High Surface Area Carbon Electrodes Research Articles

Biomass stemmed activated carbon electrodes toward a significant electric double-layer capacitor

The primary goal of the current study is to improve the specific capacitance of electric double-layer (EDLC) device using biomass (Tribulus Terrestris) derived activated carbon electrodes synthesized by chemical activation method. Furthermore, high surface area carbon electrodes are characterized using X-ray diffraction (XRD), RAMAN spectroscopy, and scanning electron microscopy (SEM) to confirm the morphological structure. Finally, the electrochemical performance of fabricated EDLC proves a good agreement data using Cyclic Voltammetry (CV), Low Impedance Spectroscopy (LIS), and Galvanostatic Charge–Discharge (GCD) analysis showing the high specific capacitance of 115 Fg−1 for the optimized 1:2 activated carbon material.

Atmospheric pressure plasma‐jet treatment of polyacrylonitrile‐nonwovens: Activation leading to high surface area carbon electrodes

AbstractCarbon nanofiber nonwovens (CFN) are powerful electrode materials with exceptional performance in energy storage devices, such as batteries and supercapacitors. Small fiber‐diameters together with hierarchical porosity endow CFN‐electrode materials with large surface areas and high electrical capacitance. Porosity of the fiber surface is often realized by corrosive activation methods such as wet‐etching or using oxidative gases at elevated temperatures. In this study, we present a chemical‐free, environmental‐friendly, and easily controllable surface activation method using an atmospheric pressure plasma‐jet. We investigate the best instant for activation along the process chain and show that the surface area of nanofiber nonwovens can be tailored by adjusting the plasma exposure‐dose. Plasma‐activated CFNs show an almost 20‐fold increase in capacitance (CspPJ = 10.1 F/g) in an electrochemical supercapacitor setup compared to nonactivated CFN (CspnoPJ = 0.55 F/g).

Electrochemical performance of poly(arylene piperidinium) membranes and ionomers in anion exchange membrane fuel cells

Awakening interest in anion exchange membrane fuel cells (AEMFC) for low temperature applications has led to an increased demand for high-performing polymers stable under alkaline conditions. In this study a poly(p-terphenylene piperidinium)-based membrane and ionomer was synthesized and applied in membrane electrode assemblies (MEAs), with porous gas-diffusion electrodes based on Pt catalysts supported by VULCAN® and high surface area carbon, respectively. The MEAs were evaluated in AEMFC single-cell tests. In order to identify specific beneficial characteristics of the polymer, the results were compared to reference tests using a commercial Aemion™-polymer. Steady-state polarisation performance measurements were carried out as well as electrode characterisations via cyclic voltammetry and electrochemical impedance spectroscopy, in addition to ex-situ characterisation of the polymer and the membrane electrode assemblies. Poly(p-terphenylene piperidinium)-based (PAP) membranes showed great potential with an in-situ measured average ohmic resistance of 0.09 Ωcm2. Mass transport limitations at higher current densities were observed for high surface area carbon electrodes, leading to an overall higher performance with the use of VULCAN®. Properties of the ionomer related to water uptake capabilities were observed to inhibit performance as well. The higher water uptake of PAP-based ionomers appears to be a key property for increasing electrode performance.

Modification of Carbon Black by Thermal Decomposition of Lead Acetylacetonate to Improve Activities for Ethanol Oxidation at Supported Pt Catalysts

