

    2016-08-01

    Photoelectrochemical water splitting uses solar power to decompose water to hydrogen and oxygen. Here we show how the photocatalytic activity of thylakoid membranes leads to overall water splitting in a bio-photo-electro-chemical (BPEC) cell via a simple process. Thylakoids extracted from spinach are introduced into a BPEC cell containing buffer solution with ferricyanide. Upon solar-simulated illumination, water oxidation takes place and electrons are shuttled by the ferri/ferrocyanide redox couple from the thylakoids to a transparent electrode serving as the anode, yielding a photocurrent density of 0.5 mA cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell and a Si photovoltaic module achieves overall water splitting with solar to hydrogen efficiency of 0.3%. These results demonstrate the promise of combining natural photosynthetic membranes and man-made photovoltaic cells in order to convert solar power into hydrogen fuel.

  7. Unraveling the hydrodynamics of split root water uptake experiments using CT scanned root architectures and three dimensional flow simulations

    Directory of Open Access Journals (Sweden)

    Nicolai eKoebernick

    2015-05-01

    Full Text Available Split root experiments have the potential to disentangle water transport in roots and soil, enabling the investigation of the water uptake pattern of a root system. Interpretation of the experimental data assumes that water flow between the split soil compartments does not occur. Another approach to investigate root water uptake is by numerical simulations combining soil and root water flow depending on the parameterization and description of the root system. Our aim is to demonstrate the synergisms that emerge from combining split root experiments with simulations. We show how growing root architectures derived from temporally repeated X-ray CT scanning can be implemented in numerical soil-plant models. Faba beans were grown with and without split layers and exposed to a single drought period during which plant and soil water status were measured. Root architectures were reconstructed from CT scans and used in the model R-SWMS (root-soil water movement and solute transport to simulate water potentials in soil and roots in 3D as well as water uptake by growing roots in different depths. CT scans revealed that root development was considerably lower with split layers compared to without. This coincided with a reduction of transpiration, stomatal conductance and shoot growth. Simulated predawn water potentials were lower in the presence of split layers. Simulations showed that this was caused by an increased resistance to vertical water flow in the soil by the split layers. Comparison between measured and simulated soil water potentials proved that the split layers were not perfectly isolating and that redistribution of water from the lower, wetter compartments to the drier upper compartments took place, thus water losses were not equal to the root water uptake from those compartments. Still, the layers increased the resistance to vertical flow which resulted in lower simulated collar water potentials that led to reduced stomatal conductance and

  8. Flow splitting in numerical simulations of oceanic dense-water outflows

    Science.gov (United States)

    Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Özgökmen, Tamay M.

    2017-05-01

    Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0 =Q0N3 /g‧2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g‧ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

  9. Water cycle investigations in Hungarian forest ecosystems

    Institute of Scientific and Technical Information of China (English)

    Judit Sitkey

    2006-01-01

    From the biological point of view the value of autotrophy plant association is determined by the carbon fixation and the carbon cycle. Among the plant associations of Hungary, forest has the largest biological carbon fixation and carbon cycle. In general,the annual water cycle is the key factor in the organic material production of the Hungarian forests. The most intensive water consumption and organic material production take place from May till July, which period is named main water consumption and respectively main growing period. In Hungary the categories of the forest climate are characterized by main tree species and based on the forest climate covers 8% of the forest area, hornbeam-oak forest climate covers 22%, sessile oak-Turkey oak forest climate covers48% and forest steppe climate covers 22%. Partly in the frame of ICP-Forests, the Department of Ecology in the Forest Research Institute carries out long term, complex ecophysiological investigations on several sample plots (so-called basic plots) throughout the whole country. The organic material production (growth), the nutrient and water cycle, the measurements of air pollutants and meteorological parameters, as well as chemical analyses are all part of the investigations. As a comparison the figure of two basic plotsforest steppe climate in the hydrological year of 2001-2002. In the Hungarian forest 60%-70% of the precipitation is used for interception, evaporation, and in the vegetation season, for the transpiration both in beech and forest steppe climate. From other point of view, only 30%-40% of the open air precipitation infiltrates into the soil and can be utilized by the forest.

  10. Light induced oxidative water splitting in photosynthesis: energetics, kinetics and mechanism.

    Science.gov (United States)

    Renger, Gernot

    2011-01-01

    The essential steps of photosynthetic water splitting take place in Photosystem II (PSII) and comprise three different reaction sequences: (i) light induced formation of the radical pair P680(+)Q(A)(-), (ii) P680(+) driven oxidative water splitting into O(2) and four protons, and (iii) two step plastoquinone reduction to plastoquinol by Q(A)(-). This mini-review briefly summarizes our state of knowledge on energetics, kinetics and mechanism of oxidative water splitting. Essential features of the two types of reactions involved are described: (a) P680(+) reduction by the redox active tyrosine Y(z) and (b) sequence of oxidation steps induced by Y(z)(ox) in the water-oxidizing complex (WOC). The rate of the former reaction is limited by the non-adiabatic electron transfer (NET) step and the multi-phase kinetics shown to originate from a sequence of relaxation processes. In marked contrast, the rate of the stepwise oxidation by Y(z)(ox) of the WOC up to the redox level S(3) is not limited by NET but by trigger reactions which probably comprise proton shifts and/or conformational changes. The overall rate of the final reaction sequence leading to formation and release of O(2) is assumed to be limited by the electron transfer step from the S(3) state of WOC to Y(z)(ox) due to involvement of an endergonic redox equilibrium. Currently discussed controversial ideas on possible pathways are briefly outlined. Several crucial points of the mechanism of oxidative water splitting, like O-O bond formation, role of local proton shift(s), details of hydrogen bonding, are still not clarified and remain a challenging topic of future research.

  11. Ultrastable low-bias water splitting photoanodes via photocorrosion inhibition and in situ catalyst regeneration

    Science.gov (United States)

    Kuang, Yongbo; Jia, Qingxin; Ma, Guijun; Hisatomi, Takashi; Minegishi, Tsutomu; Nishiyama, Hiroshi; Nakabayashi, Mamiko; Shibata, Naoya; Yamada, Taro; Kudo, Akihiko; Domen, Kazunari

    2017-01-01

    Photoelectrochemical (PEC) water splitting offers a means for distributed solar hydrogen production. However, the lack of stable and cost-effective photoanodes remains a bottleneck that hampers their practical applications. Here we show that particulate Mo-doped BiVO4 water oxidation photoanodes, without costly and complex surface modifications, can possess comparable stability to that of solar cells. The photoanode exhibits enhanced intrinsic photocorrosion inhibition and self-generation and regeneration of oxygen evolution catalysts, which allows stable oxygen evolution for >1,000 h at potentials as low as 0.4 V versus the reversible hydrogen electrode. The significantly improved photocorrosion resistance and charge separation are attributed to the unusual high-temperature treatment. In situ catalyst regeneration is found to be a site-specific and oxygen evolution rate change-induced process. Our findings indicate the potential of PEC water splitting to compete with other solar hydrogen production solutions, and should open new opportunities for the development of feasible PEC water splitting systems.

  12. Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering.

    Science.gov (United States)

    Shinagawa, Tatsuya; Takanabe, Kazuhiro

    2017-04-10

    Recent advances in power generation from renewable resources necessitate conversion of electricity to chemicals and fuels in an efficient manner. Electrocatalytic water splitting is one of the most powerful and widespread technologies. The development of highly efficient, inexpensive, flexible, and versatile water electrolysis devices is desired. This review discusses the significance and impact of the electrolyte on electrocatalytic performance. Depending on the circumstances under which the water splitting reaction is conducted, the required solution conditions, such as the identity and molarity of ions, may significantly differ. Quantitative understanding of such electrolyte properties on electrolysis performance is effective to facilitate the development of efficient electrocatalytic systems. The electrolyte can directly participate in reaction schemes (kinetics), affect electrode stability, and/or indirectly impact the performance by influencing the concentration overpotential (mass transport). This review aims to guide fine-tuning of the electrolyte properties, or electrolyte engineering, for (photo)electrochemical water splitting reactions. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  13. Stability and bandgaps of layered perovskites for one- and two-photon water splitting

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; García Lastra, Juan Maria; Hüser, Falco

    2013-01-01

    Direct production of hydrogen from water and sunlight requires stable and abundantly available semiconductors with well positioned band edges relative to the water red-ox potentials. We have used density functional theory (DFT) calculations to investigate 300 oxides and oxynitrides...... in the Ruddlesden–Popper phase of the layered perovskite structure. Based on screening criteria for the stability, bandgaps and band edge positions, we suggest 20 new materials for the light harvesting photo-electrode of a one-photon water splitting device and 5 anode materials for a two-photon device with silicon...

  14. Water splitting-biosynthetic system with CO₂ reduction efficiencies exceeding photosynthesis.

    Science.gov (United States)

    Liu, Chong; Colón, Brendan C; Ziesack, Marika; Silver, Pamela A; Nocera, Daniel G

    2016-06-03

    Artificial photosynthetic systems can store solar energy and chemically reduce CO2 We developed a hybrid water splitting-biosynthetic system based on a biocompatible Earth-abundant inorganic catalyst system to split water into molecular hydrogen and oxygen (H2 and O2) at low driving voltages. When grown in contact with these catalysts, Ralstonia eutropha consumed the produced H2 to synthesize biomass and fuels or chemical products from low CO2 concentration in the presence of O2 This scalable system has a CO2 reduction energy efficiency of ~50% when producing bacterial biomass and liquid fusel alcohols, scrubbing 180 grams of CO2 per kilowatt-hour of electricity. Coupling this hybrid device to existing photovoltaic systems would yield a CO2 reduction energy efficiency of ~10%, exceeding that of natural photosynthetic systems.

  15. Fabrication and evaluation of nickel cobalt alloy electrocatalysts for alkaline water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Sung Hoon [School of Integrative Engineering, Chung-Ang University, Heukseokno 84, Dongjak-gu, Seoul 156-756 (Korea, Republic of); Ahn, Sang Hyun; Choi, Insoo [Fuel Cell Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of); Pyo, Sung Gyu [School of Integrative Engineering, Chung-Ang University, Heukseokno 84, Dongjak-gu, Seoul 156-756 (Korea, Republic of); Kim, Hyoung-Juhn; Jang, Jong Hyun [Fuel Cell Research Center, Korea Institute of Science and Technology, Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of); Kim, Soo-Kil, E-mail: sookilkim@cau.ac.kr [School of Integrative Engineering, Chung-Ang University, Heukseokno 84, Dongjak-gu, Seoul 156-756 (Korea, Republic of)

    2014-07-01

    As a catalyst for the hydrogen evolution reaction (HER) in alkaline water splitting, NiCo alloys of various compositions were prepared through electrodeposition onto Cu substrates. The composition of each alloy catalyst was varied by controlling the molar ratio of Co{sup 2+} ions in the electrolyte. With an increase in the Co content, the morphologies of the NiCo alloys were progressively changed from a round to polygonal shape. The NiCo alloys all exhibited a Ni rich surface, as confirmed by the bulk-to-surface compositional ratio and degree of alloying. The catalytic activities of the NiCo alloys toward the HER of water splitting were electrochemically tested in a KOH electrolyte, and the specific activities were characterized by considering the electrochemical surface areas of Ni and Co. The effect of alloying was demonstrated to be a significant enhancement of HER activity, resulting from a change in the electronic structures of Ni and Co.

  16. Modeling, Simulation, and Implementation of Solar-Driven Water-Splitting Devices.

    Science.gov (United States)

    Xiang, Chengxiang; Weber, Adam Z; Ardo, Shane; Berger, Alan; Chen, YiKai; Coridan, Robert; Fountaine, Katherine T; Haussener, Sophia; Hu, Shu; Liu, Rui; Lewis, Nathan S; Modestino, Miguel A; Shaner, Matthew M; Singh, Meenesh R; Stevens, John C; Sun, Ke; Walczak, Karl

    2016-10-10

    An integrated cell for the solar-driven splitting of water consists of multiple functional components and couples various photoelectrochemical (PEC) processes at different length and time scales. The overall solar-to-hydrogen (STH) conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as on the component integration, overall device architecture, and system operating conditions. This Review focuses on the modeling- and simulation-guided development and implementation of solar-driven water-splitting prototypes from a holistic viewpoint that explores the various interplays between the components. The underlying physics and interactions at the cell level is are reviewed and discussed, followed by an overview of the use of the cell model to provide target properties of materials and guide the design of a range of traditional and unique device architectures.

  17. Manganese-based Materials Inspired by Photosynthesis for Water-Splitting

    Directory of Open Access Journals (Sweden)

    Harvey J.M. Hou

    2011-09-01

    Full Text Available In nature, the water-splitting reaction via photosynthesis driven by sunlight in plants, algae, and cyanobacteria stores the vast solar energy and provides vital oxygen to life on earth. The recent advances in elucidating the structures and functions of natural photosynthesis has provided firm framework and solid foundation in applying the knowledge to transform the carbon-based energy to renewable solar energy into our energy systems. In this review, inspired by photosynthesis robust photo water-splitting systems using manganese-containing materials including Mn-terpy dimer/titanium oxide, Mn-oxo tetramer/Nafion, and Mn-terpy oligomer/tungsten oxide, in solar fuel production are summarized and evaluated. Potential problems and future endeavors are also discussed.

  18. Acidification of Harbour sediment and removal of heavy metals induced by water splitting in electrodialytic remediation

    DEFF Research Database (Denmark)

    Nystrøm, Gunvor Marie; Ottosen, Lisbeth M.; Villumsen, Arne

    2005-01-01

    Harbor sediments are often contaminated with heavy metals, which can be removed by electrodialytic remediation. Water splitting at the anion exchange membrane in contact with the contaminated material in electrodialytic remediation is highly important for the removal of heavy metals. Here...... it was investigated how acidification caused by water splitting at the anion exchange membrane during electrodialytic remediation of contaminated harbor sediment and hence the metal removal, was influenced by different experimental conditions. Two different experimental cells were tested, where the number...... the sediment was acidified, the voltage decreased and electrical conductivity increased. After 5 days of remediation the sediment was acidified at the chosen current density (1 mA/cm(2)) and the main metal removal was observed shortly after. Thus it was crucial for the metal removal that the sediment was fully...

  19. Electrochemical Water Splitting Coupled with Organic Compound Oxidation: The Role of Active Chlorine Species

    OpenAIRE

    Park, Hyunwoong; Vecitis, Chad D.; Michael R. Hoffmann

    2009-01-01

    The need for alternative energy sources with minimal to no carbon footprint is growing. A solar-powered electrochemical system that produces hydrogen via water splitting using organic pollutants as sacrificial electron donors is a possible solution. The hybridization of a BiO_x−TiO_2/Ti anode with a stainless steel cathode powered by a photovoltaic (PV) array has been shown to achieve this process. The electrochemical degradation kinetics of a variety of organic substrates is investigated as ...

  20. Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting

    KAUST Repository

    Liang, Hanfeng

    2016-11-09

    Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as NiP have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at 10 mA cm in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications.

  1. Electrochemical Water Splitting Coupled with Organic Compound Oxidation: The Role of Active Chlorine Species

    OpenAIRE

    Park, Hyunwoong; Vecitis, Chad D.; Hoffmann, Michael R.

    2009-01-01

    The need for alternative energy sources with minimal to no carbon footprint is growing. A solar-powered electrochemical system that produces hydrogen via water splitting using organic pollutants as sacrificial electron donors is a possible solution. The hybridization of a BiO_x−TiO_2/Ti anode with a stainless steel cathode powered by a photovoltaic (PV) array has been shown to achieve this process. The electrochemical degradation kinetics of a variety of organic substrates is investigated as ...

  2. Effect of Installation of Solar Collector on Performance of Balcony Split Type Solar Water Heaters

    OpenAIRE

    Xu Ji; Ming Li; Weidong Lin; Tufeng Zheng; Yunfeng Wang

    2015-01-01

    The influences of surface orientation and slope of solar collectors on solar radiation collection of balcony split type solar water heaters for six cities in China were analyzed by employing software TRNSYS. The surface azimuth had greater effect on solar radiation collection in high latitude regions. For deviation of the surface slope angle within ±20° around the optimized angle, the variation of the total annual collecting solar radiation was less than 5%. However, with deviation of 70° to ...

  3. Virtual Breakdown Mechanism: Field-Driven Splitting of Pure Water for Hydrogen Production

    CERN Document Server

    Wang, Yifei; Wu, Wei

    2016-01-01

    Due to the low conductivity of pure water, using an electrolyte is common for achieving efficient water electrolysis. In this paper, we have broken through this common sense by using deep-sub-Debye-length nanogap electrochemical cells for the electrolysis of pure water. At such nanometer scale, the field-driven pure water splitting exhibits a completely different mechanism from the macrosystem. We have named this process 'virtual breakdown mechanism' that results in a series of fundamental changes and more than 10^5-fold enhancement of the equivalent conductivity of pure water. This fundamental discovery has been theoretically discussed in this paper and experimentally demonstrated in a group of electrochemical cells with nanogaps between two electrodes down to 37 nm. Based on our nanogap electrochemical cells, the electrolysis current from pure water is comparable to or even larger than the current from 1 mol/L sodium hydroxide solution, indicating the high-efficiency of pure water splitting as a potential f...

  4. A new approach for retrieving precipitable water from ATSR2 split-window channel data over land area

    NARCIS (Netherlands)

    Li Zhao-Liang,; Jia, L.; Su, Z.; Wan Zhengming,; Zhang Renhua,

    2003-01-01

    This paper presents a new algorithm to determine quantitatively column water vapour content ( W ) directly from ATSR2 (Along-Track Scanner Radiometer) Split-Window radiance measurements. First, the Split-Window Covariance-Variance Ratio (SWCVR) method is reviewed. The assumptions made to derive this

  5. Solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen efficiency over 30.

    Science.gov (United States)

    Jia, Jieyang; Seitz, Linsey C; Benck, Jesse D; Huo, Yijie; Chen, Yusi; Ng, Jia Wei Desmond; Bilir, Taner; Harris, James S; Jaramillo, Thomas F

    2016-10-31

    Hydrogen production via electrochemical water splitting is a promising approach for storing solar energy. For this technology to be economically competitive, it is critical to develop water splitting systems with high solar-to-hydrogen (STH) efficiencies. Here we report a photovoltaic-electrolysis system with the highest STH efficiency for any water splitting technology to date, to the best of our knowledge. Our system consists of two polymer electrolyte membrane electrolysers in series with one InGaP/GaAs/GaInNAsSb triple-junction solar cell, which produces a large-enough voltage to drive both electrolysers with no additional energy input. The solar concentration is adjusted such that the maximum power point of the photovoltaic is well matched to the operating capacity of the electrolysers to optimize the system efficiency. The system achieves a 48-h average STH efficiency of 30%. These results demonstrate the potential of photovoltaic-electrolysis systems for cost-effective solar energy storage.

  6. Photophysics and electrochemistry relevant to photocatalytic water splitting involved at solid–electrolyte interfaces

    KAUST Repository

    Shinagawa, Tatsuya

    2016-08-04

    Direct photon to chemical energy conversion using semiconductor-electrocatalyst-electrolyte interfaces has been extensively investigated for more than a half century. Many studies have focused on screening materials for efficient photocatalysis. Photocatalytic efficiency has been improved during this period but is not sufficient for industrial commercialization. Detailed elucidation on the photocatalytic water splitting process leads to consecutive six reaction steps with the fundamental parameters involved: The photocatalysis is initiated involving photophysics derived from various semiconductor properties (1: photon absorption, 2: exciton separation). The generated charge carriers need to be transferred to surfaces effectively utilizing the interfaces (3: carrier diffusion, 4: carrier transport). Consequently, electrocatalysis finishes the process by producing products on the surface (5: catalytic efficiency, 6: mass transfer of reactants and products). Successful photocatalytic water splitting requires the enhancement of efficiency at each stage. Most critically, a fundamental understanding of the interfacial phenomena is highly desired for establishing "photocatalysis by design" concepts, where the kinetic bottleneck within a process is identified by further improving the specific properties of photocatalytic materials as opposed to blind material screening. Theoretical modeling using the identified quantitative parameters can effectively predict the theoretically attainable photon-conversion yields. This article provides an overview of the state-of-the-art theoretical understanding of interfacial problems mainly developed in our laboratory. Photocatalytic water splitting (especially hydrogen evolution on metal surfaces) was selected as a topic, and the photophysical and electrochemical processes that occur at semiconductor-metal, semiconductor-electrolyte and metal-electrolyte interfaces are discussed.

  7. Stable quantum dot photoelectrolysis cell for unassisted visible light solar water splitting.

    Science.gov (United States)

    Yang, Hong Bin; Miao, Jianwei; Hung, Sung-Fu; Huo, Fengwei; Chen, Hao Ming; Liu, Bin

    2014-10-28

    Sunlight is an ideal source of energy, and converting sunlight into chemical fuels, mimicking what nature does, has attracted significant attention in the past decade. In terms of solar energy conversion into chemical fuels, solar water splitting for hydrogen production is one of the most attractive renewable energy technologies, and this achievement would satisfy our increasing demand for carbon-neutral sustainable energy. Here, we report corrosion-resistant, nanocomposite photoelectrodes for spontaneous overall solar water splitting, consisting of a CdS quantum dot (QD) modified TiO2 photoanode and a CdSe QD modified NiO photocathode, where cadmium chalcogenide QDs are protected by a ZnS passivation layer and gas evolution cocatalysts. The optimized device exhibited a maximum efficiency of 0.17%, comparable to that of natural photosynthesis with excellent photostability under visible light illumination. Our device shows spontaneous overall water splitting in a nonsacrificial environment under visible light illumination (λ > 400 nm) through mimicking nature's "Z-scheme" process. The results here also provide a conceptual layout to improve the efficiency of solar-to-fuel conversion, which is solely based on facile, scalable solution-phase techniques.

  8. Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells.

    Science.gov (United States)

    Qiu, Yongcai; Liu, Wei; Chen, Wei; Chen, Wei; Zhou, Guangmin; Hsu, Po-Chun; Zhang, Rufan; Liang, Zheng; Fan, Shoushan; Zhang, Yuegang; Cui, Yi

    2016-06-01

    Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%.

  9. Photoelectrochemical water splitting on nanoporous GaN thin films for energy conversion under visible light

    Science.gov (United States)

    Cao, Dezhong; Xiao, Hongdi; Fang, Jiacheng; Liu, Jianqiang; Gao, Qingxue; Liu, Xiangdong; Ma, Jin

    2017-01-01

    Nanoporous (NP) GaN thin films, which were fabricated by an electrochemical etching method at different voltages, were used as photoelectrodes during photoelectrochemical (PEC) water splitting in 1 M oxalic acid solution. Upon illumination at a power density of 100 mW cm‑2 (AM 1.5), water splitting is observed in NP GaN thin films, presumably resulting from the valence band edge which is more positive than the redox potential of the oxidizing species. In comparison with NP GaN film fabricated at 8 V, NP GaN obtained at 18 V shows nearly twofold enhancement in photocurrent with the maximum photo-to-hydrogen conversion efficiency of 1.05% at ~0 V (versus Ag/AgCl). This enhancement could be explained with (i) the increase of surface area and surface states, and (ii) the decrease of resistances and carrier concentration in the NP GaN thin films. High stability of the NP GaN thin films during the PEC water splitting further confirms that the NP GaN thin film could be applied to the design of efficient solar cells and solar fuel devices.

  10. Application of ZnO single crystals for light-induced water splitting under UV irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Suhak, Yuriy, E-mail: suhak@ifpan.edu.pl [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Izdebska, Katarzyna; Skupiński, Paweł; Wierzbicka, Aleksandra; Reszka, Anna; Sybilski, Piotr; Kowalski, Bogdan J.; Mycielski, Andrzej; Zytkiewicz, Zbigniew R. [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Soszko, Michał [Industrial Chemistry Research Institute, Rydygiera 8, 01-793 Warsaw (Poland); Suchocki, Andrzej [Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Institute of Physics, University of Bydgoszcz, Weyssenhoffa 11, 85-072 Bydgoszcz (Poland)

    2014-02-14

    This paper presents experimental results of implementation of ZnO single crystals as photoanodes in photoelectrochemical (PEC) cells for hydrogen generation through the process of water splitting. Both, as-grown and O{sub 2}-annealed ZnO single crystals were investigated for this purpose. A 351 nm argon laser line was used as the light source. The XRD investigations showed that used ZnO crystals are of good crystalline quality. It was found that the as-grown ZnO single crystals possess higher conversion efficiencies comparing to the O{sub 2}-annealed one. The photocurrent density was found to increase significantly with the increase of external bias applied and excitation light intensity. Time dependent photocurrent density characteristics showed that the decay of photocurrent density was not observed within the measurement time. The differences in behaviour of the as-grown and the annealed in O{sub 2} ZnO single crystals are discussed in terms of crystals intrinsic defects. - Highlights: • ZnO single crystals show excellent performance as photoanodes for water splitting. • ZnO single crystals showed good stability in aqueous solution. • Mid-gap band state introduction does not influence the efficiency of water splitting.

  11. Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells

    Science.gov (United States)

    Qiu, Yongcai; Liu, Wei; Chen, Wei; Chen, Wei; Zhou, Guangmin; Hsu, Po-Chun; Zhang, Rufan; Liang, Zheng; Fan, Shoushan; Zhang, Yuegang; Cui, Yi

    2016-01-01

    Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm−2 at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%. PMID:27386565

  12. Heterogeneous Bimetallic Phosphide/Sulfide Nanocomposite for Efficient Solar-Energy-Driven Overall Water Splitting.

    Science.gov (United States)

    Xin, Yanmei; Kan, Xiang; Gan, Li-Yong; Zhang, Zhonghai

    2017-09-14

    Solar-driven overall water splitting is highly desirable for hydrogen generation with sustainable energy sources, which need efficient, earth-abundant, robust, and bifunctional electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, we propose a heterogeneous bimetallic phosphide/sulfide nanocomposite electrocatalyst of NiFeSP on nickel foam (NiFeSP/NF), which shows superior electrocatalytic activity of low overpotentials of 91 mV at -10 mA cm(-2) for HER and of 240 mV at 50 mA cm(-2) for OER in 1 M KOH solution. In addition, the NiFeSP/NF presents excellent overall water splitting performance with a cell voltage as low as 1.58 V at a current density of 10 mA cm(-2). Combining with a photovoltaic device of a Si solar cell or integrating into photoelectrochemical (PEC) systems, the bifunctional NiFeSP/NF electrocatalyst implements unassisted solar-driven water splitting with a solar-to-hydrogen conversion efficiency of ∼9.2% and significantly enhanced PEC performance, respectively.

  13. Solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen efficiency over 30%

    Science.gov (United States)

    Jia, Jieyang; Seitz, Linsey C.; Benck, Jesse D.; Huo, Yijie; Chen, Yusi; Ng, Jia Wei Desmond; Bilir, Taner; Harris, James S.; Jaramillo, Thomas F.

    2016-10-01

    Hydrogen production via electrochemical water splitting is a promising approach for storing solar energy. For this technology to be economically competitive, it is critical to develop water splitting systems with high solar-to-hydrogen (STH) efficiencies. Here we report a photovoltaic-electrolysis system with the highest STH efficiency for any water splitting technology to date, to the best of our knowledge. Our system consists of two polymer electrolyte membrane electrolysers in series with one InGaP/GaAs/GaInNAsSb triple-junction solar cell, which produces a large-enough voltage to drive both electrolysers with no additional energy input. The solar concentration is adjusted such that the maximum power point of the photovoltaic is well matched to the operating capacity of the electrolysers to optimize the system efficiency. The system achieves a 48-h average STH efficiency of 30%. These results demonstrate the potential of photovoltaic-electrolysis systems for cost-effective solar energy storage.

  14. Comparison of clinical outcomes between in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in IVF-ICSI split insemination cycles

    Science.gov (United States)

    Lee, Sun Hee; Lee, Jae Hyun; Park, Yong-Seog; Yang, Kwang Moon

    2017-01-01

    Objective This study aimed to compare the clinical outcomes between in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in sibling oocytes. Additionally, we evaluated whether the implementation of split insemination contributed to an increase in the number of ICSI procedures. Methods A total of 571 cycles in 555 couples undergoing split insemination cycles were included in this study. Among them, 512 cycles (89.7%) were a couple's first IVF cycle. The patients were under 40 years of age and at least 10 oocytes were retrieved in all cycles. Sibling oocytes were randomly allocated to IVF or ICSI. Results Total fertilization failure was significantly more common in IVF cycles than in ICSI cycles (4.0% vs. 1.4%, pfertilization rate among retrieved oocytes (as defined by fertilization rates greater than 0% but fertilization rate of ICSI among injected oocytes was significantly higher than for IVF (72.3%±24.3% vs. 59.2%±25.9%, pfertilization rate among retrieved oocytes was significantly higher in IVF than in ICSI (59.2%±25.9% vs. 52.1%±22.5%, pfertilization failure. However, unnecessary ICSI is carried out in most split insemination cycles and the use of split insemination might make ICSI more common. PMID:28795049

  15. Photoelectrochemical splitting of water to produce a power appetizer Hydrogen: A green system for future –( A short review

    Directory of Open Access Journals (Sweden)

    Pushpendra Kumar

    2016-06-01

    Full Text Available To meet the future energy demand, Hydrogen has been accepted as a fuel for future. Out of several renewable methods to produce hydrogen, solar assisted splitting of water (Photoelectrochemical splitting of water is emerging as a most desired method to produce hydrogen which is a advancement of Photovoltaic process. However, the efficiency of PEC cell is a matter of concern. Various strategies have been adopted by different researchers to increase the efficiency of the system especially using nanotechnology as a tool. In this article, attempts have been made to summarise different approaches applied to obtain effective and viable photoelectrochemical system for splitting water to obtain hydrogen an energy carrier.

  16. Martian north polar cap summer water cycle

    CERN Document Server

    Brown, Adrian J; Becerra, Patricio; Byrne, Shane

    2016-01-01

    A key outstanding question in Martian science is 'are the polar caps gaining or losing mass and what are the implications for past, current and future climate?' To address this question, we use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of the north polar cap during late summer for multiple Martian years, to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer. We establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap. We show that in a key region in the interior of the north polar cap, the absorption band depths grow until Ls=120, when they begin to shrink, until they are obscured at the end of summer by the north polar hood. This behavior is transferable over the entire north polar cap, where in late summer regions 'flip' from being net sublimating into net condensation mode. This transition or 'mode flip' happens earlier for ...

  17. Water Cycle Multimission Observation Strategy (WACMOS)

    Science.gov (United States)

    Su, Z.

    2009-04-01

    To understand the role of the terrestrial hydrosphere-biosphere in Earth's climate system it is essential to be able to measure from space hydroclimatic variables, such as radiation, precipitation, evapotranspiration, soil moisture, clouds, water vapour, surface water and runoff, vegetation state, albedo and surface temperature, etc. Such measurements are required to further increase our understanding of the global climate and its variability, both spatially and temporally. Additionally, such observations advance our understanding of the coupling between terrestrial and atmospheric branches of the water cycle, and how this coupling may influence climate variability and predictability. To enhance the prediction of variations in the global water cycle, based on improved understanding of hydrological processes and its close linkage with the energy cycle and its sustained monitoring capability, is a key contribution to mitigation of water-related damages and sustainable human development. In many cases, the combination of space-based and high-resolution in situ data provides the essential information for effectively addressing water management issues (GEOSS 10-Year Implementation Plan - REFERENCE DOCUMENT, GEO 203-1). Recently the European Space Agency (ESA) has initiated, in its Support to Science Element programme, the Water Cycle Multimission Observation Strategy (WACMOS). WACMOS contributes to above described international efforts by supporting scientists in ESA member countries to develop and validate novel and improved multi-mission based products, and to enhance currently available global water datasets, so as to maximize the use of ESA data. In this context, the short term objectives of the project include: • Develop and validate a Product Portfolio of novel and/or improved multi-mission based geoinformation datasets at global and regional scales contributing to the objectives of the GEWEX program. WACMOS is focused on four Thematic Priorities described below

  18. Isotopes in the Arctic atmospheric water cycle

    Science.gov (United States)

    Bonne, Jean-Louis; Werner, Martin; Meyer, Hanno; Kipfstuhl, Sepp; Rabe, Benjamin; Behrens, Melanie; Schönicke, Lutz; Steen Larsen, Hans Christian; Masson-Delmotte, Valérie

    2016-04-01

    The ISO-ARC project aims at documenting the Arctic atmospheric hydrological cycle, by assessing the imprint of the marine boundary conditions (e.g. temperature variations, circulation changes, or meltwater input) to the isotopic composition of the atmospheric water cycle (H218O and HDO) with a focus on North Atlantic and Arctic oceans. For this purpose, two continuous monitoring water vapour stable isotopes cavity ring-down spectrometers have been installed in July 2015: on-board the Polarstern research vessel and in the Siberian Lena delta Samoylov research station (N 72° 22', E 126° 29'). The Polarstern measurements cover the summer 2015 Arctic campaign from July to mid-October, including six weeks in the Fram Strait region in July- August, followed by a campaign reaching the North Pole and a transect from the Norwegian Sea to the North Sea. These vapour observations are completed by water isotopic measurements in samples from the surface ocean water for Polarstern and from precipitation in Samoylov and Tiksi (120 km south-east of the station). A custom-made designed automatic calibration system has been implemented in a comparable manner for both vapour instruments, based on the injection of different liquid water standards, which are completely vaporised in dry air at high temperature. Subsequent humidity level can be adjusted from 2000 to at least 30000 ppm. For a better resilience, an independent calibration system has been added on the Samoylov instrument, allowing measurements of one standard at humidity levels ranging from 2000 to 15000 ppm: dry air is introduced in a tank containing a large amount of liquid water standard, undergoing evaporation under a controlled environment. The measurement protocol includes an automatic calibration every 25 hours. First instrument characterisation experiments depict a significant isotope-humidity effect at low humidity, dependant on the isotopic composition of the standard. For ambient air, our first isotope

  19. Bearing splitting and near-surface source ranging in the direct zone of deep water

    Science.gov (United States)

    Wu, Jun-Nan; Zhou, Shi-Hong; Peng, Zhao-Hui; Zhang, Yan; Zhang, Ren-He

    2016-12-01

    Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a bearing-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz-360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The bearing-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations. Project supported by the Program of One Hundred Talented People of the Chinese Academy of Sciences and the National Natural Science Foundation of China (Grant Nos. 11434012 and 41561144006).

  20. Explicit Kinetic Flux Vector Splitting Scheme for the 2-D Shallow Water Wave Equations

    Institute of Scientific and Technical Information of China (English)

    施卫平; 黄明游; 王婷; 张小江

    2004-01-01

    Originally, the kinetic flux vector splitting (KFVS) scheme was developed as a numerical method to solve gas dynamic problems. The main idea in the approach is to construct the flux based on the microscopical description of the gas. In this paper, based on the analogy between the shallow water wave equations and the gas dynamic equations, we develop an explicit KFVS method for simulating the shallow water wave equations. A 1D steady flow and a 2D unsteady flow are presented to show the robust and accuracy of the KFVS scheme.

  1. Martian north polar cap summer water cycle

    Science.gov (United States)

    Brown, Adrian J.; Calvin, Wendy M.; Becerra, Patricio; Byrne, Shane

    2016-10-01

    A key outstanding question in Martian science is "are the polar caps gaining or losing mass and what are the implications for past, current and future climate?" To address this question, we use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of the north polar cap during late summer for multiple Martian years, to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer. We establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap. We show that in a key region in the interior of the north polar cap, the absorption band depths grow until Ls = 120, when they begin to shrink, until they are obscured at the end of summer by the north polar hood. This behavior is transferable over the entire north polar cap, where in late summer regions 'flip' from being net sublimating into net condensation mode. This transition or 'mode flip' happens earlier for regions closer to the pole, and later for regions close to the periphery of the cap. The observations and calculations presented herein estimate that on average a water ice layer ∼70 microns thick is deposited during the Ls = 135-164 period. This is far larger than the results of deposition on the south pole during summer, where an average layer 0.6-6 microns deep has been estimated by Brown et al. (2014) Earth Planet. Sci. Lett., 406, 102-109.

  2. Highly efficient water splitting by a dual-absorber tandem cell

    Science.gov (United States)

    Brillet, Jeremie; Yum, Jun-Ho; Cornuz, Maurin; Hisatomi, Takashi; Solarska, Renata; Augustynski, Jan; Graetzel, Michael; Sivula, Kevin

    2012-12-01

    Photoelectrochemical water-splitting devices, which use solar energy to convert water into hydrogen and oxygen, have been investigated for decades. Multijunction designs are most efficient, as they can absorb enough solar energy and provide sufficient free energy for water cleavage. However, a balance exists between device complexity, cost and efficiency. Water splitters fabricated using triple-junction amorphous silicon or III-V semiconductors have demonstrated reasonable efficiencies, but at high cost and high device complexity. Simpler approaches using oxide-based semiconductors in a dual-absorber tandem approach have reported solar-to-hydrogen (STH) conversion efficiencies only up to 0.3% (ref. 4). Here, we present a device based on an oxide photoanode and a dye-sensitized solar cell, which performs unassisted water splitting with an efficiency of up to 3.1% STH. The design relies on carefully selected redox mediators for the dye-sensitized solar cell and surface passivation techniques and catalysts for the oxide-based photoanodes.

  3. Black tungsten nitride as a metallic photocatalyst for overall water splitting operable at up to 765 nm

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu Lei; Li, Yu Hang; Wang, Xue Lu; Chen, Ai Ping; Yang, Hua Gui [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai (China); Nie, Ting; Gong, Xue Qing [Key Laboratory for Advanced Materials, Centre for Computational Chemistry and Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai (China); Zheng, Li Rong [Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences (China)

    2017-06-19

    Semiconductor photocatalysts are hardly employed for overall water splitting beyond 700 nm, which is due to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs; however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Black tungsten nitride is now employed as a metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Correction: Iron-doping-enhanced photoelectrochemical water splitting performance of nanostructured WO3: a combined experimental and theoretical study.

    Science.gov (United States)

    Zhang, Teng; Zhu, Zonglong; Chen, Haining; Bai, Yang; Xiao, Shuang; Zheng, Xiaoli; Xue, Qingzhong; Yang, Shihe

    2015-09-07

    Correction for 'Iron-doping-enhanced photoelectrochemical water splitting performance of nanostructured WO3: a combined experimental and theoretical study' by Teng Zhang et al., Nanoscale, 2015, 7, 2933-2940.

  5. Rooting depths regulate the global water cycle

    Science.gov (United States)

    Miguez-Macho, Gonzalo; Fan, Ying

    2017-04-01

    Ecosystem productivity and evapotranspiration fluxes are fundamental regulators of the global carbon and water cycles. Where and how much plants grow is largely determined by atmospheric conditions and soil water availability. It is the reliance of ecosystems on soil water that links their fate tightly to precipitation and groundwater reach. Here, we explore the controls on plant root uptake imposed by climate at the large scale and by groundwater accessibility at the local drainage scale, aiming to untangle the spatial and temporal global patterns of rain-fed and groundwater-fed ecosystems. To this end, we use observed atmospheric and productivity conditions to model the seasonal evolution of root uptake and soil moisture profiles and their coupling to the water table, with a global groundwater-soil-vegetation framework at the 1km resolution. Results indicate highly variable uptake-depth across seasonal and local hydrologic gradients, and a far more common occurrence of deep (>5m) uptake than previous thought. Implications to future environmental change are briefly discussed.

  6. A Study on the Performance of the Split Reaction Water Turbine with Guide Ribs

    Science.gov (United States)

    Allen, Deuel H.; Villanueva, Eliseo P.

    2015-09-01

    The development of technologies that make use of renewable energy is of great significance presently. A new kind of turbine called Split Reaction Water Turbine (SRWT) using PVC pipes as material is a major contribution towards harnessing the energy potentials of small stream low head water resources. SRWTs of diameter to height ratio (D/H = 110 cm/160 cm) were tested at the MSU-IIT College of Engineering Fluid Engineering Laboratory. Data on volumetric flow and pressure head at the turbine inlet of the SRWT were recorded using National Instrument Data Processing System using LabView software. In later experiments, guide ribs were installed at the vane of the exit nozzles in order to determine the difference in the performance of the ribbed and the non-ribbed SRWT. Simulations of the running SRWT were conducted using SOLIDWORKS software. Results of the simulations aided in the thorough analyses of the data from the experimental runs. A comparison of data from the ribbed and non-ribbed SRWT shows that guide ribs were effective in directing the momentum of the exiting water to improve the speed of rotation. In this study, the increase in the speed of the Split Reaction Water Turbine was as much as 46%.

  7. High-Efficiency Photochemical Water Splitting of CdZnS/CdZnSe Nanostructures

    Directory of Open Access Journals (Sweden)

    Chen-I Wang

    2013-01-01

    Full Text Available We have prepared and employed TiO2/CdZnS/CdZnSe electrodes for photochemical water splitting. The TiO2/CdZnS/CdZnSe electrodes consisting of sheet-like CdZnS/CdZnSe nanostructures (8–10 μm in length and 5–8 nm in width were prepared through chemical bath deposition on TiO2 substrates. The TiO2/CdZnS/CdZnSe electrodes have light absorption over the wavelength 400–700 nm and a band gap of 1.87 eV. Upon one sun illumination of 100 mW cm−2, the TiO2/CdZnS/CdZnSe electrodes provide a significant photocurrent density of 9.7 mA cm−2 at −0.9 V versus a saturated calomel electrode (SCE. Incident photon-to-current conversion efficiency (IPCE spectrum of the electrodes displays a maximum IPCE value of 80% at 500 nm. Moreover, the TiO2/CdZnS/CdZnSe electrodes prepared from three different batches provide a remarkable photon-to-hydrogen efficiency of 7.3 ± 0.1% (the rate of the photocatalytically produced H2 by water splitting is about 172.8 mmol·h−1·g−1, which is the most efficient quantum-dots-based photocatalysts used in solar water splitting.

  8. Plasmon-Enhanced Photoelectrochemical Water Splitting with Size-Controllable Gold Nanodot Arrays

    Energy Technology Data Exchange (ETDEWEB)

    Kim, HJ; Lee, SH; Upadhye, AA; Ro, I; Tejedor-Tejedor, MI; Anderson, MA; Kim, WB; Huber, GW

    2014-10-01

    Size-controllable Au nanodot arrays (50, 63, and 83 nm dot size) with a narrow size distribution (+/- 5%) were prepared by a direct contact printing method on an indium tin oxide (ITO) substrate. Titania was added to the Au nanodots using TiO2 sols of 2-3 nm in size. This created a precisely controlled Au nanodot with 110 nm of TiO2 overcoats. Using these precisely controlled nanodot arrays, the effects of Au nanodot size and TiO2 overcoats were investigated for photoelectrochemical water splitting using a three-electrode system with a fiber-optic visible light source. From UV-vis measurement, the localized surface plasmon resonance (LSPR) peak energy (ELSPR) increased and the LSPR line width (G) decreased with decreasing Au nanodot size. The generated plasmonic enhancement for the photoelectrochemical water splitting reaction increased with decreasing Au particle size. The measured plasmonic enhancement for light on/off experiments was 25 times for the 50 nm Au size and 10 times for the 83 nm Au nanodot size. The activity of each catalyst increased by a factor of 6 when TiO2 was added to the Au nanodots for all the samples. The activity of the catalyst was proportional to the quality factor (defined as Q = E-LSPR/Gamma) of the plasmonic metal nanostructure. The enhanced water splitting performance with the decreased Au nanodot size is probably due to more generated charge carriers (electron/hole pair) by local field enhancement as the quality factor increases.

  9. Reaction pattern and mechanism of light induced oxidative water splitting in photosynthesis.

    Science.gov (United States)

    Renger, Gernot; Kühn, Philipp

    2007-06-01

    This mini review is an attempt to briefly summarize our current knowledge on light driven oxidative water splitting in photosynthesis. The reaction leading to molecular oxygen and four protons via photosynthesis comprises thermodynamic and kinetic constraints that require a balanced fine tuning of the reaction coordinates. The mode of coupling between electron (ET) and proton transfer (PT) reactions is shown to be of key mechanistic relevance for the redox turnover of Y(Z) and the reactions within the WOC. The WOC is characterized by peculiar energetics of its oxidation steps in the WOC. In all oxygen evolving photosynthetic organisms the redox state S(1) is thermodynamically most stable and therefore this general feature is assumed to be of physiological relevance. Available information on the Gibbs energy differences between the individual redox states S(i+1) and S(i) and on the activation energies of their oxidative transitions are used to construct a general reaction coordinate of oxidative water splitting in photosystem II (PS II). Finally, an attempt is presented to cast our current state of knowledge into a mechanism of oxidative water splitting with special emphasis on the formation of the essential O-O bond and the active role of the protein environment in tuning the local proton activity that depends on time and redox state S(i). The O-O linkage is assumed to take place within a multistate equilibrium at the redox level of S(3), comprising both redox isomerism and proton tautomerism. It is proposed that one state, S(3)(P), attains an electronic configuration and nuclear geometry that corresponds with a hydrogen bonded peroxide which acts as the entatic state for the generation of complexed molecular oxygen through S(3)(P) oxidation by Y(Z)(ox).

  10. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    OpenAIRE

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-01-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (∼2.5 eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350 °C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effective...

  11. Photoelectrochemical water splitting for hydrogen production with metal oxide (hematite and cupric oxide) based photocatalysts

    Science.gov (United States)

    Tang, Houwen

    Solar hydrogen is one ideal energy source to replace fossil fuel, as it is sustainable and environmentally friendly. Solar hydrogen can be generated in a number of ways. Photoelectrochemical (PEC) water splitting is one of the most promising methods for solar-to-chemical energy conversion. In this research project, metal oxide-based photocatalysts, especially hematite (α-Fe 2O3) and cupric oxide (CuO), were investigated for use as electrodes in PEC water splitting for solar hydrogen production. In our research project of hematite-based electrodes, we started with the incorporation of transition metal, particularly titanium (Ti), in hematite thin films to modify the valence and conduction band edges of hematite. We found that Ti impurities improve the electron conductivity of hematite and consequently lead to significantly enhanced photocurrents. We further investigated the Ti and Mg co-alloyed hematite. In this case, Ti is the donor and Mg is the acceptor in hematite. The co-alloying approach enhanced the solubility of Mg and Ti, which led to reduced electron effective mass and therefore increased electron mobility. Also, co-alloying tunes the carrier density and therefore allows the optimization of electrical conductivity. The densities of charged defects were found to be reduced, and therefore carrier recombinations were reduced. As a result, the Ti and Mg co-alloyed hematite thin films exhibited much improved performance in PEC water splitting as compared to pure hematite thin films. For the study of cupric oxide-based electrodes, we first investigated the possibility of reducing the electrode corrosion of cupric oxide in aqueous solutions by incorporating Ti as an electrode corrosion inhibitor. We found that Ti alloying can enhance the stability of cupric oxide in base solutions at the cost of reducing its crystallinity and optical absorption, and consequently lowering its photon-to-electron conversion efficiency. In order to balance the stability and the

  12. Two-dimensional transition metal dichalcogenide nanomaterials for solar water splitting

    Science.gov (United States)

    Andoshe, Dinsefa M.; Jeon, Jong-Myeong; Kim, Soo Young; Jang, Ho Won

    2015-05-01

    Recently, 2-dimensional (2D) transition metal dichalcogenides (TMDs) have received great attention for solar water splitting and electrocatalysis. In addition to their wide variety of electronic and microstructural properties, their promising catalytic activities for hydrogen production make 2D TMDs as earth-abundant and inexpensive catalysts that can replace noble metals. This paper reviews the electronic, structural, and optical properties of 2D TMDs. We highlight the various synthetic methods for 2D TMDs and their applications in hydrogen evolution based on photoelectrochemical and electrocatalytic cells. We also discuss perspectives and challenges of 2D TMDs for hydrogen production and artificial photosynthesis.[Figure not available: see fulltext.

  13. Vertically aligned Ta3N5 nanorod arrays for solar-driven photoelectrochemical water splitting

    KAUST Repository

    Li, Yanbo

    2012-09-18

    A vertically aligned Ta3N5 nanorod photoelectrode is fabricated by through-mask anodization and nitridation for water splitting. The Ta3N5 nanorods, working as photoanodes of a photoelectrochemical cell, yield a high photocurrent density of 3.8 mA cm -2 at 1.23 V versus a reversible hydrogen electrode under AM 1.5G simulated sunlight and an incident photon-to-current conversion efficiency of 41.3% at 440 nm, one of the highest activities reported for photoanodes so far. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Efficient photoelectrochemical water splitting with ultrathin films of hematite on three-dimensional nanophotonic structures.

