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Sample records for electrochemical double-layer capacitors

  1. A review on electrochemical double-layer capacitors

    International Nuclear Information System (INIS)

    Sharma, Pawan; Bhatti, T.S.

    2010-01-01

    Various energy storage technologies have been developed in the market for various applications. Batteries flywheels, fuel cells are a few which are much common, those are being used in several countries and also research is also carrying on these technologies to make much better them. The electrochemical double-layer capacitor (EDLC) is an emerging technology, which really plays a key part in fulfilling the demands of electronic devices and systems, for present and future. This paper presents the historical background, classification, construction, modeling, testing, and voltage balancing of the EDLC technology. The applications of EDLC in electrical vehicles, power quality, and others are also discussed and their advantages over other storages technologies are also discussed.

  2. Electrochemical double-layer capacitors based on functionalized graphene

    Science.gov (United States)

    Pope, Michael Allan

    Graphene is a promising electrode material for electrochemical double-layer capacitors (EDLCs) used for energy storage due to its high electrical conductivity and theoretical specific surface area. However, the intrinsic capacitance of graphene is known to be low and governed by the electronic side of the interface. Furthermore, graphene tends to aggregate and stack together when processed into thick electrode films. This significantly lowers the ion-accessible specific surface area (SSA). Maximizing both the SSA and the intrinsic capacitance are the main problems addressed in this thesis in an effort to improve the specific capacitance and energy density of EDLCs. In contrast to pristine graphene, functionalized graphene produced by the thermal exfoliation of graphite oxide contains residual functional groups and lattice defects. To study how these properties affect the double-layer capacitance, a model electrode system capable of measuring the intrinsic electrochemical properties of functionalized graphene was developed. To prevent artifacts and uncertainties related to measurements on porous electrodes, the functionalized graphene sheets (FGSs) were assembled as densely tiled monolayers using a Langmuir-Blodgett technique. In this way, charging can be studied in a well-defined 2D geometry. The possibility of measuring and isolating the intrinsic electrochemical properties of FGS monolayers was first demonstrated by comparing capacitance and redox probe measurements carried out on coatings deposited on passivated gold and single crystal graphite substrates. This monolayer system was then used to follow the double-layer capacitance of the FGS/electrolyte interface as the structure and chemistry of graphene was varied by thermal treatments ranging from 300 °C to 2100 °C. Elemental analysis and Raman spectroscopy were used to determine the resulting chemical and structural transformation upon heat treatment. It was demonstrated that intrinsically defective

  3. Performance of Liquid Phase Exfoliated Graphene As Electrochemical Double Layer Capacitors Electrodes

    Science.gov (United States)

    Huffstutler, Jacob; Wasala, Milinda; Richie, Julianna; Winchester, Andrew; Ghosh, Sujoy; Kar, Swastik; Talapatra, Saikat

    2014-03-01

    We will present the results of our investigations of electrochemical double layer capacitors (EDLCs) or supercapacitors (SC) fabricated using liquid-phase exfoliated graphene. Several electrolytes, such as aqueous potassium hydroxide KOH (6M), ionic 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and ionic 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate[BMP][FAP] were used. These EDLC's show good performance compared to other carbon nanomaterials based EDLC's devices. We found that the liquid phase exfoliated graphene based devices possess specific capacitance values as high as 262 F/g, when used with ionic liquid electrolyte[BMP][FAP], with power densities (~ 454 W/kg) and energy densities (~ 0.38Wh/kg). Further, these devices indicated rapid charge transfer response even without the use of any binders or specially prepared current collectors. A detailed electrochemical impedance spectroscopy analysis in order to understand the phenomenon of charge storage in these materials will be presented.

  4. Atomic Layer Deposition Alumina-Passivated Silicon Nanowires: Probing the Transition from Electrochemical Double-Layer Capacitor to Electrolytic Capacitor.

    Science.gov (United States)

    Gaboriau, Dorian; Boniface, Maxime; Valero, Anthony; Aldakov, Dmitry; Brousse, Thierry; Gentile, Pascal; Sadki, Said

    2017-04-19

    Silicon nanowires were coated by a 1-5 nm thin alumina layer by atomic layer deposition (ALD) in order to replace poorly reproducible and unstable native silicon oxide by a highly conformal passivating alumina layer. The surface coating enabled probing the behavior of symmetric devices using such electrodes in the EMI-TFSI electrolyte, allowing us to attain a large cell voltage up to 6 V in ionic liquid, together with very high cyclability with less than 4% capacitance fade after 10 6 charge/discharge cycles. These results yielded fruitful insights into the transition between an electrochemical double-layer capacitor behavior and an electrolytic capacitor behavior. Ultimately, thin ALD dielectric coatings can be used to obtain hybrid devices exhibiting large cell voltage and excellent cycle life of dielectric capacitors, while retaining energy and power densities close to the ones displayed by supercapacitors.

  5. Aging and failure mode of electrochemical double layer capacitors during accelerated constant load tests

    Energy Technology Data Exchange (ETDEWEB)

    Koetz, R.; Ruch, P.W.; Cericola, D. [General Energy Research Department, Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232 Villigen (Switzerland)

    2010-02-01

    Electrochemical double layer capacitors of the BCAP0350 type (Maxwell Technologies) were tested under constant load conditions at different voltages and temperatures. The aging of the capacitors was monitored during the test in terms of capacitance, internal resistance and leakage current. Aging was significantly accelerated by elevated temperature or increased voltage. Only for extreme conditions at voltages of 3.5 V or temperatures above 70 C the capacitors failed due to internal pressure build-up. No other failure events such as open circuit or short circuit were detected. Impedance measurements after the tests showed increased high frequency resistance, an increased distributed resistance and most likely an increase in contact resistance between electrode and current collector together with a loss of capacitance. Capacitors aged at elevated voltages (3.3 V) exhibited a tilting of the low frequency component, which implies an increase in the heterogeneity of the electrode surface. This feature was not observed upon aging at elevated temperatures (70 C). (author)

  6. Ultrathin Graphene Membranes as Flexible Electrodes for Electrochemical Double Layer Capacitors

    Science.gov (United States)

    Talapatra, Saikat; Kar, Swastik; Shah, Rakesh; Ghosh, Sujoy; An, Xiaohong; Simmons, Trevor; Washington, Morris; Nayak, Saroj

    2010-03-01

    We will present the results of our investigations of electrochemical double layer capacitors (EDLCs) or supercapacitors (SC) fabricated using graphene based ultra thin membranes. These EDLC's show far superior performance compared to other carbon nanomaterials based EDLC's devices. We found that the graphene based devices possess specific capacitance values as high as 120 F/g, with impressive power densities (˜105 kW/kg) and energy densities (˜9.2 Wh/kg). Further, these devices indicated rapid charge transfer response even without the use of any binders or specially prepared current collectors. Our ultracapacitors reflect a significant improvement over previously reported graphene-based ultracapacitors and are substantially better than those obtained with carbon nanotubes.

  7. An all-solid-state electrochemical double-layer capacitor based on a plastic crystal electrolyte

    Directory of Open Access Journals (Sweden)

    Ali eaabouimrane

    2015-08-01

    Full Text Available A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C4H94NPF6, (10 molar % with succinonitrile, SCN, (N C−CH2−CH2−C N, [SCN-10%TBA-PF6]. The resultant waxy material shows a plastic crystalline phase that extend from -36 °C up to its melting at 23 °C. It shows a high ionic conductivity reaching 4 × 10−5 S/cm in the plastic crystal phase (15 °C and ~ 3 × 10−3 S/cm in the molten state (25 °C. These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC. The EDLC was assembled and its performance was tested by cyclic voltammetry, AC impedance spectroscopy and galvanostatic charge-discharge methods. Specific capacitance values in the range of 4-7 F/g. (of electrode active material were obtained in the plastic crystal phase at 15 °C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.

  8. An All-Solid-State Electrochemical Double-Layer Capacitor Based on a Plastic Crystal Electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Abouimrane, Ali; Belharouak, Ilias [Qatar Environment and Energy Research Institute, Qatar Foundation, Doha (Qatar); Abu-Lebdeh, Yaser A., E-mail: yaser.abu-lebdeh@nrc.gc.ca [Energy, Mining and Environment Portfolio and Automotive and Surface Transportation Portfolio, National Research Council of Canada, Ottawa, ON (Canada)

    2015-08-18

    A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C{sub 4}H{sub 9}){sub 4}-NPF{sub 6}, (10 molar %) with succinonitrile, SCN, (N≡C−CH{sub 2}−CH{sub 2}−C≡N), [SCN-10%TBA-PF{sub 6}]. The resultant waxy material shows a plastic crystalline phase that extends from −36°C up to its melting at 23°C. It shows a high ionic conductivity reaching 4 × 10{sup -5} S/cm in the plastic crystal phase (15°C) and ~ 3 × 10{sup -3} S/cm in the molten state (25°C). These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC). The EDLC was assembled, and its performance was tested by cyclic voltammetry, AC impedance spectroscopy, and galvanostatic charge–discharge methods. Specific capacitance values in the range of 4–7 F/g (of electrode active material) were obtained in the plastic crystal phase at 15°C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.

  9. An All-Solid-State Electrochemical Double-Layer Capacitor Based on a Plastic Crystal Electrolyte

    International Nuclear Information System (INIS)

    Abouimrane, Ali; Belharouak, Ilias; Abu-Lebdeh, Yaser A.

    2015-01-01

    A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C 4 H 9 ) 4 -NPF 6 , (10 molar %) with succinonitrile, SCN, (N≡C−CH 2 −CH 2 −C≡N), [SCN-10%TBA-PF 6 ]. The resultant waxy material shows a plastic crystalline phase that extends from −36°C up to its melting at 23°C. It shows a high ionic conductivity reaching 4 × 10 -5 S/cm in the plastic crystal phase (15°C) and ~ 3 × 10 -3 S/cm in the molten state (25°C). These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC). The EDLC was assembled, and its performance was tested by cyclic voltammetry, AC impedance spectroscopy, and galvanostatic charge–discharge methods. Specific capacitance values in the range of 4–7 F/g (of electrode active material) were obtained in the plastic crystal phase at 15°C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.

  10. Energy and power performance of electrochemical double-layer capacitors based on molybdenum carbide derived carbon

    International Nuclear Information System (INIS)

    Thomberg, T.; Jaenes, A.; Lust, E.

    2010-01-01

    Cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectroscopy have been applied to establish the electrochemical characteristics for electric double-layer capacitor (EDLC) consisting of the 1 M (C 2 H 5 ) 3 CH 3 NBF 4 electrolyte in acetonitrile and micro/mesoporous carbon electrodes prepared from Mo 2 C, noted as C(Mo 2 C). The N 2 sorption (total BET specific surface area (S BET ≤ 1855 m 2 g -1 ), micropore area (S micro ≤ 1823 m 2 g -1 ), total pore volume (V tot ≤ 1.399 m 3 g -1 ) and pore size distribution (average NLDFT pore width d NLDFT ≥ 0.89 nm) values obtained have been correlated with the electrochemical characteristics for EDLCs (region of ideal polarizability (ΔV = 3.0 V), characteristic time constant (τ R = 1.05 s), gravimetric capacitance (C m ≤ 143 F g -1 )) dependent strongly on the C(Mo 2 C) synthesis temperature. High gravimetric energy (35 Wh kg -1 ) and gravimetric power (237 kW kg -1 ) values, normalised to the total active mass of both C(Mo 2 C) electrodes, synthesised at T synt = 800 deg. C, have been demonstrated at cell voltage 3.0 V and T = 20 deg. C.

  11. Energize Electrochemical Double Layer Capacitor by Introducing an Ambipolar Organic Redox Radical in Electrolyte.

    Science.gov (United States)

    Wang, Yonggang; Hu, Lintong; Zhang, Yue; Shi, Chao; Guo, Kai; Zhai, Tianyou; Li, Huiqiao

    2018-05-24

    Carbon based electrochemical double layer capacitors (EDLCs) generally exhibit high power and long life, but low energy density/capacitance. Pore/morphology optimization and pseudocapacitive materials modification of carbon materials have been used to improve electrode capacitance, but leading to the consumption of tap density, conductivity and stability. Introducing soluble redox mediators into electrolyte is a promising alternative to improve the capacitance of electrode. However, it is difficult to find one redox mediator that can provide additional capacitance for both positive and negative electrodes simultaneously. Here, an ambipolar organic radical, 2, 2, 6, 6-tetramethylpiperidinyloxyl (TEMPO) is first introduced to the electrolyte, which can substantially contribute additional pseudocapacitance by oxidation at the positive electrode and reduction at the negative electrode simultaneously. The EDLC with TEMPO mediator delivers an energy density as high as 51 Wh kg-1, 2.4 times of the capacitor without TEMPO, and a long cycle stability over 4000 cycles. The achieved results potentially point a new way to improve the energy density of EDLCs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Electrochemical properties of novel ionic liquids for electric double layer capacitor applications

    International Nuclear Information System (INIS)

    Sato, Takaya; Masuda, Gen; Takagi, Kentaro

    2004-01-01

    An aliphatic quaternary ammonium salt which has a methoxyethyl group on the nitrogen atom formed an ionic liquid (room temperature molten salt) when combined with the tetrafluoroborate (BF 4 - ) and bis(trifluoromethylsulfonyl)imide [TFSI; (CF 3 SO 2 ) 2 N - ] anions. The limiting oxidation and reduction potentials, specific conductivity, and some other physicochemical properties of the novel ionic liquids, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEME-BF 4 ) and DEME-TFSI have been evaluated and compared with those of 1-ethyl-3-methylimidazolium tetrafluoroborate. DEME-BF 4 is a practically useful ionic liquid for electrochemical capacitors as it has a quite wide potential window (6.0 V) and high ionic conductivity (4.8 mS cm -1 at 25 deg. C). We prepared an electric double layer capacitor (EDLC) composed of a pair of activated carbon electrodes and DEME-BF 4 as the electrolyte. This EDLC (working voltage ∼2.5 V) has both, a higher capacity above room temperature and a better charge-discharge cycle durability at 100 deg. C when compared to a conventional EDLC using an organic liquid electrolyte such as a tetraethylammonium tetrafluoroborate in propylene carbonate

  13. Temperature aspect of degradation of electrochemical double-layer capacitors (EDLC)

    Science.gov (United States)

    Baek, Dong-Cheon; Kim, Hyun-Ho; Lee, Soon-Bok

    2015-03-01

    Electric double layer capacitors (EDLC) cells have a process variation and temperature dependency in capacitance so that balancing is required when they are connected in series, which includes electronic voltage management based on capacitance monitoring. This paper measured temperature aspect of capacitance periodically to monitor health and degradation behavior of EDLC stressed under high temperatures and zero below temperatures respectively, which enables estimation of the state of health (SOH) regardless of temperature. At high temperature, capacitance saturation and delayed expression of degradation was observed. After cyclic stress at zero below temperature, less effective degradation and time recovery phenomenon were occurred.

  14. Structures and electrochemical performances of pyrolized carbons from graphite oxides for electric double-layer capacitor

    Science.gov (United States)

    Kim, Ick-Jun; Yang, Sunhye; Jeon, Min-Je; Moon, Seong-In; Kim, Hyun-Soo; Lee, Yoon-Pyo; An, Kye-Hyeok; Lee, Young-Hee

    The structural features and the electrochemical performances of pyrolized needle cokes from oxidized cokes are examined and compared with those of KOH-activated needle coke. The structure of needle coke is changed to a single phase of graphite oxide after oxidation treatment with an acidic solution having an NaClO 3/needle coke composition ratio of above 7.5, and the inter-layer distance of the oxidized needle coke is expanded to 6.9 Å with increasing oxygen content. After heating at 200 °C, the oxidized needle coke is reduced to a graphite structure with an inter-layer distance of 3.6 Å. By contrast, a change in the inter-layer distance in KOH-activated needle coke is not observed. An intercalation of pyrolized needle coke, observed on first charge, occurs at 1.0 V. This value is lower than that of KOH-activation needle coke. A capacitor using pyrolized needle coke exhibits a lower internal resistance of 0.57 Ω in 1 kHz, and a larger capacitance per weight and volume of 30.3 F g -1 and 26.9 F ml -1, in the two-electrode system over the potential range 0-2.5 V compared with those of a capacitor using KOH-activation of needle coke. This better electrochemical performance is attributed to a distorted graphene layer structure derived from the process of the inter-layer expansion and shrinkage.

  15. CVD synthesis of carbon nanotubes using a finely dispersed cobalt catalyst and their use in double layer electrochemical capacitors

    International Nuclear Information System (INIS)

    Chatterjee, A.K.; Sharon, Maheshwar; Banerjee, Rangan; Neumann-Spallart, Michael

    2003-01-01

    Carbon nanotubes (CNT) were obtained by chemical vapour deposition (CVD), decomposing turpentine oil over finely dispersed Co metal as a catalyst at 675 deg. C. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images reveal that the nanotubes are densely packed and of 10-50 nm in diameter. The XRD pattern of purified CNT shows that they are graphitic in nature. Resistivity measurements of these CNT indicate that they are highly conducting. Hall measurements of CNT reveal that electrons are the majority carriers with a carrier concentration of 1.35x10 20 cm -3 . Cyclic voltammetry (CV) and constant current charging/discharging was used to characterise the behaviour of electrochemical double layer capacitors of purified CNT with H 2 SO 4 . For CNT/2 M H 2 SO 4 /CNT, a capacitance of 12 F g -1 (based on the weight of the active material) was obtained

  16. TiO2 coated Si nanowire electrodes for electrochemical double layer capacitors in room temperature ionic liquid

    International Nuclear Information System (INIS)

    Konstantinou, F; Shougee, A; Albrecht, T; Fobelets, K

    2017-01-01

    Three TiO 2 deposition processes are used to coat the surface of Si nanowire array electrodes for electrochemical double layer capacitors in room temperature ionic liquid [Bmim][NTF 2 ]. The fabrication processes are based on wet chemistry only and temperature treatments are kept below 450 °C. Successful TiO 2 coatings are found to be those that are carried out at low pressure and with low TiO 2 coverage to avoid nanowires breakage. The best TiO 2 coated Si nanowire array electrode in [Bmim][NTF 2 ] showed energy densities of 0.9 Wh·kg −1 and power densities of 2.2 kW·kg −1 with a nanowire length of ∼10 µ m. (paper)

  17. Electrolytes for high voltage electrochemical double layer capacitors: A perspective article

    Science.gov (United States)

    Balducci, A.

    2016-09-01

    The development of innovative electrolyte components is nowadays considered one of the most important aspects for the realization of high energy electrochemical double capacitors (EDLCs). Consequently, in the last years many investigations have been dedicated towards new solvents, new salts and ionic liquids able to replace the current electrolytes. This perspective article aims to supply a critical analysis about the results obtained so far on the development of new electrolytes for high energy EDLCs and to outline the advantages as well as the limits related to the use of these innovative components. Furthermore, this article aims to give indications about the strategies could be used in the future for a further development of advanced electrolytes.

  18. Aging of electrochemical double layer capacitors with acetonitrile-based electrolyte at elevated voltages

    International Nuclear Information System (INIS)

    Ruch, P.W.; Cericola, D.; Foelske-Schmitz, A.; Koetz, R.; Wokaun, A.

    2010-01-01

    Laboratory-scale electrochemical capacitor cells with bound activated carbon electrodes and acetonitrile-based electrolyte were aged at various elevated constant cell voltages between 2.75 V and 4.0 V. During the constant voltage tests, the cell capacitance as well as the capacitance and resistance of each electrode was determined. Following each aging experiment, the cells were analyzed by means of electrochemical impedance spectroscopy, and the individual electrodes were characterized by gas adsorption and X-ray photoelectron spectroscopy. At cell voltages above 3.0 V, the positive electrode ages much faster than the negative. Both the capacitance loss and resistance increase of the cell could be totally attributed to the positive electrode. At cell voltages above 3.5 V also the negative electrode aged significantly. X-ray photoelectron spectroscopy indicated the presence of degradation products on the electrode surface with a much thicker layer on the positive electrode. Simultaneously, a significant decrease in electrode porosity could be detected by gas adsorption.

  19. Probing the characteristics of casein as green binder for non-aqueous electrochemical double layer capacitors' electrodes

    Science.gov (United States)

    Varzi, Alberto; Raccichini, Rinaldo; Marinaro, Mario; Wohlfahrt-Mehrens, Margret; Passerini, Stefano

    2016-09-01

    Casein from bovine milk is evaluated in this work as binding agent for electrochemical double layer capacitors (EDLCs) electrodes. It is demonstrated that casein provides excellent adhesion strength to the current collector (1187 kPa compared to 51 kPa achieved with PVdF), thus leading to mechanically stable electrodes. At the same time, it offers high thermal stability (above 200 °C) and electrochemical stability in organic electrolytes. Apparently though, the casein-based electrodes offer lower electronic conductivity than those based on other state-of-the-art binders, which can limit the rate performance of the resulting EDLC. In the attempt of improving the electrochemical performance, it is found that the application of a pressing step can solve this issue, leading to excellent rate capability (up to 84% capacitance retention at 50 mA cm-2) and cycling stability (96.8% after 10,000 cycles at 10 mA cm-2) in both PC- and ACN-based electrolytes. Although the adhesive power casein is known since ancient times, this report presents the first proof of concept of its employment in electrochemical power sources.

  20. Electrochemical characterization of single-walled carbon nanotubes for electrochemical double layer capacitors using non-aqueous electrolyte

    International Nuclear Information System (INIS)

    Ruch, P.W.; Koetz, R.; Wokaun, A.

    2009-01-01

    Single-walled carbon nanotubes (SWCNTs) were investigated by cyclic voltammetry and electrochemical impedance spectroscopy in a non-aqueous electrolyte, 1 M Et 4 NBF 4 in acetonitrile, suitable for supercapacitors. Further, in situ dilatometry and in situ conductance measurements were performed on single electrodes and the results compared to an activated carbon, YP17. Both materials show capacitive behavior characteristic of high surface area electrodes for supercapacitors, with the maximum full cell gravimetric capacitance being 34 F/g for YP17 and 20 F/g for SWCNTs at 2.5 V with respect to the total active electrode mass. The electronic resistance of SWCNTs and activated carbon decreases significantly during charging, showing similarities of the two materials during electrochemical doping. The SWCNT electrode expands irreversibly during the first electrochemical potential sweep as verified by in situ dilatometry, indicative of at least partial debundling of the SWCNTs. A reversible periodic swelling and shrinking during cycling is observed for both materials, with the magnitude of expansion depending on the type of ions forming the double layer.

  1. A review of molecular modelling of electric double layer capacitors.

    Science.gov (United States)

    Burt, Ryan; Birkett, Greg; Zhao, X S

    2014-04-14

    Electric double-layer capacitors are a family of electrochemical energy storage devices that offer a number of advantages, such as high power density and long cyclability. In recent years, research and development of electric double-layer capacitor technology has been growing rapidly, in response to the increasing demand for energy storage devices from emerging industries, such as hybrid and electric vehicles, renewable energy, and smart grid management. The past few years have witnessed a number of significant research breakthroughs in terms of novel electrodes, new electrolytes, and fabrication of devices, thanks to the discovery of innovative materials (e.g. graphene, carbide-derived carbon, and templated carbon) and the availability of advanced experimental and computational tools. However, some experimental observations could not be clearly understood and interpreted due to limitations of traditional theories, some of which were developed more than one hundred years ago. This has led to significant research efforts in computational simulation and modelling, aimed at developing new theories, or improving the existing ones to help interpret experimental results. This review article provides a summary of research progress in molecular modelling of the physical phenomena taking place in electric double-layer capacitors. An introduction to electric double-layer capacitors and their applications, alongside a brief description of electric double layer theories, is presented first. Second, molecular modelling of ion behaviours of various electrolytes interacting with electrodes under different conditions is reviewed. Finally, key conclusions and outlooks are given. Simulations on comparing electric double-layer structure at planar and porous electrode surfaces under equilibrium conditions have revealed significant structural differences between the two electrode types, and porous electrodes have been shown to store charge more efficiently. Accurate electrolyte and

  2. Spatiotemporal electrochemical measurements across an electric double layer capacitor electrode with application to aqueous sodium hybrid batteries

    Science.gov (United States)

    Tully, Katherine C.; Whitacre, Jay F.; Litster, Shawn

    2014-02-01

    This paper presents in-situ spatiotemporal measurements of the electrolyte phase potential within an electric double layer capacitor (EDLC) negative electrode as envisaged for use in an aqueous hybrid battery for grid-scale energy storage. The ultra-thick electrodes used in these batteries to reduce non-functional material costs require sufficiently fast through-plane mass and charge transport to attain suitable charging and discharging rates. To better evaluate the through-plane transport, we have developed an electrode scaffold (ES) for making in situ electrolyte potential distribution measurements at discrete known distances across the thickness of an uninterrupted EDLC negative electrode. Using finite difference methods, we calculate local current, volumetric charging current and charge storage distributions from the spatiotemporal electrolyte potential measurements. These potential distributions provide insight into complex phenomena that cannot be directly observed using other existing methods. Herein, we use the distributions to identify areas of the electrode that are underutilized, assess the effects of various parameters on the cumulative charge storage distribution, and evaluate an effectiveness factor for charge storage in EDLC electrodes.

  3. Performance of palladium nanoparticle–graphene composite as an efficient electrode material for electrochemical double layer capacitors

    International Nuclear Information System (INIS)

    Dar, Riyaz A.; Giri, Lily; Karna, Shashi P.; Srivastava, Ashwini K.

    2016-01-01

    Highlights: • Single step synthesis of palladium nanoparticles decorated-graphene nanocomposite. • Improved electron transfer kinetics and superior capacitive performance. • High specific capacitance of 637 F g −1 at a current density of 1.25 A g −1 . • Retention of 91.4% of its initial capacitance after 10000 cycles of testing. - Abstract: Palladium nanoparticle–graphene nanosheet composite (PdNP–GN) is demonstrated as an efficient electrode material in energy storage applications in supercapacitors. Palladium nanoparticle (PdNP) decorated graphene nanosheet (GN) composite was synthesized via a chemical approach in a single step by the simultaneous reduction of graphene oxide (GO) and palladium chloride from the aqueous phase using ascorbic acid as reducing agent. The materials were characterized by scanning and high resolution transmission electron microscopy, Raman, X-ray diffraction and energy dispersive X-ray spectroscopy which demonstrate that the metal nanoparticles have been uniformly deposited on the surface of graphene nanosheets. The synthesized material has been analyzed by cyclic voltammetry, electrochemical impedance spectrometry and chronopotentiometry using 1 M KCl as the supporting electrolyte for its application in electrochemical double layer supercapacitors. PdNPs-GN composite showed improved electron transfer kinetics and superior capacitive performance with large specific capacitance of 637 F g −1 , excellent cyclic performance and maximum energy and power densities of 56 Wh kg −1 and 1166 W kg −1 , respectively at a current density of 1.25 A g −1 . This highlights the importance of the synergetic effects of electrochemically efficient Pd nanoparticles and graphene for energy storage applications in supercapacitors.

  4. The preparation and properties of a novel electrolyte of electrochemical double layer capacitors based on LiPF6 and acetamide

    International Nuclear Information System (INIS)

    Li Qi; Zuo Xiaoxi; Liu Jiansheng; Xiao Xin; Shu Dong; Nan Junmin

    2011-01-01

    A novel electrolyte applied in electrochemical double-layer capacitors (EDLCs) has been prepared based on lithium hexafluorophosphate (LiPF 6 ) and acetamide and subsequently characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), electrochemical techniques and so on. The mixtures of LiPF 6 and acetamide at the molar ratios of 1:4 to 1:6 exist as liquids below 25 °C, which is attributed to the melting point depression of mixture and the coordination of the polar groups (C=O and NH groups) of acetamide with Li + and PF 6 − ions. The strong interaction between LiPF 6 and acetamide results in the rupture of the electrovalent bond of LiPF 6 and the breakage of hydrogen bonds among the acetamide molecules, leading to the formation of a liquid electrolyte. The LiPF 6 /acetamide electrolyte with a molar ratio of 1:5.5 exhibits a 5.2 V electrochemical window and suitable ionic conductivity at room temperature. In particular, the coin-type cells with carbon electrodes and LiPF 6 /acetamide electrolyte possess high thermal stability and electrochemical properties, showing that the as-prepared LiPF 6 /acetamide electrolyte is a promising candidate for EDLCs.

  5. Liquid Crystals of Lithium Dodecylbenzenesulfonate for Electric Double Layer Capacitors

    International Nuclear Information System (INIS)

    Kuzmin, Andrey Vasil’evich; Yurtov, Evgeny V.

    2016-01-01

    Ionic lyotropic liquid crystals based on lithium dodecylbenzenesulfonate were used as electrolytes for electric double layer capacitors with carbon fibrous electrodes. The capacitors were tasted by cyclic voltammetry, galvanostatic charge and discharge, and impedance spectroscopy. The highest specific capacitance was achieved for electrical double layer capacitor equipped with ionic lyotropic liquid crystal of lithium dodecylbenzenesulfonate 35 wt% in water. The specific capacitance of capacitor was calculated from galvanostatic discharge curves – 15 F/g of carbon fibrous material

  6. Investigation of the Characteristic Properties of Glacial Acetic Acid-Catalyzed Carbon Xerogels and Their Electrochemical Performance for Use as Electrode Materials in Electrical Double-Layer Capacitors

    Directory of Open Access Journals (Sweden)

    Nguyen Khanh Nguyen Quach

    2017-01-01

    Full Text Available Glacial acetic acid was used as a catalyst in the preparation process of carbon xerogels from the condensation of resorcinol and formaldehyde for shortening significantly the gelation time. The effect of the resorcinol/catalyst ratio over a large range of 2 to 500, the solvent exchange manner with acetone, and the pyrolysis temperature of 700 to 1000°C on the characteristic properties of the carbon xerogels were investigated. A resorcinol/catalyst ratio of 2 and a pyrolysis temperature at 800°C were found to be the optimal condition for the preparation of carbon xerogels with a well-balanced porosity between micro- and mesopores, high surface area (577.62 m2g−1, and large pore volume (0.97 cm3g−1, which are appropriate for use as electrode materials in an electrical double-layer capacitor. The carbon xerogel electrodes that were prepared under these optimal conditions exhibited a good electrochemical performance with the highest specific capacitance of 169 Fg−1 in 6 M KOH electrolyte at a scan rate of 5 mVs−1 from cyclic voltammetry.

  7. Super-capacitive electro-chemical performance of polymer blend gel polymer electrolyte (GPE) in carbon-based electrical double-layer capacitors

    International Nuclear Information System (INIS)

    Syahidah, S. Nuur; Majid, S.R.

    2013-01-01

    This study reports on the fabrication and comparative performance characteristics of a symmetrical electrical double-layer capacitor (EDLC) employed gel polymer electrolyte (GPE) assembled between carbon based electrodes. Three cells, A, B and C were fabricated using different composition of active materials (activated or porous carbon), binder (PVdF-HFP) and conductivity enhancer (super-P). The configuration of cell A: 0.9 porous carbon/0.1 PVdF-HFP, cell B: 0.45 activated carbon/0.45 porous carbon/0.1 PVdF-HFP and cell C: 0.8 activated carbon/0.1 super-P/0.1 PVdF-HFP. The GPE, comprising a poly(vinyl pyrrolidone) (PVP)/poly(vinylidene fluoride co-hexafluoroproplyne) (PVdF-HFP) blend complexed with magnesium triflate, Mg(CF 3 SO 3 ) 2 , was prepared by the solution casting technique at 60 °C. The physico-chemical properties of the GPEs were characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The ionic conductivity at the ambient temperature of the GPE is 2.16 × 10 −4 S cm −1 at 7.5 wt.% of Mg(CF 3 SO 3 ) 2 with a ∼2.6 V electro-chemical stability window. At the 1000th cycle, the specific capacitance, C s of cell A is 89 F g −1 while cell B and C are 63 and 49 F g −1 . Cell A shows excellent long-term cyclic stability (less than a 5% decrease in specific capacitance after 1000 cycles). The best operating voltage for cell A is 1.6 V with the specific capacitance 106 F g −1 after 500 cycles

  8. Materials for electrochemical capacitors

    Science.gov (United States)

    Simon, Patrice; Gogotsi, Yury

    2008-11-01

    Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

  9. Effect of Pore Structure and Chemistry on the Performance of Activated Oil Sands Petroleum Coke Electrodes for use in Electrochemical Double-Layer Capacitors

    Science.gov (United States)

    Zuliani, Jocelyn Ellen

    Electrical energy storage is a limiting barrier to widespread usage and commercialization of sustainable and renewable energy sources, such as wind and solar energy, as well as integration of electric vehicles. Electrochemical double-layer capacitors (EDLCs) are a promising energy storage technology that offers the benefits of high power density, long cycle life, rapid charging rates, and moderate energy density. The energy storage mechanism of EDLCs is physical ion adsorption on the surface of porous carbon electrodes. This thesis is an investigation of three different sections relating to EDLCs: 1) techniques to properly characterize novel porous carbon electrode materials, 2) investigation of activated oil sands petroleum coke (APC) as the electrode material for EDLCs, and 3) a systematic study of the effects of porous carbon structure and chemistry on EDLC performance. In the first section, it was shown that variations in operating conditions and testing techniques can lead to discrepancies in measured and reported capacitance. Therefore, it was concluded that a standardized approach is necessary in order to properly compare different porous carbon electrodes. In the second section, APC was investigated as a novel electrode material for EDLCs. PetCoke is a carbon dense material that can be activated with potassium hydroxide to generate high surface area porous carbon materials. These materials show promising electrochemical performance in EDLCs, with capacitance values up to 400 Fg-1 in 4M potassium hydroxide aqueous electrolytes, depending on the operating conditions. Additionally, the power density of these materials is comparable to that of other carbon nanomaterials, which are more costly and challenging to produce. Finally, the third section investigates the relationship between measured capacitance, and carbon macrostructure, meso-structure, microstructure, and oxygen content. In each of these studies, the desired parameter was varied, while all others

  10. Application of Electric Double Layer Capacitor for Solar Car

    OpenAIRE

    中西, 弘一; 岸, 純男; 仲森, 昌也; 荒賀, 浩一

    2016-01-01

    This paper describes a method for efficient work of electrical energy, using DC-DC converter as insulate between battery and Electrical Double Layer Capacitor (EDLC). In case of constant-current charge to the EDLC, the efficiency of the electric power is higher, compared to the constant-voltage charge.

  11. Layering and Ordering in Electrochemical Double Layers

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yihua [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States; Kawaguchi, Tomoya [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States; Pierce, Michael S. [Rochester Institute of Technology, School of Physics and Astronomy, Rochester, New York 14623, United States; Komanicky, Vladimir [Faculty of Science, Safarik University, 041 54 Kosice, Slovakia; You, Hoydoo [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States

    2018-02-26

    Electrochemical double layers (EDL) form at electrified interfaces. While Gouy-Chapman model describes moderately charged EDL, formation of Stern layers was predicted for highly charged EDL. Our results provide structural evidence for a Stern layer of cations, at potentials close to hydrogen evolution in alkali fluoride and chloride electrolytes. Layering was observed by x-ray crystal truncation rods and atomic-scale recoil responses of Pt(111) surface layers. Ordering in the layer is confirmed by glancing-incidence in-plane diffraction measurements.

  12. Electrochemical capacitor

    Science.gov (United States)

    Anderson, Marc A.; Liu, Kuo -Chuan; Mohr, Charles M.

    1999-10-05

    An inexpensive porous metal oxide material having high surface area, good conductivity and high specific capacitance is advantageously used in an electrochemical capacitor. The materials are formed in a sol-gel process which affords control over the properties of the resultant metal oxide materials.

  13. Capacitance of carbon-based electrical double-layer capacitors.

    Science.gov (United States)

    Ji, Hengxing; Zhao, Xin; Qiao, Zhenhua; Jung, Jeil; Zhu, Yanwu; Lu, Yalin; Zhang, Li Li; MacDonald, Allan H; Ruoff, Rodney S

    2014-01-01

    Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

  14. Novel electric double-layer capacitor with a coaxial fiber structure.

    Science.gov (United States)

    Chen, Xuli; Qiu, Longbin; Ren, Jing; Guan, Guozhen; Lin, Huijuan; Zhang, Zhitao; Chen, Peining; Wang, Yonggang; Peng, Huisheng

    2013-11-26

    A coaxial electric double-layer capacitor fiber is developed from the aligned carbon nanotube fiber and sheet, which functions as two electrodes with a polymer gel sandwiched between them. The unique coaxial structure enables a rapid transportation of ions between the two electrodes with a high electrochemical performance. These energy storage fibers are also flexible and stretchable, and can be woven into and widely used for electronic textiles. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

    Science.gov (United States)

    Brandon, Erik J.; West, William C.; Smart, Marshall C.; Yushin, Gleb; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek

    2012-01-01

    Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

  16. A critical overview of definitions and determination techniques of the internal resistance using lithium-ion, lead-acid, nickel metal-hydride batteries and electrochemical double-layer capacitors as examples

    Science.gov (United States)

    Piłatowicz, Grzegorz; Marongiu, Andrea; Drillkens, Julia; Sinhuber, Philipp; Sauer, Dirk Uwe

    2015-11-01

    The internal resistance (Ri) is one of the key parameters that determine the current state of electrochemical storage systems (ESS). It is crucial for estimating cranking capability in conventional cars, available power in modern hybrid and electric vehicles and for determining commonly used factors such as state-of-health (SoH) and state-of-function (SoF). However, ESS are complex and non-linear systems. Their Ri depends on many parameters such as current rate, temperature, SoH and state-of-charge (SoC). It is also a fact that no standardized methodologies exist and many different definitions and ways of Ri determination are being used. Nevertheless, in many cases authors are not aware of the consequences that occur when different Ri definitions are being used, such as possible misinterpretations, doubtful comparisons and false figures of merit. This paper focuses on an application-oriented separation between various Ri definitions and highlights the differences between them. The investigation was based on the following technologies: lead-acid, lithium-ion and nickel metal-hydride batteries as well as electrochemical double-layer capacitors. It is not the target of this paper to provide a standardized definition of Ri but to give researchers, engineers and manufacturers a possibility to understand what the term Ri means in their own work.

  17. Superionic state in double-layer capacitors with nanoporous electrodes

    International Nuclear Information System (INIS)

    Kondrat, S; Kornyshev, A

    2011-01-01

    In recent experiments (Chmiola et al 2006 Science 313 1760; Largeot et al 2008 J. Am. Chem. Soc. 130 2730) an anomalous increase of the capacitance with a decrease of the pore size of a carbon-based porous electric double-layer capacitor has been observed. We explain this effect by image forces which exponentially screen out the electrostatic interactions of ions in the interior of a pore. Packing of ions of the same sign becomes easier and is mainly limited by steric interactions. We call this state 'superionic' and suggest a simple model to describe it. The model reveals the possibility of a voltage-induced first order transition between a cation(anion)-deficient phase and a cation(anion)-rich phase which manifests itself in a jump of capacitance as a function of voltage. (fast track communication)

  18. Superionic state in double-layer capacitors with nanoporous electrodes.

    Science.gov (United States)

    Kondrat, S; Kornyshev, A

    2011-01-19

    In recent experiments (Chmiola et al 2006 Science 313 1760; Largeot et al 2008 J. Am. Chem. Soc. 130 2730) an anomalous increase of the capacitance with a decrease of the pore size of a carbon-based porous electric double-layer capacitor has been observed. We explain this effect by image forces which exponentially screen out the electrostatic interactions of ions in the interior of a pore. Packing of ions of the same sign becomes easier and is mainly limited by steric interactions. We call this state 'superionic' and suggest a simple model to describe it. The model reveals the possibility of a voltage-induced first order transition between a cation(anion)-deficient phase and a cation(anion)-rich phase which manifests itself in a jump of capacitance as a function of voltage.

  19. Nanostructured Electrode Materials for Electrochemical Capacitor Applications.

    Science.gov (United States)

    Choi, Hojin; Yoon, Hyeonseok

    2015-06-02

    The advent of novel organic and inorganic nanomaterials in recent years, particularly nanostructured carbons, conducting polymers, and metal oxides, has enabled the fabrication of various energy devices with enhanced performance. In this paper, we review in detail different nanomaterials used in the fabrication of electrochemical capacitor electrodes and also give a brief overview of electric double-layer capacitors, pseudocapacitors, and hybrid capacitors. From a materials point of view, the latest trends in electrochemical capacitor research are also discussed through extensive analysis of the literature and by highlighting notable research examples (published mostly since 2013). Finally, a perspective on next-generation capacitor technology is also given, including the challenges that lie ahead.

  20. Sulfonated poly(ether ether ketone) membranes for electric double layer capacitors

    International Nuclear Information System (INIS)

    Kim, Wan Ju; Kim, Dong-Won

    2008-01-01

    Sulfonated poly(ether ether ketone) (S-PEEK) with different degree of sulfonation (DS) has been prepared and evaluated as a proton conducting membrane for electric double layer capacitor (EDLC). The polymer electrolytes prepared with S-PEEK membrane exhibited ionic conductivities about 1.2 x 10 -3 -4.5 x 10 -3 S cm -1 at room temperature, which depended on both soaking solvent and degree of sulfonation. The quasi-solid-state EDLCs consisted of activated carbon electrodes and S-PEEK membrane were assembled, and their electrochemical characteristics were studied by cyclic voltammetry and charge-discharge cycle tests. The effect of DS on the electrochemical performances of EDLCs has been investigated

  1. Relation between the ion size and pore size for an electric double-layer capacitor.

    Science.gov (United States)

    Largeot, Celine; Portet, Cristelle; Chmiola, John; Taberna, Pierre-Louis; Gogotsi, Yury; Simon, Patrice

    2008-03-05

    The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.

  2. Studies on electrical double layer capacitor with a low-viscosity ionic ...

    Indian Academy of Sciences (India)

    The performance of an electrical double layer capacitor (EDLC) composed of high surface area acti- vated carbon ... Since the electric energy stored in EDLCs are raised by the ..... capacitance value, observed by us with the present system, is.

  3. Iodine encapsulation in CNTs and its application for electrochemical capacitor

    International Nuclear Information System (INIS)

    Taniguchi, Y.; Ishii, Y.; Al-zubaidi, A.; Kawasaki, S.; Rashid, M.; Syakirin, A.

    2016-01-01

    We report the experimental results for new type electrochemical capacitor using iodine redox reaction in single-walled carbon nanotubes (SWCNTs). It was found that the energy density of the present redox capacitor using SWCNTs is almost three times larger than that of the normal electric double layer capacitor.

  4. Iodine encapsulation in CNTs and its application for electrochemical capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Taniguchi, Y.; Ishii, Y.; Al-zubaidi, A.; Kawasaki, S., E-mail: kawasaki.shinji@nitech.ac.jp [Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Aichi (Japan); Rashid, M.; Syakirin, A. [Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor (Malaysia)

    2016-07-06

    We report the experimental results for new type electrochemical capacitor using iodine redox reaction in single-walled carbon nanotubes (SWCNTs). It was found that the energy density of the present redox capacitor using SWCNTs is almost three times larger than that of the normal electric double layer capacitor.

  5. Preparation and Characterization of Carbon Nanotubes-Based Composite Electrodes for Electric Double Layer Capacitors

    International Nuclear Information System (INIS)

    Seo, Min Kang; Park, Soo Jin

    2012-01-01

    In this work, we prepared activated multi-walled carbon nanotubes/polyacrylonitrile (A-MWCNTs/C) composites by film casting and activation method. Electrochemical properties of the composites were investigated in terms of serving as MWCNTs-based electrode materials for electric double layer capacitors (EDLCs). As a result, the A-MWCNTs/C composites had much higher BET specific surface area, and pore volume, and lower volume ratio of micropores than those of pristine MWCNTs/PAN ones. Furthermore, some functional groups were added on the surface of the A-MWCNTs/C composites. The specific capacitance of the A-MWCNTs/C composites was more than 4.5 times that of the pristine ones at 0.1 V discharging voltage owing to the changes of the structure and surface characteristics of the MWCNTs by activation process

  6. Sub-millimeter arbitrary arrangements of monolithically micro-scale electrical double layer capacitors

    International Nuclear Information System (INIS)

    Laszczyk, Karolina U; Kazufumi, Kobashi; Sakurai, Shunsuke; Sekiguchi, Atsuko; Futaba, Don N; Yamada, Takeo; Hata, Kenji

    2015-01-01

    We report the investigation on the reproducibility of micro-scale electric double layer capacitors (micro-EDLCs). The micro-EDLC components were fabricated parallel using photolithography, wet and dry processing. Electrodes of the micro-EDLCs are highly dense packed Single Wall Carbon Nanotubes (SWCNTs) that form a mesh structure. The micro- EDLCs are connected 1-10 in series and in parallel being unified electrical circuits to tune the capacitance and the operational voltage. To confirm the reproducibility of the cells as well as the yield we performed electrochemical measurements in order to define the performance uniformity between cells strings and individual cells connected in a string. For 1-10 cells in series and in parallel the trends for the capacitance and operational voltage satisfied electrophysics rules governing cells addition. However, the measurements of the individual cells in a string revealed the significant performance discrepancy that might result in a shorten life cycling of a circuit. (paper)

  7. Sub-millimeter arbitrary arrangements of monolithically micro-scale electrical double layer capacitors

    Science.gov (United States)

    Laszczyk, Karolina U.; Kazufumi, Kobashi; Sakurai, Shunsuke; Sekiguchi, Atsuko; Futaba, Don N.; Yamada, Takeo; Hata, Kenji

    2015-12-01

    We report the investigation on the reproducibility of micro-scale electric double layer capacitors (micro-EDLCs). The micro-EDLC components were fabricated parallel using photolithography, wet and dry processing. Electrodes of the micro-EDLCs are highly dense packed Single Wall Carbon Nanotubes (SWCNTs) that form a mesh structure. The micro- EDLCs are connected 1-10 in series and in parallel being unified electrical circuits to tune the capacitance and the operational voltage. To confirm the reproducibility of the cells as well as the yield we performed electrochemical measurements in order to define the performance uniformity between cells strings and individual cells connected in a string. For 1-10 cells in series and in parallel the trends for the capacitance and operational voltage satisfied electrophysics rules governing cells addition. However, the measurements of the individual cells in a string revealed the significant performance discrepancy that might result in a shorten life cycling of a circuit.

  8. Cooperation of micro- and meso-porous carbon electrode materials in electric double-layer capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Cheng [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, Jilin Province (China); Graduate University of Chinese Academy of Sciences, Beijing 100039 (China); Qi, Li; Wang, Hongyu [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, Jilin Province (China); Yoshio, Masaki [Advanced Research Center, Saga University, 1341 Yoga-machi, Saga 840-0047 (Japan)

    2010-07-01

    The capacitive characteristics of micro- and meso-porous carbon materials have been compared in cyclic voltammetric studies and galvanostatic charge-discharge tests. Meso-porous carbon can keep certain high capacitance values at high scan rates, whereas micro-porous carbon possesses very high capacitance values at low scan rates but fades quickly as the scan rate rises up. For better performance of electric double-layer capacitors (EDLCs), the cooperative application of both kinds of carbon materials has been proposed in the following two ways: mixing both kinds of carbons in the same electrode or using the asymmetric configuration of carbon electrodes in the same EDLC. The cooperative effect on the electrochemical performance has also been addressed. (author)

  9. Memory characteristics of an MOS capacitor structure with double-layer semiconductor and metal heterogeneous nanocrystals

    International Nuclear Information System (INIS)

    Ni Henan; Wu Liangcai; Song Zhitang; Hui Chun

    2009-01-01

    An MOS (metal oxide semiconductor) capacitor structure with double-layer heterogeneous nanocrystals consisting of semiconductor and metal embedded in a gate oxide for nonvolatile memory applications has been fabricated and characterized. By combining vacuum electron-beam co-evaporated Si nanocrystals and self-assembled Ni nanocrystals in a SiO 2 matrix, an MOS capacitor with double-layer heterogeneous nanocrystals can have larger charge storage capacity and improved retention characteristics compared to one with single-layer nanocrystals. The upper metal nanocrystals as an additional charge trap layer enable the direct tunneling mechanism to enhance the flat voltage shift and prolong the retention time. (semiconductor devices)

  10. Important parameters affecting the cell voltage of aqueous electrical double-layer capacitors

    Science.gov (United States)

    Wu, Tzu-Ho; Hsu, Chun-Tsung; Hu, Chi-Chang; Hardwick, Laurence J.

    2013-11-01

    This study discusses and demonstrates how the open-circuit potential and charges stored in the working potential window on positive and negative electrodes affect the cell voltage of carbon-based electrical double-layer capacitors (EDLCs) in aqueous electrolytes. An EDLC consisting of two activated carbon electrodes is employed as the model system for identifying these key parameters although the potential window of water decomposition can be simply determined by voltammetric methods. First, the capacitive performances of an EDLC with the same charge on positive and negative electrodes are evaluated by cyclic voltammetric, charge-discharge, electrochemical impedance spectroscopic (EIS) analyses, and inductance-capacitance-resistance meter (LCR meter). The principles for obtaining the highest acceptable cell voltage of such symmetric ECs with excellent reversibility and capacitor-like behaviour are proposed. Aqueous charge-balanced EDLCs can be operated as high as 2.0 V with high energy efficiency (about 90%) and only 4% capacitance loss after the 600-cycle stability checking. The necessity of charge balance (but not capacitance balance) for positive and negative electrodes is substantiated from the lower acceptable cell voltage of charge-unbalanced EDLCs.

  11. Nanostructured Electrode Materials for Electrochemical Capacitor Applications

    Directory of Open Access Journals (Sweden)

    Hojin Choi

    2015-06-01

    Full Text Available The advent of novel organic and inorganic nanomaterials in recent years, particularly nanostructured carbons, conducting polymers, and metal oxides, has enabled the fabrication of various energy devices with enhanced performance. In this paper, we review in detail different nanomaterials used in the fabrication of electrochemical capacitor electrodes and also give a brief overview of electric double-layer capacitors, pseudocapacitors, and hybrid capacitors. From a materials point of view, the latest trends in electrochemical capacitor research are also discussed through extensive analysis of the literature and by highlighting notable research examples (published mostly since 2013. Finally, a perspective on next-generation capacitor technology is also given, including the challenges that lie ahead.

  12. Electric double-layer capacitor based on an ionic clathrate hydrate.

    Science.gov (United States)

    Lee, Wonhee; Kwon, Minchul; Park, Seongmin; Lim, Dongwook; Cha, Jong-Ho; Lee, Huen

    2013-07-01

    Herein, we suggest a new approach to an electric double-layer capacitor (EDLC) that is based on a proton-conducting ionic clathrate hydrate (ICH). The ice-like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me4NOH⋅5 H2O show a high specific capacitance, reversible charge-discharge behavior, and a long cycle life. The ionic-hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1) The ICH does not cause leakage problems under normal EDLC operating conditions. 2) The hydrate material can be utilized itself, without requiring any pre-treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3) The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4) The hydrate solid electrolyte exhibits more-favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Preparation of porous carbon sphere from waste sugar solution for electric double-layer capacitor

    Science.gov (United States)

    Hao, Zhi-Qiang; Cao, Jing-Pei; Wu, Yan; Zhao, Xiao-Yan; Zhuang, Qi-Qi; Wang, Xing-Yong; Wei, Xian-Yong

    2017-09-01

    Waste sugar solution (WSS), which contains abundant 2-keto-L-gulonic acid, is harmful to the environment if discharged directly. For value-added utilization of the waste resource, a novel process is developed for preparation of porous carbon spheres by hydrothermal carbonization (HTC) of WSS followed by KOH activation. Additionally, the possible preparation mechanism of carbon spheres is proposed. The effects of hydrothermal and activation parameters on the properties of the carbon sphere are also investigated. The carbon sphere is applied to electric double-layer capacitor and its electrochemical performance is studied. These results show that the carbon sphere obtained by HTC at 180 °C for 12 h with the WSS/deionized water volume ratio of 2/3 possess the highest specific capacitance under identical activation conditions. The specific capacitance of the carbon spheres can reach 296.1 F g-1 at a current density of 40 mA g-1. Besides, excellent cycle life and good capacitance retention (89.6%) are observed at 1.5 A g-1 after 5000 cycles. This study not only provides a facile and potential method for the WSS treatment, but also achieves the high value-added recycling of WSS for the preparation of porous carbon spheres with superior electrochemical properties.

  14. Outstanding features of alginate-based gel electrolyte with ionic liquid for electric double layer capacitors

    Science.gov (United States)

    Soeda, Kazunari; Yamagata, Masaki; Ishikawa, Masashi

    2015-04-01

    An alginate-based gel electrolyte with an ionic liquid (Alg/IL) is investigated for electric double-layer capacitors (EDLCs) by using physicochemical and electrochemical measurements. The Alg/EMImBF4 (EMImBF4 = 1-ethyl-3-methylimidazolium tetrafluoroborate) gel electrolyte is thermally stable up to 280 °C, where EMImBF4 decomposes. Furthermore, the EDLC with the gel electrolyte can be operated even at high temperature. The cell containing Alg/EMImBF4 is also electrochemically stable even under high voltage (∼3.5 V) operation. Thus, the alginate is a suitable host polymer for the gel electrolyte for EDLCs. According to the result of charge-discharge characteristics, the voltage drop in the charge-discharge curve for the cell with Alg/EMImBF4 gel electrolyte is considerably smaller than that with liquid-phase EMImBF4 electrolyte. To clarify the effect of Alg in contact with the activated carbon electrode, we also prepared an Alg-containing ACFC electrode (Alg + ACFC), and evaluated its EDLC characteristics in liquid EMImBF4. The results prove that the presence of Alg close to the active materials significantly reduces the internal resistance of the EDLC cell, which may be attributed to the high affinity of Alg to activated carbon.

  15. Electric-Field-Induced Superconductivity Detected by Magnetization Measurements of an Electric-Double-Layer Capacitor

    NARCIS (Netherlands)

    Kasahara, Yuichi; Nishijima, Takahiro; Sato, Tatsuya; Takeuchi, Yuki; Ye, Jianting; Yuan, Hongtao; Shimotani, Hidekazu; Iwasa, Yoshihiro

    We report evidence for superconductivity induced by the application of strong electric fields onto the surface of a band insulator, ZrNCl, provided by the observation of a shielding diamagnetic signal. We introduced an electric-double-layer capacitor configuration and in situ magnetization

  16. Application of electric double layer capacitor to pulse coil power supply

    International Nuclear Information System (INIS)

    Abe, Keita; Inomoto, Michiaki; Yamada, Takuma; Kamio, Shuji; Sakumura, Morio; Cao, Qinghong; Ono, Yasushi; Kuwahata, Akihiro; Imazawa, Ryota

    2011-01-01

    We developed a new application of the electric double layer capacitor (EDLC) as a sec-order quasi-DC power supply like flying-wheel motor-generators. We constructed the power supply using IGBT switching circuit and successfully demonstrated its initial operation whose current and duration time are 100 A and 3 sec, respectively, indicating a new potential of EDLC. (author)

  17. High-Surface-Area Nitrogen-Doped Reduced Graphene Oxide for Electric Double-Layer Capacitors.

    Science.gov (United States)

    Youn, Hee-Chang; Bak, Seong-Min; Kim, Myeong-Seong; Jaye, Cherno; Fischer, Daniel A; Lee, Chang-Wook; Yang, Xiao-Qing; Roh, Kwang Chul; Kim, Kwang-Bum

    2015-06-08

    A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2)  g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Edge effects in vertically-oriented graphene based electric double-layer capacitors

    Science.gov (United States)

    Yang, Huachao; Yang, Jinyuan; Bo, Zheng; Zhang, Shuo; Yan, Jianhua; Cen, Kefa

    2016-08-01

    Vertically-oriented graphenes (VGs) have been demonstrated as a promising active material for electric double-layer capacitors (EDLCs), partially due to their edge-enriched structure. In this work, the 'edge effects', i.e., edges as the promoters of high capacitance, in VG based EDLCs are investigated with experimental research and numerical simulations. VGs with diverse heights (i.e., edge-to-basal ratios) and edge densities are prepared with varying the plasma-enabled growth time and employing different plasma sources. Electrochemical measurements show that the edges play a predominant role on the charge storage behavior of VGs. A simulation is further conducted to unveil the roles of the edges on the separation and adsorption of ions within VG channels. The initial charge distribution of a VG plane is obtained with density functional theory (DFT) calculations, which is subsequently applied to a molecular dynamics (MD) simulation system to gain the insights into the microscope EDLC structures. Compared with the basal planes, the edges present higher initial charge density (by 4.2 times), higher ion packing density (by 2.6 times), closer ion packing location (by 0.8 Å), and larger ion separation degree (by 14%). The as-obtained findings will be instructive in designing the morphology and structure of VGs for enhanced capacitive performances.

  19. Electric Double-Layer Capacitor Fabricated with Addition of Carbon Nanotube to Polarizable Electrode

    OpenAIRE

    Yoshiyuki Show

    2012-01-01

    Electrical double-layer capacitor (EDLC) was fabricated with addition of carbon nanotube (CNT) to polarization electrodes as a conducting material. The CNT addition reduced the series resistance of the EDLC by one-twentieth, while the capacitance was not increased by the CNT addition. The low series resistance leaded to the high electrical energy stored in the EDLC. In this paper, the dependence of the series resistance, the specific capacitance, the energy, and the energy efficiencies on the...

  20. Substituted Quaternary Ammonium Salts Improve Low-Temperature Performance of Double-Layer Capacitors

    Science.gov (United States)

    Brandon, Erik J.; Smart, Marshall C.; West, William C.

    2011-01-01

    Double-layer capacitors are unique energy storage devices, capable of supporting large current pulses as well as a very high number of charging and discharging cycles. The performance of doublelayer capacitors is highly dependent on the nature of the electrolyte system used. Many applications, including for electric and fuel cell vehicles, back-up diesel generators, wind generator pitch control back-up power systems, environmental and structural distributed sensors, and spacecraft avionics, can potentially benefit from the use of double-layer capacitors with lower equivalent series resistances (ESRs) over wider temperature limits. Higher ESRs result in decreased power output, which is a particular problem at lower temperatures. Commercially available cells are typically rated for operation down to only 40 C. Previous briefs [for example, Low Temperature Supercapacitors (NPO-44386), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), p. 32, and Supercapacitor Electrolyte Solvents With Liquid Range Below 80 C (NPO-44855), NASA Tech Briefs, Vol. 34, No. 1 (January 2010), p. 44] discussed the use of electrolytes that employed low-melting-point co-solvents to depress the freezing point of traditional acetonitrile-based electrolytes. Using these modified electrolyte formulations can extend the low-temperature operational limit of double-layer capacitors beyond that of commercially available cells. This previous work has shown that although the measured capacitance is relatively insensitive to temperature, the ESR can rise rapidly at low temperatures, due to decreased electrolyte conductance within the pores of the high surface- area carbon electrodes. Most of these advanced electrolyte systems featured tetraethylammonium tetrafluoroborate (TEATFB) as the salt. More recent work at JPL indicates the use of the asymmetric quaternary ammonium salt triethylmethylammonium tetrafluoroborate (TEMATFB) or spiro-(l,l')-bipyrrolidium tetrafluoroborate (SBPBF4) in a 1:1 by volume solvent

  1. Graphene electric double layer capacitor with ultra-high-power performance

    International Nuclear Information System (INIS)

    Miller, John R.; Outlaw, R.A.; Holloway, B.C.

    2011-01-01

    We have demonstrated, for the first time, efficient 120 Hz filtering by an electric double layer capacitor (EDLC). The key to this ultra-high-power performance is electrodes made from vertically oriented graphene nanosheets grown directly on metal current collectors. This design minimized both electronic and ionic resistance and produced capacitors having RC time-constants of less than 200 μs. Significantly, graphene nanosheets have a preponderance of exposed edge planes that greatly increase stored charge over designs relying on basal plane surfaces. Collectively these factors make vertically oriented graphene nanosheet electrodes ideally suited for producing high-frequency EDLCs. Capacitors constructed with these electrodes are predicted to be significantly smaller than aluminum electrolyte capacitors that they could functionally replace plus be manufactured using standard semiconductor process equipment, creating interesting commercial opportunities.

  2. Graphene double-layer capacitor with ac line-filtering performance.

    Science.gov (United States)

    Miller, John R; Outlaw, R A; Holloway, B C

    2010-09-24

    Electric double-layer capacitors (DLCs) can have high storage capacity, but their porous electrodes cause them to perform like resistors in filter circuits that remove ripple from rectified direct current. We have demonstrated efficient filtering of 120-hertz current with DLCs with electrodes made from vertically oriented graphene nanosheets grown directly on metal current collectors. This design minimized electronic and ionic resistances and produced capacitors with RC time constants of less than 200 microseconds, in contrast with ~1 second for typical DLCs. Graphene nanosheets have a preponderance of exposed edge planes that greatly increases charge storage as compared with that of designs that rely on basal plane surfaces. Capacitors constructed with these electrodes could be smaller than the low-voltage aluminum electrolyte capacitors that are typically used in electronic devices.

  3. Graphene Double-Layer Capacitor with ac Line-Filtering Performance

    Science.gov (United States)

    Miller, John R.; Outlaw, R. A.; Holloway, B. C.

    2010-09-01

    Electric double-layer capacitors (DLCs) can have high storage capacity, but their porous electrodes cause them to perform like resistors in filter circuits that remove ripple from rectified direct current. We have demonstrated efficient filtering of 120-hertz current with DLCs with electrodes made from vertically oriented graphene nanosheets grown directly on metal current collectors. This design minimized electronic and ionic resistances and produced capacitors with RC time constants of less than 200 microseconds, in contrast with ~1 second for typical DLCs. Graphene nanosheets have a preponderance of exposed edge planes that greatly increases charge storage as compared with that of designs that rely on basal plane surfaces. Capacitors constructed with these electrodes could be smaller than the low-voltage aluminum electrolyte capacitors that are typically used in electronic devices.

  4. Characteristics of powdered activated carbon treated with dielectric barrier discharge for electric double-layer capacitors

    International Nuclear Information System (INIS)

    Tashima, Daisuke; Yoshitama, Hiromu; Sakoda, Tatsuya; Okazaki, Akihito; Kawaji, Takayuki

    2012-01-01

    Highlights: ► The specific capacitance of the EDLCs could be improved by oxygen plasma treatment. ► 15 s treated EDLCs showed a 20% increase in capacitance relative to untreated EDLCs. ► The plasma treatment yields EDLCs that are suitable for high-energy applications. - Abstract: The electrochemical properties of electric double-layer capacitors (EDLCs) made with plasma-treated powdered activated carbon (treated using a dielectric barrier discharge) were examined using cyclic voltammetry (CV), Cole–Cole plots, and X-ray photoelectron spectroscopy (XPS). The dielectric barrier discharge method, which operates at atmospheric pressure, dramatically reduces the processing time and does not require vacuum equipment, making it a more practical alternative than low-pressure plasma treatment. The experimental data indicate that the specific capacitance of the EDLCs could be improved by oxygen plasma treatment. Capacitance of EDLCs made with activated carbon treated for 15 s showed 193.5 F/g that 20% increase in the specific capacitance relative to untreated EDLCs. This result indicates that the plasma treatment yields EDLCs that are suitable for high-energy applications. The enhancement of capacitance was mainly attributed to an increase in the BET surface area of the activated carbon and the creation of carboxyl groups on the surface of the carbon. The carboxyl groups induced oxidation–reduction reactions in the presence of O 2 which was included in the operation gas. In addition, the carboxyl groups improved the penetration of the electrolyte solution into the carbon electrodes.

  5. Influence of carbon conductive additives on electrochemical double-layer supercapacitor parameters

    Science.gov (United States)

    Kiseleva, E. A.; Zhurilova, M. A.; Kochanova, S. A.; Shkolnikov, E. J.; Tarasenko, A. B.; Zaitseva, O. V.; Uryupina, O. V.; Valyano, G. V.

    2018-01-01

    Electrochemical double-layer capacitors (EDLC) offer energy storage technology, highly demanded for rapid transition processes in transport and stationary applications, concerned with fast power fluctuations. Rough structure of activated carbon, widely used as electrode material because of its high specific area, leads to poor electrode conductivity. Therefore there is the need for conductive additive to decrease internal resistance and to achieve high specific power and high specific energy. Usually carbon blacks are widely used as conductive additive. In this paper electrodes with different conductive additives—two types of carbon blacks and single-walled carbon nanotubes—were prepared and characterized in organic electrolyte-based EDLC cells. Electrodes are based on original wood derived activated carbon produced by potassium hydroxide high-temperature activation at Joint Institute for High Temperatures RAS. Electrodes were prepared from slurry by cold-rolling. For electrode characterization cyclic voltammetry, impedance spectra analysis, equivalent series resistance measurements and galvanostatic charge-discharge were used.

  6. Strategy for improved frequency response of electric double-layer capacitors

    Science.gov (United States)

    Wada, Yoshifumi; Pu, Jiang; Takenobu, Taishi

    2015-10-01

    We propose a strategy for improving the response speed of electric double-layer capacitors (EDLCs) and electric double-layer transistors (EDLTs), based on an asymmetric structure with differently sized active materials and gate electrodes. We validate the strategy analytically by a classical calculation and experimentally by fabricating EDLCs with asymmetric Au electrodes (1:50 area ratio and 7.5 μm gap distance). The performance of the EDLCs is compared with that of conventional symmetric EDLCs. Our strategy dramatically improved the cut-off frequency from 14 to 93 kHz and this improvement is explained by fast charging of smaller electrodes. Therefore, this approach is particularly suitable to EDLTs, potentially expanding the applicability to medium speed (kHz-MHz) devices.

  7. Effect of nuclear radiation on the electrical properties of chemical double layer capacitors

    International Nuclear Information System (INIS)

    Laghari, J.R.; Hammoud, A.N.