    Science.gov (United States)

    Qiu, Yongcai; Leung, Siu-Fung; Zhang, Qianpeng; Hua, Bo; Lin, Qingfeng; Wei, Zhanhua; Tsui, Kwong-Hoi; Zhang, Yuegang; Yang, Shihe; Fan, Zhiyong

    2014-01-01

    Photoelectrochemical (PEC) solar water splitting represents a clean and sustainable approach for hydrogen (H2) production and substantial research are being performed to improve the conversion efficiency. Hematite (α-Fe2O3) is considered as a promising candidate for PEC water splitting due to its chemical stability, appropriate band structure, and abundance. However, PEC performance based on hematite is hindered by the short hole diffusion length that put a constraint on the active layer thickness and its light absorption capability. In this work, we have designed and fabricated novel PEC device structure with ultrathin hematite film deposited on three-dimensional nanophotonic structure. In this fashion, the nanophotonic structures can largely improve the light absorption in the ultrathin active materials. In addition, they also provide large surface area to accommodate the slow surface water oxidation process. As the result, high current density of 3.05 mA cm(-2) at 1.23 V with respect to the reversible hydrogen electrode (RHE) has been achieved on such nanophotonic structure, which is about three times of that for a planar photoelectrode. More importantly, our systematic analysis with experiments and modeling revealed that the design of high performance PEC devices needs to consider not only total optical absorption, but also the absorption profile in the active material, in addition to electrode surface area and carrier collection.

  15. Charge Transfer Mechanism in Titanium-Doped Microporous Silica for Photocatalytic Water-Splitting Applications

    Directory of Open Access Journals (Sweden)

    Wendi Sapp

    2016-02-01

    Full Text Available Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti4+ ions embedded on the inner pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. This provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support of heterogeneous catalytic systems are important in optimization of catalytic efficiency.

  16. Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode.

    Science.gov (United States)

    Abdi, Fatwa F; Han, Lihao; Smets, Arno H M; Zeman, Miro; Dam, Bernard; van de Krol, Roel

    2013-01-01

    Metal oxides are generally very stable in aqueous solutions and cheap, but their photochemical activity is usually limited by poor charge carrier separation. Here we show that this problem can be solved by introducing a gradient dopant concentration in the metal oxide film, thereby creating a distributed n(+)-n homojunction. This concept is demonstrated with a low-cost, spray-deposited and non-porous tungsten-doped bismuth vanadate photoanode in which carrier-separation efficiencies of up to 80% are achieved. By combining this state-of-the-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double- or single-junction amorphous Si solar cell in a tandem configuration, stable short-circuit water-splitting photocurrents of ~4 and 3 mA cm(-2), respectively, are achieved under 1 sun illumination. The 4 mA cm(-2) photocurrent corresponds to a solar-to-hydrogen efficiency of 4.9%, which is the highest efficiency yet reported for a stand-alone water-splitting device based on a metal oxide photoanode.

  17. A new perspective on hydrogen production by photosynthetic water-splitting

    Energy Technology Data Exchange (ETDEWEB)

    Lee, J.W.; Greenbaum, E.

    1996-05-01

    Present energy systems are heavily dependent on fossil fuels. This will eventually lead to the foreseeable depletion of fossil energy resources and, according to some reports, global climate changes due to the emission of carbon dioxide. In principle, hydrogen production by biophotolysis of water can be an ideal solar energy conversion system for sustainable development of human activities in harmony with the global environment. In photosynthetic hydrogen production research, there are currently two main efforts: (1) Direct photoevolution of hydrogen and oxygen by photosynthetic water splitting using the ferredoxin/hydrogenase pathway; (2) Dark hydrogen production by fermentation of organic reserves such as starch that are generated by photosynthesis during the light period. In this chapter, the advantages and challenges of the two approaches for hydrogen production will be discussed, in relation to a new opportunity brought by our recent discovery of a new photosynthetic water-splitting reaction which, potentially, has twice the energy efficiency of conventional watersplitting via the two light reaction Z-scheme of photosynthesis.

  18. Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode

    Science.gov (United States)

    Abdi, Fatwa F.; Han, Lihao; Smets, Arno H. M.; Zeman, Miro; Dam, Bernard; van de Krol, Roel

    2013-07-01

    Metal oxides are generally very stable in aqueous solutions and cheap, but their photochemical activity is usually limited by poor charge carrier separation. Here we show that this problem can be solved by introducing a gradient dopant concentration in the metal oxide film, thereby creating a distributed n+-n homojunction. This concept is demonstrated with a low-cost, spray-deposited and non-porous tungsten-doped bismuth vanadate photoanode in which carrier-separation efficiencies of up to 80% are achieved. By combining this state-of-the-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double- or single-junction amorphous Si solar cell in a tandem configuration, stable short-circuit water-splitting photocurrents of ~4 and 3 mA cm-2, respectively, are achieved under 1 sun illumination. The 4 mA cm-2 photocurrent corresponds to a solar-to-hydrogen efficiency of 4.9%, which is the highest efficiency yet reported for a stand-alone water-splitting device based on a metal oxide photoanode.

  19. Modeling of a split type air conditioner with integrated water heater

    Energy Technology Data Exchange (ETDEWEB)

    Techarungpaisan, P.; Theerakulpisut, S.; Priprem, S. [Mechanical Engineering Department, Faculty of Engineering, Khon Kaen University, 123 Mittrapab Rd., Muang, Khon Kaen 40002 (Thailand)

    2007-04-15

    This paper presents a steady state simulation model to predict the performance of a small split type air conditioner with integrated water heater. The mathematical model consists of submodels of system components such as evaporator, condenser, compressor, capillary tube, receiver and water heater. These submodels were built based on fundamental principles of heat transfer, thermodynamics, fluid mechanics, empirical relationships and manufacturer's data as necessary. The model was coded into a simulation program and used to predict system parameters of interest such as hot water temperature, condenser exit air temperature, evaporator exit air temperature, mass flow rate of refrigerant, heat rejection in the condenser and cooling capacity of the system. The simulation results were compared with experimental data obtained from an experimental rig built for validating the mathematical model. It was found that the experimental and simulation results are in good agreement. (author)

  20. NANOSTRUCTURED TiO2 SENSITIZED WITH PORPHYRINS FOR SOLAR WATER-SPLITTING

    Directory of Open Access Journals (Sweden)

    MARCELA-CORINA ROŞU

    2011-03-01

    Full Text Available Nanostructured TiO2 sensitized with porphyrins for Solar water-splitting.The production of hydrogen from water using solar light is very promising for generations of an ecologically pure carrier contributing to a clean, sustainable and renewable energy system. The selection of specific photocatalyst material for hydrogen production in photoelectrochemical cells (PECs is based on some important characteristics of semiconductor, such as photo-corrosion and chemical corrosion stability, photocatalytic potential, high sensitivity for UV-visible light. In the present paper, different nanocrystalline TiO2 photoanodes have been prepared via wet-chemical techniques followed by annealing treatment and sensitized with porphyrins and supramolecular complexes of porphyrins. The so obtained photocatalysts were characterized with UV-VIS absorption spectroscopy and spectrofluorimetry. The purpose of these experiments is to show if the prepared materials possess the necessary photocatalytic characteristics and if they can be used with success in H2 production from water decomposition in PECs.

  1. 1D ZnO/BiVO4 heterojunction photoanodes for efficient photoelectrochemical water splitting.

    Science.gov (United States)

    Yan, Lu; Zhao, Wei; Liu, Zhifeng

    2016-07-28

    In this paper, a novel ZnO nanorods (NRs)/BiVO4 heterojunction has been successfully prepared as a photoanode for photoelectrochemical (PEC) water splitting. Firstly, ZnO NRs were synthesized by chemical bath deposition onto indium tin oxide (ITO) coated glass. Then BiVO4 was deposited by successive ionic layer adsorption and reaction (SILAR). The photocurrent density of ZnO NRs and the ZnO NRs/BiVO4 heterojunction photoanode was evaluated under light irradiation. And the value was up to 1.72 mA cm(-2) at 1.2 V vs. Ag/AgCl based on the ZnO NRs/BiVO4 photoanode in the electrolyte solution, which is higher than that of the pure ZnO NRs photoanode at the same potential. It is demonstrated that the presence of BiVO4 has played an important role in expanding the spectral response region and reducing the photogenerated charge recombination rate. This present work provides a simple synthesis route to construct a heterojunction which serves as a photoanode for PEC water splitting.

  2. Combinatorial Investigations of High Temperature CuNb Oxide Phases for Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Skorupska, Katarzyna; Maggard, Paul A; Eichberger, Rainer; Schwarzburg, Klaus; Shahbazi, Paria; Zoellner, Brandon; Parkinson, Bruce A

    2015-12-14

    High-throughput combinatorial methods have been useful in identifying new oxide semiconductors with the potential to be applied to solar water splitting. Most of these techniques have been limited to producing and screening oxide phases formed at temperatures below approximately 550 °C. We report the development of a combinatorial approach to discover and optimize high temperature phases for photoelectrochemical water splitting. As a demonstration material, we chose to produce thin films of high temperature CuNb oxide phases by inkjet printing on two different substrates: fluorine-doped tin oxide and crystalline Si, which required different sample pyrolysis procedures. The selection of pyrolysis parameters, such as temperature/time programs, and the use of oxidizing, nonreactive or reducing atmospheres determines the composition of the thin film materials and their photoelectrochemical performance. XPS, XRD, and SEM analyses were used to determine the composition and oxidation states within the copper niobium oxide phases and to then guide the production of target Cu(1+)Nb(5+)-oxide phases. The charge carrier dynamics of the thin films produced by the inkjet printing are compared with pure CuNbO3 microcrystalline material obtained from inorganic bulk synthesis.

  3. TiO2 and Fe2O3 films for photoelectrochemical water splitting.

    Science.gov (United States)

    Krysa, Josef; Zlamal, Martin; Kment, Stepan; Brunclikova, Michaela; Hubicka, Zdenek

    2015-01-09

    Titanium oxide (TiO2) and iron oxide (α-Fe2O3) hematite films have potential applications as photoanodes in electrochemical water splitting. In the present work TiO2 and α-Fe2O3 thin films were prepared by two methods, e.g., sol-gel and High Power Impulse Magnetron Sputtering (HiPIMS) and judged on the basis of physical properties such as crystalline structure and surface topography and functional properties such as simulated photoelectrochemical (PEC) water splitting conditions. It was revealed that the HiPIMS method already provides crystalline structures of anatase TiO2 and hematite Fe2O3 during the deposition, whereas to finalize the sol-gel route the as-deposited films must always be annealed to obtain the crystalline phase. Regarding the PEC activity, both TiO2 films show similar photocurrent density, but only when illuminated by UV light. A different situation was observed for hematite films where plasmatic films showed a tenfold enhancement of the stable photocurrent density over the sol-gel hematite films for both UV and visible irradiation. The superior properties of plasmatic film could be explained by ability to address some of the hematite drawbacks by deposition of very thin films (25 nm) consisting of small densely packed particles and by doping with Sn.

  4. TiO2 and Fe2O3 Films for Photoelectrochemical Water Splitting

    Directory of Open Access Journals (Sweden)

    Josef Krysa

    2015-01-01

    Full Text Available Titanium oxide (TiO2 and iron oxide (α-Fe2O3 hematite films have potential applications as photoanodes in electrochemical water splitting. In the present work TiO2 and α-Fe2O3 thin films were prepared by two methods, e.g., sol-gel and High Power Impulse Magnetron Sputtering (HiPIMS and judged on the basis of physical properties such as crystalline structure and surface topography and functional properties such as simulated photoelectrochemical (PEC water splitting conditions. It was revealed that the HiPIMS method already provides crystalline structures of anatase TiO2 and hematite Fe2O3 during the deposition, whereas to finalize the sol-gel route the as-deposited films must always be annealed to obtain the crystalline phase. Regarding the PEC activity, both TiO2 films show similar photocurrent density, but only when illuminated by UV light. A different situation was observed for hematite films where plasmatic films showed a tenfold enhancement of the stable photocurrent density over the sol-gel hematite films for both UV and visible irradiation. The superior properties of plasmatic films could be explained by ability to address some of the hematite drawbacks by the deposition of very thin films (25 nm consisting of small densely packed particles and by doping with Sn.

  5. Surface Passivation of GaN Nanowires for Enhanced Photoelectrochemical Water-Splitting

    KAUST Repository

    Varadhan, Purushothaman

    2017-02-08

    Hydrogen production via photoelectrochemical water-splitting is a key source of clean and sustainable energy. The use of one-dimensional nanostructures as photoelectrodes is desirable for photoelectrochemical water-splitting applications due to the ultralarge surface areas, lateral carrier extraction schemes, and superior light-harvesting capabilities. However, the unavoidable surface states of nanostructured materials create additional charge carrier trapping centers and energy barriers at the semiconductor-electrolyte interface, which severely reduce the solar-to-hydrogen conversion efficiency. In this work, we address the issue of surface states in GaN nanowire photoelectrodes by employing a simple and low-cost surface treatment method, which utilizes an organic thiol compound (i.e., 1,2-ethanedithiol). The surface-treated photocathode showed an enhanced photocurrent density of −31 mA/cm at −0.2 V versus RHE with an incident photon-to-current conversion efficiency of 18.3%, whereas untreated nanowires yielded only 8.1% efficiency. Furthermore, the surface passivation provides enhanced photoelectrochemical stability as surface-treated nanowires retained ∼80% of their initial photocurrent value and produced 8000 μmol of gas molecules over 55 h at acidic conditions (pH ∼ 0), whereas the untreated nanowires demonstrated only <4 h of photoelectrochemical stability. These findings shed new light on the importance of surface passivation of nanostructured photoelectrodes for photoelectrochemical applications.

  6. Ternary NiCoP nanosheet arrays: An excellent bifunctional catalyst for alkaline overall water splitting

    Institute of Scientific and Technical Information of China (English)

    Yingjie Li; Haichuan Zhang; Ming Jiang; Yun Kuang; Xiaoming Sun; Xue Duan

    2016-01-01

    Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions (HER and OER) with high efficiency,low cost,and easy integration is extremely crucial for future renewable energy systems.Herein,ternary NiCoP nanosheet arrays (NSAs) were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization.These arrays serve as bifunctional alkaline catalysts,exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER.The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm2 for the HER and OER are as low as 133 and 308 mV,respectively,which is ascribed to excellent intrinsic electrocatalytic activity,fast electron transport,and a unique superaerophobic structure.When NiCoP was integrated as both anodic and cathodic material,the electrolyzer required a potential as low as ~1.77 V to drive a current density of 50 mA/cm2 for overall water splitting,which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C,the best known noble metal-based electrodes.Combining satisfactory working stability and high activity,this NiCoP electrode paves the way for exploring overall water splitting catalysts.

  7. Gas phase photocatalytic water splitting in silicon based µ-reactors

    DEFF Research Database (Denmark)

    Dionigi, Fabio; Vesborg, Peter Christian Kjærgaard

    to the water splitting experiments, the results obtained with SrTiO2 and TiO2 are presented. These semiconductors are well known examples of materials active under UV illumination. However to achieve high efficiency of solar energy conversion the catalysts needs to be active for longer wavelength. Ga......N:ZnO is one of the few photocatalysts that is able to achieve overall water splitting with visible light. Therefore the reaction has been studied focusing on this material. GaN:ZnO loaded with Rh2-yCryO3 showed high activity and hydrogen and oxygen could even be detected under illumination with a solar light...... to the products detection using μ-reactors. In particular a new kind of μ-reactor that has a Pyrex lid on both sides is presented. With this reactor is possible to measure the absorbance of the materials deposited inside the μ-reactor and to combine optical measurements and spectroscopy with the detection...

  8. Sunlight-Driven Hydrogen Formation by Membrane-Supported Photoelectrochemical Water Splitting

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Nathan S. [California Institute of Technology

    2014-03-26

    This report describes the significant advances in the development of the polymer-supported photoelectrochemical water-splitting system that was proposed under DOE grant number DE-FG02-05ER15754. We developed Si microwire-array photoelectrodes, demonstrated control over the material and light-absorption properties of the microwire-array photoelectrodes, developed inexpensive processes for synthesizing the arrays, and doped the arrays p-type for use as photocathodes. We also developed techniques for depositing metal-nanoparticle catalysts of the hydrogen-evolution reaction (HER) on the wire arrays, investigated the stability and catalytic performance of the nanoparticles, and demonstrated that Ni-Mo alloys are promising earth-abundant catalysts of the HER. We also developed methods that allow reuse of the single-crystalline Si substrates used for microwire growth and methods of embedding the microwire photocathodes in plastic to enable large-scale processing and deployment of the technology. Furthermore we developed techniques for controlling the structure of WO3 films, and demonstrated that structural control can improve the quantum yield of photoanodes. Thus, by the conclusion of this project, we demonstrated significant advances in the development of all components of a sunlight-driven membrane-supported photoelectrochemical water-splitting system. This final report provides descriptions of some of the scientific accomplishments that were achieved under the support of this project and also provides references to the peer-reviewed publications that resulted from this effort.

  9. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    Science.gov (United States)

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-10-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (~2.5 eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350 °C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ~0.2 eV but also increases the majority carrier density and mobility, enhancing electron-hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge.

  10. Nanosheet Supported Single-Metal Atom Bifunctional Catalyst for Overall Water Splitting.

    Science.gov (United States)

    Ling, Chongyi; Shi, Li; Ouyang, Yixin; Zeng, Xiao Cheng; Wang, Jinlan

    2017-08-09

    Nanosheet supported single-atom catalysts (SACs) can make full use of metal atoms and yet entail high selectivity and activity, and bifunctional catalysts can enable higher performance while lowering the cost than two separate unifunctional catalysts. Supported single-atom bifunctional catalysts are therefore of great economic interest and scientific importance. Here, on the basis of first-principles computations, we report a design of the first single-atom bifunctional eletrocatalyst, namely, isolated nickel atom supported on β12 boron monolayer (Ni1/β12-BM), to achieve overall water splitting. This nanosheet supported SAC exhibits remarkable electrocatalytic performance with the computed overpotential for oxygen/hydrogen evolution reaction being just 0.40/0.06 V. The ab initio molecular dynamics simulation shows that the SAC can survive up to 800 K elevated temperature, while enacting a high energy barrier of 1.68 eV to prevent isolated Ni atoms from clustering. A viable experimental route for the synthesis of Ni1/β12-BM SAC is demonstrated from computer simulation. The desired nanosheet supported single-atom bifunctional catalysts not only show great potential for achieving overall water splitting but also offer cost-effective opportunities for advancing clean energy technology.

  11. GaN nano-pyramid arrays as an efficient photoelectrode for solar water splitting

    Science.gov (United States)

    Hou, Y.; Yu, X.; Syed, Z. Ahmed; Shen, S.; Bai, J.; Wang, T.

    2016-11-01

    A prototype photoelectrode has been fabricated using a GaN nano-pyramid array structure grown on a cost-effective Si (111) substrate, demonstrating a significant improvement in performance of solar-powered water splitting compared with any planar GaN photoelectrode. Such a nano-pyramid structure leads to enhanced optical absorption as a result of a multi-scattering process which can effectively produce a reduction in reflectance. A simulation based on a finite-difference time-domain approach indicates that the nano-pyramid architecture enables incident light to be concentrated within the nano-pyramids as a result of micro-cavity effects, further enhancing optical absorption. Furthermore, the shape of the nano-pyramid further facilitates the photo-generated carrier transportation by enhancing a hole-transfer efficiency. All these features as a result of the nano-pyramid configuration lead to a large photocurrent of 1 mA cm-2 under an illumination density of 200 mW cm-2, with a peak incident photon-to-current conversion efficiency of 46.5% at ˜365 nm, around the band edge emission wavelength of GaN. The results presented are expected to pave the way for the fabrication of GaN based photoelectrodes with a high energy conversion efficiency of solar powered water splitting.

  12. Surface Passivation of GaN Nanowires for Enhanced Photoelectrochemical Water-Splitting.

    Science.gov (United States)

    Varadhan, Purushothaman; Fu, Hui-Chun; Priante, Davide; Retamal, Jose Ramon Duran; Zhao, Chao; Ebaid, Mohamed; Ng, Tien Khee; Ajia, Idirs; Mitra, Somak; Roqan, Iman S; Ooi, Boon S; He, Jr-Hau

    2017-03-08

    Hydrogen production via photoelectrochemical water-splitting is a key source of clean and sustainable energy. The use of one-dimensional nanostructures as photoelectrodes is desirable for photoelectrochemical water-splitting applications due to the ultralarge surface areas, lateral carrier extraction schemes, and superior light-harvesting capabilities. However, the unavoidable surface states of nanostructured materials create additional charge carrier trapping centers and energy barriers at the semiconductor-electrolyte interface, which severely reduce the solar-to-hydrogen conversion efficiency. In this work, we address the issue of surface states in GaN nanowire photoelectrodes by employing a simple and low-cost surface treatment method, which utilizes an organic thiol compound (i.e., 1,2-ethanedithiol). The surface-treated photocathode showed an enhanced photocurrent density of -31 mA/cm(2) at -0.2 V versus RHE with an incident photon-to-current conversion efficiency of 18.3%, whereas untreated nanowires yielded only 8.1% efficiency. Furthermore, the surface passivation provides enhanced photoelectrochemical stability as surface-treated nanowires retained ∼80% of their initial photocurrent value and produced 8000 μmol of gas molecules over 55 h at acidic conditions (pH ∼ 0), whereas the untreated nanowires demonstrated only surface passivation of nanostructured photoelectrodes for photoelectrochemical applications.

  13. Design principles for maximizing photovoltage in metal-oxide-protected water-splitting photoanodes.

    Science.gov (United States)

    Scheuermann, Andrew G; Lawrence, John P; Kemp, Kyle W; Ito, T; Walsh, Adrian; Chidsey, Christopher E D; Hurley, Paul K; McIntyre, Paul C

    2016-01-01

    Metal oxide protection layers for photoanodes may enable the development of large-scale solar fuel and solar chemical synthesis, but the poor photovoltages often reported so far will severely limit their performance. Here we report a novel observation of photovoltage loss associated with a charge extraction barrier imposed by the protection layer, and, by eliminating it, achieve photovoltages as high as 630 mV, the maximum reported so far for water-splitting silicon photoanodes. The loss mechanism is systematically probed in metal-insulator-semiconductor Schottky junction cells compared to buried junction p(+)n cells, revealing the need to maintain a characteristic hole density at the semiconductor/insulator interface. A leaky-capacitor model related to the dielectric properties of the protective oxide explains this loss, achieving excellent agreement with the data. From these findings, we formulate design principles for simultaneous optimization of built-in field, interface quality, and hole extraction to maximize the photovoltage of oxide-protected water-splitting anodes.

  14. Nickel-based anodic electrocatalysts for fuel cells and water splitting

    Science.gov (United States)

    Chen, Dayi

    Our world is facing an energy crisis, so people are trying to harvest and utilize energy more efficiently. One of the promising ways to harvest energy is via solar water splitting to convert solar energy to chemical energy stored in hydrogen. Another of the options to utilize energy more efficiently is to use fuel cells as power sources instead of combustion engines. Catalysts are needed to reduce the energy barriers of the reactions happening at the electrode surfaces of the water-splitting cells and fuel cells. Nickel-based catalysts happen to be important nonprecious electrocatalysts for both of the anodic reactions in alkaline media. In alcohol fuel cells, nickel-based catalysts catalyze alcohol oxidation. In water splitting cells, they catalyze water oxidation, i.e., oxygen evolution. The two reactions occur in a similar potential range when catalyzed by nickel-based catalysts. Higher output current density, lower oxidation potential, and complete substrate oxidation are preferred for the anode in the applications. In this dissertation, the catalytic properties of nickel-based electrocatalysts in alkaline medium for fuel oxidation and oxygen evolution are explored. By changing the nickel precursor solubility, nickel complex nanoparticles with tunable sizes on electrode surfaces were synthesized. Higher methanol oxidation current density is achieved with smaller nickel complex nanoparticles. DNA aggregates were used as a polymer scaffold to load nickel ion centers and thus can oxidize methanol completely at a potential about 0.1 V lower than simple nickel electrodes, and the methanol oxidation pathway is changed. Nickel-based catalysts also have electrocatalytic activity towards a wide range of substrates. Experiments show that methanol, ethanol, glycerol and glucose can be deeply oxidized and carbon-carbon bonds can be broken during the oxidation. However, when comparing methanol oxidation reaction to oxygen evolution reaction catalyzed by current nickel

  15. A Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chong; Tang, Jinyao; Chen, HaoMing; Liu, Bin; Yang, Peidong

    2013-02-21

    Artificial photosynthesis, the biomimetic approach to converting sunlight?s energy directly into chemical fuels, aims to imitate nature by using an integrated system of nanostructures, each of which plays a specific role in the sunlight-to-fuel conversion process. Here we describe a fully integrated system of nanoscale photoelectrodes assembled from inorganic nanowires for direct solar water splitting. Similar to the photosynthetic system in a chloroplast, the artificial photosynthetic system comprises two semiconductor light absorbers with large surface area, an interfacial layer for charge transport, and spatially separated cocatalysts to facilitate the water reduction and oxidation. Under simulated sunlight, a 0.12percent solar-to-fuel conversion efficiency is achieved, which is comparable to that of natural photosynthesis. The result demonstrates the possibility of integrating material components into a functional system that mimics the nanoscopic integration in chloroplasts. It also provides a conceptual blueprint of modular design that allows incorporation of newly discovered components for improved performance.

  16. Confinement dependence of electro-catalysts for hydrogen evolution from water splitting

    Directory of Open Access Journals (Sweden)

    Mikaela Lindgren

    2014-02-01

    Full Text Available Density functional theory is utilized to articulate a particular generic deconstruction of the electrode/electro-catalyst assembly for the cathode process during water splitting. A computational model was designed to determine how alloying elements control the fraction of H2 released during zirconium oxidation by water relative to the amount of hydrogen picked up by the corroding alloy. This model is utilized to determine the efficiencies of transition metals decorated with hydroxide interfaces in facilitating the electro-catalytic hydrogen evolution reaction. A computational strategy is developed to select an electro-catalyst for hydrogen evolution (HE, where the choice of a transition metal catalyst is guided by the confining environment. The latter may be recast into a nominal pressure experienced by the evolving H2 molecule. We arrived at a novel perspective on the uniqueness of oxide supported atomic Pt as a HE catalyst under ambient conditions.

  17. Epitaxial ferroelectric BiFeO{sub 3} thin films for unassisted photocatalytic water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Wei [Institute of Materials Research and Engineering (IMRE), A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, Kent Ridge, Singapore 119260 (Singapore); Yao, Kui; Lim, Yee-Fun; Suwardi, Ady [Institute of Materials Research and Engineering (IMRE), A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Liang, Yung C. [Department of Electrical and Computer Engineering, National University of Singapore, Kent Ridge, Singapore 119260 (Singapore)

    2013-08-05

    Considering energy band alignment and polarization effect, ferroelectric BiFeO{sub 3} thin films are proposed as the photoanode in a monolithic cell to achieve unassisted photocatalytic water splitting. Significant anodic photocurrent was observed in our epitaxial ferroelectric BiFeO{sub 3} films prepared from sputter deposition. Both negative polarization charges and thinner films were found to promote the anodic photocatalytic reaction. Ultraviolet photoelectron spectroscopy proved that the conduction and valence band edges of BiFeO{sub 3} straddle the water redox levels. Theoretical analyses show that the large switchable polarization can modify the surface properties to promote the hydrogen and oxygen evolutions on the surfaces with positive and negative polarization charges, respectively.

  18. Epitaxial ferroelectric BiFeO3 thin films for unassisted photocatalytic water splitting

    Science.gov (United States)

    Ji, Wei; Yao, Kui; Lim, Yee-Fun; Liang, Yung C.; Suwardi, Ady

    2013-08-01

    Considering energy band alignment and polarization effect, ferroelectric BiFeO3 thin films are proposed as the photoanode in a monolithic cell to achieve unassisted photocatalytic water splitting. Significant anodic photocurrent was observed in our epitaxial ferroelectric BiFeO3 films prepared from sputter deposition. Both negative polarization charges and thinner films were found to promote the anodic photocatalytic reaction. Ultraviolet photoelectron spectroscopy proved that the conduction and valence band edges of BiFeO3 straddle the water redox levels. Theoretical analyses show that the large switchable polarization can modify the surface properties to promote the hydrogen and oxygen evolutions on the surfaces with positive and negative polarization charges, respectively.

  19. Photoelectrochemical water splitting enhanced by self-assembled metal nanopillars embedded in an oxide semiconductor photoelectrode

    Science.gov (United States)

    Kawasaki, Seiji; Takahashi, Ryota; Yamamoto, Takahisa; Kobayashi, Masaki; Kumigashira, Hiroshi; Yoshinobu, Jun; Komori, Fumio; Kudo, Akihiko; Lippmaa, Mikk

    2016-06-01

    Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is of great practical interest for developing a sustainable energy system. Various nanoscale designs such as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the energy conversion efficiency of photoelectrochemical water splitting. Here we demonstrate a self-organized nanocomposite material concept for enhancing the efficiency of photocarrier separation and electrochemical energy conversion. Mechanically robust photoelectrodes are formed by embedding self-assembled metal nanopillars in a semiconductor thin film, forming tubular Schottky junctions around each pillar. The photocarrier transport efficiency is strongly enhanced in the Schottky space charge regions while the pillars provide an efficient charge extraction path. Ir-doped SrTiO3 with embedded iridium metal nanopillars shows good operational stability in a water oxidation reaction and achieves over 80% utilization of photogenerated carriers under visible light in the 400- to 600-nm wavelength range.

  20. A Fully Integrated Nanosystem of Semiconductor Nanowires for Direct Solar Water Splitting

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chong; Tang, Jinyao; Chen, Hao Ming; Liu, Bin; Yang, Peidong

    2013-06-12

    Artificial photosynthesis, the biomimetic approach to converting sunlight?s energy directly into chemical fuels, aims to imitate nature by using an integrated system of nanostructures, each of which plays a specific role in the sunlight-to-fuel conversion process. Here we describe a fully integrated system of nanoscale photoelectrodes assembled from inorganic nanowires for direct solar water splitting. Similar to the photosynthetic system in a chloroplast, the artificial photosynthetic system comprises two semiconductor light absorbers with large surface area, an interfacial layer for charge transport, and spatially separated cocatalysts to facilitate the water reduction and oxidation. Under simulated sunlight, a 0.12percent solar-to-fuel conversion efficiency is achieved, which is comparable to that of natural photosynthesis. The result demonstrates the possibility of integrating material components into a functional system that mimics the nanoscopic integration in chloroplasts. It also provides a conceptual blueprint of modular design that allows incorporation of newly discovered components for improved performance.

  1. Zn-Co layered double hydroxide modified hematite photoanode for enhanced photoelectrochemical water splitting

    Science.gov (United States)

    Xu, Dongyu; Rui, Yichuan; Li, Yaogang; Zhang, Qinghong; Wang, Hongzhi

    2015-12-01

    Zinc-cobalt layered double hydroxide (LDH) was electrodeposited on Ti-doped hematite photoanodes for the first time, and a significant enhanced performance for photoelectrochemical water splitting was demonstrated over the composite photoanodes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS) were characterized with the resulted photoanodes. With the electrodepositing treatment, the photocurrent density increased from 1.27 mA/cm2 for pristine hematite to 1.73 mA/cm2 for modified materials at 1.23 V vs. RHE (i.e. 36% improvement). The photocurrent improvement is mainly attributed to a suppression of electron-hole recombination and reduced overpotential for water oxidation at the hematite-electrolyte interface due to the formation of Zn-Co LDH layer on hematite.

  2. Solar Fuels: Photocatalytic Water Splitting Using a 2‐Photon Approach

    DEFF Research Database (Denmark)

    Seger, Brian; Mei, Bastian Timo; Bae, Dowon;

    2014-01-01

    energyphotons while the other absorbs the low energy photons. This is demonstrated in Figure 1A. While theconcept seems relatively simple, no one has yet been able to full optimize this system.2‐photon water splitting devices have many issues that need to be optimized. Both solar cells needto be optimized......While the sun provides orders of magnitude more energy than we consume on earth, it is intermittent, and thus we must have storage reservoirs for when it is dark. Plants have realized early on that storing this energy in the form of molecular fuels is quite effective. In our work, we take...... a similarapproach and look to use solar cells to electrolyze water into hydrogen fuel and an oxygen byproduct. Modelling has shown that to optimize photoelectrolysis efficiency, a 2 photon tandem device (back toback solar cells) should be used. The underlying principle is that one solar cell should absorb high...

  3. Effects of Local Nitrogen Supply on Water Uptake of Bean Plants in a Split Root System

    Institute of Scientific and Technical Information of China (English)

    Shiwei Guo; Qirong Shen; Holger Brueck

    2007-01-01

    To study the effects of local nitrogen supply on water and nutrient absorption, French bean (Phaseolus vulgaris L.)plants were grown in a split root system. Five treatments supplied with different nitrogen forms were compared:homogeneous nitrate (NN) and homogenous ammonium (AA) supply, spatially separated supply of nitrate and ammonium (NA), half of the root system supplied with N-free nutrient solution, the other half with either nitrate (NO) or ammonium (AO). The results showed that 10 d after onset of treatments, root dry matter (DM) in the nitratesupplied vessels treated with NA was more than two times higher than that in the ammonium-supplied vessels.Water uptake from the nitrate-supplied vessels treated with NA was 281% higher than under ammonium supply. In treatments NO and AO, the local supply of N resulted in clearly higher root DM, and water uptake from the nitratesupplied vessels was 82% higher than in the -N vessels. However, in AO plants, water uptake from the -N nutrient solution was 129% higher than from the ammonium-supplied vessels. This indicates a compensatory effect, which resulted in almost identical rates of total water uptake of treatments AA and AO, which had comparable shoot DM and leaf area. Ammonium supply reduced potassium and magnesium absorption. Water uptake was positively correlated with N, Mg and K uptake.

  4. An Oxygen-Insensitive Hydrogen Evolution Catalyst Coated by a Molybdenum-Based Layer for Overall Water Splitting

    KAUST Repository

    Garcia Esparza, Angel T.

    2017-04-13

    For overall water-splitting systems, it is essential to establish O2 -insensitive cathodes that allow cogeneration of H2 and O2 . An acid-tolerant electrocatalyst is described, which employs a Mo-coating on a metal surface to achieve selective H2 evolution in the presence of O2 . In operando X-ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O2 gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoOx /Pt/SrTiO3 with inhibited water formation from H2 and O2 , which is the prevailing back reaction on the bare Pt/SrTiO3 photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis.

  5. Solar water splitting with a composite silicon/metal oxide semiconductor electrode

    Science.gov (United States)

    Nakato, Yoshihiro; Kato, Naoaki; Imanishi, Akihito; Sugiura, Takashi; Ogawa, Shunsuke; Yoshida, Norimitsu; Nonomura, Shuichi

    2006-08-01

    We have studied solar water splitting with a composite semiconductor electrode, composed of an n-i-p junction amorphous silicon (a-Si, E g~ 1.7 eV) layer, an indium tin oxide (ITO) layer, and a tungsten trioxide (WO 3, E g 2.8 eV) particulate layer. The n-i-p a-Si layer, which had more accurately a structure of n-type microcrystalline ( c) 3C-SiC:H (25 nm)/i-type a-Si:H (400 nm)/p-type a-SiC x:H (25 nm), was prepared on a TiO II-covered F-doped SnO II (FTO)/glass plate by a Hot-Wire CVD method. The ITO layer (100 nm thick) was deposited on the p-type a-Si by the DC magnetron sputtering method, and the WO3 particulate layer was formed by a doctor-blade method, using a colloidal solution of commercial WO 3 powder of 10-30 nm in diameter. The composite electrode thus prepared was finally heat-treated at 300°C for 1 h. The anodic (water oxidation) photocurrent for the composite electrode in 0.1 M Na IISO 4 yielded an IPCE (incident photon to current efficiency) of about 6 % at 400 nm and was stable for more than 24 h. Besides, the onset potential lay a little (by about 0.05 V) more negative than the equilibrium hydrogen evolution potential, indicating a possibility of solar water splitting with no external bias. A preliminary result for the water photooxidation with an "n- GaP/p-Si/Pt dot" electrode is also reported briefly.

  6. 'Photosystem II: the water splitting enzyme of photosynthesis and the origin of oxygen in our atmosphere'.

    Science.gov (United States)

    Barber, James

    2016-01-01

    About 3 billion years ago an enzyme emerged which would dramatically change the chemical composition of our planet and set in motion an unprecedented explosion in biological activity. This enzyme used solar energy to power the thermodynamically and chemically demanding reaction of water splitting. In so doing it provided biology with an unlimited supply of reducing equivalents needed to convert carbon dioxide into the organic molecules of life while at the same time produced oxygen to transform our planetary atmosphere from an anaerobic to an aerobic state. The enzyme which facilitates this reaction and therefore underpins virtually all life on our planet is known as Photosystem II (PSII). It is a pigment-binding, multisubunit protein complex embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Today we have detailed understanding of the structure and functioning of this key and unique enzyme. The journey to this level of knowledge can be traced back to the discovery of oxygen itself in the 18th-century. Since then there has been a sequence of mile stone discoveries which makes a fascinating story, stretching over 200 years. But it is the last few years that have provided the level of detail necessary to reveal the chemistry of water oxidation and O-O bond formation. In particular, the crystal structure of the isolated PSII enzyme has been reported with ever increasing improvement in resolution. Thus the organisational and structural details of its many subunits and cofactors are now well understood. The water splitting site was revealed as a cluster of four Mn ions and a Ca ion surrounded by amino-acid side chains, of which seven provide direct ligands to the metals. The metal cluster is organised as a cubane structure composed of three Mn ions and a Ca2+ linked by oxo-bonds with the fourth Mn ion attached to the cubane. This structure has now been synthesised in a non-protein environment suggesting that it is a totally

  7. Radiometric Observations of Supercooled Liquid Water within a Split Front over the Sierra Nevada.

    Science.gov (United States)

    Heggli, Mark F.; Reynolds, David W.

    1985-11-01

    A storm bearing close structural resemblance to a katafront was observed from the ground with microwave radiometry and a vertically pointing Ka-band radar over the Sierra Nevada of California. The onset and duration of supercooled liquid water was determined and matched to a split front model used to describe the synoptic features of a katafront. Results indicate that prior to the passage of the upper front no supercooled liquid water was observed. This portion of the storm provided the deepest cloud and coldest cloud tops. Supercooled liquid water was most prevalent after the upper front passage, and persisted until the suspected surface front passage. The duration of measured supercooled water was 16 hours.This information broadens the knowledge regarding the presence of supercooled liquid water, and thus possible seeding potential, within winter storms so that treatment can be confined to the period of storms amenable to cloud seeding. Future studies may well confirm the ease with which these periods can be predicted on an operational basis in the Sierra Nevada.

  8. Galates with perovskite-related structure as membrane reactors for hydrogen production from water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Al Daroukh, M.; Georgi, G.; Hoffmann, M. [Leibniz Institute for Catalysis, Rostock (Germany)

    2010-12-30

    Hydrogen production from water splitting will be the most promising energy source in the future [1-2]. Dense membranes of the type La{sub a}Sr{sub b}Ga{sub c}Mg{sub d}O{sub x} were prepared from powders by solid state reaction syntheses. The Galates show a very high ionic conductivity [3]. The water splitting is achieved thermically, while the Diffusion of oxygen through the dense galate membrane is realized thermically and electrically. The electrically achieved oxygen permeability is three times higher than the thermically achieved. Due to this fact, the hydrogen production increases by the same factor. In a special reactor (Fig. 1) the dense tablet of the polyoxid is fastened between two gold rings. The tablet is coated with a platinum layer on both sides which work as electrodes. Helium with water is flowing towards the negative pole while on the other side after tablet (positive pole) an Ar or Ar/H{sub 2} flow is realized. The reactor in the furnace is heated to 1050 C and slowly cooled to the chosen reaction temperature (e.g. 800 C). In both sides of the dense tablet an electric current of 2 A is used. Two ampere corresponds to 8 volts at these high temperatures. The whole investigation was measured by a solid electrolyte device (Fig. 2) (ZIROX SGM5EL) [4]. The oxygen concentration was measured before and after the permeation. At 800 C the oxygen permeation has a value of 0.6 ml/(cm-2.min.) (Fig. 3-4). (orig.)

  9. Water Cycle in the Atmosphere and Shallow Subsurface

    Science.gov (United States)

    Tokano, Tetsuya

    The global water cycle on Earth constitutes one of the most relevant components of the terrestrial ecosystem. While the vast majority of terrestrial water is stored in the world oceans, the perpetual cycle of water between ocean, atmosphere and land in all three phases is recognised as one basic feature that characterises the Earth, and is contrasted to the rest of the Solar System. On the other hand, Mars is devoid of a liquid hydrological cycle in the atmosphere and on the surface in the form of rainfall, rivers or oceans, which favour life on Earth's surface. However, a subtle water cycle does exist on present Mars and elucidating the details of the water cycle is crucial in understanding the global water inventory.

  10. CFD study of isothermal water flow in rod bundle with split-type spacer grid

    Science.gov (United States)

    Batta, A.; Class, A. G.

    2014-06-01

    The design of rod bundles in nuclear application nowadays is assessed by CFD (computational fluid dynamics). The accuracy of CFD models need validation. Within the OECD/NEA benchmark MATiS-H (Measurement and Analysis of Turbulent Mixing in Sub-channels - Horizontal) a single-phase water flow in a 5x5 rod bundle is studied. In the benchmark, two types of spacer grids are tested, the swirl type and the split type, where the current study focuses on the split type spacer grid. Comparison of CFD results obtained at Karlsruhe Institut of Technology (KIT) with experimental results of KAERI (Korea Atomic Energy Research Institute) are presented. In the benchmark velocities components along selected lines downstream of the spacer grid are measured and compared to CFD results. The CFD code STAR CCM+ with the Realized k-ɛ model is used. Comparisons with experimental results show quantitative and qualitative agreement for the averaged values of velocity components. Comparisons of results to other benchmark partners using different modeling show that the selected mesh size and models for the analysis of the current case gives relatively accurate results. However, the used turbulent model (Realized k-ɛ does not capture the turbulent intensity correctly. Computation shows that the flow has very high mixing due to the spacer grid, which does not decay within the measurements domain (z/ DH =0-10 downstream of spacer grid). The same conclusion can be drawn from experimental data.

  11. Theoretical modeling of a gas clearance phase regulation mechanism for a pneumatically-driven split-Stirling-cycle cryocooler

    Science.gov (United States)

    Zhang, Cun-quan; Zhong, Cheng

    2015-03-01

    The concept of a new type of pneumatically-driven split-Stirling-cycle cryocooler with clearance-phase-adjustor is proposed. In this implementation, the gap between the phase-adjusting part and the cylinder of the spring chamber is used, instead of dry friction acting on the pneumatically-driven rod to control motion damping of the displacer and to adjust the phase difference between the compression piston and displacer. It has the advantages of easy damping adjustment, low cost, and simplified manufacturing and assembly. A theoretical model has been established to simulate its dynamic performance. The linear compressor is modeled under adiabatic conditions, and the displacement of the compression piston is experimentally rectified. The working characteristics of the compressor motor and the principal losses of cooling, including regenerator inefficiency loss, solid conduction loss, shuttle loss, pump loss and radiation loss, are taken into account. The displacer motion was modeled as a single-degree-of-freedom (SDOF) forced system. A set of governing equations can be solved numerically to simulate the cooler's performance. The simulation is useful for understanding the physical processes occurring in the cooler and for predicting the cooler's performance.

  12. Splitting CO2 with a ceria-based redox cycle in a solar-driven thermogravimetric analyzer.

    Science.gov (United States)

    Takacs, M; Ackermann, S; Bonk, A; Neises-von Puttkamer, M; Haueter, Ph; Scheffe, J R; Vogt, U F; Steinfeld, A

    2017-04-01

    Thermochemical splitting of CO2 via a ceria-based redox cycle was performed in a solar-driven thermogravimetric analyzer. Overall reaction rates, including heat and mass transport, were determined under concentrated irradiation mimicking realistic operation of solar reactors. Reticulated porous ceramic (RPC) structures and fibers made of undoped and Zr(4+)-doped CeO2, were endothermally reduced under radiative fluxes of 1280 suns in the temperature range 1200-1950 K and subsequently re-oxidized with CO2 at 950-1400 K. Rapid and uniform heating was observed for 8 ppi ceria RPC with mm-sized porosity due to its low optical thickness and volumetric radiative absorption, while ceria fibers with μm-sized porosity performed poorly due to its opacity to incident irradiation. The 10 ppi RPC exhibited higher fuel yield because of its higher sample density. Zr(4+)-doped ceria showed increasing reduction extents with dopant concentration but decreasing specific CO yield due to unfavorable oxidation thermodynamics and slower kinetics. © 2016 American Institute of Chemical Engineers , 63: 1263-1271, 2017.

  13. Splitting CO2 with a ceria‐based redox cycle in a solar‐driven thermogravimetric analyzer

    Science.gov (United States)

    Takacs, M.; Ackermann, S.; Bonk, A.; Neises‐von Puttkamer, M.; Haueter, Ph.; Scheffe, J. R.; Vogt, U. F.

    2016-01-01

    Thermochemical splitting of CO2 via a ceria‐based redox cycle was performed in a solar‐driven thermogravimetric analyzer. Overall reaction rates, including heat and mass transport, were determined under concentrated irradiation mimicking realistic operation of solar reactors. Reticulated porous ceramic (RPC) structures and fibers made of undoped and Zr4+‐doped CeO2, were endothermally reduced under radiative fluxes of 1280 suns in the temperature range 1200–1950 K and subsequently re‐oxidized with CO2 at 950–1400 K. Rapid and uniform heating was observed for 8 ppi ceria RPC with mm‐sized porosity due to its low optical thickness and volumetric radiative absorption, while ceria fibers with μm‐sized porosity performed poorly due to its opacity to incident irradiation. The 10 ppi RPC exhibited higher fuel yield because of its higher sample density. Zr4+‐doped ceria showed increasing reduction extents with dopant concentration but decreasing specific CO yield due to unfavorable oxidation thermodynamics and slower kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1263–1271, 2017 PMID:28405030

  14. High Efficiency Generation of Hydrogen Fuels Using Solar Thermochemical Splitting of Water

    Energy Technology Data Exchange (ETDEWEB)

    Heske, Clemens; Moujaes, Samir; Weimer, Alan; Wong, Bunsen; Siegal, Nathan; McFarland, Eric; Miller, Eric; Lewis, Michele; Bingham, Carl; Roth, Kurth; Sabacky, Bruce; Steinfeld, Aldo

    2011-09-29

    The objective of this work is to identify economically feasible concepts for the production of hydrogen from water using solar energy. The ultimate project objective was to select one or more competitive concepts for pilot-scale demonstration using concentrated solar energy. Results of pilot scale plant performance would be used as foundation for seeking public and private resources for full-scale plant development and testing. Economical success in this venture would afford the public with a renewable and limitless source of energy carrier for use in electric power load-leveling and as a carbon-free transportation fuel. The Solar Hydrogen Generation Research (SHGR) project embraces technologies relevant to hydrogen research under the Office of Hydrogen Fuel Cells and Infrastructure Technology (HFCIT) as well as concentrated solar power under the Office of Solar Energy Technologies (SET). Although the photoelectrochemical work is aligned with HFCIT, some of the technologies in this effort are also consistent with the skills and technologies found in concentrated solar power and photovoltaic technology under the Office of Solar Energy Technologies (SET). Hydrogen production by thermo-chemical water-splitting is a chemical process that accomplishes the decomposition of water into hydrogen and oxygen using only heat or a combination of heat and electrolysis instead of pure electrolysis and meets the goals for hydrogen production using only water and renewable solar energy as feed-stocks. Photoelectrochemical hydrogen production also meets these goals by implementing photo-electrolysis at the surface of a semiconductor in contact with an electrolyte with bias provided by a photovoltaic source. Here, water splitting is a photo-electrolytic process in which hydrogen is produced using only solar photons and water as feed-stocks. The thermochemical hydrogen task engendered formal collaborations among two universities, three national laboratories and two private sector

  15. Flux Vector Splitting Schemes for Water Hammer Flows in Pumping Supply Systems with Air Vessels

    Institute of Scientific and Technical Information of China (English)

    Qiang Sun; Yuebin Wu; Ying Xu; Tae Uk Jang

    2015-01-01

    To solve water hammer problems in pipeline systems, many numerical simulation approaches have been developed. This paper improves a flux vector splitting ( FVS) scheme whose grid is the same as the fixed⁃grid MOC scheme. The proposed FVS scheme is used to analyze water hammer problems caused by a pump abrupt shutdown in a pumping system with an air vessel. This paper also proposes a pump⁃valve⁃vessel model combining a pump⁃valve model with an air vessel model. The results show that the data obtained by the FVS scheme are similar to the ones obtained by the fixed⁃grid method of characteristics ( MOC ) . And the results using the pump⁃valve⁃vessel model are almost the same as the ones using both the pump⁃valve model and the air vessel model. Therefore, it is effective that the proposed FVS scheme is used to solve water hammer problems and the pump⁃valve⁃vessel model replaces both the pump⁃valve model and the air vessel model to simulate water hammer flows in the pumping system with the air vessel.