    1990-01-01

    The effects of nuclear radiation on the electrical properties of chemical double layer capacitors are determined. The capacitors were irradiated in a 2-MW nuclear reactor to different fluence levels. The exposure rate was 2.2 x 10 10 n/cm 2 · s of thermal neutrons, 9.52 x 10 8 n/cm 2 · s of fast neutrons (> 2 MeV), and 1.47 x 10 6 rad/h of gamma radiation. The properties measured during and after irradiation included the capacitance, equivalent series resistance, and open-circuit voltage. The post-irradiation effect on the leakage current was also determined. It was found that while the capacitance increased during irradiation, the equivalent series resistance and the open-circuit voltage decreased slightly during irradiation. Changes in these properties were not permanent s was evident from post-irradiation measurements. The leakage current did not show any significant change with radiation. The results indicate that chemical double layer capacitors can be suitably used as backup power source in electronic equipment operating in a radiation environment with total fluences up to 4.05 x 10 14 n/cm 2

  8. The surface chemical properties of multi-walled carbon nanotubes modified by thermal fluorination for electric double-layer capacitor

    Science.gov (United States)

    Jung, Min-Jung; Jeong, Euigyung; Lee, Young-Seak

    2015-08-01

    The surfaces of multi-walled carbon nanotubes (MWCNTs) were thermally fluorinated at various temperatures to enhance the electrochemical properties of the MWCNTs for use as electric double-layer capacitor (EDLC) electrodes. The fluorine functional groups were added to the surfaces of the MWCNTs via thermal fluorination. The thermal fluorination exposed the Fe catalyst on MWCNTs, and the specific surface area increased due to etching during the fluorination. The specific capacitances of the thermally fluorinated at 100 °C, MWCNT based electrode increased from 57 to 94 F/g at current densities of 0.2 A/g, respectively. This enhancement in capacitance can be attributed to increased polarization of the thermally fluorinated MWCNT surface, which increased the affinity between the electrode surface and the electrolyte ions.

  9. Bulk Concentration Dependence of Electrolyte Resistance Within Mesopores of Carbon Electrodes in Electric Double-Layer Capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jaekwang; Kim, Daeun; Lee, Ilbok; Son, Hyungbin; Lee, Donghyun; Yoon, Songhun [Chung-Ang University, Seoul (Korea, Republic of); Shim, Hyewon [Korea Institute of Nuclear Nonproliferation and Control, Daejeon (Korea, Republic of); Lee, Jinwoo [POSTECH, Pohang (Korea, Republic of)

    2016-02-15

    Hexagonally ordered mesoporous carbon materials were prepared and used as electrode materials in an electric double-layer capacitor. Using this electrode, the change of electrolyte resistance within the mesopores was investigated according to the bulk electrolyte concentration. Using three different electrochemical transient experiments-imaginary capacitance analysis, chronoamperometry, and hronopotentiometry-the time constant associated with electrolyte transport was determined, which was then used to obtain the electrolyte resistance within the mesopores. With decreasing electrolyte concentration, the increase in electrolyte resistance was smaller than the increase in the resistivity of the bulk electrolyte, which is indicative of a different environment for ionic transport within the mesopores. On using the confinement effect within the mesopores, the predicted higher concentration within mesopore probably results in lower electrolyte resistance, especially under low bulk concentrations.

  10. A mini review of designed mesoporous materials for energy-storage applications: from electric double-layer capacitors to hybrid supercapacitors

    Science.gov (United States)

    Lim, Eunho; Jo, Changshin; Lee, Jinwoo

    2016-04-01

    In recent years, porous materials have attracted significant attention in various research fields because of their structural merits. In particular, well-designed mesoporous structures with two- or three-dimensionally interconnected pores have been recognized as electrode materials of particular interest for achieving high-performance electrochemical capacitors (ECs). In this mini review, recent progress in the design of mesoporous electrode materials for ECs, from electric double-layer capacitors (EDLCs) and pseudocapacitors (PCs) to hybrid supercapacitors (HSCs), and research challenges for the development of new mesoporous electrode materials has been discussed.

  11. Electric Double-Layer Capacitor Fabricated with Addition of Carbon Nanotube to Polarizable Electrode

    International Nuclear Information System (INIS)

    Yoshiyuki, S.

    2012-01-01

    Electrical double-layer capacitor (EDLC) was fabricated with addition of carbon nano tube (CNT) to polarization electrodes as a conducting material. The CNT addition reduced the series resistance of the EDLC by one-twentieth, while the capacitance was not increased by the CNT addition. The low series resistance leaded to the high electrical energy stored in the EDLC. In this paper, the dependence of the series resistance, the specific capacitance, the energy, and the energy efficiencies on the CNT addition is discussed

  12. Electric Double-Layer Capacitor Fabricated with Addition of Carbon Nanotube to Polarizable Electrode

    Directory of Open Access Journals (Sweden)

    Yoshiyuki Show

    2012-01-01

    Full Text Available Electrical double-layer capacitor (EDLC was fabricated with addition of carbon nanotube (CNT to polarization electrodes as a conducting material. The CNT addition reduced the series resistance of the EDLC by one-twentieth, while the capacitance was not increased by the CNT addition. The low series resistance leaded to the high electrical energy stored in the EDLC. In this paper, the dependence of the series resistance, the specific capacitance, the energy, and the energy efficiencies on the CNT addition is discussed.

  13. Film of lignocellulosic carbon material for self-supporting electrodes in electric double-layer capacitors

    Directory of Open Access Journals (Sweden)

    Tsubasa Funabashi

    2013-09-01

    Full Text Available A novel thin, wood-based carbon material with heterogeneous pores, film of lignocellulosic carbon material (FLCM, was successfully fabricated by carbonizing softwood samples of Picea jezoensis (Jezo spruce. Simultaneous increase in the specific surface area of FLCM and its affinity for electrolyte solvents in an electric double-layer capacitor (EDLC were achieved by the vacuum ultraviolet/ozone (VUV/O3 treatment. This treatment increased the specific surface area of FLCM by 50% over that of original FLCM. The results obtained in this study confirmed that FLCM is an appropriate self-supporting EDLC electrode material without any warps and cracks.

  14. Electric-field-induced superconductivity detected by magnetization measurements of an electric-double-layer capacitor

    International Nuclear Information System (INIS)

    Kasahara, Yuichi; Takeuchi, Yuki; Ye, Jianting; Yuan, Hongtao; Shimotani, Hidekazu; Iwasa, Yoshihiro; Nishimura, Takahiro; Sato, Tatsuya

    2010-01-01

    We report evidence for superconductivity induced by the application of strong electric fields onto the surface of a band insulator, ZrNCl, provided by the observation of a shielding diamagnetic signal. We introduced an electric-double-layer capacitor configuration and in situ magnetization measurements at low temperatures as a method to detect the novel electric-field-induced superconducting state. The results showed excellent agreement with a previous report using a transistor configuration, demonstrating that the present technique is a novel method for investigating the nonequilibrium phase induced by electric fields. (author)

  15. Nanohybrid capacitor: the next generation electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Naoi, K. [Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8558 (Japan)

    2010-10-15

    Conventional electric double layer capacitors (EDLC) designed with two symmetrical activated carbon electrodes can deliver substantially more power than similar size Li-ion batteries. There is presently a major effort to increase the energy density of EDLC s up to a target value in the vicinity of 20-30 Wh kg{sup -1}.The present review article deals with the recent contributions to get this high energy density and new approaches that have been made to increase the withstanding voltage of the EDLCs. Important alternative approach to meet this goal that is under serious investigation is to develop an asymmetric (hybrid) capacitors. Hybrid capacitor systems are the promising approach to meet the goal to effectively increase the energy density. The investigation is to develop hybrid capacitors has been initiated by Li-ion capacitors. And, now Nanohybrid capacitor certainly achieves as high energy density as Li-ion capacitors with higher stability, higher safety and higher productivity. This is the new lithium-ion based hybrid capacitor using the lithium titanate (Li{sub 4}Ti{sub 5}O{sub 12}) negative intercalation electrode that can operate at unusually high current densities. The high-rate Li{sub 4}Ti{sub 5}O{sub 12} negative electrode has a unique nano-structure consisting of unusually small nano-crystalline Li{sub 4}Ti{sub 5}O{sub 12} nucleated and grafted onto carbon nano-fiber anchors (nc-Li{sub 4}Ti{sub 5}O{sub 12}/CNF). (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  16. SISGR: Improved Electrical Energy Storage with Electrochemical Double Layer Capacitance Based on Novel Carbon Electrodes, New Electrolytes, and Thorough Development of a Strong Science Base

    Energy Technology Data Exchange (ETDEWEB)

    Ruoff, Rodney S. [PI; Alam, Todd M. [co-PI; Bielawski, Christopher W. [co-PI; Chabal, Yves [co-PI; Hwang, Gyeong [co-PI; Ishii, Yoshitaka [co-PI; Rogers, Robin [co-PI

    2014-07-23

    The broad objective of the SISGR program is to advance the fundamental scientific understanding of electrochemical double layer capacitance (EDLC) and thus of ultracapacitor systems composed of a new type of electrode based on chemically modified graphene (CMG) and (primarily) with ionic liquids (ILs) as the electrolyte. Our team has studied the interplay between graphene-based and graphene-derived carbons as the electrode materials in electrochemical double layer capacitors (EDLC) systems on the one hand, and electrolytes including novel ionic liquids (ILs), on the other, based on prior work on the subject.

  17. The Effects of Self-Discharge on the Performance of Symmetric Electric Double-Layer Capacitors and Active Electrolyte-Enhanced Supercapacitors: Insights from Modeling and Simulation

    Science.gov (United States)

    Ike, Innocent S.; Sigalas, Iakovos; Iyuke, Sunny E.

    2017-02-01

    The effects of self-discharge on the performance of symmetric electric double-layer capacitors (EDLCs) and active electrolyte-enhanced supercapacitors were examined by incorporating self-discharge into electrochemical capacitor models during charging and discharging. The sources of self-discharge in capacitors were side reactions or redox reactions and several impurities and electric double-layer (EDL) instability. The effects of self-discharge during capacitor storage was negligible since it took a fully charged capacitor a minimum of 14.0 days to be entirely discharged by self-discharge in all conditions studied, hence self-discharge in storage condition can be ignored. The first and second charge-discharge cycle energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a capacitor of electrode effective conductivity α1 = 0.05 S/cm with only EDL instability self-discharge with current density J_{{VR}} = 1.25 × 10-3 A/cm2 were 72.33% and 72.34%, respectively. Also, energy efficiencies η_{{{{E}}1}} and η_{{{{E}}2}} of a similar capacitor with both side reactions and redox reactions and EDL instability self-discharges with current densities J_{{VR}} = 0.00125 A/cm2 and J_{{{{VR}}1}} = 0.0032 A/cm2 were 38.13% and 38.14% respectively, compared with 84.24% and 84.25% in a similar capacitor without self-discharge. A capacitor with only EDL instability self-discharge and that with both side reactions and redox reactions and EDL instability self-discharge lost 9.73 Wh and 28.38 Wh of energy, respectively, through self-discharge during charging and discharging. Hence, EDLCs charging and discharging time is significantly dependent on the self-discharge rate which are too large to be ignored.

  18. Modeling Electric Double-Layer Capacitors Using Charge Variation Methodology in Gibbs Ensemble

    Directory of Open Access Journals (Sweden)

    Ganeshprasad Pavaskar

    2018-01-01

    Full Text Available Supercapacitors deliver higher power than batteries and find applications in grid integration and electric vehicles. Recent work by Chmiola et al. (2006 has revealed unexpected increase in the capacitance of porous carbon electrodes using ionic liquids as electrolytes. The work has generated curiosity among both experimentalists and theoreticians. Here, we have performed molecular simulations using a recently developed technique (Punnathanam, 2014 for simulating supercapacitor system. In this technique, the two electrodes (containing electrolyte in slit pore are simulated in two different boxes using the Gibbs ensemble methodology. This reduces the number of particles required and interfacial interactions, which helps in reducing computational load. The method simulates an electric double-layer capacitor (EDLC with macroscopic electrodes with much smaller system sizes. In addition, the charges on individual electrode atoms are allowed to vary in response to movement of electrolyte ions (i.e., electrode is polarizable while ensuring these atoms are at the same electric potential. We also present the application of our technique on EDLCs with the electrodes modeled as slit pores and as complex three-dimensional pore networks for different electrolyte geometries. The smallest pore geometry showed an increase in capacitance toward the potential of 0 charge. This is in agreement with the new understanding of the electrical double layer in regions of dense ionic packing, as noted by Kornyshev’s theoretical model (Kornyshev, 2007, which also showed a similar trend. This is not addressed by the classical Gouy–Chapman theory for the electric double layer. Furthermore, the electrode polarizability simulated in the model improved the accuracy of the calculated capacitance. However, its addition did not significantly alter the capacitance values in the voltage range considered.

  19. Molecular Simulations of Graphene-Based Electric Double-Layer Capacitors

    Science.gov (United States)

    Kalluri, Raja K.; Konatham, Deepthi; Striolo, Alberto

    2011-03-01

    Towards deploying renewable energy sources it is crucial to develop efficient and cost-effective technologies to store electricity. Traditional batteries are plagued by a number of practical problems that at present limit their widespread applicability. One possible solution is represented by electric double-layer capacitors (EDLCs). To deploy EDLCs at the large scale it is necessary to better understand how electrolytes pack and diffuse within narrow charged pores. We present here simulation results for the concentrated aqueous solutions of NaCl, CsCl, and NaI confined within charged graphene-based porous materials. We discuss how the structure of confined water, the salt concentration, the ions size, and the surface charge density determine the accumulation of electrolytes within the porous network. Our results, compared to data available for bulk systems, are critical for relating macroscopic observations to molecular-level properties of the confined working fluids. Research supported by the Department of Energy.

  20. A micro-structured Si-based electrodes for high capacity electrical double layer capacitors

    International Nuclear Information System (INIS)

    Krikscikas, Valdas; Oguchi, Hiroyuki; Hara, Motoaki; Kuwano, Hiroki; Yanazawa, Hiroshi

    2014-01-01

    We challenged to make basis for Si electrodes of electric double layer capacitors (EDLC) used as a power source of micro-sensor nodes. Mcroelectromechanical systems (MEMS) processes were successfully introduced to fabricate micro-structured Si-based electrodes to obtain high surface area which leads to high capacity of EDLCs. Study of fundamental properties revealed that the microstructured electrodes benefit from good wettability to electrolytes, but suffer from electric resistance. We found that this problem can be solved by metal-coating of the electrode surface. Finally we build an EDLC consisting of Au-coated micro-structured Si electrodes. This EDLC showed capacity of 14.3 mF/cm 2 , which is about 530 times larger than that of an EDLC consisting of flat Au electrodes

  1. Double-layer capacitors with a higher energy density; Doppelschichtkondensatoren mit hoeherem Energieinhalt

    Energy Technology Data Exchange (ETDEWEB)

    Presser, Volker [Leibniz-Institut fuer Neue Materialien (INM) gGmbH, Saarbruecken (Germany). Juniorforschungs-Gruppe Energie-Materialien; Universitaet des Saarlandes, Saarbruecken (Germany)

    2013-05-15

    Electrical double-layer capacitors, also known as supercapacitors (SC) are devices for electrical energy storage used for fast acceleration of hybrid cars or for the energy recovery during breaking operations. In contrast, lithium-ion batteries (LIB) are used as energy storage devices to provide an extended travel distance for plug-in hybrid cars and electric vehicles. Current research aims to overcome the major limitations of both technologies (SC: low energy density/LIB: slow recharge and limited service life) and hybrid cells are considered a promising solution. The goal is to improve the performance and energy density of storage devices which can be achieved, as shown by the Leibniz-Institute for New Materials (INM), with the use of nanotechnology. (orig.)

  2. Nanographene derived from carbon nanofiber and its application to electric double-layer capacitors

    International Nuclear Information System (INIS)

    Mitani, Satoshi; Sathish, Marappan; Rangappa, Dinesh; Unemoto, Atsushi; Tomai, Takaaki; Honma, Itaru

    2012-01-01

    The fascinating properties of graphene are attracting considerable attention in engineering fields such as electronics, optics, and energy engineering. These properties can be controlled by controlling graphene's structure, e.g., the number of layers and the sheet size. In this study, we synthesized nanosized graphene from a platelet-type carbon nanofiber. The thickness and size of nanographene oxide are around 1 nm and 60 nm and we obtained nanographene by hydrazine reduction of nanographene oxide. We applied the nanographene to an ionic-liquid electric double-layer capacitor (EDLC), which exhibited a much larger capacitance per specific surface area than an EDLC using conventional activated carbon. Furthermore, the capacitance increased significantly with increasing cycle time. After 30th cycle, the capacitance was achieved 130 F g −1 , though the surface area was only 240 m 2 g −1 . These results suggest that nanographene structure induce the capacitance enhancement.

  3. Evaluation of electric double layer capacitor using Ketjenblack as conductive nanofiller

    International Nuclear Information System (INIS)

    Tashima, Daisuke; Yoshitama, Hiromu; Otsubo, Masahisa; Maeno, Seiji; Nagasawa, Yoshinobu

    2011-01-01

    Highlights: → The capacitances of electric double layer capacitors (EDLCs) with nanocomposite electrodes were examined. → It was found that the Ketjenblack-containing EDLCs showed fairly high capacitance (150-210 F/g) compared to EDLCs containing acetylene black with the aqueous electrolyte. → A maximum specific capacitance of 252 F/g was obtained in EDLCs containing 20 wt.% KB with a large amount of the surface functional group. → Reduction-oxidation reactions were thought to occur at the interface between the electrolyte and surface functional group, which increased the specific capacitance of the EDLCs. - Abstract: In this study, the capacitances of electric double layer capacitors (EDLCs) with nanocomposite electrodes were examined by analyzing their charge-discharge characteristics and cyclic voltammograms. In addition, the internal resistance of these EDLCs was evaluated using two kinds of conductive nanofillers: acetylene black (AB) and Ketjenblack (KB). Usually, KB exhibits higher electronic conductivity than AB. The temperature dependence of the capacitance and internal resistance of the prepared EDLCs at 0-50 deg. C using an aqueous electrolyte, organic electrolyte, and two kinds of ionic liquids was evaluated. Moreover, the influence on the capacitance and internal resistance when KB containing a surface functional group is used as the conductive nanofiller of the polarized electrode was examined. It was found that the KB-containing EDLCs showed fairly high capacitance (150-210 F/g) compared to EDLCs containing AB with the aqueous electrolyte. In addition, a maximum specific capacitance of 252 F/g was obtained in EDLCs containing 20 wt.% KB with a large amount of the surface functional group. Reduction-oxidation reactions were thought to occur at the interface between the electrolyte and surface functional group, which increased the specific capacitance of the EDLCs.

  4. Poly(Acrylic acid–Based Hybrid Inorganic–Organic Electrolytes Membrane for Electrical Double Layer Capacitors Application

    Directory of Open Access Journals (Sweden)

    Chiam-Wen Liew

    2016-05-01

    Full Text Available Nanocomposite polymer electrolyte membranes (NCPEMs based on poly(acrylic acid(PAA and titania (TiO2 are prepared by a solution casting technique. The ionic conductivity of NCPEMs increases with the weight ratio of TiO2.The highest ionic conductivity of (8.36 ± 0.01 × 10−4 S·cm−1 is obtained with addition of 6 wt % of TiO2 at ambient temperature. The complexation between PAA, LiTFSI and TiO2 is discussed in Attenuated total reflectance-Fourier Transform Infrared (ATR-FTIR studies. Electrical double layer capacitors (EDLCs are fabricated using the filler-free polymer electrolyte or the most conducting NCPEM and carbon-based electrodes. The electrochemical performances of fabricated EDLCs are studied through cyclic voltammetry (CV and galvanostatic charge-discharge studies. EDLC comprising NCPEM shows the specific capacitance of 28.56 F·g−1 (or equivalent to 29.54 mF·cm−2 with excellent electrochemical stability.

  5. Electric double-layer capacitors with tea waste derived activated carbon electrodes and plastic crystal based flexible gel polymer electrolytes

    Science.gov (United States)

    Suleman, M.; Deraman, M.; Othman, M. A. R.; Omar, R.; Hashim, M. A.; Basri, N. H.; Nor, N. S. M.; Dolah, B. N. M.; Hanappi, M. F. Y. M.; Hamdan, E.; Sazali, N. E. S.; Tajuddin, N. S. M.; Jasni, M. R. M.

    2016-08-01

    We report a novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising a plastic crystalline succinonitrile (SN) based flexible polymer gel electrolyte, incorporated with sodium trifluoromethane sulfonate (NaTf) immobilised in a host polymer poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). The cost-effective activated carbon powder possessing a specific surface area (SSA) of ~ 1700 m2g-1 containing a large proportion of meso-porosity has been derived from tea waste to use as supercapacitor electrodes. The high ionic conductivity (~3.6×10-3 S cm-1 at room temperature) and good electrochemical stability render the gel polymer electrolyte film a suitable candidate for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge studies. The performance of the EDLC cell is found to be promising in terms of high values of specific capacitance (~270 F g-1), specific energy (~ 36 Wh kg-1), and power density (~ 33 kW kg-1).

  6. Electric double-layer capacitors with tea waste derived activated carbon electrodes and plastic crystal based flexible gel polymer electrolytes

    International Nuclear Information System (INIS)

    Suleman, M; Deraman, M; Othman, M A R; Omar, R; Basri, N H; Nor, N S M; Dolah, B N M; Hanappi, M F Y M; Hamdan, E; Sazali, N E S; Tajuddin, N S M; Jasni, M R M; Hashim, M A

    2016-01-01

    We report a novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising a plastic crystalline succinonitrile (SN) based flexible polymer gel electrolyte, incorporated with sodium trifluoromethane sulfonate (NaTf) immobilised in a host polymer poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). The cost-effective activated carbon powder possessing a specific surface area (SSA) of ∼ 1700 m 2 g -1 containing a large proportion of meso-porosity has been derived from tea waste to use as supercapacitor electrodes. The high ionic conductivity (∼3.6×10 -3 S cm -1 at room temperature) and good electrochemical stability render the gel polymer electrolyte film a suitable candidate for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge studies. The performance of the EDLC cell is found to be promising in terms of high values of specific capacitance (∼270 F g -1 ), specific energy (∼ 36 Wh kg -1 ), and power density (∼ 33 kW kg -1 ). (paper)

  7. Charge storage mechanism in nanoporous carbons and its consequence for electrical double layer capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Simon, P.; Gogotsi, Y.

    2010-06-21

    Electrochemical capacitors, also known as supercapacitors, are energy storage devices that fill the gap between batteries and dielectric capacitors. Thanks to their unique features, they have a key role to play in energy storage and harvesting, acting as a complement to or even a replacement of batteries which has already been achieved in various applications. One of the challenges in the supercapacitor area is to increase their energy density. Some recent discoveries regarding ion adsorption in microporous carbon exhibiting pores in the nanometre range can help in designing the next generation of high-energy-density supercapacitors.

  8. Electrochemical capacitor based on materials with pseudocapacitive properties

    OpenAIRE

    Olivia Moreno, David

    2011-01-01

    This thesis is divided into two chapters. Chapter 1 is about energy storage device such as the electrochemical capacitor (EC) and the electrode materials used for its construction. The basic principle of supercapacitor performance, double-layer capacitance and pseudocapacitance phenomena are described in the introduction. Activated carbons, nanotubes, conducting polymers and metal oxides as well as their composites were considered as electrode materials. Symmetric and asymmetric configurat...

  9. Enhancing the performance of green solid-state electric double-layer capacitor incorporated with fumed silica nanoparticles

    Science.gov (United States)

    Chong, Mee Yoke; Numan, Arshid; Liew, Chiam-Wen; Ng, H. M.; Ramesh, K.; Ramesh, S.

    2018-06-01

    Solid polymer electrolyte (SPE) based on fumed silica nanoparticles as nanofillers, hydroxylethyl cellulose (HEC) as host polymer, magnesium trifluoromethanesulfonate salt and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid is prepared by solution casting technique. The ionic conductivity, interactions of adsorbed ions on the host polymer, structural crystallinity and thermal stability are evaluated by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Ionic conductivity studies at room temperature reveals that the SPE with 2 wt. % of fumed silica nanoparticles gives the highest conductivity compared to its counterpart. The XRD and FTIR studies confirm the dissolution of salt, ionic liquid and successful incorporation of fumed silica nanoparticles with host polymer. In order to examine the performance of SPEs, electric double-layer capacitor (EDLC) are fabricated by using activated carbon electrodes. EDLC studies demonstrate that SPE incorporated with 2 wt. % fumed silica nanoparticles gives high specific capacitance (25.0 F/g) at a scan rate of 5 mV/s compared to SPE without fumed silica. Additionally, it is able to withstand 71.3% of capacitance from its initial capacitance value over 1600 cycles at a current density of 0.4 A/g.

  10. Effects of surface chemical properties of activated carbon modified by amino-fluorination for electric double-layer capacitor.

    Science.gov (United States)

    Jung, Min-Jung; Jeong, Euigyung; Cho, Seho; Yeo, Sang Young; Lee, Young-Seak

    2012-09-01

    The surface of phenol-based activated carbon (AC) was seriatim amino-fluorinated with solution of ammonium hydroxide and hydrofluoric acid in varying ratio to fabricate electrode materials for use in an electric double-layer capacitor (EDLC). The specific capacitance of the amino-fluorinated AC-based EDLC was measured in a 1 M H(2)SO(4) electrolyte, in which it was observed that the specific capacitances increased from 215 to 389 Fg(-1) and 119 and 250 Fg(-1) with the current densities of 0.1 and 1.0 Ag(-1), respectively, in comparison with those of an untreated AC-based EDLC when the amino-fluorination was optimized via seriatim mixed solution of 7.43 mol L(-1) ammonium hydroxide and 2.06 mol L(-1) hydrofluoric acid. This enhancement of capacitance was attributed to the synergistic effects of an increased electrochemical activity due to the formation of surface N- and F-functional groups and increased, specific surface area, and mesopore volumes, all of which resulted from the amino-fluorination of the electrode material. Copyright © 2012 Elsevier Inc. All rights reserved.

  11. Preparation of hierarchical porous carbon from waste printed circuit boards for high performance electric double-layer capacitors

    Science.gov (United States)

    Du, Xuan; Wang, Li; Zhao, Wei; Wang, Yi; Qi, Tao; Li, Chang Ming

    2016-08-01

    Renewable clean energy and resources recycling have become inevitable choices to solve worldwide energy shortages and environmental pollution problems. It is a great challenge to recycle tons of waste printed circuit boards (PCB) produced every year for clean environment while creating values. In this work, low cost, high quality activated carbons (ACs) were synthesized from non-metallic fractions (NMF) of waste PCB to offer a great potential for applications of electrochemical double-layer capacitors (EDLCs). After recovering metal from waste PCB, hierarchical porous carbons were produced from NMF by carbonization and activation processes. The experimental results exhibit that some pores were formed after carbonization due to the escape of impurity atoms introduced by additives in NMF. Then the pore structure was further tailored by adjusting the activation parameters. Roles of micropores and non-micropores in charge storage were investigated when the hierarchical porous carbons were applied as electrode of EDLCs. The highest specific capacitance of 210 F g-1 (at 50 mA g-1) and excellent rate capability were achieved when the ACs possessing a proper micropores/non-micropores ratio. This work not only provides a promising method to recycle PCB, but also investigates the structure tailoring arts for a rational hierarchical porous structure in energy storage/conversion.

  12. Polyfurfuryl alcohol derived activated carbons for high power electrical double layer capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz, V. [CSIRO Division of Energy Technology, Box 312, Clayton South, Vic. 3169 (Australia); Pandolfo, A.G., E-mail: tony.pandolfo@csiro.a [CSIRO Division of Energy Technology, Box 312, Clayton South, Vic. 3169 (Australia)

    2010-10-30

    Polyfurfuryl alcohol (PFA) derived activated carbons were prepared by the acid catalysed polymerization of furfuryl alcohol, followed by potassium hydroxide activation. Activated carbons with apparent BET surface areas ranging from 1070 to 2600 m{sup 2} g{sup -1}, and corresponding average micropore sizes between 0.6 and 1.6 nm were obtained. The porosity of these carbons can be carefully controlled during activation and their performance as electrode materials in electric double layer capacitors (EDLCs) in a non-aqueous electrolyte (1 M Et{sub 4}NBF{sub 4}/ACN) is investigated. Carbon materials with a low average pore size (<{approx}0.6 nm) exhibited electrolyte accessibility issues and an associated decrease in capacitance at high charging rates. PFA carbons with larger average pore sizes exhibited greatly improved performance, with specific electrode capacitances of 150 F g{sup -1} at an operating voltage window of 0-2.5 V; which corresponds to 32 Wh kg{sup -1} and 38 kW kg{sup -1} on an active material basis. These carbons also displayed an outstanding performance at high current densities delivering up to 100 F g{sup -1} at current densities as high as 250 A g{sup -1}. The exceptionally high capacitance and power of this electrode material is attributed to its good electronic conductivity and a highly effective combination of micro- and fine mesoporosity.

  13. Polyfurfuryl alcohol derived activated carbons for high power electrical double layer capacitors

    International Nuclear Information System (INIS)

    Ruiz, V.; Pandolfo, A.G.

    2010-01-01

    Polyfurfuryl alcohol (PFA) derived activated carbons were prepared by the acid catalysed polymerization of furfuryl alcohol, followed by potassium hydroxide activation. Activated carbons with apparent BET surface areas ranging from 1070 to 2600 m 2 g -1 , and corresponding average micropore sizes between 0.6 and 1.6 nm were obtained. The porosity of these carbons can be carefully controlled during activation and their performance as electrode materials in electric double layer capacitors (EDLCs) in a non-aqueous electrolyte (1 M Et 4 NBF 4 /ACN) is investigated. Carbon materials with a low average pore size ( -1 at an operating voltage window of 0-2.5 V; which corresponds to 32 Wh kg -1 and 38 kW kg -1 on an active material basis. These carbons also displayed an outstanding performance at high current densities delivering up to 100 F g -1 at current densities as high as 250 A g -1 . The exceptionally high capacitance and power of this electrode material is attributed to its good electronic conductivity and a highly effective combination of micro- and fine mesoporosity.

  14. Evaluation of the constant potential method in simulating electric double-layer capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhenxing; Laird, Brian B., E-mail: blaird@ku.edu [Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 (United States); Yang, Yang; Olmsted, David L.; Asta, Mark [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States)

    2014-11-14

    A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO{sub 4}-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of “inner-sphere adsorbed” Li{sup +} ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li{sup +} ions to the electrode surface.

  15. Electric potential calculation in molecular simulation of electric double layer capacitors

    International Nuclear Information System (INIS)

    Wang, Zhenxing; Laird, Brian B; Olmsted, David L; Asta, Mark

    2016-01-01

    For the molecular simulation of electric double layer capacitors (EDLCs), a number of methods have been proposed and implemented to determine the one-dimensional electric potential profile between the two electrodes at a fixed potential difference. In this work, we compare several of these methods for a model LiClO 4 -acetonitrile/graphite EDLC simulated using both the traditional fixed-charged method (FCM), in which a fixed charge is assigned a priori to the electrode atoms, or the recently developed constant potential method (CPM) (2007 J. Chem. Phys . 126 084704), where the electrode charges are allowed to fluctuate to keep the potential fixed. Based on an analysis of the full three-dimensional electric potential field, we suggest a method for determining the averaged one-dimensional electric potential profile that can be applied to both the FCM and CPM simulations. Compared to traditional methods based on numerically solving the one-dimensional Poisson’s equation, this method yields better accuracy and no supplemental assumptions. (paper)

  16. Evaluation of the constant potential method in simulating electric double-layer capacitors

    International Nuclear Information System (INIS)

    Wang, Zhenxing; Laird, Brian B.; Yang, Yang; Olmsted, David L.; Asta, Mark

    2014-01-01

    A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO 4 -acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of “inner-sphere adsorbed” Li + ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li + ions to the electrode surface

  17. Preparation of activated carbon aerogels with hierarchically porous structures for electrical double layer capacitors

    International Nuclear Information System (INIS)

    Liu, Dong; Shen, Jun; Liu, Nianping; Yang, Huiyu; Du, Ai

    2013-01-01

    Activated carbon aerogels (ACAs) with hierarchically porous structures and high specific surface area have been prepared via CO 2 and KOH activation processes. The pore structures of ACAs are characterized by N 2 adsorption/desorption and scanning electron microscopy. The experimental results show that the ACAs contain three types of pores: micropores with diameters below 2 nm, small mesopores with diameters from 2 to 4 nm and large pores or channels with diameters over 30 nm. The typical sample ACAs-4, which possess pore volume of 2.73 cm 3 g −1 and specific surface area of 2119 m 2 g −1 , exhibits high specific capacitances of 250 F g −1 and 198 F g −1 at the current densities of 0.5 A g −1 and 20 A g −1 respectively in 6 M KOH aqueous solution. Furthermore, the resultant ACAs electrode materials also exhibit high power density, good cycling stability and long lifetime. With these features, ACAs are expected to be promising electrode materials for electrical double layer capacitors

  18. Development of energy storage system for DC electric rolling stock applying electric double layer capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Sekijima, Y.; Kudo, Y.; Inui, M. [Central Japan Railway Co., Aichi (Japan); Monden, Y.; Toda, S.; Aoyama, I. [Toshiba Corp., Tokyo (Japan)

    2006-07-01

    This paper provided details of an energy storage system designed for use with DC electric rolling stock through the application of an electric double layer capacitor (EDLC). The EDLC was selected due to its long life-span and its low operational costs. Testing was conducted to assess the system's basic control function, acceleration using stored energy, and behaviour during regenerative brake failure. A control circuit chip was used in the DC electric rolling stock on an inverter of the energy storage system. Tests confirmed that the control method was effective for actual rolling stocks. A full-scale energy storage system for installation on series 313 locomotives was then constructed. Braking energy was generated only from a regenerative brake. In case of brake failure, braking energy was generated from an air brake was well as an electric brake. Data from a field test conducted at the Tokaido and Chuo railway lines showed a capacity of 0.6 kWh. The EDLC was used to reduce peak air brake energy. It was concluded that storing 0.28 kW of brake energy in the EDLC can reduce peaks of air brake energy in high speed ranges. Experimental equipment was used to confirm use of the system with 0.56 kWh of EDLC, the average energy of air brake used in regenerative energy failure. 1 tab., 10 figs.

  19. Boron cross-linked graphene oxide/polyvinyl alcohol nanocomposite gel electrolyte for flexible solid-state electric double layer capacitor with high performance

    International Nuclear Information System (INIS)

    Huang, Yi-Fu; Wu, Peng-Fei; Zhang, Ming-Qiu; Ruan, Wen-Hong; Giannelis, Emmanuel P.

    2014-01-01

    Highlights: • Gel electrolyte is prepared and used in electric double layer capacitor. • Insertion of boron crosslinks into GO agglomerates opens channels for ion migration. • Solid supercapacitors show excellent specific capacitance and cycle stability. • Nanocomposite electrolyte shows better thermal stability and mechanical properties. - Abstract: A new family of boron cross-linked graphene oxide/polyvinyl alcohol (GO-B-PVA) nanocomposite gels is prepared by freeze-thaw/boron cross-linking method. Then the gel electrolytes saturated with KOH solution are assembled into electric double layer capacitors (EDLCs). Structure, thermal and mechanical properties of GO-B-PVA are explored. The electrochemical properties of EDLCs using GO-B-PVA/KOH are investigated, and compared with those using GO-PVA/KOH gel or KOH solution electrolyte. FTIR shows that boron cross-links are introduced into GO-PVA, while the boronic structure inserted into agglomerated GO sheets is demonstrated by DMA analysis. The synergy effect of the GO and the boron crosslinking benefits for ionic conductivity due to unblocking ion channels, and for improvement of thermal stability and mechanical properties of the electrolytes. Higher specific capacitance and better cycle stability of EDLCs are obtained by using the GO-B-PVA/KOH electrolyte, especially the one at higher GO content. The nanocomposite gel electrolytes with excellent electrochemical properties and solid-like character are candidates for the industrial application in high-performance flexible solid-state EDLCs

  20. Improved Electrochemical Cycling Durability in a Nickel Oxide Double-Layered Film.

    Science.gov (United States)

    Hou, Shuai; Zhang, Xiang; Tian, Yanlong; Zhao, Jiupeng; Geng, Hongbin; Qu, Huiying; Zhang, Hangchuan; Zhang, Kun; Wang, Binsheng; Gavrilyuk, Alexander; Li, Yao

    2017-11-16

    For the first time, a crystalline-amorphous double-layered NiO x film has been prepared by reactive radio frequency magnetron sputtering. This film has exhibited improved electrochemical cycling durability, whereas other electrochromic parameters have been maintained at the required level, namely, a short coloration/bleaching time (0.8 s/1.1 s) and an enhanced transmittance modulation range (62.2 %) at λ=550 nm. Additionally, the double-layered film has shown better reversibility than that of amorphous and crystalline single-layered films. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Catalytic Graphitization for Preparation of Porous Carbon Material Derived from Bamboo Precursor and Performance as Electrode of Electrical Double-Layer Capacitor

    Science.gov (United States)

    Tsubota, Toshiki; Maguchi, Yuta; Kamimura, Sunao; Ohno, Teruhisa; Yasuoka, Takehiro; Nishida, Haruo

    2015-12-01

    The combination of addition of Fe (as a catalyst for graphitization) and CO2 activation (a kind of gaseous activation) was applied to prepare a porous carbon material from bamboo powder (a waste product of superheated steam treatment). Regardless of the heat treatment temperature, many macropores were successfully formed after the heating process by removal of Fe compounds. A turbostratic carbon structure was generated in the Fe-added sample heated at 850°C. It was confirmed that the added Fe acted as a template for pore formation. Moreover, it was confirmed that the added Fe acted as a catalyst for graphitization. The resulting electrochemical performance as the electrode of an electrical double-layer capacitor, as demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy, and charge-discharge testing, could be explained based on the graphitization and activation effects. Addition of Fe could affect the electrical properties of carbon material derived from bamboo.

  2. Driving mechanisms of ionic polymer actuators having electric double layer capacitor structures.

    Science.gov (United States)

    Imaizumi, Satoru; Kato, Yuichi; Kokubo, Hisashi; Watanabe, Masayoshi

    2012-04-26

    Two solid polymer electrolytes, composed of a polyether-segmented polyurethaneurea (PEUU) and either a lithium salt (lithium bis(trifluoromethanesulfonyl)amide: Li[NTf2]) or a nonvolatile ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide: [C2mim][NTf2]), were prepared in order to utilize them as ionic polymer actuators. These salts were preferentially dissolved in the polyether phases. The ionic transport mechanism of the polyethers was discussed in terms of the diffusion coefficients and ionic transference numbers of the incorporated ions, which were estimated by means of pulsed-field gradient spin-echo (PGSE) NMR. There was a distinct difference in the ionic transport properties of each polymer electrolyte owing to the difference in the magnitude of interactions between the cations and the polyether. The anionic diffusion coefficient was much faster than that of the cation in the polyether/Li[NTf2] electrolyte, whereas the cation diffused faster than the anion in the polyether/[C2mim][NTf2] electrolyte. Ionic polymer actuators, which have a solid-state electric-double-layer-capacitor (EDLC) structure, were prepared using these polymer electrolyte membranes and ubiquitous carbon materials such as activated carbon and acetylene black. On the basis of the difference in the motional direction of each actuator against applied voltages, a simple model of the actuation mechanisms was proposed by taking the difference in ionic transport properties into consideration. This model discriminated the behavior of the actuators in terms of the products of transference numbers and ionic volumes. The experimentally observed behavior of the actuators was successfully explained by this model.

  3. Multi-electrode double layer capacitor having single electrolyte seal and aluminum-impregnated carbon cloth electrodes

    Science.gov (United States)

    Farahmandi, C. Joseph; Dispennette, John M.; Blank, Edward; Kolb, Alan C.

    1999-01-19

    A single cell, multi-electrode high performance double layer capacitor includes first and second flat stacks of electrodes adapted to be housed in a closeable two-part capacitor case which includes only a single electrolyte seal. Each electrode stack has a plurality of electrodes connected in parallel, with the electrodes of one stack being interleaved with the electrodes of the other stack to form an interleaved stack, and with the electrodes of each stack being electrically connected to respective capacitor terminals. A porous separator sleeve is inserted over the electrodes of one stack before interleaving to prevent electrical shorts between the electrodes. The electrodes are made by folding a compressible, low resistance, aluminum-impregnated carbon cloth, made from activated carbon fibers, around a current collector foil, with a tab of the foils of each electrode of each stack being connected in parallel and connected to the respective capacitor terminal. The height of the interleaved stack is somewhat greater than the inside height of the closed capacitor case, thereby requiring compression of the interleaved electrode stack when placed inside of the case, and thereby maintaining the interleaved electrode stack under modest constant pressure. The closed capacitor case is filled with an electrolytic solution and sealed. A preferred electrolytic solution is made by dissolving an appropriate salt into acetonitrile (CH.sub.3 CN). In one embodiment, the two parts of the capacitor case are conductive and function as the capacitor terminals.

  4. High Power Electric Double-Layer Capacitors based on Room-Temperature Ionic Liquids and Nanostructured Carbons

    Science.gov (United States)

    Perez, Carlos R.

    The efficient storage of electrical energy constitutes both a fundamental challenge for 21st century science and an urgent requirement for the sustainability of our technological civilization. The push for cleaner renewable forms of energy production, such as solar and wind power, strongly depends on a concomitant development of suitable storage methods to pair with these intermittent sources, as well as for mobile applications, such as vehicles and personal electronics. In this regard, Electrochemical Double-Layer Capacitors (supercapacitors) represent a vibrant area of research due to their environmental friendliness, long lifetimes, high power capability, and relative underdevelopment when compared to electrochemical batteries. Currently supercapacitors have gravimetric energies one order of magnitude lower than similarly advanced batteries, while conversly enjoying a similar advantage over them in terms of power. The challenge is to increase the gravimentric energies and conserve the high power. On the material side, research focuses on highly porous supports and electrolytes, the critical components of supercapacitors. Through the use of electrolyte systems with a wider electrochemical stability window, as well as properly tailored carbon nanomaterials as electrodes, significant improvements in performance are possible. Room Temperature Ionic Liquids and Carbide-Derived Carbons are promising electrolytes and electrodes, respectively. RTILs have been shown to be stable at up to twice the voltage of organic solvent-salt systems currently employed in supercapacitors, and CDCs are tunable in pore structure, show good electrical conductivity, and superior demonstrated capability as electrode material. This work aims to better understand the interplay of electrode and electrolyte parameters, such as pore structure and ion size, in the ultimate performance of RTIL-based supercapacitors in terms of power, energy, and temperature of operation. For this purpose, carbon

  5. Isolating the effect of pore size distribution on electrochemical double-layer capacitance using activated fluid coke

    Science.gov (United States)

    Zuliani, Jocelyn E.; Tong, Shitang; Kirk, Donald W.; Jia, Charles Q.

    2015-12-01

    Electrochemical double-layer capacitors (EDLCs) use physical ion adsorption in the capacitive electrical double layer of high specific surface area (SSA) materials to store electrical energy. Previous work shows that the SSA-normalized capacitance increases when pore diameters are less than 1 nm. However, there still remains uncertainty about the charge storage mechanism since the enhanced SSA-normalized capacitance is not observed in all microporous materials. In previous studies, the total specific surface area and the chemical composition of the electrode materials were not controlled. The current work is the first reported study that systematically compares the performance of activated carbon prepared from the same raw material, with similar chemical composition and specific surface area, but different pore size distributions. Preparing samples with similar SSAs, but different pores sizes is not straightforward since increasing pore diameters results in decreasing the SSA. This study observes that the microporous activated carbon has a higher SSA-normalized capacitance, 14.1 μF cm-2, compared to the mesoporous material, 12.4 μF cm-2. However, this enhanced SSA-normalized capacitance is only observed above a threshold operating voltage. Therefore, it can be concluded that a minimum applied voltage is required to induce ion adsorption in these sub-nanometer micropores, which increases the capacitance.

  6. New Approach for High-Voltage Electrical Double-Layer Capacitors Using Vertical Graphene Nanowalls with and without Nitrogen Doping.

    Science.gov (United States)

    Chi, Yu-Wen; Hu, Chi-Chang; Shen, Hsiao-Hsuan; Huang, Kun-Ping

    2016-09-14

    Integrating various devices to achieve high-performance energy storage systems to satisfy various demands in modern societies become more and more important. Electrical double-layer capacitors (EDLCs), one kind of the electrochemical capacitors, generally provide the merits of high charge-discharge rates, extremely long cycle life, and high efficiency in electricity capture/storage, leading to a desirable device of electricity management from portable electronics to hybrid vehicles or even smart grid application. However, the low cell voltage (2.5-2.7 V in organic liquid electrolytes) of EDLCs lacks the direct combination of Li-ion batteries (LIBs) and EDLCs for creating new functions in future applications without considering the issue of a relatively low energy density. Here we propose a guideline, "choosing a matching pair of electrode materials and electrolytes", to effectively extend the cell voltage of EDLCs according to three general strategies. Based on the new strategy proposed in this work, materials with an inert surface enable to tolerate a wider potential window in commercially available organic electrolytes in comparison with activated carbons (ACs). The binder-free, vertically grown graphene nanowalls (GNW) and nitrogen-doped GNW (NGNW) electrodes respectively provide good examples for extending the upper potential limit of a positive electrode of EDLCs from 0.1 to 1.5 V (vs Ag/AgNO3) as well as the lower potential limit of a negative electrode of EDLCs from -2.0 V to ca. -2.5 V in 1 M TEABF4/PC (propylene carbonate) compared to ACs. This newly designed asymmetric EDLC exhibits a cell voltage of 4 V, specific energy of 52 Wh kg(-1) (ca. a device energy density of 13 Wh kg(-1)), and specific power of 8 kW kg(-1) and ca. 100% retention after 10,000 cycles charge-discharge, reducing the series number of EDLCs to enlarge the module voltage and opening the possibility for directly combining EDLCs and LIBs in advanced applications.

  7. Carbons, ionic liquids and quinones for electrochemical capacitors

    Directory of Open Access Journals (Sweden)

    Raul eDiaz

    2016-04-01

    Full Text Available Carbons are the main electrode materials used in electrochemical capacitors, which are electrochemical energy storage devices with high power densities and long cycling lifetimes. However, increasing their energy density will improve their potential for commercial implementation. In this regard, the use of high surface area carbons and high voltage electrolytes are well known strategies to increase the attainable energy density, and lately ionic liquids have been explored as promising alternatives to current state of the art acetonitrile-based electrolytes. Also, in terms of safety and sustainability ionic liquids are attractive electrolyte materials for electrochemical capacitors. In addition, it has been shown that the matching of the carbon pore size with the electrolyte ion size further increases the attainable electric double layer (EDL capacitance and energy density.The use of pseudocapacitive reactions can significantly increase the attainable energy density, and quinonic-based materials offer a potentially sustainable and cost effective research avenue for both the electrode and the electrolyte. This perspective will provide an overview of the current state of the art research on electrochemical capacitors based on combinations of carbons, ionic liquids and quinonic compounds, highlighting performances and challenges and discussing possible future research avenues. In this regard, current interest is mainly focused on strategies which may ultimately lead to commercially competitive sustainable high performance electrochemical capacitors for different applications including those requiring mechanical flexibility and biocompatibility.

  8. Solid state double layer capacitor based on a polyether polymer electrolyte blend and nanostructured carbon black electrode composites

    Energy Technology Data Exchange (ETDEWEB)

    Lavall, Rodrigo L.; Borges, Raquel S.; Calado, Hallen D.R.; Welter, Cezar; Trigueiro, Joao P.C.; Silva, Glaura G. [Departamento de Quimica, Instituto de Ciencias Exatas, Universidade Federal de Minas Gerais, CEP 31270-901, Belo Horizonte (Brazil); Rieumont, Jacques [Departamento de Quimica, Instituto de Ciencias Exatas, Universidade Federal de Minas Gerais, CEP 31270-901, Belo Horizonte (Brazil); Facultad de Quimica, Universidad de La Habana, Habana 10400 (Cuba); Neves, Bernardo R.A. [Departamento de Fisica, Instituto de Ciencias Exatas, Universidade Federal de Minas Gerais, CEP 31270-901, Belo Horizonte (Brazil)

    2008-03-01

    An all solid double layer capacitor was assembled by using poly(ethylene oxide)/poly(propylene glycol)-b-poly(ethylene glycol)-b-poly(propylene glycol)-bis(2-aminopropyl ether) blend (PEO-NPPP) and LiClO{sub 4} as polymer electrolyte layer and PEO-NPPP-carbon black (CB) as electrode film. High molecular weight PEO and the block copolymer NPPP with molecular mass of 2000 Da were employed, which means that the design is safe from the point of view of solvent or plasticizer leakage and thus, a separator is not necessary. Highly conductive with large surface area nanostructured carbon black was dispersed in the polymer blend to produce the electrode composite. The electrolyte and electrode multilayers prepared by spray were studied by differential scanning calorimetry, atomic force microscopy (AFM) and impedance spectroscopy. The ionic conductivity as a function of temperature was fitted with the Williams-Landel-Ferry equation, which indicates a conductivity mechanism typical of solid polymer electrolyte. AFM images of the nanocomposite electrode showed carbon black particles of approximately 60 nm in size well distributed in a semicrystalline and porous polymer blend coating. The solid double layer capacitor with 10 wt.% CB was designed with final thickness of approximately 130 {mu}m and delivered a capacitance of 17 F g{sup -1} with a cyclability of more than 1000 cycles. These characteristics make possible the construction of a miniature device in complete solid state which will avoid electrolyte leakage and present a performance superior to other similar electric double layer capacitors (EDLCs) presented in literature, as assessed in specific capacitance by total carbon mass. (author)

  9. Development of a model for the aging of double-layer capacitors; Entwicklung eines Modells zur Alterung von Doppelschichtkondensatoren

    Energy Technology Data Exchange (ETDEWEB)

    Melzer, Michael [TU Dresden (Germany). Professur Elektrische Bahnen

    2012-05-15

    In past years, energy stores based on double-layer capacitors have been increasingly tested and used on rolling stock. The reasons for using energy stores are the recuperation of the braking work, the reduction of emissions related therewith, and the possibility of doing without overhead line installations in sensitive areas. In order to be able to assess the efficiency of such a system, it is necessary to estimate its expected service life, which is the subject matter of this paper. Examined is the dynamic influence of temperature and cell voltage on the ageing process. (orig.)

  10. Application of proton conducting polymeric electrolytes to electrochemical capacitors

    International Nuclear Information System (INIS)

    Morita, Masayuki; Qiao, Jin-Li; Yoshimoto, Nobuko; Ishikawa, Masashi

    2004-01-01

    Non-aqueous polymeric gel complexes composed of poly(ethylene oxide)-modified polymethacrylate (PEO-PMA) dissolving anhydrous H 3 PO 4 have been examined as solid electrolytes of electrochemical capacitors. High ionic conductivity of ∼10 -3 S cm -1 (at 70 deg. C) was obtained for non-aqueous gel systems based on PEO-PMA with proper amounts of organic plasticizers. The ionic conductivity depended on the composition of the gel, especially on the content of the dopant H 3 PO 4 . A test cell of the electric double layer capacitor (EDLC) was assembled using the present gel electrolyte with activated carbon fiber (ACF) cloth electrodes. It gave as high capacity as that obtained for the capacitor using an aqueous liquid electrolyte. High rate capability was obtained for the cell operating at 90 deg. C

  11. Nanoporous carbon for electrochemical capacitors.

    Energy Technology Data Exchange (ETDEWEB)

    Siegal, Michael P.; Bunker, Bruce Conrad; Limmer, Steven J.; Yelton, William Graham

    2010-05-01

    Nanoporous carbon (NPC) is a purely graphitic material with highly controlled densities ranging from less than 0.1 to 2.0 g/cm3, grown via pulsed-laser deposition. Decreasing the density of NPC increases the interplanar spacing between graphene-sheet fragments. This ability to tune the interplanar spacing makes NPC an ideal model system to study the behavior of carbon electrodes in electrochemical capacitors and batteries. We examine the capacitance of NPC films in alkaline and acidic electrolytes, and measure specific capacitances as high as 242 F/g.

  12. Nanoporous carbon for electrochemical capacitors.

    Energy Technology Data Exchange (ETDEWEB)

    Overmyer, Donald L.; Siegal, Michael P.; Bunker, Bruce Conrad; Limmer, Steven J.; Yelton, William Graham

    2010-04-01

    Nanoporous carbon (NPC) is a purely graphitic material with highly controlled densities ranging from less than 0.1 to 2.0 g/cm3, grown via pulsed-laser deposition. Decreasing the density of NPC increases the interplanar spacing between graphene-sheet fragments. This ability to tune the interplanar spacing makes NPC an ideal model system to study the behavior of carbon electrodes in electrochemical capacitors and batteries. We examine the capacitance of NPC films in alkaline and acidic electrolytes, and measure specific capacitances as high as 242 F/g.

  13. Graphene hydrogels deposited in nickel foams for high-rate electrochemical capacitors.

    Science.gov (United States)

    Chen, Ji; Sheng, Kaixuan; Luo, Peihui; Li, Chun; Shi, Gaoquan

    2012-08-28

    Graphene hydrogel/nickel foam composite electrodes for high-rate electrochemical capacitors are produced by reduction of an aqueous dispersion of graphene oxide in a nickel foam (upper half of figure). The micropores of the hydrogel are exposed to the electrolyte so that ions can enter and form electrochemical double-layers. The nickel framework shortens the distances of charge transfer. Therefore, the electrochemical capacitor exhibits highrate performance (see plots). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. High-performance hybrid (electrostatic double-layer and faradaic capacitor-based) polymer actuators incorporating nickel oxide and vapor-grown carbon nanofibers.

    Science.gov (United States)

    Terasawa, Naohiro; Asaka, Kinji

    2014-12-02

    The electrochemical and electromechanical properties of polymeric actuators prepared using nickel peroxide hydrate (NiO2·xH2O) or nickel peroxide anhydride (NiO2)/vapor-grown carbon nanofibers (VGCF)/ionic liquid (IL) electrodes were compared with actuators prepared using solely VGCFs or single-walled carbon nanotubes (SWCNTs) and an IL. The electrode in these actuator systems is equivalent to an electrochemical capacitor (EC) exhibiting both electrostatic double-layer capacitor (EDLC)- and faradaic capacitor (FC)-like behaviors. The capacitance of the metal oxide (NiO2·xH2O or NiO2)/VGCF/IL electrode is primarily attributable to the EDLC mechanism such that, at low frequencies, the strains exhibited by the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators primarily result from the FC mechanism. The VGCFs in the NiO2·xH2O/VGCF/IL and NiO2/VGCF/IL actuators strengthen the EDLC mechanism and increase the electroconductivity of the devices. The mechanism underlying the functioning of the NiO2·xH2O/VGCF/IL actuator in which NiO2·xH2O/VGCF = 1.0 was found to be different from that of the devices produced using solely VGCFs or SWCNTs, which exhibited only the EDLC mechanism. In addition, it was found that both NiO2 and VGCFs are essential with regard to producing actuators that are capable of exhibiting strain levels greater than those of SWCNT-based polymer actuators and are thus suitable for practical applications. Furthermore, the frequency dependence of the displacement responses of the NiO2·xH2O/VGCF and NiO2/VGCF polymer actuators were successfully simulated using a double-layer charging kinetic model. This model, which accounted for the oxidization and reduction reactions of the metal oxide, can also be applied to SWCNT-based actuators. The results of electromechanical response simulations for the NiO2·xH2O/VGCF and NiO2/VGCF actuators predicted the strains at low frequencies as well as the time constants of the devices, confirming that the model is applicable

  15. Superparamagnetic magnetite nanocrystals-graphene oxide nanocomposites: facile synthesis and their enhanced electric double-layer capacitor performance.

    Science.gov (United States)

    Wang, Qihua; Wang, Dewei; Li, Yuqi; Wang, Tingmei

    2012-06-01

    Superparamagnetic magnetite nanocrystals-graphene oxide (FGO) nanocomposites were successfully synthesized through a simple yet versatile one-step solution-processed approach at ambient conditions. Magnetite (Fe3O4) nanocrystals (NCs) with a size of 10-50 nm were uniformly deposited on the surfaces of graphene oxide (GO) sheets, which were confirmed by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission election microscopy (HAADF-STEM) studies. FGO with different Fe3O4 loadings could be controlled by simply manipulating the initial weight ratio of the precursors. The M-H measurements suggested that the as-prepared FGO nanocomposites have a large saturation magnetizations that made them can move regularly under an external magnetic field. Significantly, FGO nanocomposites also exhibit enhanced electric double-layer capacitor (EDLC) activity compared with pure Fe3O4 NCs and GO in terms of specific capacitance and high-rate charge-discharge.

  16. Performance of electrical double layer capacitors fabricated with gel polymer electrolytes containing Li+ and K+-salts: A comparison

    International Nuclear Information System (INIS)

    Singh, Manoj K.; Hashmi, S. A.

    2015-01-01

    The comparative performance of the solid-state electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and poly (vinaylidinefluoride-co-hexafluoropropyline) (PVdF-HFP) based gel polymer electrolytes (GPEs) containing potassium and lithium salts have been studied. The room temperature ionic conductivity of the GPEs have been found to be ∼3.8×10 −3 and 5.9×10 −3 S cm −1 for lithium and potassium based systems. The performance of EDLC cells studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques, indicate that the EDLC with potassium salt containing GPE shows excellent performance almost equivalent to the EDLC with Li-salt-based GPE

  17. Debye length dependence of the anomalous dynamics of ionic double layers in a parallel plate capacitor

    NARCIS (Netherlands)

    Kortschot, R. J.; Philipse, A. P.; Erné, B. H.

    2014-01-01

    The electrical impedance spectrum of simple ionic solutions is measured in a parallel plate capacitor at small applied ac voltage. The influence of the ionic strength is investigated using several electrolytes at different concentrations in solvents of different dielectric constants. The electric

  18. Boron cross-linked graphene oxide/polyvinyl alcohol nanocomposite gel electrolyte for flexible solid-state electric double layer capacitor with high performance

    KAUST Repository

    Huang, Yi-Fu; Wu, Peng-Fei; Zhang, Ming-Qiu; Ruan, Wen-Hong; Giannelis, Emmanuel P.

    2014-01-01

    A new family of boron cross-linked graphene oxide/polyvinyl alcohol (GO-B-PVA) nanocomposite gels is prepared by freeze-thaw/boron cross-linking method. Then the gel electrolytes saturated with KOH solution are assembled into electric double layer capacitors (EDLCs). Structure, thermal and mechanical properties of GO-B-PVA are explored. The electrochemical properties of EDLCs using GO-B-PVA/KOH are investigated, and compared with those using GO-PVA/KOH gel or KOH solution electrolyte. FTIR shows that boron cross-links are introduced into GO-PVA, while the boronic structure inserted into agglomerated GO sheets is demonstrated by DMA analysis. The synergy effect of the GO and the boron crosslinking benefits for ionic conductivity due to unblocking ion channels, and for improvement of thermal stability and mechanical properties of the electrolytes. Higher specific capacitance and better cycle stability of EDLCs are obtained by using the GO-B-PVA/KOH electrolyte, especially the one at higher GO content. The nanocomposite gel electrolytes with excellent electrochemical properties and solid-like character are candidates for the industrial application in high-performance flexible solid-state EDLCs. © 2014 Elsevier Ltd.

  19. An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes.

    Science.gov (United States)

    Fattah, N F A; Ng, H M; Mahipal, Y K; Numan, Arshid; Ramesh, S; Ramesh, K

    2016-06-06

    Solid polymer electrolyte (SPE) composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl) imide [EMI-BTI] and graphene oxide (GO) was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC). The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP)-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge-discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g -1 , which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application.

  20. Boron cross-linked graphene oxide/polyvinyl alcohol nanocomposite gel electrolyte for flexible solid-state electric double layer capacitor with high performance

    KAUST Repository

    Huang, Yi-Fu

    2014-06-01

    A new family of boron cross-linked graphene oxide/polyvinyl alcohol (GO-B-PVA) nanocomposite gels is prepared by freeze-thaw/boron cross-linking method. Then the gel electrolytes saturated with KOH solution are assembled into electric double layer capacitors (EDLCs). Structure, thermal and mechanical properties of GO-B-PVA are explored. The electrochemical properties of EDLCs using GO-B-PVA/KOH are investigated, and compared with those using GO-PVA/KOH gel or KOH solution electrolyte. FTIR shows that boron cross-links are introduced into GO-PVA, while the boronic structure inserted into agglomerated GO sheets is demonstrated by DMA analysis. The synergy effect of the GO and the boron crosslinking benefits for ionic conductivity due to unblocking ion channels, and for improvement of thermal stability and mechanical properties of the electrolytes. Higher specific capacitance and better cycle stability of EDLCs are obtained by using the GO-B-PVA/KOH electrolyte, especially the one at higher GO content. The nanocomposite gel electrolytes with excellent electrochemical properties and solid-like character are candidates for the industrial application in high-performance flexible solid-state EDLCs. © 2014 Elsevier Ltd.

  1. An Approach to Solid-State Electrical Double Layer Capacitors Fabricated with Graphene Oxide-Doped, Ionic Liquid-Based Solid Copolymer Electrolytes

    Directory of Open Access Journals (Sweden)

    N. F. A. Fattah

    2016-06-01

    Full Text Available Solid polymer electrolyte (SPE composed of semi-crystalline poly (vinylidene fluoride-hexafluoropropylene [P(VdF-HFP] copolymer, 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulphonyl imide [EMI-BTI] and graphene oxide (GO was prepared and its performance evaluated. The effects of GO nano-filler were investigated in terms of enhancement in ionic conductivity along with the electrochemical properties of its electrical double layer capacitors (EDLC. The GO-doped SPE shows improvement in ionic conductivity compared to the P(VdF-HFP-[EMI-BTI] SPE system due to the existence of the abundant oxygen-containing functional group in GO that assists in the improvement of the ion mobility in the polymer matrix. The complexation of the materials in the SPE is confirmed in X-ray diffraction (XRD and thermogravimetric analysis (TGA studies. The electrochemical performance of EDLC fabricated with GO-doped SPE is examined using cyclic voltammetry and charge–discharge techniques. The maximum specific capacitance obtained is 29.6 F∙g−1, which is observed at a scan rate of 3 mV/s in 6 wt % GO-doped, SPE-based EDLC. It also has excellent cyclic retention as it is able keep the performance of the EDLC at 94% even after 3000 cycles. These results suggest GO doped SPE plays a significant role in energy storage application.

  2. Electrochemical properties of arc-black and carbon nano-balloon as electrochemical capacitor electrodes

    International Nuclear Information System (INIS)

    Sato, T; Suda, Y; Uruno, H; Takikawa, H; Tanoue, H; Ue, H; Aoyagi, N; Okawa, T; Shimizu, K

    2012-01-01

    In this study, we used two types of carbon nanomaterials, arc-black (AcB) which has an amorphous structure and carbon nano-balloon (CNB) which has a graphitic structure as electrochemical capacitor electrodes. We made a coin electrode from these carbon materials and fabricated an electric double-layer capacitor (EDLC) that sandwiches a separator between the coin electrodes. On the other hand, RuO 2 was loaded on these carbon materials, and we fabricated a pseudo-capacitor that has an ion insertion mechanism into RuO 2 . For comparison with these carbon materials, activated carbon (AC) was also used for a capacitor electrode. The electrochemical properties of all the capacitors were evaluated in 1M H 2 SO 4 aqueous solution. As a result of EDLC performance, AcB electrode had a higher specific capacitance than AC electrode at a high scan rate (≥ 100 mV/s). In the evaluation of pseudo-capacitor performance, RuO 2 -loaded CNB electrode showed a high specific capacitance of 734 F/g per RuO 2 weight.

  3. Preparation of porous carbon spheres from 2-keto-l-gulonic acid mother liquor by oxidation and activation for electric double-layer capacitor application.

    Science.gov (United States)

    Hao, Zhi-Qiang; Cao, Jing-Pei; Zhao, Xiao-Yan; Wu, Yan; Zhu, Jun-Sheng; Dang, Ya-Li; Zhuang, Qi-Qi; Wei, Xian-Yong

    2018-03-01

    A novel strategy is proposed for the increase of specific surface area (SSA) of porous carbon sphere (PCS) by oxidation and activation. 2-keto-l-gulonic acid mother liquor (GAML) as a high-pollution waste has a relatively high value of reutilization. For its high value-added utilization, GAML is used as the precursor for preparation of PCS as carbon-based electrode materials for electric double-layer capacitor. PCS is prepared by hydrothermal carbonization, carbonization and KOH activation, and Fe(NO 3 ) 3 9H 2 O is used as an oxidizing agent during carbonization. The as-prepared PCS has excellent porosity and high SSA of 2478 m 2  g -1 . Meanwhile, the pore structure of PCS can be controlled by the adjustment of carbonization parameters (carbonization temperature and the loading of Fe(NO 3 ) 3 9H 2 O). Besides, the SSA and specific capacitance of PCS can be increased remarkably when Fe(NO 3 ) 3 9H 2 O is added in carbonization. The specific capacitance of PCS can reach 303.7 F g -1 at 40 mA g -1 . PCSs as electrode material have superior electrochemical stability. After 8000 cycles, the capacitance retention is 98.3% at 2 A g -1 . The electric double-layer capacitance of PCS is improved when CS is carbonized with Fe(NO 3 ) 3 9H 2 O, and the economic and environmental benefits are achieved by the effective recycle of GAML. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Relationship between structural properties and electrochemical characteristics of monolithic carbon xerogel-based electrochemical double-layer electrodes in aqueous and organic electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Zeller, Mario [Bavarian Center for Applied Energy Research e.V. (ZAE Bayern), Wuerzburg (Germany); Institute of Radiology, University Clinic, University of Wuerzburg (Germany); Lorrmann, Volker; Reichenauer, Gudrun; Wiener, Matthias [Bavarian Center for Applied Energy Research e.V. (ZAE Bayern), Wuerzburg (Germany); Pflaum, Jens [Bavarian Center for Applied Energy Research e.V. (ZAE Bayern), Wuerzburg (Germany); Department of Experimental Physics VI, Julius-Maximilians-University of Wuerzburg (Germany)

    2012-05-15

    The impact of the micropore width, external surface area, and meso-/macropore size on the charging performance of electrochemical double-layer capacitor (EDLC) electrodes is systematically investigated. Nonactivated carbon xerogels are used as model electrodes in aqueous and organic electrolytes. Monolithic porous model carbons with different structural parameters are prepared using a resorcinol-formaldehyde-based sol-gel process and subsequent pyrolysis of the organic precursors. Electrochemical properties are characterized by utilizing them as EDLC half-cells operated in aqueous and organic electrolytes, respectively. Experimental data derived for organic electrolytes reveals that the respective ions cannot enter the micropores within the skeleton of the meso- and macroporous carbons. Therefore the total capacitance is limited by the external surface formed by the interface between the meso-/macropores and the microporous carbon particles forming the xerogel skeleton. In contrast, for aqueous electrolytes the total capacitance solely depends on the total surface area, including interfaces at the micropore scale. For both types of electrolytes the charging rate of the electrodes is systematically enhanced when increasing the diameter of the carbon xerogel particles from 10 to 75 nm and the meso-/macropore size from 10 to 121 nm. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Electrochemical characteristics of discrete, uniform, and monodispersed hollow mesoporous carbon spheres in double-layered supercapacitors.

    Science.gov (United States)

    Chen, Xuecheng; Kierzek, Krzysztof; Wenelska, Karolina; Cendrowski, Krzystof; Gong, Jiang; Wen, Xin; Tang, Tao; Chu, Paul K; Mijowska, Ewa

    2013-11-01

    Core-shell-structured mesoporous silica spheres were prepared by using n-octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core-shell-structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double-layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer-Emmett-Teller (BET) area and larger pore size. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Morphological reason for enhancement of electrochemical double layer capacitances of various acetylene blacks by electrochemical polarization

    International Nuclear Information System (INIS)

    Kim, Taegon; Ham, Chulho; Rhee, Choong Kyun; Yoon, Seong-Ho; Tsuji, Masaharu; Mochida, Isao

    2008-01-01

    Enhancement of electrochemical capacitance and morphological variations of various acetylene blacks caused by electrochemical polarization are presented. Acetylene blacks of different mean particle diameters were modified by air-oxidation and heat treatment to diversify the morphologies of the acetylene blacks before electrochemical polarization. The various acetylene blacks were electrochemically oxidized at 1.6 V (vs. Ag/AgCl) for 10 s and the polarization step was repeated until the capacitance values did not change any longer. These polarization steps enhanced the capacitances of the acetylene blacks and the specific enhancement factors range from 2 to 5.5. Such an enhancement is strongly related to morphological modification as revealed by transmission electron microscopic observations. The electrochemical polarization resulted in formation of tiny graphene sheets on the wide graphitic carbon surfaces, which were most responsible for the observed capacitive enhancement. Although the pseudo-capacitance increased after polarization by forming oxygenated species on the surfaces, its contribution to the total capacitance was less than 10%. The mechanism of the formation of the tiny graphene sheets during the electrochemical oxidation is described schematically

  7. Reevaluation of Performance of Electric Double-layer Capacitors from Constant-current Charge/Discharge and Cyclic Voltammetry.

    Science.gov (United States)

    Allagui, Anis; Freeborn, Todd J; Elwakil, Ahmed S; Maundy, Brent J

    2016-12-09

    The electric characteristics of electric-double layer capacitors (EDLCs) are determined by their capacitance which is usually measured in the time domain from constant-current charging/discharging and cyclic voltammetry tests, and from the frequency domain using nonlinear least-squares fitting of spectral impedance. The time-voltage and current-voltage profiles from the first two techniques are commonly treated by assuming ideal R s C behavior in spite of the nonlinear response of the device, which in turn provides inaccurate values for its characteristic metrics [corrected]. In this paper we revisit the calculation of capacitance, power and energy of EDLCs from the time domain constant-current step response and linear voltage waveform, under the assumption that the device behaves as an equivalent fractional-order circuit consisting of a resistance R s in series with a constant phase element (CPE(Q, α), with Q being a pseudocapacitance and α a dispersion coefficient). In particular, we show with the derived (R s , Q, α)-based expressions, that the corresponding nonlinear effects in voltage-time and current-voltage can be encompassed through nonlinear terms function of the coefficient α, which is not possible with the classical R s C model. We validate our formulae with the experimental measurements of different EDLCs.

  8. Introduction of electric double layer capacitors in the solar-EV; Solar denki jidosha eno denki nijuso condenser no oyo

    Energy Technology Data Exchange (ETDEWEB)

    Fujinaka, M [Tokyo Denki University, Tokyo (Japan)

    1996-10-27

    A basic experiment was carried out on a supplementary power supply, in which solar cells and electric double layer capacitors(EDLC) were combined for a DC/DC converter, for the use of a solar-electric vehicle (S-EV); and in actuality, an S-EV was loaded with the power supply with a running test conducted on a public road. The EDLC was found effective and useful for avoiding temporary lowering of voltage and momentary break. An electric supply was thereby made possible for an emergency light without the use of the DC/DC converter. However, in a tunnel or a night driving and in case of failure of the DC/DC converter, an operating time of only 7 minutes or so was affordable with the EDLC having a capacity of 100F. Moreover, particularly with a heavy load, it was impossible to maintain a voltage for many hours. Under the circumstances, an S-EV design would primarily require two sets of independent DC/DC converter loaded in the future. The EDLC, young after it was developed, still has a small energy density compared with a lead storage battery. Yet, an EDLC with a higher performance being developed, there is a possibility that it will be applied to S-EV`s by utilizing its characteristics such as a high efficiency and a long service life. 4 refs., 8 figs.

  9. Reevaluation of Performance of Electric Double-layer Capacitors from Constant-current Charge/Discharge and Cyclic Voltammetry

    Science.gov (United States)

    Allagui, Anis; Freeborn, Todd J.; Elwakil, Ahmed S.; Maundy, Brent J.

    2016-12-01

    The electric characteristics of electric-double layer capacitors (EDLCs) are determined by their capacitance which is usually measured in the time domain from constant-current charging/discharging and cyclic voltammetry tests, and from the frequency domain using nonlinear least-squares fitting of spectral impedance. The time-voltage and current-voltage profiles from the first two techniques are commonly treated by assuming ideal SsC behavior in spite of the nonlinear response of the device, which in turn provides inaccurate values for its characteristic metrics. In this paper we revisit the calculation of capacitance, power and energy of EDLCs from the time domain constant-current step response and linear voltage waveform, under the assumption that the device behaves as an equivalent fractional-order circuit consisting of a resistance Rs in series with a constant phase element (CPE(Q, α), with Q being a pseudocapacitance and α a dispersion coefficient). In particular, we show with the derived (Rs, Q, α)-based expressions, that the corresponding nonlinear effects in voltage-time and current-voltage can be encompassed through nonlinear terms function of the coefficient α, which is not possible with the classical RsC model. We validate our formulae with the experimental measurements of different EDLCs.

  10. Insights into the effects of solvent properties in graphene based electric double-layer capacitors with organic electrolytes

    Science.gov (United States)

    Zhang, Shuo; Bo, Zheng; Yang, Huachao; Yang, Jinyuan; Duan, Liangping; Yan, Jianhua; Cen, Kefa

    2016-12-01

    Organic electrolytes are widely used in electric double-layer capacitors (EDLCs). In this work, the microstructure of planar graphene-based EDLCs with different organic solvents are investigated with molecular dynamics simulations. Results show that an increase of solvent polarity could weaken the accumulation of counter-ions nearby the electrode surface, due to the screen of electrode charges and relatively lower ionic desolvation. It thus suggests that solvents with low polarity could be preferable to yield high EDL capacitance. Meanwhile, the significant effects of the size and structure of solvent molecules are reflected by non-electrostatic molecule-electrode interactions, further influencing the adsorption of solvent molecules on electrode surface. Compared with dimethyl carbonate, γ-butyrolactone, and propylene carbonate, acetonitrile with relatively small-size and linear structure owns weak non-electrostatic interactions, which favors the easy re-orientation of solvent molecules. Moreover, the shift of solvent orientation in surface layer, from parallel orientation to perpendicular orientation relative to the electrode surface, deciphers the solvent twin-peak behavior near negative electrode. The as-obtained insights into the roles of solvent properties on the interplays among particles and electrodes elucidate the solvent influences on the microstructure and capacitive behavior of EDLCs using organic electrolytes.

  11. A Novel Degradation Estimation Method for a Hybrid Energy Storage System Consisting of Battery and Double-Layer Capacitor

    Directory of Open Access Journals (Sweden)

    Yuanbin Yu

    2016-01-01

    Full Text Available This paper presents a new method for battery degradation estimation using a power-energy (PE function in a battery/ultracapacitor hybrid energy storage system (HESS, and the integrated optimization which concerns both parameters matching and control for HESS has been done as well. A semiactive topology of HESS with double-layer capacitor (EDLC coupled directly with DC-link is adopted for a hybrid electric city bus (HECB. In the purpose of presenting the quantitative relationship between system parameters and battery serving life, the data during a 37-minute driving cycle has been collected and decomposed into discharging/charging fragments firstly, and then the optimal control strategy which is supposed to maximally use the available EDLC energy is presented to decompose the power between battery and EDLC. Furthermore, based on a battery degradation model, the conversion of power demand by PE function and PE matrix is applied to evaluate the relationship between the available energy stored in HESS and the serving life of battery pack. Therefore, according to the approach which could decouple parameters matching and optimal control of the HESS, the process of battery degradation and its serving life estimation for HESS has been summed up.

  12. Experimental studies on poly methyl methacrylate based gel polymer electrolytes for application in electrical double layer capacitors

    International Nuclear Information System (INIS)

    Hashmi, S A; Kumar, Ashok; Tripathi, S K

    2007-01-01

    Studies have been carried out on gel polymer electrolytes comprising poly methyl methacrylate (PMMA)-ethylene carbonate (EC)-propylene carbonate (PC)-salts, LiClO 4 , NaClO 4 and (C 2 H 5 ) 4 NClO 4 (TEAClO 4 ) with a view to using them as electrolytes in electrical double layer capacitors (EDLCs) based on activated charcoal powder electrodes. The optimum composition of gel electrolytes, PMMA (20 wt%)-EC : PC (1 : 1 v/v)-1.0 M salts exhibit high ionic conductivity of the order of ∼10 -3 S cm -1 at room temperature with good mechanical/dimensional stability, suitable for their application in EDLCs. The EDLCs have been characterized using linear sweep cyclic voltammetry, galvanostatic charge-discharge tests and ac impedance spectroscopy. The values of capacitance of 68-151 mF cm -2 (equivalent to single electrode specific capacitance of 38-78 Fg -1 of activated charcoal powder) have been observed. These values correspond to a specific energy of 5.3-10.8 Wh kg -1 and a power density of 0.19-0.22 kW kg -1 . The capacitance values have been observed to be stable up to 5000 voltammetric cycles or even more. A comparison of studies shows the predominant role of anions of the gel electrolytes in the capacitive behaviour of EDLCs

  13. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    International Nuclear Information System (INIS)

    Lian, Cheng; University of California, Riverside, CA; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-01-01

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this paper, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance–voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Finally, our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors.

  14. The electric double layer put to work : thermal physics at electrochemical interfaces

    NARCIS (Netherlands)

    Janssen, M.A.

    2017-01-01

    Where charged electrode surfaces meet fluids that contain mobile ions, so-called electric double layers (EDLs) form to screen the electric surface charge by a diffuse cloud of counterionic charge in the fluid phase. This double layer has been studied for over a century and is of paramount importance

  15. Electrochemical behavior of pitch-based activated carbon fibers for electrochemical capacitors

    International Nuclear Information System (INIS)

    Lee, Hye-Min; Kwac, Lee-Ku; An, Kay-Hyeok; Park, Soo-Jin; Kim, Byung-Joo

    2016-01-01

    Highlights: • Electrode materials for electrochemical capacitors were developed using pitch-based activated carbon fibers with steam activation. • Activated carbon fibers showed enhanced specific surface area from 1520 to 3230 m 2 /g. • The increase in the specific capacitance of the samples was determined by charged pore structure during charging and discharging. - Abstract: In the present study, electrode materials for electrochemical capacitors were developed using pitch-based activated carbon fibers with steam activation. The surface and structural characteristics of activated carbon fibers were observed using scanning electron microscopy and X-ray diffraction, respectively. Pore characteristics were investigated using N 2 /77 K adsorption isotherms. The activated carbon fibers were applied as electrodes for electrical double-layer capacitors and analyzed in relation to the activation time. The specific surface area and total pore volume of the activated carbon fibers were determined to be 1520–3230 m 2 /g and 0.61–1.87 cm 3 /g, respectively. In addition, when the electrochemical characteristics were analyzed, the specific capacitance was confirmed to have increased from 1.1 F/g to 22.5 F/g. From these results, it is clear that the pore characteristics of pitch-based activated carbon fibers changed considerably in relation to steam activation and charge/discharge cycle; therefore, it was possible to improve the electrochemical characteristics of the activated carbon fibers.

  16. Electrode Mass Balancing as an Inexpensive and Simple Method to Increase the Capacitance of Electric Double-Layer Capacitors

    Science.gov (United States)

    Andres, Britta; Engström, Ann-Christine; Blomquist, Nicklas; Forsberg, Sven; Dahlström, Christina; Olin, Håkan

    2016-01-01

    Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC’s specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes— Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)—and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost. PMID:27658253

  17. Can ionophobic nanopores enhance the energy storage capacity of electric-double-layer capacitors containing nonaqueous electrolytes?

    Science.gov (United States)

    Lian, Cheng; Liu, Honglai; Henderson, Douglas; Wu, Jianzhong

    2016-10-01

    The ionophobicity effect of nanoporous electrodes on the capacitance and the energy storage capacity of nonaqueous-electrolyte supercapacitors is studied by means of the classical density functional theory (DFT). It has been hypothesized that ionophobic nanopores may create obstacles in charging, but they store energy much more efficiently than ionophilic pores. In this study, we find that, for both ionic liquids and organic electrolytes, an ionophobic pore exhibits a charging behavior different from that of an ionophilic pore, and that the capacitance-voltage curve changes from a bell shape to a two-hump camel shape when the pore ionophobicity increases. For electric-double-layer capacitors containing organic electrolytes, an increase in the ionophobicity of the nanopores leads to a higher capacity for energy storage. Without taking into account the effects of background screening, the DFT predicts that an ionophobic pore containing an ionic liquid does not enhance the supercapacitor performance within the practical voltage ranges. However, by using an effective dielectric constant to account for ion polarizability, the DFT predicts that, like an organic electrolyte, an ionophobic pore with an ionic liquid is also able to increase the energy stored when the electrode voltage is beyond a certain value. We find that the critical voltage for an enhanced capacitance in an ionic liquid is larger than that in an organic electrolyte. Our theoretical predictions provide further understanding of how chemical modification of porous electrodes affects the performance of supercapacitors. The authors are saddened by the passing of George Stell but are pleased to contribute this article in his memory. Some years ago, DH gave a talk at a Gordon Conference that contained an approximation that George had demonstrated previously to be in error in one of his publications. Rather than making this point loudly in the discussion, George politely, quietly, and privately pointed this out

  18. Method of making a multi-electrode double layer capacitor having single electrolyte seal and aluminum-impregnated carbon cloth electrodes

    Science.gov (United States)

    Farahmandi, C. Joseph; Dispennette, John M.; Blank, Edward; Kolb, Alan C.

    2002-09-17

    A single cell, multi-electrode high performance double layer capacitor includes first and second flat stacks of electrodes adapted to be housed in a closeable two-part capacitor case which includes only a single electrolyte seal. Each electrode stack has a plurality of electrodes connected in parallel, with the electrodes of one stack being interleaved with the electrodes of the other stack to form an interleaved stack, and with the electrodes of each stack being electrically connected to respective capacitor terminals. A porous separator is positioned against the electrodes of one stack before interleaving to prevent electrical shorts between the electrodes. The electrodes are made by folding a compressible, low resistance, aluminum-impregnated carbon cloth, made from activated carbon fibers, around a current collector foil, with a tab of the foils of each electrode of each stack being connected in parallel and connected to the respective capacitor terminal. The height of the interleaved stack is somewhat greater than the inside height of the closed capacitor case, thereby requiring compression of the interleaved electrode stack when placed inside of the case, and thereby maintaining the interleaved electrode stack under modest constant pressure. The closed capacitor case is filled with an electrolytic solution and sealed. A preferred electrolytic solution is made by dissolving an appropriate salt into acetonitrile (CH.sub.3 CN). In one embodiment, the two parts of the capacitor case are conductive and function as the capacitor terminals.

  19. Capacitive behavior studies on electrical double layer capacitor using poly (vinyl alcohol)–lithium perchlorate based polymer electrolyte incorporated with TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Chin-Shen; Teoh, K.H.; Liew, Chiam-Wen; Ramesh, S., E-mail: rameshtsubra@gmail.com

    2014-01-15

    Electric double layer capacitors (EDLCs) based on activated carbon electrodes and poly (vinyl alcohol)–lithium perchlorate (PVA–LiClO{sub 4})-nanosized titania (TiO{sub 2}) doped polymer electrolyte have been fabricated. Incorporation of TiO{sub 2} into PVA–LiClO{sub 4} system increases the ionic conductivity. The highest ionic conductivity of 1.3 × 10{sup −4} S cm{sup −1} is achieved at ambient temperature upon inclusion of 8 wt.% of TiO{sub 2}. Differential scanning calorimetry (DSC) analyses reveal that addition of TiO{sub 2} into polymer system increases the flexibility of polymer chain and favors the ion migration. Scanning electron microscopy (SEM) analyses display the surface morphology of the nanocomposite polymer electrolytes. The electrochemical stability window of composite polymer electrolyte is in the range of −2.3 V to 2.3 V as shown in cyclic voltammetry (CV) studies. The performance of EDLC is evaluated by electrochemical impedance spectroscopy (EIS), CV and galvanostatic charge–discharge technique. CV test discloses a nearly rectangular shape, which signifies the capacitive behavior of an ELDC. The EDLC containing composite polymer electrolyte gives higher specific capacitance value of 12.5 F g{sup −1} compared to non-composite polymer electrolyte with capacitance value of 3.0 F g{sup −1} in charge–discharge technique. The obtained specific capacitance of EDLC is in good agreement with each method used in this present work. Inclusion of filler into the polymer electrolyte enhances the electrochemical stability of EDLC. - Highlights: • PVA–LiClO{sub 4}–TiO{sub 2} possesses ionic conductivity value of 1.30 × 10{sup −4} S cm{sup −1}. • CV indicates the electrochemical stability window in the range of −2.3 V to 2.3 V. • The EDLC gives specific capacitance value of 12.5 F g{sup −1}.

  20. Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

    Science.gov (United States)

    Choi, Poo Reum; Lee, Eunji; Kwon, Soon Hyung; Jung, Ji Chul; Kim, Myung-Soo

    2015-12-01

    The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800-1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500-600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900-1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.

  1. Carbon-Based Materials for Lithium-Ion Batteries, Electrochemical Capacitors, and Their Hybrid Devices.

    Science.gov (United States)

    Yao, Fei; Pham, Duy Tho; Lee, Young Hee

    2015-07-20

    A rapidly developing market for portable electronic devices and hybrid electrical vehicles requires an urgent supply of mature energy-storage systems. As a result, lithium-ion batteries and electrochemical capacitors have lately attracted broad attention. Nevertheless, it is well known that both devices have their own drawbacks. With the fast development of nanoscience and nanotechnology, various structures and materials have been proposed to overcome the deficiencies of both devices to improve their electrochemical performance further. In this Review, electrochemical storage mechanisms based on carbon materials for both lithium-ion batteries and electrochemical capacitors are introduced. Non-faradic processes (electric double-layer capacitance) and faradic reactions (pseudocapacitance and intercalation) are generally explained. Electrochemical performance based on different types of electrolytes is briefly reviewed. Furthermore, impedance behavior based on Nyquist plots is discussed. We demonstrate the influence of cell conductivity, electrode/electrolyte interface, and ion diffusion on impedance performance. We illustrate that relaxation time, which is closely related to ion diffusion, can be extracted from Nyquist plots and compared between lithium-ion batteries and electrochemical capacitors. Finally, recent progress in the design of anodes for lithium-ion batteries, electrochemical capacitors, and their hybrid devices based on carbonaceous materials are reviewed. Challenges and future perspectives are further discussed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. High voltage AC/AC electrochemical capacitor operating at low temperature in salt aqueous electrolyte

    Science.gov (United States)

    Abbas, Qamar; Béguin, François

    2016-06-01

    We demonstrate that an activated carbon (AC)-based electrochemical capacitor implementing aqueous lithium sulfate electrolyte in 7:3 vol:vol water/methanol mixture can operate down to -40 °C with good electrochemical performance. Three-electrode cell investigations show that the faradaic contributions related with hydrogen chemisorption in the negative AC electrode are thermodynamically unfavored at -40 °C, enabling the system to work as a typical electrical double-layer (EDL) capacitor. After prolonged floating of the AC/AC capacitor at 1.6 V and -40°C, the capacitance, equivalent series resistance and efficiency remain constant, demonstrating the absence of ageing related with side redox reactions at this temperature. Interestingly, when temperature is increased back to 24 °C, the redox behavior due to hydrogen storage reappears and the system behaves as a freshly prepared one.

  3. Solid-state electric double layer capacitors fabricated with plastic crystal based flexible gel polymer electrolytes: Effective role of electrolyte anions

    International Nuclear Information System (INIS)

    Suleman, Mohd; Kumar, Yogesh; Hashmi, S.A.

    2015-01-01

    Flexible gel polymer electrolyte (GPE) thick films incorporated with solutions of lithium trifluoromethanesulfonate (Li-triflate or LiTf) and lithium bis trifluoromethane-sulfonimide (LiTFSI) in a plastic crystal succinonitrile (SN), entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) have been prepared and characterized. The films have been used as electrolytes in the electrical double layer capacitors (EDLCs). Coconut-shell derived activated carbon with high specific surface area (∼2100 m 2 g −1 ) and mixed (micro- and meso-) porosity has been used as EDLC electrodes. The structural, thermal, and electrochemical characterization of the GPEs have been performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impedance measurements and cyclic voltammetry. The high ionic conductivity (∼10 −3 S cm −1 at 25 °C), good electrochemical stability window (>4.0 V) and flexible nature of the free-standing films of GPEs show their competence in the fabrication of EDLCs. The EDLCs have been tested using electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. The EDLCs using LiTf based electrolyte have been found to give higher values of specific capacitance, specific energy, power density (240–280 F g −1 , ∼39 Wh kg −1 and ∼19 kW kg −1 , respectively) than the EDLC cell with LiTFSI based gel electrolyte. EDLCs have been found to show stable performance for ∼10 4 charge–discharge cycles. The comparative studies indicate the effective role of electrolyte anions on the capacitive performance of the solid-state EDLCs. - Graphical abstract: Display Omitted - Highlights: • Flexible EDLCs with succinonitrile based gel electrolyte membranes are reported. • Anionic size of salts in gel electrolytes plays important role on capacitive performance. • Li-triflate incorporated gel electrolyte shows better performance over LiTFSI-based gel.

  4. Solid-state electric double layer capacitors fabricated with plastic crystal based flexible gel polymer electrolytes: Effective role of electrolyte anions

    Energy Technology Data Exchange (ETDEWEB)

    Suleman, Mohd; Kumar, Yogesh; Hashmi, S.A., E-mail: sahashmi@physics.du.ac.in

    2015-08-01

    Flexible gel polymer electrolyte (GPE) thick films incorporated with solutions of lithium trifluoromethanesulfonate (Li-triflate or LiTf) and lithium bis trifluoromethane-sulfonimide (LiTFSI) in a plastic crystal succinonitrile (SN), entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) have been prepared and characterized. The films have been used as electrolytes in the electrical double layer capacitors (EDLCs). Coconut-shell derived activated carbon with high specific surface area (∼2100 m{sup 2} g{sup −1}) and mixed (micro- and meso-) porosity has been used as EDLC electrodes. The structural, thermal, and electrochemical characterization of the GPEs have been performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impedance measurements and cyclic voltammetry. The high ionic conductivity (∼10{sup −3} S cm{sup −1} at 25 °C), good electrochemical stability window (>4.0 V) and flexible nature of the free-standing films of GPEs show their competence in the fabrication of EDLCs. The EDLCs have been tested using electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. The EDLCs using LiTf based electrolyte have been found to give higher values of specific capacitance, specific energy, power density (240–280 F g{sup −1}, ∼39 Wh kg{sup −1} and ∼19 kW kg{sup −1}, respectively) than the EDLC cell with LiTFSI based gel electrolyte. EDLCs have been found to show stable performance for ∼10{sup 4} charge–discharge cycles. The comparative studies indicate the effective role of electrolyte anions on the capacitive performance of the solid-state EDLCs. - Graphical abstract: Display Omitted - Highlights: • Flexible EDLCs with succinonitrile based gel electrolyte membranes are reported. • Anionic size of salts in gel electrolytes plays important role on capacitive performance. • Li-triflate incorporated gel electrolyte shows better

  5. Physical properties of a new Deep Eutectic Solvent based on lithium bis[(trifluoromethyl)sulfonyl]imide and N-methylacetamide as superionic suitable electrolyte for lithium ion batteries and electric double layer capacitors

    International Nuclear Information System (INIS)

    Boisset, Aurélien; Jacquemin, Johan; Anouti, Mérièm

    2013-01-01

    Highlights: • Preparation of new Deep Eutectic Solvent (DES) based on N-methylacetamide and TFSI. • Characterization of conductivity, viscosity and thermal properties of DES. • DES presents a superionic character in Walden classification. • DES is suitable electrolyte for lithium ion batteries and electric double layer capacitors. -- Abstract: Herein we present a study on the physical/chemical properties of a new Deep Eutectic Solvent (DES) based on N-methylacetamide (MAc) and lithium bis[(trifluoromethyl)sulfonyl]imide (LiTFSI). Due to its interesting properties, such as wide liquid-phase range from −60 °C to 280 °C, low vapor pressure, and high ionic conductivity up to 28.4 mS cm −1 at 150 °C and at x LiTFSI = 1/4, this solution can be practically used as electrolyte for electrochemical storage systems such as electric double-layer capacitors (EDLCs) and/or lithium ion batteries (LiBs). Firstly, relationships between its transport properties (conductivity and viscosity) as a function of composition and temperature were discussed through Arrhenius’ Law and Vogel–Tamman–Fulcher (VTF) equations, as well as by using the Walden classification. From this investigation, it appears that this complex electrolyte possesses a number of excellent transport properties, like a superionic character for example. Based on which, we then evaluated its electrochemical performances as electrolyte for EDLCs and LiBs applications by using activated carbon (AC) and lithium iron phosphate (LiFePO 4 ) electrodes, respectively. These results demonstrate that this electrolyte has a good compatibility with both electrodes (AC and LiFePO 4 ) in each testing cell driven also by excellent electrochemical properties in specific capacitance, rate and cycling performances, indicating that the LiTFSI/MAc DES can be a promising electrolyte for EDLCs and LiBs applications especially for those requiring high safety and stability

  6. Memory Effect of Metal-Oxide-Silicon Capacitors with Self-Assembly Double-Layer Au Nanocrystals Embedded in Atomic-Layer-Deposited HfO2 Dielectric

    International Nuclear Information System (INIS)

    Yue, Huang; Hong-Yan, Gou; Qing-Qing, Sun; Shi-Jin, Ding; Wei, Zhang; Shi-Li, Zhang

    2009-01-01

    We report the chemical self-assembly growth of Au nanocrystals on atomic-layer-deposited HfO 2 films aminosilanized by (3-Aminopropyl)-trimethoxysilane aforehand for memory applications. The resulting Au nanocrystals show a density of about 4 × 10 11 cm −2 and a diameter range of 5–8nm. The metal-oxide-silicon capacitor with double-layer Au nanocrystals embedded in HfO 2 dielectric exhibits a large C – V hysteresis window of 11.9V for ±11 V gate voltage sweeps at 1 MHz, a flat-band voltage shift of 1.5 V after the electrical stress under 7 V for 1 ms, a leakage current density of 2.9 × 10 −8 A/cm −2 at 9 V and room temperature. Compared to single-layer Au nanocrystals, the double-layer Au nanocrystals increase the hysteresis window significantly, and the underlying mechanism is thus discussed

  7. 1st Kassel user forum: Double-layer capacitors for high-performance applications. Proceedings '99; 1. Kasseler Anwenderforum: Doppelschichtkondensatoren fuer hohe Leistung. Tagungsband '99

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-07-01

    Double-layer capacitors ('Super Caps') have excellent perspectives as dynamic short-term stores. They have a long life of more than 200000 cycles, immunity against full discharge, and are maintenance-free. Apart from their high short-term power density, they also have an extremely high energy density which recommends them for many applications. Currently, motor car engineering, autonomous networks, power quality and solar applications are investigated. [German] Doppelschichtkondensatoren oder 'Super-Caps' sind Speicher fuer elektrische Energie und weisen, dank ihrer Eigenschaften, hervorragende Perspektiven als dynamische Kurzzeitspeicher auf. Sie besitzen eine hohe Lebenserwartung von mehr als 200000 Zyklen, Immunitaet gegen vollstaendige Entladung und Wartungsfreiheit. Neben einer hohen Leistungsdichte im Kurzzeitbereich verfuegen sie ueber eine fuer Kondensatoren extrem hohe Energiedichte. Zahlreiche Einsatzgebiete koennen auf diese Weise erschlossen werden. Derzeit stehen die Bereiche Automobiltechnik, autarke Netze, Power Quality und solare Applikationen im Vordergrund. (orig.)

  8. Preparation of activated carbon hollow fibers from ramie at low temperature for electric double-layer capacitor applications.

    Science.gov (United States)

    Du, Xuan; Zhao, Wei; Wang, Yi; Wang, Chengyang; Chen, Mingming; Qi, Tao; Hua, Chao; Ma, Mingguo

    2013-12-01

    Activated carbon hollow fibers (ACHFs) with high surface area were prepared from inexpensive, renewable ramie fibers (RFs) by a single-step activation method under lower temperature than that of other reports. The effects of activation conditions on the pore structure and turbostratic structure of ACHFs were investigated systematically. The results show that ACHFs surface area decreased but micropore volume and conductivity increased as the increase of activation temperature and activation time. The electrochemical measurements of supercapacitors fabricated from these ACHFs electrodes reveal that the electrochemical properties improved with the enhancing of activation degree. However, too high activation temperature can make the ion diffusion resistance increase. It suggests that pore structure and conductivity are as important as surface area to decide the electrochemical performances of ACHFs electrode materials. A maximum capacity of 287 F g(-1) at 50 mA g(-1) was obtained for the ACHFs electrode prepared under suitable conditions. Copyright © 2013 Elsevier Ltd. All rights reserved.

  9. Functionalized carbon nanotube based hybrid electrochemical capacitors using neutral bromide redox-active electrolyte for enhancing energy density

    Science.gov (United States)

    Tang, Xiaohui; Lui, Yu Hui; Chen, Bolin; Hu, Shan

    2017-06-01

    A hybrid electrochemical capacitor (EC) with enhanced energy density is realized by integrating functionalized carbon nanotube (FCNT) electrodes with redox-active electrolyte that has a neutral pH value (1 M Na2SO4 and 0.5 M KBr mixed aqueous solution). The negative electrode shows an electric double layer capacitor-type behavior. On the positive electrode, highly reversible Br-/Br3- redox reactions take place, presenting a battery-type behavior, which contributes to increase the capacitance of the hybrid cell. The voltage window of the whole cell is extended up to 1.5 V because of the high over-potentials of oxygen and hydrogen evolution reactions in the neutral electrolyte. Compared with raw CNT, the FCNT has better wettability in the aqueous electrolyte and contributes to increase the electric double layer capacitance of the cell. As a result, the maximum energy density of 28.3 Wh kg-1 is obtained from the hybrid EC at 0.5 A g-1 without sacrificing its power density, which is around 4 times larger than that of the electrical double layer capacitor constructed by FCNT electrodes and 1 M Na2SO4 electrolyte. Moreover, the discharge capacity retained 86.3% of its initial performance after 10000 cycles of galvanostatic charge and discharge test (10 A/g), suggesting its long life cycle even at high current loading.

  10. In situ NMR and electrochemical quartz crystal microbalance techniques reveal the structure of the electrical double layer in supercapacitors

    Science.gov (United States)

    Griffin, John M.; Forse, Alexander C.; Tsai, Wan-Yu; Taberna, Pierre-Louis; Simon, Patrice; Grey, Clare P.

    2015-08-01

    Supercapacitors store charge through the electrosorption of ions on microporous electrodes. Despite major efforts to understand this phenomenon, a molecular-level picture of the electrical double layer in working devices is still lacking as few techniques can selectively observe the ionic species at the electrode/electrolyte interface. Here, we use in situ NMR to directly quantify the populations of anionic and cationic species within a working microporous carbon supercapacitor electrode. Our results show that charge storage mechanisms are different for positively and negatively polarized electrodes for the electrolyte tetraethylphosphonium tetrafluoroborate in acetonitrile; for positive polarization charging proceeds by exchange of the cations for anions, whereas for negative polarization, cation adsorption dominates. In situ electrochemical quartz crystal microbalance measurements support the NMR results and indicate that adsorbed ions are only partially solvated. These results provide new molecular-level insight, with the methodology offering exciting possibilities for the study of pore/ion size, desolvation and other effects on charge storage in supercapacitors.

  11. Electrochemical properties of quaternary ammonium salts for electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Ue, Makoto; Takeda, Masayuki; Takehara, Masahiro; Mori, Shoichiro [Mitsubishi Chemical Corp., Inashiki, Ibaraki (Japan). Tsukuba Research Center

    1997-08-01

    The limiting reduction and oxidation potentials and electrolytic conductivities of new quaternary ammonium salts were examined for electrochemical capacitor applications, whose anions have already been tested as lithium salts for lithium battery applications. The anodic stability was in the following order BR{sub 4}{sup {minus}} < ClO{sub 4}{sup {minus}} {le} CF{sub 3}SO{sub 3}{sup {minus}} < (CF{sub 3}SO{sub 2}){sub 2}N{sup {minus}} {le} C{sub 4}F{sub 9}SO{sub 3}{sup {minus}} < BF{sub 4}{sup {minus}} < PF{sub 6}{sup {minus}} {le} AsF{sub 6}{sup {minus}} < SbF{sub 6}{sup {minus}}. The electrolytic conductivities of Me{sub 4{minus}n}Et{sub n}N(CF{sub 3}SO{sub 2}){sub 2}N (n = 0--4) were examined in comparison with Me{sub 4{minus}n}Et{sub n}NBF{sub 4} counterparts. These imide salts showed good solubility, relatively high conductivity, and anodic stability in propylene carbonate. Et{sub 4}N(CF{sub 3}SO{sub 2}){sub 2}N was found to be a good supporting salt for low permittivity organic solvents, and it afforded a highly conductive electrolyte system based on the ethylene carbonate-dimethyl carbonate mixed solvent, which is useful for electrochemical capacitor applications.

  12. Vertically Oriented Graphene Electrochemical Double Layer Capacitor with Very Fast Dynamic Response

    Science.gov (United States)

    2013-01-01

    the sheet density, but electronic problems with the RF, overwhelming the dc power supply, require further electronic refinement ( Faraday cage ). The...electronic refinement ( Faraday cage ). The plasma in the center of the mesh elements to the substrate surface or to the mesh edge is  ~ 125 micrometers...other carbon states in the plasma. In this work, the edges at 0 V in the plasma provided a similar ion focusing effect that resulted in a rate-limited

  13. Electrical double layer capacitor using poly(methyl methacrylate)–C4BO8Li gel polymer electrolyte and carbonaceous material from shells of mata kucing (Dimocarpus longan) fruit

    International Nuclear Information System (INIS)

    Arof, A.K.; Kufian, M.Z.; Syukur, M.F.; Aziz, M.F.; Abdelrahman, A.E.; Majid, S.R.

    2012-01-01

    Poly(methyl methacrylate), PMMA based gel polymer electrolytes (GPE) containing immobilized lithium bis(oxalato)borate, C 4 BO 8 Li or LiBOB dissolved in a propylene carbonate–ethylene carbonate binary solvent were prepared by heating the cast solution between 70 and 80 °C for 20 min. The electrolyte composition with 5 wt.% PMMA exhibited the highest conductivity of 3.27 and 7.46 mS cm −1 at 298 and 343 K respectively. Cyclic voltammetry studies on the GPE containing 15 wt.% PMMA and 85 wt.% (0.6 M LiBOB) dissolved in equal weight of ethylene and propylene carbonates showed that the electrochemical potential stability window of the electrolyte lies in the range between −1.7 to +1.7 V. Linear sweep voltammetry indicates the gel polymer electrolyte is stable up to 1.7 V. The electrical double layer capacitor (EDLC) using the highest conducting GPE and activated carbon derived from shells of the mata kucing (Dimocarpus longan) fruit has capacitance of ∼685 mF g −1 on the first cycle. The EDLC performance was also characterized using cyclic voltammetry and charge–discharge processes at constant current.

  14. Centrifugal spinning: A novel approach to fabricate porous carbon fibers as binder-free electrodes for electric double-layer capacitors

    Science.gov (United States)

    Lu, Yao; Fu, Kun; Zhang, Shu; Li, Ying; Chen, Chen; Zhu, Jiadeng; Yanilmaz, Meltem; Dirican, Mahmut; Zhang, Xiangwu

    2015-01-01

    Carbon nanofibers (CNFs), among various carbonaceous candidates for electric double-layer capacitor (EDLC) electrodes, draw extensive attention because their one-dimensional architecture offers both shortened electron pathways and high ion-accessible sites. Creating porous structures on CNFs yields larger surface area and enhanced capacitive performance. Herein, porous carbon nanofibers (PCNFs) were synthesized via centrifugal spinning of polyacrylonitrile (PAN)/poly(methyl methacrylate) (PMMA) solutions combined with thermal treatment and were used as binder-free EDLC electrodes. Three precursor fibers with PAN/PMMA weight ratios of 9/1, 7/3 and 5/5 were prepared and carbonized at 700, 800, and 900 °C, respectively. The highest specific capacitance obtained was 144 F g-1 at 0.1 A g-1 with a rate capability of 74% from 0.1 to 2 A g-1 by PCNFs prepared with PAN/PMMA weight ratio of 7/3 at 900 °C. These PCNFs also showed stable cycling performance. The present work demonstrates that PCNFs are promising EDLC electrode candidate and centrifugal spinning offers a simple, cost-effective strategy to produce PCNFs.

  15. Double-layer capacitors as dynamic stores for PV applications. Final report; Doppelschichtkondensatoren als dynamische Speicher fuer PV-Anwendungen. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Willer, B.; Knorr, R.; Broeker, C.; Burger, B.; Wollny, M.

    1999-07-01

    Double layer capacitors are the system of choice whenever a large number of cycles and high capacity are required. They have the advantages of high cyclic strength, high capacity, freedom of servicing, insensitivity to high temperatures and long life. Drawbacks are low energy density, high self-discharge and high cost.Applications in water pumps, pathfinders and roller blind control systems were investigated. [German] Mit den Ergebnissen steht ein detailliertes Wissen ueber den weltweiten Entwicklungsstand und die physikalischen Eigenschaften von Doppelschichtkondensatoren zur Verfuegung. Ihre Eigenschaften wurden in Bezug auf moegliche photovoltaische Anwendungen hin analysiert. Anwendungsfehlder ergeben sich vorzugsweise dann, wenn hohe Zyklenzahl und Leistungsfaehigkeit gefordert werden. Die Vorteile des neuen Energiespeichers sind seine hohe Zyklenfestigkeit und Leistungsfaehigkeit, seine Wartungsfreiheit, Temperaturunempfindlichkeit und lange Lebensdauer. Ihnen stehen die Nachteile einer geringen Energiedichte, hohen Selbstentladung und hoher Kosten gegenueber. Eine deutliche Steigerung der Gesamteffizienz von photovoltaischen Versorgungseinheiten beim Einsatz von Doppelschichtkondensatoren ergeben energetische Simulationen unterschiedlicher Systeme. Fuer ausgewaehlte photovoltaisch versorgte Anwendungen konnte die Einsatzfaehigkeit von Doppelschichtkondensatoren in Feldtests erprobt und nachgewiesen werden. Wasserpumpensysteme, Pathfinders und eine Rolladensteuerung fuer ein Fenster wurden getestet. Der Einsatz von Doppelschichtkondensatoren zur weiteren Verbreitung photovoltaischer Anwendungen ist bereits heute fuer spezielle Anwendungen sinnvoll und wirtschaftlich. Mit weiter fallenden Preisen fuer die Kondensatoren und der Entwicklung von Kondensatorsystemen mit hoeheren Spannungen werden weitere Anwendungsfelder hinzukommen. Die Basis zur Entwicklung der notwendigen Systemtechnik und ihrer Demonstration in Feldversuchen ist durch die Ergebnisse des

  16. A high-performance flexible fibre-shaped electrochemical capacitor based on electrochemically reduced graphene oxide.

    Science.gov (United States)

    Li, Yingru; Sheng, Kaixuan; Yuan, Wenjing; Shi, Gaoquan

    2013-01-11

    A fibre-shaped solid electrochemical capacitor based on electrochemically reduced graphene oxide has been fabricated, exhibiting high specific capacitance and rate capability, long cycling life and attractive flexibility.

  17. A facile one-pot fabrication of flowerlike graphene-based particles for electric double-layer capacitors

    International Nuclear Information System (INIS)

    Xia, Xiaohong; Ma, Qian; Yi, Shangqi; Chen, Hui; Liu, Hongbo; Chen, Yuxi; Yang, Li

    2014-01-01

    Flowerlike graphene-based particles had been successfully synthesized from the suspension of graphene oxide (GO) in the aqueous solution of sucrose by one-pot hydrothermal carbonization approach. Porous carbon from sucrose prompted the evolution of graphene from flat-shaped to flowerlike curved morphology, which was confirmed by the observation of scanning electron microscopy and transmission electron microscopy. The graphene-based particles possess large pore volume (0.69 cm 3  g −1 ) and surface area (470.5 m 2  g −1 ), which is about 6 times greater than that of carbonized graphene sheets (79.2 m 2  g −1 ). Electrochemical investigation indicated that the specific capacitance of the particles reached 162 F g −1 at current density of 0.1 A g −1 in 30 wt% KOH aqueous electrolytes and the capacitance maintenance achieved 90% as the current density enlarged 50 times. The keys to the ideal capacitive performance are the abilities to make full utilization of specific surface area of graphene and ensure a quick kinetic process for the diffusion of ions within curved graphene particles with considerable open edges. - Highlights: • Flowerlike graphene-based particles were synthesized by one-pot hydrothermal method. • Carbon from sucrose prompted the evolution of flat-shaped graphene to curved-shaped. • Carbonized curved particles with considerable open edges exhibit large pore volume. • A high specific capacitance and rate performance of the electrode were achieved

  18. Influence of oxidation level on capacitance of electrochemical capacitors fabricated with carbon nanotube/carbon paper composites

    International Nuclear Information System (INIS)

    Hsieh, C.-T.; Chen, W.-Y.; Cheng, Y.-S.

    2010-01-01

    Gaseous oxidation of carbon papers (CPs) decorated with carbon nanotubes (CNTs) with varying degrees of oxidation was conducted to investigate the influence of surface oxides on the performance of electrochemical capacitors fabricated with oxidized CNT/CP composites. The oxidation period was found to significantly enhance the O/C atomic ratio on the composites, and the increase in oxygen content upon oxidation is mainly contributed by the formation of C=O and C-O groups. The electrochemical behavior of the capacitors was tested in 1 M H 2 SO 4 within a potential of 0 and 1 V vs. Ag/AgCl. Both superhydrophilicity and specific capacitance of the oxidized CNT/CP composites were found to increase upon oxidation treatment. A linearity increase of capacitance with O/C ratio can be attributed to the increase of the population of surface oxides on CNTs, which imparts excess sites for redox reaction (pseudocapacitance) and for the formation of double-layer (double-layer capacitance). The technique of ac impedance combined with equivalent circuit clearly showed that oxidized CNT/CP capacitor imparts not only enhanced capacitance but also a low equivalent series resistance.

  19. Electrostatic and Electrochemical Nature of Liquid-Gated Electric-Double-Layer Transistors Based on Oxide Semiconductors

    NARCIS (Netherlands)

    Yuan, Hongtao; Shimotani, Hidekazu; Ye, Jianting; Yoon, Sungjae; Aliah, Hasniah; Tsukazaki, Atsushi; Kawasaki, Masashi; Iwasa, Yoshihiro

    2010-01-01

    The electric-double-layer (EDL) formed at liquid/solid interfaces provides a broad and interdisciplinary attraction in terms of electrochemistry, photochemistry, catalysts, energy storage, and electronics because of the large interfacial capacitance coupling and its ability for high-density charge

  20. High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte.

    Science.gov (United States)

    Wang, Xingfeng; Chandrabose, Raghu S; Chun, Sang-Eun; Zhang, Tianqi; Evanko, Brian; Jian, Zelang; Boettcher, Shannon W; Stucky, Galen D; Ji, Xiulei

    2015-09-16

    We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx-/I- couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx-/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.4-0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach -1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3- ions (+5) from I- (-1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between -20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14,000 cycles.

  1. Carbon-coated tungsten and molybdenum carbides for electrode of electrochemical capacitor

    International Nuclear Information System (INIS)

    Morishita, Takahiro; Soneda, Yasushi; Hatori, Hiroaki; Inagaki, Michio

    2007-01-01

    New electrode materials for electrochemical capacitor, tungsten carbide WC and molybdenum carbide Mo 2 C coated by porous carbon, were prepared through a simple heat treatment of the mixture of K 2 WO 4 and K 2 MoO 4 , respectively, with hydroxy propyl cellulose. Carbide changed to hydroxide during the 1st charge-discharge cycle in H 2 SO 4 aqueous electrolyte, which showed redox reaction in further charge-discharge cycles, in addition to electric double layers of the carbon formed on its surface. The carbon-coated carbide gave a high capacitance in 1 mol L -1 H 2 SO 4 electrolyte, as about 350 F cm -3 for carbon-coated WC and 550-750 F cm -3 for carbon-coated Mo 2 C. Coating of carbon inhibits the growth of carbide particles during their formation, of which the small particle size make possible to complete transformation to hydroxides during the 1st charge-discharge cycle, and also disturbs the agglomeration of tungsten and molybdenum hydroxides during charge-discharge cycles, as well as porous carbon coated act as electrode material for electric double layers of electrolyte ions

  2. Fabrication of ultrafine manganese oxide-decorated carbon nanofibers for high-performance electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ying; Lee, Sungsik; Brown, Dennis E.; Zhao, Hairui; Li, Xinsong; Jiang, Daqiang; Hao, Shijie; Zhao, Yongxiang; Cong, Daoyong; Zhang, Xin; Ren, Yang

    2016-09-01

    Ultrafine manganese oxide-decorated carbon nanofibers (MnOn-CNF) as a new type of electrode materials are facilely fabricated by direct conversion of Mn, Zn-trimesic acid (H3BTC) metal organic framework fibers (Mn-ZnBTC). The construction and evolution of Mn-ZnBTC precursors are investigated by SEM and in situ high-energy XRD. The manganese oxides are highly dispersed onto the porous carbon nanofibers formed simultaneously, verified by TEM, X-ray absorption fine structure (XAFS), Raman, ICP-AES and N2 adsorption techniques. As expected, the resulting MnOn-CNF composites are highly stable, and can be cycled up to 5000 times with a high capacitance retention ratio of 98% in electrochemical capacitor measurements. They show a high capacitance of up to 179 F g–1 per mass of the composite electrode, and a remarkable capacitance of up to 18290 F g–1 per active mass of the manganese(IV) oxide, significantly exceeding the theoretical specific capacitance of manganese(IV) oxide (1370 F g–1). The maximum energy density is up to 19.7 Wh kg–1 at the current density of 0.25 A g–1, even orders higher than those of reported electric double-layer capacitors and pseudocapacitors. The excellent capacitive performance can be ascribed to the joint effect of easy accessibility, high porosity, tight contact and superior conductivity integrated in final MnOn-CNF composites.

  3. Observation of turnover of spontaneous polarization in ferroelectric layer of pentacene/poly-(vinylidene-trifluoroethylene) double-layer capacitor under photo illumination by optical second-harmonic generation measurement

    Science.gov (United States)

    Shi, Zhemin; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2016-04-01

    The details of turnover process of spontaneous polarization and associated carrier motions in indium-tin oxide/poly-(vinylidene-trifluoroethylene)/pentacene/Au capacitor were analyzed by coupling displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement. A model was set up from DCM results to depict the relationship between electric field in semiconductor layer and applied external voltage, proving that photo illumination effect on the spontaneous polarization process lied in variation of semiconductor conductivity. The EFISHG measurement directly and selectively probed the electric field distribution in semiconductor layer, modifying the model and revealing detailed carrier behaviors involving photo illumination effect, dipole reversal, and interfacial charging in the device. A further decrease of DCM current in the low voltage region under illumination was found as the result of illumination effect, and the result was argued based on the changing of the total capacitance of the double-layer capacitors.

  4. Observation of turnover of spontaneous polarization in ferroelectric layer of pentacene/poly-(vinylidene-trifluoroethylene) double-layer capacitor under photo illumination by optical second-harmonic generation measurement

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Zhemin [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Technology, Tsinghua University, Beijing 100084 (China); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan); Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa, E-mail: iwamoto@pe.titech.ac.jp [Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)

    2016-04-28

    The details of turnover process of spontaneous polarization and associated carrier motions in indium-tin oxide/poly-(vinylidene-trifluoroethylene)/pentacene/Au capacitor were analyzed by coupling displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement. A model was set up from DCM results to depict the relationship between electric field in semiconductor layer and applied external voltage, proving that photo illumination effect on the spontaneous polarization process lied in variation of semiconductor conductivity. The EFISHG measurement directly and selectively probed the electric field distribution in semiconductor layer, modifying the model and revealing detailed carrier behaviors involving photo illumination effect, dipole reversal, and interfacial charging in the device. A further decrease of DCM current in the low voltage region under illumination was found as the result of illumination effect, and the result was argued based on the changing of the total capacitance of the double-layer capacitors.

  5. High-performance symmetric electrochemical capacitor based on graphene foam and nanostructured manganese oxide

    Directory of Open Access Journals (Sweden)

    Abdulhakeem Bello

    2013-08-01

    Full Text Available We have fabricated a symmetric electrochemical capacitor with high energy and power densities based on a composite of graphene foam (GF with ∼80 wt% of manganese oxide (MnO2 deposited by hydrothermal synthesis. Raman spectroscopy and X-ray diffraction measurements showed the presence of nanocrystalline MnO2 on the GF, while scanning and transmission electron microscopies showed needle-like manganese oxide coated and anchored onto the surface of graphene. Electrochemical measurements of the composite electrode gave a specific capacitance of 240 Fg−1 at a current density of 0.1 Ag−1 for symmetric supercapacitors using a two-electrode configuration. A maximum energy density of 8.3 Whkg−1 was obtained, with power density of 20 kWkg−1 and no capacitance loss after 1000 cycles. GF is an excellent support for pseudo-capacitive oxide materials such as MnO2, and the composite electrode provided a high energy density due to a combination of double-layer and redox capacitance mechanisms.

  6. Chemical etching of stainless steel 301 for improving performance of electrochemical capacitors in aqueous electrolyte

    Science.gov (United States)

    Jeżowski, P.; Nowicki, M.; Grzeszkowiak, M.; Czajka, R.; Béguin, F.

    2015-04-01

    The main purpose of the study was to increase the surface roughness of stainless steel 301 current collectors by etching, in order to improve the electrochemical performance of electrical double-layer capacitors (EDLC) in 1 mol L-1 lithium sulphate electrolyte. Etching was realized in 1:3:30 (HNO3:HCl:H2O) solution with times varying up to 10 min. For the considered 15 μm thick foil and a mass loss around 0.4 wt.%, pitting was uniform, with diameter of pits ranging from 100 to 300 nm. Atomic force microscopy (AFM) showed an increase of average surface roughness (Ra) from 5 nm for the as-received stainless steel foil to 24 nm for the pitted material. Electrochemical impedance spectroscopy realized on EDLCs with coated electrodes either on as-received or pitted foil in 1 mol L-1 Li2SO4 gave equivalent distributed resistance (EDR) of 8 Ω and 2 Ω, respectively, demonstrating a substantial improvement of collector/electrode interface after pitting. Correlatively, the EDLCs with pitted collector displayed a better charge propagation and low ohmic losses even at relatively high current of 20 A g-1. Hence, chemical pitting of stainless steel current collectors is an appropriate method for optimising the performance of EDLCs in neutral aqueous electrolyte.

  7. Hydrogel membrane electrolyte for electrochemical capacitors

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Polymer electrolytes are known to possess excellent physicochemical properties that are very useful for electrochemical energy systems. The mobility in polymer electrolytes is understood to be mainly due to the segmental motion of polymer chains and the ion transport is generally restricted to the amorphous ...

  8. Double layers in space

    International Nuclear Information System (INIS)

    Carlqvist, P.

    1982-07-01

    For more than a decade it has been realised that electrostatic double layers are likely to occur in space. We briefly discuss the theoretical background of such double layers. Most of the paper is devoted to an account of the observational evidence for double layers in the ionosphere and magnetosphere of the Earth. Several different experiments are reviewed including rocket and satellite measurements and ground based observations. It is concluded that the observational evidence for double layers in space is very strong. The experimental results indicate that double layers with widely different properties may exist in space. (Author)

  9. Double layers in space

    International Nuclear Information System (INIS)

    Carlqvist, P.

    1982-01-01

    For more than a decade it has been realised that electrostatic double layers are likely to occur in space. The author briefly discusses the theoretical background of such double layers. Most of the paper is devoted to an account of the observational evidence for double layers in the ionosphere and magnetosphere of the Earth. Several different experiments are reviewed including rocket and satellite measurements and ground based observations. It is concluded that the observational evidence for double layers in space is very strong. The experimental results indicate that double layers with widely different properties may exist in space. (Auth.)

  10. Novel non-covalent sulfonated multiwalled carbon nanotube from p-toluenesulfonic acid/glucose doped polypyrrole for electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Q.B.; Gao, B.; Hao, L.; Lu, X.J.; Yang, S.D.; Zhang, X.G. [Nanjing Univ. of Aeronautics and Astronautics (China). College of Material Science and Engineering

    2010-07-01

    Polypyrrole (PPy) is considered as one of the most promising electrode materials for electrochemical capacitors due to its environmental stability and fast doping and dedoping capacity. Carbon nanotube (CNT) and PPy hybrids can work synergistically to achieve the advantages of an electric double layer capacitor and faradaic pseudocapacitor. Sulfonation can be used to increase the dispersion of CNTs. In this study, multiwalled CNTs (MWCNTs) were modified with a high -SOH{sub 3}H loading carbonaceous material. Pyrolle monomers were absorbed on the surface of the MWCNT-SO{sub 3}H composite through strong electron and hydrogen bonding interactions between the -SO{sub 3}H group and the amino group of pyrrole. The pyrrole was then in-situ polymerized on the surface of the MWCNTs with the addition of an initiator. The study showed that the specific capacitance loss of the MWCNTs-SO{sub 3}H/PPy was only 3 per cent after 1000 cycles. Results of the study suggested that the composite is a promising electrode material for electrochemical capacitors. 2 refs., 2 figs.

  11. Chemical modification of graphene aerogels for electrochemical capacitor applications.

    Science.gov (United States)

    Hong, Jin-Yong; Wie, Jeong Jae; Xu, Yu; Park, Ho Seok

    2015-12-14

    Graphene aerogel is a relatively new type of aerogel that is ideal for energy storage applications because of its large surface area, high electrical conductivity and good chemical stability. Also, three dimensional interconnected macropores offer many advantages such as low density, fast ion and mass transfer, and easy access to storage sites. Such features allow graphene aerogels to be intensively applied for electrochemical capacitor applications. Despite the growing interest in graphene aerogel-based electrochemical capacitors, however, the graphene aerogels still suffer from their low capacitive performances and high fragility. Both relatively low capacitance and brittleness of physically crosslinked graphene aerogels remain a critical challenge. Until now, a number of alternative attempts have been devoted to overcome these shortcomings. In this perspective, we summarize the recent research progress towards the development of advanced graphene aerogel-based electrochemical capacitors according to the different approaches (e.g. porosity, composition and structure controls). Then, the recently proposed chemical strategies to improve the capacitive performances and mechanical durability of graphene aerogels for practical applications are highlighted. Finally, the current challenges and perspectives in this emerging material are also discussed.

  12. Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors.

    Science.gov (United States)

    Wang, Chao; Lee, Wen-Ya; Kong, Desheng; Pfattner, Raphael; Schweicher, Guillaume; Nakajima, Reina; Lu, Chien; Mei, Jianguo; Lee, Tae Hoon; Wu, Hung-Chin; Lopez, Jeffery; Diao, Ying; Gu, Xiaodan; Himmelberger, Scott; Niu, Weijun; Matthews, James R; He, Mingqian; Salleo, Alberto; Nishi, Yoshio; Bao, Zhenan

    2015-12-14

    Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10(-10) S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water.

  13. Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors

    Science.gov (United States)

    Wang, Chao; Lee, Wen-Ya; Kong, Desheng; Pfattner, Raphael; Schweicher, Guillaume; Nakajima, Reina; Lu, Chien; Mei, Jianguo; Lee, Tae Hoon; Wu, Hung-Chin; Lopez, Jeffery; Diao, Ying; Gu, Xiaodan; Himmelberger, Scott; Niu, Weijun; Matthews, James R.; He, Mingqian; Salleo, Alberto; Nishi, Yoshio; Bao, Zhenan

    2015-01-01

    Both high gain and transconductance at low operating voltages are essential for practical applications of organic field-effect transistors (OFETs). Here, we describe the significance of the double-layer capacitance effect in polar rubbery dielectrics, even when present in a very low ion concentration and conductivity. We observed that this effect can greatly enhance the OFET transconductance when driven at low voltages. Specifically, when the polar elastomer poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVDF-HFP) was used as the dielectric layer, despite a thickness of several micrometers, we obtained a transconductance per channel width 30 times higher than that measured for the same organic semiconductors fabricated on a semicrystalline PVDF-HFP with a similar thickness. After a series of detailed experimental investigations, we attribute the above observation to the double-layer capacitance effect, even though the ionic conductivity is as low as 10–10 S/cm. Different from previously reported OFETs with double-layer capacitance effects, our devices showed unprecedented high bias-stress stability in air and even in water. PMID:26658331

  14. Formation of double layers

    International Nuclear Information System (INIS)

    Leung, P.; Wong, A.Y.; Quon, B.H.

    1981-01-01

    Experiments on both stationary and propagating double layers and a related analytical model are described. Stationary double layers were produced in a multiple plasma device, in which an electron drift current was present. An investigation of the plasma parameters for the stable double layer condition is described. The particle distribution in the stable double layer establishes a potential profile, which creates electron and ion beams that excite plasma instabilities. The measured characteristics of the instabilities are consistent with the existence of the double layer. Propagating double layers are formed when the initial electron drift current is large. Ths slopes of the transition region increase as they propagate. A physical model for the formation of a double layer in the experimental device is described. This model explains the formation of the low potential region on the basis of the space charge. This space charge is created by the electron drift current. The model also accounts for the role of ions in double layer formation and explains the formation of moving double layers. (Auth.)

  15. Low-temperature direct synthesis of mesoporous vanadium nitrides for electrochemical capacitors

    Science.gov (United States)

    Lee, Hae-Min; Jeong, Gyoung Hwa; Kim, Sang-Wook; Kim, Chang-Koo

    2017-04-01

    Mesoporous vanadium nitrides are directly synthesized by a one-step chemical precipitation method at a low temperature (70 °C). Structural and morphological analyses reveal that vanadium nitride consist of long and slender nanowhiskers, and mesopores with diameters of 2-5 nm. Compositional analysis confirms the presence of vanadium in the VN structure, along with oxidized vanadium. The cyclic voltammetry and charge-discharge tests indicate that the obtained material stores charges via a combination of electric double-layer capacitance and pseudocapacitance mechanisms. The vanadium nitride electrode exhibits a specific capacitance of 598 F/g at a current density of 4 A/g. After 5000 charge-discharge cycles, the electrode has an equivalent series resistance of 1.42 Ω and retains 83% of its initial specific capacitance. This direct low-temperature synthesis of mesoporous vanadium nitrides is a simple and promising method to achieve high specific capacitance and low equivalent series resistance for electrochemical capacitor applications.

  16. Low-temperature direct synthesis of mesoporous vanadium nitrides for electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hae-Min [Institute of NT-IT Fusion Technology, Ajou University, 206 Worldcup-ro, Yeongtong-gu, Suwon 16499 (Korea, Republic of); Jeong, Gyoung Hwa [Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Banyeon 100, Ulsan 44919 (Korea, Republic of); Kim, Sang-Wook [Department of Molecular Science and Technology, Ajou University, 206 Worldcup-ro, Yeongtong-gu, Suwon 16499 (Korea, Republic of); Kim, Chang-Koo, E-mail: changkoo@ajou.ac.kr [Department of Chemical Engineering and Department of Energy Systems Research, Ajou University, 206 Worldcup-ro, Yeongtong-gu, Suwon 16499 (Korea, Republic of)

    2017-04-01

    Highlights: • Vanadium nitrides were directly synthesized by a one-step chemical precipitation method. • This method was carried out at a low temperature of 70 °C. • Vanadium nitrides had a specific capacitance of 598 F/g. • The equivalent series resistance of the vanadium nitride electrode was 1.42 Ω after 5000 cycles. - Abstract: Mesoporous vanadium nitrides are directly synthesized by a one-step chemical precipitation method at a low temperature (70 °C). Structural and morphological analyses reveal that vanadium nitride consist of long and slender nanowhiskers, and mesopores with diameters of 2–5 nm. Compositional analysis confirms the presence of vanadium in the VN structure, along with oxidized vanadium. The cyclic voltammetry and charge-discharge tests indicate that the obtained material stores charges via a combination of electric double-layer capacitance and pseudocapacitance mechanisms. The vanadium nitride electrode exhibits a specific capacitance of 598 F/g at a current density of 4 A/g. After 5000 charge-discharge cycles, the electrode has an equivalent series resistance of 1.42 Ω and retains 83% of its initial specific capacitance. This direct low-temperature synthesis of mesoporous vanadium nitrides is a simple and promising method to achieve high specific capacitance and low equivalent series resistance for electrochemical capacitor applications.

  17. Advanced Proton Conducting Polymer Electrolytes for Electrochemical Capacitors

    Science.gov (United States)

    Gao, Han

    Research on solid electrochemical energy storage devices aims to provide high performance, low cost, and safe operation solutions for emerging applications from flexible consumer electronics to microelectronics. Polymer electrolytes, minimizing device sealing and liquid electrolyte leakage, are key enablers for these next-generation technologies. In this thesis, a novel proton-conducing polymer electrolyte system has been developed using heteropolyacids (HPAs) and polyvinyl alcohol for electrochemical capacitors. A thorough understanding of proton conduction mechanisms of HPAs together with the interactions among HPAs, additives, and polymer framework has been developed. Structure and chemical bonding of the electrolytes have been studied extensively to identify and elucidate key attributes affecting the electrolyte properties. Numerical models describing the proton conduction mechanism have been applied to differentiate those attributes. The performance optimization of the polymer electrolytes through additives, polymer structural modifications, and synthesis of alternative HPAs has achieved several important milestones, including: (a) high proton mobility and proton density; (b) good ion accessibility at electrode/electrolyte interface; (c) wide electrochemical stability window; and (d) good environmental stability. Specifically, high proton mobility has been addressed by cross-linking the polymer framework to improve the water storage capability at normal-to-high humidity conditions (e.g. 50-80% RH) as well as by incorporating nano-fillers to enhance the water retention at normal humidity levels (e.g. 30-60% RH). High proton density has been reached by utilizing additional proton donors (i.e. acidic plasticizers) and by developing different HPAs. Good ion accessibility has been achieved through addition of plasticizers. Electrochemical stability window of the electrolyte system has also been investigated and expanded by utilizing HPAs with different heteroatoms

  18. Optimization of Design Parameters and Operating Conditions of Electrochemical Capacitors for High Energy and Power Performance

    Science.gov (United States)

    Ike, Innocent S.; Sigalas, Iakovos; Iyuke, Sunny E.

    2017-03-01

    Theoretical expressions for performance parameters of different electrochemical capacitors (ECs) have been optimized by solving them using MATLAB scripts as well as via the MATLAB R2014a optimization toolbox. The performance of the different kinds of ECs under given conditions was compared using theoretical equations and simulations of various models based on the conditions of device components, using optimal values for the coefficient associated with the battery-kind material ( K BMopt) and the constant associated with the electrolyte material ( K Eopt), as well as our symmetric electric double-layer capacitor (EDLC) experimental data. Estimation of performance parameters was possible based on values for the mass ratio of electrodes, operating potential range ratio, and specific capacitance of electrolyte. The performance of asymmetric ECs with suitable electrode mass and operating potential range ratios using aqueous or organic electrolyte at appropriate operating potential range and specific capacitance was 2.2 and 5.56 times greater, respectively, than for the symmetric EDLC and asymmetric EC using the same aqueous electrolyte, respectively. This enhancement was accompanied by reduced cell mass and volume. Also, the storable and deliverable energies of the asymmetric EC with suitable electrode mass and operating potential range ratios using the proper organic electrolyte were 12.9 times greater than those of the symmetric EDLC using aqueous electrolyte, again with reduced cell mass and volume. The storable energy, energy density, and power density of the asymmetric EDLC with suitable electrode mass and operating potential range ratios using the proper organic electrolyte were 5.56 times higher than for a similar symmetric EDLC using aqueous electrolyte, with cell mass and volume reduced by a factor of 1.77. Also, the asymmetric EDLC with the same type of electrode and suitable electrode mass ratio, working potential range ratio, and proper organic electrolyte

  19. Nanostructured core-shell electrode materials for electrochemical capacitors

    Science.gov (United States)

    Jiang, Long-bo; Yuan, Xing-zhong; Liang, Jie; Zhang, Jin; Wang, Hou; Zeng, Guang-ming

    2016-11-01

    Core-shell nanostructure represents a unique system for applications in electrochemical energy storage devices. Owing to the unique characteristics featuring high power delivery and long-term cycling stability, electrochemical capacitors (ECs) have emerged as one of the most attractive electrochemical storage systems since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review aims to summarize recent progress on core-shell nanostructures for advanced supercapacitor applications in view of their hierarchical architecture which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The core-shell nanostructures include carbon/carbon, carbon/metal oxide, carbon/conducting polymer, metal oxide/metal oxide, metal oxide/conducting polymer, conducting polymer/conducting polymer, and even more complex ternary core-shell nanoparticles. The preparation strategies, electrochemical performances, and structural stabilities of core-shell materials for ECs are summarized. The relationship between core-shell nanostructure and electrochemical performance is discussed in detail. In addition, the challenges and new trends in core-shell nanomaterials development have also been proposed.