  16. Decoupling hydrogen and oxygen evolution during electrolytic water splitting using an electron-coupled-proton buffer.

    Science.gov (United States)

    Symes, Mark D; Cronin, Leroy

    2013-05-01

    Hydrogen is essential to several key industrial processes and could play a major role as an energy carrier in a future 'hydrogen economy'. Although the majority of the world's hydrogen supply currently comes from the reformation of fossil fuels, its generation from water using renewables-generated power could provide a hydrogen source without increasing atmospheric CO₂ levels. Conventional water electrolysis produces H₂ and O₂ simultaneously, such that these gases must be generated in separate spaces to prevent their mixing. Herein, using the polyoxometalate H₃PMo₁₂O₄₀, we introduce the concept of the electron-coupled-proton buffer (ECPB), whereby O₂ and H₂ can be produced at separate times during water electrolysis. This could have advantages in preventing gas mixing in the headspaces of high-pressure electrolysis cells, with implications for safety and electrolyser degradation. Furthermore, we demonstrate that temporally separated O₂ and H₂ production allows greater flexibility regarding the membranes and electrodes that can be used in water-splitting cells.

  17. Decoration of PbS nanoparticles on Al-doped ZnO nanorod array thin film with hydrogen treatment as a photoelectrode for solar water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Hsu, Chih-Hsiung; Chen, Chao-Hong [Department of Chemical Engineering and Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan, ROC (China); Chen, Dong-Hwang, E-mail: chendh@mail.ncku.edu.tw [Department of Chemical Engineering and Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan, ROC (China)

    2013-03-25

    Highlights: ► AZO nanorod array thin film is used as a photoanode for solar water splitting. ► Hydrogen treatment and sensitization by PbS nanoparticles enhance photocurrent. ► A novel ITO/FTO-free composite photoelectrode is developed. ► The pre-fabrication and use of an extra TCO thin film substrate is unnecessary. -- Abstract: Al-doped ZnO (AZO) nanorod arrays thin film with hydrogen treatment is directly used as a photoelectrode for solar water splitting without an extra transparent conducting oxide (TCO) thin film because it possesses the functions of TCO thin film and photoactive 1-dimensional nanostructured semiconductor simultaneously. To enhance the absorption in the visible region, PbS nanoparticles decorated the AZO nanorods via successive ionic layer adsorption and reaction route. The PbS nanoparticles have a face-centered cubic structure and their decoration does not destroy the 1-dimensional morphology of AZO nanorod arrays. With increasing the cycle number of PbS nanoparticles decoration, the grain size and loading of PbS nanoparticles become larger gradually which leads to lower energy bandgap and stronger absorption. A maximum photocurrent density of 1.65 mW cm{sup −2} is obtained when the cycle number is 20, which is much higher than those without PbS nanoparticles sensitization or hydrogen treatment. This demonstrates that the AZO nanorod array thin film with hydrogen treatment can be directly used as a photoelectrode without an extra TCO thin film. Because the use of expensive metals can be avoided and the pre-fabrication of TCO thin film substrate is necessary no more, the fabrication of such a composite photoelectrode becomes simple and low-cost. So, it has great potentials in solar water splitting after sensitization by quantum dots capable of visible light absorption.

  18. Optimization of photoelectrochemical water splitting performance on hierarchical TiO 2 nanotube arrays

    KAUST Repository

    Zhang, Z.

    2012-02-10

    In this paper, we show that by varying the voltages during two-step anodization the morphology of the hierarchical top-layer/bottom-tube TiO 2 (TiO 2 NTs) can be finely tuned between nanoring/nanotube, nanopore/nanotube, and nanohole-nanocave/nanotube morphologies. This allows us to optimize the photoelectrochemical (PEC) water splitting performance on the hierarchical TiO 2 NTs. The optimized photocurrent density and photoconversion efficiency in this study, occurring on the nanopore/nanotube TiO 2 NTs, were 1.59 mA cm -2 at 1.23 V vs. RHE and 0.84% respectively, which are the highest values ever reported on pristine TiO 2 materials under illumination of AM 1.5G. Our findings contribute to further improvement of the energy conversion efficiency of TiO 2-based devices.

  19. Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling

    Science.gov (United States)

    Shi, Xinjian; Jeong, Hokyeong; Oh, Seung Jae; Ma, Ming; Zhang, Kan; Kwon, Jeong; Choi, In Taek; Choi, Il Yong; Kim, Hwan Kyu; Kim, Jong Kyu; Park, Jong Hyeok

    2016-06-01

    Various tandem cell configurations have been reported for highly efficient and spontaneous hydrogen production from photoelectrochemical solar water splitting. However, there is a contradiction between two main requirements of a front photoelectrode in a tandem cell configuration, namely, high transparency and high photocurrent density. Here we demonstrate a simple yet highly effective method to overcome this contradiction by incorporating a hybrid conductive distributed Bragg reflector on the back side of the transparent conducting substrate for the front photoelectrochemical electrode, which functions as both an optical filter and a conductive counter-electrode of the rear dye-sensitized solar cell. The hybrid conductive distributed Bragg reflectors were designed to be transparent to the long-wavelength part of the incident solar spectrum (λ>500 nm) for the rear solar cell, while reflecting the short-wavelength photons (λ<500 nm) which can then be absorbed by the front photoelectrochemical electrode for enhanced photocurrent generation.

  20. Preparation and characterization of nanostructured CuO thin films for photoelectrochemical splitting of water

    Indian Academy of Sciences (India)

    Diwakar Chauhan; V R Satsangi; Sahab Dass; Rohit Shrivastav

    2006-12-01

    Nanostructured copper oxide thin films (CuO) were prepared on conducting glass support (SnO2: F overlayer) via sol–gel starting from colloidal solution of copper (II) acetate in ethanol. Films were obtained by dip coating under room conditions (temperature, 25–32°C) and were subsequently sintered in air at different temperatures (400–650°C). The evolution of oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction and scanning electron microscopy. Average particle size, resistivity and band gap energy were also determined. Photoelectrochemical properties of thin films and their suitability for splitting of water were investigated. Study suggests that thin films of CuO sintered at lower temperatures (≈ 400°C) are better for photoconversion than thick films or the films sintered at much higher temperatures. Plausible explanations have been provided.

  1. Preparation and characterization of nanostructured ZnO thin films for photoelectrochemical splitting of water

    Indian Academy of Sciences (India)

    Monika Gupta; Vidhika Sharma; Jaya Shrivastava; Anjana Solanki; A P Singh; V R Satsangi; S Dass; Rohit Shrivastav

    2009-02-01

    Nanostructured zinc oxide thin films (ZnO) were prepared on conducting glass support (SnO2: F overlayer) via sol–gel starting from colloidal solution of zinc acetate 2-hydrate in ethanol and 2-methoxy ethanol. Films were obtained by spin coating at 1500 rpm under room conditions (temperature, 28–35°C) and were subsequently sintered in air at three different temperatures (400, 500 and 600°C). The evolution of oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction and scanning electron microscopy. Average particle size, resistivity and bandgap energy were also determined. Photoelectrochemical properties of thin films and their suitability for splitting of water were investigated. Study suggests that thin films of ZnO, sintered at 600°C are better for photoconversion than the films sintered at 400 or 500°C. Plausible explanations have been provided.

  2. Research Update: Strategies for efficient photoelectrochemical water splitting using metal oxide photoanodes

    Directory of Open Access Journals (Sweden)

    Seungho Cho

    2014-01-01

    Full Text Available Photoelectrochemical (PEC water splitting to hydrogen is an attractive method for capturing and storing the solar energy in the form of chemical energy. Metal oxides are promising photoanode materials due to their low-cost synthetic routes and higher stability than other semiconductors. In this paper, we provide an overview of recent efforts to improve PEC efficiencies via applying a variety of fabrication strategies to metal oxide photoanodes including (i size and morphology-control, (ii metal oxide heterostructuring, (iii dopant incorporation, (iv attachments of quantum dots as sensitizer, (v attachments of plasmonic metal nanoparticles, and (vi co-catalyst coupling. Each strategy highlights the underlying principles and mechanisms for the performance enhancements.

  3. Molybdenum Disulfide as a Protection Layer and Catalyst for Gallium Indium Phosphide Solar Water Splitting Photocathodes.

    Science.gov (United States)

    Britto, Reuben J; Benck, Jesse D; Young, James L; Hahn, Christopher; Deutsch, Todd G; Jaramillo, Thomas F

    2016-06-02

    Gallium indium phosphide (GaInP2) is a semiconductor with promising optical and electronic properties for solar water splitting, but its surface stability is problematic as it undergoes significant chemical and electrochemical corrosion in aqueous electrolytes. Molybdenum disulfide (MoS2) nanomaterials are promising to both protect GaInP2 and to improve catalysis because MoS2 is resistant to corrosion and also possesses high activity for the hydrogen evolution reaction (HER). In this work, we demonstrate that GaInP2 photocathodes coated with thin MoS2 surface protecting layers exhibit excellent activity and stability for solar hydrogen production, with no loss in performance (photocurrent onset potential, fill factor, and light-limited current density) after 60 h of operation. This represents a 500-fold increase in stability compared to bare p-GaInP2 samples tested in identical conditions.

  4. Dependence of TiO2 nanotube microstructural and electronic properties on water splitting

    Science.gov (United States)

    Freitas, R. G.; Santanna, M. A.; Pereira, E. C.

    2014-04-01

    In this work, TiO2 nanotubes were prepared by anodization in ionic liquid at 10 °C and 20 °C. Different tube diameters (50.8 nm and 70.5 nm) were obtained, and both of them exhibited an anatase phase with distinct crystallite sizes and lattice strains. The increase in the crystallite size led to a decrease in the grain boundary surface area, which could be associated with the recombination centers of the photogenerated charge carriers. Electrochemical impedance spectroscopy was used to correlate the water splitting photoactivity with the charge transfer resistance and the apparent roughness. A schematic representation of the nanotube structures consisting of two layers, compact and porous, proved to be appropriate to clarify the obtained results.

  5. Synthesis of single-crystal-like nanoporous carbon membranes and their application in overall water splitting

    KAUST Repository

    Wang, Hong

    2017-01-04

    Nanoporous graphitic carbon membranes with defined chemical composition and pore architecture are novel nanomaterials that are actively pursued. Compared with easy-to-make porous carbon powders that dominate the porous carbon research and applications in energy generation/conversion and environmental remediation, porous carbon membranes are synthetically more challenging though rather appealing from an application perspective due to their structural integrity, interconnectivity and purity. Here we report a simple bottom–up approach to fabricate large-size, freestanding and porous carbon membranes that feature an unusual single-crystal-like graphitic order and hierarchical pore architecture plus favourable nitrogen doping. When loaded with cobalt nanoparticles, such carbon membranes serve as high-performance carbon-based non-noble metal electrocatalyst for overall water splitting.

  6. Molybdenum Disulfide as a Protection Layer and Catalyst for Gallium Indium Phosphide Solar Water Splitting Photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Britto, Reuben J.; Benck, Jesse D.; Young, James L.; Hahn, Christopher; Deutsch, Todd G.; Jaramillo, Thomas F.

    2016-06-02

    Gallium indium phosphide (GaInP2) is a semiconductor with promising optical and electronic properties for solar water splitting, but its surface stability is problematic as it undergoes significant chemical and electrochemical corrosion in aqueous electrolytes. Molybdenum disulfide (MoS2) nanomaterials are promising to both protect GaInP2 and to improve catalysis since MoS2 is resistant to corrosion and also possesses high activity for the hydrogen evolution reaction (HER). In this work, we demonstrate that GaInP2 photocathodes coated with thin MoS2 surface protecting layers exhibit excellent activity and stability for solar hydrogen production, with no loss in performance (photocurrent onset potential, fill factor, and light limited current density) after 60 hours of operation. This represents a five-hundred fold increase in stability compared to bare p-GaInP2 samples tested in identical conditions.

  7. Ultralight, Flexible, and Semi-Transparent Metal Oxide Papers for Photoelectrochemical Water Splitting

    DEFF Research Database (Denmark)

    Zhang, Minwei; Hou, Chengyi; Halder, Arnab

    2017-01-01

    nanostructure and macroscopic morphology of MOs that aims to enhance their performances, but the design and controlled synthesis of ultrafine nanostructured MOs in a cost-effective and facile way remains a challenge. In this work, we have exploited the advantages of intrinsic structures of graphene oxide (GO......Thanks to their versatile functionality, metal oxides (MOs) constitute one of the key family materials in a variety of current demands for sensor, catalysis, energy storage and conversion, optical electronics, and piezoelectric mechanics. Much effort has focused on engineering specific...... were tested for their potential application in photoelectrochemical (PEC) energy conversion. In terms of PEC water splitting, copper oxide papers were used as an example and exhibited excellent performances with an extremely high photocurrent-to-weight ratio of 3 A cm-2 g-1. We have also shown...

  8. Combined Au-plasmonic nanoparticles with mesoporous carbon material (CMK-3) for photocatalytic water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Hung, Wei Hsuan, E-mail: whung@fcu.edu.tw, E-mail: yinm@sari.ac.cn; Lai, Sz Nian; Su, Cheng Yi [Department of Materials Science and Engineering, Feng Chia University, No. 100, Wenhwa Rd., Seatwen, Taichung 407, Taiwan (China); Yin, Min, E-mail: whung@fcu.edu.tw, E-mail: yinm@sari.ac.cn; Li, Dongdong; Xue, Xinzhong [Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Zhangjiang Hi-Tech Park, Pudong, Shanghai 201210 (China); Tseng, Chuan Ming [Department of Materials Engineering, Ming Chi University of Technology, 84 Gungjuan Rd., Taishan, New Taipei City 24301, Taiwan (China)

    2015-08-17

    The conventional TiO{sub 2} photoelectrode for water splitting was integrated with ordered mesoporous carbon material (CMK-3) and Au metal nanoparticles (NPs) to improve the photocatalytic efficiency under visible light irradiation. Compared to TiO{sub 2}, Au/TiO{sub 2}-CMK-3 photoelectrode demonstrated over two orders of magnitude enhancement of photocurrent under 532 nm laser irradiation due to the generation of hot electron and near field from Au NPs. Furthermore, the improvement of free carrier transport and additional long-wavelength absorption can be achieved by exploiting the superior conductivity and blackbody-like property of CMK-3. This proposed enhancement mechanism was proved by the measurements of photoluminescence emission spectrum and electrochemical impedance spectroscopy.

  9. On the chemical state of Co oxide electrocatalysts during alkaline water splitting.

    Science.gov (United States)

    Friebel, Daniel; Bajdich, Michal; Yeo, Boon Siang; Louie, Mary W; Miller, Daniel J; Sanchez Casalongue, Hernan; Mbuga, Felix; Weng, Tsu-Chien; Nordlund, Dennis; Sokaras, Dimosthenis; Alonso-Mori, Roberto; Bell, Alexis T; Nilsson, Anders

    2013-10-28

    Resonant inelastic X-ray scattering and high-resolution X-ray absorption spectroscopy were used to identify the chemical state of a Co electrocatalyst in situ during the oxygen evolution reaction. After anodic electrodeposition onto Au(111) from a Co(2+)-containing electrolyte, the chemical environment of Co can be identified to be almost identical to CoOOH. With increasing potentials, a subtle increase of the Co oxidation state is observed, indicating a non-stoichiometric composition of the working OER catalyst containing a small fraction of Co(4+) sites. In order to confirm this interpretation, we used density functional theory with a Hubbard-U correction approach to compute X-ray absorption spectra of model compounds, which agree well with the experimental spectra. In situ monitoring of catalyst local structure and bonding is essential in the development of structure-activity relationships that can guide the discovery of efficient and earth abundant water splitting catalysts.

  10. High-Performance Rh 2 P Electrocatalyst for Efficient Water Splitting

    Energy Technology Data Exchange (ETDEWEB)

    Duan, Haohong; Li, Dongguo; Tang, Yan; He, Yang; Ji, Shufang; Wang, Rongyue; Lv, Haifeng; Lopes, Pietro P.; Paulikas, Arvydas P.; Li, Haoyi; Mao, Scott X.; Wang, Chongmin; Markovic, Nenad M.; Li, Jun; Stamenkovic, Vojislav R.; Li, Yadong

    2017-04-05

    Search for active, stable and cost-efficient electrocatalysts for hydrogen production via water splitting could make substantial impact to the energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high surface area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C NCs exhibit remarkable performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) compared to Rh/C and Pt/C catalysts. The atomic structure of the rhodium phosphide nanocubes was directly observed by annular dark-field scanning transmission electron microscopy (ADF-STEM), which revealed phosphorous-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorous plays crucial role in determining the robust catalyst properties.

  11. High-Efficiency Photochemical Water Splitting of CdZnS/CdZnSe Nanostructures

    OpenAIRE

    2013-01-01

    We have prepared and employed TiO2/CdZnS/CdZnSe electrodes for photochemical water splitting. The TiO2/CdZnS/CdZnSe electrodes consisting of sheet-like CdZnS/CdZnSe nanostructures (8–10 μm in length and 5–8 nm in width) were prepared through chemical bath deposition on TiO2 substrates. The TiO2/CdZnS/CdZnSe electrodes have light absorption over the wavelength 400–700 nm and a band gap of 1.87 eV. Upon one sun illumination of 100 mW cm−2, the TiO2/CdZnS/CdZnSe electrodes provide a significant ...

  12. Thermal Oxidation Preparation of Doped Hematite Thin Films for Photoelectrochemical Water Splitting

    Directory of Open Access Journals (Sweden)

    Song Li

    2014-01-01

    Full Text Available Sn- or Ge-doped hematite thin films were fabricated by annealing alloyed films for the purpose of photoelectrochemical (PEC water splitting. The alloyed films were deposited on FTO glass by magnetron sputtering and their compositions were controlled by the target. The morphology, crystalline structure, optical properties, and photocatalytic activities have been investigated. The SEM observation showed that uniform, large area arrays of nanoflakes formed after thermal oxidation. The incorporation of doping elements into the hematite structure was confirmed by XRD. The photocurrent density-voltage characterization illustrated that the nanoflake films of Sn-doped hematite exhibited high PEC performance and the Sn concentration was optimized about 5%. The doped Ge4+ ions were proposed to occupy the empty octahedral holes and their effect on PEC performance of hematite is smaller than that of tin ions.

  13. Preparation and Characterization of Titanium Dioxide Photoelectrodes for Generation of Hydrogen by Photoelectrochemical Water Splitting

    Directory of Open Access Journals (Sweden)

    Alvaro Realpe

    2015-04-01

    Full Text Available The photoelectrochemical water splitting for the production of hydrogen was evaluated through the preparation of photoelectrodes of different substrates (glass, aluminium, graphite with TiO2 film. The film on each substrate was characterized by scanning electron microscope (SEM and x-ray diffraction (XRD. The results show that the TiO2 was deposited in dispersed form and in small clusters on the surface of the substrate and it had no effect on the crystal structure of the semiconductor; furthermore, good adhesion of the films on substrates was obtained except with graphite substrate. The hydrogen production process was carried out using UV light, halogen light and sunlight as photon sources, and it was evaluated by the current flow through the external circuit of the cell. The highest photocurrent values were obtained with the aluminium photoelectrode, averaging 1092.03 uA.

  14. Spray-drying of milk for oxygen evolution electrocatalyst and solar water splitting.

    Science.gov (United States)

    Cai, Chenyi; Kuang, Min; Chen, Xiling; Wu, Hao; Ge, Hongtao; Zheng, Gengfeng

    2017-02-01

    The development of efficient and robust electrocatalyst has been the central of the solar water splitting-based hydrogen fuel acquisition. In this work, we reported the use of cow milk, with addition of tetraethyl orthosilicate (TEOS) and melamine, for the synthesis of nitrogen-doped mesoporous carbon microspheres. Due to the large surface and enhanced charge transport behavior, the obtained samples enabled low overpotentials and a small Tafel slope toward oxygen evolution reaction, which were close or comparable to the best OER catalysts of carbon materials reported previously. Further incorporation of this catalyst and a Pt wire to a commercial solar cell, the direct solar-to-hydrogen conversion was realized, with a stability of over 30h.

  15. The effect of e-beam irradiation on water splitting protochloride

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Sam S. [Korea Univ., Seoul (Korea, Republic of)

    2013-07-01

    Photocatalysis of water splitting promises a low-cost and environmentally friendly hydrogen production via free solar energy. We used the well-controlled aerosol deposition (AD) technique to fabricate TiO2 thin film as photo-electrodes. The AD TiO2 films were irradiated with lower energy electron beam from a 0.2 MeV (1mA) electrostatic accelerator under ambient conditions. The dose absorbed to the sample is 12kGy. The current-potential curve results showed the enhancement of photocurrent density after e-beam irradiation from 39.2 to 204.3 {mu}A/cm2 at +0.20V vs. Ag/AgCl.

  16. First principles study on defectives BN nanotubes for water splitting and hydrogen storage

    Science.gov (United States)

    Bevilacqua, Andressa C.; Rupp, Caroline J.; Baierle, Rogério J.

    2016-06-01

    First principles calculations within the spin polarized density functional approximation have been addressed to investigate the energetic stability, electronic and optical properties of defective BN nanotubes. Our results show that the presence of carbon impurities interacting with vacancies gives rise to defective electronic levels inside the nanotube band gap. By calculating the absorbance index, we have obtained a strong inter-band optical absorption in the visible region (around 2.1 eV) showing that defective BN nanotubes could be an efficient catalytic semiconductor material to be used within solar energy for water splitting. In addition, we observe that the adsorption energy for one and two H2 molecules on the defective surface is in the desired window for the system to be useful as a hydrogen storage medium.

  17. Characterization of photoelectrochemical cells for water splitting by electrochemical impedance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, Tania; Andrade, Luisa; Ribeiro, Helena Aguilar; Mendes, Adelio [Laboratorio de Engenharia de Processos, Ambiente e Energia (LEPAE), Faculdade de Engenharia da Universidade do Porto, Rua Roberto Frias, 4200-465 Porto (Portugal)

    2010-10-15

    The photocurrent-voltage characteristic of a photoelectrochemical cell for solar hydrogen production via water splitting, using undoped-hematite as photoanode, was obtained. Photoelectrochemical characteristics of the cell were also investigated by electrochemical impedance spectroscopy. Both techniques were carried out in the dark and under illumination. The analysis of the frequency spectra for the real and imaginary parts of the complex impedance allowed obtaining equivalent electrical analogs for the PEC cell operating in the dark and under 1 sun simulated illumination. Additionally, different electrode configurations were used (two and three-electrode arrangements). The two-electrode configuration allowed the study of the overall charge transfer phenomena occurring at the semiconductor, within the electrolyte and at the counter-electrode side of the cell, whereas the three-electrode configuration gave more detailed information concerning the double charged layer at the semiconductor/electrolyte interface. (author)

  18. Plasmon-enhanced water splitting on TiO2-passivated GaP photocatalysts.

    Science.gov (United States)

    Qiu, Jing; Zeng, Guangtong; Pavaskar, Prathamesh; Li, Zhen; Cronin, Stephen B

    2014-02-21

    Integrating plasmon resonant nanostructures with photocatalytic semiconductors shows great promise for high efficiency photocatalytic water splitting. However, the electrochemical instability of most III-V semiconductors severely limits their applicability in photocatalysis. In this work, we passivate p-type GaP with a thin layer of n-type TiO2 using atomic layer deposition. The TiO2 passivation layer prevents corrosion of the GaP, as evidenced by atomic force microscopy and photoelectrochemical measurements. In addition, the TiO2 passivation layer provides an enhancement in photoconversion efficiency through the formation of a charge separating pn-region. Plasmonic Au nanoparticles deposited on top of the TiO2-passivated GaP further increases the photoconversion efficiency through local field enhancement. These two enhancement mechanisms are separated by systematically varying the thickness of the TiO2 layer. Because of the tradeoff between the quickly decaying plasmonic fields and the formation of the pn-charge separation region, an optimum performance is achieved for a TiO2 thickness of 0.5 nm. Finite difference time domain (FDTD) simulations of the electric field profiles in this photocatalytic heterostructure corroborate these results. The effects of plasmonic enhancement are distinguished from the natural catalytic properties of Au by evaluating similar photocatalytic TiO2/GaP structures with catalytic, non-plasmonic metals (i.e., Pt) instead of Au. This general approach of passivating narrower band gap semiconductors enables a wider range of materials to be considered for plasmon-enhanced photocatalysis for high efficiency water splitting.

  19. Tungsten carbide nanoparticles as efficient cocatalysts for photocatalytic overall water splitting

    KAUST Repository

    Garcia Esparza, Angel T.

    2012-12-17

    Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C3N 4 (mpg-C3N4) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W 2C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H2 and O2 in a stoichiometric ratio from H 2O decomposition when supported on a Na-doped SrTiO3 photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation. Platinum replacement: The phase-controlled synthesis of tungsten carbide nanoparticles from the nanoconfinement of a mesoporous graphite C 3N4 (mpg-C3N4) reactive template is shown. The nanomaterials catalyze hydrogen evolution/oxidation reactions, but are inactive in the oxygen reduction reaction. Tungsten carbide is an effective cocatalyst for photocatalytic overall water splitting (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Large-scale patterned ZnO nanorod arrays for efficient photoelectrochemical water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Yaping [School of Materials Science and Engineering, Guilin University of Technology, Guilin 541004 (China); Yan, Xiaoqin; Gu, Yousong; Chen, Xiang; Bai, Zhiming; Kang, Zhuo [State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083 (China); Long, Fei, E-mail: longf@glite.edu.cn [School of Materials Science and Engineering, Guilin University of Technology, Guilin 541004 (China); Zhang, Yue, E-mail: yuezhang@ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083 (China); Key Laboratory of New Energy Materials and Technologies, University of Science and Technology Beijing, Beijing 10083 (China)

    2015-06-01

    Highlights: • Large-scale patterned ZnO NRAs are designed and fabricated via two-beam laser interference lithography and hydrothermal synthesis. • The ZnO NRA photoanodes with square pattern achieved a maximum efficiency of 0.18%, which is improved 135% compared to the control group with no patterned ZnO NRAs. • FDTD simulation data demonstrated that the square patterned ZnO NRAs with periodic architecture have superior light harvesting efficiency. • The patterned ZnO NRAs have enhanced light-harvesting ability. The enlarged surface area accelerated the charge transfer at the photoanode/electrolyte interface. - Abstract: Nowadays, the fabrication of photoanodes with high light-harvesting capability and charge transfer efficiency is a key challenge for photoelectrochemical (PEC) water splitting. In this paper, large-scale patterned ZnO nanorod arrays (NRAs) were designed and fabricated via two-beam laser interference lithography and hydrothermal synthesis, which were further applied as PEC photoanodes for the first time. By adopting the ZnO NRA photoanodes with square pattern, the PEC cells achieved a maximum efficiency of 0.18%, which was improved 135% compared to the control group with no patterned ZnO NRAs. The large-scale highly ordered ZnO NRAs have enhanced light-harvesting ability due to the light-scattering effect. In addition, the enlarged surface area of the patterned ZnO NRAs accelerated the charge transfer at the photoanode/electrolyte interface. This research demonstrates an effective mean to realize the efficient solar water splitting, and the results suggest that large-scale highly ordered nanostructures are promising candidates in the field of energy harvesting.

  1. Zn-Co layered double hydroxide modified hematite photoanode for enhanced photoelectrochemical water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Dongyu [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620 (China); Rui, Yichuan [College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620 (China); Li, Yaogang [Engineering Research Center of Advanced Glasses Manufacturing Technology, MOE, Donghua University, Shanghai 201620 (China); Zhang, Qinghong, E-mail: zhangqh@dhu.edu.cn [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620 (China); Engineering Research Center of Advanced Glasses Manufacturing Technology, MOE, Donghua University, Shanghai 201620 (China); Wang, Hongzhi, E-mail: wanghz@dhu.edu.cn [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620 (China)

    2015-12-15

    Graphical abstract: - Highlights: • A facile way to fabricate earth-abundant α-Fe{sub 2}O{sub 3}/Zn-Co LDH composite photoanode via electrodeposition was presented. • The highest photocurrent 1.73 mA/cm{sup 2} at 1.23 V vs RHE was achieved by 60 s electrodeposition (i.e., 36% increment). • EIS indicated the enhanced charge transfer rate comes from improvement of water oxidation. - Abstract: Zinc-cobalt layered double hydroxide (LDH) was electrodeposited on Ti-doped hematite photoanodes for the first time, and a significant enhanced performance for photoelectrochemical water splitting was demonstrated over the composite photoanodes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS) were characterized with the resulted photoanodes. With the electrodepositing treatment, the photocurrent density increased from 1.27 mA/cm{sup 2} for pristine hematite to 1.73 mA/cm{sup 2} for modified materials at 1.23 V vs. RHE (i.e. 36% improvement). The photocurrent improvement is mainly attributed to a suppression of electron–hole recombination and reduced overpotential for water oxidation at the hematite-electrolyte interface due to the formation of Zn-Co LDH layer on hematite.

  2. Stability and bandgaps of layered perovskites for one- and two-photon water splitting

    Science.gov (United States)

    Castelli, Ivano E.; María García-Lastra, Juan; Hüser, Falco; Thygesen, Kristian S.; Jacobsen, Karsten W.

    2013-10-01

    Direct production of hydrogen from water and sunlight requires stable and abundantly available semiconductors with well positioned band edges relative to the water red-ox potentials. We have used density functional theory (DFT) calculations to investigate 300 oxides and oxynitrides in the Ruddlesden-Popper phase of the layered perovskite structure. Based on screening criteria for the stability, bandgaps and band edge positions, we suggest 20 new materials for the light harvesting photo-electrode of a one-photon water splitting device and 5 anode materials for a two-photon device with silicon as photo-cathode. In addition, we explore a simple rule relating the bandgap of the perovskite to the number of octahedra in the layered structure and the B-metal ion. Finally, the quality of the GLLB-SC potential used to obtain the bandgaps, including the derivative discontinuity, is validated against G0W0@LDA gaps for 20 previously identified oxides and oxynitrides in the cubic perovskite structure.

  3. Titanium-iridium oxide layer coating to suppress photocorrosion during photocatalytic water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Yongwoo; Lee, Hyunjoo [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Kwon, Yongwoo; Lee, Hyunjoo [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2015-12-15

    Photocatalysts with a small band gap energy have received a great deal of interest due their high solar conversion efficiencies. Cuprous oxide (Cu{sub 2}O) has attracted attention because of its small bandgap energy, a direct bandgap structure, its suitable band structure for water splitting, high absorption coefficient, non-toxicity, and its large abundance. However, it has poor stability due to the fickle oxidation states of copper. To enhance the stability and the production rate of hydrogen and oxygen, a TiIrOX overlayer was successfully formed on the Cu{sub 2}O under various synthesis conditions. The composition and oxidation state of the Ir species in the overlayer were optimized through the control of the Ir precursor and the amount of water. The Ir/Ti precursor molar ratio was linearly related to the surface Ir/Ti molar ratio. The addition of water converted the Ir precursor to IrO{sub 2}. The thickness of the overlayer was controlled by differing the synthesis times of the coating. Then, the largest amounts of hydrogen and oxygen were produced through the optimization of the TiIrOX overlayer with a higher IrO{sub 2} fraction and a thicker overlayer.

  4. Nanostructured materials on 3D nickel foam as electrocatalysts for water splitting.

    Science.gov (United States)

    Chaudhari, Nitin K; Jin, Haneul; Kim, Byeongyoon; Lee, Kwangyeol

    2017-08-31

    Highly efficient and low-cost electrocatalysts are essential for water spitting via electrolysis in an economically viable fashion. However, the best catalytic performance is found with noble metal-based electrocatalysts, which presents a formidable obstacle for the commercial success of electrolytic water splitting-based H2 production due to their relatively high cost and scarcity. Therefore, the development of alternative inexpensive earth-abundant electrode materials with excellent electrocatalytic properties is of great urgency. In general, efficient electrocatalysts must possess several key characteristics such as low overpotential, good electrocatalytic activity, high stability, and low production costs. Direct synthesis of nanostructured catalysts on a conducting substrate may potentially improve the performance of the resultant electrocatalysts because of their high catalytic surface areas and the synergistic effect between the electrocatalyst and the conductive substrate. In this regard, three dimensional (3D) nickel foams have been advantageously utilized as electrode substrates as they offer a large active surface area and a highly conductive continuous porous 3D network. In this review, we discuss the most recent developments in nanostructured materials directly synthesized on 3D nickel foam as potential electrode candidates for electrochemical water electrolysis, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). We also provide perspectives and outlooks for catalysts grown directly on 3D conducting substrates for future sustainable energy technologies.

  5. Efficiency maximization in solar-thermochemical fuel production: challenging the concept of isothermal water splitting.

    Science.gov (United States)

    Ermanoski, I; Miller, J E; Allendorf, M D

    2014-05-14

    Widespread adoption of solar-thermochemical fuel production depends on its economic viability, largely driven by the efficiency of use of the available solar resource. Herein, we analyze the efficiency of two-step cycles for thermochemical hydrogen production, with emphasis on efficiency. Owing to water thermodynamics, isothermal H2 production is shown to be impractical and inefficient, irrespective of reactor design or reactive oxide properties, but an optimal temperature difference between cycle steps, for which efficiency is the highest, can be determined for a wide range of other operating parameters. A combination of well-targeted pressure and temperature swing, rather than either individually, emerges as the most efficient mode of operation of a two-step thermochemical cycle for solar fuel production.

  6. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1.

    Science.gov (United States)

    Wang, Qian; Hisatomi, Takashi; Jia, Qingxin; Tokudome, Hiromasa; Zhong, Miao; Wang, Chizhong; Pan, Zhenhua; Takata, Tsuyoshi; Nakabayashi, Mamiko; Shibata, Naoya; Li, Yanbo; Sharp, Ian D; Kudo, Akihiko; Yamada, Taro; Domen, Kazunari

    2016-06-01

    Photocatalytic water splitting using particulate semiconductors is a potentially scalable and economically feasible technology for converting solar energy into hydrogen. Z-scheme systems based on two-step photoexcitation of a hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either water reduction or oxidation activity can be applied to the water splitting reaction. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles. Here, we present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. ) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a gold (Au) layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable water splitting using particulate semiconductors.

  7. Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%

    Science.gov (United States)

    Wang, Qian; Hisatomi, Takashi; Jia, Qingxin; Tokudome, Hiromasa; Zhong, Miao; Wang, Chizhong; Pan, Zhenhua; Takata, Tsuyoshi; Nakabayashi, Mamiko; Shibata, Naoya; Li, Yanbo; Sharp, Ian D.; Kudo, Akihiko; Yamada, Taro; Domen, Kazunari

    2016-06-01

    Photocatalytic water splitting using particulate semiconductors is a potentially scalable and economically feasible technology for converting solar energy into hydrogen. Z-scheme systems based on two-step photoexcitation of a hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either water reduction or oxidation activity can be applied to the water splitting reaction. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles. Here, we present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. ) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a gold (Au) layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable water splitting using particulate semiconductors.

  8. Stability of Ag@SiO2 core–shell particles in conditions of photocatalytic overall water-splitting

    NARCIS (Netherlands)

    Park, Sun Young; Han, Kai; O'Neill, Devin B.; Mul, Guido

    2017-01-01

    Core–shell nanoparticles containing plasmonic metals (Ag or Au) have been frequently reported to enhance performance of photo-electrochemical (PEC) devices. However, the stability of these particles in water-splitting conditions is usually not addressed. In this study we demonstrate that Ag@SiO2

  9. A two-step photoexcitation system for photocatalytic water splitting into hydrogen and oxygen under visible light irradiation

    Science.gov (United States)

    Abe, Ryu

    2011-10-01

    The developments of water-splitting systems that can efficiently use visible light have been a major challenge for many years in order to realize efficient conversion of solar light. We have developed a new type of photocatalysis system that can split water into H2 and O2 under visible light irradiation, which was inspired by the two-step photoexcitation (Zscheme) mechanism of natural photosynthesis in green plants. In this system, the water splitting reaction is broken up into two stages: one for H2 evolution and the other for O2 evolution; these are combined by using a shuttle redox couple (Red/Ox) in the solution. The introduction of a Z-scheme mechanism reduces the energy required to drive each photocatalysis process, extending the usable wavelengths significantly (~460 nm for H2 evolution and ~600 nm for O2evolution) from that in conventional water splitting systems (~460 nm) based on one-step photoexcitation in single semiconductor material.

  10. Performance evaluation of four different methods for circulating water in commercial-scale, split-pond aquaculture systems

    Science.gov (United States)

    The split-pond consists of a fish-culture basin that is connected to a waste-treatment lagoon by two conveyance structures. Water is circulated between the two basins with high-volume pumps and many different pumping systems are being used on commercial farms. Pump performance was evaluated with fou...

  11. Hydrogen generation via photoelectrochemical water splitting using chemically exfoliated MoS{sub 2} layers

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, R. K., E-mail: r.joshi@unsw.edu.au, E-mail: alwarappan@cecri.res.in; Sahajwalla, V. [Centre for Sustainable Materials Research and Technology, School of Materials Science and Engineering, University of New South Wales, NSW 2052 (Australia); Shukla, S.; Saxena, S. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai (India); Lee, G.-H. [Department of Material Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Alwarappan, S., E-mail: r.joshi@unsw.edu.au, E-mail: alwarappan@cecri.res.in [CSIR-Central Electrochemical Research Institute, Karaikudi 630006, Tamilnadu (India)

    2016-01-15

    Study on hydrogen generation has been of huge interest due to increasing demand for new energy sources. Photoelectrochemical reaction by catalysts was proposed as a promising technique for hydrogen generation. Herein, we report the hydrogen generation via photoelectrochecmial reaction using films of exfoliated 2-dimensional (2D) MoS{sub 2}, which acts as an efficient photocatalyst. The film of chemically exfoliated MoS{sub 2} layers was employed for water splitting, leading to hydrogen generation. The amount of hydrogen was qualitatively monitored by observing overpressure of a water container. The high photo-current generated by MoS{sub 2} film resulted in hydrogen evolution. Our work shows that 2D MoS{sub 2} is one of the promising candidates as a photocatalyst for light-induced hydrogen generation. High photoelectrocatalytic efficiency of the 2D MoS{sub 2} shows a new way toward hydrogen generation, which is one of the renewable energy sources. The efficient photoelectrocatalytic property of the 2D MoS{sub 2} is possibly due to availability of catalytically active edge sites together with minimal stacking that favors the electron transfer.

  12. Novel ZnO/Fe₂O₃ Core-Shell Nanowires for Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Hsu, Yu-Kuei; Chen, Ying-Chu; Lin, Yan-Gu

    2015-07-01

    A facile and simple fabrication of Fe2O3 as a shell layer on the surface of ZnO nanowires (NW) as a core-shell nanoelectrode is applied for the photoelectrochemical (PEC) splitting of water. An ZnO NW array of core diameter ∼80 nm was grown on a fluorine-doped tin-oxide (FTO) substrate with a hydrothermal method; subsequent deposition and annealing achieved a shell structure of the Fe2O3 layer of thickness a few nm. Fe2O3 in the α phase and ZnO in the wurtzite phase were identified as the structures of the shell and core, respectively, through analysis with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The ZnO/Fe2O3 core-shell NW showed an excellent PEC response to the oxidation of water, and also benefited from a negative shift of onset potential because of an n/n heterojunction structure. A detailed energy diagram of the ZnO/Fe2O3 core-shell NW was investigated with a Mott-Schottky analysis. This novel core-shell nanostructure can hence not only exhibit a great potential for the solar generation of hydrogen, but also offer a blueprint for the future design of photocatalysts.

  13. Investigation of porosity and heterojunction effects of a mesoporous hematite electrode on photoelectrochemical water splitting.

    Science.gov (United States)

    Liu, Jingling; Shahid, Muhammad; Ko, Young-Seon; Kim, Eunchul; Ahn, Tae Kyu; Park, Jong Hyeok; Kwon, Young-Uk

    2013-06-28

    In this paper, we report the porosity and heterojunction effects of hematite (α-Fe2O3) on the photoelectrochemical (PEC) water splitting properties. The worm-like mesoporous hematite thin films (MHFs) with a pore size of ~9 nm and a wall thickness of ~5 nm were successfully obtained through the self-assembly process. MHFs formed on FTO showed much better PEC properties than those of nonporous hematite thin films (NP-HF) owing to the suppression of charge recombination. The PEC data of MHFs under front and back illumination conditions indicated that the porous structure allows the diffusion of electrolyte deep inside the MHF increasing the number of holes to be utilized in the water oxidation reaction. A heterojunction structure was formed by introducing a thin layer of SnO2 (~15 nm in thickness) between the MHF and FTO for a dramatically enhanced PEC response, which is attributed to the efficient electron transfer. Our spectroscopic and electrochemical data show that the SnO2 layer functions as an efficient electron transmitter, but does not affect the recombination kinetics of MHFs.

  14. Nanotextured pillars of electrosprayed bismuth vanadate for efficient photoelectrochemical water splitting.

    Science.gov (United States)

    Yoon, Hyun; Mali, Mukund G; Choi, Jae Young; Kim, Min-woo; Choi, Sung Kyu; Park, Hyunwoong; Al-Deyab, Salem S; Swihart, Mark T; Yarin, Alexander L; Yoon, Sam S

    2015-03-31

    We demonstrate, for the first time, electrostatically sprayed bismuth vanadate (BiVO4) thin films for photoelectrochemical water splitting. Characterization of these films by X-ray diffraction, Raman scattering, and high-resolution scanning electron microscopy analyses revealed the formation of nanotextured pillar-like structures of highly photoactive monoclinic scheelite BiVO4. Electrosprayed BiVO4 nanostructured films yielded a photocurrent density of 1.30 and 1.95 mA/cm(2) for water and sulfite oxidation, respectively, under 100 mW/cm(2) illumination. The optimal film thickness was 3 μm, with an optimal postannealing temperature of 550 °C. The enhanced photocurrent is facilitated by formation of pillar-like structures in the deposit. We show through modeling that these structures result from the electrically-driven motion of submicron particles in the direction parallel to the substrate, as they approach the substrate, along with Brownian diffusion. At the same time, opposing thermophoretic forces slow their approach to the surface. The model of these processes proposed here is in good agreement with the experimental observations.

  15. Hydrogen generation via photoelectrochemical water splitting using chemically exfoliated MoS2 layers

    Directory of Open Access Journals (Sweden)

    R. K. Joshi

    2016-01-01

    Full Text Available Study on hydrogen generation has been of huge interest due to increasing demand for new energy sources. Photoelectrochemical reaction by catalysts was proposed as a promising technique for hydrogen generation. Herein, we report the hydrogen generation via photoelectrochecmial reaction using films of exfoliated 2-dimensional (2D MoS2, which acts as an efficient photocatalyst. The film of chemically exfoliated MoS2 layers was employed for water splitting, leading to hydrogen generation. The amount of hydrogen was qualitatively monitored by observing overpressure of a water container. The high photo-current generated by MoS2 film resulted in hydrogen evolution. Our work shows that 2D MoS2 is one of the promising candidates as a photocatalyst for light-induced hydrogen generation. High photoelectrocatalytic efficiency of the 2D MoS2 shows a new way toward hydrogen generation, which is one of the renewable energy sources. The efficient photoelectrocatalytic property of the 2D MoS2 is possibly due to availability of catalytically active edge sites together with minimal stacking that favors the electron transfer.

  16. Tandem Core-Shell Si-Ta3N5 Photoanodes for Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Narkeviciute, Ieva; Chakthranont, Pongkarn; Mackus, Adriaan J M; Hahn, Christopher; Pinaud, Blaise A; Bent, Stacey F; Jaramillo, Thomas F

    2016-12-14

    Nanostructured core-shell Si-Ta3N5 photoanodes were designed and synthesized to overcome charge transport limitations of Ta3N5 for photoelectrochemical water splitting. The core-shell devices were fabricated by atomic layer deposition of amorphous Ta2O5 onto nanostructured Si and subsequent nitridation to crystalline Ta3N5. Nanostructuring with a thin shell of Ta3N5 results in a 10-fold improvement in photocurrent compared to a planar device of the same thickness. In examining thickness dependence of the Ta3N5 shell from 10 to 70 nm, superior photocurrent and absorbed-photon-to-current efficiencies are obtained from the thinner Ta3N5 shells, indicating minority carrier diffusion lengths on the order of tens of nanometers. The fabrication of a heterostructure based on a semiconducting, n-type Si core produced a tandem photoanode with a photocurrent onset shifted to lower potentials by 200 mV. CoTiOx and NiOx water oxidation cocatalysts were deposited onto the Si-Ta3N5 to yield active photoanodes that with NiOx retained 50-60% of their maximum photocurrent after 24 h chronoamperometry experiments and are thus among the most stable Ta3N5 photoanodes reported to date.

  17. Designing metal hydride complexes for water splitting reactions: a molecular electrostatic potential approach.

    Science.gov (United States)

    Sandhya, K S; Suresh, Cherumuttathu H

    2014-08-28

    The hydridic character of octahedral metal hydride complexes of groups VI, VII and VIII has been systematically studied using molecular electrostatic potential (MESP) topography. The absolute minimum of MESP at the hydride ligand (Vmin) and the MESP value at the hydride nucleus (VH) are found to be very good measures of the hydridic character of the hydride ligand. The increasing/decreasing electron donating feature of the ligand environment is clearly reflected in the increasing/decreasing negative character of Vmin and VH. The formation of an outer sphere metal hydride-water complex showing the HH dihydrogen interaction is supported by the location and the value of Vmin near the hydride ligand. A higher negative MESP suggested lower activation energy for H2 elimination. Thus, MESP features provided a way to fine-tune the ligand environment of a metal-hydride complex to achieve high hydridicity for the hydride ligand. The applicability of an MESP based hydridic descriptor in designing water splitting reactions is tested for group VI metal hydride model complexes of tungsten.

  18. A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting.

    Science.gov (United States)

    Ye, Xiaofei; Melas-Kyriazi, John; Feng, Zhuoluo A; Melosh, Nicholas A; Chueh, William C

    2013-10-01

    Photoelectrochemical cells (PECs) have been studied extensively for dissociating water into hydrogen and oxygen. Key bottlenecks for achieving high solar-to-hydrogen efficiency in PECs include increasing solar spectrum utilization, surmounting overpotential losses, and aligning the absorber/electrochemical redox levels. We propose a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor. Unlike thermochemical and hybrid photo-thermochemical water-splitting routes, the elevated-temperature PEC is a single-step approach operating isothermally. At the heart of the solid-state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability, and ionic conduction. The MIEC, placed between the gas phase and the semiconductor light absorber, provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface. In this work, we simulate the behavior of an oxygen-ion-conducting photocathode in 1-D. Using the detailed-balance approach, in conjunction with recombination and electrochemical reaction rates, the practical efficiency is calculated as a function of temperature, solar flux, and select material properties. For a non-degenerate light absorber with a 2.0 eV band-gap and an uphill band offset of 0.3 eV, an efficiency of 17% and 11% is predicted at 723 and 873 K, respectively.