  20. Current status of environmental, health, and safety issues of electrochemical capacitors for advanced vehicle applications

    Energy Technology Data Exchange (ETDEWEB)

    Vimmerstedt, L J; Hammel, C J

    1997-04-01

    Electrochemical capacitors are a candidate for traction power assists in hybrid electric vehicles (HEVs). Other advanced automotive applications, while not the primary focus of current development efforts, are also possible. These include load leveling high-energy batteries, power conditioning electronics, electrically hated catalysts, electric power steering, and engine starter power. Higher power and longer cycle life are expected for electrochemical capacitors than for batteries. Evaluation of environmental, health, and safety (EH and S) issues of electrochemical capacitors is an essential part of the development and commercialization of electrochemical capacitors for advanced vehicles. This report provides an initial EH and S assessment. This report presents electrochemical capacitor electrochemistry, materials selection, intrinsic material hazards, mitigation of those hazards, environmental requirements, pollution control options, and shipping requirements. Most of the information available for this assessment pertains to commercial devices intended for application outside the advanced vehicle market and to experiment or prototype devices. Electrochemical capacitors for power assists in HEVs are not produced commercially now. Therefore, materials for advanced vehicle electrochemical capacitors may change, and so would the corresponding EH and S issues. Although changes are possible, this report describes issues for likely electrochemical capacitor designs.

  1. Self-Assembled Carbon-Polyoxometalate Composites for Electrochemical Capacitors

    Science.gov (United States)

    Genovese, Matthew

    The development of high performance yet cost effective energy storage devices is critical for enabling the growth of important emerging sectors from the internet of things to grid integration of renewable energy. Material costs are by far the largest contributor to the overall cost of energy storage devices and thus research into cost effective energy storage materials will play an important role in developing technology to meet real world storage demands. In this thesis, low cost high performance composite electrode materials for supercapacitors (SCs) have been developed through the surface modification of electrochemically double layer capacitive (EDLC) carbon substrates with pseudocapacitive Polyoxometalates (POMs). Significant fundamental contributions have been made to the understanding of all components of the composite electrode including the POM active layer, cation linker, and carbon substrate. The interaction of different POM chemistries in solution has been studied to elucidate the novel ways in which these molecules combine and the mechanism underlying this combination. A more thorough understanding regarding the cation linker's role in electrode fabrication has been developed through examining the linker properties which most strongly affect electrode performance. The development of porosity in biomass derived carbon materials has also been examined leading to important insights regarding the effect of substrate porosity on POM modification and electrochemical properties. These fundamental contributions enabled the design and performance optimization of POM-carbon composite SC electrodes. Understanding how POMs combine in solution, allowed for the development of mixed POM molecular coatings with tunable electrochemical properties. These molecular coatings were used to modify low cost biomass derived carbon substrates that had been structurally optimized to accommodate POM molecules. The resulting electrode composites utilizing low cost materials

  2. Leveling of battery load and extension of battery life by serial connection of electric double layer capacitors with batteries for electric vehicles. Experimental results on the small model; Denki jidoshayo denchi to denki nijuso capacitor no chokuretsu setsuzoku ni yoru denchi futan no heijunka oyobi denchijumyo no enshinka. (kogata model ni yoru jikken seika). Kogata model ni yoru jikken seika

    Energy Technology Data Exchange (ETDEWEB)

    Takehara, J.; Okubo, N.; Miyaoka, K. [Chugoku Electric Power Co. Inc., Hiroshima (Japan)

    1996-10-25

    The load leveling method of batteries for electric vehicles was studied for extension of a battery life and mileage every charging. Under large load fluctuation conditions such as deceleration and acceleration, use of electric power sources other than battery for peek load at acceleration can improve a battery life, output power capacity and mileage every charging. Combination of effective recovery of regenerative power at deceleration with its discharge at acceleration is one of the effective methods. The electric double layer capacitors are serially connected with the batteries, regenerative power is charged only into the capacitors, and both voltages of the battery and capacitor are applied to a power circuit. Battery load is reduced by load on the capacitor. Until the capacitor is re-charged by regenerative power after full discharge, power is supplied only by battery through a diode. Capacitor power is used as effectively as possible until approaching considerably low voltage. As peak load of the battery is reduced by 30%, the mileage increases by 5.7%, and the battery cycle life becomes 1.5 times longer. 7 refs., 5 figs., 3 tabs.

  3. The electric double layer has a life of its own

    NARCIS (Netherlands)

    Merlet, Céline; Limmer, David T.; Salanne, Mathieu; Van Roij, René; Madden, Paul A.; Chandler, David; Rotenberg, Benjamin

    2014-01-01

    Using molecular dynamics simulations with recently developed importance sampling methods, we show that the differential capacitance of a model ionic liquid based double-layer capacitor exhibits an anomalous dependence on the applied electrical potential. Such behavior is qualitatively incompatible

  4. A double layer review

    International Nuclear Information System (INIS)

    Block, L.P.

    1977-06-01

    A review of the main results on electrostatic double layers (sometimes called space charge layers or sheaths) obtained from theory, and laboratory and space experiments up to the spring of 1977 is given. By means of barium jets and satellite probes, double layers have now been found at the altitudes, earlier predicted theoretically. The general potential distribution above the auroral zone, suggested by inverted V-events and electric field reversals, is corroborated. (author)

  5. Hybrid nanostructured materials for high-performance electrochemical capacitors

    KAUST Repository

    Yu, Guihua

    2013-03-01

    The exciting development of advanced nanostructured materials has driven the rapid growth of research in the field of electrochemical energy storage (EES) systems which are critical to a variety of applications ranging from portable consumer electronics, hybrid electric vehicles, to large industrial scale power and energy management. Owing to their capability to deliver high power performance and extremely long cycle life, electrochemical capacitors (ECs), one of the key EES systems, have attracted increasing attention in the recent years since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review article describes the most recent progress in the development of nanostructured electrode materials for EC technology, with a particular focus on hybrid nanostructured materials that combine carbon based materials with pseudocapacitive metal oxides or conducting polymers for achieving high-performance ECs. This review starts with an overview of EES technologies and the comparison between various EES systems, followed by a brief description of energy storage mechanisms for different types of EC materials. This review emphasizes the exciting development of both hybrid nanomaterials and novel support structures for effective electrochemical utilization and high mass loading of active electrode materials, both of which have brought the energy density of ECs closer to that of batteries while still maintaining their characteristic high power density. Last, future research directions and the remaining challenges toward the rational design and synthesis of hybrid nanostructured electrode materials for next-generation ECs are discussed. © 2012 Elsevier Ltd.

  6. Preparation of activated carbon aerogel and its application to electrode material for electric double layer capacitor in organic electrolyte: Effect of activation temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Soon Hyung; Lee, Eunji; Kim, Myung-Soo; Jung, Ji Chul [Myongji University, Yongin (Korea, Republic of); Kim, Bum-Soo; Kim, Sang-Gil; Lee, Byung-Jun [Vitzrocell Co., Yesan (Korea, Republic of)

    2015-02-15

    Carbon aerogel was chemically activated with KOH at various activation temperatures with the aim of improving the electrochemical performance of carbon aerogel for EDLC electrode. Electrochemical performance of activated carbon aerogel electrode was determined by cyclic voltammetry and galvanostatic charge/discharge methods using coin-type EDLC cell in organic electrolyte. Activation temperature played an important role in determining the electrochemical performance of activated carbon aerogel for EDLC electrode. Specific capacitance of activated carbon aerogel at a high current density (5 A/g) showed a volcano-shaped curve with respect to activation temperature. Excessively high activation temperature could have an adverse effect on the electrochemical properties of activated carbon aerogel due to the low electrical conductivity caused by a collapse of characteristic structure of carbon aerogel. Among the carbon samples, carbon aerogel activated at 800 .deg. C with a high surface area and a well-developed porous structure exhibited the highest specific capacitance. In addition, carbon aerogel activated at 800 .deg. C retained a considerable specific capacitance at a high current density even after 1000 cycles of charge/discharge. Therefore, it is concluded that carbon aerogel activated with KOH at 800 .deg. C can serve as an efficient electrode material for commercial EDLC with a high power density.

  7. In situ self-sacrificed template synthesis of vanadium nitride/nitrogen-doped graphene nanocomposites for electrochemical capacitors.

    Science.gov (United States)

    Liu, Hong-Hui; Zhang, Hong-Ling; Xu, Hong-Bin; Lou, Tai-Ping; Sui, Zhi-Tong; Zhang, Yi

    2018-03-15

    Vanadium nitride and graphene have been widely used as pseudo-capacitive and electric double-layer capacitor electrode materials for electrochemical capacitors, respectively. However, the poor cycling stability of vanadium nitride and the low capacitance of graphene impeded their practical applications. Herein, we demonstrated an in situ self-sacrificed template method for the synthesis of vanadium nitride/nitrogen-doped graphene (VN/NGr) nanocomposites by the pyrolysis of a mixture of dicyandiamide, glucose, and NH 4 VO 3 . Vanadium nitride nanoparticles of the size in the range of 2 to 7 nm were uniformly embedded into the nitrogen-doped graphene skeleton. Furthermore, the VN/NGr nanocomposites with a high specific surface area and pore volume showed a high specific capacitance of 255 F g -1 at 10 mV s -1 , and an excellent cycling stability (94% capacitance retention after 2000 cycles). The excellent capacitive properties were ascribed to the excellent conductivity of nitrogen-doped graphene, high surface area, high pore volume, and the synergistic effect between vanadium nitride and nitrogen-doped graphene.

  8. Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

    International Nuclear Information System (INIS)

    Cui, Xiaojin; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2013-01-01

    By using displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier behavior in the indium-tin oxide (ITO)/Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/C60/Au(or Al) capacitors. Two DCM peaks appeared asymmetrically at around −35.5 V and +30.0 V in the dark. Correspondingly, the EFISHG response from the C60 layer was observed, but the peak positions were different with respect to DCM ones. The results show that the spontaneous polarization of the ferroelectric P(VDF-TrFE) polymeric layer directly affects the electric field in the C60 layer, and thus governs the carrier motion in this layer. As a result, the C60 layer serves like an insulator in the dark, while electrons and holes are captured and released at the interface in response to the turn-over of spontaneous polarization of ferroelectric layer. On the other hand, under white light illumination, C60 layer serves like a conductor due to the increase of photogenerated mobile carriers, and these carriers dominate the carrier motions therein. Our findings here will be helpful for analyzing carrier behaviors in organic electronic devices using ferroelectric polymers

  9. Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

    Energy Technology Data Exchange (ETDEWEB)

    Cui, Xiaojin [Department of Physical Electronics, Tokyo Institute of Technology 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan); State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa, E-mail: iwamoto@pe.titech.ac.jp [Department of Physical Electronics, Tokyo Institute of Technology 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)

    2013-12-21

    By using displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier behavior in the indium-tin oxide (ITO)/Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/C60/Au(or Al) capacitors. Two DCM peaks appeared asymmetrically at around −35.5 V and +30.0 V in the dark. Correspondingly, the EFISHG response from the C60 layer was observed, but the peak positions were different with respect to DCM ones. The results show that the spontaneous polarization of the ferroelectric P(VDF-TrFE) polymeric layer directly affects the electric field in the C60 layer, and thus governs the carrier motion in this layer. As a result, the C60 layer serves like an insulator in the dark, while electrons and holes are captured and released at the interface in response to the turn-over of spontaneous polarization of ferroelectric layer. On the other hand, under white light illumination, C60 layer serves like a conductor due to the increase of photogenerated mobile carriers, and these carriers dominate the carrier motions therein. Our findings here will be helpful for analyzing carrier behaviors in organic electronic devices using ferroelectric polymers.

  10. Hierarchically porous carbon nanosheets derived from Moringa oleifera stems as electrode material for high-performance electric double-layer capacitors

    Science.gov (United States)

    Cai, Yijin; Luo, Ying; Dong, Hanwu; Zhao, Xiao; Xiao, Yong; Liang, Yeru; Hu, Hang; Liu, Yingliang; Zheng, Mingtao

    2017-06-01

    A facile one-step pyrolysis route for the synthesis of hierarchically porous carbon nanosheets (PCNSs) derived from Moringa oleifera stems (MOSs) is reported, in which no post-activation-process in needed. The as-prepared PCNSs possesses unique porous nanosheet morphology with high specific surface area of ca. 2250 m2 g-1, large pore volume of ca. 2.3 cm3 g-1, appropriate porosity as well as heteroatom doping (N and O), endowing outstanding electrochemical properties as electrode material for high-performance supercapacitors. The PCNS-based electrodes are investigated in various aqueous electrolytes including 1.0 M Na2SO4, 1.0 M H2SO4, and 6.0 M KOH. The PCNSs exhibit a maximum specific capacitance of ca. 283 F g-1 (0.5 A g-1), excellent rate capability (ca. 72% of capacitance retention even at an ultrahigh current density of 50 A g-1), and a tremendous long-term cycling stability in the three-electrode system. Moreover, the as-assembled PCNS-based symmetric supercapacitor shows a high energy density of ca. 25.8 Wh kg-1 (in 1.0 M Na2SO4 electrolyte) and remarkable long-term cycling stability (almost no capacitance fade in aqueous electrolytes), indicating the promising of the as-prepared PCNSs for electrochemical energy storage and conversion.

  11. Elaboration of a microstructured inkjet-printed carbon electrochemical capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Pech, David; Brunet, Magali; Fabre, Norbert; Mesnilgrente, Fabien; Conedera, Veronique; Durou, Hugo [LAAS-CNRS, Universite de Toulouse, 7 av. du Colonel Roche, F-31077 Toulouse (France); Taberna, Pierre-Louis; Simon, Patrice [CIRIMAT-CNRS, Universite de Toulouse, 118 route de Narbonne, F-31062 Toulouse (France)

    2010-02-15

    Carbon-based micro-supercapacitors dedicated to energy storage in self-powered modules were fabricated with inkjet printing technology on silicon substrate. An ink was first prepared by mixing an activated carbon powder with a PTFE polymer binder in ethylene glycol stabilized with a surfactant then deposited by inkjet on patterned gold current collectors with the substrate heated at 140 C in order to assure a good homogeneity. Electrochemical micro-capacitors with electrodes in an interdigital configuration were fabricated, and characterized using electrochemical techniques in 1 M Et{sub 4}NBF{sub 4} propylene carbonate electrolyte. These micro-devices show an excellent capacitive behavior over a wide potential range of 2.5 V for a cell capacitance of 2.1 mF cm{sup -2}. The newly developed technology will allow the integration of the storage device as close as possible to the MEMS-based energy harvesting device, minimizing power losses through connections. (author)

  12. Fundamentally Addressing Bromine Storage through Reversible Solid-State Confinement in Porous Carbon Electrodes: Design of a High-Performance Dual-Redox Electrochemical Capacitor.

    Science.gov (United States)

    Yoo, Seung Joon; Evanko, Brian; Wang, Xingfeng; Romelczyk, Monica; Taylor, Aidan; Ji, Xiulei; Boettcher, Shannon W; Stucky, Galen D

    2017-07-26

    Research in electric double-layer capacitors (EDLCs) and rechargeable batteries is converging to target systems that have battery-level energy density and capacitor-level cycling stability and power density. This research direction has been facilitated by the use of redox-active electrolytes that add faradaic charge storage to increase energy density of the EDLCs. Aqueous redox-enhanced electrochemical capacitors (redox ECs) have, however, performed poorly due to cross-diffusion of soluble redox couples, reduced cycle life, and low operating voltages. In this manuscript, we propose that these challenges can be simultaneously met by mechanistically designing a liquid-to-solid phase transition of oxidized catholyte (or reduced anolyte) with confinement in the pores of electrodes. Here we demonstrate the realization of this approach with the use of bromide catholyte and tetrabutylammonium cation that induces reversible solid-state complexation of Br 2 /Br 3 - . This mechanism solves the inherent cross-diffusion issue of redox ECs and has the added benefit of greatly stabilizing the reactive bromine generated during charging. Based on this new mechanistic insight on the utilization of solid-state bromine storage in redox ECs, we developed a dual-redox EC consisting of a bromide catholyte and an ethyl viologen anolyte with the addition of tetrabutylammonium bromide. In comparison to aqueous and organic electric double-layer capacitors, this system enhances energy by factors of ca. 11 and 3.5, respectively, with a specific energy of ∼64 W·h/kg at 1 A/g, a maximum power density >3 kW/kg, and cycling stability over 7000 cycles.

  13. Gravitational double layers

    International Nuclear Information System (INIS)

    Senovilla, José M M

    2014-01-01

    I analyze the properties of thin shells through which the scalar curvature R is discontinuous in gravity theories with Lagrangian F(R) = R − 2Λ + αR 2 on the bulk. These shells/domain walls are of a new kind because they possess, in addition to the standard energy–momentum tensor, an external energy flux vector, an external scalar pressure/tension and, most exotic of all, another energy–momentum contribution resembling classical dipole distributions on a shell: a double layer. I prove that all these contributions are necessary to make the entire energy–momentum tensor divergence-free. This is the first known occurrence of such a type of double layer in a gravity theory. I present explicit examples in constant-curvature five-dimensional bulks, with a brief study of their properties: new physical behaviors arise. (fast track communications)

  14. An overview of carbon materials for flexible electrochemical capacitors.

    Science.gov (United States)

    He, Yongmin; Chen, Wanjun; Gao, Caitian; Zhou, Jinyuan; Li, Xiaodong; Xie, Erqing

    2013-10-07

    Under the background of the quick development of lightweight, flexible, and wearable electronic devices in our society, a flexible and highly efficient energy management strategy is needed for their counterpart energy-storage systems. Among them, flexible electrochemical capacitors (ECs) have been considered as one of the most promising candidates because of their significant advantages in power and energy densities, and unique properties of being flexible, lightweight, low-cost, and environmentally friendly compared with current energy storage devices. In a common EC, carbon materials play an irreplaceable and principal role in its energy-storage performance. Up till now, most progress towards flexible ECs technologies has mostly benefited from the continuous development of carbon materials. As a result, in view of the dual remarkable highlights of ECs and carbon materials, a summary of recent research progress on carbon-based flexible EC electrode materials is presented in this review, including carbon fiber (CF, consisting of carbon microfiber-CMF and carbon nanofiber-CNF) networks, carbon nanotube (CNT) and graphene coatings, CNT and/or graphene papers (or films), and freestanding three-dimensional (3D) flexible carbon-based macroscopic architectures. Furthermore, some promising carbon materials for great potential applications in flexible ECs are introduced. Finally, the trends and challenges in the development of carbon-based electrode materials for flexible ECs and their smart applications are analyzed.

  15. Carbon-based fibrous EDLC capacitors and supercapacitors

    OpenAIRE

    Lekakou, C; Moudam, O; Markoulidis, F; Andrews, T; Watts, JF; Reed, GT

    2011-01-01

    This paper investigates electrochemical double-layer capacitors (EDLCs) including two alternative types of carbon-based fibrous electrodes, a carbon fibre woven fabric (CWF) and a multiwall carbon nanotube (CNT) electrode, as well as hybrid CWF-CNT electrodes. Two types of separator membranes were also considered. An organic gel electrolyte PEO-LiCIO4-EC-THF was used to maintain a high working voltage. The capacitor cells were tested in cyclic voltammetry, charge-discharge, and impedance test...

  16. CAPMIX -Deploying Capacitors for Salt Gradient Power Extraction

    OpenAIRE

    Bijmans, M.F.M.; Burheim, O.S.; Bryjak, M.; Delgado, A.; Hack, P.; Mantegazza, F.; Tenisson, S.; Hamelers, H.V.M.

    2012-01-01

    The process of mixing sea and river water can be utilised as a power source. At present, three groups of technology are established for doing so; i) mechanical; Pressure Retarded Osmosis PRO, ii) electrochemical reactions; Reverse ElectroDialysis (RED) and Nano Battery Electrodes (NBE) and iii) ultra capacitors; Capacitive Double Layer Expansion (CDLE) and Capacitors charge by the Donnan Potentials (CDP). The chemical potential for salt gradient power systems is only limited by th...

  17. Capacitors.

    Science.gov (United States)

    Trotter, Donald M., Jr.

    1988-01-01

    Presents a historical backdrop for a discussion of capacitor design and function. Discusses the production, importance, and function of two types of miniature capacitors; electrolytic and multilayer ceramic capacitors. Describes the function of these miniature capacitors in comparison to the Leyden jar, a basic demonstration of capacitance. (CW)

  18. Catechol-chitosan redox capacitor for added amplification in electrochemical immunoanalysis.

    Science.gov (United States)

    Yan, Kun; Liu, Yi; Guan, Yongguang; Bhokisham, Narendranath; Tsao, Chen-Yu; Kim, Eunkyoung; Shi, Xiao-Wen; Wang, Qin; Bentley, William E; Payne, Gregory F

    2018-05-22

    Antibodies are common recognition elements for molecular detection but often the signals generated by their stoichiometric binding must be amplified to enhance sensitivity. Here, we report that an electrode coated with a catechol-chitosan redox capacitor can amplify the electrochemical signal generated from an alkaline phosphatase (AP) linked immunoassay. Specifically, the AP product p-aminophenol (PAP) undergoes redox-cycling in the redox capacitor to generate amplified oxidation currents. We estimate an 8-fold amplification associated with this redox-cycling in the capacitor (compared to detection by a bare electrode). Importantly, this capacitor-based amplification is generic and can be coupled to existing amplification approaches based on enzyme-linked catalysis or magnetic nanoparticle-based collection/concentration. Thus, the capacitor should enhance sensitivities in conventional immunoassays and also provide chemical to electrical signal transduction for emerging applications in molecular communication. Copyright © 2018 Elsevier B.V. All rights reserved.

  19. FABRICATION AND CHARACTERIZATION OF POLYANILINE-GRAPHENE COMPOSITE AS ELECTRODE IN ELECTROCHEMICAL CAPACITOR

    Directory of Open Access Journals (Sweden)

    H. Adelkhani

    2016-06-01

    Full Text Available In this study, polyaniline-graphene composites with different nano-structures are synthesized and the behaviour of the obtained composites serving as electrode materials in electrochemical capacitors is studied. The morphology, crystal structure, and thermal stability of the composites are examined using scanning electron microscopy (SEM, X-ray diffraction (XRD, and Thermal gravimetric analysis (TGA. Electrochemical properties are characterized by cyclic voltammetry (CV. According to the results, the obtained composites show different crystal structures and different thermal stabilities, and consequently different electrochemical capacities, when used as electrodes in electrochemical capacitors. A nano-fibre composite is shown to have a good degree of crystallization, 5.17% water content, 637oC degradation onset temperature, and 379 Fg-1 electrochemical capacity.

  20. Nanoporous carbons from cypress Ⅱ. Application to electric double layer capacitors%由柏木制备纳米孔结构炭材料Ⅱ.电双层电容器中的应用

    Institute of Scientific and Technical Information of China (English)

    Eiki Ito; Sylwia Mozia; Masaharu Okuda; Takashi Nakano; Masahiro Toyoda; Michio Inagaki

    2007-01-01

    通过过热蒸气活化法制备的柏木炭中含有大量的中孔,可用于制备以1 mol/L硫酸为电解液的双电层电容器(EDLCs).在50 mA/g电流密度下,柏木炭的质量比电容(C50)为190 F/g;在1 000 mA/g电流密度下,其质量比电容(C1000)为140 F/g.按C1000/C50定义的性能倍率约为0.72.测得的高电容量可归因于微孔和大孔所造成表面的贡献.以简易浸泡法负载少量NiO粒子后,柏木炭的质量比电容可以提高约13%,体积比电容提高约27%,而其性能倍率保持不变.%Cypress charcoals, which were prepared under super-heated steam and had a relatively large amount of mesopores, were used in electric double layer capacitors (EDLCs) in 1 mol/L H2SO4 electrolyte. The gravimetric capacitance of cypress charcoals was about 190 F/g at a current density of 50 mA/g (C50) and 140 F/g at 1 000 mA/g (C1000) and the performance rating defined by C1000/C50 was about 0.72. The capacitance observed was explained by the contributions from the surfaces from the micropores and the larger pores. By loading minute NiO particles through a simple impregnating process, the capacitance of the loaded charcoals was enhanced by about 13% in gravimetric capacitance and by about 27% in volumetric capacitance and the performance rating was kept the same.

  1. Low-dimensional carbon and MXene-based electrochemical capacitor electrodes.

    Science.gov (United States)

    Yoon, Yeoheung; Lee, Keunsik; Lee, Hyoyoung

    2016-04-29

    Due to their unique structure and outstanding intrinsic physical properties such as extraordinarily high electrical conductivity, large surface area, and various chemical functionalities, low-dimension-based materials exhibit great potential for application in electrochemical capacitors (ECs). The electrical properties of electrochemical capacitors are determined by the electrode materials. Because energy charge storage is a surface process, the surface properties of the electrode materials greatly influence the electrochemical performance of the cell. Recently, graphene, a single layer of sp(2)-bonded carbon atoms arrayed into two-dimensional carbon nanomaterial, has attracted wide interest as an electrode material for electrochemical capacitor applications due to its unique properties, including a high electrical conductivity and large surface area. Several low-dimensional materials with large surface areas and high conductivity such as onion-like carbons (OLCs), carbide-derived carbons (CDCs), carbon nanotubes (CNTs), graphene, metal hydroxide, transition metal dichalcogenides (TMDs), and most recently MXene, have been developed for electrochemical capacitors. Therefore, it is useful to understand the current issues of low-dimensional materials and their device applications.

  2. Low-dimensional carbon and MXene-based electrochemical capacitor electrodes

    International Nuclear Information System (INIS)

    Yoon, Yeoheung; Lee, Hyoyoung; Lee, Keunsik

    2016-01-01

    Due to their unique structure and outstanding intrinsic physical properties such as extraordinarily high electrical conductivity, large surface area, and various chemical functionalities, low-dimension-based materials exhibit great potential for application in electrochemical capacitors (ECs). The electrical properties of electrochemical capacitors are determined by the electrode materials. Because energy charge storage is a surface process, the surface properties of the electrode materials greatly influence the electrochemical performance of the cell. Recently, graphene, a single layer of sp 2 -bonded carbon atoms arrayed into two-dimensional carbon nanomaterial, has attracted wide interest as an electrode material for electrochemical capacitor applications due to its unique properties, including a high electrical conductivity and large surface area. Several low-dimensional materials with large surface areas and high conductivity such as onion-like carbons (OLCs), carbide-derived carbons (CDCs), carbon nanotubes (CNTs), graphene, metal hydroxide, transition metal dichalcogenides (TMDs), and most recently MXene, have been developed for electrochemical capacitors. Therefore, it is useful to understand the current issues of low-dimensional materials and their device applications. (topical review)

  3. Exceptionally High Electric Double Layer Capacitances of Oligomeric Ionic Liquids.

    Science.gov (United States)

    Matsumoto, Michio; Shimizu, Sunao; Sotoike, Rina; Watanabe, Masayoshi; Iwasa, Yoshihiro; Itoh, Yoshimitsu; Aida, Takuzo

    2017-11-15

    Electric double layer (EDL) capacitors are promising as next-generation energy accumulators if their capacitances and operation voltages are both high. However, only few electrolytes can simultaneously fulfill these two requisites. Here we report that an oligomeric ionic liquid such as IL4 TFSI with four imidazolium ion units in its structure provides a wide electrochemical window of ∼5.0 V, similar to monomeric ionic liquids. Furthermore, electrochemical impedance measurements using Au working electrodes demonstrated that IL4 TFSI exhibits an exceptionally high EDL capacitance of ∼66 μF/cm 2 , which is ∼6 times as high as those of monomeric ionic liquids so far reported. We also found that an EDL-based field effect transistor (FET) using IL4 TFSI as a gate dielectric material and SrTiO 3 as a channel material displays a very sharp transfer curve with an enhanced carrier accumulation capability of ∼64 μF/cm 2 , as determined by Hall-effect measurements.

  4. Applications of Silver Nanowires on Transparent Conducting Film and Electrode of Electrochemical Capacitor

    Directory of Open Access Journals (Sweden)

    Yuan-Jun Song

    2014-01-01

    Full Text Available Silver nanowire has potential applications on transparent conducting film and electrode of electrochemical capacitor due to its excellent conductivity. Transparent conducting film (G-film was prepared by coating silver nanowires on glass substrate using Meyer rod method, which exhibited better performance than carbon nanotube and graphene. The conductivity of G-film can be improved by increasing sintering temperature. Electrode of electrochemical capacitor (I-film was fabricated through the same method with G-film on indium tin oxide (ITO. CV curves of I-film under different scanning rates had obvious redox peaks, which indicated that I-film exhibited excellent electrochemical pseudocapacitance performance and good reversibility during charge/discharge process. In addition, the specific capacitance of I-film was measured by galvanostatic charge/discharge experiments, indicating that I-film exhibits high special capacitance and excellent electrochemical stability.

  5. Thermally Reduced Graphene Oxide Electrochemically Activated by Bis-Spiro Quaternary Alkyl Ammonium for Capacitors.

    Science.gov (United States)

    He, Tieshi; Meng, Xiangling; Nie, Junping; Tong, Yujin; Cai, Kedi

    2016-06-08

    Thermally reduced graphene oxide (RGO) electrochemically activated by a quaternary alkyl ammonium-based organic electrolytes/activated carbon (AC) electrode asymmetric capacitor is proposed. The electrochemical activation process includes adsorption of anions into the pores of AC in the positive electrode and the interlayer intercalation of cations into RGO in the negative electrode under high potential (4.0 V). The EA process of RGO by quaternary alkyl ammonium was investigated by X-ray diffraction and electrochemical measurements, and the effects of cation size and structure were extensively evaluated. Intercalation by quaternary alkyl ammonium demonstrates a small degree of expansion of the whole crystal lattice (d002) and a large degree of expansion of the partial crystal lattice (d002) of RGO. RGO electrochemically activated by bis-spiro quaternary alkyl ammonium in propylene carbonate/AC asymmetric capacitor exhibits good activated efficiency, high specific capacity, and stable cyclability.

  6. Understanding performance limitation and suppression of leakage current or self-discharge in electrochemical capacitors: a review.

    Science.gov (United States)

    Ike, Innocent S; Sigalas, Iakovos; Iyuke, Sunny

    2016-01-14

    Self-discharge is known to have considerable adverse effects on the performance and application of electrochemical capacitors (ECs). Thus, obtaining an understanding of EC self-discharge mechanism(s) and subsequent derivation and solution of EC models, subject to a particular mechanism or combination of mechanisms during charging, discharging and storage of the device, is the only way to solve problems associated with EC self-discharge. In this review, we summarize recent progress with respect to EC self-discharge by considering the two basic types, electric double-layer capacitors (EDLC) and pseudocapacitors, and their hybrids with their respective charge storage mechanisms, distinguishable self-discharge mechanisms, charge redistribution and charge/energy loss during self-discharge. It was clearly observed that most of the voltage reduction is not purely due to the self-discharge effect but is basically due to redistribution of charge carriers deep inside pores and can therefore be retrieved from a capacitor during long-time discharging. Tuning the self-discharge rate is therefore feasible for single-walled carbon nanotube (SWNT) ECs and can be achieved by simply adjusting the surface chemistry of the nanotubes. The effects of surface chemistry modification on EC self-discharge are very important in studying and suppressing the self-discharge process and will benefit potential applications of ECs with respect to energy retention. Self-discharge can be averted by the use of redox couples that are transformed to insoluble species via electrolysis and adsorbed onto the activated carbon electrode in redox-couple EDLCs, thus transforming the EDLC electrolyte into a material that can store charge. Self-discharge in ECs can also be successfully suppressed by utilizing an ion-interchange layer (ion-exchange membrane), separator or CuSO4 mobile electrolyte that can be converted into an insoluble species by electrolysis during the charge/discharge process. This will help

  7. Influence of Mixed Solvent on the Electrochemical Property of Hybrid Capacitor.

    Science.gov (United States)

    Lee, Byunggwan; Yoon, J R

    2015-11-01

    The hybrid capacitors (2245 size, cylindrical type) were prepared by using activated carbon cathode and Li4Ti5O12 anode. In order to improve the cell operation at high temperature range, propylene carbonate (PC) was used in combination with acetonitrile (AN) with volume ratio of 7:3, 5:5, and 3:7, respectively. We investigated the electrochemical behavior of the hybrid capacitors that enabled cell operation with stability at high temperature. The organic electrolyte of hybrid capacitor containing PC and AN with a volume ratio 7:3 intended to exhibit highly reversible cycle performance with good capacity retention at 60 degrees C after 2200 cycles. From this study, it has been found that the very strong influence of the solvent nature on the characteristics of hybrid capacitor, and the difference in performance associated with the two solvents.

  8. High-performance symmetric electrochemical capacitor based on graphene foam and nanostructured manganese oxide

    CSIR Research Space (South Africa)

    Bello, A

    2013-01-01

    Full Text Available We have fabricated a symmetric electrochemical capacitor with high energy and power densities based on a composite of graphene foam (GF) with 80 wt% of manganese oxide (MnO(sub2)) deposited by hydrothermal synthesis. Raman spectroscopy and X...

  9. Manganese oxide/graphene oxide composites for high-energyaqueous asymmetric electrochemical capacitors

    CSIR Research Space (South Africa)

    Jafta, CJ

    2013-11-01

    Full Text Available A high-energy aqueous asymmetric electrochemical capacitor was developed using manganese diox-ide ( -MnO2)/graphene oxide (GO) nanocomposites. The nanostructured -MnO2was prepared frommicron-sized commercial electrolytic manganese dioxide (EMD) via...

  10. Electroresistance Effect in Gold Thin Film Induced by Ionic-Liquid-Gated Electric Double Layer

    NARCIS (Netherlands)

    Nakayama, Hiroyasu; Ye, Jianting; Ohtani, Takashi; Fujikawa, Yasunori; Ando, Kazuya; Iwasa, Yoshihiro; Saitoh, Eiji

    Electroresistance effect was detected in a metallic thin film using ionic-liquid-gated electric-double-layer transistors (EDLTs). We observed reversible modulation of the electric resistance of a Au thin film. In this system, we found that an electric double layer works as a nanogap capacitor with

  11. Carbon activation process for increased surface accessibility in electrochemical capacitors

    Science.gov (United States)

    Doughty, Daniel H.; Eisenmann, Erhard T.

    2001-01-01

    A process for making carbon film or powder suitable for double capacitor electrodes having a capacitance of up to about 300 F/cm.sup.3 is disclosed. This is accomplished by treating in aqueous nitric acid for a period of about 5 to 15 minutes thin carbon films obtained by carbonizing carbon-containing polymeric material having a high degree of molecular directionality, such as polyimide film, then heating the treated carbon film in a non-oxidizing atmosphere at a non-graphitizing temperature of at least 350.degree. C. for about 20 minutes, and repeating alternately the nitric acid step and the heating step from 7 to 10 times. Capacitors made with this carbon may find uses ranging from electronic devices to electric vehicle applications.

  12. Hybrid nanostructured materials for high-performance electrochemical capacitors

    KAUST Repository

    Yu, Guihua; Xie, Xing; Pan, Lijia; Bao, Zhenan; Cui, Yi

    2013-01-01

    The exciting development of advanced nanostructured materials has driven the rapid growth of research in the field of electrochemical energy storage (EES) systems which are critical to a variety of applications ranging from portable consumer

  13. Graphene/VO2 hybrid material for high performance electrochemical capacitor

    International Nuclear Information System (INIS)

    Deng, Lingjuan; Zhang, Gaini; Kang, Liping; Lei, Zhibin; Liu, Chunling; Liu, Zong-Huai

    2013-01-01

    Graphical abstract: Graphene/VO 2 hybrid materials are prepared by one-step simultaneous hydrothermal reduction technology. The prepared graphene (1.0)/VO 2 hybrid material shows a specific capacitances of 225 F g −1 in 0.5 mol L −1 K 2 SO 4 solution. Furthermore, an asymmetric electrochemical capacitor with graphene (1.0)/VO 2 as a positive electrode and graphene as a negative electrode is assembled, and it can work in a cell voltage of 1.7 V and show excellent capacitive property. - Highlights: • Graphene/VO 2 hybrid material has been prepared by one-step hydrothermal reduction. • Graphene/VO 2 hybrid material exhibits high specific capacitance. • An asymmetric capacitor working at 1.7 V in aqueous solution is assembled based on graphene/VO 2 electrode. • The asymmetric capacitor exhibits high energy density. - Abstract: Vanadium oxides have attracted significant attention for electrochemical capacitor because of their extensive multifunctional properties. In the present work, graphene/VO 2 (RG/VO 2 ) hybrid materials with different RG amounts are prepared in a mixture of ammonium vanadate, formic acid and graphite oxide (GO) nanosheets by one-step simultaneous hydrothermal reduction technology. The hydrothermal treatment makes the reduction of GO into RG and the formation of VO 2 particles with starfruit morphology. The starfruit-like VO 2 particles are uniformly embedded in the hole constructed by RG nanosheets, which makes the electrode–electrolyte contact better. A high specific capacitance of 225 F g −1 has been achieved for RG(1.0)/VO 2 electrode with RG content of 26 wt% in 0.5 mol L −1 K 2 SO 4 electrolyte. An asymmetrical electrochemical capacitor is assembled by using RG(1.0)/VO 2 as positive electrode and RG as negative electrode, and it can be reversibly charged–discharged at a cell voltage of 1.7 V in 0.5 mol L −1 K 2 SO 4 electrolyte. The asymmetrical capacitor can deliver an energy density of 22.8 Wh kg −1 at a power density

  14. Double layers above the aurora

    International Nuclear Information System (INIS)

    Temerin, M.; Mozer, F.S.

    1987-01-01

    Two different kinds of double layers were found in association with auroral precipitation. One of these is the so-called electrostatic shock, which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much larger than the parallel electric field. This type of double layer is often found at the edges of regions of upflowing ion beams and the direction of the electric fields in the shock points toward the ion beam. The potential drop through the shock can be several kV and is comparable to the total potential needed to produce auroral acceleration. Instabilities associated with the shock may generate obliquely propagating Alfven waves, which may accelerate electrons to produce flickering auroras. The flickering aurora provides evidence that the electrostatic shock may have large temporal fluctuations. The other kind of double layer is the small-amplitude double layer found in regions of upward flowing in beams, often in association with electrostatic ion cyclotron waves. The parallel and perpendicular electric fields in these structures are comparable in magnitude. The associated potentials are a few eV. Since many such double layers are found in regions of upward flowing ion beams, the combined potential drop through a set of these double layers can be substantial

  15. Global effects of double layers

    International Nuclear Information System (INIS)

    Raad, M.A.

    1984-12-01

    Locally the formation of an electrostatic double layer in a current carrying plasma leads to a direct acceleration of particles which may penetrate far into the surrounding medium. The potential across the double layer, giving this acceleration, must be maintained by the external system and is a basic parameter for the local to global coupling. The double layer potential is associated with an electric field parallel to the magnetic field. In general this leads to a magnetohydrodynamic relaxation of the surrounding medium providing the influx of energy which is dissipated by the double layer. The double layer potential is limited as is the maximum possible rate of energy influx. If the global response of the external medium can be represented by an external circuit and if an equivalent circuit element can be found to represent the double layer, for example a negative resistance for intermediate time scales, it is possible to give a description of the dynamics and stability of the whole system. (Author)

  16. Nitrogen-Doped Holey Graphene Film-Based Ultrafast Electrochemical Capacitors.

    Science.gov (United States)

    Zhou, Qinqin; Zhang, Miao; Chen, Ji; Hong, Jong-Dal; Shi, Gaoquan

    2016-08-17

    The commercialized aluminum electrolytic capacitors (AECs) currently used for alternating current (AC) line-filtering are usually the largest components in the electronic circuits because of their low specific capacitances and bulky sizes. Herein, nitrogen-doped holey graphene (NHG) films were prepared by thermal annealing the composite films of polyvinylpyrrolidone (PVP), graphene oxide (GO), and ferric oxide (Fe2O3) nanorods followed by chemical etching with hydrochloride acid. The typical electrochemical capacitor with NHG electrodes exhibited high areal and volumetric specific capacitances of 478 μF cm(-2) and 1.2 F cm(-3) at 120 Hz, ultrafast frequency response with a phase angle of -81.2° and a resistor-capacitor time constant of 203 μs at 120 Hz, as well as excellent cycling stability. Thus, it is promising to replace conventional AEC for AC line-filtering in miniaturized electronics.

  17. Probing the electrochemical double layer of an ionic liquid using voltammetry and impedance spectroscopy: a comparative study of carbon nanotube and glassy carbon electrodes in [EMIM](+)[EtSO(4)](-).

    Science.gov (United States)

    Zheng, J P; Goonetilleke, P C; Pettit, C M; Roy, D

    2010-05-15

    Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) are compared as techniques for analyzing double layer capacitances of ionic liquids (ILs) at the surfaces of two carbon-based electrodes. These systems are relevant for energy storage supercapacitors and often are associated with unconventional electrochemical properties. Certain theoretical and experimental aspects of CV and EIS necessary for quantitative evaluation of the capacitance characteristics of such systems are explored. The experiments use 1-ethyl-3-methyl imidazolium ethylsulfate as a model IL electrolyte in combination with a porous electrode of carbon nanotubes (CNTs). The results are compared with those obtained with a nonporous glassy carbon (GC) electrode. The time is constant, and hence the power delivery characteristics of the experimental cell are affected by the electrolyte resistance and residual faradaic reactions of the IL, as well as by the spatially inhomogeneous electrode surfaces. It is shown that adequate characterization of these IL-electrode systems can be achieved by combining CV with EIS. A phenomenological framework for utilizing this combination is discussed.

  18. Electrochemical capacitor behavior of copper sulfide (CuS) nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Justin Raj, C.; Kim, Byung Chul; Cho, Won-Je; Lee, Won-Gil; Seo, Yongseong; Yu, Kook-Hyun, E-mail: yukook@dongguk.edu

    2014-02-15

    Highlights: • The electrochemical supercapacitor electrode was fabricated using CuS nanoplatelets. • CuS electrodes shows better electrochemical properties in aqueous LiClO{sub 4} electrolyte. • The heat treated CuS electrode shows an excellent pseudocapacitance performance than bare CuS electrode. -- Abstract: Copper sulfide (CuS) nanoplatelets have been fabricated by simple low temperature chemical bath deposition technique for electrochemical supercapacitor electrodes. The morphology and structural properties of the electrodes were analyzed using scanning electron microscopy and X-ray diffraction. The effect of heat treatment on electrochemical properties of CuS electrodes were examined by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge tests. Results show that bare and heat treated CuS has pseudocapacitive characteristic within the potential range of −0.6 to 0.3 V (vs. Ag/AgCl) in aqueous 1 M LiClO{sub 4} solution. The pseudocapacitance is induced mainly by lithium ions insertion/extraction with the CuS electrodes. The specific capacitance of 72.85 F g{sup −1} was delivered by heat treated CuS film at a scan rate of 5 mV s{sup −1} with an energy and power density of 6.23 W h kg{sup −1} and 1.75 kW kg{sup −1} at 3 Ag{sup −1} constant discharge current which is comparatively higher than that of as deposited CuS electrode.

  19. Porous carbon nanospheres derived from chlorination of bis(cyclopentadienyl)titanium dichloride and their electrochemical capacitor performance

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez-Garcia, Pedro, E-mail: pegonzal@quim.ucm.es [Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense, E-28040 Madrid (Spain); Centeno, T.A. [Instituto Nacional del Carbon-CSIC, Apartado 73, E-33080 Oviedo (Spain); Urones-Garrote, Esteban [Centro de Microscopia y Citometria, Universidad Complutense, E-28040 Madrid (Spain); Avila-Brande, David; Otero-Diaz, L. Carlos [Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense, E-28040 Madrid (Spain)

    2011-10-17

    Highlights: {yields} Microporous carbon nanospheres have been produced via chlorination reaction of bis(cyclopentadienyl)titanium dichloride. {yields} The materials present a structure formed by disordered arrangements of graphene-like layers, sp{sup 2}/sp{sup 3} ratio {approx}95-97% and mass-density below pure graphite. {yields} The increase in the reaction temperature decreases the particle size distribution and improves the surface area and the micropore volume. {yields} Electrochemical performance for the 900 deg. C sample shows a specific capacitance of 106 F g{sup -1} in H{sub 2}SO{sub 4} electrolyte and 80 F g{sup -1} in (C{sub 2}H{sub 5}){sub 4}NBF{sub 4}/acetonitrile medium. - Abstract: Conglomerated and accreted porous carbon spheres have been obtained by the chlorination reaction of bis(cyclopentadienyl)titanium dichloride as carbon precursor. The spheres size distribution, derived from scanning electron microscopy observations, shows that the diameter intervals decreases from 70-525 nm at 400 deg. C to 40-370 nm at 900 deg. C. High-resolution transmission electron microscopy observations indicate that the spheres are formed by open and curved randomly stacked graphene-like layers. Electron energy loss spectroscopy studies show relative sp{sup 2}/sp{sup 3} ratio higher than 95% and mass-density values (1.1-1.6 g cm{sup -3}) smaller than graphite. Nitrogen adsorption measurements reveal the presence of micro and mesopores whose contributions to the total porosity greatly depend on the preparation temperature. Galvanostatic charging-discharging measurements on the carbon material synthesized at 900 deg. C provide a specific capacitance of 106 F g{sup -1} in the aqueous H{sub 2}SO{sub 4} electrolyte and 80 F g{sup -1} in the aprotic (C{sub 2}H{sub 5}){sub 4}NBF{sub 4}/acetonitrile medium. These high values suggest the potentiality of this material for electrical energy storage in electrochemical double layer capacitors.

  20. On the physics of relativistic double layers

    International Nuclear Information System (INIS)

    Carlqvist, P.

    1982-06-01

    A model of a strong, time-independent, and relativistic double layer is studied. Besides double layers having the electric field parallel to the current the model also describes a certain type of oblique double layers. The 'Langmuir condition' (ratio of ion current density to electron current density) as well as an expression for the potential drop of the double layer are derived. Furthermore, the distribution of charged particles, electric field, and potential within the double layer are clarified and discussed. It is found that the properties of relativistic double layers differ substantially from the properties of corresponding non-relativistic double layers. (Author)

  1. Development of pseudocapacitive molybdenum oxide–nitride for electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Ting, Yen-Jui Bernie [Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada); Wu, Haoran [Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada); Kherani, Nazir P. [Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada); Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada); Lian, Keryn, E-mail: keryn.lian@utoronto.ca [Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada)

    2015-03-15

    A thin film Mo oxide–nitride pseudocapacitive electrode was synthesized by electrodeposition of Mo oxide on Ti and a subsequent low-temperature (400 °C) thermal nitridation. Two nitridation environments, N{sub 2} and NH{sub 3}, were used and the results were compared. Surface analyses of these nitrided films showed partial conversion of Mo oxide to nitrides, with a lower conversion percentage being the film produced in N{sub 2}. However, the electrochemical analyses showed that the surface of the N{sub 2}-treated film had better pseudocapacitive behaviors and outperformed that nitrided in NH{sub 3}. Cycle life of the resultant N{sub 2}-treated Mo oxide–nitride was also much improved over Mo oxide. A two-electrode cell using Mo oxide–nitride electrodes was demonstrated and showed high rate performance. - Highlights: • Mo(O,N){sub x} was developed by electrodeposition and nitridation in N{sub 2} or NH{sub 3}. • N{sub 2} treated Mo(O,N){sub x} showed a capacitive performance superior to that treated by NH{sub 3}. • The promising electrochemical performance was due to the formation of γ-Mo{sub 2}N.

  2. Electrochemical etching of a niobium foil in methanolic HF for electrolytic capacitor

    International Nuclear Information System (INIS)

    Kim, Kyungmin; Park, Jiyoung; Cha, Gihoon; Yoo, Jeong Eun; Choi, Jinsub

    2013-01-01

    Electrochemical etching of niobium foil in order to enlarge the surface area for the application in electrolytic capacitor was carried out in a methanolic electrolyte. We found that the pit density and depth are not linearly proportional to concentration of HF and applied potential: there is the optimal concentration of HF at each applied potential. The optimal etching condition was obtained at 50 V in 0.99 vol.% HF, which exhibited the capacitance of 350 μF cm −2 . Pit density and depth of pits on electrochemical etched Nb foil under different conditions were counted from SEM images and electrochemical impedance spectroscopy (EIS) of the etched Nb foils was carried out for the capacitance measurement. Equivalent circuit model showing less than 5% error was suggested for applying to the etched niobium foil. - Highlights: • Surface enlargement of Nb foil can be achieved by electrochemical etching in methanolic HF. • Electrolytic capacitor of etched niobium foil exhibits a capacitance of 350 μF cm −2 . • The method provides a way of developing commercially viable process

  3. Electrochemical performance of a hybrid lithium-ion capacitor with a graphite anode preloaded from lithium bis(trifluoromethane)sulfonimide-based electrolyte

    International Nuclear Information System (INIS)

    Decaux, C.; Lota, G.; Raymundo-Piñero, E.; Frackowiak, E.; Béguin, F.

    2012-01-01

    A hybrid LiC capacitor combining a lithium-ion battery type (graphite) electrode and an electrical double-layer (activated carbon) one has been developed by preloading graphite from 2 mol L −1 lithium bis(trifluoromethane)sulfonimide (LiTFSI) organic electrolyte. The graphite intercalation compound was formed by applying ca. 10 successive charge/self-discharge pulses. The optimized hybrid device operates in the voltage range from 1.5 to 4.2 V and displays 60% higher gravimetric capacitance than an electric double-layer (EDL) capacitor using the same activated carbon for both electrodes. As a result, the energy density reaches 80 Wh kg −1 , which is four times higher than the value for the EDL capacitor with the same total mass of carbon.

  4. Multilayered films of cobalt oxyhydroxide nanowires/manganese oxide nanosheets for electrochemical capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Huajun [State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014 (China); ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering and AIBN, The University of Queensland, St Lucia, Brisbane, QLD 4072 (Australia); Tang, Fengqiu; Mukherji, Aniruddh; Yan, Xiaoxia; Wang, Lianzhou (Max) Lu, Gao Qing [ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering and AIBN, The University of Queensland, St Lucia, Brisbane, QLD 4072 (Australia); Lim, Melvin [Division of Environmental and Water Resources Engineering, School of Civil and Environmental Engineering, Nanyang Technological University, 639798 (Singapore)

    2010-01-15

    Multilayered films of cobalt oxyhydroxide nanowires (CoOOHNW) and exfoliated manganese oxide nanosheet (MONS) are fabricated by potentiostatic deposition and electrostatic self-assembly on indium-tin oxide coated glass substrates. The morphology and chemical composition of these films are characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectra (XPS) and the potential application as electrochemical supercapacitors are investigated using cyclic voltammetry and charge-discharge measurements. These ITO/CoOOHNW/MONS multilayered film electrodes exhibit excellent electrochemical capacitance properties, including high specific capacitance (507 F g{sup -1}) and long cycling durability (less 2% capacity loss after 5000 charge/discharge cycles). These characteristics indicate that these newly developed films may find important application for electrochemical capacitors. (author)

  5. The Electrochemical Characteristics of Hybrid Capacitor Prepared by Chemical Activation of NaOH

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jeong Eun; Bae, Ga Yeong; Yang, Jeong Min; Lee, Jong Dae [Chungbuk National Univ., Chungju (Korea, Republic of)

    2013-06-15

    Active carbons with high specific surface area and micro pore structure were prepared from the coconut shell char using the chemical activation method of NaOH. The preparation process has been optimized through the analysis of experimental variables such as activating chemical agents to char ratio and the flow rate of gas during carbonization. The active carbons with the surface area (2,481m{sup 2}/g) and mean pore size (2.32 nm) were obtained by chemical activation with NaOH. The electrochemical performances of hybrid capacitor were investigated using LiMn{sub 2}O{sub 4}, LiCoO{sub 2} as the positive electrode and prepared active carbon as the negative electrode. The electrochemical behaviors of hybrid capacitor using organic electrolytes (LiPF{sub 6}, TEABF{sub 4}) were characterized by constant current charge/discharge, cyclic voltammetry, cycle and leakage tests. The hybrid capacitor using LiMn{sub 2}O{sub 4}/AC electrodes had better capacitance than other hybrid systems and was able to deliver a specific energy as high as 131 Wh/kg at a specific power of 1,448 W/kg.

  6. The Electrochemical Characteristics of Hybrid Capacitor Prepared by Chemical Activation of NaOH

    International Nuclear Information System (INIS)

    Choi, Jeong Eun; Bae, Ga Yeong; Yang, Jeong Min; Lee, Jong Dae

    2013-01-01

    Active carbons with high specific surface area and micro pore structure were prepared from the coconut shell char using the chemical activation method of NaOH. The preparation process has been optimized through the analysis of experimental variables such as activating chemical agents to char ratio and the flow rate of gas during carbonization. The active carbons with the surface area (2,481m 2 /g) and mean pore size (2.32 nm) were obtained by chemical activation with NaOH. The electrochemical performances of hybrid capacitor were investigated using LiMn 2 O 4 , LiCoO 2 as the positive electrode and prepared active carbon as the negative electrode. The electrochemical behaviors of hybrid capacitor using organic electrolytes (LiPF 6 , TEABF 4 ) were characterized by constant current charge/discharge, cyclic voltammetry, cycle and leakage tests. The hybrid capacitor using LiMn 2 O 4 /AC electrodes had better capacitance than other hybrid systems and was able to deliver a specific energy as high as 131 Wh/kg at a specific power of 1,448 W/kg

  7. Electrical modeling of semiconductor bridge (SCB) BNCP detonators with electrochemical capacitor firing sets

    Energy Technology Data Exchange (ETDEWEB)

    Marx, K.D. [Sandia National Labs., Livermore, CA (United States); Ingersoll, D.; Bickes, R.W. Jr. [Sandia National Labs., Albuquerque, NM (United States)

    1998-11-01

    In this paper the authors describe computer models that simulate the electrical characteristics and hence, the firing characteristics and performance of a semiconductor bridge (SCB) detonator for the initiation of BNCP [tetraammine-cis-bis (5-nitro-2H-tetrazolato-N{sup 2}) cobalt(III) perchlorate]. The electrical data and resultant models provide new insights into the fundamental behavior of SCB detonators, particularly with respect to the initiation mechanism and the interaction of the explosive powder with the SCB. One model developed, the Thermal Feedback Model, considers the total energy budget for the system, including the time evolution of the energy delivered to the powder by the electrical circuit, as well as that released by the ignition and subsequent chemical reaction of the powder. The authors also present data obtained using a new low-voltage firing set which employed an advanced electrochemical capacitor having a nominal capacitance of 350,000 {micro}F at 9 V, the maximum voltage rating for this particular device. A model for this firing set and detonator was developed by making measurements of the intrinsic capacitance and equivalent series resistance (ESR < 10 m{Omega}) of a single device. This model was then used to predict the behavior of BNCP SCB detonators fired alone, as well as in a multishot, parallel-string configuration using a firing set composed of either a single 9 V electrochemical capacitor or two of the capacitors wired in series and charged to 18 V.

  8. Activated Porous Carbon Spheres with Customized Mesopores through Assembly of Diblock Copolymers for Electrochemical Capacitor.

    Science.gov (United States)

    Tang, Jing; Wang, Jie; Shrestha, Lok Kumar; Hossain, Md Shahriar A; Alothman, Zeid Abdullah; Yamauchi, Yusuke; Ariga, Katsuhiko

    2017-06-07

    A series of porous carbon spheres with precisely adjustable mesopores (4-16 nm), high specific surface area (SSA, ∼2000 m 2 g -1 ), and submicrometer particle size (∼300 nm) was synthesized through a facile coassembly of diblock polymer micelles with a nontoxic dopamine source and a common postactivation process. The mesopore size can be controlled by the diblock polymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO) templates, and has an almost linear dependence on the square root of the degree of polymerization of the PS blocks. These advantageous structural properties make the product a promising electrode material for electrochemical capacitors. The electrochemical capacitive performance was studied carefully by using symmetrical cells in a typical organic electrolyte of 1 M tetraethylammonium tetrafluoroborate/acetonitrile (TEA BF 4 /AN) or in an ionic liquid electrolyte of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF 4 ), displaying a high specific capacitance of 111 and 170 F g -1 at 1 A g -1 , respectively. The impacts of pore size distribution on the capacitance performance were thoroughly investigated. It was revealed that large mesopores and a relatively low ratio of micropores are ideal for realizing high SSA-normalized capacitance. These results provide us with a simple and reliable way to screen future porous carbon materials for electrochemical capacitors and encourage researchers to design porous carbon with high specific surface area, large mesopores, and a moderate proportion of micropores.

  9. Performance of flexible capacitors based on polypyrrole/carbon fiber electrochemically prepared from various phosphate electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Wei; Han, Gaoyi, E-mail: han_gaoyis@sxu.edu.cn; Chang, Yunzhen; Li, Miaoyu; Xiao, Yaoming, E-mail: ymxiao@sxu.edu.cn; Zhou, Haihan; Zhang, Ying; Li, Yanping

    2016-11-30

    Highlights: • PPy/CFs have been fabricated by electrodepositing polypyrrole on carbon fibers. • The electrolytes in deposition solution have effect on PPy/CFs’ capacitive behavior. • Cells of PPy/CFs obtained from NaH{sub 2}PO{sub 4} electrolyte has good stability in PVA/H{sub 3}PO{sub 4}. - Abstract: In order to investigate the influence of electrolytes in electro-deposition solution on the capacitive properties of polypyrrole (PPy), we have chosen phosphoric acid, phosphate, hydrogen phosphate and dihydrogen phosphate as electrolyte in deposition solution respectively and electrochemically deposited PPy on carbon fibers (CFs) via galvanostatic method. The morphologies of the PPy/CFs samples have been characterized by scanning electron microscope. The specific capacitance of PPy/CFs samples has been evaluated in different electrolytes through three-electrode test system. The assembled flexible capacitors by using PPy/CFs as electrodes and H{sub 3}PO{sub 4}/polyvinyl alcohol as gel electrolyte have been systematically measured by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results show that the electrochemical capacitors based on PPy/CFs prepared from deposition solution containing NaH{sub 2}PO{sub 4}·2H{sub 2}O electrolyte exhibit higher specific capacitance, flexibility and excellent stability (retaining 96.8% of initial capacitance after 13,000 cycles), and that three cells connected in series can power a light-emitting diode.

  10. Some theoretical aspects of electrostatic double layers

    International Nuclear Information System (INIS)

    Carlqvist, P.

    1978-11-01

    A review is presented of the main results of the theoretical work on electrostatic double layers. The general properties of double layers are first considered. Then the time-independent double layer is discussed. The discussion deals with the potential drop, the thickness, and some necessary criteria for the existence and stability of the layer. As a complement to the study of the timeindependent double layer a few remarks are also made upon the timedependent double layer. Finally the question of how double layers are formed and maintained is treated. Several possible formation mechanisms are considered. (author)

  11. Electrophoretically deposited graphene oxide and carbon nanotube composite for electrochemical capacitors

    International Nuclear Information System (INIS)

    Ajayi, Obafunso A; Wong, Chee Wei; Guitierrez, Daniel H; Peaslee, David; Cheng, Arthur; Chen, Bin; Gao, Theodore

    2015-01-01

    We report a scalable one-step electrode fabrication approach for synthesizing composite carbon-based supercapacitors with synergistic outcomes. Multi-walled carbon nanotubes (MWCNTs) were successfully integrated into our modified electrophoretic deposition process to directly form composite MWCNT–GO electrochemical capacitor electrodes (where GO is graphene oxide) with superior performance to solely GO electrodes. The measured capacitance improved threefold, reaching a maximum specific capacitance of 231 F g"−"1. Upon thermal reduction, MWCNT–GO electrode sheet resistance decreased by a factor of 8, significantly greater than the 2× decrease of those without MWCNTs. (paper)

  12. Capacity improvement of the carbon-based electrochemical capacitor by zigzag-edge introduced graphene

    Science.gov (United States)

    Tamura, Naoki; Tomai, Takaaki; Oka, Nobuto; Honma, Itaru

    2018-01-01

    The electrochemical properties of graphene edge has been attracted much attention. Especially, zigzag edge has high electrochemical activity because neutral radical exits on edge. However, due to a lack of efficient production method for zigzag graphene, the electrochemical properties of zigzag edge have not been experimentally demonstrated and the capacitance enhancement of carbonaceous materials in energy storage devices by the control in their edge states is still challenge. In this study, we fabricated zigzag-edge-rich graphene by a one-step method combining graphene exfoliation in supercritical fluid and anisotropic etching by catalytic nanoparticles. This efficient production of zigzag-edge-rich graphene allows us to investigate the electrochemical activity of zigzag edge. By cyclic voltammetry, we revealed the zigzag edge-introduced graphene exhibited unique redox reaction in aqueous acid solution. Moreover, by the calculation on the density function theory (DFT), this unique redox potential for zigzag edge-introduced graphene can be attributed to the proton-insertion/-extraction reactions at the zigzag edge. This finding indicates that the graphene edge modification can contribute to the further increase in the capacitance of the carbon-based electrochemical capacitor.

  13. Transition from single to multiple double layers

    International Nuclear Information System (INIS)

    Chan, C.; Hershkowitz, N.

    1982-01-01

    It is shown that laboratory double layers become multiple double layers when the ratio of Debye length to system length is decreased. This result exhibits characteristics described by boundary layer theory

  14. Nickel oxide/hydroxide nanoplatelets synthesized by chemical precipitation for electrochemical capacitors

    International Nuclear Information System (INIS)

    Wu, M.-S.; Hsieh, H.-H.

    2008-01-01

    Nickel hydroxide powder prepared by directly chemical precipitation method at room temperature has a nanoplatelet-like morphology and could be converted into nickel oxide at annealing temperature higher than 300 deg. C, confirmed by the thermal gravimetric analysis and X-ray diffraction. Annealing temperature influences significantly both the electrical conductivity and the specific surface area of nickel oxide/hydroxide powder, and consequently determines the capacitor behavior. Electrochemical capacitive behavior of the synthesized nickel hydroxide/oxide film is investigated by cyclic voltammetry and electrochemical impedance spectroscope methods. After 300 deg. C annealing, the highest specific capacitance of 108 F g -1 is obtained at scan rate of 10 mV s -1 . When annealing temperature is lower than 300 deg. C, the electrical conductivity of nickel hydroxide dominates primarily the capacitive behavior. When annealing temperature is higher than 300 deg. C, both electrical conductivity and specific surface area of the nickel oxide dominate the capacitive behavior

  15. Covalent organic framework-derived microporous carbon nanoparticles coated with conducting polypyrrole as an electrochemical capacitor

    Science.gov (United States)

    Kim, Dong Jun; Yoon, Jung Woon; Lee, Chang Soo; Bae, Youn-Sang; Kim, Jong Hak

    2018-05-01

    We report a high-performance electrochemical capacitor based on covalent organic framework (COF)-derived microporous carbon (MPC) nanoparticles and electrochemically polymerized polypyrrole (Ppy) as a pseudocapacitive material. The COF, Schiff-based network-1 (SNW-1) nanoparticles are prepared via a condensation reaction between melamine and terephthalaldehyde, and the resultant MPC film is prepared via a screen-printing method. The MPC film exhibits a bimodal porous structure with micropores and macropores, resulting in both a large surface area and good electrolyte infiltration. Ppy is synthesized potentio-statically (0.8 V vs. Ag/AgCl) by varying the reaction time, and successful synthesis of Ppy is confirmed via Raman spectroscopy. The specific capacitance with the Ppy coating is enhanced by up to 2.55 F cm-2 due to the synergetic effect of pseudocapacitance and reduced resistance.

  16. Fe3O4/carbon hybrid nanoparticle electrodes for high-capacity electrochemical capacitors.

    Science.gov (United States)

    Lee, Jun Seop; Shin, Dong Hoon; Jun, Jaemoon; Lee, Choonghyeon; Jang, Jyongsik

    2014-06-01

    Fe3O4/carbon hybrid nanoparticles (FeCHNPs) were fabricated using dual-nozzle electrospraying, vapor deposition polymerization (VDP), and carbonization. FeOOH nanoneedles decorated with polypyrrole (PPy) nanoparticles (FePNPs) were fabricated by electrospraying pristine PPy mixed with FeCl3 solution, followed by heating stirring reaction. A PPy coating was then formed on the FeOOH nanoneedles through a VDP process. FeCHNPs were produced through carbonization of PPy and FeOOH phase transitions. These hybrid carbon nanoparticles (NPs) were used to build electrodes of electrochemical capacitors. The specific capacitance of the FeCHNPs was 455 F g(-1), which is larger than that of pristine PPy NPs (105 F g(-1)) or other hybrid PPy NPs. Furthermore, the FeCHNP-based capacitors exhibited better cycle stability during charge-discharge cycling than other hybrid NP capacitors. This is because the carbon layer on the Fe3 O4 surface formed a protective coating, preventing damage to the electrode materials during the charge-discharge processes. This fabrication technique is an effective approach for forming stable carbon/metal oxide nanostructures for energy storage applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Self-discharge of AC/AC electrochemical capacitors in salt aqueous electrolyte

    International Nuclear Information System (INIS)

    García-Cruz, L.; Ratajczak, P.; Iniesta, J.; Montiel, V.; Béguin, F.

    2016-01-01

    The self-discharge (SD) of electrochemical capacitors based on activated carbon electrodes (AC/AC capacitors) in aqueous lithium sulfate was examined after applying a three-hour cell potential hold at U i values from 1.0 to 1.6 V. The leakage current measured during the potentiostatic period as well as the amplitude of self-discharge increased with U i ; the cell potential drop was approximately doubled by 10 °C increase of temperature. The potential decay of both negative and positive electrodes was explored separately, by introducing a reference electrode and it was found that the negative electrode contributes essentially to the capacitor self-discharge. A diffusion-controlled mechanism was found at U i ≤ 1.4 V and U i ≤ 1.2 V for the positive and negative electrodes, respectively. At higher U i of 1.6 V, both electrodes display an activation-controlled mechanism due to water oxidation and subsequent carbon oxidation at the positive electrode and water or oxygen reduction at the negative electrode.

  18. The influence of current collector corrosion on the performance of electrochemical capacitors

    Science.gov (United States)

    Wojciechowski, Jarosław; Kolanowski, Łukasz; Bund, Andreas; Lota, Grzegorz

    2017-11-01

    This paper discusses the effect of current collector (stainless steel 316L) corrosion on the performance of electrochemical capacitors operated in aqueous electrolytes. This topic seems to be often neglected in scientific research. The studied electrolytes were 1 M H2SO4, 1 M KI, 1 M Na2SO4, 1 M KOH and 6 M KOH. The corrosion process was investigated by means of selected direct and alternating current techniques. The surface of the current collectors as well as the corrosion products were characterised using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and atomic force microscopy. Stainless steel 316L in alkaline solutions is characterised by the lowest values of corrosion potentials whereas the potentials in acidic media become the most noble. Our studies show that corrosion potentials increase with decreasing pH value. This phenomenon can be explained with the formation of passive oxide films on the stainless steel current collectors. The passive oxide films are usually thicker and more porous in alkaline solutions than that in the other electrolytes. The processes occurring at the electrode/electrolyte interfaces strongly influence the working parameters of electrochemical capacitors such as voltage, working potentials of single electrodes, self-discharge as well as the internal resistance and cycling stability.

  19. Electrochemical capacitance of NiO/Ru{sub 0.35}V{sub 0.65}O{sub 2} asymmetric electrochemical capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Chang-Zhou; Gao, Bo; Zhang, Xiao-Gang [College of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

    2007-11-08

    A designed asymmetric hybrid electrochemical capacitor was presented where NiO and Ru{sub 0.35}V{sub 0.65}O{sub 2} as the positive and negative electrode, respectively, both stored charge through reversible faradic pseudocapacitive reactions of the anions (OH{sup -}) with electroactive materials. And the two electrodes had been individually tested in 1 M KOH aqueous electrolyte to define the adequate balance of the active materials in the hybrid system as well as the working voltage of the capacitor based on them. The electrochemical tests demonstrated that the maximum specific capacitance and energy density of the asymmetric hybrid electrochemical capacitor were 102.6 F g{sup -1} and 41.2 Wh kg{sup -1}, respectively, delivered at a current density of 7.5 A cm{sup -2}. And the specific energy density decreased to 23.0 Wh kg{sup -1} when the specific power density increased up to 1416.7 W kg{sup -1}. The hybrid electrochemical capacitor also exhibited a good electrochemical stability with 83.5% of the initial capacitance over consecutive 1500 cycle numbers. (author)

  20. Recent progress in layered double hydroxide based materials for electrochemical capacitors: design, synthesis and performance.

    Science.gov (United States)

    Zhao, Mingming; Zhao, Qunxing; Li, Bing; Xue, Huaiguo; Pang, Huan; Chen, Changyun

    2017-10-19

    As representative two-dimensional (2D) materials, layered double hydroxides (LDHs) have received increasing attention in electrochemical energy storage and conversion because of the facile tunability between their composition and morphology. The high dispersion of active species in layered arrays, the simple exfoliation into monolayer nanosheets and chemical modification offer the LDHs an opportunity as active electrode materials in electrochemical capacitors (ECs). LDHs are favourable in providing large specific surface areas, good transport features as well as attractive physicochemical properties. In this review, our purpose is to provide a detailed summary of recent developments in the synthesis and electrochemical performance of the LDHs. Their composites with carbon (carbon quantum dots, carbon black, carbon nanotubes/nanofibers, graphene/graphene oxides), metals (nickel, platinum, silver), metal oxides (TiO 2 , Co 3 O 4 , CuO, MnO 2 , Fe 3 O 4 ), metal sulfides/phosphides (CoS, NiCo 2 S 4 , NiP), MOFs (MOF derivatives) and polymers (PEDOT:PSS, PPy (polypyrrole), P(NIPAM-co-SPMA) and PET) are also discussed in this review. The relationship between structures and electrochemical properties as well as the associated charge-storage mechanisms is discussed. Moreover, challenges and prospects of the LDHs for high-performance ECs are presented. This review sheds light on the sustainable development of ECs with LDH based electrode materials.

  1. Synthesis and characterization of a nanocomposite of goethite nanorods and reduced graphene oxide for electrochemical capacitors

    International Nuclear Information System (INIS)

    Shou Qingliang; Cheng Jipeng; Zhang Li; Nelson, Bradley J.; Zhang Xiaobin

    2012-01-01

    We report a one-step synthesis of a nanocomposite of goethite (α-FeOOH) nanorods and reduced graphene oxide (RGO) using a solution method in which ferrous cations serve as a reducing agent of graphite oxide (GO) to graphene and a precursor to grow goethite nanorods. As-prepared goethite nanorods have an average length of 200 nm and a diameter of 30 nm and are densely attached on both sides of the RGO sheets. The electrochemical properties of the nanocomposite were characterized by cyclic voltammetry (CV) and chronopotentiometry (CP) charge–discharge tests. The results showed that goethite/RGO composites have a high electrochemical capacitance of 165.5 F g −1 with an excellent recycling capability making the material promising for electrochemical capacitors. - Graphical abstract: The reduced graphene oxide sheets are decorated with goethite nanorods. The as-prepared composite exhibits a high electrochemical capacitance with good recycling capability, which is promising for supercapacitor applications. Higlights: ► Ferrous ions act as reductant of graphite oxide and precursor of goethite nanorods. ► Goethite nanorods are attached on both sides of the reduced graphene oxide sheets. ► Composite exhibits a high specific capacitance and a good recycling capability. ► Composite is promising for supercapacitor applications.

  2. The theory of double layers

    International Nuclear Information System (INIS)

    Schamel, H.

    1982-01-01

    Numerical and in some degree laboratory experiments suggest the existence of at least two different kinds of time-independent double layers: a strictly monotonic transition of the electrostatic potential and a transition accompanied by a negative spike at the low potential side (ion acoustic DL). An interpretation of both is presented in terms of analytic BGK modes. The first class of DLs commonly observed in voltage- or beam-driven plasmas needs for its existence beam-type distributions satisfying a Bohm criterion. The potential drop is at least of the order of Tsub(e), and stability arguments favour currents which satisfy the Langmuir condition. The second class found in current-driven plasma simulations is correlated with ion holes. This latter kind of nonlinear wave-solutions is linearly based on the slow ion-acoustic mode and exists due to a vortex-like distortion of the ion distribution in the thermal range. During the growth of an ion hole which is triggered by ion-acoustic fluctuations, the partial reflection of streaming electrons causes different plasma states on both sides of the potential dip and makes the ion hole asymmetric giving rise to an effective potential drop. This implies that the amplitude of this second type of double layers has an upper limit of 1-2 Tsub(e) and presumes a temperature ratio of Tsub(e)/Tsub(i) > or approximately 3 in coincidence with the numerical results. (Auth.)

  3. Microwave assisted synthesis of MnO2 on nickel foam-graphene for electrochemical capacitor

    International Nuclear Information System (INIS)

    Bello, A.; Fashedemi, O.O.; Fabiane, M.; Lekitima, J.N.; Ozoemena, K.I.; Manyala, N.

    2013-01-01

    Highlights: •Three-dimensional synthesis of graphene using CVD. •Hydrothermal deposition (microwave irradiation) of MnO 2 on graphene. •Morphologies of the composite reveals flower-like nanostructures of MnO 2 on graphene. •Composite exhibit excellent electrochemical performance. -- Abstract: A green chemistry approach (hydrothermal microwave irradiation) has been used to deposit manganese oxide on nickel foam-graphene. The 3D graphene was synthesized using nickel foam template by chemical vapor deposition (CVD) technique. Raman spectroscopy, X-ray diffraction (XRD), scanning electron and transmission electron microscopies (SEM and TEM) have been used to characterize structure and surface morphology of the composite, respectively. The Raman spectroscopy measurements on the samples reveal that 3D graphene consists of mostly few layers with low defect density. The composite was tested in a three electrode configuration for electrochemical capacitor, and exhibited a specific capacitance of 305 F g −1 at a current density of 1 A g −1 and showed excellent cycling stability. The obtained results demonstrate that microwave irradiation technique could be a promising approach to synthesis graphene based functional materials for electrochemical applications

  4. Effects of ion insertion on cycling performance of miniaturized electrochemical capacitor of carbon nanotubes array.

    Science.gov (United States)

    Tsai, Dah-Shyang; Chang, Chuan-hua; Chiang, Wei-Wen; Lee, Kuei-Yi; Huang, Ying-Sheng

    2014-10-24

    Capacity degradation and ion insertion of a miniaturized electrochemical capacitor are studied using ionic liquid [EMI] [TFSI] as the electrolyte. This capacitor is featured with two comb-like electrodes of vertical carbon nanotubes, ∼70 μm in height and 20 μm in interelectrode gap. We quantify the levels of ion insertion damage with Raman spectroscopy after the electrode experiences 120 consecutive voltammetric cycles to various potential limits. Distinct structural damage emerges due to [EMI] when the negative potential reaches -1.7 V, and those due to [TFSI] arise when the positive potential reaches 1.7 V vs. RHE. Judging from the peak broadenings, [EMI] is more detrimental than [TFSI]. When the voltage window ΔU is set as less than or equal to 2.8 V, both electrode potentials are within the two intercalation limits, little or no decay is observed in 10(4) charge/discharge cycles. When ΔU is 3.4 V, the positive potential exceeds the upper limit, but the negative potential stays within the lower limit, the cell capacitance decreases moderately. When ΔU increases to 3.8 V, both electrodes suffer from damages because of exceeding the intercalation limits. And the cell capacitance decreases substantially, even leading to a premature failure.

  5. Nanosized Ni-Mn Oxides Prepared by the Citrate Gel Process and Performances for Electrochemical Capacitors

    Institute of Scientific and Technical Information of China (English)

    Jianxin ZHOU; Xiangqian SHEN; Maoxiang JING

    2006-01-01

    Nanosized Ni-Mn oxide powders have been successfully prepared by thermal decomposition of the Ni-Mn citrate gel precursors. The powder materials derived from calcination of the gel precursors with various molar ratios of nickel and manganese at different temperatures and time were characterized using thermal analysis (TG-DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET).The optimized processing conditions of calcination at 400℃ for 1 h with Ni/Mn molar ratio 6 were proved to produce the nanosized Ni-Mn oxide powders with a high specific surface area of 109.62 m2/g and nanometer particle sizes of 15~30 nm. The capacitance characteristics of the nanosized Ni-Mn oxide electrode in various concentrations of KOH solutions were studied by the cyclic voltammetry (CV) and exhibited both a doublelayer capacitance and a Faradaic capacitance which could be attributed to the electrode consisting of Ni-Mn oxides and residual carbons from the organic gel thermal decomposition. A specific capacitance of 194.8 F/g was obtained for the electrode at the sweep rate of 10 mV/s in 4 mol/L KOH electrolyte and the capacitor showed quite high cyclic stability and is promising for advanced electrochemical capacitors.

  6. Investigation of Synergy Between Electrochemical Capacitors, Flywheels, and Batteries in Hybrid Energy Storage for PV Systems

    Energy Technology Data Exchange (ETDEWEB)

    Miller, John; Sibley, Lewis, B.; Wohlgemuth, John

    1999-06-01

    This report describes the results of a study that investigated the synergy between electrochemical capacitors (ECs) and flywheels, in combination with each other and with batteries, as energy storage subsystems in photovoltaic (PV) systems. EC and flywheel technologies are described and the potential advantages and disadvantages of each in PV energy storage subsystems are discussed. Seven applications for PV energy storage subsystems are described along with the potential market for each of these applications. A spreadsheet model, which used the net present value method, was used to analyze and compare the costs over time of various system configurations based on flywheel models. It appears that a synergistic relationship exists between ECS and flywheels. Further investigation is recommended to quantify the performance and economic tradeoffs of this synergy and its effect on overall system costs.

  7. Manganese oxide electrochemical capacitor with potassium poly(acrylate) hydrogel electrolyte

    Science.gov (United States)

    Lee, Kuang-Tsin; Wu, Nae-Lih

    An aqueous gel electrolyte has for the first time been successfully applied to the MnO 2· nH 2O-based pseudocapacitive electrochemical capacitors (ECs). The gel electrolyte is made of potassium poly(acrylate) (PAAK) polymer and aqueous solution of KCl. With the selected composition, PAAK:KCl:H 2O = 9.0%:6.7%:84.3% by weight, the gel shows no fluidity, possessing an ionic conductivity in the order of 10 -1 S cm -1. The gel electrolyte has been found to give substantially higher specific capacitances than those in the liquid electrolyte with the same salt (KCl) composition (1 M) and high power capability (>10 kW/kg).

  8. Manganese oxide electrochemical capacitor with potassium poly(acrylate) hydrogel electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kuang-Tsin; Wu, Nae-Lih [Department of Chemical Engineering, National Taiwan University, Taipei 106 (China)

    2008-04-15

    An aqueous gel electrolyte has for the first time been successfully applied to the MnO{sub 2}.nH{sub 2}O-based pseudocapacitive electrochemical capacitors (ECs). The gel electrolyte is made of potassium poly(acrylate) (PAAK) polymer and aqueous solution of KCl. With the selected composition, PAAK:KCl:H{sub 2}O = 9.0%:6.7%:84.3% by weight, the gel shows no fluidity, possessing an ionic conductivity in the order of 10{sup -1} S cm{sup -1}. The gel electrolyte has been found to give substantially higher specific capacitances than those in the liquid electrolyte with the same salt (KCl) composition (1 M) and high power capability (>10 kW/kg). (author)

  9. Investigation of Synergy Between Electrochemical Capacitors, Flywheels, and Batteries in Hybrid Energy Storage for PV Systems

    International Nuclear Information System (INIS)

    Miller, John; Sibley Lewis, B.; Wohlgemuth, John

    1999-01-01

    This report describes the results of a study that investigated the synergy between electrochemical capacitors (ECs) and flywheels, in combination with each other and with batteries, as energy storage subsystems in photovoltaic (PV) systems. EC and flywheel technologies are described and the potential advantages and disadvantages of each in PV energy storage subsystems are discussed. Seven applications for PV energy storage subsystems are described along with the potential market for each of these applications. A spreadsheet model, which used the net present value method, was used to analyze and compare the costs over time of various system configurations based on flywheel models. It appears that a synergistic relationship exists between ECS and flywheels. Further investigation is recommended to quantify the performance and economic tradeoffs of this synergy and its effect on overall system costs

  10. Electrochemical capacitors based on nitrogen-enriched cobalt (II) phthalocyanine/multi-walled carbon nanotube nanocomposites

    CSIR Research Space (South Africa)

    Lekitima, JN

    2013-11-01

    Full Text Available nanotubes (MWCNTaf and MWCNTPhNH2) have been studied for application as an electrochemical capacitor in H2SO4. Both MWCNTaf/CoTPyzPz and MWCNTPhNH2/CoTPyzPz gave superior specific capacitance of 1984 and 2028 F.g-1 respectively . This high capacitance... electrodes in (i) 1.0 M H2SO4 electrolyte and (ii) 1.0M Na2SO4 at a scan rate of 10mVs-1. Figure 3 and 4 show the charge-discharge profiles of all the materials. The curves for CoTPyzPz, MWCNTPhNH2/CoTPyzPz and MWCNTaf/CoTPyzPz showed that potential...

  11. In situ chemical synthesis of ruthenium oxide/reduced graphene oxide nanocomposites for electrochemical capacitor applications.

    Science.gov (United States)

    Kim, Ji-Young; Kim, Kwang-Heon; Yoon, Seung-Beom; Kim, Hyun-Kyung; Park, Sang-Hoon; Kim, Kwang-Bum

    2013-08-07

    An in situ chemical synthesis approach has been developed to prepare ruthenium oxide/reduced graphene oxide (RGO) nanocomposites. It is found that as the C/O ratio increases, the number density of RuO2 nanoparticles decreases, because the chemical interaction between the Ru ions and the oxygen-containing functional groups provides anchoring sites where the nucleation of particles takes place. For electrochemical capacitor applications, the microwave-hydrothermal process was carried out to improve the conductivity of RGO in RuO2/RGO nanocomposites. The significant improvement in capacitance and high rate capability might result from the RuO2 nanoparticles used as spacers that make the interior layers of the reduced graphene oxide electrode available for electrolyte access.

  12. Characterization of manganese dioxide electrodeposited by pulse and direct current for electrochemical capacitor

    International Nuclear Information System (INIS)

    Adelkhani, H.; Ghaemi, M.

    2010-01-01

    This paper describes the electrochemical capacitor behavior of manganese dioxide (MD, MnO 2 ) samples that were prepared by direct current (DCMD) and pulse current (PCMD) electrodeposition. The capacitive characteristics of the samples were studied in 0.5 M aqueous Na 2 SO 4 solution using the cyclic voltammetry (CV) method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), chemical composition analyses and the Barrett-Joyner-Halenda (BJH) method were employed to characterize the samples. In the study of the effect of scan rate on capacitance, it was revealed that PCMD displayed higher capacities than DCMD for all scan rates. The higher capacitive performance of PCMD was attributed to its porosity (specific surface area, pore volume, and pore-size distribution), chemical composition and structural properties.

  13. Double Layer Dynamics in a Collisionless Magnetoplasma

    DEFF Research Database (Denmark)

    Iizuka, S.; Michelsen, Poul; Juul Rasmussen, Jens

    and propagation of a double layer. The period of the oscillations is determined by the propagation length of the double layer. The current is limited during the propagation of the double layer by a growing negative potential barrier formed on the low potential tail. Similar phenomena appear when a potential......An experimental investigation of the dynamics of double layers is presented. The experiments are performed in a Q-machine plasma and the double layers are generated by applying a positive step potential to a cold collector plate terminating the plasma column. The double layer is created...... at the grounded plasma source just after the pulse is applied and it propagates towards the collector with a speed around the ion acoustic speed. When the collector is biased positively, large oscillations are obserced in the plasma current. These oscillations are found to be related to a recurring formation...

  14. Effects of electrolytic composition on the electric double-layer capacitance at smooth-surface carbon electrodes in organic media

    International Nuclear Information System (INIS)

    Kim, In-Tae; Egashira, Minato; Yoshimoto, Nobuko; Morita, Masayuki

    2010-01-01

    As a fundamental research on the optimization of electrolyte composition in practical electrochemical capacitor device, double-layer capacitance at Glassy Carbon (GC) and Boron-doped Diamond (BDD), as typical smooth-surface carbon electrodes, has been studied as a function of the electrolyte composition in organic media. Specific capacitance (differential capacitance: F cm -2 ) determined by an AC impedance method, in which no contribution of mass-transport effects is included, corresponded well to integrated capacitance evaluated by conventional cyclic voltammetry. The specific capacitance at the GC electrode varied with polarized potential and showed clear PZC (potential of zero charge), while the potential dependence of the capacitance at BDD was very small. The effects of the solvent and the electrolytic salt on the capacitance behavior were common for both electrodes. That is, the sizes of the solvent molecule and the electrolytic ion (cation) strongly affected the capacitance at these smooth-surface carbon electrodes.

  15. Three Dimensional Double Layers in Magnetized Plasmas

    DEFF Research Database (Denmark)

    Jovanovic, D.; Lynov, Jens-Peter; Michelsen, Poul

    1982-01-01

    Experimental results are presented which demonstrate the formation of fully three dimensional double layers in a magnetized plasma. The measurements are performed in a magnetized stationary plasma column with radius 1.5 cm. Double layers are produced by introducing an electron beam with radius 0.......4 cm along the magnetic field from one end of the column. The voltage drop across the double layer is found to be determined by the energy of the incoming electron beam. In general we find that the width of the double layer along the external magnetic field is determined by plasma density and beam...

  16. Electrochemical Capacitors Based on Aligned Carbon Nanotubes Directly Synthesized on Tantalum Substrates

    International Nuclear Information System (INIS)

    Kim, Byung Woo; Chung, Hae Geun; Kim, Woong; Min, Byoung Koun; Kim, Hong Gon

    2010-01-01

    We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on tantalum substrate via waterassisted chemical vapor deposition and evaluate their properties as electrochemical capacitors. The mean diameter of the carbon nanotubes was 7.1 ± 1.5 nm, and 70% of them had double walls. The intensity ratio of G-band to D-band in Raman spectra was as high as 5, indicating good quality of the carbon nanotubes. Owing to the alignment and low equivalent series resistance, the carbon nanotube based supercapacitors showed good rate performance. Rectangular shape of cyclic voltammogram was maintained even at the scan rate of > 1 V/s in 1 M sulfuric acid aqueous solution. Specific capacitance was well-retained (∼94%) even when the discharging current density dramatically increased up to 145 A/g. Consequently, specific power as high as 60 kW/kg was obtained from as-grown carbon nanotubes in aqueous solution. Maximum specific energy of ∼20 Wh/kg was obtained when carbon nanotubes were electrochemically oxidized and operated in organic solution. Demonstration of direct synthesis of carbon nanotubes on tantalum current collectors and their applications as supercapacitors could be an invaluable basis for fabrication of high performance carbon nanotube supercapacitors

  17. Enabling high-rate electrochemical flow capacitors based on mesoporous carbon microspheres suspension electrodes

    Science.gov (United States)

    Tian, Meng; Sun, Yueqing; Zhang, Chuanfang (John); Wang, Jitong; Qiao, Wenming; Ling, Licheng; Long, Donghui

    2017-10-01

    Electrochemical flow capacitor (EFC) is a promising technology for grid energy storage, which combines the fast charging/discharging capability of supercapacitors with the scalable energy capacity of flow batteries. In this study, we report a high-power-density EFC using mesoporous carbon microspheres (MCMs) as suspension electrodes. By using a simple yet effective spray-drying technique, monodispersed MCMs with average particle size of 5 μm, high BET surface area of 1150-1267 m2 g-1, large pore volume of 2-4 cm3 g-1 and controllable mesopore size of 7-30 nm have been successfully prepared. The resultant MCMs suspension electrode shows excellent stability and considerable high capacitance of 100 F g-1 and good cycling ability (86% of initial capacitance after 10000 cycles). Specially, the suspension electrode exhibits excellent rate performance with 75% capacitance retention from 2 to 100 mV s-1, significantly higher than that of microporous carbon electrodes (20∼30%), due to the developed mesoporous channels facilitating for rapid ion diffusion. In addition, the electrochemical responses on both negative and positive suspension electrodes are studied, based on which an optimal capacitance matching between them is suggested for large-scale EFC unit.

  18. Synthesis and charge storage properties of double-layered NiSi nanocrystals

    International Nuclear Information System (INIS)

    Yoon, Jong-Hwan

    2010-01-01

    Based on bidirectional diffusion of Ni atoms, double-layered nickel silicide (NiSi) nanocrystals (NCs) for multilevel charge storage were fabricated, and their charge storage properties were examined. The double layer was produced by long-term thermal annealing (for 4 h at 900 o C) of a sandwich structure comprised of a thin Ni film of 0.3 nm sandwiched between two silicon-rich oxide (SiO 1.36 ) layers. Transmission electron microscopic image clearly exhibits a distinct NiSi nanocrystal double layer with a gap of about 7 nm between the mean positions of particle distribution in each NC layer. Capacitance-voltage measurements on the metal/oxide/semiconductor (MOS) capacitors with the double-layered NiSi nanocrystals are shown to have the apparent two plateaus of charge storage, the large memory window of about 9 V and the improved charge retention stability.

  19. Dynamical Aspects of Electrostatic Double Layers

    DEFF Research Database (Denmark)

    Raadu, M.A.; Juul Rasmussen, J.

    1988-01-01

    Electrostatic double layers have been proposed as an acceleration mechanism in solar flares and other astrophysical objects. They have been extensively studied in the laboratory and by means of computer simulations. The theory of steady-state double layers implies several existence criteria...

  20. Electrochemical performances and capacity fading behaviors of activated carbon/hard carbon lithium ion capacitor

    International Nuclear Information System (INIS)

    Sun, Xianzhong; Zhang, Xiong; Liu, Wenjie; Wang, Kai; Li, Chen; Li, Zhao; Ma, Yanwei

    2017-01-01

    Highlights: • Three-electrode pouch cell is used to investigate the capacity fading of AC/HC LIC. • the electrode potential swing is critical for the cycleability of a LIC cell. • Different capacity fading behaviors are discussed. • A large-capacity LIC pouch cell has been assembled with a specific energy of 18.1 Wh kg −1 based on the total weight. - Abstract: Lithium ion capacitor (LIC) is one of the most promising electrochemical energy storage devices, which offers rapid charging-discharging capability and long cycle life. We have fabricated LIC pouch cells using an electrochemically-driven lithium pre-doping method through a three-electrode pouch cell structure. The active materials of cathode and anode of LIC cell are activated carbon and pre-lithiated hard carbon, respectively. The electrochemical performances and the capacity fading behaviors of LICs in the voltage range of 2.0 − 4.0 V have been studied. The specific energy and specific power reach 73.6 Wh kg −1 and 11.9 kW kg −1 based on the weight of the active materials in both cathode and anode, respectively. Since the cycling performance is actually determined by hard carbon anode, the anode potential swings are emphasized. The capacity fading of LIC upon cycling is proposed to be caused by the increases of internal resistance and the consumption of lithium stored in anode. Finally, a large-capacity LIC pouch cell has been assembled with a maximum specific energy of 18.1 Wh kg −1 and a maximum specific power of 3.7 kW kg −1 based on the weight of the whole cell.

  1. Enhanced Cycleability of Amorphous MnO₂ by Covering on α-MnO₂ Needles in an Electrochemical Capacitor.

    Science.gov (United States)

    Liu, Quanbing; Ji, Shan; Yang, Juan; Wang, Hui; Pollet, Bruno G; Wang, Rongfang

    2017-08-24

    An allomorph MnO₂@MnO₂ core-shell nanostructure was developed via a two-step aqueous reaction method. The data analysis of Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction and N₂ adsorption-desorption isotherms experiments indicated that this unique architecture consisted of a porous layer of amorphous-MnO₂ nano-sheets which were well grown onto the surface of α-MnO₂ nano-needles. Cyclic voltammetry experiments revealed that the double-layer charging and Faradaic pseudo -capacity of the MnO₂@MnO₂ capacitor electrode contributed to a specific capacitance of 150.3 F·g -1 at a current density of 0.1 A·g -1 . Long cycle life experiments on the as-prepared MnO₂@MnO₂ sample showed nearly a 99.3% retention after 5000 cycles at a current density of 2 A·g -1 . This retention value was found to be significantly higher than those reported for amorphous MnO₂-based capacitor electrodes. It was also found that the remarkable cycleability of the MnO₂@MnO₂ was due to the supporting role of α-MnO₂ nano-needle core and the outer amorphous MnO₂ layer.

  2. Instability limits for spontaneous double layer formation

    International Nuclear Information System (INIS)

    Carr, J. Jr.; Galante, M. E.; McCarren, D.; Scime, E. E.; Sears, S.; VanDervort, R. W.; Magee, R. M.; Reynolds, E.

    2013-01-01

    We present time-resolved measurements that demonstrate that large amplitude electrostatic instabilities appear in pulsed, expanding helicon plasmas at the same time as particularly strong double layers appear in the expansion region. A significant cross-correlation between the electrostatic fluctuations and fluctuations in the number of ions accelerated by the double layer electric field is observed. No correlation is observed between the electrostatic fluctuations and ions that have not passed through the double layer. These measurements confirm that the simultaneous appearance of the electrostatic fluctuations and the double layer is not simple coincidence. In fact, the accelerated ion population is responsible for the growth of the instability. The double layer strength, and therefore, the velocity of the accelerated ions, is limited by the appearance of the electrostatic instability

  3. A study of nitroxide polyradical/activated carbon composite as the positive electrode material for electrochemical hybrid capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hui-qiao; Zou, Ying; Xia, Yong-yao [Chemistry Department and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433 (China)

    2007-01-01

    We present a new concept of the hybrid electrochemical capacitor technology in which a poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) nitroxide polyradical/activated carbon composite (PTMA-AC) is used as the positive electrode material and activated carbon is used as the negative electrode material. On the positive electrode, both reversible reduction and oxidation of nitroxide polyradical and non-faradic ion sorption/de-sorption of activated carbon are involved during charge and discharge process. The capacity of the composite electrode is 30% larger than that of the pure activated carbon electrode. A hybrid capacitor fabricated by the PTMA-AC composite positive electrode and the activated carbon negative electrode shows a good cycling life, it can be charged/discharged for over 1000 cycles with slight capacity loss. The hybrid capacitor also has a good rate capability, it maintains 80% of the initial capacity even at the high discharge current of up to 20C. (author)

  4. Simulation of plasma double-layer structures

    International Nuclear Information System (INIS)

    Borovsky, J.E.; Joyce, G.

    1982-01-01

    Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2-dimensional particle-in-cell method. The investigation of planar double layers indicates that these one-dimensional potential structures are susceptible to periodic disruption by instabilities in the low-potential plasmas. Only a slight increase in the double-layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double-layer electric-field alignment of accelerated particles and strong magnetization results in their magnetic-field alignment. The numerial simulations of spatially periodic two-dimensional double layers also exhibit cyclical instability. A morphological invariance in two-dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron-beam excited electrostatic electron-cyclotron waves and (ion-beam driven) solitary waves are present in the plasmas adjacent to the double layers

  5. Double layers and circuits in astrophysics

    International Nuclear Information System (INIS)

    Alfven, H.

    1986-05-01

    As the rate of energy release in a double layer with voltage DeltaV is P corresponding to IDeltaV, a double layer must be treated part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by menas of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroroal particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the sun's axis which may give radiations detectable from earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested in X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts like double layers, critical velocity, pinch effects and circuits is made. It is found that students using these textbooks remain essentially ignorant of even the existence of these, in spite of the fact that some of them have been well known for half a centry (e.g., double layers, Langmuir, 1929: pinch effect, Bennet, 1934). The conclusion is that astrophysics is too important to be left in the hands of the astrophysicist. Earth bound and space telescope data must be treated by scientists who are familiar with laboratory and magnetospheric physics and circuit theory, and of course with modern plasma theory. At least by volume the universe consists to more than 99 percent of plasma, and electromagnetic forces are 10/sup39/ time stronger than gravitation

  6. Stationary Double Layers in a Collisionless Magnetoplasma

    DEFF Research Database (Denmark)

    Noriyoshi, Sato; Mieno, Tetsu; Hatakeyama, Rikizo

    1983-01-01

    of the plate on the low-potential side, being accompanied with current limitation. This localized potential drop moves along the plasma column, but finally stops and results in the formation of the stationary double layer in the presence of sufficient plasma supply from the plate on the high-potential side.......Stationary double layers are generated in a magnetoplasma by applying potential differences between two heated plates on which the plasma is produced by surface ionization. By measuring the double-layer formation process, a localized potential drop is found to be formed initially in front...

  7. Improved electrochemical performance of LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} cathode material by double-layer coating with graphene oxide and V{sub 2}O{sub 5} for lithium-ion batteries

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Wenbin, E-mail: wenbin.luo@hotmail.com; Zheng, Baolin

    2017-05-15

    Highlights: • Citric acid assisted sol-gel method was used for synthesizing LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2}. • The pristine LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} was surface-modified by double-layer coating. • The double coating layer consists of graphene oxide and V{sub 2}O{sub 5}. • Electrochemical performance was improved by double-layer coating. - Abstract: LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} cathode material synthesized by a sol-gel method was surface-modified by double-layer coating. The results of X-ray diffraction (XRD) confirm that the intrinsic structure was no change after surface modification. A double-layer structure consisting of an inner V{sub 2}O{sub 5} (VO) layer and an outer conductive graphene oxide (GO) layer was coated on the surface of active material, as confirmed by transmission electron microscopy (TEM). The results of field emission scanning electron microscope (FE-SEM) equipped with an energy dispersive spectroscope (EDS) show that both graphene oxide and V{sub 2}O{sub 5} uniformly covered LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} cathode material. The double-layer-coated LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} cathode material shows improved electrochemical performance with a capacity retention of 74.2% after 50 cycles in a range of 2.5–4.5 V at 55 °C, compared with only 67.8% capacity retention for the pristine material. In addition, the double-layer-coated LiNi{sub 0.5}Co{sub 0.2}Mn{sub 0.3}O{sub 2} releases 116.6 mAh g{sup −1} under a high current rate, while the pristine material only remains at 105.7 mAh g{sup −1}. The results can be ascribed to the double coating layer not only avoids the side reaction between electrolyte and active material but also promotes Li{sup +} and electronic conductivity. Differential capacity (dQ/dV) and electrochemical impedance spectroscopy (EIS) measurements reveal that the double coating layer effectively suppresses the increase of the electrode

  8. Self-activation of cellulose: A new preparation methodology for activated carbon electrodes in electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Bommier, Clement; Xu, Rui; Wang, Wei; Wang, Xingfeng; Wen, David; Lu, Jun; Ji, Xiulei

    2015-04-01

    Current synthetic methods of biomass-derived activated carbon call for a costly chemical or physical activation process. Herein, we report a simple one-step annealing synthesis yielding a high surface area cellulose-derived activated carbon. We discover that simply varying the flow rate of Argon during pyrolysis enables ‘self-activation’ reactions that can tune the specific surface areas of the resulting carbon, ranging from 98 m2/g to values as high as 2600 m2/g. Furthermore, we, for the first time, observe a direct evolution of H2 from the pyrolysis, which gives strong evidence towards an in situ self-activation mechanism. Surprisingly, the obtained activated carbon is a crumbled graphene nanostructure composed of interconnected sheets, making it ideal for use in an electrochemical capacitor. The cellulose-derived nanoporous carbon exhibits a capacitance of 132 F g-1 at 1 A g-1, a performance comparable to the state-of-the-art activated carbons. This work presents a fundamentally new angle to look at the synthesis of activated carbon, and highlights the importance of a controlled inert gas flow rate during synthesis in general, as its contributions can have a very large impact on the final material properties.

  9. High-energy MnO2 nanowire/graphene and graphene asymmetric electrochemical capacitors.

    Science.gov (United States)

    Wu, Zhong-Shuai; Ren, Wencai; Wang, Da-Wei; Li, Feng; Liu, Bilu; Cheng, Hui-Ming

    2010-10-26

    In order to achieve high energy and power densities, we developed a high-voltage asymmetric electrochemical capacitor (EC) based on graphene as negative electrode and a MnO(2) nanowire/graphene composite (MGC) as positive electrode in a neutral aqueous Na(2)SO(4) solution as electrolyte. MGC was prepared by solution-phase assembly of graphene sheets and α-MnO(2) nanowires. Such aqueous electrolyte-based asymmetric ECs can be cycled reversibly in the high-voltage region of 0-2.0 V and exhibit a superior energy density of 30.4 Wh kg(-1), which is much higher than those of symmetric ECs based on graphene//graphene (2.8 Wh kg(-1)) and MGC//MGC (5.2 Wh kg(-1)). Moreover, they present a high power density (5000 W kg(-1) at 7.0 Wh kg(-1)) and acceptable cycling performance of ∼79% retention after 1000 cycles. These findings open up the possibility of graphene-based composites for applications in safe aqueous electrolyte-based high-voltage asymmetric ECs with high energy and power densities.

  10. Disordered carbon negative electrode for electrochemical capacitors and high-rate batteries

    International Nuclear Information System (INIS)

    Ogihara, Nobuhiro; Igarashi, Yoshiyuki; Kamakura, Ayumu; Naoi, Katsuhiko; Kusachi, Yuki; Utsugi, Koji

    2006-01-01

    In order to understand the properties of high-rate capability and cycleability for a disordered carbon negative electrode in LiPF 6 /PC based electrolyte solution, the cell performance tests with various rates and depth of discharges (DODs) has been studied by spectroscopic and electrochemical analyses. From the charge-discharge measurements, a surface carbon-edge redox reaction occurring between a carbonyl (C edge =O) and a lithium alkoxide (C edge -OLi) that delivers a large capacity was found fast and high cycleability at only shallow DOD (2.0-0.4 V). The limited or shallow charge-discharge cycling utilizing such facile and reversible action of the C edge =O/C edge -OLi of the disordered carbon is suited to an application for an negative electrode of asymmetric hybrid capacitors. A deep DOD discharge (2.0-0.0 V) revealed the existence of some complex processes involving a lithium cluster deposition at pores or microvoids as well as a lithium ion intercalation at graphene layers. The cluster deposition at pores was found to be relatively fast and reproducible. The lithium ion intercalation at graphenes and the subsequent cluster deposition at microvoids were found to be slow and degrade the cycleability after 100 cycles because of the accumulation of a thick and low-ion-conductive solid electrolyte interface (SEI) film on surface

  11. Aqueous based asymmetrical-bipolar electrochemical capacitor with a 2.4 V operating voltage

    Science.gov (United States)

    Wu, Haoran; Lian, Keryn

    2018-02-01

    A novel asymmetrical-bipolar electrochemical capacitor system leveraging the contributions of a Zn-CNT asymmetrical electrode and a KOH-H2SO4 dual-pH electrolyte was developed. The positive and negative electrodes operated in electrolytes with different pH, exploiting the maximum potential of both electrodes, which led to a cell voltage of 2.4 V. The potential tracking of both electrodes revealed that the Zn negative electrode could maintain a potential at -1.2 V, while the CNT positive electrode can be charged to +1.2 V without significant irreversible reactions. A bipolar ion exchange membrane has effectively separated the acid and alkaline from neutralization, which resulted in stable performance of the device with capacitance retention of 94% and coulombic efficiency of 99% over 10,000 cycles. This asymmetrical-bipolar design overcomes the thermodynamic limit of water decomposition, opening a new avenue towards high energy and high power density aqueous-based ECs.

  12. Coating manganese oxide onto graphite electrodes by immersion for electrochemical capacitors

    International Nuclear Information System (INIS)

    Lin, C.-C.; Chen, H.-W.

    2009-01-01

    In this study, manganese oxide was coated on a graphite electrode by immersion. Durations for immersion were varied to control the amount of manganese oxide coated onto the electrode surface. Maximum capacitance of 556 mF cm -2 was obtained in 0.5 M LiCl and with better/superior conditions (immersion time = 80 min and potential scan rate = 10 mV s -1 ). In addition, cyclic voltammograms of the prepared electrode at different potential scan rates exhibited the approximately rectangular and symmetric current-potential characteristics of a capacitor. Furthermore, the chronopotentiometry (CP) charge-discharge curves of the electrode prepared at 80 min of immersion time with a constant current of 1 mA were symmetric and similar isosceles triangles, which demonstrate its high electrochemical reversibility and good stability. Finally, under scanning electron microscope (SEM), the surface of the electrode prepared at 80 min of immersion time and after 1500 cycles of potential cycling revealed that numerously three-dimensional network of macropores appeared on large spherical grains

  13. Double layer dynamics in a collisionless magnetoplasma

    International Nuclear Information System (INIS)

    Iizuka, Satoru; Michelsen, P.; Rasmussen, J.J.; Schrittwieser, R.; Hatakeyama, Rikizo; Saeki, Koichi; Sato, Noriyoshi.

    1985-01-01

    Investigations of double layer dynamics are performed in a Q-machine plasma by applying a positive step potential to a cold end-plate collector. The double layer created at the grounded plasma source just after the pulse is applied propagates towards the collector with the plasma flow speed. Large oscillations occur in the plasma current which is related to a recurring formation and propagation of the double layer. The current is limited during the propagation by a growing negative potential dip formed on the low-potential tail. Similar phenomena appear on the low-potential tail of the stationary double layer formed by applying a potential difference between two plasma sources. (author)

  14. Double layer dynamics in a collisionless magnetoplasma

    DEFF Research Database (Denmark)

    Iizuka, S.; Michelsen, Poul; Juul Rasmussen, Jens

    1985-01-01

    Investigations of double layer dynamics are performed in a Q-machine plasma by applying a positive step potential to a cold end-plate collector. The double layer created at the grounded plasma source just after the pulse is applied propagates towards the collector with the plasma flow speed. Large...... oscillations occur in the plasma current which is related to a recurring formation and propagation of the double layer. The current is limited during the propagation by a growing negative potential dip formed on the low-potential tail. Similar phenomena appear on the low-potential tail of the stationary double...... layer formed by applying a potential difference between two plasma sources...

  15. Numerical simulations on ion acoustic double layers

    International Nuclear Information System (INIS)

    Sato, T.; Okuda, H.

    1980-07-01

    A comprehensive numerical study of ion acoustic double layers has been performed for both periodic as well as for nonperiodic systems by means of one-dimensional particle simulations. For a nonperiodic system, an external battery and a resistance are used to model the magnetospheric convection potential and the ionospheric Pedersen resistance. It is found that the number of double layers and the associated potential buildup across the system increases with the system length

  16. Activated carbon and single-walled carbon nanotube based electrochemical capacitor in 1 M LiPF6 electrolyte

    International Nuclear Information System (INIS)

    Azam, M.A.; Jantan, N.H.; Dorah, N.; Seman, R.N.A.R.; Manaf, N.S.A.; Kudin, T.I.T.; Yahya, M.Z.A.

    2015-01-01

    Highlights: • Activated carbon and single-walled CNT based electrochemical capacitor. • Electrochemical analysis by means of CV, charge/discharge and impedance. • 1 M LiPF 6 non-aqueous solution as an electrolyte. • AC/SWCNT electrode exhibits a maximum capacitance of 60.97 F g −1 . - Abstract: Carbon nanotubes have been extensively studied because of their wide range of potential application such as in nanoscale electric circuits, textiles, transportation, health, and the environment. Carbon nanotubes feature extraordinary properties, such as electrical conductivities higher than those of copper, hardness and thermal conductivity higher than those of diamond, and strength surpassing that of steel, among others. This research focuses on the fabrication of an energy storage device, namely, an electrochemical capacitor, by using carbon materials, i.e., activated carbon and single-walled carbon nanotubes, of a specific weight ratio as electrode materials. The electrolyte functioning as an ion carrier is 1 M lithium hexafluorophosphate. Variations in the electrochemical performance of the device, including its capacitance, charge/discharge characteristics, and impedance, are reported in this paper. The electrode proposed in this work exhibits a maximum capacitance of 60.97 F g −1 at a scan rate of 1 mV s −1

  17. Activated carbon and single-walled carbon nanotube based electrochemical capacitor in 1 M LiPF{sub 6} electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Azam, M.A., E-mail: asyadi@utem.edu.my [Carbon Research Technology Research Group, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka (Malaysia); Jantan, N.H.; Dorah, N.; Seman, R.N.A.R.; Manaf, N.S.A. [Carbon Research Technology Research Group, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka (Malaysia); Kudin, T.I.T. [Ionics Materials & Devices Research Laboratory, Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor (Malaysia); Yahya, M.Z.A. [Ionics Materials & Devices Research Laboratory, Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor (Malaysia); National Defence University of Malaysia, Kem Sungai Besi, 57000 Kuala Lumpur (Malaysia)

    2015-09-15

    Highlights: • Activated carbon and single-walled CNT based electrochemical capacitor. • Electrochemical analysis by means of CV, charge/discharge and impedance. • 1 M LiPF{sub 6} non-aqueous solution as an electrolyte. • AC/SWCNT electrode exhibits a maximum capacitance of 60.97 F g{sup −1}. - Abstract: Carbon nanotubes have been extensively studied because of their wide range of potential application such as in nanoscale electric circuits, textiles, transportation, health, and the environment. Carbon nanotubes feature extraordinary properties, such as electrical conductivities higher than those of copper, hardness and thermal conductivity higher than those of diamond, and strength surpassing that of steel, among others. This research focuses on the fabrication of an energy storage device, namely, an electrochemical capacitor, by using carbon materials, i.e., activated carbon and single-walled carbon nanotubes, of a specific weight ratio as electrode materials. The electrolyte functioning as an ion carrier is 1 M lithium hexafluorophosphate. Variations in the electrochemical performance of the device, including its capacitance, charge/discharge characteristics, and impedance, are reported in this paper. The electrode proposed in this work exhibits a maximum capacitance of 60.97 F g{sup −1} at a scan rate of 1 mV s{sup −1}.

  18. Electroresistance effect in gold thin film induced by ionic-liquid-gated electric double layer

    International Nuclear Information System (INIS)

    Nakayama, Hiroyasu; Ohtani, Takashi; Fujikawa, Yasunori; Ando, Kazuya; Saitoh, Eiji; Ye, Jianting; Iwasa, Yoshihiro

    2012-01-01

    Electroresistance effect was detected in a metallic thin film using ionic-liquid-gated electric-double-layer transistors (EDLTs). We observed reversible modulation of the electric resistance of a Au thin film. In this system, we found that an electric double layer works as a nanogap capacitor with 27 (-25) MV cm -1 of electric field by applying only 1.7 V of positive (negative) gate voltage. The experimental results indicate that the ionic-liquid-gated EDLT technique can be used for controlling the surface electronic states on metallic systems. (author)

  19. Anomalous or regular capacitance? The influence of pore size dispersity on double-layer formation

    Science.gov (United States)

    Jäckel, N.; Rodner, M.; Schreiber, A.; Jeongwook, J.; Zeiger, M.; Aslan, M.; Weingarth, D.; Presser, V.

    2016-09-01

    The energy storage mechanism of electric double-layer capacitors is governed by ion electrosorption at the electrode surface. This process requires high surface area electrodes, typically highly porous carbons. In common organic electrolytes, bare ion sizes are below one nanometer but they are larger when we consider their solvation shell. In contrast, ionic liquid electrolytes are free of solvent molecules, but cation-anion coordination requires special consideration. By matching pore size and ion size, two seemingly conflicting views have emerged: either an increase in specific capacitance with smaller pore size or a constant capacitance contribution of all micro- and mesopores. In our work, we revisit this issue by using a comprehensive set of electrochemical data and a pore size incremental analysis to identify the influence of certain ranges in the pore size distribution to the ion electrosorption capacity. We see a difference in solvation of ions in organic electrolytes depending on the applied voltage and a cation-anion interaction of ionic liquids in nanometer sized pores.

  20. Influence of the charge double layer on solid oxide fuel cell stack behavior

    Science.gov (United States)

    Whiston, Michael M.; Bilec, Melissa M.; Schaefer, Laura A.

    2015-10-01

    While the charge double layer effect has traditionally been characterized as a millisecond phenomenon, longer timescales may be possible under certain operating conditions. This study simulates the dynamic response of a previously developed solid oxide fuel cell (SOFC) stack model that incorporates the charge double layer via an equivalent circuit. The model is simulated under step load changes. Baseline conditions are first defined, followed by consideration of minor and major deviations from the baseline case. This study also investigates the behavior of the SOFC stack with a relatively large double layer capacitance value, as well as operation of the SOFC stack under proportional-integral (PI) control. Results indicate that the presence of the charge double layer influences the SOFC stack's settling time significantly under the following conditions: (i) activation and concentration polarizations are significantly increased, or (ii) a large value of the double layer capacitance is assumed. Under normal (baseline) operation, on the other hand, the charge double layer effect diminishes within milliseconds, as expected. It seems reasonable, then, to neglect the charge double layer under normal operation. However, careful consideration should be given to potential variations in operation or material properties that may give rise to longer electrochemical settling times.

  1. Capacitor with a composite carbon foam electrode

    Science.gov (United States)

    Mayer, Steven T.; Pekala, Richard W.; Kaschmitter, James L.

    1999-01-01

    Carbon aerogels used as a binder for granularized materials, including other forms of carbon and metal additives, are cast onto carbon or metal fiber substrates to form composite carbon thin film sheets. The thin film sheets are utilized in electrochemical energy storage applications, such as electrochemical double layer capacitors (aerocapacitors), lithium based battery insertion electrodes, fuel cell electrodes, and electrocapacitive deionization electrodes. The composite carbon foam may be formed by prior known processes, but with the solid partides being added during the liquid phase of the process, i.e. prior to gelation. The other forms of carbon may include carbon microspheres, carbon powder, carbon aerogel powder or particles, graphite carbons. Metal and/or carbon fibers may be added for increased conductivity. The choice of materials and fibers will depend on the electrolyte used and the relative trade off of system resistivity and power to system energy.

  2. Post-modification by γ-radiation of VDF-based polymers: Electrochemical capacitor membrane application

    International Nuclear Information System (INIS)

    Dumas, L.

    2012-01-01

    This work deals with the modification of VDF-based polymer induced by γ-radiation as the polymer may be used in electrochemical super-capacitors. The main objective was to limit the swelling of the fluorinated matrix with a given electrolyte while a good wetting of the polymer by the liquid was also required. As the main basic process involved in polymer radiolysis is the formation of radicals, a part of the work was dedicated to the study of such species by using Electron Spin Resonance spectroscopy. A simulation model of ESR spectra was established in order to identify and quantify each radical species. The effect of several parameters such as radiation dose, annealing time or the nature of polymer matrix on the concentration of each species where investigated. A relation with the evolution of the crosslink density of the network formed during the radiolysis was proposed. In addition, one of the key steps of this work was to study the radiation crosslinking ability of VDF-based polymers and find a way to increase the crosslink density. This was achieved by incorporating, prior to the radiation process, a radiation sensitive cross linker: TAIC. Finally, a new strategy based on the modification of surface properties of PVDF was investigated. It consists in the radiation grafting of penta-fluor-styrene onto PVDF surface followed by the chemo-selective functionalization of the grafted segments. As a conclusion, the different approaches used in this thesis allowed us to understand the radiolysis of VDF-based polymers and take advantage of the elementary process involved in this type of chemistry, to build up robust and promising strategies for tuning properties. (author)

  3. Solution-Processed Graphene/MnO 2 Nanostructured Textiles for High-Performance Electrochemical Capacitors

    KAUST Repository

    Yu, Guihua

    2011-07-13

    Large scale energy storage system with low cost, high power, and long cycle life is crucial for addressing the energy problem when connected with renewable energy production. To realize grid-scale applications of the energy storage devices, there remain several key issues including the development of low-cost, high-performance materials that are environmentally friendly and compatible with low-temperature and large-scale processing. In this report, we demonstrate that solution-exfoliated graphene nanosheets (∼5 nm thickness) can be conformably coated from solution on three-dimensional, porous textiles support structures for high loading of active electrode materials and to facilitate the access of electrolytes to those materials. With further controlled electrodeposition of pseudocapacitive MnO2 nanomaterials, the hybrid graphene/MnO2-based textile yields high-capacitance performance with specific capacitance up to 315 F/g achieved. Moreover, we have successfully fabricated asymmetric electrochemical capacitors with graphene/MnO 2-textile as the positive electrode and single-walled carbon nanotubes (SWNTs)-textile as the negative electrode in an aqueous Na 2SO4 electrolyte solution. These devices exhibit promising characteristics with a maximum power density of 110 kW/kg, an energy density of 12.5 Wh/kg, and excellent cycling performance of ∼95% capacitance retention over 5000 cycles. Such low-cost, high-performance energy textiles based on solution-processed graphene/MnO2 hierarchical nanostructures offer great promise in large-scale energy storage device applications. © 2011 American Chemical Society.

  4. Cauliflower-derived porous carbon without activation for electrochemical capacitor and CO2 capture applications

    Science.gov (United States)

    Du, Juan; Yu, Yifeng; Lv, Haijun; Chen, Chunlin; Zhang, Jian; Chen, Aibing

    2018-01-01

    Carbon materials have attracted great attention in CO2 capture and energy storage due to their excellent characteristics such as tunable pore structure, modulated surface properties and superior bulk conductivities, etc. Biomass, provided by nature with non-toxic, widespread, abundant, and sustainable advantages, is considered to be a very promising precursor of carbons for the view of economic, environmental, and societal issues. However, the preparation of high-performance biomass-derived carbons is still a big challenge because of the multistep process for their synthesis and subsequent activation. Herein, hierarchically porous structured carbon materials have been prepared by directly carbonizing dried cauliflowers without any addition of agents and activation process, featuring with large specific surface area, hierarchically porous structure and improved pore volume, as well as suitable nitrogen content. Being used as a solid-state CO2 adsorbent, the obtained product exhibited a high CO2 adsorption capacity of 3.1 mmol g-1 under 1 bar and 25 °C and a remarkable reusability of 96.7% retention after 20 adsorption/regeneration cycles. Our study reveals that choosing a good biomass source was significant as the unique structure of precursor endows the carbonized product with abundant pores without the need of any post-treatment. Used as an electrode material in electrochemical capacitor, the non-activated porous carbon displayed a fairly high specific capacitance of 228.9 F g-1 at 0.5 A g-1 and an outstanding stability of 99.2% retention after 5000 cycles at 5 A g-1. [Figure not available: see fulltext.

  5. α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials.

    Science.gov (United States)

    Lee, K K; Deng, S; Fan, H M; Mhaisalkar, S; Tan, H R; Tok, E S; Loh, K P; Chin, W S; Sow, C H

    2012-04-28

    We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes. This journal is © The Royal Society of Chemistry 2012

  6. Experiments on ion acoustic typed double layers

    International Nuclear Information System (INIS)

    Chan, C.; Cho, M.H.; Intrator, T.; Hershkowitz, N.

    1984-01-01

    The formation of small amplitude double layers with potential drops the order of the electron temperature, was examined experimentally by pulsing a grid and thereby changing the electron drift across the target chamber of a triple plasma device. The rarefactive part of a long wavelength, low frequency ion wave grew in amplitude due to the presence of slowly drifting electrons. The corresponding current limitation led to the formation of the double layers. Depending on the plasma conditions, the asymmetric double layers either transform into a weak monotonic layer, a propagating shock, or a series of rarefactive solitary pulses. The rarefactive pulses propagate with Mach number less than one and resemble solitary plasma holes with density cavities in both the electron and the ion density profiles

  7. Self-Assembled Nanorod Structures on Nanofibers for Textile Electrochemical Capacitor Electrodes with Intrinsic Tactile Sensing Capabilities.

    Science.gov (United States)

    Shi, HaoTian H; Khalili, Nazanin; Morrison, Taylor; Naguib, Hani E

    2018-05-21

    A novel polyaniline nanorod (PAniNR) three-dimensional structure was successfully grown on flexible polyacrylonitrile (PAN) nanofiber substrate as the electrode material for electrochemical capacitors (ECs), constructed via self-stabilized dispersion polymerization process. The electrode offered desired mechanical properties such as flexibility and bendability, whereas it maintained optimal electrochemical characteristics. The electrode and the assembled EC cell also achieved intrinsic piezoresistive sensing properties, leading to real-time monitoring of excess mechanical pressure and bending during cell operations. The PAniNR@PAN electrodes show an average diameter of 173.6 nm, with the PAniNR growth of 50.7 nm in length. Compared to the electrodes made from pristine PAni, the gravimetric capacitance increased by 39.8% to 629.6 F/g with aqueous acidic electrolyte. The electrode and the assembled EC cell with gel electrolyte were responsive to tensile, compressive, and bending stresses with a sensitivity of 0.95 MPa -1 .

  8. Correlation among physical and electrochemical behaviour of nanostructured electrolytic manganese dioxide from leach liquor and synthetic for aqueous asymmetric capacitor.

    Science.gov (United States)

    Minakshi Sundaram, Manickam; Biswal, Avijit; Mitchell, David; Jones, Rob; Fernandez, Carlos

    2016-02-14

    An attempt has been made to correlate the differences in structural parameters, surface areas, morphology etc. with the electrochemical capacitive behaviour of the EMDs. The nanostructured electrolytic manganese dioxides (EMD) have been synthesized through electrodepositing MnO2 from two different leach liquors and a synthetic analogue thereof. The structural and chemical state was determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) respectively. Multiplet structure determination led to estimates of the manganese valence states present in the EMD. The EMDs have been tested in an asymmetric capacitor which we have developed. This used activated carbon as the negative electrode and the various EMDs as the positive electrode. Aqueous 2 M NaOH solution was used as the electrolyte. The capacitor achieved 1.6 V corresponding to a capacitance of ∼50 F g(-1) of the EMDs from leach liquors. The EMD derived from the synthetic solution showed an inferior capacitance of 25 F g(-1). Extended cycling (2000 cycles), showed 100% capacity retention was achieved for one EMD produced from the leach liquor derived from low-grade manganese ore/residue. This outstanding capacitor performance was correlated with the presence of a nanofibrous morphology. These findings open up the possibility of extracting a high performance EMD product from a low cost, low-grade source of manganese.

  9. Electric double layer capacitance on hierarchical porous carbons in an organic electrolyte

    OpenAIRE

    Yamada, Hirotoshi; Moriguchi, Isamu; Kudo, Tetsuichi

    2008-01-01

    Nanoporous carbons were prepared by using colloidal crystal as a template. Nitrogen adsorption/desorption isotherms and transmission electron microscope images revealed that the porous carbons exhibit hierarchical porous structures with meso/macropores and micropores. Electric double layer capacitor performance of the porous carbons was investigated in an organic electrolyte of 1 M LiClO4 in propylene carbonate and dimethoxy ethane. The hierarchical porous carbons exhibited large specific dou...

  10. Mesoporous Carbon Design for Ionic Liquid-Based, Double-Layer Supercapacitors

    OpenAIRE

    2010-01-01

    Abstract The use of pyrrolidinium-based ionic liquids (ILs) in asymmetric electric double-layer capacitors (AEDLC) with positive and negative carbon electrodes of different weight is a powerful strategy for developing safe, high specific-energy supercapacitors operating at > 3.5 V. The preparation and characterization of ordered (OTC) and disordered (DTC) template carbons, the latter obtained by a fast and low-cost method, are reported. The porosity and capacitance features of the ...

  11. Progress in MOSFET double-layer metalization

    Science.gov (United States)

    Gassaway, J. D.; Trotter, J. D.; Wade, T. E.

    1980-01-01

    Report describes one-year research effort in VLSL fabrication. Four activities are described: theoretical study of two-dimensional diffusion in SOS (silicon-on-sapphire); setup of sputtering system, furnaces, and photolithography equipment; experiments on double layer metal; and investigation of two-dimensional modeling of MOSFET's (metal-oxide-semiconductor field-effect transistors).

  12. Pseudo-Capacitors: SPPS Deposition and Electrochemical Analysis of α-MoO3 and Mo2N Coatings

    Science.gov (United States)

    Golozar, Mehdi; Chien, Ken; Lian, Keryn; Coyle, Thomas W.

    2013-06-01

    Solution precursor plasma spraying (SPPS) is a novel thermal spray process in which a solution precursor is injected into the high-temperature zone of a DC-arc plasma jet to allow solvent evaporation from the precursor droplets, solute precipitation, and precipitate pyrolysis prior to substrate impact. This investigation explored the potential of SPPS to fabricate α-MoO3 coatings with fine grain sizes, high porosity levels, and high surface area: characteristics needed for application as pseudo-capacitor electrodes. Since molybdenum nitride has shown a larger electrochemical stability window and higher specific area capacitance, the α-MoO3 deposits were subsequently converted into molybdenum nitride. A multistep heat-treatment procedure resulted in a topotactic phase-transformation mechanism, which retained the high surface area lath-shaped features of the original α-MoO3. The electrochemical behaviors of molybdenum oxide and molybdenum nitride deposits formed under different deposition conditions were studied using cyclic voltammetry to assess the influence of the resulting microstructure on the charge storage behavior and potential for use in pseudo-capacitors.

  13. Ionic diffusion in the double layer at model electrode/molten salt interfaces

    International Nuclear Information System (INIS)

    Tankeshwar, K.; Tosi, M.P.

    1991-08-01

    The anisotropic ionic diffusion coefficients in model electrochemical cells in the molten-salt regime for the electrolyte are evaluated from the ionic density profiles reported in simulation work of Grout and coworkers. A local description of the diffusion processes for counterions and coions in the electrical double layer is obtained from the data. (author). 10 refs, 1 fig., 1 tab

  14. Carbon-Based Fibrous EDLC Capacitors and Supercapacitors

    Directory of Open Access Journals (Sweden)

    C. Lekakou

    2011-01-01

    Full Text Available This paper investigates electrochemical double-layer capacitors (EDLCs including two alternative types of carbon-based fibrous electrodes, a carbon fibre woven fabric (CWF and a multiwall carbon nanotube (CNT electrode, as well as hybrid CWF-CNT electrodes. Two types of separator membranes were also considered. An organic gel electrolyte PEO-LiCIO4-EC-THF was used to maintain a high working voltage. The capacitor cells were tested in cyclic voltammetry, charge-discharge, and impedance tests. The best separator was a glass fibre-fine pore filter. The carbon woven fabric electrode and the corresponding supercapacitor exhibited superior performance per unit area, whereas the multiwall carbon nanotube electrode and corresponding supercapacitor demonstrated excellent specific properties. The hybrid CWF-CNT electrodes did not show a combined improved performance due to the lack of carbon nanotube penetration into the carbon fibre fabric.

  15. Solvothermal Synthesis of Fe2O3 Loaded Activated Carbon as Electrode Materials for High-performance Electrochemical Capacitors

    International Nuclear Information System (INIS)

    Li, Ying; Kang, Litao; Bai, Gailing; Li, Peiyang; Deng, Jiachun; Liu, Xuguang; Yang, Yongzhen; Gao, Feng; Liang, Wei

    2014-01-01

    This article describes a facile solvothermal synthesis method to prepare Fe 2 O 3 /AC composites for electrochemical capacitors from Iron (III) chloride hexahydrate (FeCl 3 ·6H 2 O), activated carbon (AC, from petroleum coke), and four different precipitants (i.e., NaOH, CH 3 COONa, HMT, CO(NH 2 ) 2 ). X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Thermogravimetric (TG) analysis show that the products consisted of nanosized α-Fe 2 O 3 (weight ratios: 48.1, 47.9, 44.2, 44.3%) loaded onto AC particles (∼ 20 μm). Significantly, both kind and dosage of precipitants exhibit effects on the specific capacitances of Fe 2 O 3 /AC composites. The highest specific capacitance reaches up to 240 F g −1 (at a current density of 1 A g −1 in 6 M KOH aqueous electrolyte) when the molar ratio of CH 3 COONa: FeCl 3 is 9. On the other hand, the sample prepared with NaOH: FeCl 3 molar ratio being 1.5 exhibits excellent rate capability with specific capacitance of 215 F g −1 at 1 A g −1 , and 89.3, 82.3, 78.1, 72.6 and 65.1% capacity retention at 2, 5, 10, 20, and 40 A g −1 , respectively. These electrochemical performances are superior to other materials consisted of Fe 2 O 3 /carbon nanotube (CNT), graphene oxide (GO) or reduced graphene oxide (rGO) composites, demonstrating the great potential of Fe 2 O 3 /AC composites in the development of high-performance electrode materials for electrochemical capacitors

  16. An Electrochemical Capacitor with Applicable Energy Density of 7.4 Wh/kg at Average Power Density of 3000 W/kg.

    Science.gov (United States)

    Zhai, Teng; Lu, Xihong; Wang, Hanyu; Wang, Gongming; Mathis, Tyler; Liu, Tianyu; Li, Cheng; Tong, Yexiang; Li, Yat

    2015-05-13

    Electrochemical capacitors represent a new class of charge storage devices that can simultaneously achieve high energy density and high power density. Previous reports have been primarily focused on the development of high performance capacitor electrodes. Although these electrodes have achieved excellent specific capacitance based on per unit mass of active materials, the gravimetric energy densities calculated based on the weight of entire capacitor device were fairly small. This is mainly due to the large mass ratio between current collector and active material. We aimed to address this issue by a 2-fold approach of minimizing the mass of current collector and increasing the electrode performance. Here we report an electrochemical capacitor using 3D graphene hollow structure as current collector, vanadium sulfide and manganese oxide as anode and cathode materials, respectively. 3D graphene hollow structure provides a lightweight and highly conductive scaffold for deposition of pseudocapacitive materials. The device achieves an excellent active material ratio of 24%. Significantly, it delivers a remarkable energy density of 7.4 Wh/kg (based on the weight of entire device) at the average power density of 3000 W/kg. This is the highest gravimetric energy density reported for asymmetric electrochemical capacitors at such a high power density.

  17. Double layers are not particle accelerators

    International Nuclear Information System (INIS)

    Bryant, D.A.; Bingham, R.; Angelis, U. de.

    1991-02-01

    It is pointed out that the continuing advocacy of electrostatic double layers as particle accelerators in the aurora and other space and astrophysical plasmas is fundamentally unsound. It is suggested furthermore that there is little reason to invoke static or quasi-static electric fields as the cause of auroral electron acceleration. Stochastic acceleration by electrostatic wave turbulence appears to present a natural explanation for this and for electron acceleration in other space and astrophysical plasmas. (author)

  18. Double layers, waves and particle acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Bryant, D.A.; Perry, C.H.; Bingham, R.; de Angelis, U.