  19. Experimental study on split air conditioner with new hybrid equiment of energy storage and water heater all year round

    Energy Technology Data Exchange (ETDEWEB)

    Shaowei Wang; Zhenyan Liu [Shanghai Jiao Tong Univ. (China). School of Mechanical and Power Engineering; Yuan Li; Keke Zhao; Zhigang Wang [Qingdao Hisense Group Co. Ltd. (China)

    2005-11-01

    This paper presents a split air conditioner with a new hybrid equipment of energy storage and water heater all year round (ACWES). The authors made a special design on the storage tank to adjust the refrigerant capacity in the storage coils under different functions, instead of adding an accumulator to the system. An ACWES prototype, rebuilt from an original split air conditioner, has been finished, and experimental study of the operation processes of the prototype was done from which some important conclusions and suggestions have been made, which were helpful in the primary design and improvement of an ACWES system for potential users. (author)

  20. Experimental study on split air conditioner with new hybrid equipment of energy storage and water heater all year round

    Energy Technology Data Exchange (ETDEWEB)

    Wang Shaowei [School of Mechanical and Power Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China)]. E-mail: wswtop@sjtu.edu.cn; Liu Zhenyan [School of Mechanical and Power Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China); Li Yuan [Qingdao Hisense Group Co. Ltd., Qingdao 266030 (China); Zhao Keke [Qingdao Hisense Group Co. Ltd., Qingdao 266030 (China); Wang Zhigang [Qingdao Hisense Group Co. Ltd., Qingdao 266030 (China)

    2005-11-15

    This paper presents a split air conditioner with a new hybrid equipment of energy storage and water heater all year round (ACWES). The authors made a special design on the storage tank to adjust the refrigerant capacity in the storage coils under different functions, instead of adding an accumulator to the system. An ACWES prototype, rebuilt from an original split air conditioner, has been finished, and experimental study of the operation processes of the prototype was done from which some important conclusions and suggestions have been made, which were helpful in the primary design and improvement of an ACWES system for potential users.

  1. Research progress of socio-economic water cycle in China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    China has made great progress in the study of socio-economic water cycle. She has completed national water resources appraisement and medium to long-term water supply planning. She has been engaging in study on water-deficient regions in North China and Northwest China for about half a century. For solving water shortage problem in northern China, she has put forward the famous South-to-North Water Transferring Projects, which has been set as one of the four biggest national projects in the Tenth Five-Year-Plan period although there are still debates. For promoting water use efficiency, China has been reforming her water management system, including water right system and water price system. There has already been a case of water right purchase. China has also done a lot of research on the interaction between human activity, water and ecosystem. For meeting the need of sustainability and coordinating water resources development and environmental protection, the study of ecological water requirement became very hot in recent years. There are three focuses of socio-economic water cycle study now in China: water transfer projects from the south to the north, water resources management and ecological water requirement.

  2. Drivers and Effects of Virtual Water Cycling

    Science.gov (United States)

    D'Odorico, P.

    2016-12-01

    The increasing global demand for farmland products by the growing and increasingly burgeoning human population is placing unprecedented pressure on the global agricultural system and its water resources. Many regions of the world that are not self-sufficient because of their chronic water scarcity or lack of suitable agricultural land strongly depend on the importation of agricultural commodities and associated embodied (or "virtual") water. International trade, however, may become unreliable when the supplies in the international food market are scarce. As a result, transboundary investments in agricultural land have become a priority for a number of governments and corporations that are trying to expand their agricultural production while securing good profits. This global "land rush" is often driven by the need for a secure access to water resources for agriculture. The globalization of water and land through trade and foreign land acquisitions is leading to a displacement of land use and a disconnection between human populations and the water resources they rely on. Despite the recognized importance of these phenomena in reshaping the patterns of water dependency through teleconnections between consumer behavior and production areas, their effect on global and regional food security, remains poorly quantified. New teleconnections are also emerging from the increasing water use for energy production. Competition in water use for food and energy security constitutes the core of an emerging debate that is generating new questions on the environmental, ethical, economic, and policy implications of human appropriation of water resources. This lecture will examine the ways societies virtually modify their access to water through trade and foreign land acquisitions to meet their growing food and energy needs.

  3. Photocatalytic water splitting for hydrogen generation on cubic, orthorhombic, and tetragonal KNbO3 microcubes

    Science.gov (United States)

    Zhang, Tingting; Zhao, Kun; Yu, Jiaguo; Jin, Jian; Qi, Yang; Li, Huiquan; Hou, Xinjuan; Liu, Gang

    2013-08-01

    Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was

  4. Hydrogen-treated TiO2 nanowire arrays for photoelectrochemical water splitting.

    Science.gov (United States)

    Wang, Gongming; Wang, Hanyu; Ling, Yichuan; Tang, Yuechao; Yang, Xunyu; Fitzmorris, Robert C; Wang, Changchun; Zhang, Jin Z; Li, Yat

    2011-07-13

    We report the first demonstration of hydrogen treatment as a simple and effective strategy to fundamentally improve the performance of TiO(2) nanowires for photoelectrochemical (PEC) water splitting. Hydrogen-treated rutile TiO(2) (H:TiO(2)) nanowires were prepared by annealing the pristine TiO(2) nanowires in hydrogen atmosphere at various temperatures in a range of 200-550 °C. In comparison to pristine TiO(2) nanowires, H:TiO(2) samples show substantially enhanced photocurrent in the entire potential window. More importantly, H:TiO(2) samples have exceptionally low photocurrent saturation potentials of -0.6 V vs Ag/AgCl (0.4 V vs RHE), indicating very efficient charge separation and transportation. The optimized H:TiO(2) nanowire sample yields a photocurrent density of ∼1.97 mA/cm(2) at -0.6 V vs Ag/AgCl, in 1 M NaOH solution under the illumination of simulated solar light (100 mW/cm(2) from 150 W xenon lamp coupled with an AM 1.5G filter). This photocurrent density corresponds to a solar-to-hydrogen (STH) efficiency of ∼1.63%. After eliminating the discrepancy between the irradiance of the xenon lamp and solar light, by integrating the incident-photon-to-current-conversion efficiency (IPCE) spectrum of the H:TiO(2) nanowire sample with a standard AM 1.5G solar spectrum, the STH efficiency is calculated to be ∼1.1%, which is the best value for a TiO(2) photoanode. IPCE analyses confirm the photocurrent enhancement is mainly due to the improved photoactivity of TiO(2) in the UV region. Hydrogen treatment increases the donor density of TiO(2) nanowires by 3 orders of magnitudes, via creating a high density of oxygen vacancies that serve as electron donors. Similar enhancements in photocurrent were also observed in anatase H:TiO(2) nanotubes. The capability of making highly photoactive H:TiO(2) nanowires and nanotubes opens up new opportunities in various areas, including PEC water splitting, dye-sensitized solar cells, and photocatalysis.

  5. Research Update: Photoelectrochemical water splitting and photocatalytic hydrogen production using ferrites (MFe2O4) under visible light irradiation

    OpenAIRE

    Ralf Dillert; Dereje H. Taffa; Michael Wark; Thomas Bredow; Detlef W. Bahnemann

    2015-01-01

    The utilization of solar light for the photoelectrochemical and photocatalytic production of molecular hydrogen from water is a scientific and technical challenge. Semiconductors with suitable properties to promote solar-driven water splitting are a desideratum. A hitherto rarely investigated group of semiconductors are ferrites with the empirical formula MFe2O4 and related compounds. This contribution summarizes the published results of the experimental investigations on the photoelectrochem...

  6. Water Cycling under Climate Change. Interactions between the water cycle, vegetation and a changing (sub)tropical climate

    NARCIS (Netherlands)

    de Boer, H.J.

    2012-01-01

    The water cycle is an essential component of the climate system because the physical properties of water in its liquid, solid and gaseous phases allow for the redistribution of energy in the oceans and atmosphere. At the scale of individual organisms, water and energy are also essential for the bioc

  7. Collaboration essential for an energy neutral urban water cycle.

    Science.gov (United States)

    Frijns, Jos; Mulder, Mirabella; Roorda, Jelle; Schepman, Hans; Voskamp, Tom

    2013-01-01

    Two Dutch water boards prepared a Master Plan with measures to substantially reduce their energy use by 2027. In total, more than 100 measures were identified such as bubble aeration and heat recovery from effluent. Together these measures result in a 90-95% reduction in energy use at the water boards. However, for the whole urban water cycle, thus including the energy required for warm water use in households, the total energy reduction from these measures at the water boards is only 5-6%. To attain the objective to have an energy neutral urban water cycle, collaboration with other sectors such as housing, energy, agriculture and industry will be essential. Active collaboration of the water boards through the incorporation of energy efficient water measures as part of the carbon neutral effort of cities is recognized to be a promising strategy.

  8. Tailoring Multilayered BiVO4 Photoanodes by Pulsed Laser Deposition for Water Splitting.

    Science.gov (United States)

    Murcia-López, Sebastián; Fàbrega, Cristian; Monllor-Satoca, Damián; Hernández-Alonso, María D; Penelas-Pérez, Germán; Morata, Alex; Morante, Juan R; Andreu, Teresa

    2016-02-17

    Pulsed laser deposition (PLD) is proposed as promising technique for the fabrication of multilayered BiVO4-based photoanodes. For this purpose, bare BiVO4 films and two heterojunctions, BiVO4/SnO2 and BiVO4/WO3/SnO2, have been prepared using consecutive ablation of assorted targets in a single batch. The ease, high versatility and usefulness of this technique in engineering the internal configuration of the photoanode with stoichiometric target-to-substrate transfer are demonstrated. The obtained photocurrent densities are among the highest reported values for undoped BiVO4 without oxygen evolution catalysts (OEC). A detailed analysis of the influence of SnO2 and WO3 layers on the charge transport properties because of the changes at the internal FTO/semiconductor interface is performed through transient photocurrent measurements (TPC), showing that the BiVO4/WO3/SnO2 heterostructure attains a significant decrease in the internal losses and reaches high photocurrent values. This study is expected to open the door to the fabrication of other systems based on ternary (or even more complex) metal oxides as photoanodes for water splitting, which is a promising alternative for obtaining materials able to fulfill the different requierements in the development of more efficient systems for this process.

  9. A graded catalytic-protective layer for an efficient and stable water-splitting photocathode

    Science.gov (United States)

    Gu, Jing; Aguiar, Jeffery A.; Ferrere, Suzanne; Steirer, K. Xerxes; Yan, Yong; Xiao, Chuanxiao; Young, James L.; Al-Jassim, Mowafak; Neale, Nathan R.; Turner, John A.

    2017-01-01

    Achieving solar-to-hydrogen efficiencies above 15% is key for the commercial success of photoelectrochemical water-splitting devices. While tandem cells can reach those efficiencies, increasing the catalytic activity and long-term stability remains a significant challenge. Here we show that annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulfide (MoSx) deposited onto GaInP2 results in a photocathode with high catalytic activity (current density of 11 mA cm‑2 at 0 V versus the reversible hydrogen electrode under 1 sun illumination) and stability (retention of 80% of initial photocurrent density over a 20 h durability test) for the hydrogen evolution reaction. Microscopy and spectroscopy reveal that annealing results in a graded MoSx/MoOx/TiO2 layer that retains much of the high catalytic activity of amorphous MoSx but with stability similar to crystalline MoS2. Our findings demonstrate the potential of utilizing a hybridized, heterogeneous surface layer as a cost-effective catalytic and protective interface for solar hydrogen production.

  10. Enabling Overall Water Splitting on Photocatalysts by CO-Covered Noble Metal Co-catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Berto, Tobias F.; Sanwald, Kai E.; Byers, J. Paige; Browning, Nigel D.; Gutiérrez, Oliver Y.; Lercher, Johannes A.

    2016-10-17

    Photocatalytic overall water splitting requires co-catalysts that efficiently promote the generation of H-2 but do not catalyze its reverse oxidation. We demonstrate that CO chemisorbed on metal co-catalysts (Rh, Pt, Pd) suppresses the back reaction while maintaining the rate of H-2 evolution. On Rh/GaN:ZnO, the highest H-2 production rates were obtained with 4-40 mbar of CO, the back reaction remaining suppressed below 7 mbar of O-2. The O-2 and H-2 evolution rates compete with CO oxidation and the back reaction. The rates of all reactions increased with increasing photon absorption. However, due to different dependencies on the rate of charge carrier generation, the selectivities for O-2 and H-2 formation increased in comparison to CO oxidation and the back reaction with increasing photon flux and/or quantum efficiency. Under optimum conditions, the impact of CO to prevent the back reaction is identical to that of a Cr2O3 layer covering the active metal particle.

  11. Efficient photoelectrochemical water splitting over anodized p-type NiO porous films.

    Science.gov (United States)

    Hu, Chenyan; Chu, Kenneth; Zhao, Yihua; Teoh, Wey Yang

    2014-11-12

    NiO photocathodes were fabricated by alkaline etching-anodizing nickel foil in an organic-based electrolyte. The resulting films have a highly macroporous surface structure due to rapid dissolution of the oxide layer as it is formed during the anodization process. We are able to control the films' surface structures by varying the anodization duration and voltage. With an onset potential of +0.53 V versus the reversible hydrogen electrode (RHE), the photocurrent efficiency of the NiO electrodes showed dependencies on their surface roughness factor, which determines the extent of semiconductor-electrolyte interface and the associated quality of the NiO surface sites. A maximum incident photon-to-current conversion efficiency (IPCE(max)) of 22% was obtained from NiO film with a roughness factor of 8.4. Adding an Al2O3 blocking layer minimizes surface charge recombination on the NiO and hence increased the IPCE(max) to 28%. The NiO/Al2O3 films were extremely stable during photoelectrochemical water splitting tests lasting up to 20 h, continuously producing hydrogen and oxygen in the stoichiometric 2:1 ratio. The NiO/Al2O3 and NiO films fabricated using the alkaline anodization process produced 12 and 6 times as much hydrogen, respectively, as those fabricated using commercial NiO nanoparticles.

  12. Hematite-based photoelectrochemical water splitting supported by inverse opal structures of graphene.

    Science.gov (United States)

    Yoon, Ki-Yong; Lee, Jung-Soo; Kim, Kwanghyun; Bak, Chang Hong; Kim, Sun-I; Kim, Jin-Baek; Jang, Ji-Hyun

    2014-12-24

    By coupling α-Fe2O3 with a 3D graphene inverse opal (3D-GIO) conducting electrode, the short diffusion length of carriers and low absorption coefficient in α-Fe2O3 for photoelectrochemical applications were successfully addressed. GIO was directly grown on FTO substrate under low temperature conditions, removing the need for a graphene transfer process. α-Fe2O3 nanoparticles (NPs) were hydrothermally deposited on the surface of GIO, creating α-Fe2O3/GIO. The photocurrent density of α-Fe2O3/GIO in water splitting reactions reached 1.62 mA/cm(2) at 1.5 V vs RHE, which is 1.4 times greater than that of optimized α-Fe2O3. The EIS and IPCE data confirm reduced electron-hole recombination and fast electron transfer processes due to the short distance between active materials and the conducting electrode in the α-Fe2O3/GIO system. Our result may pave the way for designing devices in advanced energy conversion applications as well as a high efficiency hematite-based PEC system.

  13. Metal on metal oxide nanowire Co-catalyzed Si photocathode for solar water splitting.

    Science.gov (United States)

    Sun, Ke; Madsen, Kristian; Andersen, Pål; Bao, Weining; Sun, Zhelin; Wang, Deli

    2012-05-17

    We report a systematic study of Si|ZnO and Si|ZnO| metal photocathodes for effective photoelectrochemical cells and hydrogen generation. Both ZnO nanocrystalline thin films and vertical nanowire arrays were studied. Si|ZnO electrodes showed increased cathodic photocurrents due to improved charge separation by the formation of a p/n junction, and Si|ZnO:Al (n(+)-ZnO) and Si|ZnO(N(2)) (thin films prepared in N(2)/Ar gas) lead to a further increase in cathodic photocurrents. Si|ZnONW (nanowire array) photocathodes dramatically increased the photocurrents and thus photoelectrochemical conversion efficiency due to the enhanced light absorption and enlarged surface area. The ZnO film thickness and ZnO nanowire length were important to the enhancements. A thin metal coating on ZnO showed increased photocurrent due to a catalyzed hydrogen evolution reaction and Ni metal showed comparable catalytic activities to those of Pt and Pd. Moreover, photoelectrochemical instability of Si|ZnO electrodes was minimized by metal co-catalysts. Our results indicate that the metal and ZnO on p-type Si serve as co-catalysts for photoelectrochemical water splitting, which can provide a possible low-cost and scalable method to fabricate high efficiency photocathodes for practical applications in clean solar energy harvesting.

  14. A graded catalytic–protective layer for an efficient and stable water-splitting photocathode

    Energy Technology Data Exchange (ETDEWEB)

    Gu, Jing; Aguiar, Jeffery A.; Ferrere, Suzanne; Steirer, K. Xerxes; Yan, Yong; Xiao, Chuanxiao; Young, James L.; Al-Jassim, Mowafak; Neale, Nathan R.; Turner, John A.

    2017-01-09

    Achieving solar-to-hydrogen efficiencies above 15% is key for the commercial success of photoelectrochemical water splitting devices. While tandem cells can reach those efficiencies, increasing the catalytic activity and long-term stability remains a significant challenge. Here we show that annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulfide (MoSx) deposited onto GaInP2 results in a photocathode with high catalytic activity (current density of 11 mA/cm2 at 0 V vs. the reversible hydrogen electrode under 1 sun illumination) and stability (retention of 80% of initial photocurrent density over a 20 h durability test) for the hydrogen evolution reaction. Microscopy and spectroscopy reveal that annealing results in a graded MoSx/MoOx/TiO2 layer that retains much of the high catalytic activity of amorphous MoSx but with stability similar to crystalline MoS2. Our findings demonstrate the potential of utilizing a hybridized, heterogeneous surface layer as a cost-effective catalytic and protective interface for solar hydrogen production.

  15. Surface Morphology and Growth of Anodic Titania Nanotubes Films: Photoelectrochemical Water Splitting Studies

    Directory of Open Access Journals (Sweden)

    Chin Wei Lai

    2015-01-01

    become the most studied material as they exhibit promising functional properties. In the present study, anodic TiO2 films with different surface morphologies can be synthesized in an organic electrolyte of ethylene glycol (EG by controlling an optimum content of ammonium fluoride (NH4F using electrochemical anodization technique. Based on the results obtained, well-aligned and bundle-free TiO2 nanotube arrays with diameter of 100 nm and length of 8 µm were successfully synthesized in EG electrolyte containing ≈5 wt% of NH4F for 1 h at 60 V. However, formation of nanoporous structure and compact oxide layer would be favored if the content of NH4F was less than 5 wt%. In the photoelectrochemical (PEC water splitting studies, well-aligned TiO2 nanotubular structure exhibited higher photocurrent density of ≈1 mA/cm2 with photoconversion efficiency of ≈2% as compared to the nanoporous and compact oxide layer due to the higher active surface area for the photon absorption to generate more photo-induced electrons during photoexcitation stage.

  16. Electrodeposition of Sn-Ni Alloy Coatings for Water-Splitting Application from Alkaline Medium

    Science.gov (United States)

    Shetty, Sandhya; Hegde, A. Chitharanjan

    2016-09-01

    In this work, Sn-Ni alloy coatings were developed onto the surface of copper from a newly formulated electrolytic bath by a simple and cost-effective electrodeposition technique using gelatin as an additive. The electrocatalytic behavior of coatings deposited at different current densities (c.d.'s) for water-splitting applications, in terms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), has been researched. The experimental results showed that the electrocatalytic activity of Sn-Ni coatings has a close relationship with its composition, surface morphology, and phase structure depending on the c.d. used, supported by scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD) analyses. Cyclic voltammetry and chronopotentiometry techniques have demonstrated that Sn-Ni alloy deposited at 4.0 A dm-2 (having 37.6 wt pct Ni) and 1.0 A dm-2 (having 19.6 wt pct Ni) exhibit, respectively, the highest electrocatalytic behavior for HER and OER in 1.0-M KOH solution. Sn-Ni alloy coatings were found to be stable under working conditions of electrolysis, confirmed by electrochemical corrosion tests. High electrocatalytic activity of Sn-Ni alloy coatings for both HER and OER is specific to their composition, surface morphology, and active surface area.

  17. Enhanced photoelectrochemical water splitting performance of anodic TiO(2) nanotube arrays by surface passivation.

    Science.gov (United States)

    Gui, Qunfang; Xu, Zhen; Zhang, Haifeng; Cheng, Chuanwei; Zhu, Xufei; Yin, Min; Song, Ye; Lu, Linfeng; Chen, Xiaoyuan; Li, Dongdong

    2014-10-08

    One-dimensional anodic titanium oxide nanotube (TONT) arrays provide a direct pathway for charge transport, and thus hold great potential as working electrodes for electrochemical energy conversion and storage devices. However, the prominent surface recombination due to the large amount surface defects hinders the performance improvement. In this work, the surface states of TONTs were passivated by conformal coating of high-quality Al2O3 onto the tubular structures using atomic layer deposition (ALD). The modified TONT films were subsequently employed as anodes for photoelectrochemical (PEC) water splitting. The photocurrent (0.5 V vs Ag/AgCl) recorded under air mass 1.5 global illumination presented 0.8 times enhancement on the electrode with passivation coating. The reduction of surface recombination rate is responsible for the substantially improved performance, which is proposed to have originated from a decreased interface defect density in combination with a field-effect passivation induced by a negative fixed charge in the Al2O3 shells. These results not only provide a physical insight into the passivation effect, but also can be utilized as a guideline to design other energy conversion devices.

  18. Upscaling of integrated photoelectrochemical water-splitting devices to large areas

    Science.gov (United States)

    Turan, Bugra; Becker, Jan-Philipp; Urbain, Félix; Finger, Friedhelm; Rau, Uwe; Haas, Stefan

    2016-09-01

    Photoelectrochemical water splitting promises both sustainable energy generation and energy storage in the form of hydrogen. However, the realization of this vision requires laboratory experiments to be engineered into a large-scale technology. Up to now only few concepts for scalable devices have been proposed or realized. Here we introduce and realize a concept which, by design, is scalable to large areas and is compatible with multiple thin-film photovoltaic technologies. The scalability is achieved by continuous repetition of a base unit created by laser processing. The concept allows for independent optimization of photovoltaic and electrochemical part. We demonstrate a fully integrated, wireless device with stable and bias-free operation for 40 h. Furthermore, the concept is scaled to a device area of 64 cm2 comprising 13 base units exhibiting a solar-to-hydrogen efficiency of 3.9%. The concept and its successful realization may be an important contribution towards the large-scale application of artificial photosynthesis.

  19. Nanocatalysts for Solar Water Splitting and a Perspective on Hydrogen Economy.

    Science.gov (United States)

    Grewe, Tobias; Meggouh, Mariem; Tüysüz, Harun

    2016-01-01

    In this review article, nanocatalysts for solar hydrogen production are the focus of discussion as they can contribute to the development of sustainable hydrogen production in order to meet future energy demands. Achieving this task is subject of scientific aspirations in the field of photo- and photoelectrocatalysis for solar water splitting where systems of single catalysts or tandem configurations are being investigated. In search of a suitable catalyst, a number of crucial parameters are laid out which need to be considered for material design, in particular for nanostructured materials that provide exceptional physical and chemical properties in comparison to their bulk counterparts. Apart from synthetic approaches for nanocatalysts, key parameters and properties of nanostructured photocatalysts such as light absorption, charge carrier generation, charge transport, separation and recombination, and other events that affect nanoscale catalysts are discussed. To provide a deeper understanding of these key parameters and properties, their contribution towards existing catalyst systems is evaluated for photo- and photoelectrocatalytic solar hydrogen evolution. Finally, an insight into hydrogen production processes is given, stressing the current development of sustainable hydrogen sources and presenting a perspective towards a hydrogen-based economy.

  20. Nano-ferrites for water splitting: Unprecedented high photocatalytic hydrogen production under visible light

    KAUST Repository

    Mangrulkar, Priti A.

    2012-01-01

    In the present investigation, hydrogen production via water splitting by nano-ferrites was studied using ethanol as the sacrificial donor and Pt as co-catalyst. Nano-ferrite is emerging as a promising photocatalyst with a hydrogen evolution rate of 8.275 μmol h -1 and a hydrogen yield of 8275 μmol h -1 g -1 under visible light compared to 0.0046 μmol h -1 for commercial iron oxide (tested under similar experimental conditions). Nano-ferrites were tested in three different photoreactor configurations. The rate of hydrogen evolution by nano-ferrite was significantly influenced by the photoreactor configuration. Altering the reactor configuration led to sevenfold (59.55 μmol h -1) increase in the hydrogen evolution rate. Nano-ferrites have shown remarkable stability in hydrogen production up to 30 h and the cumulative hydrogen evolution rate was observed to be 98.79 μmol h -1. The hydrogen yield was seen to be influenced by several factors like photocatalyst dose, illumination intensity, irradiation time, sacrificial donor and presence of co-catalyst. These were then investigated in detail. It was evident from the experimental data that nano-ferrites under optimized reaction conditions and photoreactor configuration could lead to remarkable hydrogen evolution activity under visible light. Temperature had a significant role in enhancing the hydrogen yield. © 2012 The Royal Society of Chemistry.

  1. Ultrathin metal-organic framework array for efficient electrocatalytic water splitting

    Science.gov (United States)

    Duan, Jingjing; Chen, Sheng; Zhao, Chuan

    2017-06-01

    Two-dimensional metal-organic frameworks represent a family of materials with attractive chemical and structural properties, which are usually prepared in the form of bulk powders. Here we show a generic approach to fabricate ultrathin nanosheet array of metal-organic frameworks on different substrates through a dissolution-crystallization mechanism. These materials exhibit intriguing properties for electrocatalysis including highly exposed active molecular metal sites owning to ultra-small thickness of nanosheets, improved electrical conductivity and a combination of hierarchical porosity. We fabricate a nickel-iron-based metal-organic framework array, which demonstrates superior electrocatalytic performance towards oxygen evolution reaction with a small overpotential of 240 mV at 10 mA cm-2, and robust operation for 20,000 s with no detectable activity decay. Remarkably, the turnover frequency of the electrode is 3.8 s-1 at an overpotential of 400 mV. We further demonstrate the promise of these electrodes for other important catalytic reactions including hydrogen evolution reaction and overall water splitting.

  2. Photoelectrochemical water splitting and hydrogen generation by a spontaneously formed InGaN nanowall network

    Energy Technology Data Exchange (ETDEWEB)

    Alvi, N. H., E-mail: nhalvi@isom.upm.es, E-mail: r.noetzel@isom.upm.es; Soto Rodriguez, P. E. D.; Kumar, Praveen; Gómez, V. J.; Aseev, P.; Nötzel, R., E-mail: nhalvi@isom.upm.es, E-mail: r.noetzel@isom.upm.es [ISOM Institute for Systems Based on Optoelectronics and Microtechnology, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Alvi, A. H. [Department of Physics, Government College University, Faisalabad (Pakistan); Alvi, M. A. [Department of Chemistry, Government College University, Faisalabad (Pakistan); Willander, M. [Department of Science and Technology (ITN), Campus Norrköping, Linköping University, 60174 Norrköping (Sweden)

    2014-06-02

    We investigate photoelectrochemical water splitting by a spontaneously formed In-rich InGaN nanowall network, combining the material of choice with the advantages of surface texturing for light harvesting by light scattering. The current density for the InGaN-nanowalls-photoelectrode at zero voltage versus the Ag/AgCl reference electrode is 3.4 mA cm{sup −2} with an incident-photon-to-current-conversion efficiency (IPCE) of 16% under 350 nm laser illumination with 0.075 W·cm{sup −2} power density. In comparison, the current density for a planar InGaN-layer-photoelectrode is 2 mA cm{sup −2} with IPCE of 9% at zero voltage versus the Ag/AgCl reference electrode. The H{sub 2} generation rates at zero externally applied voltage versus the Pt counter electrode per illuminated area are 2.8 and 1.61 μmol·h{sup −1}·cm{sup −2} for the InGaN nanowalls and InGaN layer, respectively, revealing ∼57% enhancement for the nanowalls.

  3. Upscaling of integrated photoelectrochemical water-splitting devices to large areas

    Science.gov (United States)

    Turan, Bugra; Becker, Jan-Philipp; Urbain, Félix; Finger, Friedhelm; Rau, Uwe; Haas, Stefan

    2016-01-01

    Photoelectrochemical water splitting promises both sustainable energy generation and energy storage in the form of hydrogen. However, the realization of this vision requires laboratory experiments to be engineered into a large-scale technology. Up to now only few concepts for scalable devices have been proposed or realized. Here we introduce and realize a concept which, by design, is scalable to large areas and is compatible with multiple thin-film photovoltaic technologies. The scalability is achieved by continuous repetition of a base unit created by laser processing. The concept allows for independent optimization of photovoltaic and electrochemical part. We demonstrate a fully integrated, wireless device with stable and bias-free operation for 40 h. Furthermore, the concept is scaled to a device area of 64 cm2 comprising 13 base units exhibiting a solar-to-hydrogen efficiency of 3.9%. The concept and its successful realization may be an important contribution towards the large-scale application of artificial photosynthesis. PMID:27601181

  4. A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodes

    Science.gov (United States)

    Yang, Jinhui; Cooper, Jason K.; Toma, Francesca M.; Walczak, Karl A.; Favaro, Marco; Beeman, Jeffrey W.; Hess, Lucas H.; Wang, Cheng; Zhu, Chenhui; Gul, Sheraz; Yano, Junko; Kisielowski, Christian; Schwartzberg, Adam; Sharp, Ian D.

    2017-03-01

    Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chemical transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochemical energy conversion can be engineered by plasma-enhanced atomic layer deposition. The collective properties of tailored Co3O4/Co(OH)2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chemically sensitive interfaces. These films comprise compact and continuous nanocrystalline Co3O4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chemically labile Co(OH)2 is introduced to ensure a high concentration of catalytically active sites. Application of this coating to photovoltaic p+n-Si junctions yields best reported performance characteristics for crystalline Si photoanodes.

  5. Electrodeposition of Sn-Ni Alloy Coatings for Water-Splitting Application from Alkaline Medium

    Science.gov (United States)

    Shetty, Sandhya; Hegde, A. Chitharanjan

    2017-02-01

    In this work, Sn-Ni alloy coatings were developed onto the surface of copper from a newly formulated electrolytic bath by a simple and cost-effective electrodeposition technique using gelatin as an additive. The electrocatalytic behavior of coatings deposited at different current densities (c.d.'s) for water-splitting applications, in terms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), has been researched. The experimental results showed that the electrocatalytic activity of Sn-Ni coatings has a close relationship with its composition, surface morphology, and phase structure depending on the c.d. used, supported by scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD) analyses. Cyclic voltammetry and chronopotentiometry techniques have demonstrated that Sn-Ni alloy deposited at 4.0 A dm-2 (having 37.6 wt pct Ni) and 1.0 A dm-2 (having 19.6 wt pct Ni) exhibit, respectively, the highest electrocatalytic behavior for HER and OER in 1.0-M KOH solution. Sn-Ni alloy coatings were found to be stable under working conditions of electrolysis, confirmed by electrochemical corrosion tests. High electrocatalytic activity of Sn-Ni alloy coatings for both HER and OER is specific to their composition, surface morphology, and active surface area.

  6. Protected, back-illuminated silicon photocathodes or photoanodes for water splitting tandem stacks (Conference Presentation)

    Science.gov (United States)

    Vesborg, Peter C.; Bae, Dowon; Seger, Brian J.; Chorkendorff, Ib; Hansen, Ole; Pedersen, Thomas; Mei, Bastian; Frydendal, Rasmus

    2016-10-01

    Silicon is a promising contender in the race for low-bandgap absorbers for use in a solar driven monolithic water splitting cell (PEC). However, given its role as the low-bandgap material the silicon must sit behind the corresponding high-bandgap material and as such, it will be exposed to (red) light from the dry back-side - not from the wet front side, where the electrochemistry takes place.[1,2] Depending on the configuration of the selective contacts (junctions) this may lead to compromises between high absorption and low recombination.[2,3] We discuss the tradeoffs and compare modeling results to measurements. Regardless of configuration, the wet surface of the silicon is prone to passivation or corrosion and must therefore be carefully protected in service in order to remain active. We demonstrate the use of TiO2 as an effective protection layer for both photoanodes and photocathodes in acid electrolyte [4] and NiCoOx for photoanodes in alkaline electrolyte. [3] References: [1]: B. Seger et alia, Energ. Environ. Sci., 7 (8), 2397-2413 (2014), DOI:10.1039/c4ee01335b [2]: D. Bae et alia, Energ. Environ. Sci., 8 (2), 650-660 (2015), DOI: 10.1039/c4ee03723e [3]: D. Bae et alia, submitted, (2016) [4]: B. Mei et alia, J. Phys. Chem. C., 119 (27), 15019-15027 (2015), DOI: 10.1021/acs.jpcc.5b04407

  7. Fe-Cr-Al containing oxide semiconductors as potential solar water-splitting materials.

    Science.gov (United States)

    Sliozberg, Kirill; Stein, Helge S; Khare, Chinmay; Parkinson, Bruce A; Ludwig, Alfred; Schuhmann, Wolfgang

    2015-03-01

    A high-throughput thin film materials library for Fe-Cr-Al-O was obtained by reactive magnetron cosputtering and analyzed with automated EDX and XRD to elucidate compositional and structural properties. An automated optical scanning droplet cell was then used to perform photoelectrochemical measurements of 289 compositions on the library, including electrochemical stability, potentiodynamic photocurrents and photocurrent spectroscopy. The photocurrent onset and open circuit potentials of two semiconductor compositions (n-type semiconducting: Fe51Cr47Al2Ox, p-type semiconducting Fe36.5Cr55.5Al8Ox) are favorable for water splitting. Cathodic photocurrents are observed at 1.0 V vs RHE for the p-type material exhibiting an open circuit potential of 0.85 V vs RHE. The n-type material shows an onset of photocurrents at 0.75 V and an open circuit potential of 0.6 V. The p-type material showed a bandgap of 1.55 eV, while the n-type material showed a bandgap of 1.97 eV.

  8. Efficient solar hydrogen production by photocatalytic water splitting: From fundamental study to pilot demonstration

    Energy Technology Data Exchange (ETDEWEB)

    Jing, Dengwei; Guo, Liejin; Zhao, Liang; Zhang, Ximin; Liu, Huan; Li, Mingtao; Shen, Shaohua; Liu, Guanjie; Hu, Xiaowei; Zhang, Xianghui; Zhang, Kai; Ma, Lijin; Guo, Penghui [State Key Lab of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, 28 Xianning West Road, Xi' an 710049 (China)

    2010-07-15

    Photocatalytic water splitting with solar light is one of the most promising technologies for solar hydrogen production. From a systematic point of view, whether it is photocatalyst and reaction system development or the reactor-related design, the essentials could be summarized as: photon transfer limitations and mass transfer limitations (in the case of liquid phase reactions). Optimization of these two issues are therefore given special attention throughout our study. In this review, the state of the art for the research of photocatalytic hydrogen production, both outcomes and challenges in this field, were briefly reviewed. Research progress of our lab, from fundamental study of photocatalyst preparation to reactor configuration and pilot level demonstration, were introduced, showing the complete process of our effort for this technology to be economic viable in the near future. Our systematic and continuous study in this field lead to the development of a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar rector for the first time. We have demonstrated the feasibility for efficient photocatalytic hydrogen production under direct solar light. The exiting challenges and difficulties for this technology to proceed from successful laboratory photocatalysis set-up up to an industrially relevant scale are also proposed. These issues have been the object of our research and would also be the direction of our study in future. (author)

  9. Self-Supported Nickel Iron Layered Double Hydroxide-Nickel Selenide Electrocatalyst for Superior Water Splitting Activity.

    Science.gov (United States)

    Dutta, Soumen; Indra, Arindam; Feng, Yi; Song, Taeseup; Paik, Ungyu

    2017-09-19

    The design of efficient, low-cost, and stable electrocatalyst systems toward energy conversion is highly demanding for their practical use. Large scale electrolytic water splitting is considered as a promising strategy for clean and sustainable energy production. Herein, we report a self-supported NiFe layered double hydroxide (LDH)-NiSe electrocatalyst by stepwise surface-redox-etching of Ni foam (NF) through a hydrothermal process. The as-prepared NiFe LDH-NiSe/NF catalyst exhibits far better performance in alkaline water oxidation, proton reduction, and overall water splitting compared to NiSex/NF or NiFe LDH/NF. Only 240 mV overpotential is required to obtain a water oxidation current density of 100 mA cm(-2), whereas the same for the hydrogen evolution reaction is 276 mV in 1.0 M KOH. The synergistic effect from NiSe and NiFe LDH leads to the evolution of a highly efficient catalyst system for water splitting by achieving 10 mA cm(-2) current density at only 1.53 V in a two-electrode alkaline electrolyzer. In addition, the designed electrode produces stable performance for a long time even at higher current density to demonstrate its robustness and prospective as a real-life energy conversion system.

  10. The KCaSrTa5O15 photocatalyst with tungsten bronze structure for water splitting and CO2 reduction.

    Science.gov (United States)

    Takayama, Tomoaki; Tanabe, Kentaro; Saito, Kenji; Iwase, Akihide; Kudo, Akihiko

    2014-11-28

    KCaSrTa5O15 with tungsten bronze structure and a band gap of 4.1 eV showed activity for water splitting without cocatalysts. The activity was improved by loading the NiO cocatalyst. The apparent quantum yield of optimized NiO-loaded KCaSrTa5O15 was 2.3% at 254 nm for water splitting. When CO2 gas was bubbled into the reactant aqueous solution, Ag cocatalyst-loaded KCaSrTa5O15 produced CO and H2 as reduction products of CO2 and H2O, respectively, and O2 as an oxidation product of H2O. The carbon source of CO was confirmed to be CO2 molecules by using (13)CO2. The ratio of the number of electrons to that of holes calculated from the amounts of products (CO, H2 and O2) was almost unity. Additionally, the ratio of the turnover number of electrons consumed for CO production to the total number of an Ag atom of the cocatalyst that was the active site for CO2 reduction was 8.6 at 20 h. These results indicate that water was consumed as an electron donor for this photocatalytic CO2 reduction in an aqueous medium. Thus, KCaSrTa5O15 with tungsten bronze structure has arisen as a new photocatalyst that is active for water splitting and CO2 reduction utilizing water as an electron donor.

  11. Gas phase photocatalytic water splitting with Rh2−yCryO3/GaN:ZnO in μ-reactors

    DEFF Research Database (Denmark)

    Dionigi, Fabio; Vesborg, Peter Christian Kjærgaard; Pedersen, Thomas

    2011-01-01

    Activity for photocatalytic water splitting with solar light and water vapour and its dependence on relative humidity has been measured using Rh2−yCryO3–GaN:ZnO catalyst.......Activity for photocatalytic water splitting with solar light and water vapour and its dependence on relative humidity has been measured using Rh2−yCryO3–GaN:ZnO catalyst....

  12. Earth observation Water Cycle Multi-Mission Observation Strategy (WACMOS

    Directory of Open Access Journals (Sweden)

    Z. Su

    2010-10-01

    Full Text Available Observing and monitoring the different components of the global water cycle and their dynamics are essential steps to understand the climate of the Earth, forecast the weather, predict natural disasters like floods and droughts, and improve water resources management. Earth observation technology is a unique tool to provide a global understanding of many of the essential variables governing the water cycle and monitor their evolution over time from global to basin scales. In the coming years an increasing number of Earth observation missions will provide an unprecedented capacity to quantify several of these variables on a routine basis. In this context, the European Space Agency (ESA, in collaboration with the Global Energy and Water Cycle Experiment (GEWEX of the World Climate Research Program (WCRP, launched the Water Cycle Multi-Mission Observation Strategy (WACMOS project in 2009. The project aims at developing and validating a novel set of geo-information products relevant to the water cycle covering the following thematic areas: evapotranspiration, soil moisture, cloud characterization and water vapour. The generation of these products is based on a number of innovative techniques and methods aiming at exploiting the synergies of different types of Earth observation data available today to the science community. This paper provides an overview of the major findings of the project with the ultimate goal of demonstrating the potential of innovative multi-mission based strategies to improve current observations by maximizing the synergistic use of the different types of information provided by the currently available observation systems.

  13. Passivating surface states on water splitting hematite photoanodes with alumina overlayers

    KAUST Repository

    Le Formal, Florian

    2011-01-24

    Hematite is a promising material for inexpensive solar energy conversion via water splitting but has been limited by the large overpotential (0.5-0.6 V) that must be applied to afford high water oxidation photocurrent. This has conventionally been addressed by coating it with a catalyst to increase the kinetics of the oxygen evolution reaction. However, surface recombination at trapping states is also thought to be an important factor for the overpotential, and herein we investigate a strategy to passivate trapping states using conformal overlayers applied by atomic layer deposition. While TiO2 overlayers show no beneficial effect, we find that an ultra-thin coating of Al2O3 reduces the overpotential required with state-of-the-art nano-structured photo-anodes by as much as 100 mV and increases the photocurrent by a factor of 3.5 (from 0.24 mA cm-2 to 0.85 mA cm-2) at +1.0 V vs. the reversible hydrogen electrode (RHE) under standard illumination conditions. The subsequent addition of Co2+ ions as a catalyst further decreases the overpotential and leads to a record photocurrent density at 0.9 V vs. RHE (0.42 mA cm-2). A detailed investigation into the effect of the Al2O3 overlayer by electrochemical impedance and photoluminescence spectroscopy reveals a significant change in the surface capacitance and radiative recombination, respectively, which distinguishes the observed overpotential reduction from a catalytic effect and confirms the passivation of surface states. Importantly, this work clearly demonstrates that two distinct loss processes are occurring on the surface of high-performance hematite and suggests a viable route to individually address them. © The Royal Society of Chemistry 2011.

  14. Direct thermal water splitting by concentrated solar radiation for hydrogen production. Phase O: Proof of concept experiment

    Science.gov (United States)

    Genequand, P.

    1980-01-01

    The direct production of hydrogen from water and solar energy concentrated into a high temperature aperture is described. A solar powered reactor able to dissociate water vapor and to separate the reaction product at high temperature was developed, and direct water splitting has been achieved in a laboratory reactor. Water vapor and radiative heating from a carbon dioxide laser are fed into the reactor, and water vapor enriched in hydrogen and water vapor enriched in oxygen are produced. The enriched water vapors are separated through a separation membrane, a small disc of zirconium dioxide heated to a range of 1800 k to 2800 k. To avoid water vapor condensation within the reactor, the total pressure within the reactor was limited to 0.15 torr. A few modifications would enable the reactor to be operated at an increased pressure of a few torrs. More substantial modifications would allow for a reaction pressure of 0.1 atmosphere.

  15. A bio-inspired, small molecule electron-coupled-proton buffer for decoupling the half-reactions of electrolytic water splitting.

    Science.gov (United States)

    Rausch, Benjamin; Symes, Mark D; Cronin, Leroy

    2013-09-18

    Electron-coupled-proton buffers (ECPBs) allow H2 and O2 evolution to be separated from each other in time during the electrolysis of water. Natural photosynthetic systems achieve an analogous feat during water splitting and employ a range of intermediate redox mediators such as quinone derivatives to aid this process. Drawing on this natural example, we show that a low molecular weight quinone derivative is capable of decoupling H2 evolution from O2 evolution at scale during electrochemical water splitting. This work could significantly lower the cost of ECPBs, paving the way for their more widespread adoption in water splitting.

  16. Combinatorial Development of Water Splitting Catalysts Based on the Oxygen Evolving Complex of Photosystem II

    Energy Technology Data Exchange (ETDEWEB)

    Woodbury, Neal [Arizona State University

    2010-03-31

    The use of methods to create large arrays of potential catalysts for the reaction H2O ½ O2 + 2H+ on the anode of an electrolysis system were investigated. This reaction is half of the overall reaction involved in the splitting of water into hydrogen and oxygen gas. This method consisted of starting with an array of electrodes and developing patterned electrochemical approaches for creating a different, defined peptide at each position in the array. Methods were also developed for measuring the rate of reaction at each point in the array. In this way, the goal was to create and then tests many thousands of possible catalysts simultaneously. This type of approach should lead to an ability to optimize catalytic activity systematically, by iteratively designing and testing new libraries of catalysts. Optimization is important to decrease energy losses (over-potentials) associated with the water splitting reaction and thus for the generation of hydrogen. Most of the efforts in this grant period were focused on developing the chemistry and analytical methods required to create pattern peptide formation either using a photolithography approach or an electrochemical approach for dictating the positions of peptide bond formation. This involved testing a large number of different reactions and conditions. We have been able to find conditions that have allowed us to pattern peptide bond formation on both glass slides using photolithographic methods and on electrode arrays made by the company Combimatrix. Part of this effort involved generating novel approaches for performing mass spectroscopy directly from the patterned arrays. We have also been able to demonstrate the ability to measure current at each electrode due to electrolysis of water. This was performed with customized instrumentation created in collaboration with Combimatrix. In addition, several different molecular designs for peptides that bound metals (primarily Mn) were developed and synthesized and metal

  17. An oxygen-insensitive hydrogen evolution catalyst coated by a molybdenum-based layer for overall water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Esparza, Angel T.; Shinagawa, Tatsuya; Ould-Chikh, Samy; Qureshi, Muhammad; Peng, Xuyuan; Takanabe, Kazuhiro [KAUST Catalysis Center (KCC) and Physical Science and Engineering Division - PSE, King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia); Wei, Nini; Anjum, Dalaver H. [Advanced Nanofabrication, Imaging and Characterization Core Lab, King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia); Clo, Alain [Research Computing, King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia); Weng, Tsu-Chien [Center for High Pressure Science and Technology Advanced Research, Shanghai (China); Nordlund, Dennis; Sokaras, Dimosthenis [Stanford Synchrotron Radiation Lightsource, Menlo Park, CA (United States); Kubota, Jun [Department of Chemical Engineering, Fukuoka University (Japan); Domen, Kazunari [Department of Chemical System Engineering, School of Engineering, The University of Tokyo (Japan)

    2017-05-15

    For overall water-splitting systems, it is essential to establish O{sub 2}-insensitive cathodes that allow cogeneration of H{sub 2} and O{sub 2}. An acid-tolerant electrocatalyst is described, which employs a Mo-coating on a metal surface to achieve selective H{sub 2} evolution in the presence of O{sub 2}. In operando X-ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O{sub 2} gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoO{sub x}/Pt/SrTiO{sub 3} with inhibited water formation from H{sub 2} and O{sub 2}, which is the prevailing back reaction on the bare Pt/SrTiO{sub 3} photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Review of the Two-Step H2O/CO2-Splitting Solar Thermochemical Cycle Based on Zn/ZnO Redox Reactions

    Directory of Open Access Journals (Sweden)

    Aldo Steinfeld

    2010-11-01

    Full Text Available This article provides a comprehensive overview of the work to date on the two‑step solar H2O and/or CO2 splitting thermochemical cycles with Zn/ZnO redox reactions to produce H2 and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-step cycle encompasses: (1 The endothermic dissociation of ZnO to Zn and O2 using concentrated solar energy as the source for high-temperature process heat; and (2 the non-solar exothermic oxidation of Zn with H2O/CO2 to generate H2/CO, respectively; the resulting ZnO is then recycled to the first step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life cycle and economic analyses.

  19. Cycle Simulation of HotWater Fired Absorption Chiller

    Science.gov (United States)

    Esaki, Shuji; Iramina, Kazuyasu; Kobayashi, Takahiro; Ohnou, Masayuki; Kaneko, Toshiyuki; Soga, Takashi

    The design limits were examined to determine the lowest temperature for hot water that can be used as a heat source to drive a hot water fired absorption chiller. Advantage was taken of the fact that the cycle calculation method using the minimum temperature difference is quite effective. This minimum temperature difference was the lower of the two temperature differences used to get the logarithmic mean temperature difference that need to design the evaporator, absorber, condenser and generator in an absorption refrigerator. This report proposes a new solution algorithm employing this minimum temperature difference to make a cycle simulation of the hot water fired absorption chiller. It shows the lowest usable temperature for hot water and makes clear the chilled water and cooling water temperature conditions that can provide the lowest temperature.

  20. Photodeposition of copper and chromia on gallium oxide: the role of co-catalysts in photocatalytic water splitting.

    Science.gov (United States)

    Busser, G Wilma; Mei, Bastian; Pougin, Anna; Strunk, Jennifer; Gutkowski, Ramona; Schuhmann, Wolfgang; Willinger, Marc-Georg; Schlögl, Robert; Muhler, Martin

    2014-04-01

    Split second: The photocatalytic activity of gallium oxide (β-Ga2 O3) depends strongly on the co-catalysts CuOx and chromia, which can be efficiently deposited in a stepwise manner by photoreduction of Cu(2+) and CrO4 (2-). The water-splitting activity can be tuned by varying the Cu loading in the range 0.025-1.5 wt %, whereas the Cr loading is not affecting the rate as long as small amounts (such as 0.05 wt %) are present. Chromia is identified as highly efficient co-catalyst in the presence of CuOx : it is essential for the oxidation of water.

  1. New insight into calcium tantalate nanocomposite photocatalysts for overall water splitting and reforming of alcohols and biomass derivatives

    Science.gov (United States)

    Wang, Ping; Weide, Philipp; Muhler, Martin; Marschall, Roland; Wark, Michael

    2015-10-01

    The photocatalytic properties of different calcium tantalate nanocomposite photocatalysts with optimized phase composition were studied without the addition of any co-catalysts in the photoreforming of different alcohols including the biomass conversion by-product glycerol, as well as after modification with double-layered NiOx (Ni/NiO) co-catalyst in overall water splitting (OWS). Nanocomposite photocatalyst consisting of cubic α-CaTa2O6/orthorhombic β-CaTa2O6 coexisting phases always possesses the highest photocatalytic performance. For overall water splitting, a loading of 0.5 wt. % NiOx exhibits the best activities with stable stoichiometric H2 and O2 evolution rates.

  2. New insight into calcium tantalate nanocomposite photocatalysts for overall water splitting and reforming of alcohols and biomass derivatives

    Directory of Open Access Journals (Sweden)

    Ping Wang

    2015-10-01

    Full Text Available The photocatalytic properties of different calcium tantalate nanocomposite photocatalysts with optimized phase composition were studied without the addition of any co-catalysts in the photoreforming of different alcohols including the biomass conversion by-product glycerol, as well as after modification with double-layered NiOx (Ni/NiO co-catalyst in overall water splitting (OWS. Nanocomposite photocatalyst consisting of cubic α-CaTa2O6/orthorhombic β-CaTa2O6 coexisting phases always possesses the highest photocatalytic performance. For overall water splitting, a loading of 0.5 wt. % NiOx exhibits the best activities with stable stoichiometric H2 and O2 evolution rates.

  3. Visible Light Enabled Photocatalytic Splitting of Water over Spatially Isolated Semiconductors Supported Mesoporous Materials

    Science.gov (United States)

    Peng, Rui

    Hydrogen generation from photocatalytic splitting of water is an ideal scenario that possesses promise for the sustainable development of human society and the establishment of the ultimate "green," infinitely renewable energy system. This work contains a series of novel photocatalytic systems in which the photoactive chromophores and/or the co-catalysts were incorporated into highly periodically cubic-phased MCM-48 mesoporous materials to achieve significantly higher photocatalytic efficiencies compared with conventional semiconductor photocatalysts. Cubic-phased MCM-48 mesoporous materials were chosen as supports to accommodate the photoactive species throughout the entire work. Several unique and iconic properties of these materials, such as large surface area, highly uniform mesoscale pores arrayed in a long-range periodicity, and an interconnected network of three-dimensional sets of pores that were recognized as positive parameters facilitated the photogenerated charge transfer and promoted the photocatalytic performance of the encapsulated photoactive species. It was validated that in the CdS/TiO2-incorporated MCM-48 photocatalytic system, the solar hydrogen conversion efficiency was prevalently governed by the photogenerated electron injection efficiency from the CdS conduction band to that of TiO2. The use of MCM-48 mesoporous host materials enabled the high and even dispersion of both CdS and TiO 2 so that the intimate and sufficient contact between CdS and TiO 2 was realized. In addition, with the presence of both TiO2 and MCM-48 mesoporous support, the photostability of CdS species was dramatically enhanced compared with that of bare CdS or CdS-incorporated MCM-48 photocatalysts. In advance, by loading the RuO2 co-catalyst into the CdS/TiO 2-incorporated MCM-48 photocatalytic system, the photocatalytic splitting of pure water to generate both hydrogen and oxygen under visible light illumination was achieved. In the various Pd-assisted, TiO2-incorporated

  4. Oxygen related recombination defects in Ta{sub 3}N{sub 5} water splitting photoanode

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Gao; Yu, Tao, E-mail: yscfei@nju.edu.cn, E-mail: yutao@nju.edu.cn; Zou, Zhigang [National Laboratory of Solid State Microstructures and Ecomaterials and Renewable Energy Research Center (ERERC) at Department of Physics, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Jiangsu Key Laboratory for Nano Technology, Nanjing 210093 (China); Yan, Shicheng, E-mail: yscfei@nju.edu.cn, E-mail: yutao@nju.edu.cn [National Laboratory of Solid State Microstructures and Ecomaterials and Renewable Energy Research Center (ERERC) at Department of Physics, Nanjing University, Nanjing 210093 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Jiangsu Key Laboratory for Nano Technology, Nanjing 210093 (China); College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093 (China)

    2015-10-26

    A key route to improving the performance of Ta{sub 3}N{sub 5} photoelectrochemical film devices in solar driving water splitting to hydrogen is to understand the nature of the serious recombination of photo-generated carriers. Here, by using the temperature-dependent photoluminescence (PL) spectrum, we confirmed that for the Ta{sub 3}N{sub 5} films prepared by nitriding Ta{sub 2}O{sub 5} precursor, one PL peak at 561 nm originates from deep-level defects recombination of the oxygen-enriched Ta{sub 3}N{sub 5} phases, and another one at 580 nm can be assigned to band recombination of Ta{sub 3}N{sub 5} itself. Both of the two bulk recombination processes may decrease the photoelectrochemical performance of Ta{sub 3}N{sub 5}. It was difficult to remove the oxygen-enriched impurities in Ta{sub 3}N{sub 5} films by increasing the nitriding temperatures due to their high thermodynamically stability. In addition, a broadening PL peak between 600 and 850 nm resulting from oxygen related surface defects was observed by the low-temperature PL measurement, which may induce the surface recombination of photo-generated carriers and can be removed by increasing the nitridation temperature. Our results provided direct experimental evidence to understand the effect of oxygen-related crystal defects in Ta{sub 3}N{sub 5} films on its photoelectric performance.

  5. MWCNT/WO{sub 3} nanocomposite photoanode for visible light induced water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Yousefzadeh, Samira [Physics Department, Sharif University of Technology, P.O. Box 11155-9161, Tehran (Iran, Islamic Republic of); Reyhani, Ali [Physics Department, Faculty of Science, Imam Khomeini International University, P.O. Box 34149-16818, Qazvin (Iran, Islamic Republic of); Naseri, Naimeh [Physics Department, Sharif University of Technology, P.O. Box 11155-9161, Tehran (Iran, Islamic Republic of); Moshfegh, Alireza Z., E-mail: moshfegh@sharif.edu [Physics Department, Sharif University of Technology, P.O. Box 11155-9161, Tehran (Iran, Islamic Republic of); Institute for Nanoscience and Nanotechnology, Sharif University of Technology, P.O. Box 14588-89694, Tehran (Iran, Islamic Republic of)

    2013-08-15

    The Multi-walled carbon nanotube (MWCNT)/WO{sub 3} nanocomposite thin films with different MWCNT’s weight percentages were prepared by sol–gel method as visible light induced photoanode in water splitting reaction. Weight percentage of MWCNT in the all nanocomposite thin films was confirmed by TGA/DSC analysis. According to XPS analysis, oxygenated groups at the surface of the MWCNT and stoichiometric formation of WO{sub 3} thin films were determined, while the crystalline structure of the nanocomposite samples was studied by XRD indicating (0 0 2) peak of MWCNT in the monoclinic phase of WO{sub 3}. The influence of different weight percentage (wt%) of MWCNT on WO{sub 3} photoactivity showed that the electron conductivity, charge transfer and electron life time had improved as compared with the pure WO{sub 3}. Based on linear sweep voltammetry and chronoamperometry measurements, the (1 wt%) MWCNT/WO{sub 3} nanocomposite thin films photoanode has a maximum photocurrent density of ∼4.5 A/m{sup 2} and electron life time of about 57 s. - Graphical abstract: Photocurrent density versus time at constant potential (0.7 V) for the WO{sub 3} films containing different MWCNT weight percentages annealed at 400 °C under 1000 Wm{sup −2} visible photo-illumination. Display Omitted - Highlights: • MWCNT/ WO{sub 3} nanocomposite thin films were synthesized using sol–gel derived method. • TGA/DSC confirmed the weight percentage of MWCNT in the all nanocomposite thin films. • XPS analysis revealed that WO{sub 3} was attached on the oxygenated group of MWCNT surface. • The Highest Photoelectrochemical activity is achieved for (1 wt%)MWCNT/WO{sub 3} thin film.

  6. A simplified theoretical guideline for overall water splitting using photocatalyst particles

    KAUST Repository

    Garcia Esparza, Angel T.

    2015-10-02

    Particulate photocatalytic water splitting is the most disruptive and competitive solution for the direct production of solar fuels. Despite more than four decades of work in the field of photocatalysis using powdered semiconductors decorated with catalyst particles, there is no clear consensus on the factors limiting the solar-to-hydrogen efficiency (STH). To understand the intrinsic limitations of the system, we numerically simulated simplified two-dimensional photocatalytic models using classical semiconductor device equations. This work presents the sensitivity of quantum efficiency (QE) to the various semiconductor properties, such as absorption properties and carrier mobilities, and to the dispersion of catalyst particles, which create heterojunctions, the driving force for charge separation. As a result, a pinch-off effect was prevalent underneath the hydrogen evolution site, suggesting an undesired energetic barrier for electron diffusion to the catalyst. The simulation using the values reported in the literature revealed that the QE was exclusively governed by recombination in the bulk of the photocatalyst particles, hindering the charge separation efficiency before reaching the catalysts on the surface. Using some of the reported parameters, our simulation shows that a typical defective n-type semiconductor particle (∼100 nm) ideally exhibits a QE of <5% in the visible light range per particle, which reaches only approximately 10% in a slurry after 4 consecutive absorbing units (1.4% STH, from simulated solar irradiation). Although the present model contains rigid limitations, we use these trends as an initial guideline to pursue photocatalysis by a design strategy, which may result in possible alternatives to achieve higher efficiencies. © 2016 The Royal Society of Chemistry.

  7. Homo-Tandem Polymer Solar Cells withVOC>1.8 V for Efficient PV-Driven Water Splitting

    KAUST Repository

    Gao, Yangqin

    2016-03-06

    Efficient homo-tandem and triple-junction polymer solar cells are constructed by stacking identical subcells composed of the wide-bandgap polymer PBDTTPD, achieving power conversion efficiencies >8% paralleled by open-circuit voltages >1.8 V. The high-voltage homo-tandem is used to demonstrate PV-driven electrochemical water splitting with an estimated solar-to-hydrogen conversion efficiency of ≈6%. © 2016 WILEY-VCH Verlag GmbH & Co.

  8. Enhanced photoelectrochemical water splitting from Si quantum dots/TiO{sub 2} nanotube arrays composite electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhong [Department of Materials Science, Fudan University, Shanghai 200433 (China); Cui, Xiaoli, E-mail: xiaolicui@fudan.edu.cn [Department of Materials Science, Fudan University, Shanghai 200433 (China); Hao, Hongchen; Lu, Ming [Department of Optical Science and Engineering, and Shanghai Ultra-Precision Optical Manufacturing Engineering Center, Fudan University, Shanghai 200433 (China); Lin, Yuehe [School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164-2920 (United States)

    2015-06-15

    Graphical abstract: Si quantum dots were firstly applied to modify TiO{sub 2} nanotubes and enhanced visible light response was demonstrated for the resulted Si QDs/TiO{sub 2} nanocomposite. Si QDs are promising in photoelectrochemical water splitting and photocatalysis since their low cost, abundance and environmentally-friendliness. - Highlights: • A novel nanocomposite Si QDs/TiO{sub 2} nanotubes was fabricated and characterized. • Enhanced photoelectrochemical water splitting was firstly demonstrated for Si QDs/TiO{sub 2}. • The visible light response of TiO{sub 2} increased with the presence of Si QDs. - Abstract: This work firstly introduced Si quantum dots (QDs) to modify TiO{sub 2} nanotube arrays for photoelectrochemical water splitting. A systematic study using surface and optical characterization tools reveals the nature of the combination of Si QDs and TiO{sub 2} nanotube arrays. Scanning electron microscopy and X-ray photoelectron spectroscopy results show that Si QDs were assembled on the surface of vertically aligned TiO{sub 2} nanotube arrays. The UV–vis diffuse reflectance spectra indicate the improved visible light absorbance. The enhanced photoelectrochemical water splitting was demonstrated under visible light illumination and the photocurrent density was 1.6 times larger than that of pristine TiO{sub 2} electrodes. Electrochemical impedance behavior was measured for the electrodes and the impedance is slightly reduced for the nanocomposite electrode with the presence of Si QDs. This work demonstrated that Si QDs would be a novel and effective choice for improving the utilization of visible light for TiO{sub 2} nanotubes.

  9. Atomic layer deposition grown MO{sub x} thin films for solar water splitting: Prospects and challenges

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Trilok; Lehnen, Thomas; Leuning, Tessa; Mathur, Sanjay, E-mail: sanjay.mathur@uni-koeln.de [Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, D-50939 Cologne (Germany)

    2015-01-15

    The magnitude of energy challenge not only calls for efficient devices but also for abundant, inexpensive, and stable photoactive materials that can enable efficient light harvesting, charge separation and collection, as well as chemical transformations. Photoelectrochemical systems based on semiconductor materials have the possibility to transform solar energy directly into chemical energy the so-called “solar hydrogen.” The current challenge lies in the harvesting of a larger fraction of electromagnetic spectrum by enhancing the absorbance of electrode materials. In this context, atomically precise thin films of metal oxide semiconductors and their multilayered junctions are promising candidates to integrate high surface areas with well-defined electrode–substrate interface. Given its self-limited growth mechanism, the atomic layer deposition (ALD) technique offers a wide range of capabilities to deposit and modify materials at the nanoscale. In addition, it opens new frontiers for developing precursor chemistry that is inevitable to design new processes. Herein, the authors review the properties and potential of metal oxide thin films deposited by ALD for their application in photoelectrochemical water splitting application. The first part of the review covers the basics of ALD processes followed by a brief discussion on the electrochemistry of water splitting reaction. The second part focuses on different MO{sub x} films deposited by atomic layer deposition for water splitting applications; in this section, The authors discuss the most explored MO{sub x} semiconductors, namely, Fe{sub 2}O{sub 3}, TiO{sub 2}, WO{sub 3}, and ZnO, as active materials and refer to their application as protective coatings, conductive scaffolds, or in heterojunctions. The third part deals with the current challenges and future prospects of ALD processed MO{sub x} thin films for water splitting reactions.

  10. Photoelectrochemical water splitting on chromium-doped titanium dioxide nanotube photoanodes prepared by single-step anodizing

    Energy Technology Data Exchange (ETDEWEB)

    Momeni, Mohamad Mohsen, E-mail: mm.momeni@cc.iut.ac.ir; Ghayeb, Yousef

    2015-07-15

    Graphical abstract: Current–potential curves with chopped light measured in 1 M NaOH with a scan rate of 5 mV s{sup −1} for the different samples. - Highlights: • Cr-doped TiO{sub 2} nanotube layers (Cr–TiO{sub 2}NTs) were synthesized by anodizing of titanium in a single-step process. • Photoelectrochemical water splitting of Cr–TiO{sub 2}NTs is higher than that of pure TiO{sub 2} nanotubes (TiO{sub 2}NTs). • Quantity effect of chromium in these composite for photoelectrochemical water splitting is investigated. • Maximum hydrogen production of 37 μL/cm{sup 2} after 240 min is obtained. - Abstract: Cr-doped TiO{sub 2} nanotubes (Cr–TiO{sub 2}NTs) with different amounts of chromium were obtained directly by the electrochemical anodic oxidation of titanium foils in a single-step process using potassium chromate as the chromium source. The effects of chromium amount in anodizing solution on the morphologies, structure, photoabsorption and photoelectrochemical water splitting of the TiO{sub 2} nanotube array film were investigated. Diffuse reflectance spectra showed an increase in the visible absorption relative to undoped TiO{sub 2}NTs. The photoelectrochemical performance was examined under visible irradiation in 1 M NaOH electrolyte. Photo-electrochemical characterization shows that chromium doping efficiently enhances the photo-catalytic water splitting performance of Cr-doped TiO{sub 2} nanotube samples. The sample (Cr–TiO{sub 2}NTs-1) exhibited better photo-catalytic activity than the undoped TiO{sub 2}NTs and Cr–TiO{sub 2}NTs fabricated using other chromium concentrations. This can be attributed to the effective separation of photogenerated electron–hole upon the substitutional introduction of appropriate Cr amount in to the TiO{sub 2} nanotube structure.

  11. Efficient Electrochemical and Photoelectrochemical Water Splitting by a 3D Nanostructured Carbon Supported on Flexible Exfoliated Graphene Foil.

    Science.gov (United States)

    Hou, Yang; Qiu, Ming; Zhang, Tao; Ma, Ji; Liu, Shaohua; Zhuang, Xiaodong; Yuan, Chris; Feng, Xinliang

    2017-01-01

    A novel 3D Co-Nx |P-complex-doped carbon grown on flexible exfoliated graphene foil is designed and constructed for both electrochemical and photoelectrochemical water splitting. The coordination of Co-Nx active centers hybridized with that of neighboring P atoms enhances the electron transfer and optimizes the charge distribution of the carbon surface, which synergistically promotes reaction kinetics by providing more exposed active sites. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. A new class of photo-catalytic materials and a novel principle for efficient water splitting under infrared and visible light - MgB2 as unexpected example

    OpenAIRE

    Kravets, V. G.; A. N. Grigorenko

    2015-01-01

    Water splitting is unanimously recognized as environment friendly, potentially low cost and renewable energy solution based on the future hydrogen economy. Especially appealing is photo-catalytic water splitting whereby a suitably chosen catalyst dramatically improves efficiency of the hydrogen production driven by direct sunlight and allows it to happen even at zero driving potential. Here, we suggest a new class of stable photo-catalysts and the corresponding principle for catalytic water s...

  13. Modeling and remote sensing of human induced water cycle change

    Science.gov (United States)

    Pokhrel, Yadu N.

    2016-04-01

    The global water cycle has been profoundly affected by human land-water management especially during the last century. Since the changes in water cycle can affect the functioning of a wide range of biophysical and biogeochemical processes of the Earth system, it is essential to account for human land-water management in land surface models (LSMs) which are used for water resources assessment and to simulate the land surface hydrologic processes within Earth system models (ESMs). During the last two decades, noteworthy progress has been made in modeling human impacts on the water cycle but sufficient advancements have not yet been made, especially in representing human factors in large-scale LSMs toward integrating them into ESMs. In this study, an integrated modeling framework of continental-scale water cycle, with explicit representation of climate and human induced forces (e.g., irrigation, groundwater pumping) is developed and used to reconstruct the observed water cycle changes in the past and to attribute the observed changes to climatic and human factors. The new model builds upon two different previously developed models: a global LSM called the Human Impacts and GroundWater in the MATSIRO (HiGW-MAT) and a high-resolution regional groundwater model called the LEAF-Hydro-Flood. The model is used to retro-simulate the hydrologic stores and fluxes in close dialogue with in-situ and GRACE satellite based observations at a wide range of river basin scales around the world, with a particular focus on the changes in groundwater dynamics in northwest India, Pakistan, and the High Plains and Central Valley aquifers in the US.

  14. Structural Changes in the Mn4Ca Cluster and the Mechanism of Photosynthetic Water Splitting

    Energy Technology Data Exchange (ETDEWEB)

    Pushkar, Y.; Yano, J.; Sauer, K.; Boussac, A.; Yachandra, V.K.

    2007-10-25

    Photosynthetic water oxidation, where water is oxidized to dioxygen, is a fundamental chemical reaction that sustains the biosphere. This reaction is catalyzed by a Mn4Ca complex in the photosystem II (PS II) oxygen-evolving complex (OEC): a multiproteinassembly embedded in the thylakoid membranes of green plants, cyanobacteria, and algae. The mechanism of photosynthetic water oxidation by the Mn4Ca cluster in photosystem II is the subject of much debate, although lacking structural characterization of the catalytic intermediates. Biosynthetically exchanged Ca/Sr-PS II preparations and x-ray spectroscopy, including extended x-ray absorption fine structure (EXAFS), allowed us to monitor Mn-Mn and Ca(Sr)-Mn distances in the four intermediate S states, S0 through S3, of the catalytic cycle that couples the one-electron photochemistry occurring at the PS II reaction center with the four-electron water-oxidation chemistry taking place at the Mn4Ca(Sr) cluster. We have detected significant changes in the structure of the complex, especially in the Mn-Mn and Ca(Sr)-Mn distances, on the S2-to-S3 and S3-to-S0 transitions. These results implicate the involvement of at least one common bridging oxygen atom between the Mn-Mn and Mn-Ca(Sr) atoms in the O-O bond formation. Because PS II cannot advance beyond the S2 state in preparations that lack Ca(Sr), these results show that Ca(Sr) is one of the critical components in the mechanism of the enzyme. The results also show that Ca is not just a spectator atom involved in providing a structural framework, but is actively involved in the mechanism of water oxidation and represents a rare example of a catalytically active Ca cofactor.

  15. Surface modifications of chalcopyrite CuInS2 thin films for photochatodes in photoelectrochemical water splitting under sunlight irradiation

    Science.gov (United States)

    Gunawan; Haris, A.; Widiyandari, H.; Septina, W.; Ikeda, S.

    2017-02-01

    Copper chalcopyrite semiconductors include a wide range of compounds that are of interest for photoelectrochemical water splitting which enables them to be used as photochatodes for H2 generation. Among them, CuInS2 is one of the most important materials due to its optimum band gap energy for sunlight absorption. In the present study, we investigated the application of CuInS2 fabricated by electrodeposition as photochatodes for water splitting. Thin film of CuInS2 chalcopyrite was formed on Mo-coated glass substrate by stacked electrodeposition of copper and indium followed by sulfurization under H2S flow. The films worked as a H2 liberation electrode under cathodic polarization from a solution containing Na2SO4 after loading Pt deposits on the film. Introduction of an n-type CdS layer by chemical bath deposition on the CuInS2 surface before the Pt loading resulted appreciable improvements of H2 liberation efficiency and a higher photocurrent onset potential. Moreover, the use of In2S3 layer as an alternative n-type layer to the CdS significantly improved the H2 liberation performance: the CuInS2 film modified with In2S3 and Pt deposits worked as an efficient photocathode for photoelectrochemical water splitting.

  16. Regional Quasi-Three-Dimensional Unsaturated-Saturated Water Flow Model Based on a Vertical-Horizontal Splitting Concept

    Directory of Open Access Journals (Sweden)

    Yan Zhu

    2016-05-01

    Full Text Available Due to the high nonlinearity of the three-dimensional (3-D unsaturated-saturated water flow equation, using a fully 3-D numerical model is computationally expensive for large scale applications. A new unsaturated-saturated water flow model is developed in this paper based on the vertical/horizontal splitting (VHS concept to split the 3-D unsaturated-saturated Richards’ equation into a two-dimensional (2-D horizontal equation and a one-dimensional (1-D vertical equation. The horizontal plane of average head gradient in the triangular prism element is derived to split the 3-D equation into the 2-D equation. The lateral flow in the horizontal plane of average head gradient represented by the 2-D equation is then calculated by the water balance method. The 1-D vertical equation is discretized by the finite difference method. The two equations are solved simultaneously by coupling them into a unified nonlinear system with a single matrix. Three synthetic cases are used to evaluate the developed model code by comparing the modeling results with those of Hydrus1D, SWMS2D and FEFLOW. We further apply the model to regional-scale modeling to simulate groundwater table fluctuations for assessing the model applicability in complex conditions. The proposed modeling method is found to be accurate with respect to measurements.

  17. Epitaxial growth of ZnO Nanodisks with large exposed polar facets on nanowire arrays for promoting photoelectrochemical water splitting.

    Science.gov (United States)

    Chen, Haining; Wei, Zhanhua; Yan, Keyou; Bai, Yang; Zhu, Zonglong; Zhang, Teng; Yang, Shihe

    2014-11-01

    Single-crystalline and branched 1D arrays, ZnO nanowires/nanodisks (NWs/NDs) arrays, are fabricated to significantly enhance the performance of photoelectrochemical (PEC) water splitting. The epitaxial growth of the ZnO NDs with large exposed polar facets on ZnO NWs exhibits a laminated structure, which dramatically increases the light scattering capacity of the NWs arrays, especially in the wavelength region around 400 nm. The ND branching of the 1D arrays in the epitaxial fashion not only increase surface area and light utilization, but also support fast charge transport, leading to the considerable increase of photocurrent. Moreover, the tiny size NDs can facilitate charge separation and reduce charge recombination, while the large exposed polar facets of NDs reduce the external potential bias needed for water splitting. These advantages land the ZnO NWs/NDs arrays a four times higher power conversion efficiency than the ZnO NWs arrays. By sensitizing the ZnO NWs/NDs with CdS and CdSe quantum dots, the PEC performance can be further improved. This work advocates a trunk/leaf in forest concept for the single-crystalline NWs/NDs in array with enlarged exposure of polar facets, which opens the way for optimizing light harvesting and charge separation and transport, and thus the PEC water splitting.

  18. Au/TiO2-CeO2 Catalysts for Photocatalytic Water Splitting and VOCs Oxidation Reactions

    Directory of Open Access Journals (Sweden)

    Roberto Fiorenza

    2016-08-01

    Full Text Available Photocatalytic water splitting for H2 production and photocatalytic oxidation of 2-propanol, an example of volatile organic compounds, were investigated over TiO2 catalysts loaded with gold and/or ceria. In the water splitting reaction the presence of gold only slightly affected the performance of TiO2 whereas the presence of CeO2 had a more remarkable positive effect. In the 2-propanol oxidation Au/TiO2 was the most active sample in terms of alcohol conversion whereas Au/TiO2-CeO2 exhibited the highest CO2 yield. On the basis of characterization experiments (X-Ray Diffraction (XRD, Energy Dispersive X-ray Analysis EDX, surface area measurements, Diffuse Reflectance Spectroscopy (DRS and Raman spectroscopy, it was suggested that the interaction of Au with TiO2 causes an increase in the charge separation between the photo-excited electron/hole pairs, leading to an enhanced photocatalytic activity (to acetone over Au/TiO2 and to CO2 over Au/TiO2-CeO2, whereas the presence of ceria, acting as a hole trap, positively mainly affects the formation of hydrogen by water splitting.

  19. Origin of enhanced visible light driven water splitting by (Rh, Sb)-SrTiO3.

    Science.gov (United States)

    Modak, Brindaban; Ghosh, Swapan K

    2015-06-21

    A systematic calculation, using hybrid density functional theory, has been carried out to investigate the origin of the enhancement of photo-conversion efficiency of Rh-doped SrTiO3 with codoping of Sb. In the case of Rh-doped SrTiO3, partially unoccupied states are introduced above the valence band, thus lowering the hole oxidation at the valence band (VB) drastically, which explains the poor oxygen evolution activity of Rh-doped SrTiO3. We show that the partially occupied t2g subset of the Rh 4d orbital is completely filled in the presence of Sb due to the transfer of the extra electron to the Rh center. As a result, acceptor states are completely passivated in the case of (Rh, Sb)-codoped SrTiO3 and a continuous band structure with reduced band gap is formed, which is responsible for the observed enhanced photocatalytic activity of (Rh, Sb)-codoped SrTiO3. We have shown that the relative positions of the band edges of (Rh, Sb)-codoped SrTiO3 with respect to the water redox levels are in favor of the spontaneous release of both hydrogen and oxygen during water splitting, which is consistent with the experimental observation. We have also studied the effect of codoping in different proportions (1 : 2 and 2 : 1) of Rh and Sb. Although 1 : 2 (Rh, Sb)-codoping leads to the formation of a clean band structure with the reduction of the band gap by a larger extent, it shows lower photo-conversion efficiency due to its charge non-compensated nature. In addition, the presence of acceptor states above the VB limits the oxygen evolution efficiency of 2 : 1 (Rh, Sb)-codoped SrTiO3. Thus, the present approach successfully reproduces the experimental features of the Rh-monodoped as well as (Rh, Sb)-codoped SrTiO3 and also explains their origin.

  20. Embryo splitting

    Directory of Open Access Journals (Sweden)

    Karl Illmensee

    2010-04-01

    Full Text Available Mammalian embryo splitting has successfully been established in farm animals. Embryo splitting is safely and efficiently used for assisted reproduction in several livestock species. In the mouse, efficient embryo splitting as well as single blastomere cloning have been developed in this animal system. In nonhuman primates embryo splitting has resulted in several pregnancies. Human embryo splitting has been reported recently. Microsurgical embryo splitting under Institutional Review Board approval has been carried out to determine its efficiency for blastocyst development. Embryo splitting at the 6–8 cell stage provided a much higher developmental efficiency compared to splitting at the 2–5 cell stage. Embryo splitting may be advantageous for providing additional embryos to be cryopreserved and for patients with low response to hormonal stimulation in assisted reproduction programs. Social and ethical issues concerning embryo splitting are included regarding ethics committee guidelines. Prognostic perspectives are presented for human embryo splitting in reproductive medicine.

  1. Power cycles with ammonia-water mixtures as working fluid

    Energy Technology Data Exchange (ETDEWEB)

    Thorin, Eva

    2000-05-01

    It is of great interest to improve the efficiency of power generating processes, i.e. to convert more of the energy in the heat source to power. This is favorable from an environmental point of view and can also be an economic advantage. To use an ammonia-water mixture instead of water as working fluid is a possible way to improve the efficiency of steam turbine processes. This thesis includes studies of power cycles with ammonia-water mixtures as working fluid utilizing different kinds of heat sources for power and heat generation. The thermophysical properties of the mixture are also studied. They play an important role in the calculations of the process performance and for the design of its components, such as heat exchangers. The studies concern thermodynamic simulations of processes in applications suitable for Swedish conditions. Available correlations for the thermophysical properties are compared and their influence on simulations and heat exchanger area predictions is investigated. Measurements of ammonia-water mixture viscosities using a vibrating wire viscometer are also described. The studies performed show that power cycles with ammonia-water mixtures as the working fluid are well suited for utilization of waste heat from industry and from gas engines. The ammonia-water power cycles can give up to 32 % more power in the industrial waste heat application and up to 54 % more power in the gas engine bottoming cycle application compared to a conventional Rankine steam cycle. However, ammonia-water power cycles in small direct-fired biomass-fueled cogeneration plants do not show better performance than a conventional Rankine steam cycle. When different correlations for the thermodynamic properties are used in simulations of a simple ammonia-water power cycle the difference in efficiency is not larger than 4 %, corresponding to about 1.3 percentage points. The differences in saturation properties between the correlations are, however, considerable at high

  2. Research Update: Photoelectrochemical water splitting and photocatalytic hydrogen production using ferrites (MFe2O4 under visible light irradiation

    Directory of Open Access Journals (Sweden)

    Ralf Dillert

    2015-10-01

    Full Text Available The utilization of solar light for the photoelectrochemical and photocatalytic production of molecular hydrogen from water is a scientific and technical challenge. Semiconductors with suitable properties to promote solar-driven water splitting are a desideratum. A hitherto rarely investigated group of semiconductors are ferrites with the empirical formula MFe2O4 and related compounds. This contribution summarizes the published results of the experimental investigations on the photoelectrochemical and photocatalytic properties of these compounds. It will be shown that the potential of this group of compounds in regard to the production of solar hydrogen has not been fully explored yet.

  3. Climatic Features of Cloud Water Distribution and Cycle over China

    Institute of Scientific and Technical Information of China (English)

    LI Xingyu; GUO Xueliang; ZHU Jiang

    2008-01-01

    Analyses of cloud water path (CWP) data over China available from the International Satellite Cloud Climatology Project (ISCCP) are performed for the period 1984-2004. Combined with GPCP precipitation data, cloud water cycle index (CWCI) is also calculated. The climatic distributions of CWP are found to be dependent on large-scale circulation, topographical features, water vapor transport and similar distribution features which are found in CWCI except in the Sichuan Basin. Influenced by the Asia monsoon, CWP over China exhibits very large seasonal variations in different regions. The seasonal cycles of CWCI in different regions are consistent and the largest CWCI occurs in July. The long-term trends of CWP and CWCI are investigated, too. Increasing trends of CWP are found during the period with the largest increase found in winter. The decreasing trends of CWCI dominate most regions of China. The differences in long-term trends between CWP and CWCI suggest that CWP only can influence the variation of CWCI to a certain extent and that other factors need to be involved in cloud water cycle researches. This phenomenon reveals the complexity of the hydrological cycle related to cloud water.

  4. Investigation of advanced nanostructured multijunction photoanodes for enhanced solar hydrogen generation via water splitting

    Science.gov (United States)

    Ishihara, Hidetaka

    As the worldwide demand for fossil-based fuel increases every day and the fossil reserve continues to be depleted, the need for alternative/renewable energy sources has gained momentum. Electric, hybrid, and hydrogen cars have been at the center of discussion lately among consumers, automobile manufacturers, and politicians, alike. The development of a fuel-cell based engine using hydrogen has been an ambitious research area over the last few decades-ever since Fujishima showed that hydrogen can be generated via the solar-energy driven photo-electrolytic splitting of water. Such solar cells are known as Photo-Electro-Chemical (PEC) solar cells. In order to commercialize this technology, various challenges associated with photo-conversion efficiency, chemical corrosion resistance, and longevity need to be overcome. In general, metal oxide semiconductors such as titanium dioxide (TiO 2, titania) are excellent candidates for PEC solar cells. Titania nanotubes have several advantages, including biocompatibility and higher chemical stability. Nevertheless, they can absorb only 5-7% of the solar spectrum which makes it difficult to achieve the higher photo-conversion efficiency required for successful commercial applications. A two-prong approach was employed to enhance photo-conversion efficiency: 1) surface modification of titania nanotubes using plasma treatment and 2) nano-capping of the titania nanotubes using titanium disilicide. The plasma surface treatment with N2 was found to improve the photo-current efficiency of titania nanotubes by 55%. Similarly, a facile, novel approach of nano-capping titania nanotubes to enhance their photocurrent response was also investigated. Electrochemically anodized titania nanotubes were capped by coating a 25 nm layer of titanium disilicide using RF magnetron sputtering technique. The optical properties of titania nanotubes were not found to change due to the capping; however, a considerable increase (40%) in the photocurrent

  5. Plasmonic enhancement of visible-light water splitting with Au-TiO2 composite aerogels.

    Science.gov (United States)

    DeSario, Paul A; Pietron, Jeremy J; DeVantier, Devyn E; Brintlinger, Todd H; Stroud, Rhonda M; Rolison, Debra R

    2013-09-07

    We demonstrate plasmonic enhancement of visible-light-driven splitting of water at three-dimensionally (3D) networked gold-titania (Au-TiO2) aerogels. The sol-gel-derived ultraporous composite nanoarchitecture, which contains 1 to 8.5 wt% Au nanoparticles and titania in the anatase form, retains the high surface area and mesoporosity of unmodified TiO2 aerogels and maintains stable dispersion of the ~5 nm Au guests. A broad surface plasmon resonance (SPR) feature centered at ~550 nm is present for the Au-TiO2 aerogels, but not Au-free TiO2 aerogels, and spans a wide range of the visible spectrum. Gold-derived SPR in Au-TiO2 aerogels cast as films on transparent electrodes drives photoelectrochemical oxidation of aqueous hydroxide and extends the photocatalytic activity of TiO2 from the ultraviolet region to visible wavelengths exceeding 700 nm. Films of Au-TiO2 aerogels in which Au nanoparticles are deposited on pre-formed TiO2 aerogels by a deposition-precipitation method (DP Au/TiO2) also photoelectrochemically oxidize aqueous hydroxide, but less efficiently than 3D Au-TiO2, despite having an essentially identical Au nanoparticle weight fraction and size distribution. For example, 3D Au-TiO2 containing 1 wt% Au is as active as DP Au/TiO2 with 4 wt% Au. The higher photocatalytic activity of 3D Au-TiO2 derives only in part from its ability to retain the surface area and porosity of unmodified TiO2 aerogel. The magnitude of improvement indicates that in the 3D arrangement either a more accessible photoelectrochemical reaction interphase (three-phase boundary) exists or more efficient conversion of excited surface plasmons into charge carriers occurs, thereby amplifying reactivity over DP Au/TiO2. The difference in photocatalytic efficiency between the two forms of Au-TiO2 demonstrates the importance of defining the structure of Au[parallel]TiO2 interfaces within catalytic Au-TiO2 nanoarchitectures.

  6. Semiconductor-Electrocatalyst Interfaces: Theory, Experiment, and Applications in Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Nellist, Michael R; Laskowski, Forrest A L; Lin, Fuding; Mills, Thomas J; Boettcher, Shannon W

    2016-04-19

    Light-absorbing semiconductor electrodes coated with electrocatalysts are key components of photoelectrochemical energy conversion and storage systems. Efforts to optimize these systems have been slowed by an inadequate understanding of the semiconductor-electrocatalyst (sem|cat) interface. The sem|cat interface is important because it separates and collects photoexcited charge carriers from the semiconductor. The photovoltage generated by the interface drives "uphill" photochemical reactions, such as water splitting to form hydrogen fuel. Here we describe efforts to understand the microscopic processes and materials parameters governing interfacial electron transfer between light-absorbing semiconductors, electrocatalysts, and solution. We highlight the properties of transition-metal oxyhydroxide electrocatalysts, such as Ni(Fe)OOH, because they are the fastest oxygen-evolution catalysts known in alkaline media and are (typically) permeable to electrolyte. We describe the physics that govern the charge-transfer kinetics for different interface types, and show how numerical simulations can explain the response of composite systems. Emphasis is placed on "limiting" behavior. Electrocatalysts that are permeable to electrolyte form "adaptive" junctions where the interface energetics change during operation as charge accumulates in the catalyst, but is screened locally by electrolyte ions. Electrocatalysts that are dense, and thus impermeable to electrolyte, form buried junctions where the interface physics are unchanged during operation. Experiments to directly measure the interface behavior and test the theory/simulations are challenging because conventional photoelectrochemical techniques do not measure the electrocatalyst potential during operation. We developed dual-working-electrode (DWE) photoelectrochemistry to address this limitation. A second electrode is attached to the catalyst layer to sense or control current/voltage independent from that of the

  7. Effect of heat recovery water heater system on the performance of residential split air conditioner using hydrocarbon refrigerant (HCR22)

    Science.gov (United States)

    Aziz, A.; Thalal; Amri, I.; Herisiswanto; Mainil, A. K.

    2017-09-01

    This This paper presents the performance of residential split air conditioner (RSAC) using hydrocarbon refrigerant (HCR22) as the effect on the use of heat recovery water heater system (HRWHS). In this study, RSAC was modified with addition of dummy condenser (trombone coil type) as heat recovery water heater system (HRWHS). This HRWHS is installed between a compressor and a condenser by absorbing a part of condenser waste heat. The results show that RSAC with HRWHS is adequate to generate hot water with the temperature range about 46.58˚C - 48.81˚C when compared to without HRWHS and the use of dummy condenser does not give significant effect to the split air conditioner performance. When the use of HRWHS, the refrigerant charge has increase about 19.05%, the compressor power consumption has slightly increase about 1.42% where cooling capacity almost the same with slightly different about 0.39%. The condenser heat rejection is lower about 2.68% and the COP has slightly increased about 1.05% when compared to without HRWHS. The use of HRWHS provide free hot water, it means there is energy saving for heating water without negative impact to the system performance of RSAC.

  8. A new class of photo-catalytic materials and a novel principle for efficient water splitting under infrared and visible light - MgB2 as unexpected example

    CERN Document Server

    Kravets, V G

    2015-01-01

    Water splitting is unanimously recognized as environment friendly, potentially low cost and renewable energy solution based on the future hydrogen economy. Especially appealing is photo-catalytic water splitting whereby a suitably chosen catalyst dramatically improves efficiency of the hydrogen production driven by direct sunlight and allows it to happen even at zero driving potential. Here, we suggest a new class of stable photo-catalysts and the corresponding principle for catalytic water splitting in which infrared and visible light play the main role in producing the photocurrent and hydrogen. The new class of catalysts based on ionic binary metals with layered graphite-like structures which effectively absorb visible and infrared light facilitating the reaction of water splitting, suppress the inverse reaction of ion recombination by separating ions due to internal electric fields existing near alternating layers, provide the sites for ion trapping of both polarities, and finally deliver the electrons an...

  9. Prussian Blue Analogues Derived Penroseite (Ni,Co)Se2 Nanocages Anchored on 3D Graphene Aerogel for Efficient Water Splitting

    KAUST Repository

    Xu, Xun

    2017-08-14

    Efficient water splitting demands highly active, low cost, and robust electrocatalysts. In this study, we report the synthesis of penroseite (Ni,Co)Se2 nanocages anchored on 3D graphene aerogel using Prussian blue analogues as precursor and further their applications in overall water splitting electrolysis. The synergy between the high activity of (Ni,Co)Se2 and the good conductivity of graphene leads to superior performance of the hybrid toward the water splitting in basic solutions. The (Ni,Co)Se2-GA only requires a low cell voltage of 1.60 V to reach the current density of 10 mA cm-2, making the (Ni,Co)Se2-GA hybrid a competitive alternative to noble metal based catalysts for water splitting.

  10. Tracer Cycles and Water Ages in Heterogeneous Catchments and Aquifers

    Science.gov (United States)

    Kirchner, J. W.; Jasechko, S.

    2015-12-01

    Estimates of catchment mean transit times are often based on seasonal cycles of stable isotope tracers in precipitation and streamflow. In many cases these transit time estimates are derived directly from sine-wave fitting to the observed seasonal isotope cycles. Broadly similar results are also obtained from time-domain convolutions or explicit tracer modeling, because here too the dominant tracer signal that these techniques seek to match is the seasonal isotopic cycle. Here I use simple benchmark tests to show that estimates of mean transit times based on seasonal tracer cycles will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. A similar bias arises in estimates of mean transit times in nonstationary catchments. Since typical real-world catchments are both spatially heterogeneous and nonstationary, this analysis poses a fundamental challenge to tracer-based estimates of mean transit times. I propose an alternative storage metric, the fraction of "young water" in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that young water fractions are virtually free of aggregation bias; that is, they can be accurately estimated from tracer cycles in highly heterogeneous mixtures of subcatchments with strongly contrasting transit time distributions. They can also be reliably estimated in strongly nonstationary catchments. Young water fractions can be estimated separately for individual flow regimes, allowing direct determination of how shifts in hydraulic regime alter the fraction of water reaching the stream by fast flowpaths. One can also estimate the chemical composition of idealized "young water" and "old water" end-members, using relationships between young water fractions and solute concentrations across

  11. A Seamless Framework for Global Water Cycle Monitoring and Prediction

    Science.gov (United States)

    Sheffield, J.; Wood, E. F.; Chaney, N.; Fisher, C. K.; Caylor, K. K.

    2013-12-01

    The Global Earth Observation System of Systems (GEOSS) Water Strategy ('From Observations to Decisions') recognizes that 'water is essential for ensuring food and energy security, for facilitating poverty reduction and health security, and for the maintenance of ecosystems and biodiversity', and that water cycle data and observations are critical for improved water management and water security - especially in less developed regions. The GEOSS Water Strategy has articulated a number of goals for improved water management, including flood and drought preparedness, that include: (i) facilitating the use of Earth Observations for water cycle observations; (ii) facilitating the acquisition, processing, and distribution of data products needed for effective management; (iii) providing expertise, information systems, and datasets to the global, regional, and national water communities. There are several challenges that must be met to advance our capability to provide near real-time water cycle monitoring, early warning of hydrological hazards (floods and droughts) and risk assessment under climate change, regionally and globally. Current approaches to monitoring and predicting hydrological hazards are limited in many parts of the world, and especially in developing countries where national capacity is limited and monitoring networks are inadequate. This presentation describes the development of a seamless monitoring and prediction framework at all time scales that allows for consistent assessment of water variability from historic to current conditions, and from seasonal and decadal predictions to climate change projections. At the center of the framework is an experimental, global water cycle monitoring and seasonal forecast system that has evolved out of regional and continental systems for the US and Africa. The system is based on land surface hydrological modeling that is driven by satellite remote sensing precipitation to predict current hydrological conditions

  12. Enhancing the photoelectrochemical water splitting characteristics of titanium and tungsten oxide based materials via doping and sensitization

    Science.gov (United States)

    Gakhar, Ruchi

    To better utilize solar energy for clean energy production, efforts are needed to overcome the natural diurnal variation and the diffuse nature of sunlight. Photoelectrochemical (PEC) hydrogen generation by water splitting is a promising approach to harvest solar energy. Hydrogen gas is a clean and high energy capacity fuel. However, the solar-to-hydrogen conversion efficiency is determined mainly by the properties of the materials employed as photoanodes. Improving the power-conversion efficiency of PEC water splitting requires the design of inexpensive and efficient photoanodes that have strong visible light absorption, fast charge separation, and lower charge recombination rate. In the present study, PEC characteristics of various semiconducting photoelectrodes such as TiO2, WO3 and CuWO4 were investigated. Due to the inherent wide gap, such metal oxides absorb only ultraviolet radiation. Since ultraviolet radiation only composes of 4% of the sun's spectrum, the wide band gap results in lower charge collection and efficiency. Thusto improve optical absorption and charge separation, it is necessary to modify the band gap with low band gap materials.The two approaches followed for modification of band gap are doping and sensitization. Here, TiO2 and WO3 based photoanodes were sensitized with ternary quatum dots, while doping was the primary method utilized to investigate the modification of the band gap of CuWO4. The first part of this dissertation reports the synthesis of ternary quantum dot - sensitized titania nanotube array photoelectrodes. Ternary quantum dots with varying band gaps and composition (MnCdSe, ZnCdSe and CdSSe) were tethered to the surface of TiO2 nanotubes using succcessive ionic layer adsorption and reaction (SILAR) technique. The stoichiometry of ternary quantum dots was estimated to beMn0.095Cd0.95Se, Zn0.16Cd0.84Se and CdS0.54Se0.46. The effect of varying number of sensitization cycles and annealing temperature on optical and

  13. Proton cycling, buffering, and reaction stoichiometry in natural waters

    NARCIS (Netherlands)

    Hofmann, A.F.; Middelburg, J.J.; Soetaert, K.; Wolf-Gladrow, D.A.; Meysman, F.J.R.

    2010-01-01

    Ongoing acidification of the global ocean necessitates a solid understanding of how biogeochemical processes are driving proton cycling and observed pH changes in natural waters. The standard way of calculating the pH evolution of an aquatic system is to specify first how biogeochemical processes af

  14. NiCo2S4 nanowires array as an efficient bifunctional electrocatalyst for full water splitting with superior activity

    Science.gov (United States)

    Liu, Danni; Lu, Qun; Luo, Yonglan; Sun, Xuping; Asiri, Abdullah M.

    2015-09-01

    The present communication reports the topotactic conversion of NiCo2O4 nanowires array on carbon cloth (NiCo2O4 NA/CC) into NiCo2S4 NA/CC, which is used as an efficient bifunctional electrocatalyst for water splitting with good durability and superior activity in 1.0 M KOH. This NiCo2S4 NA/CC electrode produces 100 mA cm-2 at an overpotential of 305 mV for hydrogen evolution and 100 mA cm-2 at an overpotential of 340 mV for oxygen evolution. To afford a 10 mA cm-2 water-splitting current, the alkaline water electrolyzer made from NiCo2S4 NA/CC needs a cell voltage of 1.68 V, which is 300 mV less than that for NiCo2O4 NA/CC, and has good stability.The present communication reports the topotactic conversion of NiCo2O4 nanowires array on carbon cloth (NiCo2O4 NA/CC) into NiCo2S4 NA/CC, which is used as an efficient bifunctional electrocatalyst for water splitting with good durability and superior activity in 1.0 M KOH. This NiCo2S4 NA/CC electrode produces 100 mA cm-2 at an overpotential of 305 mV for hydrogen evolution and 100 mA cm-2 at an overpotential of 340 mV for oxygen evolution. To afford a 10 mA cm-2 water-splitting current, the alkaline water electrolyzer made from NiCo2S4 NA/CC needs a cell voltage of 1.68 V, which is 300 mV less than that for NiCo2O4 NA/CC, and has good stability. Electronic supplementary information (ESI) available: Experimental section and ESI Figures. See DOI: 10.1039/c5nr04064g

  15. CoSe₂ and NiSe₂ Nanocrystals as Superior Bifunctional Catalysts for Electrochemical and Photoelectrochemical Water Splitting.