    1993-09-01

    The author's conclusions that static potential differences, including those associated with double layers, could not be the cause of auroral electron acceleration, and that resonance with electrostatic wave turbulence provided a possible mechanism were dismissed in a recent publication as being totally incorrect. In this reply, the author finds the criticism to be built upon a number of misconceptions and factual errors which render it invalid. He is, therefore, able to re-affirm his earlier conclusions.

  19. Multiferroic properties of BiFeO3/Bi4Ti3O12 double-layered thin films fabricated by chemical solution deposition

    International Nuclear Information System (INIS)

    Yi, Seung Woo; Kim, Sang Su; Kim, Jin Won; Jo, Hyun Kyung; Do, Dalhyun; Kim, Won-Jeong

    2009-01-01

    Multiferroic BiFeO 3 /Bi 4 Ti 3 O 12 (BFO/BTO) double-layered film was fabricated on a Pt(111)/Ti/SiO 2 /Si(100) substrate by a chemical solution deposition method. The effect of an interfacial BTO layer on electrical and magnetic properties of BFO was investigated by comparing those of pure BFO and BTO films prepared by the same condition. The X-ray diffraction result showed that no additional phase was formed in the double-layered film, except BFO and BTO phases. The remnant polarization (2P r ) of the double-layered film capacitor was 100 μC/cm 2 at 250 kV/cm, which is much larger than that of the pure BFO film capacitor. The magnetization-magnetic field hysteresis loop revealed weak ferromagnetic response with remnant magnetization (2M r ) of 0.4 kA/m. The values of dielectric constant and dielectric loss of the double-layered film capacitor were 240 and 0.03 at 100 kHz, respectively. Leakage current density measured from the double-layered film capacitor was 6.1 x 10 -7 A/cm 2 at 50 kV/cm, which is lower than the pure BFO and BTO film capacitors.

  20. Effect of the capacity design of activated carbon cathode on the electrochemical performance of lithium-ion capacitors

    International Nuclear Information System (INIS)

    Shi, Zhiqiang; Zhang, Jin; Wang, Jing; Shi, Jingli; Wang, Chengyang

    2015-01-01

    Highlights: • MCMB with the optimal pre-lithiation capacity as negative electrode in LIC. • The capacity design of cathode affects the electrochemical performance of LIC. • The optimal designed capacity of positive electrode has been proposed. - ABSTRACT: Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated mesocarbon microbeads (MCMB) anode. The effect of AC cathode capacity design on the electrochemical performance of LIC is investigated by the galvanostatic charging-discharging and electrochemical impedance tests. As the designed capacity of AC positive electrode is lower than 50 mAh g −1 , the working potential of negative electrode is always in the low and stable plateau, which is conductive to the sufficient utilization and the working potential stability of positive electrode. When the designed capacity of positive electrode is higher than 50 mAh g −1 , the instability of negative electrode directly causes the reduced utilization and shortened working potential range of the positive electrode, which is responsible for the capacity attenuation and cycle performance deterioration of LIC. The positive electrode capacity design can realize the optimization of electrochemical performance of LIC. LIC50 exhibits the optimal electrochemical performance, high energy density up to 92.3 Wh kg −1 and power density as high as 5.5 kW kg −1 (based on active material mass of two electrodes), excellent capacity retention of 97.0 % after 1000 cycles. The power density and cycle performance of LIC can be further improved by reducing the AC positive electrode designed capacity

  1. Effect of pre-lithiation degrees of mesocarbon microbeads anode on the electrochemical performance of lithium-ion capacitors

    International Nuclear Information System (INIS)

    Zhang, Jin; Shi, Zhiqiang; Wang, Chengyang

    2014-01-01

    Highlights: • MCMB with different pre-lithiation capacity as negative electrode in LIC. • Pre-lithiation improves the electrochemical performance of LIC. • The optimal pre-lithiation capacity has been proposed. - Abstract: Lithium ion capacitors are assembled with pre-lithiated mesocarbon microbeads (LMCMB) anode and activated carbon (AC) cathode. The effect of pre-lithiation degrees on the crystal structure of MCMB electrode and the electrochemical capacitance behavior of LIC are investigated by X-ray diffraction (XRD) and the charge-discharge test of three-electrode cell. The structure of graphite still maintained when the pre-lithiation capacity is less than 200 mAh g −1 , phase transition takes place with the increase of pre-lithiation capacity from 250 mAh g −1 to 350 mAh g −1 . Pre-lithiation degrees of MCMB anode greatly affect the charge-discharge process and behavior, which impact on the electrochemical performance of LIC. The LIC with pre-lithiation capacity of 300 mAh g −1 has the optimal electrochemical performance. The energy density of LIC300 is up to 92.3 Wh kg −1 , the power density as high as 5.5 kW kg −1 and the capacity retention is 97.0% after 1000 cycles. The excellent electrochemical performance benefits from the appropriate pre-lithiation capacity of negative electrode. The appropriate pre-lithiation ensures the working voltage of negative electrode in low and relative stable charge-discharge platform corresponding to the mutual phase transition from the second stage graphite intercalation compound (LiC 12 ) to the first stage graphite intercalation compound (LiC 6 ). The stable charge-discharge platform of negative electrode is conductive to the sufficient utilization of AC positive electrode

  2. Self-Assembled α-Fe2O3 mesocrystals/graphene nanohybrid for enhanced electrochemical capacitors.

    Science.gov (United States)

    Yang, Shuhua; Song, Xuefeng; Zhang, Peng; Sun, Jing; Gao, Lian

    2014-06-12

    Self-assembled α-Fe2O3 mesocrystals/graphene nanohybrids have been successfully synthesized and have a unique mesocrystal porous structure, a large specific surface area, and high conductivity. Mesocrystal structures have recently attracted unparalleled attention owing to their promising application in energy storage as electrochemical capacitors. However, mesocrystal/graphene nanohybrids and their growth mechanism have not been clearly investigated. Here we show a facile fabrication of short rod-like α-Fe2O3 mesocrystals/graphene nanohybrids by self-assembly of FeOOH nanorods as the primary building blocks on graphene under hydrothermal conditions, accompanied and promoted by concomitant phase transition from FeOOH to α-Fe2O3. A systematic study of the formation mechanism is also presented. The galvanostatic charge/discharge curve shows a superior specific capacitance of the as-prepared α-Fe2O3 mesocrystals/graphene nanohybrid (based on total mass of active materials), which is 306.9 F g(-1) at 3 A g(-1) in the aqueous electrolyte under voltage ranges of up to 1 V. The nanohybrid with unique sufficient porous structure and high electrical conductivity allows for effective ion and charge transport in the whole electrode. Even at a high discharge current density of 10 A g(-1), the enhanced ion and charge transport still yields a higher capacitance (98.2 F g(-1)), exhibiting enhanced rate capability. The α-Fe2O3 mesocrystal/graphene nanohybrid electrode also demonstrates excellent cyclic performance, which is superior to previously reported graphene-based hematite electrode, suggesting it is highly stable as an electrochemical capacitor. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Electrochemically induced transformation of NiS nanoparticles into Ni(OH)2 in KOH aqueous solution toward electrochemical capacitors

    International Nuclear Information System (INIS)

    Hou Linrui; Yuan Changzhou; Li Diankai; Yang Long; Shen Laifa; Zhang Fang; Zhang Xiaogang

    2011-01-01

    Highlights: → NiS is synthesized by means of the H 2 O/CS 2 interface under hydrothermal treatment. → NiS itself owns poor electrochemical capacitance in 2 M KOH solution. → NiS is electrochemically induced and transformed into electroactive Ni(OH) 2 . → Ni(OH) 2 is responsible for good energy storage of the NiS in the KOH solution. → The new formed Ni(OH) 2 delivers large energy density at high rates. - Abstract: Nickel sulfide nanoparticles (NPs) are first synthesized by virtue of a unique H 2 O/CS 2 interface under mild hydrothermal treatment. Electrochemical data reveals that the as-synthesized NiS NPs themselves own poor supercapacitive behavior at initial cyclic voltammetry (CV) cycles in 2 M KOH solution, while a specific capacitance of 893 F g -1 can be surprisingly obtained at a current density of 5 A g -1 just after continuous 320 CV cycles. X-ray diffraction and Fourier transform infrared techniques demonstrate that what is really responsible for the good electrochemical capacitance in the KOH aqueous solution is the new electrochemically formed Ni(OH) 2 phase, rather than NiS NPs themselves. The Ni(OH) 2 is slowly formed during the continuous CV cycling process, in which the electrochemically induced phase transformation from NiS to Ni(OH) 2 phase takes place. Furthermore, the new Ni(OH) 2 phase demonstrates the great ability of delivering large specific capacitance at high rates.

  4. Alternating current line-filter based on electrochemical capacitor utilizing template-patterned graphene

    OpenAIRE

    Zhenkun Wu; Liyi Li; Ziyin Lin; Bo Song; Zhuo Li; Kyoung-Sik Moon; Ching-Ping Wong; Shu-Lin Bai

    2015-01-01

    Aluminum electrolytic capacitors (AECs) are widely used for alternating current (ac) line-filtering. However, their bulky size is becoming more and more incompatible with the rapid development of portable electronics. Here we report a scalable process to fabricate miniaturized graphene-based ac line-filters on flexible substrates at room temperature. In this work, graphene oxide (GO) is reduced by patterned metal interdigits at room temperature and used directly as the electrode material. The...

  5. Some dynamical properties of very strong double layers in a triple plasma device

    International Nuclear Information System (INIS)

    Carpenter, T.; Torven, S.

    1987-01-01

    Experimental results on three dynamic properties of very strong double layers observed in a triple plasma device are presented. First, it is observed that when an inductance of sufficient size is inserted in series with the external bias supply used to produce the double layer, disruptions in the plasma current occur accompanied by disruptions in the double layer potential. Second, it is observed that with all external reactances reduced as much as possible, a sort of jitter-motion occurs in the position of the double layer around its equilibrium position. Third, when the external bias supply is pulsed, the initial potential distribution is observed to have an essentially uniform slope, as in the case of a vacuum capacitor. The disruption phenomenon may be explained in terms of the behavior of the potential structure as a function of the bias voltage and this explanation is discussed along with the experimental evidence for its validity. A comparable understanding of the other two phenomena has not been achieved, but in both cases there are qualitative difference between the behavior reported here and what has been observed in Q-machines and these difference are discussed. (author)

  6. Numerical double layer solutions with ionization

    International Nuclear Information System (INIS)

    Andersson, D.; Soerensen, J.

    1982-08-01

    Maxwell's equation div D = ro in one dimension is solved numerically, taking ionization into account. Time independent anode sheath and double layer solutions are obtained. By varying voltage, neutral gas pressure, temperature of the trapped ions on the cathode side and density and temperature of the trapped electrones on the anode side, diagrams are constructed that show permissible combinations of these parameters. Results from a recent experiment form a subset. Distribution functions, the Langmuir condition, some scaling laws and a possible application to the lower ionosphere are discussed. (Authors)

  7. Equilibrium double layers in extended Pierce diodes

    International Nuclear Information System (INIS)

    Ciubotariu-Jassy, C.I.

    1992-01-01

    The extended Pierce diode is similar to the standard (or classical) Pierce diode, but has passive circuit elements in place of the short circuit between the electrodes. This device is important as an approximation to real bounded plasma systems. It consists of two parallel plane electrodes (an emitter located at x=0 and a collector located at x=l) and a collisionless cold electron beam travelling between them. The electrons are neutralized by a background of comoving massive ions. This situation is analysed in this paper and new equilibrium double layer (DL) plasma structures are obtained. (author) 6 refs., 3 figs

  8. Studies on Me/Al-layered double hydroxides (Me = Ni and Co) as electrode materials for electrochemical capacitors

    International Nuclear Information System (INIS)

    Liu Xianming; Zhang Yihe; Zhang Xiaogang; Fu Shaoyun

    2004-01-01

    Me/Al-layered double hydroxides (Me=Ni and Co) prepared by the chemical co-precipitation method have been shown to be outstanding novel materials for electrochemical capacitors. The crystalline structure and the electrochemical properties of the electrodes have been studied by considering the effect of the mole ratio of nickel/cobalt. X-ray diffraction analysis shows that the materials belong to hexagonal system with layered structure. Cyclic voltammetric measurements indicate that Me/Al-layered double hydroxides with the Ni/Co mole ratio of 4:6 exhibit excellent capacitive properties within the potential range of 0.0-0.6 V versus Hg/HgO in 6 mol/L KOH electrolyte. Charge/discharge behaviors have been observed with the highest specific capacitance values of 960 F/g at the current density of 400 mA/g. Impedance studies show that the enhanced electrical properties and high frequency response are attributed to the presence of Co oxides

  9. Alternating current line-filter based on electrochemical capacitor utilizing template-patterned graphene.

    Science.gov (United States)

    Wu, Zhenkun; Li, Liyi; Lin, Ziyin; Song, Bo; Li, Zhuo; Moon, Kyoung-Sik; Wong, Ching-Ping; Bai, Shu-Lin

    2015-06-17

    Aluminum electrolytic capacitors (AECs) are widely used for alternating current (ac) line-filtering. However, their bulky size is becoming more and more incompatible with the rapid development of portable electronics. Here we report a scalable process to fabricate miniaturized graphene-based ac line-filters on flexible substrates at room temperature. In this work, graphene oxide (GO) is reduced by patterned metal interdigits at room temperature and used directly as the electrode material. The as-fabricated device shows a phase angle of -75.4° at 120 Hz with a specific capacitance of 316 µF/cm(2) and a RC time constant of 0.35 ms. In addition, it retains 97.2% of the initial capacitance after 10000 charge/discharge cycles. These outstanding performance characteristics of our device demonstrate its promising to replace the conventional AECs for ac line filtering.

  10. Ultrastrong Stationary Double Layers in a Nondischarge Magnetoplasma

    DEFF Research Database (Denmark)

    Sato, N.; Hatakeyama, R.; Iizuka, S.

    1981-01-01

    Ultrastrong stationary double layers are generated in a magnetoplasma by simply applying potential differences between two plasma sources. The potential drop ϕD of the double layer is increased up to eϕD/Te≃2×103 (Te is the electron temperature in eV) with no difficulties caused by gas discharge....... There are always large spiky fluctuations on the low-potential tail of the double layers....

  11. Double layer formed by beam driven ion-acoustic turbulence

    International Nuclear Information System (INIS)

    Ludwig, G.O.; Ferreira, J.L.; Montes, A.

    1987-08-01

    Small amplitudes steady-state ion-acoustic double layers are observed to form in a plasma transversed by a beam of cold electrons. The importance of turbulence in maintaining the double layer is demonstrated. The measured wave spectrum is in approximate agreement with models deriveted from renornalized turbulence theory. The general features of the double layer are compared with results from particle simulation studies. (author) [pt

  12. Short-term memory of TiO2-based electrochemical capacitors: empirical analysis with adoption of a sliding threshold

    International Nuclear Information System (INIS)

    Lim, Hyungkwang; Kim, Inho; Kim, Jin-Sang; Jeong, Doo Seok; Seong Hwang, Cheol

    2013-01-01

    Chemical synapses are important components of the large-scaled neural network in the hippocampus of the mammalian brain, and a change in their weight is thought to be in charge of learning and memory. Thus, the realization of artificial chemical synapses is of crucial importance in achieving artificial neural networks emulating the brain’s functionalities to some extent. This kind of research is often referred to as neuromorphic engineering. In this study, we report short-term memory behaviours of electrochemical capacitors (ECs) utilizing TiO 2 mixed ionic–electronic conductor and various reactive electrode materials e.g. Ti, Ni, and Cr. By experiments, it turned out that the potentiation behaviours did not represent unlimited growth of synaptic weight. Instead, the behaviours exhibited limited synaptic weight growth that can be understood by means of an empirical equation similar to the Bienenstock–Cooper–Munro rule, employing a sliding threshold. The observed potentiation behaviours were analysed using the empirical equation and the differences between the different ECs were parameterized. (paper)

  13. Pomelo peels-derived porous activated carbon microsheets dual-doped with nitrogen and phosphorus for high performance electrochemical capacitors

    Science.gov (United States)

    Wang, Zhen; Tan, Yongtao; Yang, Yunlong; Zhao, Xiaoning; Liu, Ying; Niu, Lengyuan; Tichnell, Brandon; Kong, Lingbin; Kang, Long; Liu, Zhen; Ran, Fen

    2018-02-01

    In this work, biomass pomelo peel is used to fabricate the porous activated carbon microsheets, and diammonium hydrogen phosphate (DHP) is employed to dual-dope carbon with nitrogen and phosphorus elements. With the benefit of DHP inducement and dual-doping of nitrogen and phosphorus, the prepared carbon material has a higher carbon yield, and exhibits higher specific surface area (about 807.7 m2/g), and larger pore volume (about 0.4378 cm3/g) with hierarchically structure of interconnected thin microsheets compared to the pristine carbon. The material exhibits not only high specific capacitance (240 F/g at 0.5 A/g), but also superior cycling performance (approximately 100% of capacitance retention after 10,000 cycles at 2 A/g) in 2 M KOH aqueous electrolyte. Furthermore, the assembled symmetric electrochemical capacitor in 1 M Na2SO4 aqueous electrolyte exhibits a high energy density of 11.7 Wh/kg at a power density of 160 W/kg.

  14. Rapid synthesis of graphene/amorphous α-MnO2 composite with enhanced electrochemical performance for electrochemical capacitor

    International Nuclear Information System (INIS)

    Pang, Mingjun; Long, Guohui; Jiang, Shang; Ji, Yuan; Han, Wei; Wang, Biao; Liu, Xilong; Xi, Yunlong

    2015-01-01

    Highlights: • Graphene/MnO 2 is successfully fabricated by a facile co-precipitation method. • The graphene/MnO 2 electrode reaches 367 Fg −1 in 1 M KOH electrolyte. • The electrode exhibits good cycling performance of 73.9% retention after 1000 cycles. - Abstract: Nanostructured graphene/amorphous α-MnO 2 composites have been synthesized by a facile co-precipitation method under the alkaline condition, in which graphene nanosheets as a supporting substrate to grow MnO 2 . Characterizations of prepared samples’ morphology and microstructures indicate MnO 2 is successfully formed on the surface of graphene by electrostatic interaction. Moreover, the electrochemical properties of the synthesized electrode materials for supercapacitors are studied in a three-electrode experimental setup using a 1 M KOH aqueous solution as the electrolyte. As a result, the specific capacitance of graphene/MnO 2 composite (weight ratio of graphene to MnO 2 is 1:1) determined by a galvanostatic charge–discharge method at a current density of 1 Ag −1 reaches 367 Fg −1 , which is 1.8 and 4.6 fold higher than that of pure graphene and MnO 2 . The capacity retention of the graphene/MnO 2 composite is 73.9% of the original capacitance after 1000 cycles, indicating graphene/MnO 2 composite is a promising electrode material for supercapacitors

  15. Fuel cell/electrochemical capacitor hybrid for intermittent high power applications

    Energy Technology Data Exchange (ETDEWEB)

    Jarvis, L P; Atwater, T B; Cygan, P J [Army Communications-Electronics Command (CECOM), Fort Monmouth, NJ (United States). Research and Development Center

    1999-05-01

    A hybrid power source was demonstrated to successfully power a simulated power load encountered in portable military electronics and communications equipment. The hybrid system consisted of a 25 W proton exchange membrane fuel cell (PEMFC) stack connected in parallel with a 70 F capacitor bank. The cyclic regime of 18.0 W for 2 min followed by 2.5 W for 18 min was chosen as the baseline for the simulation of power load. The operating potential cut-off voltage for pass/failure was set to 3.0 V. At room temperature (23-25 C), the PEMFC alone could not handle the described baseline regime with the PEMFC operating potential dropping below the cut-off voltage within 10 s. The hybrid, however, continuously powered the same regime for 25 h. Its operating potential never reached the voltage cut-off point, not even during the high load of 18.0 W. The tests with hybrid configuration were aborted after 25 h of operation with no signs of output degradation, suggesting that further extended operation was possible. (orig.)

  16. Performance evaluation of CNT/polypyrrole/MnO2 composite electrodes for electrochemical capacitors

    International Nuclear Information System (INIS)

    Sivakkumar, S.R.; Ko, Jang Myoun; Kim, Dong Young; Kim, B.C.; Wallace, G.G.

    2007-01-01

    A ternary composite of CNT/polypyrrole/hydrous MnO 2 is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques. For comparative purpose, binary composites such as CNT/hydrous MnO 2 and polypyrrole/hydrous MnO 2 are prepared and also investigated for their physical and electrochemical performances. The specific capacitance (SC) values of the ternary composite, CNT/hydrous MnO 2 and polypyrrole/hydrous MnO 2 binary composites estimated by CV technique in 1.0 M Na 2 SO 4 electrolyte are 281, 150 and 35 F g -1 at 20 mV s -1 and 209, 75 and 7 F g -1 at 200 mV s -1 , respectively. The electrochemical stability of ternary composite electrode is investigated by switching the electrode back and forth for 10,000 times between 0.1 and 0.9 V versus Ag/AgCl at 100 mV s -1 . The electrode exhibits good cycling stability, retaining up to 88% of its initial charge at 10,000th cycle. A full cell assembled with the ternary composite electrodes shows a SC value of 149 F g -1 at a current loading of 1.0 mA cm -2 during initial cycling, which decreased drastically to a value of 35 F g -1 at 2000th cycle. Analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmet-Teller (BET) surface area measurement and inductively coupled plasma-atomic emission spectrometry (ICP-AES) are also used to characterize the composite materials

  17. Performance evaluation of CNT/polypyrrole/MnO{sub 2} composite electrodes for electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Sivakkumar, S.R. [Department of Applied Chemistry and Biotechnology, Hanbat National University, San 16-1, Dukmyung-Dong, Yusung-Gu, Daejeon 305-719 (Korea, Republic of); Ko, Jang Myoun [Department of Applied Chemistry and Biotechnology, Hanbat National University, San 16-1, Dukmyung-Dong, Yusung-Gu, Daejeon 305-719 (Korea, Republic of)]. E-mail: jmko@hanbat.ac.kr; Kim, Dong Young [Optoelectronic Materials Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650 (Korea, Republic of); Kim, B.C. [ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522 (Australia); Wallace, G.G. [ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522 (Australia)

    2007-09-15

    A ternary composite of CNT/polypyrrole/hydrous MnO{sub 2} is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques. For comparative purpose, binary composites such as CNT/hydrous MnO{sub 2} and polypyrrole/hydrous MnO{sub 2} are prepared and also investigated for their physical and electrochemical performances. The specific capacitance (SC) values of the ternary composite, CNT/hydrous MnO{sub 2} and polypyrrole/hydrous MnO{sub 2} binary composites estimated by CV technique in 1.0 M Na{sub 2}SO{sub 4} electrolyte are 281, 150 and 35 F g{sup -1} at 20 mV s{sup -1} and 209, 75 and 7 F g{sup -1} at 200 mV s{sup -1}, respectively. The electrochemical stability of ternary composite electrode is investigated by switching the electrode back and forth for 10,000 times between 0.1 and 0.9 V versus Ag/AgCl at 100 mV s{sup -1}. The electrode exhibits good cycling stability, retaining up to 88% of its initial charge at 10,000th cycle. A full cell assembled with the ternary composite electrodes shows a SC value of 149 F g{sup -1} at a current loading of 1.0 mA cm{sup -2} during initial cycling, which decreased drastically to a value of 35 F g{sup -1} at 2000th cycle. Analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmet-Teller (BET) surface area measurement and inductively coupled plasma-atomic emission spectrometry (ICP-AES) are also used to characterize the composite materials.

  18. Surface-modified reduced graphene oxide electrodes for capacitors by ionic liquids and their electrochemical properties

    International Nuclear Information System (INIS)

    Kim, Jieun; Kim, Seok

    2014-01-01

    Highlights: • Reduced graphene oxide surface was modified by introduction of ionic liquids. • Microstructure and capacitance of modified electrode were dependent on the ionic liquids contents. • Modification gives electrode better charge transport and higher specific capacitance. • Modified electrode showed the better capacitive performance such as rate capability and cycle stability. - Abstract: In this work, reduced graphene oxide (rGO)/ionic liquids (IL) composites with different weight ratios of IL to rGO were synthesized by a simple method. In these composites, IL contributed to the exfoliation of rGO sheets and to the improvement of the electrochemical properties of the resulting composites by enhancing the ion diffusion and charge transport. The structure of the composites was examined by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM images showed that IL was coated on the surface of rGO in a translucent manner. The electrochemical analysis of the prepared composites was carried out by performing cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS). Among the prepared composites, the one with a weight ratio of rGO to IL of 1:7 showed the highest specific capacitance of 147.5 F g −1 at a scan rate of 10 mV s −1 . In addition, the rate capability and cycle performance of the composites were enhanced compared to pristine rGO. These enhanced properties make the composites suitable as electrode materials for the better performance supercapacitors

  19. Rapid synthesis of graphene/amorphous α-MnO{sub 2} composite with enhanced electrochemical performance for electrochemical capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Mingjun [Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, College of Physics, Jilin University, Jiefang Road 2519, Changchun 130012 (China); Long, Guohui [College of Life Sciences, Jilin Agricultural University, Changchun 130118 (China); Jiang, Shang [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Ji, Yuan, E-mail: jiyuan@jlu.edu.cn [Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, College of Physics, Jilin University, Jiefang Road 2519, Changchun 130012 (China); Han, Wei [Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, College of Physics, Jilin University, Jiefang Road 2519, Changchun 130012 (China); Wang, Biao [Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, College of Physics, Jilin University, Jiefang Road 2519, Changchun 130012 (China); School of Science, University of Science and Technology Liaoning, Anshan 114051 (China); Liu, Xilong; Xi, Yunlong [Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, College of Physics, Jilin University, Jiefang Road 2519, Changchun 130012 (China)

    2015-04-15

    Highlights: • Graphene/MnO{sub 2} is successfully fabricated by a facile co-precipitation method. • The graphene/MnO{sub 2} electrode reaches 367 Fg{sup −1} in 1 M KOH electrolyte. • The electrode exhibits good cycling performance of 73.9% retention after 1000 cycles. - Abstract: Nanostructured graphene/amorphous α-MnO{sub 2} composites have been synthesized by a facile co-precipitation method under the alkaline condition, in which graphene nanosheets as a supporting substrate to grow MnO{sub 2}. Characterizations of prepared samples’ morphology and microstructures indicate MnO{sub 2} is successfully formed on the surface of graphene by electrostatic interaction. Moreover, the electrochemical properties of the synthesized electrode materials for supercapacitors are studied in a three-electrode experimental setup using a 1 M KOH aqueous solution as the electrolyte. As a result, the specific capacitance of graphene/MnO{sub 2} composite (weight ratio of graphene to MnO{sub 2} is 1:1) determined by a galvanostatic charge–discharge method at a current density of 1 Ag{sup −1} reaches 367 Fg{sup −1}, which is 1.8 and 4.6 fold higher than that of pure graphene and MnO{sub 2}. The capacity retention of the graphene/MnO{sub 2} composite is 73.9% of the original capacitance after 1000 cycles, indicating graphene/MnO{sub 2} composite is a promising electrode material for supercapacitors.

  20. On the negative resistance of double layers

    International Nuclear Information System (INIS)

    Raadu, M.A.; Silevitch, M.B.

    1982-08-01

    It is known that large amplitudes oscillations can occur in the current flowing through a plasma diode, typically when a constant potential is applied across the device. Burger (1965) suggested via a computer simulation that the oscillation characteristics was a function of the quantities T sub (e) and T sub (i), namely the respective time for an electron and an ion to cross the electric field region inside the diode. On the rapid time scale T sub (e) the self consistent equilibrium configuration, was unstable. Norris (1964) had previously arrived at the same conclusion using analytical arguments. In that work, it was concluded that the instability occurred since the diode acted as a negative resistance on the T sub (e) scale. A positive feedback effect forced the system away from equilibrium. Silevitch (1981) used the Burger mechanism to suggest an explanation for the flickering aurora phenomenon. He extended the Norris argument and showed by a variational method that a plausible analytic model for a double layer (DL) behaved as a negative resistance on the T sub (e) scale. In this present work we re-examine the negative resistance calculation by taking a more detailed account of the constraints which are imposed on the electron distributions that exist in the DL region. Specifically, we shall focus at the high potential side of the DL. (Authors)

  1. Electrodeposition of Manganese-Nickel Oxide Films on a Graphite Sheet for Electrochemical Capacitor Applications

    Directory of Open Access Journals (Sweden)

    Hae-Min Lee

    2014-01-01

    Full Text Available Manganese-nickel (Mn-Ni oxide films were electrodeposited on a graphite sheet in a bath consisting of manganese acetate and nickel chloride, and the structural, morphological, and electrochemical properties of these films were investigated. The electrodeposited Mn-Ni oxide films had porous structures covered with nanofibers. The X-ray diffractometer pattern revealed the presence of separate manganese oxide (g-MnO2 and nickel oxide (NiO in the films. The electrodeposited Mn-Ni oxide electrode exhibited a specific capacitance of 424 F/g in Na2SO4 electrolyte. This electrode maintained 86% of its initial specific capacitance over 2000 cycles of the charge-discharge operation, showing good cycling stability.

  2. MnO2/multiwall carbon nanotube/Ni-foam hybrid electrode for electrochemical capacitor

    Science.gov (United States)

    Chen, L. H.; Li, L.; Qian, W. J.; Dong, C. K.

    2018-01-01

    The ternary composites of manganese dioxide/multiwall carbon nanotube/Ni-foam (MnO2/MWNT/Ni-foam) for supercapacitors were fabricated via a hydrothermal method after direct growth of MWNTs on the Ni-foam. The structural properties of the electrodes were characterized by SEM and TEM. The electrode exhibited excellent electrochemical properties from the investigation based on the three-electrode setup. Low contact resistance Rs of about 0.291 Ω between MnO2/MWNT and Ni-foam was reached benefited from the direct growth structure. High capacitance of 355.1 F/g at the current density of 2 A/g was achieved, with good capacitive response at high current density. The MnO2/MWNT/Ni-foam electrode exhibits good stability performance after 2000 cycles at a current of 40 mA.

  3. Anomalous dc resistivity and double layers in the auroral ionosphere

    International Nuclear Information System (INIS)

    Kindel, J.M.; Barnes, C.; Forslund, D.W.

    1980-01-01

    There are at least four candidate instabilities which might account for anomalous dc rereresistivity in the auroral ionosphere. These are: the ion-acoustic instability, the Buneman instability, the ion-cyclotron instability and double layers. Results are reported of computer simulations of these four instabilities which suggest that double layers are most likely to be responsible for sistivity in the auroral zone

  4. Ion-acoustic solitary waves near double layers

    International Nuclear Information System (INIS)

    Kuehl, H.H.; Imen, K.

    1985-01-01

    The possibility of ion-acoustic solitary-wave solutions in the uniform plasma on the high-potential side of double layer is investigated. Based on a fluid model of the double layer, it is found that both compressive and rarefactive solitary waves are allowed. Curves are presented which show the regions in parameter space in which these solutions exist

  5. Silicon epitaxy on textured double layer porous silicon by LPCVD

    International Nuclear Information System (INIS)

    Cai Hong; Shen Honglie; Zhang Lei; Huang Haibin; Lu Linfeng; Tang Zhengxia; Shen Jiancang

    2010-01-01

    Epitaxial silicon thin film on textured double layer porous silicon (DLPS) was demonstrated. The textured DLPS was formed by electrochemical etching using two different current densities on the silicon wafer that are randomly textured with upright pyramids. Silicon thin films were then grown on the annealed DLPS, using low-pressure chemical vapor deposition (LPCVD). The reflectance of the DLPS and the grown silicon thin films were studied by a spectrophotometer. The crystallinity and topography of the grown silicon thin films were studied by Raman spectroscopy and SEM. The reflectance results show that the reflectance of the silicon wafer decreases from 24.7% to 11.7% after texturing, and after the deposition of silicon thin film the surface reflectance is about 13.8%. SEM images show that the epitaxial silicon film on textured DLPS exhibits random pyramids. The Raman spectrum peaks near 521 cm -1 have a width of 7.8 cm -1 , which reveals the high crystalline quality of the silicon epitaxy.

  6. Investigation of surface charge density on solid–liquid interfaces by modulating the electrical double layer

    International Nuclear Information System (INIS)

    Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

    2015-01-01

    A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid–liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid–liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid–liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid–liquid interfaces. (paper)

  7. Scalable integration of Li5FeO4 towards robust, high-performance lithium-ion hybrid capacitors.

    Science.gov (United States)

    Park, Min-Sik; Lim, Young-Geun; Hwang, Soo Min; Kim, Jung Ho; Kim, Jeom-Soo; Dou, Shi Xue; Cho, Jaephil; Kim, Young-Jun

    2014-11-01

    Lithium-ion hybrid capacitors have attracted great interest due to their high specific energy relative to conventional electrical double-layer capacitors. Nevertheless, the safety issue still remains a drawback for lithium-ion capacitors in practical operational environments because of the use of metallic lithium. Herein, single-phase Li5FeO4 with an antifluorite structure that acts as an alternative lithium source (instead of metallic lithium) is employed and its potential use for lithium-ion capacitors is verified. Abundant Li(+) amounts can be extracted from Li5FeO4 incorporated in the positive electrode and efficiently doped into the negative electrode during the first electrochemical charging. After the first Li(+) extraction, Li(+) does not return to the Li5FeO4 host structure and is steadily involved in the electrochemical reactions of the negative electrode during subsequent cycling. Various electrochemical and structural analyses support its superior characteristics for use as a promising lithium source. This versatile approach can yield a sufficient Li(+)-doping efficiency of >90% and improved safety as a result of the removal of metallic lithium from the cell. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Batch fabrication of mesoporous boron-doped nickel oxide nanoflowers for electrochemical capacitors

    International Nuclear Information System (INIS)

    Yang, Jing-He; Yu, Qingtao; Li, Yamin; Mao, Liqun; Ma, Ding

    2014-01-01

    Highlights: • A new facile liquid-phase method has been employed for synthesis boron-doped NiO nanoflowers. • The specific surface area of NiO is as high as 200 m 2 g −1 . • NiO nanoflowers exhibit a high specific capacitance of ∼1309 F g −1 at a charge and discharge current density of 3 A g −1 . • NiO nanoflowers have excellent cycling ability and even after 2500 cycles there is no significant reduction in specific capacitance. - Abstract: Boron-doped nickel oxide (B-NiO) nanoflowers are prepared by simple thermal decomposition of nickel hydroxide. B-NiO is porous sphere with a diameter of about 400 nm. B-NiO nanoflowers are composed of approximately 30 nm nanoplates and the thickness of the nanosheets is approximately 3 nm. The specific surface area of the material is as high as 200 m 2 g −1 and the pore size distribution curves of B-NiO has three typical peaks in the range of mesoporous (5 nm, 13 nm and 18 nm). As an electrode for supercapacitors, the crystalline B-NiO nanoflowers have favorable characteristics, for instance, a specific capacitance of 1309 F g −1 at a current density of 3 A g −1 and no significant reduction in Coulombic efficiency after 2500 cycles at 37.5 A g −1 . This remarkable electrochemical performance will make B-NiO nanoflowers a promising electrode material for high performance supercapacitors

  9. High-performance super capacitors based on activated anthracite with controlled porosity

    Science.gov (United States)

    Lee, Hyun-Chul; Byamba-Ochir, Narandalai; Shim, Wang-Geun; Balathanigaimani, M. S.; Moon, Hee

    2015-02-01

    Mongolian anthracite is chemically activated using potassium hydroxide as an activation agent to make activated carbon materials. Prior to the chemical activation, the chemical agent is introduced by two different methods as follows, (1) simple physical mixing, (2) impregnation. The physical properties such as specific surface area, pore volume, pore size distribution, and adsorption energy distribution are measured to assess them as carbon electrode materials for electric double-layer capacitors (EDLC). The surface functional groups and morphology are also characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses respectively. The electrochemical results for the activated carbon electrodes in 3 M sulfuric acid electrolyte solution indicate that the activated Mongolian anthracite has relatively large specific capacitances in the range of 120-238 F g-1 and very high electrochemical stability, as they keep more than 98% of initial capacitances until 1000 charge/discharge cycles.

  10. Carbon Onions: Synthesis and Electrochemical Applications

    Energy Technology Data Exchange (ETDEWEB)

    McDonough, John K. [Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Science and Engineering; Gogotsi, Y. [Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Science and Engineering

    2013-01-01

    Onion-like carbon structures have been synthesized in many ways and large scale production is currently under study. The annealing method can satisfy the need for large scale production, though the ideal spherical shape is unachievable, and the temperature attainable in this method is not sufficient for treating the entire particle. The arc-discharge method provides an alternate pathway toward large scale synthesis. Due to its structure and electrochemical properties, carbon onions can be used as materials for electrochemical double layer capacitors (EDLC) and can be used to store energy across a much wider temperature range, which gives these materials advantages over conventional EDLCs. This and other aspects of carbon onions are discussed in this article.

  11. Double layers formed by beam driven ion-acoustic turbulence

    International Nuclear Information System (INIS)

    Ludwig, G.O.; Ferreira, J.L.; Montes, A.

    1987-01-01

    Small amplitude steady-state ion-acoustic layers are observed to form in a plasma traversed by a beam of cold electrons. The importance of turbulence in maintaining the double layer is demonstrated. The measured wave spectrum is in approximate agrreement with models derived from renormalized turbulence theory. The general features of the double layer are compared with results from particle simulation studies. (author) [pt

  12. Generation mechanism and properties of plasma double layers

    International Nuclear Information System (INIS)

    Sanduloviciu, M.; Lozneanu, E.

    1985-01-01

    The generation mechanism of plasma double layers is studied surveying the results of some experiments. The main mechanism is the same in the cases of collisional and collisionless plasmas. Inelastic quantum collision processes taking place between plasma electrons, accelerated in a local field up to near the same oriented velocity and the neutral particles of the background gases create the necessary conditions for double layer formation. (D.Gy.)

  13. A hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor for energy storage.

    Science.gov (United States)

    Zheng, Jun-Sheng; Zhang, Lei; Shellikeri, Annadanesh; Cao, Wanjun; Wu, Qiang; Zheng, Jim P

    2017-02-07

    Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg -1 . The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

  14. Nonlocal Poisson-Fermi double-layer models: Effects of nonuniform ion sizes on double-layer structure

    Science.gov (United States)

    Xie, Dexuan; Jiang, Yi

    2018-05-01

    This paper reports a nonuniform ionic size nonlocal Poisson-Fermi double-layer model (nuNPF) and a uniform ionic size nonlocal Poisson-Fermi double-layer model (uNPF) for an electrolyte mixture of multiple ionic species, variable voltages on electrodes, and variable induced charges on boundary segments. The finite element solvers of nuNPF and uNPF are developed and applied to typical double-layer tests defined on a rectangular box, a hollow sphere, and a hollow rectangle with a charged post. Numerical results show that nuNPF can significantly improve the quality of the ionic concentrations and electric fields generated from uNPF, implying that the effect of nonuniform ion sizes is a key consideration in modeling the double-layer structure.

  15. General access to metal oxide (Metal = Mn, Co, Ni) double-layer nanospheres for application in lithium ion batteries and supercapacitors

    International Nuclear Information System (INIS)

    Xia, Yuan; Wang, Gang; Zhang, Xing; Wang, Beibei; Wang, Hui

    2016-01-01

    Highlights: • A series of metal oxide double layer nanospheres were prepared. • The obtained materials show excellent performances in lithium ion batteries and supercapacitors. • The unique structure of double layers is beneficial for superior electrochemical performances. - Abstract: In this work, a series of metal oxide double-layer nanospheres (DLNs), such as Mn 2 O 3 , Co 3 O 4 , NiO, NiCo 2 O 4 , and MnCo 2 O 4 have been successfully synthesized through a general template method. The layers of nanospheres were assembled by different nanostructure units and the removing of the SiO 2 template formed a void of several ten nanometers between the double layers, resulting large specific surface areas for them. The energy storage performances of the as-prepared double-layer nanospheres were further investigated in lithium ion battery and supercapacitor systems. Based on their unique nanostructures, the double-layer nanospheres exhibit excellent electrochemical performance with long cycle stability and high specific capacities or capacitances. The best of these, DLNs-NiCo 2 O 4 can deliver a reversible capacity of 1107 mAh g −1 at 0.25C after 200 cycles in lithium ion battery system, and shows a capacitance of 1088 F g −1 with capacitance loss of less than 3% at 5 A g −1 after 5000 cycles in supercapacitors.

  16. Nanocomposites for electrochemical capacitors

    CERN Document Server

    Inamuddin

    2018-01-01

    The book explores recent developments in the area of composite applications for supercapacitor electrodes based von conducting polymers, graphene, biomass, or carbonaceous quantum dots. Synthesis strategies of composite materials and electrode preparation methods are discussed in detail.

  17. Mesoporous carbon design for ionic liquid-based, double-layer supercapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Lazzari, M.; Soavi, F.; Mastragostino, M. [Dipartimento di Scienza dei Metalli, Elettrochimica e Tecniche Chimiche, University of Bologna (Italy)

    2010-10-15

    The use of pyrrolidinium-based ionic liquids (ILs) in asymmetric electric double-layer capacitors (AEDLC) with positive and negative carbon electrodes of different weight is a powerful strategy for developing safe, high specific-energy supercapacitors operating at >3.5 V. The preparation and characterisation of ordered (OTC) and disordered (DTC) template carbons, the latter obtained by a fast and low-cost method, are reported. The porosity and capacitance features of the template carbons are discussed in view of their application in IL-based AEDLCs and compared with the properties of aero/cryo/xerogel carbons and a commercial activated carbon. The performance of an N-butyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide-based AEDLC assembled with DTC carbon electrodes operating at 3.9 V featuring high specific energy of 47 Wh kg{sup -1} is then reported. The impact of porosity and surface chemistry of carbons on the electrode capacitive response in IL and on the performance of the IL-based AEDLC in terms of energy, power and weight distribution of module components is discussed. The effect of IL nature and carbon porosity on the time constant of the double-layer charging process was also investigated by voltammetric and impedance studies. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  18. Electric double-layer capacitance between an ionic liquid and few-layer graphene.

    Science.gov (United States)

    Uesugi, Eri; Goto, Hidenori; Eguchi, Ritsuko; Fujiwara, Akihiko; Kubozono, Yoshihiro

    2013-01-01

    Ionic-liquid gates have a high carrier density due to their atomically thin electric double layer (EDL) and extremely large geometrical capacitance Cg. However, a high carrier density in graphene has not been achieved even with ionic-liquid gates because the EDL capacitance CEDL between the ionic liquid and graphene involves the series connection of Cg and the quantum capacitance Cq, which is proportional to the density of states. We investigated the variables that determine CEDL at the molecular level by varying the number of graphene layers n and thereby optimising Cq. The CEDL value is governed by Cq at n 4. This transition with n indicates a composite nature for CEDL. Our finding clarifies a universal principle that determines capacitance on a microscopic scale, and provides nanotechnological perspectives on charge accumulation and energy storage using an ultimately thin capacitor.

  19. Pseudo-capacitor device for aqueous electrolytes

    Science.gov (United States)

    Prakash, Jai; Thackeray, Michael M.; Dees, Dennis W.; Vissers, Donald R.; Myles, Kevin M.

    1998-01-01

    A pseudo-capacitor having a high energy storage capacity develops a double layer capacitance as well as a Faradaic or battery-like redox reaction, also referred to as pseudo-capacitance. The Faradaic reaction gives rise to a capacitance much greater than that of the typical ruthenate oxide ultracapacitor which develops only charge separation-based double layer capacitance. The capacitor employs a lead and/or bismuth/ruthenate and/or iridium system having the formula A.sub.2 ›B.sub.2-x Pb.sub.x !O.sub.7-y, where A=Pb, Bi, and B=Ru, Ir, and Ocapacitor. The amount of expensive ruthenate and iridium can be substantially reduced in the pseudo-capacitor by increasing the lead content while improving energy storage capacity.

  20. Observations of propagating double layers in a high current discharge

    International Nuclear Information System (INIS)

    Lindberg, L.

    1988-01-01

    Observations of current disruptions and strong electric fields along the magnetic field in a high-density (2 x 10 19 m - 3 , highly-ionized, moving, and expanding plasma column are reported. The electric field is interpreted in terms of propagating, strong electric double layers (3-5kV). An initial plasma column is formed in an axial magnetic field (0.1T) by means of a conical theta-pinch plasma gun. When an axial current (max 5kA, 3-5 kV) is drawn through the column spontaneous disruptions and double-layer formation occur within a few microseconds. Floating, secondary emitting Langmuir probes are used. They often indicate very high positive potential peaks (1-2 kV above the anode potential during a few μs) in the plasma on the positive side of the double layer. Short, intense bursts of HF radiation are detected at the disruptions

  1. Some recent trends in computer simulations of aqueous double layers

    International Nuclear Information System (INIS)

    Spohr, E.

    2003-01-01

    Recent molecular simulations of the electric double layer between an aqueous and a metallic phase are reviewed. Several trends in the field can be identified: (i) the increasing use of ab initio simulation methods, most notably the Car-Parrinello method, allows to combine a statistical mechanical description of the double layer with a description of elementary chemical processes on the electronic structure level; (ii) the application of free-energy methods in one and (recently) two dimensions to describe chemical reactivity within and beyond the framework of the Marcus theory of electron transfer; and (iii) at high concentrations, direct simulations of two-phase systems with an aqueous solution and a charged or uncharged solid phase or surface can model the entire double layer region

  2. Cycle stability of the electrochemical capacitors patterned with vertically aligned carbon nanotubes in an LiPF6-based electrolyte.

    Science.gov (United States)

    Chiou, Yi-Deng; Tsai, Dah-Shyang; Lam, Hoa Hung; Chang, Chuan-hua; Lee, Kuei-Yi; Huang, Ying-Sheng

    2013-09-07

    The miniature ultracapacitors, with interdigitated electrodes of vertically aligned carbon nanotubes (VACNTs) and an inter-electrode gap of 20 μm, have been prepared in the LiPF6 organic electrolyte with and without PVdF-HFP gel. PVdF-HFP between two opposing electrodes enhances the device reliability, but lessens its power performance because of the extra diffusion resistance. Also noteworthy are the gel influences on the cycle stability. When the applied voltage is 2.0 or 2.5 V, both the LiPF6 and the gel capacitors exhibit excellent stability, typified by a retention ratio of ≥95% after 10,000 cycles. Their coulombic efficiencies quickly rise up, and hold steady at 100%. Nonetheless, when the applied voltage is 3.5 or 4.0 V, the cycle stability deteriorates, since the negative electrode potential descends below 0.9 V (vs. Li), leading to electrolyte decomposition and SEI formation. For the LiPF6 capacitor, its retention ratio could be around 60% after 10,000 cycles and the coulombic efficiency of 100% is difficult to reach throughout its cycle life. On the other hand, the gel capacitor cycles energy with a much higher retention ratio, >80% after 10,000 cycles, and a better coulombic efficiency, even though electrolyte decomposition still occurs. We attribute the superior stability of the gel capacitor to its extra diffusion resistance which slows down the performance deterioration.

  3. Double layer -- a particle accelerator in the magnetosphere

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Xiangrong [Los Alamos National Laboratory

    2015-07-16

    Slides present the material under the following topics: Introduction (What is a double layer (DL)? Why is it important? Key unsolved problems); Theory -- time-independent solutions of 1D Vlasov--Poisson system; Particle-in-cell simulations (Current-driven DLs); and Electron acceleration by DL (Betatron acceleration). Key problems include the generation mechanism, stability, and electron acceleration. In summary, recent observations by Van Allen Probes show large number of DLs in the outer radiation belt, associated with enhanced flux of relativistic electrons. Simulations show that ion acoustic double layers can be generated by field-aligned currents. Thermal electrons can gain energy via betatron acceleration in a dipole magnetic field.

  4. Double layers do accelerate particles in the auroral zone

    International Nuclear Information System (INIS)

    Borovsky, J.E.

    1992-01-01

    In response to a recent report [D. A. Bryant, R. Bingham, and U. de Angelis, Phys. Rev. Lett. 68, 37 (1991)] that makes the claim that electrostatic fields are weak in the auroral zone and that electrostatic fields cannot accelerate particles, it is pointed out that the evidence for electrostatic fields in the auroral zone is overwhelming and that these electrostatic fields often are accelerating electrons to produce aurora. The literature cited in the article above as evidence against double layers (strong electric fields) is reexamined and is found not to be evidence against double layers

  5. Circuit effects on pierce instabilities, and double-layer formation

    International Nuclear Information System (INIS)

    Raadu, M.A.; Silevitch, M.B.

    1982-11-01

    The role of the Pierce instability in the formation of double layers is considered and compared with that of the Buneman instability. Pierce instabilities have been identified in a double-layer experiment, where they lead to ion trapping. Here the effects of external circuit elements are considered. In the case of immobile ions the onset criteria are unaffected, but in the unstable range the growth rate is reduced by the external impedance. Required experimental values of the circuit elements are estimated. The possible relevance to computer simulations is noted. (Authors)

  6. Electric Double-Layer Interaction between Dissimilar Charge-Conserved Conducting Plates.

    Science.gov (United States)

    Chan, Derek Y C

    2015-09-15

    Small metallic particles used in forming nanostructured to impart novel optical, catalytic, or tribo-rheological can be modeled as conducting particles with equipotential surfaces that carry a net surface charge. The value of the surface potential will vary with the separation between interacting particles, and in the absence of charge-transfer or electrochemical reactions across the particle surface, the total charge of each particle must also remain constant. These two physical conditions require the electrostatic boundary condition for metallic nanoparticles to satisfy an equipotential whole-of-particle charge conservation constraint that has not been studied previously. This constraint gives rise to a global charge conserved constant potential boundary condition that results in multibody effects in the electric double-layer interaction that are either absent or are very small in the familiar constant potential or constant charge or surface electrochemical equilibrium condition.

  7. Na-ion capacitor using sodium pre-doped hard carbon and activated carbon

    International Nuclear Information System (INIS)

    Kuratani, Kentaro; Yao, Masaru; Senoh, Hiroshi; Takeichi, Nobuhiko; Sakai, Tetsuo; Kiyobayashi, Tetsu

    2012-01-01

    We assembled a sodium-ion capacitor (Na-IC) by combining sodium pre-doped hard carbon (HC) as the negative- and activated carbon (AC) as the positive-electrode. The electrochemical properties were compared with two lithium-ion capacitors (Li-ICs) in which the negative electrodes were prepared with Li pre-doped HC and mesocarbon microbeads (MCMB). The positive and negative electrodes were prepared using the established doctor blade method. The negative electrodes were galvanostatically pre-doped with Na or Li to 80% of the full capacity of carbons. The potential of the negative electrodes after pre-doping was around 0.0 V vs. Na/Na + or Li/Li + , which resulted in the higher output potential difference of the Na-IC and Li-ICs than that of the conventional electrochemical double-layer capacitors (EDLCs) because AC positive electrode works in the same principle both in the ion capacitors and in the EDLC. The state-of-charge of the negative electrode varied 80 ± 10% during the electrochemical charging and discharging. The capacity of the cell was evaluated using galvanostatic charge–discharge measurement. At the discharge current density of 10 mA cm −2 , the Na-IC maintained 70% of the capacity that obtained at the current density of 0.5 mA cm −2 , which was comparable to the Li-ICs. At 50 mA cm −2 , the capacities of the Li-IC(MCMB) and the Na-IC dropped to 20% whereas the Li-IC(HC) retained 30% of the capacity observed at 0.5 mA cm −2 . The capacities of the Na-IC and Li-ICs decreased by 9% and 3%, respectively, after 1000 cycles of charging and discharging.

  8. Nitrogen-doped carbon spheres: A new high-energy-density and long-life pseudo-capacitive electrode material for electrochemical flow capacitor.

    Science.gov (United States)

    Hou, Shujin; Wang, Miao; Xu, Xingtao; Li, Yandong; Li, Yanjiang; Lu, Ting; Pan, Likun

    2017-04-01

    One of the most challenging issues in developing electrochemical flow capacitor (EFC) technology is the design and synthesis of active electrode materials with high energy density and long cycle life. However, in practical cases, the energy density and cycle ability obtained currently cannot meet the practical need. In this work, we propose a new active material, nitrogen-doped carbon spheres (NCSs), as flowable electrodes for EFC application. The NCSs were prepared via one-pot hydrothermal synthesis in the presence of resorcinol/formaldehyde as carbon precursors and melamine as nitrogen precursor, followed by carbonization in nitrogen flow at various temperatures. The results of EFC experiments demonstrate that NCSs obtained at 800°C exhibit a high energy density of 13.5Whkg -1 and an excellent cycle ability, indicating the superiority of NCSs for EFC application. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Double-layer Tablets of Lornoxicam: Validation of Quantification ...

    African Journals Online (AJOL)

    Purpose: To formulate double-layer tablets of lornoxicam (LRX) prepared by direct compression method and ... including direct compression method which is ..... Mechanisms of potassium chloride release from compressed, hydrophilic, polymeric matrices: effect of entrapped air. J Pharm Sci 1983; 72(10): 1189-1191. 17.

  10. Double layer effects in the electroreduction of transition metal ions

    Czech Academy of Sciences Publication Activity Database

    Fawcett, W. R.; Hromadová, Magdaléna

    2008-01-01

    Roč. 12, č. 4 (2008), s. 347-351 ISSN 1432-8488 R&D Projects: GA AV ČR KJB400400603; GA MŠk LC510 Institutional research plan: CEZ:AV0Z40400503 Keywords : sphere electrode reactions * crystal gold electrodes * diffuse double - layer Subject RIV: CG - Electrochemistry Impact factor: 1.597, year: 2008

  11. Double-layer Tablets of Lornoxicam: Validation of Quantification ...

    African Journals Online (AJOL)

    Double-layer Tablets of Lornoxicam: Validation of Quantification Method, In vitro Dissolution and Kinetic Modelling. ... Satisfactory results were obtained from all the tablet formulations met compendial requirements. The slowest drug release rate was obtained with tablet cores based on PVP K90 (1.21 mg%.h-1).

  12. On the magnetism of Heisenberg double-layer antiferromagnets

    International Nuclear Information System (INIS)

    Uijen, C.M.J. van.

    1980-01-01

    The author investigates the sublattice magnetization and the susceptibility of the double-layer Heisenberg antiferromagnet K 3 M 2 F 7 by employing the techniques of elastic and quasi-elastic critical magnetic scattering of neutrons. (G.T.H.)

  13. Gastroesophageal anastomosis: single-layer versus double-layer technique

    International Nuclear Information System (INIS)

    Aslam, V.A.; Bilal, A.; Khan, A.; Ahmed, M.

    2008-01-01

    Considerable controversy exists regarding the optimum technique for gastroesophageal anastomosis. Double layer technique has long been considered important for safe healing but there is evidence that single layer technique is also safe and can be performed in much shorter time. The purpose of this study was to compare the outcome of single layer and double layer techniques for gastroesophageal anastomosis. A prospective randomized study was conducted in cardiothoracic unit, Lady Reading Hospital from Jan 2006 to Jan 2008. Fifty patients with oesophageal carcinoma undergoing subtotal oesophagectomy were randomized to have the anastomosis by single layer continuous or double layer continuous technique (group A (n=24) and B (n=26) respectively). The demographic data, operative and anastomosis time, postoperative complications and hospital mortality were recorded on a proforma and analyzed on SPSS 10. There was no significant difference between group A and B in terms of age, gender, postoperative complications and duration of hospital stay. Anastomotic leak occurred in 4.2% patients in group A and 7.7% in group B (p=NS). Mean anastomosis time was 10.04 minutes in group A and 19.2 minutes in group B (p=0.0001). Mean operative time was 163.83 minutes and 170.96 minutes in group A and B respectively. Overall hospital mortality was 2%; no deaths occurred due to anastomotic leak. Single layer continuous technique is equally safe and can be performed in shorter time and at a lower cost than the double layer technique. (author)

  14. Free double layers in mercury-arc discharges

    International Nuclear Information System (INIS)

    Maciel, H.S.; Allen, J.E.

    1989-01-01

    A study has been carried out of free double layers formed within the plasma volume of a low-pressure mercury-arc discharge at high current densities. The free double layer is observed to form as a visible boundary, which drifts slowly from the central section of the discharge. Current-driven instabilities are observed as the discharge current is gradually increased to a critical value, at which current limitation is observed to occur. This process, which is accompanied by high-current spikes, ceases when the free double layer becomes visible as a sharp boundary dividing the discharge column into two regions of different luminosities. The layer is observed to form in the later stages of current limitation, the onset of which occurs for a ratio of drift to thermal speed of electrons of about unity. Electrical energy is converted by the layer into kinetic energy of the changed particles. Accordingly high-energy ions were measured by means of an electrostatic energy analyser. The multiple-sheath character of the free 'double layer'', which is inferred from probe measurements of potential profiles, is discussed and comparisons with other space-charge structures with the same topology are made. (author)

  15. Water transport and desalination through double-layer graphyne membranes.

    Science.gov (United States)

    Akhavan, Mojdeh; Schofield, Jeremy; Jalili, Seifollah

    2018-05-16

    Non-equilibrium molecular dynamics simulations of water-salt solutions driven through single and double-layer graphyne membranes by a pressure difference created by rigid pistons are carried out to determine the relative performance of the membranes as filters in a reverse osmosis desalination process. It is found that the flow rate of water through a graphyne-4 membrane is twice that of a graphyne-3 membrane for both single and double-layer membranes. Although the addition of a second layer to a single-layer membrane reduces the membrane permeability, the double-layer graphyne membranes are still two or three orders of magnitude more permeable than commercial reverse osmosis membranes. The minimum reduction in flow rate for double-layer membranes occurs at a layer spacing of 0.35 nm with an AA stacking configuration, while at a spacing of 0.6 nm the flow rate is close to zero due to a high free energy barrier for permeation. This is caused by the difference in the environments on either side of the membrane sheets and the formation of a compact two-dimensional layer of water molecules in the interlayer space which slows down water permeation. The distribution of residence times of water molecules in the interlayer region suggests that at the critical layer spacing of 0.6 nm, a cross-over occurs in the mechanism of water flow from the collective movement of hydrogen-bonded water sheets to the permeation of individual water molecules. All membranes are demonstrated to have a high salt rejection fraction and the double-layered graphyne-4 membranes can further increase the salt rejection by trapping ions that have passed through the first membrane from the feed solution in the interlayer space.

  16. Influence of Concentration and Electrodeposition Time on the Electrochemical Super capacitor Performance of Poly(3,4-Ethylenedioxy thiophene)/Graphene Oxide Hybrid Material

    International Nuclear Information System (INIS)

    Azman, N. H. N.; Lim, H. N.; Sulaiman, Y.; Lim, H. N.; Sulaiman, Y.

    2016-01-01

    Poly(3,4-ethylenedioxy thiophene)/graphene oxide (PEDOT/GO) composites with wrinkled paper-like sheets morphology were electro polymerized potentiostatically at 1.2 V with different electrodeposition times (1-30 min) and various concentrations of GO (0.5, 1.0, 1.5, and 2.0 mg/ml). The electrochemical properties of PEDOT/GO composites as an electrode material for super capacitor were investigated using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD). The CV results revealed that PEDOT/GO containing 1.0 mg/ml GO and electro polymerized for 10 minutes exhibited the highest specific capacitance (157.17 F/g). This optimum PEDOT/GO was found to have energy and power density of 18.24 W/kg and 496.64 Wh/kg, respectively, at 1.0 A/g current density. The resistance of charge transfer obtained for PEDOT/GO is very low (13.10 Ω) compared to PEDOT (638.98Ω), proving that PEDOT/GO has a good super capacitive performance due to the synergistic effect of the high conductivity of PEDOT and large surface area of GO

  17. Noncovalent Pi-Pi Stacking at the Carbon-Electrolyte Interface: Controlling the Voltage Window of Electrochemical Supercapacitors.

    Science.gov (United States)

    Li, Mengya; Westover, Andrew S; Carter, Rachel; Oakes, Landon; Muralidharan, Nitin; Boire, Timothy C; Sung, Hak-Joon; Pint, Cary L

    2016-08-03

    A key parameter in the operation of an electrochemical double-layer capacitor is the voltage window, which dictates the device energy density and power density. Here we demonstrate experimental evidence that π-π stacking at a carbon-ionic liquid interface can modify the operation voltage of a supercapacitor device by up to 30%, and this can be recovered by steric hindrance at the electrode-electrolyte interface introduced by poly(ethylene oxide) polymer electrolyte additives. This observation is supported by Raman spectroscopy, electrochemical impedance spectroscopy, and differential scanning calorimetry that each independently elucidates the signature of π-π stacking between imidazole groups in the ionic liquid and the carbon surface and the role this plays to lower the energy barrier for charge transfer at the electrode-electrolyte interface. This effect is further observed universally across two separate ionic liquid electrolyte systems and is validated by control experiments showing an invariant electrochemical window in the absence of a carbon-ionic liquid electrode-electrolyte interface. As interfacial or noncovalent interactions are usually neglected in the mechanistic picture of double-layer capacitors, this work highlights the importance of understanding chemical properties at supercapacitor interfaces to engineer voltage and energy capability.

  18. Improved Mechanical Compatibility and Cytocompatibility of Ta/Ti Double-Layered Composite Coating

    Science.gov (United States)

    Ding, Ding; Xie, Youtao; Li, Kai; Huang, Liping; Zheng, Xuebin

    2017-08-01

    In order to improve the mechanical compatibility and cytocompatibility of titanium implants, a composite coating with double layers composed of tantalum and titanium was designed and prepared using plasma spraying technology. In the composite coating, the upper tantalum layer provides a good biocompatibility, and the sublayer of titanium with a porous structure ensures the low elastic modulus. Results show that the fabricated composite coating exhibits a relatively low elastic modulus of 26.7 GPa, which is close to the elastic modulus of human cortical bone. In vitro cytocompatibility evaluation of the composite coating shows that the human bone marrow stromal cells exhibit enhanced adhesion and spreading performance on the double-layered composite coating in comparison with the single-layered titanium coating. In order to eliminate the misgivings of chemical stability of the composite coating in clinical application, electrochemical corrosion of the coating was examined. The results obtained revealed a very weak galvanic corrosion between the tantalum and titanium in the composite coating, which would ensure the safety of the coating in vivo.

  19. Facile chemical synthesis of nanoporous layered δ-MnO{sub 2} thin film for high-performance flexible electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Yu; Wang, Jun; Jiang, Xionghua; Zheng, Yanfeng [The Key Laboratory of Low-Carbon Chemistry and Energy Conservation of Guangdong Province, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Chen, Zhenxing, E-mail: chenzx65@mail.sysu.edu.cn [The Key Laboratory of Low-Carbon Chemistry and Energy Conservation of Guangdong Province, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China)

    2013-04-15

    Layered δ-MnO{sub 2} thin films with a three-dimensional nanostructure are successfully fabricated on stainless steel foil substrates for flexible electrochemical capacitors by a facile and effective chemical bath deposition technology from ethanol and potassium permanganate solution at 15 °C. The as-prepared thin films display nanoporous morphology and a water contact angle of 20°. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses reveal that the thin films are composed of δ-MnO{sub 2}. Electrochemical data demonstrate that the δ-MnO{sub 2} thin film electrodes can deliver a high special capacitance of 447 F/g at 2 mV/s, and provide a good capacitance retention ratio of 87% after 1000 continuous cycles at 10 mV/s in 0.5 M Na{sub 2}SO{sub 4}. Compressive and tensile bending tests show that the as-prepared electrodes can steadily work over a wide range of applied curvatures between −2.5 cm{sup −1} (tension) and 2.5 cm{sup −1} (compression). Only a small decrease in special capacitance (0.9% at a curvature of 2.5 cm{sup −1} under compressive strain, or 1.2% at a curvature of −2.5 cm{sup −1} under tensile strain) is observed even after bending for 200 cycles, indicating the excellent mechanical flexibility and electrochemical stability of the δ-MnO{sub 2} thin film electrodes.

  20. Double layers in a modestly collisional electronegative discharge

    CERN Document Server

    Sheridan, T E

    1999-01-01

    The effect of ion-neutral collisions on the structure and ion flux emanating from a steady-state, planar discharge with two negative components is investigated. The positive ion component is modelled as a cold fluid subject to constant-mobility collisions, while the electrons and negative ions obey Boltzmann relations. The model includes the collisionless limit. When the negative ions are sufficiently cold three types of discharge structures are found. For small negative ion concentrations or high collisionality, the discharge is 'stratified', with an electronegative core and an electropositive edge. For the opposite conditions, the discharge is 'uniform' with the negative ion density remaining significant at the edge of the plasma. Between these cases lies the special case of a double-layer-stratified discharge, where quasi-neutrality is violated at the edge of the electronegative core. Double-layer-stratified solutions are robust in that they persist for moderate collisionality. Numerical solutions for fini...

  1. An Aqueous Metal-Ion Capacitor with Oxidized Carbon Nanotubes and Metallic Zinc Electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Yuheng; Amal, Rose; Wang, Da-Wei, E-mail: da-wei.wang@unsw.edu.au [School of Chemical Engineering, The University of New South Wales (UNSW), Sydney, NSW (Australia)

    2016-10-03

    An aqueous metal ion capacitor comprising of a zinc anode, oxidized carbon nanotubes (oCNTs) cathode, and a zinc sulfate electrolyte is reported. Since the shuttling cation is Zn{sup 2+}, this typical metal ion capacitor is named as zinc-ion capacitor (ZIC). The ZIC integrates the divalent zinc stripping/plating chemistry with the surface-enabled pseudocapacitive cation adsorption/desorption on oCNTs. The surface chemistry and crystallographic structure of oCNTs were extensively characterized by combining X-ray photoelectron spectroscopy, Fourier-transformed infrared spectroscopy, Raman spectroscopy, and X-ray powder diffraction. The function of the surface oxygen groups in surface cation storage was elucidated by a series of electrochemical measurement and the surface-enabled ZIC showed better performance than the ZIC with an un-oxidized CNT cathode. The reaction mechanism at the oCNT cathode involves the additional reversible Faradaic process, while the CNTs merely show electric double layer capacitive behavior involving a non-Faradaic process. The aqueous hybrid ZIC comprising the oCNT cathode exhibited a specific capacitance of 20 mF cm{sup −2} (corresponding to 53 F g{sup −1}) in the range of 0–1.8 V at 10 mV s{sup −1} and a stable cycling performance up to 5000 cycles.

  2. An Aqueous Metal-ion Capacitor with Oxidised Carbon Nanotubes and Metallic Zinc Electrodes

    Directory of Open Access Journals (Sweden)

    Yuheng Tian

    2016-10-01

    Full Text Available An aqueous metal ion capacitor comprising of a zinc anode, an oxidized carbon nanotubes (oCNTs cathode and a zinc sulfate electrolyte is reported. Since the shuttling cation is Zn2+, this typical metal ion capacitor is named as zinc-ion capacitor (ZIC. The ZIC integrates the divalent zinc stripping/plating chemistry with the surface-enabled pseudocapacitive cation adsorption/desorption on oCNTs. The surface chemistry and crystallographic structure of oCNTs were extensively characterized by combining X-ray photoelectron spectroscopy, Fourier-transformed infrared spectroscopy, Raman spectroscopy and X-ray powder diffraction. The function of the surface oxygen groups in surface cation storage was elucidated by a series of electrochemical measurement and the surface-enabled ZIC showed better performance than the ZIC with an un-oxidized CNT cathode. The reaction mechanism at the oCNT cathode involves the additional reversible Faradaic process, while the CNTs merely show electric double layer capacitive behavior involving a non-Faradaic process. The aqueous hybrid ZIC comprising the oCNT cathode exhibited a specific capacitance of 20 mF cm-2 (corresponding to 53 F g-1 in the range of 0-1.8 V at 10 mV s-1 and a stable cycling performance up to 5000 cycles.

  3. Electrostatic supersolitons and double layers at the acoustic speed

    International Nuclear Information System (INIS)

    Verheest, Frank; Hellberg, Manfred A.

    2015-01-01

    Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication

  4. Electrostatic supersolitons and double layers at the acoustic speed

    Energy Technology Data Exchange (ETDEWEB)

    Verheest, Frank, E-mail: frank.verheest@ugent.be [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B–9000 Gent (Belgium); School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa); Hellberg, Manfred A., E-mail: hellberg@ukzn.ac.za [School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa)

    2015-01-15

    Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.

  5. The effect of dispersion status with functionalized graphenes for electric double-layer capacitors

    International Nuclear Information System (INIS)

    Chen, Y.-R.; Chiu, K.-F.; Lin, H.C.; Hsieh, C.-Y.; Tsai, C.B.; Chu, B.T.T.

    2014-01-01

    Highlights: • MrGO/NMP can reduce the IR drops and R ct of the supercapacitors. • M-rGO can provide excellent plane-to-point conducting network. • M-rGO can effectively enhance high rate performance of supercapacitors. • M-rGO additive can deliver high capacity under high rate cycling. - Abstract: Graphene with oxygen (M-rGO and H-rGO) and nitrogen (N-rGO) related functional groups have been fabricated. Reduced graphenes including H-rGO, M-rGO and N-rGO were mixed with activated carbons as the composite electrodes and characterized for supercapacitors. The effects of the functional groups on graphenes as the conductive additive have been investigated. It was found that a suitable content of functional groups can improve the stability of dispersion, and therefore reduce the internal resistance (IR drop) and charge transfer resistance (R ct ) resulting in higher rate capability. The supercapacitor with M-rGO and KS6 as additive at the activated carbon electrode can be operated at a rate as high as 6 A/g and exhibits a capacitance of 208 F/g, whereas the supercapacitor using only KS6 as additive shows a capacitance of only 107 F/g. The graphene contained supercapacitor has been cycled over 2000 times at 4 A/g with almost no capacitance fading

  6. The effect of dispersion status with functionalized graphenes for electric double-layer capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y.-R., E-mail: d98527015@ntu.edu.tw [Department of Materials Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan (China); Department of Materials Science and Engineering, Feng Chia University, 100 Wen Hwa Rd, 407 Taichung, Taiwan (China); Chiu, K.-F. [Department of Materials Science and Engineering, Feng Chia University, 100 Wen Hwa Rd, 407 Taichung, Taiwan (China); Lin, H.C. [Department of Materials Science and Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan (China); Hsieh, C.-Y. [Enerage Inc., No. 5, Ligong 3rd Rd, Wujie Township, Yilan County 26841, Taiwan (China); Tsai, C.B. [Taiwan Textile Research Institute, No. 6, Chengtian Rd, Tucheng City, Taipei 23674, Taiwan (China); Chu, B.T.T. [Laboratory for Functional Polymers, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf (Switzerland)

    2014-12-15

    Highlights: • MrGO/NMP can reduce the IR drops and R{sub ct} of the supercapacitors. • M-rGO can provide excellent plane-to-point conducting network. • M-rGO can effectively enhance high rate performance of supercapacitors. • M-rGO additive can deliver high capacity under high rate cycling. - Abstract: Graphene with oxygen (M-rGO and H-rGO) and nitrogen (N-rGO) related functional groups have been fabricated. Reduced graphenes including H-rGO, M-rGO and N-rGO were mixed with activated carbons as the composite electrodes and characterized for supercapacitors. The effects of the functional groups on graphenes as the conductive additive have been investigated. It was found that a suitable content of functional groups can improve the stability of dispersion, and therefore reduce the internal resistance (IR drop) and charge transfer resistance (R{sub ct}) resulting in higher rate capability. The supercapacitor with M-rGO and KS6 as additive at the activated carbon electrode can be operated at a rate as high as 6 A/g and exhibits a capacitance of 208 F/g, whereas the supercapacitor using only KS6 as additive shows a capacitance of only 107 F/g. The graphene contained supercapacitor has been cycled over 2000 times at 4 A/g with almost no capacitance fading.

  7. Single-particle thermal diffusion of charged colloids: Double-layer theory in a temperature gradient

    NARCIS (Netherlands)

    Dhont, J.K.G.; Briels, Willem J.

    2008-01-01

    The double-layer contribution to the single-particle thermal diffusion coefficient of charged, spherical colloids with arbitrary double-layer thickness is calculated and compared to experiments. The calculation is based on an extension of the Debye-Hückel theory for the double-layer structure that

  8. One-step electrochemical composite polymerization of polypyrrole integrated with functionalized graphene/carbon nanotubes nanostructured composite film for electrochemical capacitors

    International Nuclear Information System (INIS)

    Ding Bing; Lu Xiangjun; Yuan Changzhou; Yang Sudong; Han Yongqin; Zhang Xiaogang; Che Qian

    2012-01-01

    Graphical abstract: A novel one-step electrochemical co-deposition strategy was first proposed to prepare unique polypyrrole/reduced graphene oxide/carbon nanotubes (PPy/F-RGO/CNTs) ternary composites, where F-RGO, CNTs, and PPy were electrodeposited simultaneously to construct a three-dimensional (3-D) highly porous film electrode. Highlights: ► Isolated, water-soluble graphene was obtained through benzenesulfonic functionalization. ► PPy/F-RGO/CNTs ternary composite film was prepared via one-step electrochemical co-deposition route. ► PPy/F-RGO/CNTs film shows 3-D highly porous nanostructure and high electrical conductivity. ► PPy/F-RGO/CNTs film exhibits high capacitance, good high-rate performance with a remarkable cycling stability. - Abstract: A novel one-step electrochemical composite polymerization strategy was first proposed to prepare unique polypyrrole/reduced graphene oxide/carbon nanotubes (PPy/F-RGO/CNTs) ternary composites, where F-RGO, CNTs, and PPy were electrodeposited simultaneously to construct a three-dimensional (3-D) highly porous film electrode. Such ternary composite film electrode exhibits a high specific capacitance of 300 F g −1 at 1 A g −1 as well as a remarkable cycling stability at high rates, which is related to its unique nanostructure and high electrical conductivity. F-RGO and CNTs act as an electron-transporting backbone of a 3-D porous nanostructure, leaving adequate working space for facile electrolyte penetration and better faradaic utilization of the electro-active PPy. Furthermore, the straightforward approach proposed here can be readily extended to prepare other composite film electrodes with good electrochemical performance for energy storage.

  9. Electrochemical performance of lithium-ion capacitors evaluated under high temperature and high voltage stress using redox stable electrolytes and additives

    Science.gov (United States)

    Boltersdorf, Jonathan; Delp, Samuel A.; Yan, Jin; Cao, Ben; Zheng, Jim P.; Jow, T. Richard; Read, Jeffrey A.

    2018-01-01

    Lithium-ion capacitors (LICs) were investigated for high power, moderate energy density applications for operation in extreme environments with prolonged cycle-life performance. The LICs were assembled as three-layered pouch cells in an asymmetric configuration employing Faradaic pre-lithiated hard carbon anodes and non-Faradaic ion adsorption-desorption activated carbon (AC) cathodes. The capacity retention was measured under high stress conditions, while the design factor explored was electrolyte formulation using a set of carbonates and electrolyte additives, with a focus on their stability. The LIC cells were evaluated using critical performance tests under the following high stress conditions: long-term voltage floating-cycling stability at room temperature (2.2-3.8 V), high temperature storage at 3.8 V, and charge voltages up to 4.4 V. The rate performance of different electrolytes and additives was measured after the initial LIC cell formation for a 1C-10C rate. The presence of vinylene carbonate (VC) and tris (trimethylsilyl) phosphate (TMSP) were found to be essential to the improved electrochemical performance of the LIC cells under all testing conditions.

  10. Double layers in the laboratory and above the aurora

    International Nuclear Information System (INIS)

    Block, L.P.

    1980-11-01

    Recent laboratory double layer experiments have simulated, much better than before, the conditions prevailing on auroral field lines at high altitudes. In particular, magnetic fields strong enough to magnetize the electrons (but not quite the ions) have been used. Particle and wave spectra have been measured. Wave-particle interaction has been shown to play a minor role in the only case that has been quantitatively analyzed. The three-dimensional potential distribution has been mapped. The particle budget requires the radial electric field to be outward in the no magnetic field case but inward with magnetic field, in agreement with what is observed above the aurora. (author)

  11. Patch holography using a double layer microphone array

    DEFF Research Database (Denmark)

    Gomes, Jesper Skovhus

    a closed local element mesh that surrounds the microphone array, and with a part of the mesh coinciding with a patch, the entire source is not needed in the model. Since the array has two layers, sources/reflections behind the array are also allowed. The Equivalent Source Method (ESM) is another technique...... in which the sound field is represented by a set of monopoles placed inside the source. In this paper these monopoles are distributed so that they surround the array, and the reconstruction is compared with the IBEM-based approach. The comparisons are based on computer simulations with a planar double...... layer array and sources with different shapes....

  12. Electrostatic double-layer interaction between stacked charged bilayers

    Science.gov (United States)

    Hishida, Mafumi; Nomura, Yoko; Akiyama, Ryo; Yamamura, Yasuhisa; Saito, Kazuya

    2017-10-01

    The inapplicability of the DLVO theory to multilayered anionic bilayers is found in terms of the co-ion-valence dependence of the lamellar repeat distance. Most of the added salt is expelled from the interlamellar space to the bulk due to the Gibbs-Donnan effect on multiple bilayers with the bulk. The electrostatic double-layer interaction is well expressed by the formula recently proposed by Trefalt. The osmotic pressure due to the expelled ions, rather than the van der Waals interaction, is the main origin of the attractive force between the bilayers.

  13. Ion acoustic double layers in the presence of plasma source

    International Nuclear Information System (INIS)

    Okuda, H.; Ashour-Abdalla, M.

    1982-01-01

    Steady-state plasma turbulence and the formation of negative potential spikes and double layers in the presence of ion acoustic instabilities have been studied by means of one-dimensional particle simulations in which the velocities of a small fraction of electrons are replaced by the initial drifting Maxwellian at a constant rate. A steady state is found where negative potential spikes appear randomly in space and time giving rise to an anomalous resistivity much greater than previously found. Comparisons of the simulation results with laboratory and space plasmas are discussed

  14. Highly porous carbon with large electrochemical ion absorption capability for high-performance supercapacitors and ion capacitors

    Science.gov (United States)

    Wang, Shijie; Wang, Rutao; Zhang, Yabin; Zhang, Li

    2017-11-01

    Carbon-based supercapacitors have attracted extensive attention as the complement to batteries, owing to their durable lifespan and superiority in high-power-demand fields. However, their widespread use is limited by the low energy storage density; thus, a high-surface-area porous carbon is urgently needed. Herein, a highly porous carbon with a Brunauer-Emmett-Teller specific surface area up to 3643 m2 g-1 has been synthesized by chemical activation of papayas for the first time. This sp2-bonded porous carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form narrow mesopores of 2 ˜ 5 nm in width, which can be systematically tailored with varied activation levels. Two-electrode symmetric supercapacitors constructed by this porous carbon achieve energy density of 8.1 Wh kg-1 in aqueous electrolyte and 65.5 Wh kg-1 in ionic-liquid electrolyte. Furthermore, half-cells (versus Li or Na metal) using this porous carbon as ion sorption cathodes yield high specific capacity, e.g., 51.0 and 39.3 mAh g-1 in Li+ and Na+ based organic electrolyte. These results underline the possibility of obtaining the porous carbon for high-performance carbon-based supercapacitors and ion capacitors in a readily scalable and economical way.

  15. Highly porous carbon with large electrochemical ion absorption capability for high-performance supercapacitors and ion capacitors.

    Science.gov (United States)

    Wang, Shijie; Wang, Rutao; Zhang, Yabin; Zhang, Li

    2017-11-03

    Carbon-based supercapacitors have attracted extensive attention as the complement to batteries, owing to their durable lifespan and superiority in high-power-demand fields. However, their widespread use is limited by the low energy storage density; thus, a high-surface-area porous carbon is urgently needed. Herein, a highly porous carbon with a Brunauer-Emmett-Teller specific surface area up to 3643 m 2 g -1 has been synthesized by chemical activation of papayas for the first time. This sp 2 -bonded porous carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form narrow mesopores of 2 ∼ 5 nm in width, which can be systematically tailored with varied activation levels. Two-electrode symmetric supercapacitors constructed by this porous carbon achieve energy density of 8.1 Wh kg -1 in aqueous electrolyte and 65.5 Wh kg -1 in ionic-liquid electrolyte. Furthermore, half-cells (versus Li or Na metal) using this porous carbon as ion sorption cathodes yield high specific capacity, e.g., 51.0 and 39.3 mAh g -1 in Li + and Na + based organic electrolyte. These results underline the possibility of obtaining the porous carbon for high-performance carbon-based supercapacitors and ion capacitors in a readily scalable and economical way.

  16. The double layers in the plasma sheet boundary layer during magnetic reconnection

    Science.gov (United States)

    Guo, J.; Yu, B.

    2014-11-01

    We studied the evolutions of double layers which appear after the magnetic reconnection through two-dimensional electromagnetic particle-in-cell simulation. The simulation results show that the double layers are formed in the plasma sheet boundary layer after magnetic reconnection. At first, the double layers which have unipolar structures are formed. And then the double layers turn into bipolar structures, which will couple with another new weak bipolar structure. Thus a new double layer or tripolar structure comes into being. The double layers found in our work are about several ten Debye lengths, which accords with the observation results. It is suggested that the electron beam formed during the magnetic reconnection is responsible for the production of the double layers.

  17. Preparation of mesoporous NiO with a bimodal pore size distribution and application in electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Wang Dengchao; Ni Wenbin; Pang Huan; Lu Qingyi; Huang Zhongjie [Key Laboratory of Analytical Chemistry for Life Science (MOE), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210008 (China); Zhao Jianwei, E-mail: zhaojw@nju.edu.c [Key Laboratory of Analytical Chemistry for Life Science (MOE), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210008 (China)

    2010-09-01

    Mesoporous nickel oxide with a porous structure exhibiting a bimodal pore size distribution (2.6 and 30.3 nm diameter pores) has been synthesized in this paper. Firstly, a mesoporous precursor of coordination complex Ni{sub 3}(btc){sub 2}.12H{sub 2}O (btc = 1,3,5-benzenrtricarboxylic acid) is synthesized based on the metal-organic coordination mechanism by a hydrothermal method. Then mesoporous NiO with a bimodal size distribution is obtained by calcining the precursor in the air, and characterized by transmission electron microscopy and N{sub 2} adsorption measurements. Such unique multiple porous structure indicates a promising application of the obtained NiO as electrode materials for supercapacitors. The electrochemical behavior has been investigated by cyclic voltammogram, electrochemical impedance spectra and chronopotentiometry in 3 wt.% KOH aqueous electrolyte. The results reveal that the prepared NiO has high-capacitance retention at high scan rate and exhibits excellent cycle-life stability due to its special mesoporous character with bimodal size distribution.

  18. Synthesis and characterization of pulsed polymerized poly(3,4-ethylenedioxythiophene) electrodes for high-performance electrochemical capacitors

    International Nuclear Information System (INIS)

    Pandey, G.P.; Rastogi, A.C.

    2013-01-01

    Poly(3,4-ethylenedioxythiophene) (PEDOT) is electrochemically prepared as a film on flexible thin graphite substrate by short galvanic pulse method in organic media. For comparative studies, PEDOT films are also prepared by potentiostatic polymerization method. The nucleation and growth mechanism for PEDOT film polymerized by short current pulses is presented with morphological and structural studies. The growth of PEDOT is continuous during the pulse off period as confirmed by the deposited mass of PEDOT by these two different methods. The SEM studies of pulse polymerized PEDOT films with different pulse on time show the features of highly porous and ridge like structures which help in rapid migration of dopant ClO 4 − ions during the charge and discharge processes. The X-ray photoelectron spectroscopy (XPS) studies confirm that in the pulse polymerized PEDOT films polymer chains are fully conjugated with the dopant ClO 4 − ions. The electrochemical characterization of PEDOT films show that pulse polymerized PEDOT films exhibited high specific capacitance (126.5 F g −1 ) with an improved energy density and rate kinetics as comparison to the potentiostatically deposited PEDOT films (100 F g −1 ) in aqueous electrolyte.

  19. In situ one-pot synthesis of graphene–polyaniline nanofiber composite for high-performance electrochemical capacitors

    International Nuclear Information System (INIS)

    Jin, Yuhong; Fang, Mou; Jia, Mengqiu

    2014-01-01

    In this work, graphene–polyaniline nanofiber (G/PANI-F) composite is prepared through a new and one-pot method that includes the reduction of graphene oxide (GO) by aniline and then followed by in-situ polymerization. Aniline plays the two roles in this method: as a chemical reducing agent to reduce GO to graphene and as a monomer to prepare polyaniline nanofiber (PANI-F). Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy and transmission electron microscopy are employed to confirm that GO can be reduced by aniline and PANI-F can be deposited on the surface of graphene. The electrochemical properties of G/PANI-F composite electrode are measured by using cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. The G/PANI-F composite electrode exhibits enhanced specific capacitance of 965 F g −1 at 0.5 A g −1 and the capacity retention is 90% after 2000 cycles.

  20. Electrostatic double layers and a plasma evacuation process

    International Nuclear Information System (INIS)

    Raadu, M.A.; Carlqvist, P.

    1979-12-01

    An evacuation process due to the growth of current driven instabilities in a plasma is discussed. The process, which leads to localized extreme density reductions, is related to the formation of electrostatic double layers. The initial linear phase is treated using the superposition of unstable plasma waves. In the long wave length, non-dispersive limit a density dip, which is initially present as a small disturbance, grows rapidly and remains localized in the plasma. The process works for a variety of plasma conditions provided a certain current density is exceeded. For a particular choice of plasma parameters the non-linear development is followed, by solving the coupled Vlasov-Poisson equations by finite difference methods. The evacuation process is found to work even more effectively in the non-linear phase and leads to an extreme density reduction within the dip. It is suggested that the growth of such structures produces weak points within the plasma that can lead to the formation of double layers. (Auth.)

  1. Evolution of plasma double layers in laser-ablation plumes

    International Nuclear Information System (INIS)

    Gurlui, S.; Sanduloviciu, M.; Mihesan, C.; Ziskind, M.; Focsa, C.

    2005-01-01

    The double layers (DLs) are one of the most complex problems of the plasma physics. These layers are apparently important not only in laboratory plasmas and laser-ablation plasma plumes but also in natural phenomena, e.g. the aurora and fire balls.This work studies the dynamics of the double layers in a laser ablation plume from different targets irradiated by a Nd: YAG 10 ns pulsed laser. The plasma formation was studied by means of both Langmuir probe and mass spectrometry methods using an experimental set-up developed for the study of environmental or technological interest samples. The ionic current distribution in plasma plume formation was recorded in different experimental conditions. We have found that it depends on the laser energy, the pressure of the buffer gas and the probe position. The periodical oscillations recorded in different experimental conditions prove that these plasma formations (DLs) are local physical systems able to accumulate and release energy. Acting as storing and releasing energy elements, the DLs can sustain periodical or non-periodical variations of the current or of the other global parameters of the plasma. (author)

  2. Simultaneous control of thermoelectric properties in p- and n-type materials by electric double-layer gating: New design for thermoelectric device

    Science.gov (United States)

    Takayanagi, Ryohei; Fujii, Takenori; Asamitsu, Atsushi

    2015-05-01

    We report a novel design of a thermoelectric device that can control the thermoelectric properties of p- and n-type materials simultaneously by electric double-layer gating. Here, p-type Cu2O and n-type ZnO were used as the positive and negative electrodes of the electric double-layer capacitor structure. When a gate voltage was applied between the two electrodes, holes and electrons accumulated on the surfaces of Cu2O and ZnO, respectively. The thermopower was measured by applying a thermal gradient along the accumulated layer on the electrodes. We demonstrate here that the accumulated layers worked as a p-n pair of the thermoelectric device.

  3. A high energy and power Li-ion capacitor based on a TiO2 nanobelt array anode and a graphene hydrogel cathode.

    Science.gov (United States)

    Wang, Huanwen; Guan, Cao; Wang, Xuefeng; Fan, Hong Jin

    2015-03-25

    A novel hybrid Li-ion capacitor (LIC) with high energy and power densities is constructed by combining an electrochemical double layer capacitor type cathode (graphene hydrogels) with a Li-ion battery type anode (TiO(2) nanobelt arrays). The high power source is provided by the graphene hydrogel cathode, which has a 3D porous network structure and high electrical conductivity, and the counter anode is made of free-standing TiO(2) nanobelt arrays (NBA) grown directly on Ti foil without any ancillary materials. Such a subtle designed hybrid Li-ion capacitor allows rapid electron and ion transport in the non-aqueous electrolyte. Within a voltage range of 0.0-3.8 V, a high energy of 82 Wh kg(-1) is achieved at a power density of 570 W kg(-1). Even at an 8.4 s charge/discharge rate, an energy density as high as 21 Wh kg(-1) can be retained. These results demonstrate that the TiO(2) NBA//graphene hydrogel LIC exhibits higher energy density than supercapacitors and better power density than Li-ion batteries, which makes it a promising electrochemical power source. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Electrodeposited Mn3O4-NiO-Co3O4 as a composite electrode material for electrochemical capacitor

    International Nuclear Information System (INIS)

    Rusi; Majid, S.R.

    2015-01-01

    Highlights: • Composite electrodes were synthesized by in situ electrodeposition method. • The highest specific capacitance of composite electrode is 7404 F g −1 . • The power density of composite electrode is 99 kW kg −1 at current density of 20 A g −1 . • The addition of K 3 Fe(CN) 6 in KOH electrolyte has improved the electrochemical performance. - Abstract: A simple and easy galvanostatic electrodeposition method is used to synthesise a composite electrode consisting of manganese oxide (Mn 3 O 4 ), nickel oxide (NiO) and cobalt oxide (Co 3 O 4 ). The influence of Co 3 O 4 on the morphology of fixed Mn 3 O 4 -NiO particles is investigated with a field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The nature and elemental of the composite are examined by means of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The electrochemical performances of an Mn 3 O 4 -NiO-Co 3 O 4 nanostructure/SS composite electrode are studied by cyclic voltammetry (CV) and galvanostatic charge-discharge (CD) in various electrolytes, i.e. 0.5 M Na 2 SO 4 , 0.5 M KOH, 0.5 M Na 2 SO 4 /0.04 M K 3 Fe(CN) 6 and 0.5 M KOH/0.04 M K 3 Fe(CN) 6 electrolytes. The composite electrode prepared from 0.15 M Co deposition solution exhibits the optimum specific capacitance of 7404 F g −1 with high energy and power density of 1028 Wh kg −1 and 99 kW kg −1 at 20 A g −1 in mix KOH/0.04 M K 3 Fe(CN) 6 electrolyte, respectively. The results show that the incorporation of K 3 Fe(CN) 6 in KOH electrolyte influences the capacitance of Mn 3 O 4 -NiO-Co 3 O 4 composite electrodes

  5. Hybrid capacitors utilizing halogen-based redox reactions at interface between carbon positive electrode and aqueous electrolytes

    Science.gov (United States)

    Yamazaki, Shigeaki; Ito, Tatsuya; Murakumo, Yuka; Naitou, Masashi; Shimooka, Toshiharu; Yamagata, Masaki; Ishikawa, Masashi

    2016-09-01

    We propose novel hybrid capacitors (HCs) with electrolyte-involved redox reactions of bromide or iodide species by pretreatment of an activated carbon positive electrode. The treatment is simple; impregnation of pores at an activated carbon fiber cloth (ACFC) as a positive electrode with bromine- or iodine-containing water before cell assembly. The treated positive electrode is applied to a HC cell with a non-treated negative electrode of ACFC and its electrochemical performance is investigated by galvanostatic cycling and leakage current tests. Few studies on such "electrolytic" charge storage systems have provided acceptable capacitor performance because of inevitable self-discharge caused by diffusion of charged species form an electrode to the other one through an electrolyte. Nevertheless, our electrolyte-redox-based HCs show excellent performance without undesirable diffusion of charged species. Moreover, the present HC utilizing a bromide redox system fulfills a practical cell voltage of 1.8 V in spite of an aqueous electrolyte system. This high voltage provides excellent energy density, which is 5 times higher than that in a conventional aqueous electric double-layer capacitor (EDLC), and 1.2 times higher even than that in a 2.7 V-class non-aqueous EDLC, while keeping high charge-discharge rate capability.

  6. Modeling Electric Double-Layers Including Chemical Reaction Effects

    DEFF Research Database (Denmark)

    Paz-Garcia, Juan Manuel; Johannesson, Björn; Ottosen, Lisbeth M.

    2014-01-01

    A physicochemical and numerical model for the transient formation of an electric double-layer between an electrolyte and a chemically-active flat surface is presented, based on a finite elements integration of the nonlinear Nernst-Planck-Poisson model including chemical reactions. The model works...... for symmetric and asymmetric multi-species electrolytes and is not limited to a range of surface potentials. Numerical simulations are presented, for the case of a CaCO3 electrolyte solution in contact with a surface with rate-controlled protonation/deprotonation reactions. The surface charge and potential...... are determined by the surface reactions, and therefore they depends on the bulk solution composition and concentration...

  7. Drag Effect in Double-Layer Dipolar Fermi Gases

    International Nuclear Information System (INIS)

    Tanatar, B; Renklioglu, B; Oktel, M O

    2014-01-01

    We consider two parallel layers of two-dimensional spin-polarized dipolar Fermi gas without any tunneling between the layers. The effective interactions describing screening and correlation effects between the dipoles in a single layer (intra-layer) and across the layers (interlayer) are modeled within the Hubbard approximation. We calculate the rate of momentum transfer between the layers when the gas in one layer has a steady flow. The momentum transfer induces a steady flow in the second layer which is assumed initially at rest. This is the drag effect familiar from double-layer semiconductor and graphene structures. Our calculations show that the momentum relaxation time has temperature dependence similar to that in layers with charged particles which we think is related to the contributions from the collective modes of the system

  8. Thermal analysis of a double layer phase change material floor

    International Nuclear Information System (INIS)

    Jin Xing; Zhang Xiaosong

    2011-01-01

    Phase change materials (PCMs) can be used to shift the cooling or heating load from the peak period to the off-peak period. In this paper, a new double layer phase change material (PCM) floor is put forward. The two layers of PCM have different melting temperature. The system is used to store heat or cold energy in the off-peak period and release them in the peak period during heating or cooling. According to the numerical model built in this paper, the thermal performances of the floor are analyzed. The results show that the optimal melting temperatures of PCMs exist. The fluctuations of the floor surface temperatures and the heat fluxes will be reduced and the system still can provide a certain amount of heat or cold energy after the heat pump or chiller has been turned off for a long time. Compared to the floor without PCM, the energy released by the floor with PCM in peak period will be increased by 41.1% and 37.9% during heating and cooling when the heat of fusion of PCM is 150 kJ/kg. - Highlights: → A new double layer phase change material floor is put forward. → The system is used to store heat or cold energy in the off-peak period and release them in the peak period during heating or cooling. → The optimal melting temperatures of PCMs in the system exist. → The heat and cold energy released by the floor with PCM in peak period can be increased by 41.1% and 37.9%.

  9. Layer by Layer Ex-Situ Deposited Cobalt-Manganese Oxide as Composite Electrode Material for Electrochemical Capacitor.

    Science.gov (United States)

    Rusi; Chan, P Y; Majid, S R

    2015-01-01

    The composite metal oxide electrode films were fabricated using ex situ electrodeposition method with further heating treatment at 300°C. The obtained composite metal oxide film had a spherical structure with mass loading from 0.13 to 0.21 mg cm(-2). The structure and elements of the composite was investigated using X-ray diffraction (XRD) and energy dispersive X-ray (EDX). The electrochemical performance of different composite metal oxides was studied by cyclic voltammetry (CV) and galvanostatic charge-discharge (CD). As an active electrode material for a supercapacitor, the Co-Mn composite electrode exhibits a specific capacitance of 285 Fg(-1) at current density of 1.85 Ag(-1) in 0.5 M Na2SO4 electrolyte. The best composite electrode, Co-Mn electrode was then further studied in various electrolytes (i.e., 0.5 M KOH and 0.5 M KOH/0.04 M K3Fe(CN) 6 electrolytes). The pseudocapacitive nature of the material of Co-Mn lead to a high specific capacitance of 2.2 x 10(3) Fg(-1) and an energy density of 309 Whkg(-1) in a 0.5 M KOH/0.04 M K3Fe(CN) 6 electrolyte at a current density of 10 Ag(-1). The specific capacitance retention obtained 67% of its initial value after 750 cycles. The results indicate that the ex situ deposited composite metal oxide nanoparticles have promising potential in future practical applications.

  10. In situ one-pot preparation of reduced graphene oxide/polyaniline composite for high-performance electrochemical capacitors

    International Nuclear Information System (INIS)

    Chen, Nali; Ren, Yapeng; Kong, Peipei; Tan, Lin; Feng, Huixia; Luo, Yongchun

    2017-01-01

    Highlights: • A new method to prepare reduced graphene oxide/polyaniline composite is developed. • Aniline serves as a reduction for graphene oxide under weak alkali condition. • Different characterizations confirm that GO can be effectively reduced by aniline. • A high specific capacitance of 524.4 F·g"−"1 is obtained at 0.5 A·g"−"1. - Abstract: Reduced graphene oxide/polyaniline (rGO/PANI) composites are prepared through an effective in situ one-pot synthesis route that includes the reduction of graphene oxide (GO) by aniline under weak alkali condition via hydrothermal method and then followed by in situ polymerization of aniline. X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope and transmission electron microscope are employed to reveal that GO is successfully reduced by aniline under weak alkali condition and PANI can be deposited on the surfaces of reduced graphene oxide (rGO) sheets. The effect of rGO is optimized by tuning the mass ratios of aniline to GO to improve the electrochemical performance of rGO/PANI composites. The maximum specific capacitance of rGO/PANI composites achieves 524.4 F/g with a mass ratio of aniline to GO 10:1 at a current density of 0.5 A/g, in comparison to the specific capacitance of 397 F/g at the same current density of pure PANI. Particularly, the specific capacity retention rate is 81.1% after 2000 cycles at 100 mv/s scan rate, which is an improvement over that of pure PANI (55.5%).

  11. In situ one-pot preparation of reduced graphene oxide/polyaniline composite for high-performance electrochemical capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Nali [College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, Gansu (China); State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, Gansu (China); Ren, Yapeng; Kong, Peipei; Tan, Lin [College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, Gansu (China); Feng, Huixia, E-mail: fenghx@lut.cn [College of Petrochemical Technology, Lanzhou University of Technology, Lanzhou 730050, Gansu (China); Luo, Yongchun, E-mail: luoyc@lut.cn [State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, Gansu (China)

    2017-01-15

    Highlights: • A new method to prepare reduced graphene oxide/polyaniline composite is developed. • Aniline serves as a reduction for graphene oxide under weak alkali condition. • Different characterizations confirm that GO can be effectively reduced by aniline. • A high specific capacitance of 524.4 F·g{sup −1} is obtained at 0.5 A·g{sup −1}. - Abstract: Reduced graphene oxide/polyaniline (rGO/PANI) composites are prepared through an effective in situ one-pot synthesis route that includes the reduction of graphene oxide (GO) by aniline under weak alkali condition via hydrothermal method and then followed by in situ polymerization of aniline. X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope and transmission electron microscope are employed to reveal that GO is successfully reduced by aniline under weak alkali condition and PANI can be deposited on the surfaces of reduced graphene oxide (rGO) sheets. The effect of rGO is optimized by tuning the mass ratios of aniline to GO to improve the electrochemical performance of rGO/PANI composites. The maximum specific capacitance of rGO/PANI composites achieves 524.4 F/g with a mass ratio of aniline to GO 10:1 at a current density of 0.5 A/g, in comparison to the specific capacitance of 397 F/g at the same current density of pure PANI. Particularly, the specific capacity retention rate is 81.1% after 2000 cycles at 100 mv/s scan rate, which is an improvement over that of pure PANI (55.5%).

  12. Vented Capacitor

    Science.gov (United States)

    Brubaker, Michael Allen; Hosking, Terry Alan

    2006-04-11

    A technique of increasing the corona inception voltage (CIV), and thereby increasing the operating voltage, of film/foil capacitors is described. Intentional venting of the capacitor encapsulation improves the corona inception voltage by allowing internal voids to equilibrate with the ambient environment.

  13. CoCr/NiFe double layers studied by FMR and VSM

    NARCIS (Netherlands)

    Stam, M.T.H.C.W.; Gerritsma, G.J.; Lodder, J.C.; Popma, T.J.A.

    1987-01-01

    CoCr/NiFe double layers were investigated by FMR and VSM. The FMR linewidth of NiFe of the double layer is about twice that of a single NiFe layer. The resonance field is the same in both cases. Using the VSM the coercive field of the CoCr layer of the double layer was obtained. It is approximately

  14. Obliquely Propagating Non-Monotonic Double Layer in a Hot Magnetized Plasma

    International Nuclear Information System (INIS)

    Kim, T.H.; Kim, S.S.; Hwang, J.H.; Kim, H.Y.

    2005-01-01

    Obliquely propagating non-monotonic double layer is investigated in a hot magnetized plasma, which consists of a positively charged hot ion fluid and trapped, as well as free electrons. A model equation (modified Korteweg-de Vries equation) is derived by the usual reductive perturbation method from a set of basic hydrodynamic equations. A time stationary obliquely propagating non-monotonic double layer solution is obtained in a hot magnetized-plasma. This solution is an analytic extension of the monotonic double layer and the solitary hole. The effects of obliqueness, external magnetic field and ion temperature on the properties of the non-monotonic double layer are discussed

  15. In situ synthesized heteropoly acid/polyaniline/graphene nanocomposites to simultaneously boost both double layer- and pseudo-capacitance for supercapacitors.

    Science.gov (United States)

    Cui, Zhiming; Guo, Chun Xian; Yuan, Weiyong; Li, Chang Ming

    2012-10-05

    It is challenging to simultaneously increase double layer- and pseudo-capacitance for supercapacitors. Phosphomolybdic acid/polyaniline/graphene nanocomposites (PMo(12)-PANI/GS) were prepared by using PMo(12) as a bifunctional reagent for not only well dispersing graphene for high electrochemical double layer capacitance but also in situ chemically polymerizing aniline for high pseudocapacitance, resulting in a specific capacitance of 587 F g(-1), which is ~1.5 and 6 times higher than that of PANI/GS (392 F g(-1)) and GS (103 F g(-1)), respectively. The nanocomposites also exhibit good reversibility and stability. Other kinds of heteropolyacids such as molybdovanadophosphoric acids (PMo(12-x)V(x), x = 1, 2 and 3) were also used to prepare PMo(12-x)V(x)-PANI/GS nanocomposites, also showing enhanced double layer- and pseudo-capacitance. This further proves the proposed concept to simultaneously boost both double layer- and pseudo-capacitance and demonstrates that it could be a universal approach to significantly improve the capacitance for supercapacitors.

  16. Emergence of a Stern Layer from the Incorporation of Hydration Interactions into the Gouy-Chapman Model of the Electrical Double Layer.

    Science.gov (United States)

    Brown, Matthew A; Bossa, Guilherme Volpe; May, Sylvio

    2015-10-27

    In one of the most commonly used phenomenological descriptions of the electrical double layer, a charged solid surface and a diffuse region of mobile ions are separated from each other by a thin charge-depleted Stern layer. The Stern layer acts as a capacitor that improves the classical Gouy-Chapman model by increasing the magnitude of the surface potential and limiting the maximal counterion concentration. We show that very similar Stern-like properties of the diffuse double layer emerge naturally from adding a nonelectrostatic hydration repulsion to the electrostatic Coulomb potential. The interplay of electrostatic attraction and hydration repulsion of the counterions and the surface leads to the formation of a diffuse counterion layer that remains well separated from the surface. In addition, hydration repulsions between the ions limit and control the maximal ion concentration and widen the width of the diffuse double layer. Our mean-field model, which we express in terms of electrostatic and hydration potentials, is physically consistent and conceptually similar to the classical Gouy-Chapman model. It allows the incorporation of ion specificity, accounts for hydration properties of charged surfaces, and predicts Stern layer properties, which we analyze in terms of the effective size of the hydrated counterions.

  17. The Importance of Ion Size and Electrode Curvature on Electrical Double Layers in Ionic Liquids

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Guang [Clemson University; Qiao, Rui [ORNL; Huang, Jingsong [ORNL; Dai, Sheng [ORNL; Sumpter, Bobby G [ORNL; Meunier, Vincent [ORNL

    2010-01-01

    Room-temperature ionic liquids (ILs) are an emerging class of electrolytes for supercapacitors. We investigate the effects of ion size and electrode curvature on the electrical double layers (EDLs) in two ILs 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], using a combination of molecular dynamics (MD) and quantum density functional theory (DFT) simulations. The sizes of the counter-ion and co-ion affect the ion distribution and orientational structure of EDLs. The EDL capacitances near both planar and cylindrical electrodes were found to follow the order: [BMIM][Cl] (near the positive electrode) > [BMIM][PF(6)] (near the positive electrode) {approx} [BMIM][Cl] (near the negative electrode) {approx} [BMIM][PF(6)] (near the negative electrode). The EDL capacitance was also found to increase as the electrode curvature increases. These capacitance data can be fit to the Helmholtz model and the recently proposed exohedral electrical double-cylinder capacitor (xEDCC) model when the EDL thickness is properly parameterized, even though key features of the EDLs in ILs are not accounted for in these models. To remedy the shortcomings of existing models, we propose a 'Multiple Ion Layers with Overscreening' (MILO) model for the EDLs in ILs that takes into account two critical features of such EDLs, i.e., alternating layering of counter-ions and co-ions and charge overscreening. The capacitance computed from the MILO model agrees well with the MD prediction. Although some input parameters of the MILO model must be obtained from MD simulations, the MILO model may provide a new framework for understanding many important aspects of EDLs in ILs (e.g., the variation of EDL capacitance with the electrode potential) that are difficult to interpret using classical EDL models and experiments.

  18. Plasmons in spatially separated double-layer graphene nanoribbons

    International Nuclear Information System (INIS)

    Bagheri, Mehran; Bahrami, Mousa

    2014-01-01

    Motivated by innovative progresses in designing multi-layer graphene nanostructured materials in the laboratory, we theoretically investigate the Dirac plasmon modes of a spatially separated double-layer graphene nanoribbon system, made up of a vertically offset armchair and metallic graphene nanoribbon pair. We find striking features of the collective excitations in this novel Coulomb correlated system, where both nanoribbons are supposed to be either intrinsic (undoped/ungated) or extrinsic (doped/gated). In the former, it is shown the low-energy acoustical and the high-energy optical plasmon modes are tunable only by the inter-ribbon charge separation. In the later, the aforementioned plasmon branches are modified by the added doping factor. As a result, our model could be useful to examine the existence of a linear Landau-undamped low-energy acoustical plasmon mode tuned via the inter-ribbon charge separation as well as doping. This study might also be utilized for devising novel quantum optical waveguides based on the Coulomb coupled graphene nanoribbons

  19. Ray-theory approach to electrical-double-layer interactions.

    Science.gov (United States)

    Schnitzer, Ory

    2015-02-01

    A novel approach is presented for analyzing the double-layer interaction force between charged particles in electrolyte solution, in the limit where the Debye length is small compared with both interparticle separation and particle size. The method, developed here for two planar convex particles of otherwise arbitrary geometry, yields a simple asymptotic approximation limited to neither small zeta potentials nor the "close-proximity" assumption underlying Derjaguin's approximation. Starting from the nonlinear Poisson-Boltzmann formulation, boundary-layer solutions describing the thin diffuse-charge layers are asymptotically matched to a WKBJ expansion valid in the bulk, where the potential is exponentially small. The latter expansion describes the bulk potential as superposed contributions conveyed by "rays" emanating normally from the boundary layers. On a special curve generated by the centers of all circles maximally inscribed between the two particles, the bulk stress-associated with the ray contributions interacting nonlinearly-decays exponentially with distance from the center of the smallest of these circles. The force is then obtained by integrating the traction along this curve using Laplace's method. We illustrate the usefulness of our theory by comparing it, alongside Derjaguin's approximation, with numerical simulations in the case of two parallel cylinders at low potentials. By combining our result and Derjaguin's approximation, the interaction force is provided at arbitrary interparticle separations. Our theory can be generalized to arbitrary three-dimensional geometries, nonideal electrolyte models, and other physical scenarios where exponentially decaying fields give rise to forces.

  20. Numerical simulation of diffuse double layer around microporous electrodes based on the Poisson–Boltzmann equation

    International Nuclear Information System (INIS)

    Kitazumi, Yuki; Shirai, Osamu; Yamamoto, Masahiro; Kano, Kenji

    2013-01-01

    Graphical abstract: - Highlights: • Diffuse double layers overlap with each other in the micropore. • The overlapping of the diffuse double layer affects the double layer capacitance. • The electric field becomes weak in the micropore. • The electroneutrality is unsatisfactory in the micropore. - Abstract: The structure of the diffuse double layer around a nm-sized micropore on porous electrodes has been studied by numerical simulation using the Poisson–Boltzmann equation. The double layer capacitance of the microporous electrode strongly depends on the electrode potential, the electrolyte concentration, and the size of the micropore. The potential and the electrolyte concentration dependence of the capacitance is different from that of the planner electrode based on the Gouy's theory. The overlapping of the diffuse double layer becomes conspicuous in the micropore. The overlapped diffuse double layer provides the mild electric field. The intensified electric field exists at the rim of the orifice of the micropore because of the expansion of the diffuse double layers. The characteristic features of microporous electrodes are caused by the heterogeneity of the electric field around the micropores

  1. Large-amplitude double layers in a dusty plasma with an arbitrary ...

    Indian Academy of Sciences (India)

    Formation of large-amplitude double layers in a dusty plasma whose constituents are electrons, ions, warm dust grains and positive ion beam are studied using Sagdeev's pseudopotential technique. Existence of double layers is investigated. It is found that both the temperature of dust particles and ion beam temperature ...

  2. Experimental validation of sound field control with a circular double-layer array of loudspeakers

    DEFF Research Database (Denmark)

    Chang, Jiho; Jacobsen, Finn

    2013-01-01

    This paper is concerned with experimental validation of a recently proposed method of controlling sound fields with a circular double-layer array of loudspeakers [Chang and Jacobsen, J. Acoust. Soc. Am. 131(6), 4518-4525 (2012)]. The double-layer of loudspeakers is realized with 20 pairs of closed...

  3. Coulomb drag in anisotropic systems: a theoretical study on a double-layer phosphorene

    NARCIS (Netherlands)

    Saberi-Pouya, S.; Vazifehshenas, T.; Farmanbar Gelepordsari, M.; Salavati-Fard, T.

    2016-01-01

    We theoretically study the Coulomb drag resistivity in a double-layer electron system with highly anisotropic parabolic band structure using Boltzmann transport theory. As an example, we consider a double-layer phosphorene on which we apply our formalism. This approach, in principle, can be tuned

  4. Effect of negative ions on the formation of weak ion acoustic double layers

    International Nuclear Information System (INIS)

    Kalita, M.K.; Bujarbarua, S.

    1985-01-01

    Using kinetic theory, small amplitude double layers associated with ion acoustic waves in a plasma containing negative species of ions were investigated. Analytic solution for the double layer potential was carried out. The limiting values of the negative ion density for the existence of this type of DL were calculated and the application of this result to space plasmas is discussed. (author)

  5. Double Layer of a Gold Electrode Probed by AFM Force Measurements

    NARCIS (Netherlands)

    Barten, D.; Kleijn, J.M.; Duval, J.F.L.; Leeuwen, van H.P.; Lyklema, J.; Cohen Stuart, M.A.

    2003-01-01

    Colloidal probe atomic force microscopy was used to determine the electric double layer interactions between a gold electrode and a spherical silica probe. The double layer properties of the gold/solution interface were varied through the pH and salt concentration of the electrolyte, as well as by

  6. Current limitation by an electric double layer in ion laser discharges

    International Nuclear Information System (INIS)

    Torven, S.

    1977-12-01

    A theory for current limitation in ion laser discharges is investigated. The basic mechanism considered is saturation of the positive ion flux at an electric double layer by the limited flux of neutral atoms. The result is compared with a recently published synthesis of a large number of experimental data which agree well with those predicted by the double layer model

  7. An investigation of the double layers caused by space vehicles moving through the ionosphere

    International Nuclear Information System (INIS)

    Liu Sanqiu; Liao Jingjing

    2010-01-01

    On the basis of non-steady-state nonlinear coupling equations of high-frequency field, density disturbance and potential, the evolution of double layers in the wake region of space vehicles moving through the ionosphere is numerically simulated in the non-static limit case. The results show that the interactions among plasmas, the vehicle and high-frequency electromagnetic waves radiated from the antenna system of the vehicle can lead to the formation of double layers. It is shown that the double layer is a nonlinear entity-caviton. Potential disturbance far away from the vehicle and the peak value of potential near the vehicle in the double layer are obvious. This is very important for detecting space vehicles with a stealth characteristic and preventing space vehicles from being harmed by double layers.

  8. Relative permittivity in the electrical double layer from nonlinear optics

    Science.gov (United States)

    Boamah, Mavis D.; Ohno, Paul E.; Geiger, Franz M.; Eisenthal, Kenneth B.

    2018-06-01

    Second harmonic generation (SHG) spectroscopy has been applied to probe the fused silica/water interface at pH 7 and the uncharged 11 ¯ 02 sapphire/water interface at pH 5.2 in contact with aqueous solutions of NaCl, NaBr, NaI, KCl, RbCl, and CsCl as low as several 10 μM. For ionic strengths up to about 0.1 mM, the SHG responses were observed to increase, reversibly for all salts surveyed, when compared to the condition of zero salt added. Further increases in the salt concentration led to monotonic decreases in the SHG response. The SHG increases followed by decreases are found to be consistent with recent reports of phase interference and phase matching in nonlinear optics. By varying the relative permittivity employed in common mean field theories used to describe electrical double layers and by comparing our results to available literature data, we find that models recapitulating the experimental observations are the ones in which (1) the relative permittivity of the diffuse layer is that of bulk water, with other possible values as low as 30, (2) the surface charge density varies with salt concentration, and (3) the charge in the Stern layer or its thickness varies with salt concentration. We also note that the experimental data exhibit sensitivity depending on whether the salt concentration is increased from low to high values or decreased from high to low values, which, however, is not borne out in the fits, at least within the current uncertainties associated with the model point estimates.

  9. Determination of Surface Potential and Electrical Double-Layer Structure at the Aqueous Electrolyte-Nanoparticle Interface

    Directory of Open Access Journals (Sweden)

    Matthew A. Brown

    2016-01-01

    Full Text Available The structure of the electrical double layer has been debated for well over a century, since it mediates colloidal interactions, regulates surface structure, controls reactivity, sets capacitance, and represents the central element of electrochemical supercapacitors. The surface potential of such surfaces generally exceeds the electrokinetic potential, often substantially. Traditionally, a Stern layer of nonspecifically adsorbed ions has been invoked to rationalize the difference between these two potentials; however, the inability to directly measure the surface potential of dispersed systems has rendered quantitative measurements of the Stern layer potential, and other quantities associated with the outer Helmholtz plane, impossible. Here, we use x-ray photoelectron spectroscopy from a liquid microjet to measure the absolute surface potentials of silica nanoparticles dispersed in aqueous electrolytes. We quantitatively determine the impact of specific cations (Li^{+}, Na^{+}, K^{+}, and Cs^{+} in chloride electrolytes on the surface potential, the location of the shear plane, and the capacitance of the Stern layer. We find that the magnitude of the surface potential increases linearly with the hydrated-cation radius. Interpreting our data using the simplest assumptions and most straightforward understanding of Gouy-Chapman-Stern theory reveals a Stern layer whose thickness corresponds to a single layer of water molecules hydrating the silica surface, plus the radius of the hydrated cation. These results subject electrical double-layer theories to direct and falsifiable tests to reveal a physically intuitive and quantitatively verified picture of the Stern layer that is consistent across multiple electrolytes and solution conditions.

  10. Determination of Surface Potential and Electrical Double-Layer Structure at the Aqueous Electrolyte-Nanoparticle Interface

    Science.gov (United States)

    Brown, Matthew A.; Abbas, Zareen; Kleibert, Armin; Green, Richard G.; Goel, Alok; May, Sylvio; Squires, Todd M.

    2016-01-01

    The structure of the electrical double layer has been debated for well over a century, since it mediates colloidal interactions, regulates surface structure, controls reactivity, sets capacitance, and represents the central element of electrochemical supercapacitors. The surface potential of such surfaces generally exceeds the electrokinetic potential, often substantially. Traditionally, a Stern layer of nonspecifically adsorbed ions has been invoked to rationalize the difference between these two potentials; however, the inability to directly measure the surface potential of dispersed systems has rendered quantitative measurements of the Stern layer potential, and other quantities associated with the outer Helmholtz plane, impossible. Here, we use x-ray photoelectron spectroscopy from a liquid microjet to measure the absolute surface potentials of silica nanoparticles dispersed in aqueous electrolytes. We quantitatively determine the impact of specific cations (Li+ , Na+ , K+ , and Cs+ ) in chloride electrolytes on the surface potential, the location of the shear plane, and the capacitance of the Stern layer. We find that the magnitude of the surface potential increases linearly with the hydrated-cation radius. Interpreting our data using the simplest assumptions and most straightforward understanding of Gouy-Chapman-Stern theory reveals a Stern layer whose thickness corresponds to a single layer of water molecules hydrating the silica surface, plus the radius of the hydrated cation. These results subject electrical double-layer theories to direct and falsifiable tests to reveal a physically intuitive and quantitatively verified picture of the Stern layer that is consistent across multiple electrolytes and solution conditions.

  11. Large amplitude ion-acoustic solitary waves and double layers in multicomponent plasma with positrons

    International Nuclear Information System (INIS)

    Sabry, R.

    2009-01-01

    A finite amplitude theory for ion-acoustic solitary waves and double layers in multicomponent plasma consisting of hot positrons, cold ions, and electrons with two-electron temperature distributions is presented. Conditions are obtained under which large amplitude stationary ion-acoustic solitary waves and double layers can exist. For the physical parameters of interest, the ion-acoustic solitary wave (double layers) profiles and the relationship between the maximum soliton (double layers) amplitude and the Mach number are found. Also, we have presented the region of existence of the large amplitude ion-acoustic waves by analyzing the structure of the pseudopotential. For the selected range of parameters, it is found that only positive solitary waves and double layers can exist. An analysis for the small amplitude limit through the Sagdeev pseudopotential analysis and the reductive perturbation theory shows the existence of positive and negative ion-acoustic solitary waves and double layers. The effects of positron concentration and temperature ratio on the characteristics of the solitary ion-acoustic waves and double layers (namely, the amplitude and width) are discussed in detail. The relevance of this investigation to space and laboratory plasmas is pointed out.

  12. Photon induced non-linear quantized double layer charging in quaternary semiconducting quantum dots.

    Science.gov (United States)

    Nair, Vishnu; Ananthoju, Balakrishna; Mohapatra, Jeotikanta; Aslam, M

    2018-03-15

    Room temperature quantized double layer charging was observed in 2 nm Cu 2 ZnSnS 4 (CZTS) quantum dots. In addition to this we observed a distinct non-linearity in the quantized double layer charging arising from UV light modulation of double layer. UV light irradiation resulted in a 26% increase in the integral capacitance at the semiconductor-dielectric (CZTS-oleylamine) interface of the quantum dot without any change in its core size suggesting that the cause be photocapacitive. The increasing charge separation at the semiconductor-dielectric interface due to highly stable and mobile photogenerated carriers cause larger electrostatic forces between the quantum dot and electrolyte leading to an enhanced double layer. This idea was supported by a decrease in the differential capacitance possible due to an enhanced double layer. Furthermore the UV illumination enhanced double layer gives us an AC excitation dependent differential double layer capacitance which confirms that the charging process is non-linear. This ultimately illustrates the utility of a colloidal quantum dot-electrolyte interface as a non-linear photocapacitor. Copyright © 2017 Elsevier Inc. All rights reserved.

  13. Time-dependent density functional theory for the charging kinetics of electric double layer containing room-temperature ionic liquids.

    Science.gov (United States)

    Lian, Cheng; Zhao, Shuangliang; Liu, Honglai; Wu, Jianzhong

    2016-11-28

    Understanding the charging kinetics of electric double layers is of fundamental importance for the design and development of novel electrochemical devices such as supercapacitors and field-effect transistors. In this work, we study the dynamic behavior of room-temperature ionic liquids using a classical time-dependent density functional theory that accounts for the molecular excluded volume effects, the electrostatic correlations, and the dispersion forces. While the conventional models predict a monotonic increase of the surface charge with time upon application of an electrode voltage, our results show that dispersion between ions results in a non-monotonic increase of the surface charge with the duration of charging. Furthermore, we investigate the effects of van der Waals attraction between electrode/ionic-liquid interactions on the charging processes.

  14. Microscopic Insights into the Electrochemical Behavior of Non-aqueous Electrolytes in Supercapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Deen [ORNL; Wu, Jianzhong [ORNL

    2013-01-01

    Electric double-layer capacitors (EDLC) are electrical devices that store energy by adsorption of ionic species at the inner surface of porous electrodes. Compared with aqueous electrolytes, ionic liquid and organic electrolytes have the advantage of larger potential windows, making them attractive for the next generation of EDLC with superior energy and power densities. The performance of both ionic liquid and organic electrolyte EDLC hinges on the judicious selection of the electrode pore size and the electrolyte composition that requires a comprehension of the charging behavior from a microscopic view. In this perspective, we discuss predictions from the classical density functional theory (CDFT) on the dependence of the capacitance on the pore size for ionic-liquid and organic-electrolyte EDLC. CDFT is applicable to electrodes with the pore size ranging from that below the ionic dimensionality to mesoscopic scales, thus unique for investigating the electrochemical behavior of the confined electrolytes for EDLC applications.

  15. Switchable capacitor

    NARCIS (Netherlands)

    Rottenberg, Xavier; Jansen, Henricus V.; Tilmans, H.A.C.; Tilmans, Hendrikus; De Raedt, Walter

    2011-01-01

    A micro electromechanical switchable capacitor is disclosed, comprising a substrate, a bottom elecrode, a dielaectric layer deposited on at least part of sai bottum electrode, a conductive floating electrode deposited on at least part of said dielectric layer, an armature positioned proximate to the

  16. Switchable capacitor

    NARCIS (Netherlands)

    Rottenberg, X.; Jansen, Henricus V.; Tilmans, H.A.C.; De Raedt, W.

    2003-01-01

    A micro electromechanical switchable capacitor is disclosed, comprising a substrate, a bottom elecrode, a dielaectric layer deposited on at least part of sai bottum electrode, a conductive floating electrode deposited on at least part of said dielectric layer, an armature positioned proximate to the

  17. Rotary capacitor

    CERN Multimedia

    CERN PhotoLab

    1971-01-01

    The rotating wheel of the rotary capacitor representing the most critical part of the new radio-frequency system of the synchro-cyclotron. The three rows of teeth on the circumference of the wheel pass between four rows of stator blades with a minimum clearance of 1 mm at a velocity of 1700 rev/min.

  18. Electron emission from a double-layer metal under femtosecond laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shuchang; Li, Suyu; Jiang, Yuanfei; Chen, Anmin, E-mail: amchen@jlu.edu.cn; Ding, Dajun; Jin, Mingxing, E-mail: mxjin@jlu.edu.cn

    2015-01-01

    In this paper we theoretically investigate electron emission during femtosecond laser ablation of single-layer metal (copper) and double-layer structures. The double-layer structure is composed of a surface layer (copper) and a substrate layer (gold or chromium). The calculated results indicate that the double-layer structure brings a change to the electron emission from the copper surface. Compared with the ablation of a single-layer, a double-layer structure may be helpful to decrease the relaxation time of the electron temperature, and optimize the electron emission by diminishing the tailing phenomenon under the same absorbed laser fluence. With the increase of the absorbed laser fluence, the effect of optimization becomes significant. This study provides a way to optimize the electron emission which can be beneficial to generate laser induced ultrafast electron pulse sources.

  19. Conditions for double layers in the Earth's magnetosphere and perhaps in other astrophysical objects

    International Nuclear Information System (INIS)

    Lyons, L.R.

    1987-01-01

    Double layers (i.e., electric fields parallel to B) form along auroral field lines in the Earth's magnetosphere. They form in order to maintain current continuity in the ionosphere in the presence of a magnetospheric electric field E with DEL.E not= O. Features which govern the formation of the double layers are: 1) the divergence of E; 2) the conductivity of the ionosphere; and 3) the current-voltage characteristics of auroral magnetic field lines. Astrophysical situations where DEL.E not= O is applied to a conducting plasma similar to the Earth's ionosphere are potential candidates for the formation of double layers. The region with DEL.E not= O can be generated within, or along field lines connected to, the conducting plasma. In addition to DEL.E, shear neutral flow in the conducting plasma can also form double layers. (author)

  20. Conditions for double layers in the Earth's magnetosphere and perhaps in other astrophysical objects

    International Nuclear Information System (INIS)

    Lyons, L.R.

    1987-01-01

    Double layers form along auroral field lines in the Earth's magnetosphere. They form in order to maintain current continuity in the ionosphere in the presence of a magnetospheric electric field E with nabla x E is not equal to 0. Features which govern the formation of the double layers are: (1) the divergence of E, (2) the conductivity of the ionosphere, and (3) the current-voltage characteristics of auroral magnetic field lines. Astrophysical situations where nabla x E is not equal to 0 is applied to a conducting plasma similar to the Earth's ionosphere are potential candidates for the formation of double layers. The region with nabla x E is not equal to 0 can be generated within, or along field lines connected to, the conducting plasma. In addition to nabla x E, shear neutral flow in the conducting plasma can also form double layers

  1. Experimental investigation of Cu-based, double-layered, microchannel heat exchangers

    International Nuclear Information System (INIS)

    Lu, Bin; Meng, W J; Mei, Fanghua

    2013-01-01

    Cu-based, single- and double-layered, microchannel heat exchangers (MHEs) were fabricated and assembled. Comparative measurements on liquid flow characteristics and heat transfer performance were conducted on these devices. Results were compared at the individual microchannel level as well as at the device level. The present results demonstrate that double-layered MHEs exhibit similar heat transfer performance while suffering a much lower pressure drop penalty compared to single-layered MHEs. Another Cu-based, double-layered, liquid–liquid counter-flow MHE was fabricated, assembled and tested. Results show that a low-volume, multilayered, high-performance, liquid-to-liquid MHE is achievable following the manufacturing protocols of the present double-layered, liquid–liquid counter-flow MHE. (paper)

  2. Long-term stability of a one-dimensional current-driven double layer

    International Nuclear Information System (INIS)

    Hori, N.; Yamamoto, T.

    1988-01-01

    Long-term (>an electron transit time over the system) stability of a one-dimensional current-driven double layer is studied by numerical experiments using particles. In these experiments, the potential difference across the system is self-consistently determined by the space charge distributions inside the system. Each boundary of the system supplies a nondrifting half-Maxwellian plasma. The current density is increased by increasing the number density of the source plasma at the injection (right) boundary. A double layer can be developed by injection of a sufficiently high current density. For a fixed level of current injection, plasmas carrying no current with various densities (n/sup ts/ 0 ) are loaded on the left side of the system. Whether or not the generated double layer can maintain its potential drop for a long period depends on the density (n/sup ts/ 0 ) relative to the initial density (n/sup */ 0 ) near the injection boundary: (1) the double layer is found to grow when n/sup ts/ 0 = n/sup */ 0 ; (2) the steady double layer is seen for a long period when n/sup ts/ 0 approx. >n/sup */ 0 ; (3) the double layer is found to decay when n/sup ts/ 0 is even higher than n/sup */ 0 . A new concept of the current polarizability P/sub c/ = J/n/sup number/ is introduced for understanding these results, where J is the current density flowing through the double layer and n/sup number/ is the plasma density at the injection front, i.e., the low-potential edge of the double layer

  3. Large-amplitude ion-acoustic double layers in a plasma with warm ions

    International Nuclear Information System (INIS)

    Roychoudury, R.K.; Bhattacharyya, S.; Varshni, Y.P.

    1990-01-01

    The conditions for the existence of an ion-acoustic double layer in a plasma with warm ions and two distinct groups of hot electrons have been studied using the Sagdeev potential method. A comparison is made with the published results of Bharuthram and Shukla for cold ions and a two temperature electron population. Numerical studies have been made to find out the effect of a finite ion temperature on the Mach number of the double layers

  4. Ion-acoustic double layers in multi-species plasmas maintained by negative ions

    International Nuclear Information System (INIS)

    Verheest, F.

    1989-01-01

    A study is made of ion-acoustic double layers in a plasma consisting of any number of cold positive and negative ion (and cold electron) species in addition to one isothermal electron population. The Sagdeev potential is obtained in general, together with limits on both compressive and rarefactive solutions for ion-acoustic double layers and/or solitons. Weak ion-acoustic double layers are described by a modified Korteweg-de Vries equation. Such double layers are not possible in plasmas with only positive ion species and one electron population. When one or more negative ion and/or cold electron species are included above a certain threshold density, rarefactive ion-acoustic double layers occur, but no compressive ones. The double-layer form of the potential is given, together with an application to a plasma with one positive and one negative ion component. It is shown that there is indeed such a threshold density for the negative ion density, depending on the charge-to-mass ratios of both types of ions. The threshold density is determined numerically for a range of such ratios and discussed in view of possible relevance to auroral and experimental plasmas. In the discussion, cold electrons can play the role of the negative ion species. (author)

  5. Double-layer appearance after evacuation of a chronic subdural hematoma.

    Science.gov (United States)

    Sucu, Hasan Kamil; Akar, Ömer

    2014-01-01

    To investigate the reason for and the course of the double-layer appearance in the postoperative computed tomographies (CTs) of chronic subdural hematoma (CSDHs). We reviewed CSDH cases that were operated on during the last 3 years, between January 2008 and December 2010. We checked the preoperative, early postoperative, and late postoperative CTs of these patients. We investigated the relationship between the formation of a double-layer appearance and the prognoses and demographic characteristics of the patients. Our database included 119 cases. A double-layer appearance was found in the postoperative CTs of 34 cases. The mean age of double-layer cases was older (72.5 ± 12.1) than that of the remaining 85 cases (63.1 ± 17.8). We did not find any relationship between the double-layer appearance and the reoperation/recurrence/death rates. The double-layer appearance after evacuation of a CSDH might be caused by enlargement of the subarachnoid space and is not related to the presence of any residual hematoma. This appearance is not considered as a reason for reoperation.

  6. Double-layer structure in polar mesospheric clouds observed from SOFIE/AIM

    Directory of Open Access Journals (Sweden)

    H. Gao

    2017-02-01

    Full Text Available Double-layer structures in polar mesospheric clouds (PMCs are observed by using Solar Occultation for Ice Experiment (SOFIE data between 2007 and 2014. We find 816 and 301 events of double-layer structure with percentages of 10.32 and 7.25 % compared to total PMC events, and the mean distances between two peaks are 3.06 and 2.73 km for the Northern Hemisphere (NH and Southern Hemisphere (SH respectively. Double-layer PMCs almost always have less mean ice water content (IWC than daily IWC during the core of the season, but they are close to each other at the beginning and the end. The result by averaging over all events shows that the particle concentration has obvious double peaks, while the particle radius exhibits an unexpected monotonic increase with decreasing altitude. By further analysis of the background temperature and water vapour residual profiles, we conclude that the lower layer is a reproduced one formed at the bottom of the upper layer. 56.00 and 47.51 % of all double-layer events for the NH and SH respectively have temperature enhancements larger than 2 K locating between their double peaks. The longitudinal anti-correlation between the gravity waves' (GWs' potential energies and occurrence frequencies of double-layer PMCs suggests that the double-layer PMCs tend to form in an environment where the GWs have weaker intensities.