    Science.gov (United States)

    Kwak, In Hye; Im, Hyung Soon; Jang, Dong Myung; Kim, Young Woon; Park, Kidong; Lim, Young Rok; Cha, Eun Hee; Park, Jeunghee

    2016-03-02

    Catalysts for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER) are central to key renewable energy technologies, including fuel cells and water splitting. Despite tremendous effort, the development of low-cost electrode catalysts with high activity remains a great challenge. In this study, we report the synthesis of CoSe2 and NiSe2 nanocrystals (NCs) as excellent bifunctional catalysts for simultaneous generation of H2 and O2 in water-splitting reactions. NiSe2 NCs exhibit superior electrocatalytic efficiency in OER, with a Tafel slope (b) of 38 mV dec(-1) (in 1 M KOH), and HER, with b = 44 mV dec(-1) (in 0.5 M H2SO4). In comparison, CoSe2 NCs are less efficient for OER (b = 50 mV dec(-1)), but more efficient for HER (b = 40 mV dec(-1)). It was found that CoSe2 NCs contained more metallic metal ions than NiSe2, which could be responsible for their improved performance in HER. Robust evidence for surface oxidation suggests that the surface oxide layers are the actual active sites for OER, and that CoSe2 (or NiSe2) under the surface act as good conductive layers. The higher catalytic activity of NiSe2 is attributed to their oxide layers being more active than those of CoSe2. Furthermore, we fabricated a Si-based photoanode by depositing NiSe2 NCs onto an n-type Si nanowire array, which showed efficient photoelectrochemical water oxidation with a low onset potential (0.7 V versus reversible hydrogen electrode) and high durability. The remarkable catalytic activity, low cost, and scalability of NiSe2 make it a promising candidate for practical water-splitting solar cells.

  16. New class of photocatalytic materials and a novel principle for efficient water splitting under infrared and visible light: MgB2 as unexpected example.

    Science.gov (United States)

    Kravets, V G; Grigorenko, A N

    2015-11-30

    Water splitting is unanimously recognized as environment friendly, potentially low cost and renewable energy solution based on the future hydrogen economy. Especially appealing is photocatalytic water splitting whereby a suitably chosen catalyst dramatically improves efficiency of the hydrogen production driven by direct sunlight and allows it to happen even at zero driving potential. Here, we suggest a new class of stable photocatalysts and the corresponding principle for catalytic water splitting in which infrared and visible light play the main role in producing the photocurrent and hydrogen. The new class of catalysts - ionic or covalent binary metals with layered graphite-like structures - effectively absorb visible and infrared light facilitating the reaction of water splitting, suppress the inverse reaction of ion recombination by separating ions due to internal electric fields existing near alternating layers, provide the sites for ion trapping of both polarities, and finally deliver the electrons and holes required to generate hydrogen and oxygen gases. As an example, we demonstrate conversion efficiency of ~27% at bias voltage Vbias = 0.5V for magnesium diboride working as a catalyst for photoinduced water splitting. We discuss its advantages over some existing materials and propose the underlying mechanism of photocatalytic water splitting by binary layered metals.

  17. Hydrotalcite-like Ni(OH)2 Nanosheets in Situ Grown on Nickel Foam for Overall Water Splitting.

    Science.gov (United States)

    Rao, Yuan; Wang, Yang; Ning, Hui; Li, Peng; Wu, Mingbo

    2016-12-14

    Designing economical and high-efficiency electrocatalysts for overall water splitting is urgently needed but remains a long and arduous task. Herein, we synthesized hydrotalcite-like Ni(OH)2 nanosheets growing on Ni foam (Ni(OH)2/NF) via a facile one-pot hydrothermal method. With the assistance of a rotating oven, Ni(OH)2 nanosheets demonstrate a regular hexagonal morphology and homogeneous distribution. The resultant Ni(OH)2/NF electrode shows superior electrocatalytic activity and durability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as the overall water splitting. The Ni(OH)2/NF electrode delivers 20 mA·cm(-2) at an overpotential of 172 mV for HER, 50 mA·cm(-2) at an overpotential of 330 mV for OER, and 10 mA·cm(-2) at a cell voltage of 1.68 V for water electrolysis in 1.0 M KOH. The present study demonstrates a feasible and effective strategy to prepare highly efficient electrocatalysts for water electrolysis.

  18. Life cycle assessment of advanced waste water treatment

    DEFF Research Database (Denmark)

    Larsen, Henrik Fred; Hansen, Peter Augusto

    .g. pharmaceuticals, heavy metals and endocrine disrupters). As part of this work a holistic based prioritisation among technologies and optimisations is to be done. Tools for this prioritisation include life cycle assessment (LCA) and cost/efficiency. The LCA is performed as a comparative LCA and the concept...... of induced impacts as compared to avoided impacts is introduced in the life cycle impact assessment (LCIA) part. Furthermore, as novel approaches, potential ecotoxicity impact from a high number of micropollutants and the potential impact from pathogens (and whole effluent toxicity) are to be included......The EU FP6 NEPTUNE project is related to the EU Water Framework Directive and the main goal is to develop new and optimize existing waste water treatment technologies (WWTT) and sludge handling methods for municipal waste water. Besides nutrients, a special focus area is micropollutants (e...

  19. Electrolyte engineering toward efficient water splitting at mild pH

    KAUST Repository

    Shinagawa, Tatsuya

    2017-08-28

    The development of processes for the conversion of H2O/CO2 driven by electricity generated in renewable manners is essential to achieve sustainable energy and chemical cycles, in which the electrocatalytic oxygen evolution reaction (OER) is one of the bottlenecks. In this contribution, the influences of the electrolyte molarity and identity on OER at alkaline to neutral pH were investigated at an appreciable current density of ~10 mA cm-2, revealing (1) the clear boundary of reactant switching between H2O/OH- due to the diffusion limitation of OH- and (2) the substantial contribution of the mass transport of the buffered species in buffered mild pH conditions. These findings propose a strategy of electrolyte engineering: tuning the electrolyte properties to maximize the mass-transport flux. The concept was successfully demonstrated for OER as well as overall water electrolysis in buffered mild pH conditions, shedding light on the development of practical solar fuel production systems.

  20. Water Cycle Management: A New Paradigm of Wastewater Reuse and Safety Control

    National Research Council Canada - National Science Library

    Wang, Xiaochang C; Zhang, Chongmiao; Ma, Xiaoyan; Luo, Li

    2015-01-01

    .... It introduces a new water cycle management concept for designing water systems that mimic the hydrological cycle, where reclaimed water is produced, stored/regulated, supplied and used in a semi...

  1. Self-supported nanoporous NiCo2O4 nanowires with cobalt-nickel layered oxide nanosheets for overall water splitting

    Science.gov (United States)

    Yin, Jie; Zhou, Panpan; An, Li; Huang, Liang; Shao, Changwei; Wang, Jun; Liu, Hongyan; Xi, Pinxian

    2016-01-01

    Water splitting via the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in producing H2 and O2 is a very important process in the energy field. Developing an efficient catalyst which can be applied to both HER and OER is crucial. Here, a bifunctional catalyst, CFP/NiCo2O4/Co0.57Ni0.43LMOs, has been successfully fabricated. It exhibits remarkable performance for OER in 0.1 M KOH producing a current density of 10 mA cm-2 at an overpotential of 0.34 V (1.57 V vs. RHE), better than that of the commercial Ir/C (20%) catalyst. Simultaneously, it also exhibits good catalytic performance for HER in 0.5 M H2SO4 producing a current density of 10 mA cm-2 at an overpotential of 52 mV and a Tafel slope of 34 mV dec-1, approaching that of the commercial Pt/C (20%) nanocatalyst. Particularly, CFP/NiCo2O4/Co0.57Ni0.43LMOs present better durability under harsh OER and HER cycling conditions than commercial Ir/C and Pt/C. Furthermore, an H-type electrolyzer was fabricated by applying CFP/NiCo2O4/Co0.57Ni0.43LMOs as the cathode and anode electrocatalyst, which can be driven by a single-cell battery. This bifunctional catalyst will be very promising in overall water splitting.Water splitting via the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in producing H2 and O2 is a very important process in the energy field. Developing an efficient catalyst which can be applied to both HER and OER is crucial. Here, a bifunctional catalyst, CFP/NiCo2O4/Co0.57Ni0.43LMOs, has been successfully fabricated. It exhibits remarkable performance for OER in 0.1 M KOH producing a current density of 10 mA cm-2 at an overpotential of 0.34 V (1.57 V vs. RHE), better than that of the commercial Ir/C (20%) catalyst. Simultaneously, it also exhibits good catalytic performance for HER in 0.5 M H2SO4 producing a current density of 10 mA cm-2 at an overpotential of 52 mV and a Tafel slope of 34 mV dec-1, approaching that of the commercial Pt/C (20%) nanocatalyst

  2. Increasing water cycle extremes in California and in relation to ENSO cycle under global warming.

    Science.gov (United States)

    Yoon, Jin-Ho; Wang, S-Y Simon; Gillies, Robert R; Kravitz, Ben; Hipps, Lawrence; Rasch, Philip J

    2015-10-21

    Since the winter of 2013-2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)--in particular, extreme El Niño and La Niña events that modulate California's climate not only through its warm and cold phases but also its precursor patterns.

  3. Down-conversion photoluminescence sensitizing plasmonic silver nanoparticles on ZnO nanorods to generate hydrogen by water splitting photochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Kung, Po-Yen; Huang, Li-Wen; Shen, Tin-Wei; Wang, Wen-Lin; Su, Yen-Hsun [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China); Lin, Melody I. [Department of Physics, University of California, Berkeley, California, 94720 (United States)

    2015-01-12

    Silver nanoparticles fabricated onto the surface of the ZnO nanorods form the photoanode and generate photoelectric current due to surface plasmon resonance, which serves as anode electrodes in photoelectrochemical hydrogen production. In order to increase the absorption spectrum of photoanode, organic pigments were utilized as photo-sensitizers to generate down-conversion photoluminescence to excite surface plasmon resonances of silver nanoparticles. The way of using light to carry the energy in electronic scattering regime runs the system for the enhancement of solar water splitting efficiency. It was significantly tuned in environmentally sustainable applications for power generation and development of alternative energy.

  4. Water pulses and biogeochemical cycles in arid and semiarid ecosystems.

    Science.gov (United States)

    Austin, Amy T; Yahdjian, Laura; Stark, John M; Belnap, Jayne; Porporato, Amilcare; Norton, Urszula; Ravetta, Damián A; Schaeffer, Sean M

    2004-10-01

    The episodic nature of water availability in arid and semiarid ecosystems has significant consequences on belowground carbon and nutrient cycling. Pulsed water events directly control belowground processes through soil wet-dry cycles. Rapid soil microbial response to incident moisture availability often results in almost instantaneous C and N mineralization, followed by shifts in C/N of microbially available substrate, and an offset in the balance between nutrient immobilization and mineralization. Nitrogen inputs from biological soil crusts are also highly sensitive to pulsed rain events, and nitrogen losses, particularly gaseous losses due to denitrification and nitrate leaching, are tightly linked to pulses of water availability. The magnitude of the effect of water pulses on carbon and nutrient pools, however, depends on the distribution of resource availability and soil organisms, both of which are strongly affected by the spatial and temporal heterogeneity of vegetation cover, topographic position and soil texture. The 'inverse texture hypothesis' for net primary production in water-limited ecosystems suggests that coarse-textured soils have higher NPP than fine-textured soils in very arid zones due to reduced evaporative losses, while NPP is greater in fine-textured soils in higher rainfall ecosystems due to increased water-holding capacity. With respect to belowground processes, fine-textured soils tend to have higher water-holding capacity and labile C and N pools than coarse-textured soils, and often show a much greater flush of N mineralization. The result of the interaction of texture and pulsed rainfall events suggests a corollary hypothesis for nutrient turnover in arid and semiarid ecosystems with a linear increase of N mineralization in coarse-textured soils, but a saturating response for fine-textured soils due to the importance of soil C and N pools. Seasonal distribution of water pulses can lead to the accumulation of mineral N in the dry season

  5. A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cells

    KAUST Repository

    Kageshima, Yosuke

    2016-04-18

    A novel “photovoltaics (PV) + electrolyzer” concept is presented using a simple, small, and completely stand-alone non-biased device for solar-driven overall water splitting. Three or four spherical-shaped p-n junction silicon balls were successfully connected in series, named “SPHELAR.” SPHELAR possessed small projected areas of 0.20 (3PVs) and 0.26 cm2 (4PVs) and exhibited working voltages sufficient for water electrolysis. Impacts of the configuration on the PV module performance were carefully analyzed, revealing that a drastic increase in the photocurrent (≈20%) was attained by the effective utilization of a reflective sheet. Separate investigations on the electrocatalyst performance showed that non-noble metal based materials with reasonably small sizes (<0.80 cm2) exhibited substantial currents at the PV working voltage. By combining the observations of the PV characteristics, light management and electrocatalyst performance, solar-driven overall water splitting was readily achieved, reaching solar-to-hydrogen efficiencies of 7.4% (3PVs) and 6.4% (4PVs).

  6. Teaching Systems Thinking in the Context of the Water Cycle

    Science.gov (United States)

    Lee, Tammy D.; Gail Jones, M.; Chesnutt, Katherine

    2017-06-01

    Complex systems affect every part of our lives from the ecosystems that we inhabit and share with other living organisms to the systems that supply our water (i.e., water cycle). Evaluating events, entities, problems, and systems from multiple perspectives is known as a systems thinking approach. New curriculum standards have made explicit the call for teaching with a systems thinking approach in our science classrooms. However, little is known about how elementary in-service or pre-service teachers understand complex systems especially in terms of systems thinking. This mixed methods study investigated 67 elementary in-service teachers' and 69 pre-service teachers' knowledge of a complex system (e.g., water cycle) and their knowledge of systems thinking. Semi-structured interviews were conducted with a sub-sample of participants. Quantitative and qualitative analyses of content assessment data and questionnaires were conducted. Results from this study showed elementary in-service and pre-service teachers applied different levels of systems thinking from novice to intermediate. Common barriers to complete systems thinking were identified with both in-service and pre-service teachers and included identifying components and processes, recognizing multiple interactions and relationships between subsystems and hidden dimensions, and difficulty understanding the human impact on the water cycle system.

  7. Changes in continental Europe water cycle in a changing climate

    Science.gov (United States)

    Rouholahnejad, Elham; Schirmer, Mario; Abbaspour, Karim

    2015-04-01

    Changes in atmospheric water vapor content provide strong evidence that the water cycle is already responding to a warming climate. According to IPCC's last report on Climate Change (AR5), the water cycle is expected to intensify in a warmer climate as the atmosphere can hold more water vapor. This changes the frequency of precipitation extremes, increases evaporation and dry periods, and effects the water redistribution in land. This process is represented by most global climate models (GCMs) by increased summer dryness and winter wetness over large areas of continental mid to high latitudes in the Northern Hemisphere, associated with a reduction in water availability at continental scale. Observing changes in precipitation and evaporation directly and at continental scale is difficult, because most of the exchange of fresh water between the atmosphere and the surface happens the oceans. Long term precipitation records are available only from over the land and there are no measurement of evaporation or redistribution of precipitation over the land area. On the other hand, understanding the extent of climate change effects on various components of the water cycle is of strategic importance for public, private sectors, and policy makers when it comes to fresh water management. In order to better understand the extent of climate change impacts on water resources of continental Europe, we developed a distributed hydrological model of Europe at high spatial and temporal resolution using the Soil and Water Assessment Tool (SWAT). The hydrological model was calibrated for 1970 to 2006 using daily observation of streamflow and nitrate loads from 360 gauging stations across Europe. A vegetation growth routine was added to the model to better simulate evapotranspiration. The model results were calibrated with available agricultural crop yield data from other sources. As of future climate scenarios, we used the ISI-MIP project results which provides bias-corrected climate

  8. IS BLOOD LACTATE REMOVAL DURING WATER IMMERSED CYCLING FASTER THAN DURING CYCLING ON LAND?

    Directory of Open Access Journals (Sweden)

    Fabrízio Di Masi

    2007-06-01

    Full Text Available The aim of the present study was to compare lactate removal during active recovery performed during cycling in water immersion (CW and during cycling on land (CL, after a similar exercise bout in male adults. Eleven healthy and physically active men, aged between 20 and 26 years old participated in the experiment. Before the experimental tests, the ventilatory threshold of the subjects was determined. Each subject completed the experimental tests twice, with one week separating the two periods of experiment. The subjects exercised on the treadmill during 6 min at a speed 10% above the speed corresponding to their ventilatory threshold. Subsequently, the subjects recovered from the exercise bout either on a stationary bike (CL or on a aquatic-specific bike (CW. On the subsequent week the subjects performed the same protocol but with a different recovery condition. Recovery condition assignment for the first test was counterbalanced (six subjects started with one condition and five with the other. Capillary blood samples were collected after each test and during the recovery period (at 3, 6, 9 and 15 minutes and blood lactate was measured. The blood lactate values during CW were lower than during CL and significant differences were observed at the 6th minute (p < 0.05 and at the 15th minute of recovery (p < 0.05. Therefore, we may conclude that active recovery using cycling in water immersion may be more efficient than cycling on land for blood lactate removal.

  9. Enhancing water cycle measurements for future hydrologic research

    Science.gov (United States)

    Loescher, H.W.; Jacobs, J.M.; Wendroth, O.; Robinson, D.A.; Poulos, G.S.; McGuire, K.; Reed, P.; Mohanty, B.P.; Shanley, J.B.; Krajewski, W.

    2007-01-01

    The Consortium of Universities for the Advancement of Hydrologic Sciences, Inc., established the Hydrologic Measurement Facility to transform watershed-scale hydrologic research by facilitating access to advanced instrumentation and expertise that would not otherwise be available to individual investigators. We outline a committee-based process that determined which suites of instrumentation best fit the needs of the hydrological science community and a proposed mechanism for the governance and distribution of these sensors. Here, we also focus on how these proposed suites of instrumentation can be used to address key scientific challenges, including scaling water cycle science in time and space, broadening the scope of individual subdisciplines of water cycle science, and developing mechanistic linkages among these subdisciplines and spatio-temporal scales. ?? 2007 American Meteorological Society.

  10. Water cycles in closed ecological systems: effects of atmospheric pressure

    Science.gov (United States)

    Rygalov, Vadim Y.; Fowler, Philip A.; Metz, Joannah M.; Wheeler, Raymond M.; Bucklin, Ray A.; Sager, J. C. (Principal Investigator)

    2002-01-01

    In bioregenerative life support systems that use plants to generate food and oxygen, the largest mass flux between the plants and their surrounding environment will be water. This water cycle is a consequence of the continuous change of state (evaporation-condensation) from liquid to gas through the process of transpiration and the need to transfer heat (cool) and dehumidify the plant growth chamber. Evapotranspiration rates for full plant canopies can range from 1 to 10 L m-2 d-1 (1 to 10 mm m-2 d-1), with the rates depending primarily on the vapor pressure deficit (VPD) between the leaves and the air inside the plant growth chamber. VPD in turn is dependent on the air temperature, leaf temperature, and current value of relative humidity (RH). Concepts for developing closed plant growth systems, such as greenhouses for Mars, have been discussed for many years and the feasibility of such systems will depend on the overall system costs and reliability. One approach for reducing system costs would be to reduce the operating pressure within the greenhouse to reduce structural mass and gas leakage. But managing plant growth environments at low pressures (e.g., controlling humidity and heat exchange) may be difficult, and the effects of low-pressure environments on plant growth and system water cycling need further study. We present experimental evidence to show that water saturation pressures in air under isothermal conditions are only slightly affected by total pressure, but the overall water flux from evaporating surfaces can increase as pressure decreases. Mathematical models describing these observations are presented, along with discussion of the importance for considering "water cycles" in closed bioregenerative life support systems.

  11. Terrestrial water cycle and the impact of climate change.

    Science.gov (United States)

    Tao, Fulu; Yokozawa, Masayuki; Hayashi, Yousay; Lin, Erda

    2003-06-01

    The terrestrial water cycle and the impact of climate change are critical for agricultural and natural ecosystems. In this paper, we assess both by running a macro-scale water balance model under a baseline condition and 2 General Circulation Model (GCM)-based climate change scenarios. The results show that in 2021-2030, water demand will increase worldwide due to climate change. Water shortage is expected to worsen in western Asia, the Arabian Peninsula, northern and southern Africa, northeastern Australia, southwestern North America, and central South America. A significant increase in surface runoff is expected in southern Asia and a significant decrease is expected in northern South America. These changes will have implications for regional environment and socioeconomics.

  12. Terrestrial Water Cycle and the Impact of Climate Change

    Energy Technology Data Exchange (ETDEWEB)

    Fulu Tao; Erda Lin [Chinese Academy of Agricultural Sciences, Beijing (China). Agrometeorology Inst.; Yokozawa, Masayuki; Hayashi, Yousay [National Inst. for Agro-Environmental Sciences, Tsukuba (Japan)

    2003-06-01

    The terrestrial water cycle and the impact of climate change are critical for agricultural and natural ecosystems. In this paper, we assess both by running a macro-scale water balance model under a baseline condition and 2 General Circulation Model (GCM)-based climate change scenarios. The results show that in 2021-2030, water demand will increase worldwide due to climate change. Water shortage is expected to worsen in western Asia, the Arabian Peninsula, northern and southern Africa, northeastern Australia, southwestern North America, and central South America. A significant increase in surface runoff is expected in southern Asia and a significant decrease is expected in northern South America. These changes will have implications for regional environment and socio-economics.

  13. Climate change and the water cycle in newly irrigated areas.

    Science.gov (United States)

    Abrahão, Raphael; García-Garizábal, Iker; Merchán, Daniel; Causapé, Jesús

    2015-02-01

    Climate change is affecting agriculture doubly: evapotranspiration is increasing due to increments in temperature while the availability of water resources is decreasing. Furthermore, irrigated areas are expanding worldwide. In this study, the dynamics of climate change impacts on the water cycle of a newly irrigated watershed are studied through the calculation of soil water balances. The study area was a 752-ha watershed located on the left side of the Ebro river valley, in Northeast Spain. The soil water balance procedures were carried out throughout 1827 consecutive days (5 years) of hydrological and agronomical monitoring in the study area. Daily data from two agroclimatic stations were used as well. Evaluation of the impact of climate change on the water cycle considered the creation of two future climate scenarios for comparison: 2070 decade with climate change and 2070 decade without climate change. The main indicators studied were precipitation, irrigation, reference evapotranspiration, actual evapotranspiration, drainage from the watershed, and irrigation losses. The aridity index was also applied. The results represent a baseline scenario in which adaptation measures may be included and tested to reduce the impacts of climate change in the studied area and other similar areas.

  14. WaterNet: The NASA water cycle solutions network - Danubian regional applications

    Science.gov (United States)

    Matthews, Dave; Brilly, Mitja; Kobold, Mira; Zagar, Mark; Houser, Paul

    2008-11-01

    WaterNet is a new international network of researchers, stakeholders, and end-users of remote sensing tools that will benefit the water resources management community. This paper provides an overview and it discusses the concept of solutions networks focusing on the WaterNet. It invites Danubian research and applications teams to join our WaterNet network. The NASA Water cycle Solutions Network's goal is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend NASA research results to augment decision support tools and meet national needs. Our team will develop WaterNet by engaging relevant NASA water cycle research resources and community-of-practice organizations, to develop what we term an "actionable database" that can be used to communicate and connect NASA Water cycle research Results (NWRs) towards the improvement of water-related Decision Support Tools (DSTs). Recognizing that the European Commission and European Space Agency have also developed many related Water Research products (EWRs), we seek to learn about these and network with the EU teams to include their information in the WaterNet actionable data base and Community of Practice. WaterNet will then develop strategies to connect researchers and decision-makers via innovative communication strategies, improved user access to NASA and EU - Danubian resources, improved water cycle research community appreciation for user requirements, improved policymaker, management and stakeholder knowledge of research and application products, and improved identification of pathways for progress. Finally, WaterNet will develop relevant benchmarking and metrics, to understand the network's characteristics, to optimize its performance, and to establish sustainability. This paper provides examples of several NASA products based on remote sensing and land data assimilation systems that integrate remotely sensed and in

  15. WaterNet: The NASA water cycle solutions network - Danubian regional applications

    Energy Technology Data Exchange (ETDEWEB)

    Matthews, Dave [Hydromet DSS, LLC, Silverthorne, CO 80498-1848 (United States); Brilly, Mitja [FGG University of Ljubljana (Slovenia); Kobold, Mira; Zagar, Mark [Environmental Agency of the Republic of Slovenia, Ljubljana (Slovenia); Houser, Paul [Center for Research on Environment and Water and George Mason University, Calverton, MD 20705 (United States)], E-mail: hydrometdss@comcast.net

    2008-11-01

    WaterNet is a new international network of researchers, stakeholders, and end-users of remote sensing tools that will benefit the water resources management community. This paper provides an overview and it discusses the concept of solutions networks focusing on the WaterNet. It invites Danubian research and applications teams to join our WaterNet network. The NASA Water cycle Solutions Network's goal is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend NASA research results to augment decision support tools and meet national needs. Our team will develop WaterNet by engaging relevant NASA water cycle research resources and community-of-practice organizations, to develop what we term an 'actionable database' that can be used to communicate and connect NASA Water cycle research Results (NWRs) towards the improvement of water-related Decision Support Tools (DSTs). Recognizing that the European Commission and European Space Agency have also developed many related Water Research products (EWRs), we seek to learn about these and network with the EU teams to include their information in the WaterNet actionable data base and Community of Practice. WaterNet will then develop strategies to connect researchers and decision-makers via innovative communication strategies, improved user access to NASA and EU - Danubian resources, improved water cycle research community appreciation for user requirements, improved policymaker, management and stakeholder knowledge of research and application products, and improved identification of pathways for progress. Finally, WaterNet will develop relevant benchmarking and metrics, to understand the network's characteristics, to optimize its performance, and to establish sustainability. This paper provides examples of several NASA products based on remote sensing and land data assimilation systems that integrate

  16. Trade-Offs between Energy Saving and Reliability in Low Duty Cycle Wireless Sensor Networks Using a Packet Splitting Forwarding Technique

    Directory of Open Access Journals (Sweden)

    Leonardi Alessandro

    2010-01-01

    Full Text Available One of the challenging topics and design constraints in Wireless Sensor Networks (WSNs is the reduction of energy consumption because, in most application scenarios, replacement of power resources in sensor devices might be unfeasible. In order to minimize the power consumption, some nodes can be put to sleep during idle times and wake up only when needed. Although it seems the best way to limit the consumption of energy, other performance parameters such as network reliability have to be considered. In a recent paper, we introduced a new forwarding algorithm for WSNs based on a simple splitting procedure able to increase the network lifetime. The forwarding technique is based on the Chinese Remainder Theorem and exhibits very good results in terms of energy efficiency and complexity. In this paper, we intend to investigate a trade-off between energy efficiency and reliability of the proposed forwarding scheme when duty-cycling techniques are considered too.

  17. Band-gap determination from diffuse reflectance measurements of semiconductor films, and application to photoelectrochemical water-splitting

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, A.B. [CSIRO Industrial Physics, P.O. Box 218, Lindfield, NSW 2070 (Australia); CSIRO Energy Transformed National Research Flagship, PO Box 330, Newcastle, NSW 2300 (Australia)

    2007-09-06

    Measurements of the diffuse reflectance of TiO{sub 2} semiconductor coatings, such as are used for water splitting, are analysed using the Kubelka-Munk radiative transfer model. The widely used practice of determining the band gap of the coating directly from the diffuse reflectance is found to be inaccurate, since the diffuse reflectance depends on parameters such as the thickness, refractive index and surface roughness of the coating. However, it is shown that the absorption coefficient can be derived from the diffuse reflectance using an inversion method; the band gap can then be obtained from the absorption coefficient. Finally, the diffuse reflectance of carbon-doped TiO{sub 2} presented by Khan et al. [Science 297 (2002) 2243-2245] is analysed; it is found that while the band-gap wavelength is extended into the visible region, it is overestimated. Moreover, light at visible wavelengths is only very weakly absorbed, and is expected to make only a minor contribution to the water-splitting efficiency. (author)

  18. Water splitting over new niobate photocatalysts with tungsten-bronze-type structure and effect of transition metal-doping.

    Science.gov (United States)

    Miseki, Yugo; Kudo, Akihiko

    2011-02-18

    Photophysical properties and photocatalytic activities for water splitting over KM(2)Nb(5)O(15) (M = Sr and Ba) and K(2)LnNb(5)O(15) (Ln = La, Pr, Nd, and Sm) with tungsten bronze-type structure were investigated. Single phases of KM(2)Nb(5)O(15) and K(2)LnNb(5)O(15) were successfully prepared by solid-state reaction (SSR) method and polymerizable complex (PC) method. The band gaps of these niobates were estimated to be 3.1-3.5 eV. These metal oxides loaded with an activated NiO(x) cocatalyst showed photocatalytic activities for water splitting into H(2) and O(2) under UV irradiation. When K(2)LaNb(5)O(15) was doped by Rh ions, a new visible-light absorption band was observed around 400-500 nm in addition to the band gap absorption band of the K(2)LaNb(5)O(15) host. K(2)LaNb(5)O(15):Rh showed photocatalytic activities for H(2) or O(2) evolution from an aqueous solution containing a sacrificial reagent under visible-light irradiation.

  19. Hydrogen-doped Brookite TiO2 Nanobullets Array as a Novel Photoanode for Efficient Solar Water Splitting

    Science.gov (United States)

    Choi, Mingi; Lee, June Ho; Jang, Youn Jeong; Kim, Donghyung; Lee, Jae Sung; Jang, Hyun Myung; Yong, Kijung

    2016-01-01

    As a representative photocatalyst for photoelectrochemical solar water splitting, TiO2 has been intensively studied but most researches have focused on the rutile and anatsase phases because brookite, another important crystalline polymorph of TiO2, rarely exists in nature and is difficult to synthesize. In this work, hydrogen doped brookite (H:brookite) nanobullet arrays were synthesized via a well-designed solution reaction for the first time. H:brookite shows highly improved PEC properties with excellent stability, enhanced photocurrent, and significantly high Faradaic efficiency for overall solar water splitting. To support the experimental data, ab initio density functional theory calculations were also conducted. At the interstitial doping site that has minimum formation energy, the hydrogen atoms act as shallow donors and exist as H+. which has the minimum formation energy among three states of hydrogen (H+. H0, and H−). The calculated density of states of H:brookite shows a narrowed bandgap and an increased electron density compared to the pristine brookite. The combined experimental and theoretical results provide frameworks for the exploration of the PEC properties of doped brookite and extend our knowledge regarding the undiscovered properties of brookite of TiO2. PMID:27782198

  20. Expression of a clostridial [FeFe]-hydrogenase in Chlamydomonas reinhardtii prolongs photo-production of hydrogen from water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Noone, Seth; Ratcliff, Kathleen; Davis, ReAnna; Subramanian, Venkataramanan; Meuser, Jonathan; Posewitz, Matthew C.; King, Paul W.; Ghirardi, Maria L.

    2017-03-01

    The high oxygen (O2) sensitivity of green algal [FeFe]-hydrogenases is a significant limitation for the sustained production of hydrogen gas (H2) from photosynthetic water splitting. To address this limitation we replaced the native [FeFe]-hydrogenases with a more O2-tolerant clostridial [FeFe]-hydrogenase CaI in Chlamydomonas reinhardtii strain D66..delta..HYD (hydA1-hydA2-) that contains insertionally inactivated [FeFe]-hydrogenases genes. Expression and translocation of CaI in D66..delta..HYD led to the recovery of H2 photoproduction at ~ 20% of the rates of the wild-type parent strain D66. We show for the first time that a bacterial [FeFe]-hydrogenase can be expressed, localized and matured to a catalytically active form that couples to photosynthetic electron transport in the green alga C. reinhardtii. The lower rates of O2 inactivation of CaI led to more sustained H2 photoproduction when cultures were challenged with O2 or kept under prolonged illumination at solar intensities. These results provide new insights into the requisites for attaining photobiological H2 production from water splitting using a more O2-tolerant hydrogenase.

  1. Thickness control in electrophoretic deposition of WO{sub 3} nanofiber thin films for solar water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Yuanxing; Lee, Wei Cheat; Canciani, Giacomo E.; Draper, Thomas C.; Al-Bawi, Zainab F. [Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ (United Kingdom); Bedi, Jasbir S. [School of Public Health & Zoonoses, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana 141004 Punjab (India); Perry, Christopher C. [Division of Biochemistry, School of Medicine, Loma Linda University, Loma Linda, CA 92350 (United States); Chen, Qiao, E-mail: qiao.chen@sussex.ac.uk [Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ (United Kingdom)

    2015-12-15

    Graphical abstract: - Highlights: • A novel method combining electrospinning and electrophoretic deposition was established for the creation of nanostructured semiconductor thin films. • The created thin films displayed a high chemical stability with a controllable thickness. • The PEC water splitting performance of the thin films was optimized by fine-tuning the thickness of the films. • A maximum photoconversion efficiency was achieved by 18 μm nanofibrous thin films. - Abstract: Electrophoretic deposition (EPD) of ground electrospun WO{sub 3} nanofibers was applied to create photoanodes with controlled morphology for the application of photoelectrochemical (PEC) water splitting. The correlations between deposition parameters and film thicknesses were investigated with theoretical models to precisely control the morphology of the nanostructured porous thin film. The photoconversion efficiency was further optimized as a function of film thickness. A maximum photoconversion efficiency of 0.924% from electrospun WO{sub 3} nanofibers that EPD deposited on a substrate was achieved at a film thickness of 18 μm.

  2. Discovery of earth abundant light absorbers for solar water splitting: Mn2V2O7 and beyond

    Science.gov (United States)

    Yan, Qimin; Newhouse, Pawl F.; Li, Guo; Yu, Jie; Chen, Wei; Persson, Kristin; Gregoire, John; Neaton, Jeffrey

    2015-03-01

    Utilizing a first-principles data driven discovery approach with high-throughput computations and machine learning techniques, we screen for transition metal oxide (TMO) compounds with low band gaps and optimal band edges for solar water splitting applications. Combining the computational screening with the high-throughput experimental synthesis efforts, we identify the complex oxide β-Mn2V2O7 as exhibiting a band gap and band edges that are near optimal for photocatalytic water splitting. Experiments, corroborated by theory, indicate that β-Mn2V2O7 has a near-direct band gap near 1.8 eV. Our calculations further reveal a valence band maximum composed of mixed O-p/Mn-d states, and a conduction band maximum of V d-character, leading to dipole-allowed direct transitions at the band edges. Photoelectrochemical measurements indicate appreciable photocurrent from Mn2V2O7 samples, corroborating our predictions. We further discuss design principles for guiding the discovery of more promising metal oxides with optimal band energetics for solar fuels applications. This work was supported by the DOE through the Materials Project and the Joint Center for Artificial Photosynthesis. Computational resources provided by NERSC.

  3. Nanoporous BiVO4 photoanodes with dual-layer oxygen evolution catalysts for solar water splitting.

    Science.gov (United States)

    Kim, Tae Woo; Choi, Kyoung-Shin

    2014-02-28

    Bismuth vanadate (BiVO4) has a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Here, we demonstrate that a nanoporous morphology (specific surface area of 31.8 square meters per gram) effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE). We enhanced the propensity for surface-reaching holes to instigate water-splitting chemistry by serially applying two different oxygen evolution catalyst (OEC) layers, FeOOH and NiOOH, which reduces interface recombination at the BiVO4/OEC junction while creating a more favorable Helmholtz layer potential drop at the OEC/electrolyte junction. The resulting BiVO4/FeOOH/NiOOH photoanode achieves a photocurrent density of 2.73 milliamps per square centimenter at a potential as low as 0.6 V versus RHE.

  4. Efficient water-splitting device based on a bismuth vanadate photoanode and thin-film silicon solar cells.

    Science.gov (United States)

    Han, Lihao; Abdi, Fatwa F; van de Krol, Roel; Liu, Rui; Huang, Zhuangqun; Lewerenz, Hans-Joachim; Dam, Bernard; Zeman, Miro; Smets, Arno H M

    2014-10-01

    A hybrid photovoltaic/photoelectrochemical (PV/PEC) water-splitting device with a benchmark solar-to-hydrogen conversion efficiency of 5.2% under simulated air mass (AM) 1.5 illumination is reported. This cell consists of a gradient-doped tungsten-bismuth vanadate (W:BiVO4 ) photoanode and a thin-film silicon solar cell. The improvement with respect to an earlier cell that also used gradient-doped W:BiVO4 has been achieved by simultaneously introducing a textured substrate to enhance light trapping in the BiVO4 photoanode and further optimization of the W gradient doping profile in the photoanode. Various PV cells have been studied in combination with this BiVO4 photoanode, such as an amorphous silicon (a-Si:H) single junction, an a-Si:H/a-Si:H double junction, and an a-Si:H/nanocrystalline silicon (nc-Si:H) micromorph junction. The highest conversion efficiency, which is also the record efficiency for metal oxide based water-splitting devices, is reached for a tandem system consisting of the optimized W:BiVO4 photoanode and the micromorph (a-Si:H/nc-Si:H) cell. This record efficiency is attributed to the increased performance of the BiVO4 photoanode, which is the limiting factor in this hybrid PEC/PV device, as well as better spectral matching between BiVO4 and the nc-Si:H cell.

  5. MOF-derived Co-doped nickel selenide/C electrocatalysts supported on Ni foam for overall water splitting

    KAUST Repository

    Ming, Fangwang

    2016-09-01

    It is of prime importance to develop dual-functional electrocatalysts with good activity for overall water splitting, which remains a great challenge. Herein, we report the synthesis of a Co-doped nickel selenide (a mixture of NiSe and NiSe)/C hybrid nanostructure supported on Ni foam using a metal-organic framework as the precursor. The resulting catalyst exhibits excellent catalytic activity toward the oxygen evolution reaction (OER), which only requires an overpotential of 275 mV to drive a current density of 30 mA cm. This overpotential is much lower than those reported for precious metal free OER catalysts. The hybrid is also capable of catalyzing the hydrogen evolution reaction (HER) efficiently. A current density of -10 mA cm can be achieved at 90 mV. In addition, such a hybrid nanostructure can achieve 10 and 30 mA cm at potentials of 1.6 and 1.71 V, respectively, along with good durability when functioning as both the cathode and the anode for overall water splitting in basic media.

  6. Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting.

    Science.gov (United States)

    Kibria, M G; Zhao, S; Chowdhury, F A; Wang, Q; Nguyen, H P T; Trudeau, M L; Guo, H; Mi, Z

    2014-04-30

    Solar water splitting is one of the key steps in artificial photosynthesis for future carbon-neutral, storable and sustainable source of energy. Here we show that one of the major obstacles for achieving efficient and stable overall water splitting over the emerging nanostructured photocatalyst is directly related to the uncontrolled surface charge properties. By tuning the Fermi level on the nonpolar surfaces of gallium nitride nanowire arrays, we demonstrate that the quantum efficiency can be enhanced by more than two orders of magnitude. The internal quantum efficiency and activity on p-type gallium nitride nanowires can reach ~51% and ~4.0 mol hydrogen h(-1) g(-1), respectively. The nanowires remain virtually unchanged after over 50,000 μmol gas (hydrogen and oxygen) is produced, which is more than 10,000 times the amount of photocatalyst itself (~4.6 μmol). The essential role of Fermi-level tuning in balancing redox reactions and in enhancing the efficiency and stability is also elucidated.

  7. Hydrogen-doped Brookite TiO2 Nanobullets Array as a Novel Photoanode for Efficient Solar Water Splitting

    Science.gov (United States)

    Choi, Mingi; Lee, June Ho; Jang, Youn Jeong; Kim, Donghyung; Lee, Jae Sung; Jang, Hyun Myung; Yong, Kijung

    2016-10-01

    As a representative photocatalyst for photoelectrochemical solar water splitting, TiO2 has been intensively studied but most researches have focused on the rutile and anatsase phases because brookite, another important crystalline polymorph of TiO2, rarely exists in nature and is difficult to synthesize. In this work, hydrogen doped brookite (H:brookite) nanobullet arrays were synthesized via a well-designed solution reaction for the first time. H:brookite shows highly improved PEC properties with excellent stability, enhanced photocurrent, and significantly high Faradaic efficiency for overall solar water splitting. To support the experimental data, ab initio density functional theory calculations were also conducted. At the interstitial doping site that has minimum formation energy, the hydrogen atoms act as shallow donors and exist as H+. which has the minimum formation energy among three states of hydrogen (H+. H0, and H-). The calculated density of states of H:brookite shows a narrowed bandgap and an increased electron density compared to the pristine brookite. The combined experimental and theoretical results provide frameworks for the exploration of the PEC properties of doped brookite and extend our knowledge regarding the undiscovered properties of brookite of TiO2.

  8. Nitrogen, Phosphorus, and Fluorine Tri-doped Graphene as a Multifunctional Catalyst for Self-Powered Electrochemical Water Splitting.

    Science.gov (United States)

    Zhang, Jintao; Dai, Liming

    2016-10-10

    Electrocatalysts are required for clean energy technologies (for example, water-splitting and metal-air batteries). The development of a multifunctional electrocatalyst composed of nitrogen, phosphorus, and fluorine tri-doped graphene is reported, which was obtained by thermal activation of a mixture of polyaniline-coated graphene oxide and ammonium hexafluorophosphate (AHF). It was found that thermal decomposition of AHF provides nitrogen, phosphorus, and fluorine sources for tri-doping with N, P, and F, and simultaneously facilitates template-free formation of porous structures as a result of thermal gas evolution. The resultant N, P, and F tri-doped graphene exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The trifunctional metal-free catalyst was further used as an OER-HER bifunctional catalyst for oxygen and hydrogen gas production in an electrochemical water-splitting unit, which was powered by an integrated Zn-air battery based on an air electrode made from the same electrocatalyst for ORR. The integrated unit, fabricated from the newly developed N, P, and F tri-doped graphene multifunctional metal-free catalyst, can operate in ambient air with a high gas production rate of 0.496 and 0.254 μL s(-1) for hydrogen and oxygen gas, respectively, showing great potential for practical applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Iron-doping-enhanced photoelectrochemical water splitting performance of nanostructured WO3: a combined experimental and theoretical study.

    Science.gov (United States)

    Zhang, Teng; Zhu, Zonglong; Chen, Haining; Bai, Yang; Xiao, Shuang; Zheng, Xiaoli; Xue, Qingzhong; Yang, Shihe

    2015-02-21

    In this paper, we have studied Fe-doping of nanostructured tungsten trioxide (WO3) and its pronounced effect in promoting the photoelectrochemical (PEC) water splitting performance. Vertically aligned Fe-doped WO3 nanoflakes on fluorine-doped tin oxide (FTO) were synthesized via the hydrothermal method. An X-ray photoelectron spectroscopy (XPS) analysis confirmed the Fe(3+) substitution at the W(6+) site in the prepared films. Broadened visible light absorption was observed in doped films, likely due to the formation of extra band states through doping. The Fe-doping was shown to greatly improve the PEC water splitting performance of WO3. More specifically, the 2 mol% Fe-doped WO3 achieved a photocurrent density of 0.88 mA cm(-2) at 1.23 V versus RHE, approximately 30% higher than that of the undoped WO3 (0.69 mA cm(-2) at 1.23 V versus RHE). This enhancement was attributed to the reduced band gap and the doping-enhanced charge carrier density as confirmed by the absorption spectra and the Mott-Schottky plots, respectively. Finally, first-principles density functional theory (DFT) calculations confirmed that the formation of oxygen vacancies was favored after Fe-doping, contributing to the increased charge carrier density in slightly doped films.

  10. Nanostructured Silicon Photocathodes for Solar Water Splitting Patterned by the Self-Assembly of Lamellar Block Copolymers.

    Science.gov (United States)

    Shen, Lang; He, Chunlin; Qiu, Jing; Lee, Sung-Min; Kalita, Abinasha; Cronin, Stephen B; Stoykovich, Mark P; Yoon, Jongseung

    2015-12-02

    We studied a type of nanostructured silicon photocathode for solar water splitting, where one-dimensionally periodic lamellar nanopatterns derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface of single-crystalline silicon in configurations with and without a buried metallurgical junction. The resulting nanostructured silicon photocathodes with the characteristic lamellar morphology provided suppressed front-surface reflection and increased surface area, which collectively contributed to the enhanced photocatalytic performance in the hydrogen evolution reaction. The augmented light absorption in the nanostructured silicon directly translated to the increase of the saturation current density, while the onset potential decreased with the etching depth because of the increased levels of surface recombination. The pp(+)-silicon photocathodes, compared to the n(+)pp(+)-silicon with a buried solid-state junction, exhibited a more pronounced shift of the current density-potential curves upon the introduction of the nanostructured surface owing to the corresponding increase in the liquid/silicon junction area. Systematic studies on the morphology, optical properties, and photoelectrochemical characteristics of nanostructured silicon photocathodes, in conjunction with optical modeling based on the finite-difference time-domain method, provide quantitative description and optimal design rules of lamellar-patterned silicon photocathodes for solar water splitting.

  11. The governance of major innovation in the water cycle : Examining three prominent technologies

    NARCIS (Netherlands)

    Lulofs, Kristiaan R.D.; Bressers, Johannes T.A.

    The growing absolute and relative water scarcity requires drastic change in the water cycle in order to target an efficient and robust water supply. The water cycle consists of the production of water, water use, collection of wastewater and its treatment. This article addresses whether the market

  12. The governance of major innovation in the water cycle : Examining three prominent technologies

    NARCIS (Netherlands)

    Lulofs, Kristiaan R.D.; Bressers, Johannes T.A.

    2017-01-01

    The growing absolute and relative water scarcity requires drastic change in the water cycle in order to target an efficient and robust water supply. The water cycle consists of the production of water, water use, collection of wastewater and its treatment. This article addresses whether the market i

  13. System analysis and optimisation of a Kalina split-cycle for waste heat recovery on large marine diesel engines

    DEFF Research Database (Denmark)

    Larsen, Ulrik; Nguyen, Tuong-Van; Knudsen, Thomas

    2014-01-01

    Waste heat recovery systems can produce power from heat without using fuel or emitting CO2, therefore their implementation is becoming increasingly relevant. The Kalina cycle is proposed as an efficient process for this purpose. The main reason for its high efficiency is the non-isothermal phase...... by 3.4e5.9%. A simplified cost analysis suggests higher purchase costs as result of increased process complexity. © 2013 Elsevier Ltd. All rights reserved....

  14. Raman Spectroscopy Applied to Mars Water Cycle Studies

    Science.gov (United States)

    Nikolakakos, G.; Whiteway, J. A.

    2014-12-01

    One of the key findings during the Phoenix and Mars Science Laboratory landed Mars missions has been the detection of perchlorate, a highly deliquescent salt. Perchlorates are of great interest on Mars due to their high affinity for water vapour as well as their ability to greatly depress the freezing point of water when in solution. This has intriguing biological implications as resulting brines could potentially provide a habitable environment for living organisms. Additionally, it has been speculated that these salts may play a significant role in influencing the hydrological cycle on Mars. In order to experimentally study brine formation on Mars and assess the feasibility of a future landed detection tool, a stand-off Raman spectroscopy instrument and environmental simulation chamber have been developed at York University. A sample of magnesium perchlorate has been subjected to the water vapour pressure, background pressure and temperatures found at polar Martian latitudes. Results indicate that at a water vapour pressure of ~20 Pa, Raman spectroscopy is able to detect the onset of brine formation and provide an estimate of the quantity of water taken up by the sample. At the lower water vapour pressures typically found on Mars ( ~1 Pa), it appears that slower dynamics inhibit the onset of water uptake over relevant time scales. The experimental setup and current results will be presented.

  15. The NASA Energy and Water Cycle Extreme (NEWSE) Integration Project

    Science.gov (United States)

    House, P. R.; Lapenta, W.; Schiffer, R.

    2008-01-01

    Skillful predictions of water and energy cycle extremes (flood and drought) are elusive. To better understand the mechanisms responsible for water and energy extremes, and to make decisive progress in predicting these extremes, the collaborative NASA Energy and Water cycle Extremes (NEWSE) Integration Project, is studying these extremes in the U.S. Southern Great Plains (SGP) during 2006-2007, including their relationships with continental and global scale processes, and assessment of their predictability on multiple space and time scales. It is our hypothesis that an integrative analysis of observed extremes which reflects the current understanding of the role of SST and soil moisture variability influences on atmospheric heating and forcing of planetary waves, incorporating recently available global and regional hydro- meteorological datasets (i.e., precipitation, water vapor, clouds, etc.) in conjunction with advances in data assimilation, can lead to new insights into the factors that lead to persistent drought and flooding. We will show initial results of this project, whose goals are to provide an improved definition, attribution and prediction on sub-seasonal to interannual time scales, improved understanding of the mechanisms of decadal drought and its predictability, including the impacts of SST variability and deep soil moisture variability, and improved monitoring/attributions, with transition to applications; a bridging of the gap between hydrological forecasts and stakeholders (utilization of probabilistic forecasts, education, forecast interpretation for different sectors, assessment of uncertainties for different sectors, etc.).

  16. Spatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splitting.

    Science.gov (United States)

    Tang, Zhen-Kun; Yin, Wen-Jin; Le Zhang; Wen, Bo; Zhang, Deng-Yu; Liu, Li-Min; Lau, Woon-Ming

    2016-01-01

    The electronic structures and photocatalytic properties of bismuth oxyhalide bilayers (BiOX1/BiOX2, X1 and X2 are Cl, Br, I) are studied by density functional theory. Briefly, their compositionally tunable bandgaps range from 1.85 to 3.41 eV, suitable for sun-light absorption, and all bilayers have band-alignments good for photocatalytic water-splitting. Among them, heterogeneous BiOBr/BiOI bilayer is the best as it has the smallest bandgap. More importantly, photo-excitation of BiOBr/BiOI leads to electron supply to the conduction band minimum with localized states belonging mainly to bismuth of BiOBr where the H(+)/H2 half-reaction of water-splitting can be sustained. Meanwhile, holes generated by such photo-excitation are mainly derived from the iodine states of BiOI in the valence band maximum; thus, the O2/H2O half-reaction of water splitting is facilitated on BiOI. Detailed band-structure analysis also indicates that this intriguing spatial separation of photo-generated electron-hole pairs and the two half-reactions of water splitting are good for a wide photo-excitation spectrum from 2-5 eV; as such, BiOBr/BiOI bilayer can be an efficient photocatalyst for water-splitting, particularly with further optimization of its optical absorptivity.

  17. eWaterCycle: A global operational hydrological forecasting model

    Science.gov (United States)

    van de Giesen, Nick; Bierkens, Marc; Donchyts, Gennadii; Drost, Niels; Hut, Rolf; Sutanudjaja, Edwin

    2015-04-01

    Development of an operational hyper-resolution hydrological global model is a central goal of the eWaterCycle project (www.ewatercycle.org). This operational model includes ensemble forecasts (14 days) to predict water related stress around the globe. Assimilation of near-real time satellite data is part of the intended product that will be launched at EGU 2015. The challenges come from several directions. First, there are challenges that are mainly computer science oriented but have direct practical hydrological implications. For example, we aim to make use as much as possible of existing standards and open-source software. For example, different parts of our system are coupled through the Basic Model Interface (BMI) developed in the framework of the Community Surface Dynamics Modeling System (CSDMS). The PCR-GLOBWB model, built by Utrecht University, is the basic hydrological model that is the engine of the eWaterCycle project. Re-engineering of parts of the software was needed for it to run efficiently in a High Performance Computing (HPC) environment, and to be able to interface using BMI, and run on multiple compute nodes in parallel. The final aim is to have a spatial resolution of 1km x 1km, which is currently 10 x 10km. This high resolution is computationally not too demanding but very memory intensive. The memory bottleneck becomes especially apparent for data assimilation, for which we use OpenDA. OpenDa allows for different data assimilation techniques without the need to build these from scratch. We have developed a BMI adaptor for OpenDA, allowing OpenDA to use any BMI compatible model. To circumvent memory shortages which would result from standard applications of the Ensemble Kalman Filter, we have developed a variant that does not need to keep all ensemble members in working memory. At EGU, we will present this variant and how it fits well in HPC environments. An important step in the eWaterCycle project was the coupling between the hydrological and

  18. The Wedge Splitting Test: Influence of Aggregate Size and Water-to-Cement Ratio

    DEFF Research Database (Denmark)

    Pease, Bradley Justin; Skocek, Jan; Geiker, Mette Rica;

    2007-01-01

    of various concrete mixtures there are limitations to the current analysis techniques. To date these techniques analyze the result of one WST specimen, thereby providing an estimate of material properties from single result. This paper utilizes a recent improvement to the inverse analysis technique, which......Since the development of the wedge splitting test (WST), techniques have been used to extract material properties that can describe the fracture behavior of the tested materials. Inverse analysis approaches are commonly used to estimate the stress-crack width relationship; which is described...... by the elastic modulus, tensile strength, fracture energy, and the assumed softening behavior. The stress-crack width relation can be implemented in finite element models for computing the cracking behavior of cementitious systems. While inverse analysis provides information about the material properties...

  19. Suppression of the water splitting back reaction on GaN:ZnO photocatalysts loaded with core/shell cocatalysts, investigated using a μ-reactor

    DEFF Research Database (Denmark)

    Dionigi, Fabio; Vesborg, Peter Christian Kjærgaard; Pedersen, Thomas

    2012-01-01

    Using silicon-based l-reactors, we have studied the photocatalytic water splitting reaction and the catalytic back reaction on the same catalysts. GaN:ZnO without cocatalyst and loaded with Rh, Pt, Cr2O3/Rh, Cr2O3/Pt, and Rh–Cr mixed oxide has been tested for gas-phase photocatalytic water splitt...

  20. Transport-limited water splitting at ion-selective interfaces during concentration polarization

    DEFF Research Database (Denmark)

    Nielsen, Christoffer Peder; Bruus, Henrik

    2014-01-01

    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in ...

  1. [Tablet splitting].

    Science.gov (United States)

    Quinzler, R; Haefeli, W E

    2006-06-01

    The splitting of scored tablets provides many advantages. One benefit is to achieve dose flexibility to account for the huge interindividual differences in dose requirements for instance in paediatric and geriatric patients, which are often not covered by the available strengths in the market. Moreover, large-sized tablets can easier be swallowed if broken before swallowing and medication costs can often be reduced by splitting brands with higher strength. But not all tablets, mostly unscored tablets, are suitable for splitting. Splitting of extended release formulations can result in an overdose by uncontrolled release of the active component and degradation of the compound can occur if an enteric coating is destroyed by the splitting process. Whether tablets are suitable for splitting depends on the properties of the active component (e.g. light sensitivity), the galenics, the shape of the tablet, and the shape of the scoreline. Moreover, not all patients are informed, able, or willing to split tablets and the majority of the elderly population is not capable to break tablets. When split tablets are prescribed it is therefore important to view the shape of the tablet, to assess the patients ability and willingness to break tablets, to properly inform the patient about the appropriate way of splitting, and if necessary to suggest (and instruct) the use of a tablet splitting device.

  2. Tracking evolution of urban biogeochemical cycles: salinization of fresh water

    Science.gov (United States)

    Kaushal, S.; McDowell, W. H.; Wollheim, W. M.; Duan, S.; Gorman, J. K.; Haq, S.; Hohman, S.; Smith, R. M.; Mayer, P. M.

    2014-12-01

    The built environment often changes quickly in response to human activities, thus contributing to an evolution of stream chemistry over time. Depending upon development and management strategies, these changes can result in pulses and/or long-term trends. Here, we explore patterns of evolving salinization of fresh water over time, and we evaluate the potential water quality implications of fresh water salinization. We show that there has been global salinization of freshwater across urbanizing landscapes over a century. We also show that human-accelerated weathering in watersheds and river alkalinization can further influence regional rates of salinization (in addition to anthropogenic sources such as road salts, sewage leaks, etc.). Finally, we investigate how salinization of fresh water can impact stream sediment fluxes of carbon, nutrients, and sulfate in watersheds across a land use gradient at the Baltimore Long-Term Ecological Research (LTER) site. The impacts of salinization on mobilization and uptake of carbon, nutrients, and sulfate in streams warrant further consideration in water quality management strategies. Overall, we propose that salinization can be a "universal tracer" of watershed urbanization globally with major regional consequences for drinking water and evolution of biogeochemical cycles in freshwater ecosystems.

  3. Visible photoelectrochemical water splitting into H2 and O2 in a dye-sensitized photoelectrosynthesis cell.

    Science.gov (United States)

    Alibabaei, Leila; Sherman, Benjamin D; Norris, Michael R; Brennaman, M Kyle; Meyer, Thomas J

    2015-05-12

    A hybrid strategy for solar water splitting is exploited here based on a dye-sensitized photoelectrosynthesis cell (DSPEC) with a mesoporous SnO2/TiO2 core/shell nanostructured electrode derivatized with a surface-bound Ru(II) polypyridyl-based chromophore-catalyst assembly. The assembly, [(4,4'-(PO3H2)2bpy)2Ru(4-Mebpy-4'-bimpy)Ru(tpy)(OH2)](4+) ([Ru(a) (II)-Ru(b) (II)-OH2](4+), combines both a light absorber and a water oxidation catalyst in a single molecule. It was attached to the TiO2 shell by phosphonate-surface oxide binding. The oxide-bound assembly was further stabilized on the surface by atomic layer deposition (ALD) of either Al2O3 or TiO2 overlayers. Illumination of the resulting fluorine-doped tin oxide (FTO)|SnO2/TiO2|-[Ru(a) (II)-Ru(b) (II)-OH2](4+)(Al2O3 or TiO2) photoanodes in photoelectrochemical cells with a Pt cathode and a small applied bias resulted in visible-light water splitting as shown by direct measurements of both evolved H2 and O2. The performance of the resulting DSPECs varies with shell thickness and the nature and extent of the oxide overlayer. Use of the SnO2/TiO2 core/shell compared with nanoITO/TiO2 with the same assembly results in photocurrent enhancements of ∼ 5. Systematic variations in shell thickness and ALD overlayer lead to photocurrent densities as high as 1.97 mA/cm(2) with 445-nm, ∼ 90-mW/cm(2) illumination in a phosphate buffer at pH 7.

  4. Experimental and Computational Studies on the Design of Dyes for Water-splitting Dye-sensitized Photoelectrochemical Tandem Cells

    Science.gov (United States)

    Mendez-Hernandez, Dalvin D.

    Solar energy is a promising alternative for addressing the world's current and future energy requirements in a sustainable way. Because solar irradiation is intermittent, it is necessary to store this energy in the form of a fuel so it can be used when required. The light-driven splitting of water into oxygen and hydrogen (a useful chemical fuel) is a fascinating theoretical and experimental challenge that is worth pursuing because the advance of the knowledge that it implies and the availability of water and sunlight. Inspired by natural photosynthesis and building on previous work from our laboratory, this dissertation focuses on the development of water-splitting dye-sensitized photoelectrochemical tandem cells (WSDSPETCs). The design, synthesis, and characterization of high-potential porphyrins and metal-free phthalocyanines with phosphonic anchoring groups are reported. Photocurrents measured for WSDSPETCs made with some of these dyes co-adsorbed with molecular or colloidal catalysts on TiO2 electrodes are reported as well. To guide in the design of new molecules we have used computational quantum chemistry extensively. Linear correlations between calculated frontier molecular orbital energies and redox potentials were built and tested at multiple levels of theory (from semi-empirical methods to density functional theory). Strong correlations (with r2 values > 0.99) with very good predictive abilities (rmsd reaction center of Photosystem II. It was found that the inclusion of explicit solvent molecules, hydrogen bonded to specific sites within the molecular triad, was essential to explain the observed thermal relaxation. These results are relevant for both advancing the knowledge about natural photosynthesis and for the future design of new molecules for WSDSPETCs.

  5. DFT Investigation on the Electronic and Water Adsorption Properties of Pristine and N-Doped TiO2 Nanotubes for Photocatalytic Water Splitting Applications

    Science.gov (United States)

    Enriquez, John Isaac G.; Moreno, Joaquin Lorenzo V.; David, Melanie Y.; Arboleda, Nelson B.; Lin, Ong Hui; Villagracia, Al Rey C.

    2017-02-01

    Experimental studies have shown the production of hydrogen through a photocatalytic water splitting process using a titanium dioxide nanotube (TiO2NT) as a photoelectrode. In this study, a theoretical model of pristine and nitrogen-doped TiO2NT based on a TiO2 anatase (101) surface is presented. Spin unrestricted density functional theory calculations were performed to provide a detailed description of the geometries, electronic properties, and adsorption of water (H2O) on pristine and N-doped TiO2NT. The calculations show that doping with N will improve the photocatalytic properties of TiO2NT in two ways: First, the energy barrier of the dissociation reaction of water into hydroxyl radical and hydrogen atom is reduced; and second, the defect-induced states above the valence band lowers the band gap which will result in enhanced visible-light-driven photoactivity. Based on the position of the Fermi level relative to the defect induced energy levels, an optimal doping concentration of around 1.4% is proposed, which is in good agreement with experimental results. This study provides an atomic/molecular level understanding of the photocatalytic water splitting process and may serve as a groundwork for the rational design of more efficient photocatalysts.

  6. Supercritical Water Reactor Cycle for Medium Power Applications

    Energy Technology Data Exchange (ETDEWEB)

    BD Middleton; J Buongiorno

    2007-04-25

    Scoping studies for a power conversion system based on a direct-cycle supercritical water reactor have been conducted. The electric power range of interest is 5-30 MWe with a design point of 20 MWe. The overall design objective is to develop a system that has minimized physical size and performs satisfactorily over a broad range of operating conditions. The design constraints are as follows: Net cycle thermal efficiency {ge}20%; Steam turbine outlet quality {ge}90%; and Pumping power {le}2500 kW (at nominal conditions). Three basic cycle configurations were analyzed. Listed in order of increased plant complexity, they are: (1) Simple supercritical Rankine cycle; (2) All-supercritical Brayton cycle; and (3) Supercritical Rankine cycle with feedwater preheating. The sensitivity of these three configurations to various parameters, such as reactor exit temperature, reactor pressure, condenser pressure, etc., was assessed. The Thermoflex software package was used for this task. The results are as follows: (a) The simple supercritical Rankine cycle offers the greatest hardware simplification, but its high reactor temperature rise and reactor outlet temperature may pose serious problems from the viewpoint of thermal stresses, stability and materials in the core. (b) The all-supercritical Brayton cycle is not a contender, due to its poor thermal efficiency. (c) The supercritical Rankine cycle with feedwater preheating affords acceptable thermal efficiency with lower reactor temperature rise and outlet temperature. (d) The use of a moisture separator improves the performance of the supercritical Rankine cycle with feedwater preheating and allows for a further reduction of the reactor outlet temperature, thus it was selected for the next step. Preliminary engineering design of the supercritical Rankine cycle with feedwater preheating and moisture separation was performed. All major components including the turbine, feedwater heater, feedwater pump, condenser, condenser pump

  7. Diurnal cycles in water quality across the periodic table

    Science.gov (United States)

    Kirchner, James

    2014-05-01

    Diurnal cycles in water quality can provide important clues to the processes that regulate aquatic chemistry, but they often are masked by longer-term, larger-amplitude variability, making their detection and quantification difficult. Here I outline methods that can detect diurnal cycles even when they are massively obscured by statistically ill-behaved noise. I demonstrate these methods using high-frequency water quality data from the Plylimon catchment in mid-Wales (Neal et al., 2013; Kirchner and Neal, 2013). Several aspects combine to make the Plynlimon data set unique worldwide. Collected at 7-hour intervals, the Plynlimon data set is much more densely sampled than typical long-term weekly or monthly water quality data. This 7-hour sampling was also continued for two years, much longer than typical intensive sampling campaigns, and the resulting time series encompass a wide range of climatic and hydrological conditions. Furthermore, each sample was analyzed for a wide range of solutes with diverse sources in the natural environment. However, the 7-hour sampling frequency is both coarse and irregular in comparison to diurnal cycles, making their detection and quantification difficult. Nonetheless, the methods outlined here enable detection of statistically significant diurnal cycles in over 30 solutes at Plynlimon, including alkali metals (Li, Na, K, Rb, and Cs), alkaline earths (Be, Mg, Ca, Sr, and Ba), transition metals (Al, Ti, Mn, Fe, Co, Ni, Zn, Mo, Cd, and Pb), nonmetals (B, NO3, Si, As, and Se), lanthanides and actinides (La, Ce, Pr, and U), as well as total dissolved nitrogen (TDN), dissolved organic carbon (DOC), Gran alkalinity, pH, and electrical conductivity. These solutes span every row of the periodic table, and more than six orders of magnitude in concentration. Many of these diurnal cycles are subtle, representing only a few percent, at most, of the total variance in the concentration time series. Nonetheless they are diagnostically useful

  8. Modeling, simulation, and fabrication of a fully integrated, acid-stable, scalable solar-driven water-splitting system.

    Science.gov (United States)

    Walczak, Karl; Chen, Yikai; Karp, Christoph; Beeman, Jeffrey W; Shaner, Matthew; Spurgeon, Joshua; Sharp, Ian D; Amashukeli, Xenia; West, William; Jin, Jian; Lewis, Nathan S; Xiang, Chengxiang

    2015-02-01

    A fully integrated solar-driven water-splitting system comprised of WO3 /FTO/p(+) n Si as the photoanode, Pt/TiO2 /Ti/n(+) p Si as the photocathode, and Nafion as the membrane separator, was simulated, assembled, operated in 1.0 M HClO4 , and evaluated for performance and safety characteristics under dual side illumination. A multi-physics model that accounted for the performance of the photoabsorbers and electrocatalysts, ion transport in the solution electrolyte, and gaseous product crossover was first used to define the optimal geometric design space for the system. The photoelectrodes and the membrane separators were then interconnected in a louvered design system configuration, for which the light-absorbing area and the solution-transport pathways were simultaneously optimized. The performance of the photocathode and the photoanode were separately evaluated in a traditional three-electrode photoelectrochemical cell configuration. The photocathode and photoanode were then assembled back-to-back in a tandem configuration to provide sufficient photovoltage to sustain solar-driven unassisted water-splitting. The current-voltage characteristics of the photoelectrodes showed that the low photocurrent density of the photoanode limited the overall solar-to-hydrogen (STH) conversion efficiency due to the large band gap of WO3 . A hydrogen-production rate of 0.17 mL hr(-1) and a STH conversion efficiency of 0.24 % was observed in a full cell configuration for >20 h with minimal product crossover in the fully operational, intrinsically safe, solar-driven water-splitting system. The solar-to-hydrogen conversion efficiency, ηSTH , calculated using the multiphysics numerical simulation was in excellent agreement with the experimental behavior of the system. The value of ηSTH was entirely limited by the performance of the photoelectrochemical assemblies employed in this study. The louvered design provides a robust platform for implementation of various types of

  9. Change in Water Cycle- Important Issue on Climate Earth System

    Science.gov (United States)

    Singh, Pratik

    Change in Water Cycle- Important Issue on Climate Earth System PRATIK KUMAR SINGH1 1BALDEVRAM MIRDHA INSTITUTE OF TECHNOLOGY,JAIPUR (RAJASTHAN) ,INDIA Water is everywhere on Earth and is the only known substance that can naturally exist as a gas, liquid, and solid within the relatively small range of air temperatures and pressures found at the Earth's surface.Changes in the hydrological cycle as a consequence of climate and land use drivers are expected to play a central role in governing a vast range of environmental impacts.Earth's climate will undergo changes in response to natural variability, including solar variability, and to increasing concentrations of green house gases and aerosols.Further more, agreement is widespread that these changes may profoundly affect atmospheric water vapor concentrations, clouds and precipitation patterns.As we know that ,a warmer climate, directly leading to increased evaporation, may well accelerate the hydrological cycle, resulting in an increase in the amount of moisture circulating through the atmosphere.The Changing Water Cycle programmer will develop an integrated, quantitative understanding of the changes taking place in the global water cycle, involving all components of the earth system, improving predictions for the next few decades of regional precipitation, evapotranspiration, soil moisture, hydrological storage and fluxes.The hydrological cycle involves evaporation, transpiration, condensation, precipitation, and runoff. NASA's Aqua satellite will monitor many aspects of the role of water in the Earth's systems, and will do so at spatial and temporal scales appropriate to foster a more detailed understanding of each of the processes that contribute to the hydrological cycle. These data and the analyses of them will nurture the development and refinement of hydrological process models and a corresponding improvement in regional and global climate models, with a direct anticipated benefit of more accurate weather and

  10. Photoelectrochemical cell/dye-sensitized solar cell tandem water splitting systems with transparent and vertically aligned quantum dot sensitized TiO2 nanorod arrays

    Science.gov (United States)

    Shin, Kahee; Yoo, Ji-Beom; Park, Jong Hyeok

    2013-03-01

    The present work reports fabrication of vertically aligned CdS sensitized TiO2 nanorod arrays grown on transparent conducting oxide substrate with high transparency as a photoanode in photoelectrochemical cell for water splitting. To realize an unassisted water splitting system, the photoanode and dye-sensitized solar cell tandem structures are tried and their electrochemical behaviors are also investigated. The hydrothermally grown TiO2 nanorod arrays followed by CdS nanoparticle decoration can improve the light absorption of long wavelength light resulting in increased photocurrent density. Two different techniques (electrodeposition and spray pyrolysis deposition) of CdS nanoparticle sensitization are carried out and their water splitting behaviors in the tandem cell are compared.

  11. Facilely Tuning Porous NiCo2 O4 Nanosheets with Metal Valence-State Alteration and Abundant Oxygen Vacancies as Robust Electrocatalysts Towards Water Splitting.

    Science.gov (United States)

    Zhu, Chengzhou; Fu, Shaofang; Du, Dan; Lin, Yuehe

    2016-03-14

    Great efforts in developing clean electrochemical water splitting technology leads to the rational design and synthesis of highly efficient oxygen evolution reaction (OER) catalysts with low overpotential and fast reaction kinetics. Herein, we focus on the role that morphology and composition play in the OER performance to rationally design freestanding 3D porous NiCo2O4 nanosheets with metal valence states alteration and abundant oxygen vacancies as robust electrocatalysts towards water splitting. Besides metal valence-state alteration, surface modification regarding the evolution of oxygen vacancies is facilely realized upon the sodium borohydride treatment, which is beneficial for the enhanced OER performance. Taking advantage of the porous nanostructures and abundant surface activity sites with high reactivity, the resultant nanostructures exhibit excellent OER activity and stability in alkaline electrolytes that outperform that of pristine NiCo2O4 and commercial RuO2, thus holding great potential for the water splitting.

  12. Transport-limited water splitting at ion-selective interfaces during concentration polarization

    OpenAIRE

    Nielsen, Christoffer Peder; Bruus, Henrik

    2013-01-01

    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in qualitative agreement with experimental results published in the literature. The analytical results are furthermore in agreement with direct numerical simulations. As part of the analysis, we find app...

  13. A learning process of water cycle as complex system

    Science.gov (United States)

    Schertzer, D.; Deroubaix, J. F.; Tchiguirinskaia, I.; Tassin, B.; Thevenot, D.

    2009-04-01

    Water cycle is a very good example of a complex geosystem which has many societal impacts and drivers. A permanent and ubiquitous question is how to increase public awareness and understanding of its extreme behaviours, as well as of the related uncertainties. For instance, CEREVE is highly solicited to help the general public, particularly the youth, and the local politicians to get better acquainted with the new water culture in general and with flood risks in particular, in the nearby county Val-de-Marne. Since 2001, May is the month of the "Festival de l'Oh"(which sounds like "Festival de l'Eau", i.e. the water festival co-organized by the county council and city of Paris. "Oh » at the same time partly displays the chemical composition of water and is an exclamation for atonishment). This festival starts with the Scientific Days of Environment that involve researchers and students of the county, as well as collaborators of all around the world. This conference is open to the public who can be informed from the latest research developments, in particular with the help of some general synthesis and panel discussions. On the other hand, (young) researchers can present their own works to a large public. This conference is followed by a Professional Forum where students, heads of water public services or private operators can meet. In the framework of the water festival preparation, there are several water forums for the secondary schools. All along the year, there are regular pedagogical activities for secondary schools, in particular in the framework of Water Houses scattered across the county. We will discuss the importance to better evaluate the effective impact of these pedagogical events on the public awareness and understanding, and to make the learning process more adaptive and interactive, as well as to better address the underlying fundamental problems, e.g. the present limitations of current modelling and data processing.

  14. Bioinspired solar water splitting, sensitized solar cells, and ultraviolet sensor based on semiconductor nanocrystal antenna/graphene nanoassemblies

    Science.gov (United States)

    Chang, Haixin; Lv, Xiaojun; Zheng, Zijian; Wu, Hongkai

    2012-02-01

    Graphene, two-dimensional carbon crystal with only one atom thickness, provides a general platform for nanoscale even atomic scale optoelectronics and photonics. Graphene has many advantages for optoelectronics such as high conductivity, high electronic mobility, flexibility and transparency. However, graphene also has disadvantages such as low light absorption which are unfavorable for optoelectronic devices. On the other hand, many natural photonic systems provide wonderful solution to enhance light absorption for solar energy harvesting and conversion, such as chlorophyll in green plants. Herein, learning from nature, we described bioinspired photocatalytic solar-driven water splitting, sensitized solar cells and ultraviolet optoelectronic sensors enabled by introducing photosensitive semiconductor nanocrystal antenna to graphene for constructing a series of graphene/nanocrystal nanoassemblies. We have demonstrated that high performance optoelectronic devices can come true with the introducing of photosensitive nanocrystal antenna elements.

  15. Topotactic epitaxy of SrTiO{sub 3} mesocrystal superstructures with anisotropic construction for efficient overall water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Peng; Fujitsuka, Mamoru; Majima, Tetsuro [The Institute of Scientific and Industrial Research (SANKEN), Osaka University (Japan); Ochi, Tomoya [Department of Chemistry, Graduate School of Science, Kobe University (Japan); Kobori, Yasuhiro [Department of Chemistry, Graduate School of Science, Kobe University (Japan); Molecular Photoscience Research Center, Kobe University (Japan); Tachikawa, Takashi [Department of Chemistry, Graduate School of Science, Kobe University (Japan); Molecular Photoscience Research Center, Kobe University (Japan); PRESTO, Science and Technology Agency (JST), Saitama (Japan)

    2017-05-02

    The higher-order structures of semiconductor-based photocatalysts play crucial roles in their physicochemical properties for efficient light-to-energy conversion. A novel perovskite SrTiO{sub 3} mesocrystal superstructure with well-defined orientation of assembled cubic nanocrystals was synthesized by topotactic epitaxy from TiO{sub 2} mesocrystals through a facile hydrothermal treatment. The SrTiO{sub 3} mesocrystal exhibits three times the efficiency for the hydrogen evolution of conventional disordered systems in alkaline aqueous solution. It also exhibits a high quantum yield of 6.7 % at 360 nm in overall water splitting and even good durability up to 1 day. Temporal and spatial spectroscopic observations revealed that the synergy of the efficient electron flow along the internal nanocube network and efficient collection at the larger external cubes produces remarkably long-lived charges for enhanced photocatalysis. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Iron-doping-enhanced photoelectrochemical water splitting performance of nanostructured WO3: a combined experimental and theoretical study

    Science.gov (United States)

    Zhang, Teng; Zhu, Zonglong; Chen, Haining; Bai, Yang; Xiao, Shuang; Zheng, Xiaoli; Xue, Qingzhong; Yang, Shihe

    2015-02-01

    In this paper, we have studied Fe-doping of nanostructured tungsten trioxide (WO3) and its pronounced effect in promoting the photoelectrochemical (PEC) water splitting performance. Vertically aligned Fe-doped WO3 nanoflakes on fluorine-doped tin oxide (FTO) were synthesized via the hydrothermal method. An X-ray photoelectron spectroscopy (XPS) analysis confirmed the Fe3+ substitution at the W6+ site in the prepared films. Broadened visible light absorption was observed in doped films, likely due to the formation of extra band states through doping. The Fe-doping was shown to greatly improve the PEC water splitting performance of WO3. More specifically, the 2 mol% Fe-doped WO3 achieved a photocurrent density of 0.88 mA cm-2 at 1.23 V versus RHE, approximately 30% higher than that of the undoped WO3 (0.69 mA cm-2 at 1.23 V versus RHE). This enhancement was attributed to the reduced band gap and the doping-enhanced charge carrier density as confirmed by the absorption spectra and the Mott-Schottky plots, respectively. Finally, first-principles density functional theory (DFT) calculations confirmed that the formation of oxygen vacancies was favored after Fe-doping, contributing to the increased charge carrier density in slightly doped films.In this paper, we have studied Fe-doping of nanostructured tungsten trioxide (WO3) and its pronounced effect in promoting the photoelectrochemical (PEC) water splitting performance. Vertically aligned Fe-doped WO3 nanoflakes on fluorine-doped tin oxide (FTO) were synthesized via the hydrothermal method. An X-ray photoelectron spectroscopy (XPS) analysis confirmed the Fe3+ substitution at the W6+ site in the prepared films. Broadened visible light absorption was observed in doped films, likely due to the formation of extra band states through doping. The Fe-doping was shown to greatly improve the PEC water splitting performance of WO3. More specifically, the 2 mol% Fe-doped WO3 achieved a photocurrent density of 0.88 mA cm-2 at 1

  17. A rational approach towards enhancing solar water splitting: a case study of Au-RGO/N-RGO-TiO2

    Science.gov (United States)

    Bharad, Pradnya A.; Sivaranjani, Kumarsrinivasan; Gopinath, Chinnakonda S.

    2015-06-01

    A rational approach was employed to enhance the solar water splitting (SWS) efficiency by systematically combining various important factors that helps to increase the photocatalytic activity. The rational approach includes four important parameters, namely, charge generation through simulated sunlight absorption, charge separation and diffusion, charge utilization through redox reaction, and the electronic integration of all of the above three factors. The complexity of the TiO2 based catalyst and its SWS activity was increased systematically by adding reduced graphene oxide (RGO) or N-doped RGO and/or nanogold. Au-N-RGO-TiO2 shows the maximum apparent quantum yield (AQY) of 2.46% with a H2 yield (525 μmol g-1 h-1) from aqueous methanol, and overall water splitting activity (22 μmol g-1 h-1 AQY = 0.1%) without any sacrificial agent under one sun conditions. This exercise helps to understand the factors which help to enhance the SWS activity. Activity enhancement was observed when there is synergy among the components, especially the simulated sunlight absorption (or one sun conditions), charge separation/conduction and charge utilization. Electronic integration among the components provides the synergy for efficient solar light harvesting. In our opinion, the above synergy helps to increase the overall utilization of charge carriers towards the higher activity.A rational approach was employed to enhance the solar water splitting (SWS) efficiency by systematically combining various important factors that helps to increase the photocatalytic activity. The rational approach includes four important parameters, namely, charge generation through simulated sunlight absorption, charge separation and diffusion, charge utilization through redox reaction, and the electronic integration of all of the above three factors. The complexity of the TiO2 based catalyst and its SWS activity was increased systematically by adding reduced graphene oxide (RGO) or N-doped RGO and

  18. Core-shell hematite nanorods: a simple method to improve the charge transfer in the photoanode for photoelectrochemical water splitting.

    Science.gov (United States)

    Gurudayal; Chee, Png Mei; Boix, Pablo P; Ge, Hu; Yanan, Fang; Barber, James; Wong, Lydia Helena

    2015-04-01

    We report a simple method to produce a stable and repeatable photoanode for water splitting with a core-shell hematite (α-Fe2O3) nanorods system by combining spray pyrolysis and hydrothermal synthesis. Impedance spectroscopy revealed passivation of the surface states by the shell layer, which results in an increase of the charge injection through the hematite conduction band. In pristine hematite more holes are accumulated on the surface and the charge transfer to the electrolyte occurs through surface states, whereas in the core-shell hematite photoanode the majority of hole transfer process occurs through the valence band. As a result the photoactivity of the core-shell nanorods, 1.2 mA cm(-2), at 1.23 V vs RHE, is twice that of pristine hematite nanorods. The alteration of the interface energetics is supported by TEM, showing that the crystallinity of the surface has been improved by the deposition of the shell.

  19. Electrosprayed heterojunction WO3/BiVO4 films with nanotextured pillar structure for enhanced photoelectrochemical water splitting

    Science.gov (United States)

    Mali, Mukund G.; Yoon, Hyun; Kim, Min-woo; Swihart, Mark T.; Al-Deyab, Salem S.; Yoon, Sam S.

    2015-04-01

    We demonstrate that the addition of a tungsten oxide (WO3) layer beneath a bismuth vanadate (BiVO4) photocatalyst layer with a nanotextured pillar morphology significantly increases the photocurrent density in photoelectrochemical water splitting. The WO3-BiVO4 bilayer films produced a photocurrent of up to 3.3 mA/cm2 under illumination at 100 mW/cm2 (AM1.5 spectrum). The bilayer film was characterized by scanning electron microscopy, X-ray diffraction, and photoelectrochemical methods, which confirmed the superiority of the bilayer film in terms of its morphology and charge separation and transport ability. Both WO3 and BiVO4 were deposited by electrostatic spraying under open-air conditions, which resulted in nanotextured pillars of BiVO4 atop a smooth WO3 film. The optimal coating conditions are also reported.

  20. Synthesis of nanovoid Bi(2)WO(6) 2D ordered arrays as photoanodes for photoelectrochemical water splitting.

    Science.gov (United States)

    Zhang, Liwu; Bahnemann, Detlef

    2013-02-01

    Herein we report a facile and economic method to prepare nanovoid Bi(2)WO(6) 2D ordered arrays employing a simple self-assembly procedure. The electrochemical properties and performance of the 2D nanoarray as a photoanode for water splitting are investigated and compared with a conventional photoanode of similar thickness. The 2D array photoanode shows a much higher photocurrent density and photon-to-H(2) conversion efficiency even with a small content of the Bi(2)WO(6) material. The enhancement is further studied and explained on the basis of the superiority of light scattering and photogenerated hole diffusion within the 2D array structure. This work provides a facile method to improve the efficiency of solar energy conversion systems by minimizing the charge-carrier diffusion length and reducing the light reflection, as well as reducing the amount of the semiconductor material (often costly and/or rare) present in the photoanode.

  1. Clean TiO2 nanocuboid film tightly attached on a conductive substrate for highly efficient photoelectrochemical water splitting

    Science.gov (United States)

    Meng, Ming; Liu, Kuili; Gan, Zhixing; Zhang, Xiantu; Zhang, Honghui; Sun, Xianke; Zhou, Xiaodong; Chen, Yuanyuan; Feng, Yamin

    2016-12-01

    Anatase TiO2 film consisting of nanocuboids with co-exposed {1 0 1}, {0 0 1} and {1 0 0} facets have been successfully synthesized via thermally annealing amorphous anodized TiO2 nanotube arrays in ambient fluorine. When employed as a photoanode material in photoelectrochemical water splitting, the film of the clean TiO2 nanocuoboids yields a photocurrent density of up to 0.65 mA cm-2 at 0.22 V versus the Ag/AgCl electrode with Faradic efficiency of 100% and exhibits excellent stability, which can be attributed to enhanced photogenerated charge separation and transport to the collecting electrode. This film could also potentially be used for other facet-related applications such as TiO2 based dye-sensitized solar cells, sensors and lithium batteries.

  2. Interface engineering of titanium oxide protected a-Si:H/a-Si:H photoelectrodes for light induced water splitting

    Science.gov (United States)

    Ziegler, Jürgen; Yang, Florent; Wagner, Stephan; Kaiser, Bernhard; Jaegermann, Wolfram; Urbain, Félix; Becker, Jan-Philipp; Smirnov, Vladimir; Finger, Friedhelm

    2016-12-01

    TiO2 is a common protection layer on semiconductor electrodes for photoelectrochemical water splitting. We investigate the interface formation of TiO2 on amorphous silicon tandem solar cells by X-ray photoelectron spectroscopy. In order to optimize the contact properties, we prepare TiOx interface layers with various oxygen content by reactive magnetron sputter deposition. We observe, that a TiOx interface layer can reduce the silicon oxide growth during the film deposition on the amorphous silicon, but it forms a non-ohmic contact. The electrochemical investigation shows, that the benefit due to the reduction of the silicon oxide is counteracted by the unfavorable contact formation of TiOx interface layers prepared with low oxygen content.

  3. Synergistic promotion of photoelectrochemical water splitting efficiency of TiO2 nanorods using metal-semiconducting nanoparticles

    Science.gov (United States)

    Subramanian, Alagesan; Pan, Zhenghui; Li, Hongfei; Zhou, Lisha; Li, Wanfei; Qiu, Yongcai; Xu, Yijun; Hou, Yuan; Muzi, Chen; Zhang, Yuegang

    2017-10-01

    Highly efficient photoelectrochemical (PEC) water splitting has been achieved by TiO2 nanorods (TNRs) decorated with Au nanoparticles (AuNPs) and graphene quantum dots (GQDs). The experimental analysis has indicated that the AuNPs has contributed to the plasmon resonance energy transfer/surface plasmon resonance-mediated hot electron injection and the GQDs contributed to the improved electron injection. The synergistic effect, which could be due to exciton-plasmon interactions and/or nonresonance energy transfer between the AuNPs and GQDs, is attributed to the superior PEC activity of the TNRs, which lead to a high photocurrent density of 1.75 mA cm-2 at 1.23 V vs RHE.

  4. Design Energy Efficient Water Utilization Systems Allowing Operation Split%考虑操作分解的热集成用水网络设计

    Institute of Scientific and Technical Information of China (English)

    廖祖维; 武锦涛; 蒋斌波; 王靖岱; 阳永荣

    2008-01-01

    This article deals with the design of energy efficient water utilization systems allowing operation split. Practical features such as operating flexibility and capital cost have made the number of sub operations an impor-tant parameter of the problem. By treating the direct and indirect heat transfers separately, target freshwater and en-ergy consumption as well as the operation split conditions are first obtained. Subsequently, a mixed integer non-linear programming (MINLP) model is established for the design of water network and the heat exchanger network (HEN). The proposed systematic approach is limited to a single contaminant. Example from literature is used to illustrate the applicability of the approach.

  5. Light-Driven Overall Water Splitting Enabled by a Photo-Dember Effect Realized on 3D Plasmonic Structures.

    Science.gov (United States)

    Chen, Min; Gu, Jiajun; Sun, Cheng; Zhao, Yixin; Zhang, Ruoxi; You, Xinyuan; Liu, Qinglei; Zhang, Wang; Su, Yishi; Su, Huilan; Zhang, Di

    2016-07-26

    Photoelectric conversion driven by sunlight has a broad range of energy/environmental applications (e.g., in solar cells and water splitting). However, difficulties are encountered in the separation of photoexcited charges. Here, we realize a long-range (∼1.5 μm period) electric polarization via asymmetric localization of surface plasmons on a three-dimensional silver structure (3D-Ag). This visible-light-responsive effect-the photo-Dember effect, can be analogous to the thermoelectric effect, in which hot carriers are thermally generated instead of being photogenerated. The induced electric field can efficiently separate photogenerated charges, enabling sunlight-driven overall water splitting on a series of dopant-free commercial semiconductor particles (i.e., ZnO, CeO2, TiO2, and WO3) once they are combined with the 3D-Ag substrate. These photocatalytic processes can last over 30 h on 3D-Ag+ZnO, 3D-Ag+CeO2, and 3D-Ag+TiO2, thus demonstrating good catalytic stability for these systems. Using commercial WO3 powder as a reference, the amount of O2 generated with 3D-Ag+CeO2 surpasses even its recently reported counterpart in which sacrificial reagents had to be involved to run half-reactions. This plasmon-mediated charge separation strategy provides an effective way to improve the efficiency of photoelectric energy conversion, which can be useful in photovoltaics and photocatalysis.

  6. Plasmon-Sensitized Graphene/TiO2 Inverse Opal Nanostructures with Enhanced Charge Collection Efficiency for Water Splitting.

    Science.gov (United States)

    Boppella, Ramireddy; Kochuveedu, Saji Thomas; Kim, Heejun; Jeong, Myung Jin; Marques Mota, Filipe; Park, Jong Hyeok; Kim, Dong Ha

    2017-03-01

    In this contribution we have developed TiO2 inverse opal based photoelectrodes for photoelectrochemical (PEC) water splitting devices, in which Au nanoparticles (NPs) and reduced graphene oxide (rGO) have been strategically incorporated (TiO2@rGO@Au). The periodic hybrid nanostructure showed a photocurrent density of 1.29 mA cm(-2) at 1.23 V vs RHE, uncovering a 2-fold enhancement compared to a pristine TiO2 reference. The Au NPs were confirmed to extensively broaden the absorption spectrum of TiO2 into the visible range and to reduce the onset potential of these photoelectrodes. Most importantly, TiO2@rGO@Au hybrid exhibited a 14-fold enhanced PEC efficiency under visible light and a 2.5-fold enrichment in the applied bias photon-to-current efficiency at much lower bias potential compared with pristine TiO2. Incident photon-to-electron conversion efficiency measurements highlighted a synergetic effect between Au plasmon sensitization and rGO-mediated facile charge separation/transportation, which is believed to significantly enhance the PEC activity of these nanostructures under simulated and visible light irradiation. Under the selected operating conditions the incorporation of Au NPs and rGO into TiO2 resulted in a remarkable boost in the H2 evolution rate (17.8 μmol/cm(2)) compared to a pristine TiO2 photoelectrode reference (7.6 μmol/cm(2)). In line with these results and by showing excellent stability as a photoelectrode, these materials are herin underlined to be of promising interest in the PEC water splitting reaction.

  7. A one-dimensional porous carbon-supported Ni/Mo2C dual catalyst for efficient water splitting.

    Science.gov (United States)

    Yu, Zi-You; Duan, Yu; Gao, Min-Rui; Lang, Chao-Chao; Zheng, Ya-Rong; Yu, Shu-Hong

    2017-02-01

    The development of active, stable and low-cost electrocatalysts towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for overall water splitting remains a big challenge. Herein, we report a new porous carbon-supported Ni/Mo2C (Ni/Mo2C-PC) composite catalyst derived by thermal treatment of nickel molybdate nanorods coated with polydopamine, which efficiently and robustly catalyses the HER and OER with striking kinetic metrics in alkaline electrolyte. The catalyst affords low onset potentials of -60 mV for the HER and 270 mV for the OER, as well as small overpotentials of 179 mV for the HER and 368 mV for the OER at a current density of 10 mA cm(-2). These results compare favorably to Mo2C-PC, Ni-PC, and most other documented Ni- and Mo-based catalysts. The high activity of Ni/Mo2C-PC is likely due to electron transfer from Ni to Mo2C, leading to a higher Ni valence and a lower Mo valence in the Ni/Mo2C-PC catalyst, as these are HER and OER active species and thus account for the enhanced activity. Remarkably, our home-made alkaline electrolyser, assembled with Ni/Mo2C-PC as a bifunctional catalyst, can enable a water-splitting current density of 10 mA cm(-2) to be achieved at a low cell voltage of 1.66 V.

  8. Light Driven Energy Research at LCLS: Planned Pump-Probe X-ray Spectroscopy Studies on Photosynthetic Water Splitting

    Science.gov (United States)

    Bergmann, Uwe

    2010-02-01

    Arguably the most important chemical reaction on earth is the photosynthetic splitting of water to molecular oxygen by the Mn-containing oxygen-evolving complex (Mn-OEC) in the protein known as photosystem II (PSII). It is this reaction which has, over the course of some 3.8 billion years, gradually filled our atmosphere with O2 and consequently enabled and sustained the evolution of complex aerobic life. Coupled to the reduction of carbon dioxide, biological photosynthesis contributes foodstuffs for nutrition while recycling CO2 from the atmosphere and replacing it with O2. By utilizing sunlight to power these energy-requiring reactions, photosynthesis also serves as a model for addressing societal energy needs as we enter an era of diminishing fossil hydrocarbon resources. Understanding, at the molecular level, the dynamics and mechanism of how nature has solved this problem is of fundamental importance and could be critical to aid in the design of manufactured devices to accomplish the conversion of sunlight into useful electrochemical energy and transportable fuel in the foreseeable future. In order to understand the photosynthetic splitting of water by the Mn-OEC we need to be able to follow the reaction in real time at an atomic level. A powerful probe to study the electronic and molecular structure of the Mn-OEC is x-ray spectroscopy. Here, in particular x-ray emission spectroscopy (XES) has two crucial qualities for LCLS based time-dependent pump-probe studies of the Mn-OEC: a) it directly probes the Mn oxidation state and ligation, b) it can be performed with wavelength dispersive optics to avoid the necessity of scanning in pump probe experiments. Recent results and the planned time dependent experiments at LCLS will be discussed. )

  9. Life Cycle Assessment of Waste Water Treatment Plants in Ireland

    Directory of Open Access Journals (Sweden)

    Greg Mcnamara

    2016-09-01

      The Urban Wastewater Treatment Directive 91/271/EEC introduced a series of measures for the purpose of protecting the environment from the adverse effects of effluent discharge from wastewater treatment plants.  There are environmental costs associated with attaining the required level of water quality set out in the directive such as greenhouse gas emissions due to energy production, and ecotoxicity from sludge application to land.  The goal of this study is to assess the environmental costs in an Irish context, focusing specifically on the effects of variation in scale and discharge limitation. Life cycle assessment is the analytical tool used to evaluate the environmental impact.  The life cycle impact assessment methodology developed by the Centre of Environmental Science, Leiden University (2010 has been adopted and implemented using GaBi 6.0 life cycle assessment software.  Two plants of varying size and location were chosen for the study. The study found that energy consumption and sludge application to land are the largest contributors to the overall environmental impact associated with the treatment process at both plants.  Economies of scale were observed in energy usage during secondary aeration.   

  10. Life cycle assessment for sustainable metropolitan water systems planning.

    Science.gov (United States)

    Lundie, Sven; Peters, Gregory M; Beavis, Paul C

    2004-07-01

    Life Cycle Assessment (LCA) is useful as an information tool for the examination of alternative future scenarios for strategic planning. Developing a life cycle assessment for a large water and wastewater system involves making methodological decisions about the level of detail which is retained through different stages of the process. In this article we discuss a methodology tailored to strategic planning needs which retains a high degree of model segmentation in order to enhance modeling of a large, complex system. This is illustrated by a case study of Sydney Water, which is Australia's largest water service provider. A prospective LCA was carried out to examine the potential environmental impacts of Sydney Water's total operations in the year 2021. To our knowledge this is the first study to create an LCA model of an integrated water and wastewater system with this degree of complexity. A "base case" system model was constructed to represent current operating assets as augmented and upgraded to 2021. The base case results provided a basis for the comparison of alternative future scenarios and for conclusions to be drawn regarding potential environmental improvements. The scenarios can be roughly classified in two categories: (1) options which improve the environmental performance across all impact categories and (2) options which improve one indicator and worsen others. Overall environmental improvements are achieved in all categories by the scenarios examining increased demand management, energy efficiency, energy generation, and additional energy recovery from biosolids. The scenarios which examined desalination of seawater and the upgrades of major coastal sewage treatment plants to secondary and tertiary treatment produced an improvement in one environmental indicator but deteriorations in all the other impact categories, indicating the environmental tradeoffs within the system. The desalination scenario produced a significant increase in greenhouse gas

  11. Synergistic Effect of Surface Plasmonic particles and Surface Passivation layer on ZnO Nanorods Array for Improved Photoelectrochemical Water Splitting

    Science.gov (United States)

    Liu, Yichong; Yan, Xiaoqin; Kang, Zhuo; Li, Yong; Shen, Yanwei; Sun, Yihui; Wang, Li; Zhang, Yue

    2016-01-01

    One-dimensional zinc oxide nanorods array exhibit excellent electron mobility and thus hold great potential as photoanode for photoelelctrochemical water splitting. However, the poor absorption of visible light and the prominent surface recombination hider the performance improvement. In this work, Au nanoparticles and aluminium oxide were deposited onto the surface of ZnO nanorods to improve the PEC performance. The localized surface plasmon resonance of Au NPs could expand the absorption spectrum to visible region. Simultaneously, the surface of passivation with Au NPs and Al2O3 largely suppressed the photogenerated electron-hole recombination. As a result, the optimal solar-to-hydrogen efficiency of ZnO/Au/Al2O3 with 5 cycles was 6.7 times that of pristine ZnO, ascribed to the synergistic effect of SPR and surface passivation. This research reveals that the synergistic effect could be used as an important method to design efficient photoanodes for photoelectrochemical devices. PMID:27443692

  12. Parameter Estimation of Induction Motors Using Water Cycle Optimization

    Directory of Open Access Journals (Sweden)

    M. Yazdani-Asrami

    2013-12-01

    Full Text Available This paper presents the application of recently introduced water cycle algorithm (WCA to optimize the parameters of exact and approximate induction motor from the nameplate data. Considering that induction motors are widely used in industrial applications, these parameters have a significant effect on the accuracy and efficiency of the motors and, ultimately, the overall system performance. Therefore, it is essential to develop algorithms for the parameter estimation of the induction motor. The fundamental concepts and ideas which underlie the proposed method is inspired from nature and based on the observation of water cycle process and how rivers and streams flow to the sea in the real world. The objective function is defined as the minimization of the real values of the relative error between the measured and estimated torques of the machine in different slip points. The proposed WCA approach has been applied on two different sample motors. Results of the proposed method have been compared with other previously applied Meta heuristic methods on the problem, which show the feasibility and the fast convergence of the proposed approach.