  7. Ion acoustic waves and double-layers in electronegative expanding plasmas

    International Nuclear Information System (INIS)

    Plihon, Nicolas; Chabert, Pascal

    2011-01-01

    Ion acoustic waves and double-layers are observed in expanding plasmas in electronegative gases, i.e., plasmas containing an appreciable fraction of negative ions. The reported experiments are performed in argon gas with a variable amount of SF 6 . When varying the amount of SF 6 , the negative ion fraction increases and three main regimes were identified previously: (i) the plasma smoothly expands at low negative ion fraction, (ii) a static double-layer (associated with an abrupt potential drop and ion acceleration) forms at intermediate negative ion fraction, (iii) double-layers periodically form and propagate (in the plasma expansion direction) at high negative ion fraction. In this paper, we show that transition phases exist in between these regimes, where fluctuations are observed. These fluctuations are unstable slow ion acoustic waves, propagating in the direction opposite to the plasma expansion. These fluctuations are excited by the most unstable eigenmodes and display turbulent features. It is suggested that the static double layer forms when the ion acoustic fluctuations become non-linearly unstable: the double layer regime being a bifurcated state of the smoothly expanding regime. For the highest negative ion fraction, a coexistence of (upstream propagating) slow ion acoustic fluctuations and (downstream) propagating double layers was observed.

  8. Self-sacrifice Template Formation of Hollow Hetero-Ni7S6/Co3S4 Nanoboxes with Intriguing Pseudo-capacitance for High-performance Electrochemical Capacitors

    Science.gov (United States)

    Hua, Hui; Liu, Sijia; Chen, Zhiyi; Bao, Ruiqi; Shi, Yaoyao; Hou, Linrui; Pang, Gang; Hui, Kwun Nam; Zhang, Xiaogang; Yuan, Changzhou

    2016-02-01

    Herein, we report a simple yet efficient self-sacrifice template protocol to smartly fabricate hollow hetero-Ni7S6/Co3S4 nanoboxes (Ni-Co-S NBs). Uniform nickel cobalt carbonate nanocubes are first synthesized as the precursor via solvothermal strategy, and subsequently chemically sulfidized into hollow heter-Ni-Co-S NBs through anion-exchange process. When evaluated as electrode for electrochemical capacitors (ECs), the resultant hetero-Ni-Co-S NBs visually exhibit attractive pesudo-capacitance in KOH just after continuously cyclic voltammetry (CV) scanning for 100 cycles. New insights into the underlying energy-storage mechanism of the hollow hetero-Ni-Co-S electrode, based on physicochemical characterizations and electrochemical evaluation, are first put forward that the electrochemically induced phase transformation gradually occurrs during CV sweep from the hetero-Ni-Co-S to bi-component-active NiOOH and CoOOH, which are the intrinsic charge-storage phases for the appealing Faradaic capacitance (~677 F g-1 at 4 A g-1) of hollow Ni-Co-S NBs at high rates after cycling. When further coupled with negative activated carbon (AC), the AC//hetero-Ni-Co-S asymmetric device with extended electrochemical window of 1.5 V demonstrates high specific energy density of ~31 Wh kg-1. Of significance, we strongly envision that hollow design concept and new findings here hold great promise for enriching synthetic methodologies, and electrochemistry of complex metal sulfides for next-generation ECs.

  9. Flexible and weaveable capacitor wire based on a carbon nanocomposite fiber.

    Science.gov (United States)

    Ren, Jing; Bai, Wenyu; Guan, Guozhen; Zhang, Ye; Peng, Huisheng

    2013-11-06

    A flexible and weaveable electric double-layer capacitor wire is developed by twisting two aligned carbon nanotube/ordered mesoporous carbon composite fibers with remarkable mechanical and electronic properties as electrodes. This capacitor wire exhibits high specific capacitance and long life stability. Compared with the conventional planar structure, the capacitor wire is also lightweight and can be integrated into various textile structures that are particularly promising for portable and wearable electronic devices. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Electrochemical force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kalinin, Sergei V.; Jesse, Stephen; Collins, Liam F.; Rodriguez, Brian J.

    2017-01-10

    A system and method for electrochemical force microscopy are provided. The system and method are based on a multidimensional detection scheme that is sensitive to forces experienced by a biased electrode in a solution. The multidimensional approach allows separation of fast processes, such as double layer charging, and charge relaxation, and slow processes, such as diffusion and faradaic reactions, as well as capturing the bias dependence of the response. The time-resolved and bias measurements can also allow probing both linear (small bias range) and non-linear (large bias range) electrochemical regimes and potentially the de-convolution of charge dynamics and diffusion processes from steric effects and electrochemical reactivity.

  11. Towards understanding the effects of van der Waals strengths on the electric double-layer structures and capacitive behaviors

    Science.gov (United States)

    Yang, Huachao; Bo, Zheng; Yang, Jinyuan; Yan, Jianhua; Cen, Kefa

    2017-10-01

    Solid-liquid interactions are considered to play a crucial role in charge storage capability of electric double-layer capacitors (EDLCs). In this work, effects of van der Waals (VDW) strengths on the EDL structures and capacitive performances within two representative electrolytes of solvated aqueous solutions and solvent-free ionic liquids are illuminated by molecular dynamics simulations. Single crystalline metals with similar lattice constant but diverse VDW potentials are employed as electrodes. Upon enhancing VDW strengths, capacitance of aqueous electrolytes first increases conspicuously by ∼34.0% and then descends, manifesting a non-monotonic trend, which goes beyond traditional perspectives. Such unusual observation is interpreted by the excluded-volume effects stemmed from ion-solvent competitions. Stimulated by predominant coulombic interactions, more ions are aggregated at the interface despite of the increasing VDW potentials, facilitating superior screening efficiency and capacitance. However, further enhancing strengths preferentially attracts more solvents instead of ions to the electrified surface, which in turn strikingly repels ions from Helmholtz layers, deteriorating electrode capacitance. An essentially similar feather is also recognized for ionic liquids, while the corresponding mechanisms are prominently ascribed to the suppressed ionic separations issued from cation-anion competitions. We highlight that constructing electrode materials with a moderate-hydrophilicity could further advance the performances of EDLCs.

  12. Fundamental measure theory for the electric double layer: implications for blue-energy harvesting and water desalination

    International Nuclear Information System (INIS)

    Härtel, Andreas; Janssen, Mathijs; Samin, Sela; Roij, René van

    2015-01-01

    Capacitive mixing (CAPMIX) and capacitive deionization (CDI) are promising candidates for harvesting clean, renewable energy and for the energy efficient production of potable water, respectively. Both CAPMIX and CDI involve water-immersed porous carbon (supercapacitors) electrodes at voltages of the order of hundreds of millivolts, such that counter-ionic packing is important for the electric double layer (EDL) which forms near the surfaces of these porous materials. Thus, we propose a density functional theory (DFT) to model the EDL, where the White-Bear mark II fundamental measure theory functional is combined with a mean-field Coulombic and a mean spherical approximation-type correction to describe the interplay between dense packing and electrostatics, in good agreement with molecular dynamics simulations. We discuss the concentration-dependent potential rise due to changes in the chemical potential in capacitors in the context of an over-ideal theoretical description and its impact on energy harvesting and water desalination. Compared to less elaborate mean-field models our DFT calculations reveal a higher work output for blue-energy cycles and a higher energy demand for desalination cycles. (paper)

  13. A COMPARATIVE STUDY OF SINGLE VERSUS DOUBLE LAYER CLOSURE ON LOWER SEGMENT CAESAREAN SCAR

    Directory of Open Access Journals (Sweden)

    Kirtirekha Mohapatra

    2016-10-01

    Full Text Available BACKGROUND There are few issues in modern obstetrics that have been as controversial as management of a woman with a prior caesarean delivery. Hence, it is required to have evidence based correct practice of this surgical procedure. Healing of the uterine incision and the strength of the scar should be the most important consideration. The aim of the study is to compare the effect of technique of uterine closure (Single Layer vs. Double Layer on subsequent pregnancies and to find out, which technique has a better maternal and neonatal outcome by strengthening the scar. MATERIALS AND METHODS 500 cases of previous caesarean section pregnancies were taken, 250 from single layer closure group and 250 from double layer closure group. The mode of delivery during present pregnancy was noted. Integrity of scar, thickness of scar, presence of adhesion were documented. The neonates were observed. Results were compared so as to draw an inference about the better method. RESULTS Mean age between the two groups were similar. Majority did not have history of premature rupture of membrane during previous pregnancy. Postoperative complications were more when double layer closure of uterine scar was done in index surgery. Interpregnancy gap of <3 years was more commonly present in double layer closure group (52.8% in double layer versus 34.8% in single layer. Single layer had more scar tenderness (21.2%, thinned out scars (34.6%, incomplete ruptures (7.1% and complete ruptures (2.8% than double layer closure group. Neonatal outcomes were not statistically different in both the groups. CONCLUSION Double layer uterine closure seems to have better impact on scar integrity as compared to single layer uterine closure.

  14. Electric double layer effect on observable characteristics of the tunnel current through a bridged electrochemical contact

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Medvedev, I.G.; Ulstrup, Jens

    2007-01-01

    Scanning tunneling microscopy and electrical conductivity of redox molecules in conducting media (aqueous or other media) acquire increasing importance both as novel single-molecule science and with a view on molecular scale functional elements. Such configurations require full and independent el...

  15. A high energy and power sodium-ion hybrid capacitor based on nitrogen-doped hollow carbon nanowires anode

    Science.gov (United States)

    Li, Dongdong; Ye, Chao; Chen, Xinzhi; Wang, Suqing; Wang, Haihui

    2018-04-01

    The sodium ion hybrid capacitor (SHC) has been attracting much attention. However, the SHC's power density is significantly confined to a low level due to the sluggish ion diffusion in the anode. Herein, we propose to use an electrode with a high double layer capacitance as the anode in the SHC instead of insertion anodes. To this aim, nitrogen doped hollow carbon nanowires (N-HCNWs) with a high specific surface area are prepared, and the high capacitive contribution during the sodium ion storage process is confirmed by a series of electrochemical measurements. A new SHC consisting of a N-HCNW anode and a commercial active carbon (AC) cathode is fabricated for the first time. Due to the hybrid charge storage mechanism combining ion insertion and capacitive process, the as-fabricated SHC strikes a balance between the energy density and power density, a energy density of 108 Wh kg-1 and a power density of 9 kW kg-1 can be achieved, which overwhelms the electrochemical performances of most reported AC-based SHCs.

  16. Competitive effect of KOH activation on the electrochemical performances of carbon nanotubes for EDLC: Balance between porosity and conductivity

    International Nuclear Information System (INIS)

    Xu Bin; Wu Feng; Su Yuefeng; Cao Gaoping; Chen Shi; Zhou Zhiming; Yang Yusheng

    2008-01-01

    This work is focused on the competitive effects on the performance of the electric double layer capacitors (EDLCs) between porosity increase and simultaneous conductivity decrease for KOH-activated carbon nanotubes (CNTs). A series of the CNTs have been activated with KOH to enhance their surface areas for application in EDLCs. The microstructure of the activated carbon nanotubes (ACNTs) is characterized with N 2 adsorption, transmission electron microscopy (TEM) observation and electric conductivity measurement. Their electrochemical performances are evaluated in aqueous KOH electrolyte with galvanostatic charge/discharge, cyclic voltammetry, and ac impedance spectroscopy. It is found that the KOH activation enhances the specific surface area of the CNTs and its specific capacitance but decreases its electric conductivity and the rate performance in EDLC. By controlling the activation of the CNTs to balance the porosity and conductivity, ACNTs with both high capacitance and good rate performance are obtained

  17. Numerical simulation of white double-layer coating with different submicron particles on the spectral reflectance

    International Nuclear Information System (INIS)

    Chai, Jiale; Cheng, Qiang; Si, Mengting; Su, Yang; Zhou, Yifan; Song, Jinlin

    2017-01-01

    The spectral selective coating is becoming more and more popular against solar irradiation not only in keeping the coated objects stay cool but also retain the appearance of the objects by reducing the glare of reflected sunlight. In this work a numerical study is investigated to design the double-layer coating with different submicron particles to achieve better performance both in thermal and aesthetic aspects. By comparison, the performance of double-layer coating with TiO_2 and ZnO particles is better than that with single particles. What's more, the particle diameter, volume fraction of particle as well as substrate condition is also investigated. The results show that an optimized double-layer coating with particles should be the one with an appropriate particle diameter, volume fraction and the black substrate. - Highlights: • The double-layer coating has a great influence on both thermal and aesthetic aspects. • The double-layer coating performs better than the uniform one with single particles. • The volume fraction, particle diameter and substrate conditions are optimized.

  18. Fracture Characteristics Analysis of Double-layer Rock Plates with Both Ends Fixed Condition

    Directory of Open Access Journals (Sweden)

    S. R. Wang

    2014-07-01

    Full Text Available In order to research on the fracture and instability characteristics of double-layer rock plates with both ends fixed, the three-dimension computational model of double-layer rock plates under the concentrated load was built by using PFC3D technique (three-dimension particle flow code, and the mechanical parameters of the numerical model were determined based on the physical model tests. The results showed the instability process of the double-layer rock plates had four mechanical response phases: the elastic deformation stage, the brittle fracture of upper thick plate arching stage, two rock-arch bearing stage and two rock-arch failure stage; moreover, with the rock plate particle radius from small to large change, the maximum vertical force of double rock-arch appeared when the particle size was a certain value. The maximum vertical force showed an upward trend with the increase of the rock plate temperature, and in the case of the same thickness the maximum vertical force increased with the increase of the upper rock plate thickness. When the boundary conditions of double-layer rock plates changed from the hinged support to the fixed support, the maximum horizontal force observably decreased, and the maximum vertical force showed small fluctuations and then tended towards stability with the increase of cohesive strength of double-layer rock plates.

  19. Multilayer capacitors, method for making multilayer capacitors

    Science.gov (United States)

    Ma, Beihai; Balachandran, Uthamalingam

    2018-03-06

    The invention provides a stacked capacitor configuration comprising subunits each with a thickness of as low as 20 microns. Also provided is combination capacitor and printed wire board wherein the capacitor is encapsulated by the wire board. The invented capacitors are applicable in micro-electronic applications and high power applications, whether it is AC to DC or DC to AC, or DC to DC.

  20. Current limitation and formation of plasma double layers in a non-uniform magnetic field

    International Nuclear Information System (INIS)

    Plamondon, R.; Teichmann, J.; Torven, S.

    1986-07-01

    Formation of strong double layers has been observed experimentally in a magnetised plasma column maintained by a plasma source. The magnetic field is approximately axially homogenous except in a region at the anode where the electric current flows into a magnetic mirror. The double layer has a stationary position only in the region of non-uniform magnetic field or at the aperture separating the source and the plasma column. It is characterized by a negative differential resistance in the current-voltage characteristic of the device. The parameter space,where the double layer exists, has been studied as well as the corresponding potential profiles and fluctuation spectra. The electric current and the axial electric field are oppositely directed between the plasma source and a potential minimum which is formed in the region of inhomogeneous magnetic field. Electron reflection by the resulting potential barrier is found to be an important current limitation mechanism. (authors)

  1. Density functional theory of the electrical double layer: the RFD functional

    International Nuclear Information System (INIS)

    Gillespie, Dirk; Valisko, Monika; Boda, Dezso

    2005-01-01

    Density functional theory (DFT) of electrolytes is applied to the electrical double layer under a wide range of conditions. The ions are charged, hard spheres of different size and valence, and the wall creating the double layer is uncharged, weakly charged, and strongly charged. Under all conditions, the density and electrostatic potential profiles calculated using the recently proposed RFD electrostatic functional (Gillespie et al 2002 J. Phys.: Condens. Matter 14 12129; 2003 Phys. Rev. E 68 031503) compare well to Monte Carlo simulations. When the wall is strongly charged, the RFD functional results agree with the results of a simpler perturbative electrostatic DFT, but the two functionals' results qualitatively disagree when the wall is uncharged or weakly charged. The RFD functional reproduces these phenomena of weakly charged double layers. It also reproduces bulk thermodynamic quantities calculated from pair correlation functions

  2. XPS and TEM study of W-DLC/DLC double-layered film

    International Nuclear Information System (INIS)

    Takeno, Takanori; Komiyama, Takao; Miki, Hiroyuki; Takagi, Toshiyuki; Aoyama, Takashi

    2009-01-01

    A double-layered film of tungsten-containing diamond-like carbon (W-DLC) and DLC, (W-DLC)/DLC, was investigated. A film of 1.6 μm in thickness was deposited onto silicon substrate. The investigate double-layered coating was deposited by using the combination of PECVD and co-sputtering of tungsten metal target. Structure, interface and chemical bonding state of the investigated film were analyzed by Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). From the results of the analyses, the structure of double-layered film is that amorphous phase of carbon is continued from DLC to W-DLC and tungsten metal clusters are dispersed in W-DLC layer.

  3. Low frequency solitons and double layers in a magnetized plasma with two temperature electrons

    Energy Technology Data Exchange (ETDEWEB)

    Rufai, O. R. [Department of Physics, University of the Western Cape, Private Bag X17, Bellville 7535 (South Africa); Bharuthram, R. [Office of the Deputy Vice Chancellor (Academic), University of the Western Cape, Bellville (South Africa); Singh, S. V. [Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai-410218 (India); School of Chemistry and Physics, University of Kwa-Zulu Natal, Durban (South Africa); Lakhina, G. S. [Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai-410218 (India)

    2012-12-15

    Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.

  4. Low frequency solitons and double layers in a magnetized plasma with two temperature electrons

    International Nuclear Information System (INIS)

    Rufai, O. R.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.

    2012-01-01

    Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.

  5. Capacitor Discharge - A Capacitor Tutorial [video

    OpenAIRE

    Naval Postgraduate School Physics

    2014-01-01

    NPS Physics Physics Demonstrations Here's a capacitor discharge demonstrated by physicist Dr. Dernardo. Dr. D gives a nice capacitor lesson along with some fireworks. Charging and Discharging a Capacitor is dangerous. Do not try this at home. Dr. Bruce Denardo uses eleven 9V batteries, connected in series for a total of 99 creating a pretty large spark.

  6. Study on dynamic deformation synchronized measurement technology of double-layer liquid surfaces

    Science.gov (United States)

    Tang, Huiying; Dong, Huimin; Liu, Zhanwei

    2017-11-01

    Accurate measurement of the dynamic deformation of double-layer liquid surfaces plays an important role in many fields, such as fluid mechanics, biomechanics, petrochemical industry and aerospace engineering. It is difficult to measure dynamic deformation of double-layer liquid surfaces synchronously for traditional methods. In this paper, a novel and effective method for full-field static and dynamic deformation measurement of double-layer liquid surfaces has been developed, that is wavefront distortion of double-wavelength transmission light with geometric phase analysis (GPA) method. Double wavelength lattice patterns used here are produced by two techniques, one is by double wavelength laser, and the other is by liquid crystal display (LCD). The techniques combine the characteristics such as high transparency, low reflectivity and fluidity of liquid. Two color lattice patterns produced by laser and LCD were adjusted at a certain angle through the tested double-layer liquid surfaces simultaneously. On the basis of the refractive indexes difference of two transmitted lights, the double-layer liquid surfaces were decoupled with GPA method. Combined with the derived relationship between phase variation of transmission-lattice patterns and out-of plane heights of two surfaces, as well as considering the height curves of the liquid level, the double-layer liquid surfaces can be reconstructed successfully. Compared with the traditional measurement method, the developed method not only has the common advantages of the optical measurement methods, such as high-precision, full-field and non-contact, but also simple, low cost and easy to set up.

  7. Experiment and simulation of double-layered RC plates under impact loadings. Part 1: Impact tests for double-layered RC plates

    International Nuclear Information System (INIS)

    Shirai, T.; Ueda, M.; Taniguchi, H.; Kambayashi, A.; Ohno, T.; Ishikawa, N.

    1993-01-01

    At a nuclear power plant facility, it should be of interest and important problem to ensure structures against impact loads induced by projectile impacts or plant-internal accidents. It has been well known that local damage consists of spalling of concrete from the impacted area and scabbing of concrete from the back face of the target together with projectile penetration into the target. There are several techniques for improving the impact resistance of RC slabs, that is, lining with a steel plate on the impacted and/or rear face of the slab, making the slab a double-layered composite slab with an elastic absorber and employing a fiber reinforced concrete or a high-strength concrete as the slab materials. Of the many measures available for withstanding impact loads, the use of a double-layered reinforced concrete (RC) slab with absorber is expected to have the higher resistance in reducing or preventing local damage. This paper presents the results of an experimental investigation on the impact resistance of double-layered RC plates subjected to the impact of projectile. In the experiment, the effects of two parameters; the combination of two RC plates having different thicknesses and the existence of an absorber in the middle layer, are mainly investigated. And, the effects of the concrete thickness (7,9 and 11 cm) and the concrete strength (a normal-:35MPa, a lightweight-:40MPa and a high-strength:57MPa) of target were also examined. RC plates, 0.6m-square, were used for test specimens. The projectile has a mass of 0.43kg, made of steel with a flat nose. An average projectile velocity was about 170m/sec. A rubber plate shaped into a square with the same size of RC plate was used for a double-layered specimen as an absorber which was put between two RC plates. It could be concluded that double-layering and presence of an absorber had a considerable effect on the increase of impact resistance of RC plate. In order to reduce local damage, it is more effective to

  8. Development of ion-acoustic double layers through ion-acoustic fluctuations

    International Nuclear Information System (INIS)

    Sekar, A.N.; Saxena, Y.C.

    1985-01-01

    Experimental results on the formation of ion acoustic double layers resembling asymmetric ion-holes are presented. In a double plasma device, modified suitably to inject electron beam into the target plasma, modulation of the beam through step potential leads to excitation of ion-acoustic fluctuation. The ion-acoustic fluctuation, growing away from the grids separating source and target plasmas, developed into weak asymmetric ion-acoustic double layer. The observations are in qualitative agreement with theoretical models and computer simulations. (author)

  9. Read/write performance of perpendicular double-layered cylindrical media

    International Nuclear Information System (INIS)

    Yamada, H.; Shimatsu, T.; Watanabe, I.; Tsuchiyama, R.; Aoi, H.; Muraoka, H.; Nakamura, Y.

    2005-01-01

    A cylindrical magnetic storage system using perpendicular double-layered media has been developed. CoCrTa/CoZrNb deposited on a rotating cylindrical substrate shows perpendicular anisotropy and magnetic properties, which have almost the same characteristics as conventional disk-media. The fundamental read/write characteristics of perpendicular double-layered cylindrical media were measured using a single-pole-type (SPT) writer with a sliding-contact-type slider and a merged giant magneto-resistive (GMR) reader with a one-pad-type slider designed for use with cylindrical media. Preliminary studies for improving the characteristics of the recording layer are also described

  10. Current carrying properties of double layers and low frequency auroral fluctuations

    International Nuclear Information System (INIS)

    Singh, N.; Schunk, R.W.

    1982-01-01

    Numerical simulations showed recurring interruption and recovery of electron and ion currents through double layers. The time period tau of the recurring phenomena is governed by the ion dynamics; for ions with a drift V/sub i/ entering the simulation plasma such that V/sub i/ V/sub ti/ ion-acoustic modes also appear in the electron- and ion-current fluctuations. The electron current fluctuations are governed by the ion current through the Langmuir criterion. It is suggested that some low frequency auroral fluctuations could possibly be explained by current fluctuations through double layers

  11. Plasmon resonance in single- and double-layer CVD graphene nanoribbons

    DEFF Research Database (Denmark)

    Wang, Di; Emani, Naresh K.; Chung, Ting Fung

    2015-01-01

    Dynamic tunability of the plasmonic resonance in graphene nanoribbons is desirable in the near-infrared. We demonstrated a constant blue shift of plasmonic resonances in double-layer graphene nanoribbons with respect to single-layer graphene nanoribbons. © OSA 2015.......Dynamic tunability of the plasmonic resonance in graphene nanoribbons is desirable in the near-infrared. We demonstrated a constant blue shift of plasmonic resonances in double-layer graphene nanoribbons with respect to single-layer graphene nanoribbons. © OSA 2015....

  12. Influence of Fabric Parameters on Thermal Comfort Performance of Double Layer Knitted Interlock Fabrics

    Directory of Open Access Journals (Sweden)

    Afzal Ali

    2017-03-01

    Full Text Available The aim of this study was to analyse the effects of various fabric parameters on the thermal resistance, thermal conductivity, thermal transmittance, thermal absorptivity and thermal insulation of polyester/cotton double layer knitted interlock fabrics. It was found that by increasing fibre content with higher specific heat increases the thermal insulation while decreases the thermal transmittance and absorptivity of the fabric. It was concluded that double layer knitted fabrics developed with higher specific heat fibres, coarser yarn linear densities, higher knitting loop length and fabric thickness could be adequately used for winter clothing purposes.

  13. Ion-acoustic double-layers in a magnetized plasma with nonthermal electrons

    Energy Technology Data Exchange (ETDEWEB)

    Rios, L. A. [Centro Brasileiro de Pesquisas Físicas and Instituto Nacional de Ciência e Tecnologia de Sistemas Complexos, Rua Xavier Sigaud 150, 22290-180 Rio de Janeiro (Brazil); Galvão, R. M. O. [Centro Brasileiro de Pesquisas Físicas and Instituto Nacional de Ciência e Tecnologia de Sistemas Complexos, Rua Xavier Sigaud 150, 22290-180 Rio de Janeiro (Brazil); Instituto de Física, Universidade de São Paulo, 05508-900 São Paulo (Brazil)

    2013-11-15

    In the present work we investigate the existence of obliquely propagating ion-acoustic double layers in magnetized two-electron plasmas. The fluid model is used to describe the ion dynamics, and the hot electron population is modeled via a κ distribution function, which has been proved to be appropriate for modeling non-Maxwellian plasmas. A quasineutral condition is assumed to investigate these nonlinear structures, which leads to the formation of double-layers propagating with slow ion-acoustic velocity. The problem is investigated numerically, and the influence of parameters such as nonthermality is discussed.

  14. Arrangements of a pair of loudspeakers for sound field control with double-layer arrays

    DEFF Research Database (Denmark)

    Chang, Jiho; Agerkvist, Finn T.; Olsen, Martin

    2013-01-01

    Recent studies have attempted to control sound fields, and also to reduce room reflections with a circular or spherical array of loudspeakers. One of the attempts was to suppress sound waves propagating to the walls outside the array with a circular double-layer array of loudspeakers. The double-layer...... array represents a set of a monopole and a dipole in the Kirchhoff-Helmholtz integral equation, and thus the distance between these layers should be short compared with the wavelength. In practice, however, this condition is occasionally hard to satisfy because of the sizes of loudspeaker cabinets...

  15. Double-layer ion acceleration triggered by ion magnetization in expanding radiofrequency plasma sources

    International Nuclear Information System (INIS)

    Takahashi, Kazunori; Charles, Christine; Boswell, Rod W.; Fujiwara, Tamiya

    2010-01-01

    Ion energy distribution functions downstream of the source exit in magnetically expanding low-pressure plasmas are experimentally investigated for four source tube diameters ranging from about 5 to 15 cm. The magnetic-field threshold corresponding to a transition from a simple expanding plasma to a double layer-containing plasma is observed to increase with a decrease in the source tube diameter. The results demonstrate that for the four geometries, the double layer and the accelerated ion beam form when the ion Larmour radius in the source becomes smaller than the source tube radius, i.e., when the ions become magnetized in the source tube.

  16. Ionic liquids in a poly ethylene oxide cross-linked gel polymer as an electrolyte for electrical double layer capacitor

    Science.gov (United States)

    Chaudoy, V.; Tran Van, F.; Deschamps, M.; Ghamouss, F.

    2017-02-01

    In the present work, we developed a gel polymer electrolyte via the incorporation of a room temperature ionic liquid into a cross-linked polymer matrix. The cross-linked gel electrolyte was prepared using a free radical polymerization of methacrylate and dimethacrylate oligomers dissolved in 1-propyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide. Combining the advantages of the ionic liquids and of conventional polymers, the cross-linked gel polymer electrolyte was used both as a separator and as an electrolyte for a leakage-free and non-flammable EDLC supercapacitor. The quasi-all solid-state supercapacitors showed rather good capacitance, power and energy densities by comparison to a liquid electrolyte-based EDLC.

  17. Double-Layered Lateral Meniscus in an 8-Year-Old Child: Report of a Rare Case

    OpenAIRE

    Araki, Susumu; Kubo, Mitsuhiko; Kumagai, Kosuke; Imai, Shinji

    2016-01-01

    Reports of congenital abnormalities of the lateral meniscus include discoid meniscus, accessory meniscus, double-layered meniscus, and ring-shaped meniscus. Particularly, only a few cases of double-layered meniscus have been reported. We report a case of double-layered lateral meniscus, in which an additional semicircular meniscus was observed under the normal lateral meniscus. The accessory hemimeniscus was resected by means of arthroscopic surgery. This case demonstrates an interesting and ...

  18. High electrochemical capacitor performance of oxygen and nitrogen enriched activated carbon derived from the pyrolysis and activation of squid gladius chitin

    Science.gov (United States)

    Raj, C. Justin; Rajesh, Murugesan; Manikandan, Ramu; Yu, Kook Hyun; Anusha, J. R.; Ahn, Jun Hwan; Kim, Dong-Won; Park, Sang Yeup; Kim, Byung Chul

    2018-05-01

    Activated carbon containing nitrogen functionalities exhibits excellent electrochemical property which is more interesting for several renewable energy storage and catalytic applications. Here, we report the synthesis of microporous oxygen and nitrogen doped activated carbon utilizing chitin from the gladius of squid fish. The activated carbon has large surface area of 1129 m2 g-1 with microporous network and possess ∼4.04% of nitrogen content in the form of pyridinic/pyrrolic-N, graphitic-N and N-oxide groups along with oxygen and carbon species. The microporous oxygen/nitrogen doped activated carbon is utilize for the fabrication of aqueous and flexible supercapacitor electrodes, which presents excellent electrochemical performance with maximum specific capacitance of 204 Fg-1 in 1 M H2SO4 electrolyte and 197 Fg-1 as a flexible supercapacitor. Moreover, the device displays 100% of specific capacitance retention after 25,000 subsequent charge/discharge cycles in 1 M H2SO4 electrolyte.

  19. Double-layer imprint lithography on wafers and foils from the submicrometer to the millimeter scale

    NARCIS (Netherlands)

    Moonen, P.F.; Yakimets, I.; Peter, M.; Meinders, E.R.; Huskens, J.

    2011-01-01

    In this paper, a thermal imprint technique, double-layer nanoimprint lithography (dlNIL), is introduced, allowing complete filling of features in the dimensional range of submicrometer to millimeter. The imprinting and filling quality of dlNIL was studied on Si substrates as a model system and

  20. High-frequency permeability in double-layered structure of amorphous Co-Ta-Zr films

    International Nuclear Information System (INIS)

    Ochiai, Y.; Hayakawa, M.; Hayashi, K.; Aso, K.

    1988-01-01

    The high-frequency permeability of amorphous Co-Ta-Zr films was studied and the frequency dependence was described in terms of the eddy-current-loss formula. For the double-layered structure intervened with SiO 2 film, the degradation of the permeability became apparent with the decrease of SiO 2 thickness

  1. The recording characteristics of particulate double layers with hard-magnetic and soft-magnetic underlayers

    NARCIS (Netherlands)

    Lalbahadoersing, S.; Groenland, J.P.J.; Luitjens, S.B.; Lodder, J.C.

    2002-01-01

    Particulate double-layer tape samples with magnetic underlayers have been investigated by performing magnetic recording measurements and by computer simulation.The presence of soft-magnetic underlayers resulted in decreased signal output and better overwrite behavior. Hard-magnetic underlayers

  2. Analytical and Numerical Modeling of Tsunami Wave Propagation for double layer state in Bore

    Science.gov (United States)

    Yuvaraj, V.; Rajasekaran, S.; Nagarajan, D.

    2018-04-01

    Tsunami wave enters into the river bore in the landslide. Tsunami wave propagation are described in two-layer states. The velocity and amplitude of the tsunami wave propagation are calculated using the double layer. The numerical and analytical solutions are given for the nonlinear equation of motion of the wave propagation in a bore.

  3. Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

    Energy Technology Data Exchange (ETDEWEB)

    Amour, Rabia [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria); Tribeche, Mouloud [Plasma Physics Group, Theoretical Physics Laboratory, Faculty of Sciences - Physics, U.S.T.H.B, Bab-Ezzouar, B.P. 32, El Alia, Algiers 16111 (Algeria)], E-mail: mouloud-tribeche@lycos.com

    2009-05-11

    A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

  4. Small amplitude variable charge dust Bernstein-Greene-Kruskal double layers

    International Nuclear Information System (INIS)

    Amour, Rabia; Tribeche, Mouloud

    2009-01-01

    A first theoretical attempt is made to investigate small amplitude, variable charge dust Bernstein-Greene-Kruskal (BGK) double layers (DLs). The nature of the dust BGK-DLs (compressive or rarefactive), their strength and thickness depend sensitively on the net negative charge residing on the grain surface, the dust grain dynamics and, more interestingly, on the ion-to-electron temperatures ratio.

  5. Vertically aligned carbon nanotubes/diamond double-layered structure for improved field electron emission stability

    Energy Technology Data Exchange (ETDEWEB)

    Yang, L., E-mail: qiaoqin.yang@mail.usask.ca; Yang, Q.; Zhang, C.; Li, Y.S.

    2013-12-31

    A double-layered nanostructure consisting of a layer of vertically aligned Carbon Nanotubes (CNTs) and a layer of diamond beneath has been synthesized on silicon substrate by Hot Filament Chemical Vapor Deposition. The synthesis was achieved by first depositing a layer of diamond on silicon and then depositing a top layer of vertically aligned CNTs by applying a negative bias on the substrate holder. The growth of CNTs was catalyzed by a thin layer of spin-coated iron nitride. The surface morphology and structure of the CNTs/diamond double-layered structure were characterized by Scanning Electron Microscope, Energy Dispersive X-ray spectrum, and Raman Spectroscopy. Their field electron emission (FEE) properties were measured by KEITHLEY 237 high voltage measurement unit, showing much higher FEE current stability than single layered CNTs. - Highlights: • A new double-layered nanostructure consisting of a layer of vertically aligned CNTs and a layer of diamond beneath has been synthesized by hot filament chemical vapor deposition. • This double-layered structure exhibits superior field electron emission stability. • The improvement of emission stability is due to the combination of the unique properties of diamond and CNTs.

  6. Double layer mixed matrix membrane adsorbers improving capacity and safety hemodialysis

    Science.gov (United States)

    Saiful; Borneman, Z.; Wessling, M.

    2018-05-01

    Double layer mixed matrix membranes adsorbers have been developed for blood toxin removal by embedding activated carbon into cellulose acetate macroporous membranes. The membranes are prepared by phase inversion method via water vapor induced phase separation followed by an immersion precipitation step. Double layer MMM consisting of an active support and a separating layer. The active support layer consists of activated carbon particles embedded in macroporous cellulose acetate; the separating layer consists of particle free cellulose acetate. The double layer membrane possess an open and interconnected macroporous structure with a high loading of activated carbon available for blood toxins removal. The MMM AC has a swelling degree of 6.5 %, porosity of 53 % and clean water flux of 800 Lm-2h-1bar-1. The prepared membranes show a high dynamic Creatinine (Crt) removal during hemodilysis process. The Crt removal by adsorption contributes to amore than 83 % of the total removal. The double layer adsorptive membrane proves hemodialysis membrane can integrated with adsorption, in which blood toxins are removed in one step.

  7. The electric double layer at high surface potentials: The influence of excess ion polarizability

    NARCIS (Netherlands)

    Hatlo, M. M.; van Roij, R.H.H.G.; Lue, L.

    2012-01-01

    By including the excess ion polarizability into the Poisson-Boltzmann theory, we show that the decrease in differential capacitance with voltage, observed for metal electrodes above a threshold potential, can be understood in terms of thickening of the double layer due to ion-induced polarizability

  8. Electrical double layer at various electrode potentials: A modification by vibration

    Czech Academy of Sciences Publication Activity Database

    Zhan, H.; Červenka, Jiří; Prawer, S.; Garrett, D.J.

    2017-01-01

    Roč. 121, č. 8 (2017), s. 4760-4764 ISSN 1932-7447 Institutional support: RVO:68378271 Keywords : electrical double layer * vibration * high concentration * model Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.536, year: 2016

  9. Electric double layer transistors with ferroelectric BaTiO3 channels

    NARCIS (Netherlands)

    Ito, M.; Matsubara, Y.; Kozuka, Y.; Takahashi, K. S.; Kagawa, F.; Ye, J. T.; Iwasa, Y.; Ueno, K.; Tokura, Y.; Kawasaki, M.

    2014-01-01

    We report the surface conduction of a BaTiO3 thin film using electric double layer transistor (EDLT) structure. A transistor operation was observed at 220 K with an on/off ratio exceeding 10(5), demonstrating that ionic liquid gating is effective to induce carriers at the surface of ferroelectric

  10. Control of sound fields with a circular double-layer array of loudspeakers

    DEFF Research Database (Denmark)

    Chang, Jiho; Jacobsen, Finn

    2012-01-01

    by the Kirchhoff-Helmholtz integral theorem a double-layer array of loudspeakers is used. Several solution methods are suggested and examined with computer simulations: pure contrast control, pure pressure matching, and a weighted combination. In order to compare the performance of the methods two performance...

  11. Sound field separation with a double layer velocity transducer array (L)

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren; Jacobsen, Finn

    2011-01-01

    of the array. The technique has been examined and compared with direct velocity based reconstruction, as well as with a technique based on the measurement of the sound pressure and particle velocity. The double layer velocity method circumvents some of the drawbacks of the pressure-velocity based...

  12. Large acoustic solitons and double layers in plasmas with two positive ion species

    International Nuclear Information System (INIS)

    Verheest, Frank; Hellberg, Manfred A.; Saini, Nareshpal Singh; Kourakis, Ioannis

    2011-01-01

    Large nonlinear acoustic waves are discussed in a plasma made up of cold supersonic and adiabatic subsonic positive ions, in the presence of hot isothermal electrons, with the help of Sagdeev pseudopotential theory. In this model, no solitons are found at the acoustic speed, and no compositional parameter ranges exist where solutions of opposite polarities can coexist. All nonlinear modes are thus super-acoustic, but polarity changes are possible. The upper limits on admissible structure velocities come from different physical arguments, in a strict order when the fractional cool ion density is increased: infinite cold ion compression, warm ion sonic point, positive double layers, negative double layers, and finally, positive double layers again. However, not all ranges exist for all mass and temperature ratios. Whereas the cold and warm ion sonic point limitations are always present over a wide range of mass and temperature ratios, and thus positive polarity solutions can easily be obtained, double layers have a more restricted existence range, specially if polarity changes are sought.

  13. Electric-double-layer potential distribution in multiple-layer immiscible electrolytes

    NARCIS (Netherlands)

    Das, S.; Hardt, Steffen

    2011-01-01

    In this Brief Report, we calculate the electric-double-layer (EDL) electrostatic potential in a system of several layers of immiscible electrolytes. Verwey-Niessen theory predicts that at the interface between two immiscible electrolytes back-to-back EDLs are formed. The present analysis extends

  14. Does electrical double layer formation lead to salt exclusion or to uptake?

    NARCIS (Netherlands)

    Lyklema, J.

    2005-01-01

    When electric double layers are formed, cases have been reported where this formation nvolves expulsion of electrolyte into the solution and cases in which electrolyte is absorbed from the solution. Both situations are experimentally and theoretically documented, but they cannot be simultaneously

  15. Ion acoustic solitons/double layers in two-ion plasma revisited

    International Nuclear Information System (INIS)

    Lakhina, G. S.; Singh, S. V.; Kakad, A. P.

    2014-01-01

    Ion acoustic solitons and double layers are studied in a collisionless plasma consisting of cold heavier ion species, a warm lighter ion species, and hot electrons having Boltzmann distributions by Sagdeev pseudo-potential technique. In contrast to the previous results, no double layers and super-solitons are found when both the heavy and lighter ion species are treated as cold. Only the positive potential solitons are found in this case. When the thermal effects of the lighter ion species are included, in addition to the usual ion-acoustic solitons occurring at M > 1 (where the Mach number, M, is defined as the ratio of the speed of the solitary wave and the ion-acoustic speed considering temperature of hot electrons and mass of the heavier ion species), slow ion-acoustic solitons/double layers are found to occur at low Mach number (M < 1). The slow ion-acoustic mode is actually a new ion-ion hybrid acoustic mode which disappears when the normalized number density of lighter ion species tends to 1 (i.e., no heavier species). An interesting property of the new slow ion-acoustic mode is that at low number density of the lighter ion species, only negative potential solitons/double layers are found whereas for increasing densities there is a transition first to positive solitons/double layers, and then only positive solitons. The model can be easily applicable to the dusty plasmas having positively charged dust grains by replacing the heavier ion species by the dust mass and doing a simple normalization to take account of the dust charge

  16. Single Layered Versus Double Layered Intestinal Anastomosis: A Randomized Controlled Trial

    Science.gov (United States)

    Mohapatra, Vandana; Singh, Surendra; Rath, Pratap Kumar; Behera, Tapas Ranjan

    2017-01-01

    Introduction Gastrointestinal anastomosis is one of the most common procedures being performed in oesophagogastric, hepatobiliary, bariatric, small bowel and colorectal surgery; however, the safety and efficacy of single layer or double layer anastomotic technique is still unclear. Aim To assess and compare the efficacy, safety and cost effectiveness of single layered versus double layered intestinal anastomosis. Materials and Methods This prospective, double-blind, randomized controlled comparative study comprised of patients who underwent intestinal resection and anastomosis. They were randomly assigned to undergo either single layered extra-mucosal anastomosis (Group-A) or double layered intestinal anastomosis (Group-B). Primary outcome measures included average time taken for anastomosis, postoperative complications, mean duration of hospital stay and cost of suture material used; secondary outcome measures assessed the postoperative return of bowel function. Statistical analysis was done by Chi-square test and student t-test. Results A total of 97 participants were randomized. Fifty patients were allocated to single layered extramucosal continuous anastomosis (Group-A) and 47 patients to double layered anastomosis (Group-B). The patients in each group were well matched for age, sex and diagnosis. The mean time taken for anastomosis (15.12±2.27 minutes in Group-A versus 24.38±2.26 minutes in Group-B) and the length of hospital stay (5.90±1.43 days in Group-A versus 7.29±1.89 days in Group-B) was significantly shorter in Group-A {p-value anastomosis. However, there was no significant difference in the complication rates between the two groups. Conclusion It can be concluded that single layered extramucosal continuous intestinal anastomosis is equally safe and perhaps more cost effective than the conventional double layered method and may represent the optimal choice for routine surgical practice. PMID:28764239

  17. Understanding of carbon-based supercapacitors ageing mechanisms by electrochemical and analytical methods

    Science.gov (United States)

    Liu, Yinghui; Soucaze-Guillous, Benoît; Taberna, Pierre-Louis; Simon, Patrice

    2017-10-01

    In order to shed light on ageing mechanisms of Electrochemical Double Layer Capacitor (EDLC), two kinds of activated carbons are studied in tetraethyl ammonium tetrafluoroborate (Et4NBF4) in acetonitrile. In floating mode, it turns out that two different ageing mechanisms are observed, depending on the activated carbon electrode materials used. On one hand, carbon A exhibits a continuous capacitance and series resistance fall-off; on the other hand, for carbon B, only the series resistance degrades after ageing while the capacitance keeps unchanged. Additional electrochemical characterizations (Electrochemical Impedance Spectroscopy - EIS - and diffusion coefficient calculations) were carried out showing that carbon A's ageing behavior is suspected to be primarily related to the carbon degradation while for carbon B a passivation occurs leading to the formation of a Solid Electrolyte Interphase-Like (SEI-L) film. These hypotheses are supported by TG-IR and Raman spectroscopy analysis. The outcome forms the latter is an increase of carbon defects on carbon A on positive electrode.

  18. Effectiveness evaluation of double-layered satellite network with laser and microwave hybrid links based on fuzzy analytic hierarchy process

    Science.gov (United States)

    Zhang, Wei; Rao, Qiaomeng

    2018-01-01

    In order to solve the problem of high speed, large capacity and limited spectrum resources of satellite communication network, a double-layered satellite network with global seamless coverage based on laser and microwave hybrid links is proposed in this paper. By analyzing the characteristics of the double-layered satellite network with laser and microwave hybrid links, an effectiveness evaluation index system for the network is established. And then, the fuzzy analytic hierarchy process, which combines the analytic hierarchy process and the fuzzy comprehensive evaluation theory, is used to evaluate the effectiveness of the double-layered satellite network with laser and microwave hybrid links. Furthermore, the evaluation result of the proposed hybrid link network is obtained by simulation. The effectiveness evaluation process of the proposed double-layered satellite network with laser and microwave hybrid links can help to optimize the design of hybrid link double-layered satellite network and improve the operating efficiency of the satellite system.

  19. Soft template synthesis of mesoporous Co3O4/RuO2.xH2O composites for electrochemical capacitors

    International Nuclear Information System (INIS)

    Liu Yang; Zhao Weiwei; Zhang Xiaogang

    2008-01-01

    Co 3 O 4 /RuO 2 .xH 2 O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO 3 ) 2 .6H 2 O and RuCl 3 .0.5H 2 O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 deg. C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m 2 g -1 . The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 deg. C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM)

  20. Superelastic Graphene Aerogel/Poly(3,4-Ethylenedioxythiophene/MnO2 Composite as Compression-Tolerant Electrode for Electrochemical Capacitors

    Directory of Open Access Journals (Sweden)

    Peng Lv

    2017-11-01

    Full Text Available Ultra-compressible electrodes with high electrochemical performance, reversible compressibility and extreme durability are in high demand in compression-tolerant energy storage devices. Herein, an ultra-compressible ternary composite was synthesized by successively electrodepositing poly(3,4-ethylenedioxythiophene (PEDOT and MnO2 into the superelastic graphene aerogel (SEGA. In SEGA/PEDOT/MnO2 ternary composite, SEGA provides the compressible backbone and conductive network; MnO2 is mainly responsible for pseudo reactions; the middle PEDOT not only reduces the interface resistance between MnO2 and graphene, but also further reinforces the strength of graphene cellar walls. The synergistic effect of the three components in the ternary composite electrode leads to high electrochemical performances and good compression-tolerant ability. The gravimetric capacitance of the compressible ternary composite electrodes reaches 343 F g−1 and can retain 97% even at 95% compressive strain. And a volumetric capacitance of 147.4 F cm−3 is achieved, which is much higher than that of other graphene-based compressible electrodes. This value of volumetric capacitance can be preserved by 80% after 3500 charge/discharge cycles under various compression strains, indicating an extreme durability.

  1. Atomic Layer-Deposited Molybdenum Oxide/Carbon Nanotube Hybrid Electrodes: The Influence of Crystal Structure on Lithium-Ion Capacitor Performance.

    Science.gov (United States)

    Fleischmann, Simon; Zeiger, Marco; Quade, Antje; Kruth, Angela; Presser, Volker

    2018-05-25

    Merging of supercapacitors and batteries promises the creation of electrochemical energy storage devices that combine high specific energy, power, and cycling stability. For that purpose, lithium-ion capacitors (LICs) that store energy by lithiation reactions at the negative electrode and double-layer formation at the positive electrode are currently investigated. In this study, we explore the suitability of molybdenum oxide as a negative electrode material in LICs for the first time. Molybdenum oxide-carbon nanotube hybrid materials were synthesized via atomic layer deposition, and different crystal structures and morphologies were obtained by post-deposition annealing. These model materials are first structurally characterized and electrochemically evaluated in half-cells. Benchmarking in LIC full-cells revealed the influences of crystal structure, half-cell capacity, and rate handling on the actual device level performance metrics. The energy efficiency, specific energy, and power are mainly influenced by the overpotential and kinetics of the lithiation reaction during charging. Optimized LIC cells show a maximum specific energy of about 70 W·h·kg -1 and a high specific power of 4 kW·kg -1 at 34 W·h·kg -1 . The longevity of the LIC cells is drastically increased without significantly reducing the energy by preventing a deep cell discharge, hindering the negative electrode from crossing its anodic potential limit.

  2. Modeling of electrochemical hydrogen storage in metal hydride electrodes

    NARCIS (Netherlands)

    Ledovskikh, A.; Danilov, D.; Vermeulen, P.; Notten, P.H.L.

    2010-01-01

    The recently presented Electrochemical Kinetic Model (EKM), describing the electrochemical hydrogen storage in hydride-forming materials, has been extended by the description of the solid/electrolyte interface, i.e. the charge transfer kinetics and electrical double layer charging. A complete set of

  3. Modeling of electrochemical hydrogen storage in metal hydride electrodes

    NARCIS (Netherlands)

    Ledovskikh, A.; Danilov, D.; Vermeulen, P.; Notten, P.H.L.

    2010-01-01

    The recently presented electrochemical kinetic model, describing the electrochemical hydrogen storage in hydride-forming materials, was extended by the description of the solid/electrolyte interface, i.e., the charge-transfer kinetics and electrical double-layer charging. A complete set of equations

  4. Improved performance of CdSe/CdS/PbS co-sensitized solar cell with double-layered TiO2 films as photoanode

    Science.gov (United States)

    Zhang, Xiaolong; Lin, Yu; Wu, Jihuai; Jing, Jing; Fang, Biaopeng

    2017-07-01

    Improving the photovoltaic performance of CdSe/CdS/PbS co-sensitized double-layered TiO2 solar cells is reported. Double-layered TiO2 films with TiO2 microspheres as the light blocking layers were prepared. PbS, CdS and CdSe quantum dots (QDs) were assembled onto TiO2 photoanodes by simple successive ionic layer absorption and reaction (SILAR) to fabricate CdSe/CdS/PbS co-sensitized solar cells. An improved power conversion efficiency (PCE) of 5.11% was achieved for CdSe/CdS/PbS co-sensitized solar cells at one sun illumination (AM 1.5 G, 100 mW cm-2), which had an improvement of 22.6% over that of the CdSe/CdS co-sensitized solar cells (4.17%). This enhancement is mainly attributed to their better ability of the absorption of solar light with the existence of PbS QDs, the reduction of charge recombination of the excited electron and longer lifetime of electrons, which have been proved with the photovoltaic studies and electrochemical impedance spectroscopy (EIS).

  5. A green and efficient method to produce graphene for electrochemical capacitors from graphene oxide using sodium carbonate as a reducing agent

    Science.gov (United States)

    Jin, Yuhong; Huang, Shuo; Zhang, Mei; Jia, Mengqiu; Hu, Dong

    2013-03-01

    The green and efficient synthesis of graphene using sodium carbonate (Na2CO3) as a chemical reducing agent was studied. Extensive characterization confirmed the formation of graphene from graphene oxide using a Na2CO3 solution. The C/O atomic ratio of the as-prepared graphene has increased from 2.48 to 8.15 after reduction as determined by X-ray photoelectron spectroscopy. The conductivity of as-prepared graphene sheets is as high as 10 S m-1. After electrochemical measurements, gravimetric capacitances of 228 and 166 F g-1 at current densities of 5 and 25 mA cm-2, respectively, were obtained with KOH electrolyte.

  6. First steps towards the realization of a double layer perceptron based on organic memristive devices

    Directory of Open Access Journals (Sweden)

    A. V. Emelyanov

    2016-11-01

    Full Text Available Memristors are widely considered as promising elements for the efficient implementation of synaptic weights in artificial neural networks (ANNs since they are resistors that keep memory of their previous conductive state. Whereas demonstrations of simple neural networks (e.g., a single-layer perceptron based on memristors already exist, the implementation of more complicated networks is more challenging and has yet to be reported. In this study, we demonstrate linearly nonseparable combinational logic classification (XOR logic task using a network implemented with CMOS-based neurons and organic memrisitive devices that constitutes the first step toward the realization of a double layer perceptron. We also show numerically the ability of such network to solve a principally analogue task which cannot be realized by digital devices. The obtained results prove the possibility to create a multilayer ANN based on memristive devices that paves the way for designing a more complex network such as the double layer perceptron.

  7. First steps towards the realization of a double layer perceptron based on organic memristive devices

    Science.gov (United States)

    Emelyanov, A. V.; Lapkin, D. A.; Demin, V. A.; Erokhin, V. V.; Battistoni, S.; Baldi, G.; Dimonte, A.; Korovin, A. N.; Iannotta, S.; Kashkarov, P. K.; Kovalchuk, M. V.

    2016-11-01

    Memristors are widely considered as promising elements for the efficient implementation of synaptic weights in artificial neural networks (ANNs) since they are resistors that keep memory of their previous conductive state. Whereas demonstrations of simple neural networks (e.g., a single-layer perceptron) based on memristors already exist, the implementation of more complicated networks is more challenging and has yet to be reported. In this study, we demonstrate linearly nonseparable combinational logic classification (XOR logic task) using a network implemented with CMOS-based neurons and organic memrisitive devices that constitutes the first step toward the realization of a double layer perceptron. We also show numerically the ability of such network to solve a principally analogue task which cannot be realized by digital devices. The obtained results prove the possibility to create a multilayer ANN based on memristive devices that paves the way for designing a more complex network such as the double layer perceptron.

  8. Double-layered ZnO nanostructures for efficient perovskite solar cells

    KAUST Repository

    Mahmood, Khalid; S. Swain, Bhabani; Amassian, Aram

    2014-01-01

    To date, a single layer of TiO2 or ZnO has been the most successful implementations of any electron transport layer (ETL) in solution-processed perovskite solar cells. In a quest to improve the ETL, we explore a new nanostructured double-layer ZnO film for mesoscopic perovskite-based thin film photovoltaics. This approach yields a maximum power conversion efficiency of 10.35%, which we attribute to the morphology of oxide layer and to faster electron transport. The successful implementation of the low-temperature hydrothermally processed double-layer ZnO film as ETL in perovskite solar cells highlights the opportunities to further improve the efficiencies by focusing on the ETL in this rapidly developing field. This journal is

  9. Acoustic radiation force on a double-layer microsphere by a Gaussian focused beam

    International Nuclear Information System (INIS)

    Wu, Rongrong; Cheng, Kaixuan; Liu, Jiehui; Mao, Yiwei; Gong, Xiufen; Liu, Xiaozhou

    2014-01-01

    A new model for calculating the radiation force on double-layer microsphere is proposed based on the ray acoustics approach. The axial acoustic radiation force resulting from a focused Gaussian beam incident on spherical shells immersed in water is examined theoretically in relation to its thickness and the contents of its double-layer. The attenuation both in the water and inside the sphere is considered in this method, which cannot be ignored while the high frequency ultrasonic is used. Results of numerical calculations are presented for fat and low density polyethylene materials, with the hollow region filled with animal oil, water, or air. These results show how the acoustic impedance and the sound velocity of both layers, together with the thickness of the shell, affect the acoustic radiation force.

  10. Volume ignition of laser driven fusion pellets and double layer effects

    International Nuclear Information System (INIS)

    Cicchitelli, L.; Eliezer, S.; Goldsworthy, M.P.; Green, F.; Hora, H.; Ray, P.S.; Stening, R.J.; Szichman, H.

    1988-01-01

    The realization of an ideal volume compression of laser-irradiated fusion pellets opens the possibility for an alternative to spark ignition proposed for many years for inertial confinement fusion. A re-evaluation of the difficulties of the central spark ignition of laser driven pellets is given. The alternative volume compression theory, together with volume burn and volume ignition, have received less attention and are re-evaluated in view of the experimental verification generalized fusion gain formulas, and the variation of optimum temperatures derived at self-ignition. Reactor-level DT fusion with MJ-laser pulses and volume compression to 50 times the solid-state density are estimated. Dynamic electric fields and double layers at the surface and in the interior of plasmas result in new phenomena for the acceleration of thermal electrons to suprathermal electrons. Double layers also cause a surface tension which stabilizes against surface wave effects and Rayleigh-Taylor instabilities. (author)

  11. Application of double-layered skin phantoms for optical flow imaging during laser tattoo treatments

    Science.gov (United States)

    Lee, Byeong-il; Song, Woosub; Kim, Hyejin; Kang, Hyun Wook

    2016-05-01

    The feasible application of double-layered skin phantoms was evaluated to identify artificial blood flow with a Doppler optical coherence tomography (DOCT) system for laser tattoo treatments. Polydimethylsiloxane (PDMS) was used to fabricate the artificial phantoms with flow channels embedded. A double-integrating sphere system with an inverse adding-doubling method quantified both the absorption and the reduced scattering coefficients for epidermis and dermis phantoms. Both OCT and caliper measurements confirmed the double-layered phantom structure (epidermis = 136 ± 17 µm vs. dermis = 3.0 ± 0.1 mm). The DOCT method demonstrated that high flow rates were associated with high image contrast, visualizing the position and the shape of the flow channel. Application of the channel-embedded skin phantoms in conjunction with DOCT can be a reliable technique to assess dynamic variations in the blood flow during and after laser tattoo treatments.

  12. Formation of presheath and current-free double layer in a two-electron-temperature plasma

    International Nuclear Information System (INIS)

    Sato, Kunihiro; Miyawaki, Fujio

    1992-02-01

    Development of the steady-state potential in a two-temperature-electron plasma in contact with the wall is investigated analytically. It is shown that if the hot- to cold electron temperature ratio is greater than ten, the potential drop in the presheath, which is allowed to have either a small value characterized by the cold electrons or a large value by the hot electrons, discontinuously changes at a critical value for the hot- to total electron density ratio. It is also found that the monotonically decreasing potential structure which consists of the first presheath, a current-free double layer, the second presheath, and the sheath can be steadily formed in a lower range of the hot- to total electron density ratio around the critical value. The current-free double layer is set up due to existence of the two electron species and cold ions generated by ionization so as to connect two presheath potentials at different levels. (author)

  13. Analysis of adsorption behavior of cations onto quartz surface by electrical double-layer model

    International Nuclear Information System (INIS)

    Kitamura, Akira; Yamamoto, Tadashi; Fujiwara, Kenso; Nishikawa, Sataro; Moriyama, Hirotake

    1999-01-01

    In a study of the adsorption behavior of cations onto quartz, the distribution coefficient of a variety of cations was determined using the batch method, and using the titration method, the surface charge densities of quartz in a number of electrolyte solutions. The two values thus determined were analyzed applying the electrical double-layer model, from which optimum parameter values were derived for double-layer electrostatics and intrinsic adsorption equilibrium constants. Based on these parameter values, the mechanism of cation adsorption is discussed: A key factor governing this mechanism proved to be the hydration behavior of cations. Consideration of the Coulomb interaction between the adsorbate ions and adsorbent surface led to the finding of a simple rule governing in common the adsorption equilibrium constants of different metal ions. (author)

  14. Observation of a current-limited double layer in a linear turbulent-heating device

    International Nuclear Information System (INIS)

    Inuzuka, H.; Torii, Y.; Nagatsu, M.; Tsukishima, T.

    1985-01-01

    Time- and space-resolved measurements of strong double layers (DLs) have been carried out for the first time on a linear turbulent-heating device, together with those of fluctuation spectra and precise current measurements. A stable stong DL is formed even when the electric current through the DL is less than the so-called Bohm value. Discussion of the formation and decay processes is given, indicating a transition from an ion-acoustic DL to a monotonic DL

  15. Effect of the surface charge discretization on electric double layers. A Monte Carlo simulation study

    OpenAIRE

    Madurga Díez, Sergio; Martín-Molina, Alberto; Vilaseca i Font, Eudald; Mas i Pujadas, Francesc; Quesada-Pérez, Manuel

    2007-01-01

    The structure of the electric double layer in contact with discrete and continuously charged planar surfaces is studied within the framework of the primitive model through Monte Carlo simulations. Three different discretization models are considered together with the case of uniform distribution. The effect of discreteness is analyzed in terms of charge density profiles. For point surface groups,a complete equivalence with the situation of uniformly distributed charge is found if profiles are...

  16. Influence of nonelectrostatic ion-ion interactions on double-layer capacitance

    Science.gov (United States)

    Zhao, Hui

    2012-11-01

    Recently a Poisson-Helmholtz-Boltzmann (PHB) model [Bohinc , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.85.031130 85, 031130 (2012)] was developed by accounting for solvent-mediated nonelectrostatic ion-ion interactions. Nonelectrostatic interactions are described by a Yukawa-like pair potential. In the present work, we modify the PHB model by adding steric effects (finite ion size) into the free energy to derive governing equations. The modified PHB model is capable of capturing both ion specificity and ion crowding. This modified model is then employed to study the capacitance of the double layer. More specifically, we focus on the influence of nonelectrostatic ion-ion interactions on charging a double layer near a flat surface in the presence of steric effects. We numerically compute the differential capacitance as a function of the voltage under various conditions. At small voltages and low salt concentrations (dilute solution), we find out that the predictions from the modified PHB model are the same as those from the classical Poisson-Boltzmann theory, indicating that nonelectrostatic ion-ion interactions and steric effects are negligible. At moderate voltages, nonelectrostatic ion-ion interactions play an important role in determining the differential capacitance. Generally speaking, nonelectrostatic interactions decrease the capacitance because of additional nonelectrostatic repulsion among excess counterions inside the double layer. However, increasing the voltage gradually favors steric effects, which induce a condensed layer with crowding of counterions near the electrode. Accordingly, the predictions from the modified PHB model collapse onto those computed by the modified Poisson-Boltzmann theory considering steric effects alone. Finally, theoretical predictions are compared and favorably agree with experimental data, in particular, in concentrated solutions, leading one to conclude that the modified PHB model adequately predicts the diffuse

  17. Preparation of Fe-Pt perpendicular double-layered media with high electric resistivity backlayer

    International Nuclear Information System (INIS)

    Uchida, Masaru; Suzuki, Toshio; Ouchi, Kazuhiro

    2001-01-01

    High electric resistivity materials, oxide-added Fe-Si, were investigated as a soft-magnetic backlayer for Fe-Pt perpendicular double-layered media. It was found that there is a possibility of using (Fe-Si)-MgO as a backlayer. To promote a hetero-epitaxial growth of ordered Fe-Pt FCT(0 0 1), the backlayer needed a BCC(2 0 0) crystal orientation, in a situation where surface topology also played an important role

  18. Observation of negative potential depression on double layer during a phase of current disruption

    International Nuclear Information System (INIS)

    Fujita, H.; Matsuo, K.; Yagura, S.

    1984-01-01

    The negative potential depression with a depth of approximately electron temperature is observed on the low potential tail of the double layer just at the moment when the electron current passing through the layer is disrupted. The depression is confirmed to serve as an electron thermal barrier and form an ion hole from phase-space measurements of electrons and ions, respectively. The depth of the depression becomes maximum when the density around the depression becomes most inhomogeneous. (author)

  19. Fabrication of lithium titanate/graphene composites with high rate capability as electrode materials for hybrid electrochemical supercapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Xue, Rong, E-mail: xuerongsmile@qq.com; Yan, Jingwang, E-mail: yanjw@dicp.ac.cn; Jiang, Liang, E-mail: jiangliang@dicp.ac.cn; Yi, Baolian, E-mail: blyi@dicp.ac.cn

    2015-06-15

    A lithium titanate (Li{sub 4}Ti{sub 5}O{sub 12})/graphene composite (LTO/graphene) is fabricated with a one-pot sol–gel method. Graphite oxide is dispersed in an aqueous solution of lithium acetate and tetrabutyl titanate followed by heat treatment in H{sub 2}/Ar. The LTO/graphene composite with reduced aggregation and improved homogeneity is investigated as an anode material for electrochemical capacitors. Electron transport is improved by the conductive graphene network in the insulating Li{sub 4}Ti{sub 5}O{sub 12} particles. The charge transfer resistance at the particle/electrolyte interface is reduced from 83.1 Ω to 55.4 Ω. The specific capacity of LTO/graphene composite is 126 mAh g{sup −1} at 20C. The energy density and power density of a hybrid electrochemical supercapacitor with a LTO/graphene negative electrode and an activated carbon positive electrode are 120.8 Wh kg{sup −1} and 1.5 kW kg{sup −1}, respectively, which is comparable to that of conventional electrochemical double layer capacitors (EDLCs). The LTO/graphene composite fabricated by the one-pot sol–gel method is a promising anode material for hybrid electrochemical supercapacitors. - Highlights: • A Li{sub 4}Ti{sub 5}O{sub 12}/graphene composite was fabricated with a one-pot sol–gel method. • The Li{sub 4}Ti{sub 5}O{sub 12}/graphene composite showed a reduced aggregation and an improved homogeneity. • The Li{sub 4}Ti{sub 5}O{sub 12}/graphene based hybrid supercapacitor exhibited higher energy and power densities.

  20. Fabrication of lithium titanate/graphene composites with high rate capability as electrode materials for hybrid electrochemical supercapacitors

    International Nuclear Information System (INIS)

    Xue, Rong; Yan, Jingwang; Jiang, Liang; Yi, Baolian

    2015-01-01

    A lithium titanate (Li 4 Ti 5 O 12 )/graphene composite (LTO/graphene) is fabricated with a one-pot sol–gel method. Graphite oxide is dispersed in an aqueous solution of lithium acetate and tetrabutyl titanate followed by heat treatment in H 2 /Ar. The LTO/graphene composite with reduced aggregation and improved homogeneity is investigated as an anode material for electrochemical capacitors. Electron transport is improved by the conductive graphene network in the insulating Li 4 Ti 5 O 12 particles. The charge transfer resistance at the particle/electrolyte interface is reduced from 83.1 Ω to 55.4 Ω. The specific capacity of LTO/graphene composite is 126 mAh g −1 at 20C. The energy density and power density of a hybrid electrochemical supercapacitor with a LTO/graphene negative electrode and an activated carbon positive electrode are 120.8 Wh kg −1 and 1.5 kW kg −1 , respectively, which is comparable to that of conventional electrochemical double layer capacitors (EDLCs). The LTO/graphene composite fabricated by the one-pot sol–gel method is a promising anode material for hybrid electrochemical supercapacitors. - Highlights: • A Li 4 Ti 5 O 12 /graphene composite was fabricated with a one-pot sol–gel method. • The Li 4 Ti 5 O 12 /graphene composite showed a reduced aggregation and an improved homogeneity. • The Li 4 Ti 5 O 12 /graphene based hybrid supercapacitor exhibited higher energy and power densities