  13. Community of Practice Applications from WaterNet: The NASA Water Cycle Solutions Network

    Science.gov (United States)

    Matthews, D.; Brilly, M.; Gregoric, G.; Polajnar, J.; Houser, P.; Rodell, M.; Lehning, M.

    2009-04-01

    WaterNet is a new international network of researchers, stakeholders, and end-users of remote sensing tools that will benefit the water resources management community. It addresses a means for enhancing the social and economic developments of nations by increased use of practical research products from the terrestrial water cycle for making informed decisions. This paper provides a summary of the Water Cycle Community of Practice (CoP) plans and examples of Land Surface Model (LSM) applications for extreme events - floods, droughts, and heavy snowstorms in Europe. It discusses the concept of NASA's solutions networks focusing on the WaterNet. It invites EGU teams to join our WaterNet network. The NASA Water cycle Solutions Network's goal is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend NASA research results to augment decision support tools and meet national needs. Our team is developing WaterNet by engaging relevant NASA water cycle research and community-of-practice organizations, to develop what we term an "actionable database" that can be used to communicate and connect NASA Water cycle research Results (NWRs) towards the improvement of water-related Decision Support Tools (DSTs). Recognizing that the European Commission and European Space Agency have also developed many related research products (EWRs), we seek to learn about these and network with the EU teams to include their information in the WaterNet actionable data base. Recognizing the many existing highly valuable water-related science and application networks in the US and EU, we focus the balance of our efforts on enabling their interoperability - facilitating access and communications among decision-makers and scientists. We present results of our initial focus on identification, collection, and analysis of the two end points, these being the NWRs and EWRs and water related DSTs. We

  14. The Urban Water Cycle and how it Modulates the Microclimate and the Energy Cycle

    Science.gov (United States)

    Bou-Zeid, E.; Wang, Z.; Ramamurthy, P.; Li, D.; Sun, T.; Smith, J. A.

    2012-12-01

    Urbanization is the land-use modification with the largest and most manifest impacts on hydrologic storage and fluxes. This perturbation of the water cycle also has considerable ramifications on the surface energy budget and the microclimatology in built terrain: reducing the potential for water storage and subsequent evaporation reduces the fraction of incoming radiative energy dissipated through surface evaporation, and consequently increases the sensible heating of the urban atmosphere and solid surfaces (buildings, roads, …). However, the complexity of the involved physical processes and their interactions have so far been oversimplified, leading to considerable biases in model output when compared to observations. Using novel sensing techniques that include wireless sensor networks, this study seeks to build a better understanding of the Urban Water Cycle. Our findings indicate that "impervious surfaces" in urban area are not really impervious and not always dry. The role of evaporation from gravel-covered roofs and from concrete, brick, stone and asphalt surfaces can be considerable, leading to lower sensible heating. In addition, the different thermal properties of the various urban materials lead to extreme spatial heterogeneity in surface conditions that is much higher than over natural terrain. Building on this understanding, an improved urban canopy model is developed that includes much better representation of surface heterogeneity and of hydrological and thermal storage and transport processes, including analytical solutions of the heat equation and numerical solutions of the Richards equation in the urban surface. The model development will be detailed and applications focusing on the role of evaporation in mitigating summer building cooling needs and urban heat island effects will be presented.

  15. Life cycle energy analysis of reclaimed water reuse projects in Beijing.

    Science.gov (United States)

    Fan, Yupeng; Guo, Erhui; Zhai, Yuanzheng; C Chang, Andrew; Qiao, Qi; Kang, Peng

    2017-05-01

    To illustrate the benefits of water reuse project, the process-based life cycle analysis (LCA) could be combined with input-output life cycle analysis to evaluate the water reuse project. Energy is the only evaluation parameter used in this study. Life cycle assessment of all energy inputs (LCEA) is completed mainly by the life cycle inventory (LCI), taking into account the full life cycle including the construction, the operation, and the demolition phase of the project. Assessment of benefit from water reuse during the life cycle should focus on sewage discharge reduction and water-saving benefits. The results of LCEA of Beijing water reuse project built in 2014 in a comprehensive way shows that the benefits obtained from the reclaimed water reuse far exceed the life cycle energy consumption. In this paper, we apply the LCEA model to estimate the benefits of reclaimed water reuse projects quantitatively.

  16. Inland Waters and the North American Carbon Cycle

    Science.gov (United States)

    Butman, D. E.; Striegl, R. G.; Stackpoole, S. M.; del Giorgio, P.; Prairie, Y.; Pilcher, D.; Raymond, P. A.; Alcocer, J.; Paz, F.

    2016-12-01

    Inland aquatic ecosystems process, store, and release carbon to the atmosphere and coastal margins. The form of this carbon is a function of terrestrial and aquatic primary and secondary production, the weathering of materials in soils and subsurface environments, the hydrologic controls on the movement of carbon from land to inland waters, and the connectivity between streams, rivers, lakes, reservoirs and groundwater. The 2007 1st State of the Carbon Cycle reported fluxes for the continental United States (CONUS) only. Streams and rivers exported 30-40 Tg C yr-1 to coastal environments, and 17-25 Tg C yr-1 were buried in lake and reservoir sediments. Remarkably, the 2007 report did not quantify gas emissions, which represent over half of the total carbon fluxes through inland water in the US. Current research has shown that 71-149 Tg C yr-1 exits freshwater systems either through atmospheric emissions of carbon dioxide or as inorganic and organic carbon fluxes to the coast from the CONUS. These estimates did not include the Laurentian Great Lakes. Variation in the magnitude of these fluxes across regions of the CONUS has been linked to differences in precipitation and terrestrial net ecosystem production. Similar comprehensive assessments have not been done for Canada or Mexico. Here we provide, as part of the 2nd State of the Carbon Cycle report, estimates for the river coastal export and vertical emissions of carbon from inland waters of North America, and report major data gaps, and weaknesses in methodologies. These findings stress that strong international partnerships are needed to improve assessment, monitoring, and modeling of human impacts on the magnitude and timing of aquatic fluxes in the future.

  17. Transport-limited water splitting at ion-selective interfaces during concentration polarization

    CERN Document Server

    Nielsen, Christoffer P

    2013-01-01

    We present an analytical model of salt- and water-ion transport across an ion-selective interface based on an assumption of local equilibrium of the water-dissociation reaction. The model yields current-voltage characteristics and curves of water-ion current versus salt-ion current, which are in qualitative agreement with experimental results published in the literature. The analytical results are furthermore in agreement with direct numerical simulations. As part of the analysis, we find approximate solutions to the classical problem of pure salt transport across an ion-selective interface. These solutions provide closed-form expressions for the current-voltage characteristics, which include the overlimiting current due to the development of an extended space charge region. Finally, we discuss how the addition of an acid or a base affects the transport properties of the system and thus provide predictions accessible to further experimental tests of the model.

  18. Thermochemical Water Splitting for Hydrogen Production Utilizing Nuclear Heat from an HTGR

    Institute of Scientific and Technical Information of China (English)

    WU Xinxin; ONUKI Kaoru

    2005-01-01

    A very promising technology to achieve a carbon free energy system is to produce hydrogen from water, rather than from fossil fuels. Iodine-sulfur (IS) thermochemical water decomposition is one promising process. The IS process can be used to efficiently produce hydrogen using the high temperature gas-cooled reactor (HTGR) as the energy source supplying gas at 1000℃. This paper describes that demonstration experiment for hydrogen production was carried out by an IS process at a laboratory scale. The results confirmed the feasibility of the closed-loop operation for recycling all the reactants besides the water, H2, and O2. Then the membrane technology was developed to enhance the decomposition efficiency. The maximum attainable one-pass conversion rate of HI exceeds 90% by membrane technology, whereas the equilibrium rate is about 20%.

  19. Coverage-dependent amplifiers of vegetation change on global water cycle dynamics

    Science.gov (United States)

    Feng, Huihui; Zou, Bin; Luo, Juhua

    2017-07-01

    The terrestrial water cycle describes the circulation of water worldwide from one store to another via repeated evapotranspiration (E) from land and precipitation (P) back to the surface. The cycle presents significant spatial variability, which is strongly affected by natural climate and anthropogenic influences. As one of the major anthropogenic influences, vegetation change unavoidably alters surface property and subsequent the terrestrial water cycle, while its contribution is yet difficult to isolate from the mixed influences. Here, we use satellite and in-situ datasets to identify the terrestrial water cycle dynamics in spatial detail and to evaluate the impact of vegetation change. Methodologically, the water cycle is identified by the indicator of difference between evapotranspiration and precipitation (E-P). Then the scalar form of the indicator's trend (ΔE + ΔP) is used for evaluating the dynamics of water cycle, with the positive value means acceleration and negative means deceleration. Then, the contributions of climate and vegetation change are isolated by the trajectory-based method. Our results indicate that 4 accelerating and 4 decelerating water cycles can be identified, affecting 42.11% of global land. The major water cycle type is characterized by non-changing precipitation and increasing evapotranspiration (PNO-EIN), which covers 20.88% of globally land. Vegetation change amplifies both accelerating and decelerating water cycles. It tends to intensify the trend of the decelerating water cycles, while climate change weakens the trend. In the accelerating water cycles, both vegetation and climate change present positive effect to intensify the trend. The effect of plant cover change varies with the coverage. In particular, vegetation change intensifies the water cycle in moderately vegetated regions (0.1 0.85), the water cycle is accelerated because of the significant increase of precipitation. We conclude that vegetation change acts as an

  20. Reservoir in Global Water Cycle: Macro Scale Hydrologic Modeling for Water Management

    Science.gov (United States)

    Zhou, T.; Nijssen, B.; Haddeland, I.; Gao, H.; Lettenmaier, D. P.

    2014-12-01

    Man-made reservoirs play a key role in the terrestrial water system. They support purposes, such as irrigation, hydropower generation, and flood control, which can substantially change water fluxes at the land surface and redistribute the storage of surface water in space and time. Although most developed countries have sophisticated observing systems for many variables in the natural surface water cycle, long-term and consistent records that focus on water management and human impacts on the global water cycle are much more limited, and most land surface models ignore water management activities. We describe a continental-scale model of reservoir storage, which is combined with a soil moisture deficit-based irrigation scheme within the Variable Infiltration Capacity (VIC) macro-scale hydrological model to simulate the effects of water management in the major river basins of the world. The model is forced with merged NCEP/NCAR and satellite meteorological data at a spatial resolution of 0.25 degrees latitude-longitude, for the period 1948 to 2010. A total of 167 of the largest reservoirs in the world with a total storage capacity around 3900 km3 (nearly 60% of the global total reservoir storage) are simulated. We successfully predict the monthly reservoir storage time series for most of a set of 23 global reservoirs for which observed storage is available either via in situ or satellite remote sensing measurements. We evaluate, on a continental and global basis, the magnitude of inter-seasonal and inter-annual reservoir storage variations in comparison with other terms in the land surface water cycle, including Snow Water Equivalent (SWE) and soil moisture.

  1. Light saturation curves show competence of the water splitting complex in inactive Photosystem II reaction centers.

    Science.gov (United States)

    Nedbal, L; Gibas, C; Whitmarsh, J

    1991-12-01

    Photosystem II complexes of higher plants are structurally and functionally heterogeneous. While the only clearly defined structural difference is that Photosystem II reaction centers are served by two distinct antenna sizes, several types of functional heterogeneity have been demonstrated. Among these is the observation that in dark-adapted leaves of spinach and pea, over 30% of the Photosystem II reaction centers are unable to reduce plastoquinone to plastoquinol at physiologically meaningful rates. Several lines of evidence show that the impaired reaction centers are effectively inactive, because the rate of oxidation of the primary quinone acceptor, QA, is 1000 times slower than in normally active reaction centers. However, there are conflicting opinions and data over whether inactive Photosystem II complexes are capable of oxidizing water in the presence of certain artificial electron acceptors. In the present study we investigated whether inactive Photosystem II complexes have a functional water oxidizing system in spinach thylakoid membranes by measuring the flash yield of water oxidation products as a function of flash intensity. At low flash energies (less that 10% saturation), selected to minimize double turnovers of reaction centers, we found that in the presence of the artificial quinone acceptor, dichlorobenzoquinone (DCBQ), the yield of proton release was enhanced 20±2% over that observed in the presence of dimethylbenzoquinone (DMBQ). We argue that the extra proton release is from the normally inactive Photosystem II reaction centers that have been activated in the presence of DCBQ, demonstrating their capacity to oxidize water in repetitive flashes, as concluded by Graan and Ort (Biochim Biophys Acta (1986) 852: 320-330). The light saturation curves indicate that the effective antenna size of inactive reaction centers is 55±12% the size of active Photosystem II centers. Comparison of the light saturation dependence of steady state oxygen evolution

  2. Conceptual model for simulating the water cycle of the Copenhagen area, Denmark

    DEFF Research Database (Denmark)

    Jeppesen, Jan; Christensen, Steen; Ladekarl, Ulla Lyngs

    2008-01-01

    A complete water cycle model has been constructed for the Copenhagen area (966 km2) in order to study the development of the water cycle during the period 1850-2003. The urban water cycle is quantified in terms of root zone water balance, water supply, waste water, storm water, groundwater flow......, and the interactions between these systems. The water cycle is simulated by combining a root-zone model, a grid distribution tool, and a modified Modflow-2000 model using existing flow packages and a new sewer package that simulates the interactions between ground water and sewers (or rain drains). Long time series...... cycle. It is also the hope that the model will provide a better and more complete overview of the consequences of different water management scenarios. The model concept and selected simulation results is presented....

  3. Photoactive PDI-cobalt complex immobilized on reduced graphene oxide for photoelectrochemical water splitting.

    Science.gov (United States)

    Balapanuru, Janardhan; Chiu, Gordon; Su, Chenliang; Zhou, Na; Hai, Zhu; Xu, Qing-Hua; Loh, Kian Ping

    2015-01-14

    We report the synthesis of a perylene derivative (perylene tetracarboxylic di(propyl imidazole), abbreviated as PDI) that is coordinated with Co(II) ions to form a coordination polymer [PDI-Co(Cl)2(H2O)2]n (abbreviated as PDI-Co). The PDI-Co complex combines the photoactivity of the perylene dye with the electrocatalytic activity of the "Co(II)" center for photoelectrochemical hydrogen evolution reaction (HER). To improve charge transfer interactions, the PDI-Co complex is immobilized on reduced graphene oxide (rGO) via noncovalent interactions to form the rGO-PDI-Co complex. The composite shows good performance in multiple cycle testing and the turnover number (TON vs Co(II)) of this hybrid material for hydrogen evolution reaction (754 after 5 h) is considerably higher than previously reported dye-sensitized cobalt-based catalysts.

  4. Adsorption characteristics of water vapor on ferroaluminophosphate for desalination cycle

    KAUST Repository

    Kim, Youngdeuk

    2014-07-01

    The adsorption characteristics of microporous ferroaluminophosphate adsorbent (FAM-Z01, Mitsubishi Plastics) are evaluated for possible application in adsorption desalination and cooling (AD) cycles. A particular interest is its water vapor uptake behavior at assorted adsorption temperatures and pressures whilst comparing them to the commercial silica gels of AD plants. The surface characteristics are first carried out using N2 gas adsorption followed by the water vapor uptake analysis for temperature ranging from 20°C to 80°C. We propose a hybrid isotherm model, composing of the Henry and the Sips isotherms, which can be integrated to satisfactorily fit the experimental data of water adsorption on the FAM-Z01. The hybrid model is selected to fit the unusual isotherm shapes, that is, a low adsorption in the initial section and followed by a rapid vapor uptake leading to a likely micropore volume filling by hydrogen bonding and cooperative interaction in micropores. It is shown that the equilibrium adsorption capacity of FAM-Z01 can be up to 5 folds higher than that of conventional silica gels. Owing to the quantum increase in the adsorbate uptake, the FAM-Z01 has the potential to significantly reduce the footprint of an existing AD plant for the same output capacity. © 2014 Elsevier B.V.

  5. Life Cycle Assessment and Cost Analysis of Water and ...

    Science.gov (United States)

    changes in drinking and wastewater infrastructure need to incorporate a holistic view of the water service sustainability tradeoffs and potential benefits when considering shifts towards new treatment technology, decentralized systems, energy recovery and reuse of treated wastewater. The main goal of this study is to determine the influence of scale on the energy and cost performance of different transitional membrane bioreactors (MBR) in decentralized wastewater treatment (WWT) systems by performing a life cycle assessment (LCA) and cost analysis. LCA is a tool used to quantify sustainability-related metrics from a systems perspective. The study calculates the environmental and cost profiles of both aerobic MBRs (AeMBR) and anaerobic MBRs (AnMBR), which not only recover energy from waste, but also produce recycled water that can displace potable water for uses such as irrigation and toilet flushing. MBRs represent an intriguing technology to provide decentralized WWT services while maximizing resource recovery. A number of scenarios for these WWT technologies are investigated for different scale systems serving various population density and land area combinations to explore the ideal application potentials. MBR systems are examined from 0.05 million gallons per day (MGD) to 10 MGD and serve land use types from high density urban (100,000 people per square mile) to semi-rural single family (2,000 people per square mile). The LCA and cost model was built with ex

  6. Deprotonation of g-C3N4 with Na ions for efficient nonsacrificial water splitting under visible light

    DEFF Research Database (Denmark)

    Guo, Feng; Chen, Jingling; Zhang, Minwei

    2016-01-01

    Developing a photocatalyst with the necessary characteristics of being cheap, efficient and robust for visible-light-driven water splitting remains a serious challenge within the photocatalysis field. Herein, an effective strategy, deprotonating g-C3N4 with Na ions from low-cost precursors...

  7. A hole inversion layer at the BiVO4/Bi4V2O11 interface produces a high tunable photovoltage for water splitting

    Science.gov (United States)

    dos Santos, Wayler S.; Rodriguez, Mariandry; Afonso, André S.; Mesquita, João P.; Nascimento, Lucas L.; Patrocínio, Antônio O. T.; Silva, Adilson C.; Oliveira, Luiz C. A.; Fabris, José D.; Pereira, Márcio C.

    2016-01-01

    The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%. PMID:27503274

  8. The effect of Rhδ+ dopant in SrTiO3 on the active oxidation state of co-catalytic Pt nanoparticles in overall water splitting

    NARCIS (Netherlands)

    Zoontjes, M.G.C.; Han, K.; Huijben, M.; Wiel, van der W.G.; Mul, G.

    2016-01-01

    We report on the oxidation state of Pt nanoparticles when deposited on SrTiO3 or Rh-doped SrTiO3 under realistic solar water-splitting conditions. The oxidation state was investigated using state-of-the-art analysis of the reaction in a continuously stirred tank reactor (CSTR) connected to a micro g

  9. A hole inversion layer at the BiVO4/Bi4V2O11 interface produces a high tunable photovoltage for water splitting

    Science.gov (United States)

    Dos Santos, Wayler S.; Rodriguez, Mariandry; Afonso, André S.; Mesquita, João P.; Nascimento, Lucas L.; Patrocínio, Antônio O. T.; Silva, Adilson C.; Oliveira, Luiz C. A.; Fabris, José D.; Pereira, Márcio C.

    2016-08-01

    The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.

  10. A hole inversion layer at the BiVO4/Bi4V2O11 interface produces a high tunable photovoltage for water splitting.

    Science.gov (United States)

    Dos Santos, Wayler S; Rodriguez, Mariandry; Afonso, André S; Mesquita, João P; Nascimento, Lucas L; Patrocínio, Antônio O T; Silva, Adilson C; Oliveira, Luiz C A; Fabris, José D; Pereira, Márcio C

    2016-08-09

    The conversion of solar energy into hydrogen fuel by splitting water into photoelectrochemical cells (PEC) is an appealing strategy to store energy and minimize the extensive use of fossil fuels. The key requirement for efficient water splitting is producing a large band bending (photovoltage) at the semiconductor to improve the separation of the photogenerated charge carriers. Therefore, an attractive method consists in creating internal electrical fields inside the PEC to render more favorable band bending for water splitting. Coupling ferroelectric materials exhibiting spontaneous polarization with visible light photoactive semiconductors can be a likely approach to getting higher photovoltage outputs. The spontaneous electric polarization tends to promote the desirable separation of photogenerated electron- hole pairs and can produce photovoltages higher than that obtained from a conventional p-n heterojunction. Herein, we demonstrate that a hole inversion layer induced by a ferroelectric Bi4V2O11 perovskite at the n-type BiVO4 interface creates a virtual p-n junction with high photovoltage, which is suitable for water splitting. The photovoltage output can be boosted by changing the polarization by doping the ferroelectric material with tungsten in order to produce the relatively large photovoltage of 1.39 V, decreasing the surface recombination and enhancing the photocurrent as much as 180%.

  11. PEC HOUSE - A competence center devoted to the photoelectrochemical splitting of water and production of hydrogen - Midyear report 2008

    Energy Technology Data Exchange (ETDEWEB)

    Sivula, K.; Warren, S. C.; Capezzali, M.; Formal, F. le; Paracchino, A.; Puettgen, H. B.; Graetzel, M.

    2008-07-15

    PEC House, the photoelectrochemistry centre of competence at the Swiss Federal Institute of Technology of Lausanne (EPFL), has been established to advance the technology of semiconductor-based photoelectrochemical (PEC) water splitting to produce H{sub 2} and O{sub 2} using sunlight as the energy input. The overall objective of the research is to design and develop novel semiconductor-based materials capable of harvesting and converting solar energy into chemical energy by oxidation of water into oxygen and hydrogen. Since its inception nine months ago, PEC House research activities have centered on assembling tools and techniques for the development of the next generation of photoelectrochemical technology, alongside furthering the development of the state-of-the-art {alpha}-Fe{sub 2}O{sub 3} photoanodes conceived by EPFL. Here, we present the midterm 2008 results on the centre's development as well as describe current research efforts with iron oxide photoanodes. Three specific project deliverables are also satisfied by presenting results with our new deposition equipment, identifying the most promising underlayer materials for iron oxide photoanodes, and reporting on the progress of new materials and techniques under development for the second phase of the research activities. (author)

  12. Exclusive Hydrogen Generation by Electrocatalysts Coated with an Amorphous Chromium-Based Layer Achieving Efficient Overall Water Splitting

    KAUST Repository

    Qureshi, Muhammad

    2017-08-08

    Successful conversion of renewable energy to useful chemicals requires efficient devices that can electrocatalyze or photocatalyze redox reactions, e.g., overall water splitting. Excellent electrocatalysts for the hydrogen evolution reaction (HER), such as Pt, can also cause other side-reactions, including the water-forming back-reaction from H2 and O2 products. A Cr-based amorphous layer coated on catalysts can work as a successful surface modifier that avoids the back-reaction, but its capabilities and limitations toward other species have not been studied. Herein, we investigated the Cr-based layer on Pt from perspectives of both electrocatalysis and photocatalysis using redox-active molecules/ions (O2, ferricyanide, IO3–, S2O82–, H2O2, and CO gas). Our systematic study revealed that utilization of the Cr-based layer realized an exclusive cathodic reaction only to HER, even in the presence of the aforementioned reactive species, suggesting that Cr-based layers work as membranes, as well as corrosion and poison inhibition layers. However, the Cr-based layer experienced self-oxidation and dissolved into the aqueous phase when a strong oxidizing agent or low pH was present. Presented herein are fundamental and critical aspects of the Cr-based modifier, which is essential for the successful and practical development of solar fuel production systems.

  13. Life Cycle Assesment of Daugavgriva Waste Water Treatment Plant

    Science.gov (United States)

    Romagnoli, F.; Sampaio, F.; Blumberga, D.

    2009-01-01

    This paper presents the assessment of the environmental impacts caused by the treatment of Riga's waste water in the Daugavgriva plant with biogas energy cogeneration through the life cycle assessment (LCA). The LCA seems to be a good tool to assess and evaluate the most serious environmental impacts of a facility The results showed clearly that the impact category contributing the most to the total impact -eutrophicationcomes from the wastewater treatment stage. Climate change also seems to be a relevant impact coming from the wastewater treatment stage and the main contributor to the Climate change is N2O. The main environmental benefits, in terms of the percentages of the total impact, associated to the use of biogas instead of any other fossil fuel in the cogeneration plant are equal to: 3,11% for abiotic depletation, 1,48% for climate change, 0,51% for acidification and 0,12% for eutrophication.

  14. Our Environment in Hot Water: Comparing Water Heaters, A Life Cycle Approach Comparing Tank and Tankless Water Heaters in California

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Alison; McMahon, James; Masanet, Eric; Lutz, Jim

    2008-08-13

    Residential water heating is a large source of energy use in California homes. This project took a life cycle approach to comparing tank and tankless water heaters in Northern and Southern California. Information about the life cycle phases was calculated using the European Union's Methodology study for EcoDesign of Energy-using Products (MEEUP) and the National Renewable Energy Laboratory's Life Cycle Inventory (NREL LCI) database. In a unit-to-unit comparison, it was found that tankless water heaters would lessen impacts of water heating by reducing annual energy use by 2800 MJ/year (16% compared to tank), and reducing global warming emissions by 175 kg CO2 eqv./year (18% reduction). Overall, the production and combustion of natural gas in the use phase had the largest impact. Total waste, VOCs, PAHs, particulate matter, and heavy-metals-to-air categories were also affected relatively strongly by manufacturing processes. It was estimated that tankless water heater users would have to use 10 more gallons of hot water a day (an increased usage of approximately 20%) to have the same impact as tank water heaters. The project results suggest that if a higher percentage of Californians used tankless water heaters, environmental impacts caused by water heating would be smaller.

  15. Evaluating the hydrological consistency of satellite based water cycle components

    KAUST Repository

    Lopez Valencia, Oliver M.

    2016-06-15

    Advances in multi-satellite based observations of the earth system have provided the capacity to retrieve information across a wide-range of land surface hydrological components and provided an opportunity to characterize terrestrial processes from a completely new perspective. Given the spatial advantage that space-based observations offer, several regional-to-global scale products have been developed, offering insights into the multi-scale behaviour and variability of hydrological states and fluxes. However, one of the key challenges in the use of satellite-based products is characterizing the degree to which they provide realistic and representative estimates of the underlying retrieval: that is, how accurate are the hydrological components derived from satellite observations? The challenge is intrinsically linked to issues of scale, since the availability of high-quality in-situ data is limited, and even where it does exist, is generally not commensurate to the resolution of the satellite observation. Basin-scale studies have shown considerable variability in achieving water budget closure with any degree of accuracy using satellite estimates of the water cycle. In order to assess the suitability of this type of approach for evaluating hydrological observations, it makes sense to first test it over environments with restricted hydrological inputs, before applying it to more hydrological complex basins. Here we explore the concept of hydrological consistency, i.e. the physical considerations that the water budget impose on the hydrologic fluxes and states to be temporally and spatially linked, to evaluate the reproduction of a set of large-scale evaporation (E) products by using a combination of satellite rainfall (P) and Gravity Recovery and Climate Experiment (GRACE) observations of storage change, focusing on arid and semi-arid environments, where the hydrological flows can be more realistically described. Our results indicate no persistent hydrological

  16. The NASA Energy and Water cycle Extreme (NEWSE) Integration Project

    Science.gov (United States)

    Houser, P. R.; Lapenta, W.; Schiffer, R.

    2008-05-01

    Skillful predictions of water and energy cycle extremes (flood and drought) are elusive. To better understand the mechanisms responsible for water and energy extremes, and to make decisive progress in predicting these extremes, the collaborative NASA Energy and Water cycle Extremes (NEWSE) Integration Project, is studying these extremes in the U.S. Southern Great Plains (SGP) during 2006-2007, including their relationships with continental and global scale processes, and assessment of their predictability on multiple space and time scales. It is our hypothesis that an integrative analysis of observed extremes which reflects the current understanding of the role of SST and soil moisture variability influences on atmospheric heating and forcing of planetary waves, incorporating recently available global and regional hydro- meteorological datasets (i.e., precipitation, water vapor, clouds, etc.) in conjunction with advances in data assimilation, can lead to new insights into the factors that lead to persistent drought and flooding. We will show initial results of this project, whose goals are toprovide an improved definition, attribution and prediction on sub-seasonal to interannual time scales, improved understanding of the mechanisms of decadal drought and its predictability, including the impacts of SST variability and deep soil moisture variability, and improved monitoring/attributions, with transition to applications; a bridging of the gap between hydrological forecasts and stakeholders (utilization of probabilistic forecasts, education, forecast interpretation for different sectors, assessment of uncertainties for different sectors, etc.). *The NEWSE Team is: Romanou, Anastasiam, Columbia U.; Brian Soden, U. Miami; William Lapenta, NASA- MSFC; Megan Larko, CREW; Bing Lin, NASA-LaRC; Christa Peters-Lidard, NASA-GSFC; Xiquan Dong, U. North Dakota; Debbie Belvedere, CREW; Mathew Sapiano, U. Maryland; Duane Waliser, NASA-JPL; Eni Njoku, NASA/JPL; Eric Fetzer, NASA

  17. Inverse opal structured α-Fe2O3 on graphene thin films: enhanced photo-assisted water splitting

    Science.gov (United States)

    Zhang, Kan; Shi, Xinjian; Kim, Jung Kyu; Lee, Jae Sung; Park, Jong Hyeok

    2013-02-01

    A graphene interlayer was successfully inserted into inverse opaline hematite (α-Fe2O3) photoanodes for solar water splitting using the template assisted electrodeposition method. Finding the optimal thermal annealing temperature is crucial for the successful attainment of the inverse opaline hematite nanostructure on a graphene thin film. This is because an appropriate temperature is required to convert pre-deposited Fe0 into hematite with optimum crystalline structure and to simultaneously remove the soft polystyrene template without thermal degradation of the graphene film on a transparent conductive substrate. Different from the conventional strategies based on graphene-semiconductor systems, this novel mechanism has been proposed whereby the graphene interlayer can act as both an electron transfer layer and an electrolyte blocking barrier, by which it not only reduces the charge recombination at the substrate-electrolyte interface but also helps electron transportation from α-Fe2O3 to the substrate of the photoanode. Therefore, both photocurrent density and incident photon-to-current efficiency (IPCE) have been remarkably improved, which are several times higher than those of the pure inverse opaline hematite photoanode.A graphene interlayer was successfully inserted into inverse opaline hematite (α-Fe2O3) photoanodes for solar water splitting using the template assisted electrodeposition method. Finding the optimal thermal annealing temperature is crucial for the successful attainment of the inverse opaline hematite nanostructure on a graphene thin film. This is because an appropriate temperature is required to convert pre-deposited Fe0 into hematite with optimum crystalline structure and to simultaneously remove the soft polystyrene template without thermal degradation of the graphene film on a transparent conductive substrate. Different from the conventional strategies based on graphene-semiconductor systems, this novel mechanism has been proposed

  18. Highly stable copper oxide composite as an effective photocathode for water splitting via a facile electrochemical synthesis strategy

    KAUST Repository

    Zhang, Zhonghai

    2012-01-01

    Hydrogen generation through photoelectrochemical (PEC) water splitting using solar light as an energy resource is believed to be a clean and efficient way to overcome the global energy and environmental problems. Extensive research effort has been focused on n-type metal oxide semiconductors as photoanodes, whereas studies of p-type metal oxide semiconductors as photocathodes where hydrogen is generated are scarce. In this paper, highly efficient and stable copper oxide composite photocathode materials were successfully fabricated by a facile two-step electrochemical strategy, which consists of electrodeposition of a Cu film on an ITO glass substrate followed by anodization of the Cu film under a suitable current density and then calcination to form a Cu 2O/CuO composite. The synthesized Cu 2O/CuO composite was composed of a thin layer of Cu 2O with a thin film of CuO on its top as a protecting coating. The rational control of chemical composition and crystalline orientation of the composite materials was easily achieved by varying the electrochemical parameters, including electrodeposition potential and anodization current density, to achieve an enhanced PEC performance. The best photocathode material among all materials prepared was the Cu 2O/CuO composite with Cu 2O in (220) orientation, which showed a highly stable photocurrent of -1.54 mA cm -2 at a potential of 0 V vs reversible hydrogen electrode at a mild pH under illumination of AM 1.5G. This photocurrent density was more than 2 times that generated by the bare Cu 2O electrode (-0.65 mAcm -2) and the stability was considerably enhanced to 74.4% from 30.1% on the bare Cu 2O electrode. The results of this study showed that the top layer of CuO in the Cu 2O/CuO composite not only minimized the Cu 2O photocorrosion but also served as a recombination inhibitor for the photogenerated electrons and holes from Cu 2O, which collectively explained much enhanced stability and PEC activity of the Cu 2O/CuO composite

  19. Zooplankton abundance in subtropical waters: is there a lunar cycle?

    Directory of Open Access Journals (Sweden)

    Santiago Hernández-León

    2001-07-01

    Full Text Available Based on historical data of abundance, we report evidence of changes in zooplankton abundance in the 0-200 m layer related to the moon cycle confirming that this phenomenon is produced in the marine environment, similarly to the one described for freshwater ecosystems. A clear decrease in the abundance of copepodites plus copepods was observed from the second to the fourth quarter of the moon when the seasonal variability was suppressed. During the full moon phase the large zooplankton and micronekton of the deep scattering layers (DSL would not reach the upper mixed layer in order to avoid predation because of the relatively high level of illumination. Thus epipelagic zooplankton abundance increases as the effect of a lower predatory pressure. Conversely, during the new moon phase the diel migrants reach the surface waters and epiplankton abundance considerably decreases. Recent oceanic sediment trap data in subtropical waters indicate that the particle flux increases at about 30 days period. Thus, the effect of diel vertical migrants could promote not only the variability in their resources and the intensity of the active flux, but could also drive the variability in the gravitational flux.

  20. Investigating Water Splitting with CaFe2O4 Photocathodes by Electrochemical Impedance Spectroscopy.

    Science.gov (United States)

    Díez-García, María Isabel; Gómez, Roberto

    2016-08-24

    Artificial photosynthesis constitutes one of the most promising alternatives for harvesting solar energy in the form of fuels, such as hydrogen. Among the different devices that could be developed to achieve efficient water photosplitting, tandem photoelectrochemical cells show more flexibility and offer high theoretical conversion efficiency. The development of these cells depends on finding efficient and stable photoanodes and, particularly, photocathodes, which requires having reliable information on the mechanism of charge transfer at the semiconductor/solution interface. In this context, this work deals with the preparation of thin film calcium ferrite electrodes and their photoelectrochemical characterization for hydrogen generation by means of electrochemical impedance spectroscopy (EIS). A fully theoretical model that includes elementary steps for electron transfer to the electrolyte and surface recombination with photogenerated holes is presented. The model also takes into account the complexity of the semiconductor/solution interface by including the capacitances of the space charge region, the surface states and the Helmholtz layer (as a constant phase element). After illustrating the predicted Nyquist plots in a general manner, the experimental results for calcium ferrite electrodes at different applied potentials and under different illumination intensities are fitted to the model. The excellent agreement between the model and the experimental results is illustrated by the simultaneous fit of both Nyquist and Bode plots. The concordance between both theory and experiments allows us to conclude that a direct transfer of electrons from the conduction band to water prevails for hydrogen photogeneration on calcium ferrite electrodes and that most of the carrier recombination occurs in the material bulk. In more general vein, this study illustrates how the use of EIS may provide important clues about the behavior of photoelectrodes and the main strategies

  1. Global operational hydrological forecasts through eWaterCycle

    Science.gov (United States)

    van de Giesen, Nick; Bierkens, Marc; Donchyts, Gennadii; Drost, Niels; Hut, Rolf; Sutanudjaja, Edwin

    2015-04-01

    Central goal of the eWaterCycle project (www.ewatercycle.org) is the development of an operational hyper-resolution hydrological global model. This model is able to produce 14 day ensemble forecasts based on a hydrological model and operational weather data (presently NOAA's Global Ensemble Forecast System). Special attention is paid to prediction of situations in which water related issues are relevant, such as floods, droughts, navigation, hydropower generation, and irrigation stress. Near-real time satellite data will be assimilated in the hydrological simulations, which is a feature that will be presented for the first time at EGU 2015. First, we address challenges that are mainly computer science oriented but have direct practical hydrological implications. An important feature in this is the use of existing standards and open-source software to the maximum extent possible. For example, we use the Community Surface Dynamics Modeling System (CSDMS) approach to coupling models (Basic Model Interface (BMI)). The hydrological model underlying the project is PCR-GLOBWB, built by Utrecht University. This is the motor behind the predictions and state estimations. Parts of PCR-GLOBWB have been re-engineered to facilitate running it in a High Performance Computing (HPC) environment, run parallel on multiple nodes, as well as to use BMI. Hydrological models are not very CPU intensive compared to, say, atmospheric models. They are, however, memory hungry due to the localized processes and associated effective parameters. To accommodate this memory need, especially in an ensemble setting, a variation on the traditional Ensemble Kalman Filter was developed that needs much less on-chip memory. Due to the operational nature, the coupling of the hydrological model with hydraulic models is very important. The idea is not to run detailed hydraulic routing schemes over the complete globe but to have on-demand simulation prepared off-line with respect to topography and

  2. Water cycle at Gale crater through MSL/REMS observations

    Science.gov (United States)

    Harri, Ari-Matti; Genzer, Maria; Kemppinen, Osku; Gomez-Elvira, Javier; Savijärvi, Hannu; McConnochie, Tim; De la Torre, Manuel; Haberle, Robert; Polkko, Jouni; Paton, Mark; Richardson, Mark I.; Newman, Claire E.; Siili, Tero; Makinen, Terhi

    2016-10-01

    The Mars Science laboratory (MSL) has been successfully operating at the Gale crater since early August 2012 and has provided a wealth of extremely valuable data. That includes atmospheric observations by the REMS instrument performing atmospheric pressure, temperature of the air, ground temperature, wind speed and direction, relative humidity (REMS-H), and UV measurements.The REMS-H relative humidity device is based on polymeric capacitive humidity sensors developed by Vaisala Inc. and it makes use of three (3) humidity sensor heads. The humidity device is mounted on the REMS boom providing ventilation with the ambient atmosphere through a filter protecting the device from airborne dust.The REMS-H humidity instrument has created an unprecedented data record of more than two full Martian. REMS-H measured the relative humidity and temperature at 1.6 m height for a period of 5 minutes every hour as part of the MSL/REMS instrument package. We focus on describing the annual in situ water cycle with the new REMS-H instrument calibration for the period of two Martian years. The results will be constrained through comparison with independent indirect observations and through modeling efforts.We inferred the hourly atmospheric VMR from the REMS-H observations and compared these VMR measurements with predictions of VMR from our 1D column Martian atmospheric model and regolith to investigate the local water cycle, exchange processes and the local climate in Gale Crater. The strong diurnal variation suggests there are surface-atmosphere exchange processes at Gale Crater during all seasons, which depletes moisture to the ground in the evening and nighttime and release the moisture back to the atmosphere during the daytime. On the other hand, these processes do not result in significant water deposition on the ground, because frost has not been detected in Gale Crater by any of the MSL observations. Hence, our modelling results presumably indicate that adsorption processes take

  3. Rapid Evolution of the Photosystem II Electronic Structure during Water Splitting

    CERN Document Server

    Davis, Katherine M; Palenik, Mark; Yan, Lifen; Purohit, Vatsal; Robison, Gregory; Kosheleva, Irina; Henning, Robert W; Seidler, Gerald T; Pushkar, Yulia

    2015-01-01

    Photosynthetic water oxidation is a fundamental process that sustains the biosphere. A Mn$_{4}$Ca cluster embedded in the photosystem II protein environment is responsible for the production of atmospheric oxygen. Here, time-resolved x-ray emission spectroscopy (XES) was used to observe the process of oxygen formation in real time. These experiments reveal that the oxygen evolution step, initiated by three sequential laser flashes, is accompanied by rapid (within 50 $\\mu$s) changes to the Mn K$\\beta$ XES spectrum. However, no oxidation of the Mn$_{4}$Ca core above the all Mn$^{\\text{IV}}$ state was detected to precede O-O bond formation. A new mechanism featuring Mn$^{\\text{IV}}$=O formation in the S$_{3}$ state is proposed to explain the spectroscopic results. This chemical formulation is consistent with the unique reactivity of the S$_{3}$ state and explains facilitation of the following S$_{3}$ to S$_{0}$ transition, resolving in part the kinetic limitations associated with O-O bond formation. In the propo...

  4. ZnO Hemisphere Pits Nanowire/CdS Photoelectrode for High-Efficiency Photoelectrochemical Water Splitting

    Science.gov (United States)

    Chen, Peiyang; Liu, Zhifeng; Geng, Xuemin; Wang, Jialu; Zhang, Min; Liu, Junqi; Yan, Lu

    2017-03-01

    In this paper, a ZnO hemisphere pits nanowire (HPW) photoelectrode is fabricated by using polystyrene (PS) nanospheres as templates, and CdS is deposited on ZnO nanowires to improve further its photoelectrochemical performance. Firstly, PS nanospheres are deposited on ZnO seed layers by air-liquid interface self-assembling method. Subsequently, ZnO HPWs are grown which effected by PS nanospheres. Finally, CdS nanoparticles were deposited on the ZnO HPWs to construct ZnO/CdS heterojunction photoanodes by successive ionic layer adsorption and reaction method. This hemisphere pits nanowires composite structure demonstrated a highly efficient photoelectrocatalytic performance with a remarkable photocurrent density of 2.27 mA cm-2 determined at 0.8 V versus Ag/AgCl. The enhanced performance of ZnO hemisphere pits nanowires/CdS nanoparticles (ZnO/CdS) composite photoanodes originated from the enhanced light absorption in the visible region and reduced photogenerated charges recombination rate. Furthermore, compared with ordinary nanowire arrays, hemisphere pits nanowire structure can reflect light more times to facilitate light harvesting. This work exhibits the important significance in constructing photoelectrodes for photoelectrochemical water splitting and other photoelectric devices.

  5. A superlattice of alternately stacked Ni-Fe hydroxide nanosheets and graphene for efficient splitting of water.

    Science.gov (United States)

    Ma, Wei; Ma, Renzhi; Wang, Chengxiang; Liang, Jianbo; Liu, Xiaohe; Zhou, Kechao; Sasaki, Takayoshi

    2015-02-24

    Cost-effective electrocatalysts based on nonprecious metals for efficient water splitting are crucial for various technological applications represented by fuel cell. Here, 3d transition metal layered double hydroxides (LDHs) with varied contents of Ni and Fe were successfully synthesized through a homogeneous precipitation. The exfoliated Ni-Fe LDH nanosheets were heteroassembled with graphene oxide (GO) as well as reduced graphene oxide (rGO) into superlattice-like hybrids, in which two kinds of oppositely charged nanosheets are stacked face-to-face in alternating sequence. Heterostructured composites of Ni2/3Fe1/3 LDH nanosheets and GO (Ni2/3Fe1/3-GO) exhibited an excellent oxygen evolution reaction (OER) efficiency with a small overpotential of about 0.23 V and Tafel slope of 42 mV/decade. The activity was further improved via the combination of Ni2/3Fe1/3 LDH nanosheets with more conductive rGO (Ni2/3Fe1/3-rGO) to achieve an overpotential as low as 0.21 V and Tafel plot of 40 mV/decade. The catalytic activity was enhanced with an increased Fe content in the bimetallic Ni-Fe system. Moreover, the composite catalysts were found to be effective for hydrogen evolution reaction. An electrolyzer cell powered by a single AA battery of 1.5 V was demonstrated by using the bifunctional catalysts.

  6. Thermal oxidation synthesis of crystalline iron-oxide nanowires on low-cost steel substrates for solar water splitting

    Science.gov (United States)

    Dlugosch, T.; Chnani, A.; Muralidhar, P.; Schirmer, A.; Biskupek, J.; Strehle, S.

    2017-08-01

    Iron-oxide and in particular its crystallographic phase hematite (α-Fe2O3) is a promising candidate for non-toxic, earth abundant and low cost photo-anodes in the field of photo-electrochemical water splitting. We report here on the synthesis of α-Fe2O3 nanowires by thermal oxidation of low-cost steel substrates. Nanowires grown in this manner exhibit often a blade-like shape but can also possess a wire-like geometry partly decorated at their tip with an iron-rich ellipsoidal head consisting also of crystalline iron-oxide. We show furthermore that these ellipsoidal heads represent suitable growth sites leading in some cases to an additional growth of so-called antenna nanowires. Besides nanowires also nanoflakes were frequently observed at the surface. We discuss the influence of the oxidation temperature and other synthesis parameters as well as dispute the current growth models. Finally, we show that our α-Fe2O3 nanostructures on steel are also photo-electrochemically active supporting in principle their use as photo-anode material.

  7. Surface passivation and protection of Pt loaded multicrystalline pn+ silicon photocathodes by atmospheric plasma oxidation for improved solar water splitting

    Science.gov (United States)

    Fan, Ronglei; Tang, Chengshuang; Xin, Yu; Su, Xiaodong; Wang, Xiaodong; Shen, Mingrong

    2016-12-01

    In the traditional methods such as atomic layer deposition and sputtering, a thin metal oxide layer was usually deposited before the loading of catalysts to protect Si photoelectrodes from oxidation during solar water splitting, and this often results in the transfer of photogenerated carriers from Si to electrolyte more or less inhibited. We here use an atmospheric plasma oxidation method to improve this. A SiO2 protective layer, also an effective passivation layer of Si to increase the life time of carriers, is fabricated on Pt loaded multicrystalline pn+-Si photocathodes. Compared with the un-protected one, the energy conversion efficiency of the plasma-treated Pt/pn+-Si photocathode increases from 6.2% to 8.9% under 100 mW/cm2 Xe lamp, and its stability improves from less than 1-22 h under continuous H2 production. This research provides a conceptual strategy to ensure the direct contact among the Si/Pt/electrolyte and protect and passivate the other part of Si simultaneously.

  8. BiVO4 photoanodes for water splitting with high injection efficiency, deposited by reactive magnetron co-sputtering

    Science.gov (United States)

    Gong, Haibo; Freudenberg, Norman; Nie, Man; van de Krol, Roel; Ellmer, Klaus

    2016-04-01

    Photoactive bismuth vanadate (BiVO4) thin films were deposited by reactive co-magnetron sputtering from metallic Bi and V targets. The effects of the V-to-Bi ratio, molybdenum doping and post-annealing on the crystallographic and photoelectrochemical (PEC) properties of the BiVO4 films were investigated. Phase-pure monoclinic BiVO4 films, which are more photoactive than the tetragonal BiVO4 phase, were obtained under slightly vanadium-rich conditions. After annealing of the Mo-doped BiVO4 films, the photocurrent increased 2.6 times compared to undoped films. After optimization of the BiVO4 film thickness, the photocurrent densities (without a catalyst or a blocking layer or a hole scavenger) exceeded 1.2 mA/cm2 at a potential of 1.23 VRHE under solar AM1.5 irradiation. The surprisingly high injection efficiency of holes into the electrolyte is attributed to the highly porous film morphology. This co-magnetron sputtering preparation route for photoactive BiVO4 films opens new possibilities for the fabrication of large-scale devices for water splitting.

  9. BiVO4 photoanodes for water splitting with high injection efficiency, deposited by reactive magnetron co-sputtering

    Directory of Open Access Journals (Sweden)

    Haibo Gong

    2016-04-01

    Full Text Available Photoactive bismuth vanadate (BiVO4 thin films were deposited by reactive co-magnetron sputtering from metallic Bi and V targets. The effects of the V-to-Bi ratio, molybdenum doping and post-annealing on the crystallographic and photoelectrochemical (PEC properties of the BiVO4 films were investigated. Phase-pure monoclinic BiVO4 films, which are more photoactive than the tetragonal BiVO4 phase, were obtained under slightly vanadium-rich conditions. After annealing of the Mo-doped BiVO4 films, the photocurrent increased 2.6 times compared to undoped films. After optimization of the BiVO4 film thickness, the photocurrent densities (without a catalyst or a blocking layer or a hole scavenger exceeded 1.2 mA/cm2 at a potential of 1.23 VRHE under solar AM1.5 irradiation. The surprisingly high injection efficiency of holes into the electrolyte is attributed to the highly porous film morphology. This co-magnetron sputtering preparation route for photoactive BiVO4 films opens new possibilities for the fabrication