Direct ethanol fuel cells (DEFC) are a type of promising energy-conversion device with high efficiency. The investigation of anode catalysts for DEFC is extremely important in improving energy efficiency. Improvement of the catalytic activity and long-term stability of Pt catalysts supported on some metal oxides has been reported for ethanol oxidation in acidic conditions. This synergistic effect mainly arises from the bifunctional effect and charge transfer between metal oxides and Pt catalysts.[1] In our study, thermal decomposition of Pb(acac)2 (acac = acetylecetonate) was used to rapidly prepare lead oxide supports on titanium foil and high surface area carbon electrode materials for electrocatalysis. On titanium electrodes, a thin layer of lead oxide was first prepared, followed by drop coating with a certain amount of a Pt nanoparticle solution. For high surface area carbon electrodes, Pt nanoparticles were adsorbed onto a carbon black-lead oxide composite, followed by painting a catalyst ink onto carbon fibre paper.The catalysts were characterized by X-ray diffraction and energy dispersive X-ray spectrometry. The electrochemical performance of the catalysts for ethanol oxidation was studied through cyclic voltammetry, chronoamperometry and in a proton exchange membrane electrolysis cell. Durability was studied through investigating the composition change before and after performing cyclic voltammetry. The lead oxide support was found to have a significant influence on onset potential, current density and product distribution for ethanol oxidation. Acknowledgments: This work was supported by the Natural Sciences and Engineering, Research Council of Canada and Memorial University.[1] G.M. Alvarenga, H.M. Villullas, Current Opinion in Electrochemistry, 4, 39, (2017).

(Invited) Pt/Metal Oxide/Ti and Pt/Metal Oxide/Carbon Composite Films for Ethanol Oxidation

Metal oxides such as RuO2 and SnO2 can promote the oxidation of organic fuels at Pt nanoparticles in a number of ways. These include changing the d-band level of the Pt via electron transfer (electronic effect) and providing surface –OH functionality for the oxidation of adsorbed CO (bifunctional effect) [1]. Carbon black coated with a mixture of Ru and Sn oxides has been shown to increase the activity of Pt for ethanol oxidation without a significant loss of selectivity for its complete oxidation to CO2 [2].Here we report on the use of various mixed metal oxide composites prepared by thermal decomposition of metal acetylacetonate complexes (M(acac)n). Oxide layers were deposited onto Ti foil and high surface area carbon electrodes, and drop coated with preformed Pt nanoparticles. Cyclic voltammetry in H2SO4(aq) and polarization experiments in a proton exchange membrane cell were used to study the co-catalytic effects of the oxide layers. The use of acetylacetonate precursors provides a versatile method for screening libraries of oxide supported catalysts, as well as the production and screening of electrodes for fuel cells.Initially, decomposition of Ru(acac)3 and Sn(acac)2 and their mixtures on Ti foil electrodes was investigated. These experiments reproduced the effects previously observed with oxide layers deposited on glassy carbon from KRuO4 and SnCl4 [3]. Deposits formed from both complexes increased the activity for ethanol oxidation of Pt nanoparticles drop coated onto their surfaces, while use of mixtures produced a strong synergistic effect. Deposits formed by thermal decomposition of a variety of other acac complexes, including Ga(acac)3, Zr(acac)4, and In(acac)3, also increased the activity of Pt nanoparticles for ethanol oxidation.Mixed Ru+Sn oxides were also produced by thermal decomposition of Ru(acac)3 and Sn(acac)2 on carbon black, in order to better characterize the oxide deposits and produce catalysts that could be used in fuel cells. X-ray diffraction and energy dispersive X-ray spectrometry confirmed the presence of a mixed oxide. Preformed Pt nanoparticles were adsorbed onto the oxide coated carbon, supported on carbon fiber paper, and the resulting electrodes were evaluated for ethanol oxidation in a proton exchange membrane cell at 80 °C. Acknowledgments: This work was supported by the Natural Sciences and Engineering Research Council of Canada and Memorial University.[1] G.M. Alvarenga, H.M. Villullas, Current Opinion in Electrochemistry, 2017, 4, 39-44[2] D.D. James, R.B. Moghaddam, B. Chen, P.G. Pickup, Journal of the Electrochemical Society, 2018, 165, F215-F219[3] R. B. Moghaddam and P. G. Pickup, Electrochim. Acta, 2012, 65, 210– 215

Large Capacity Enhancement of Carbon Electrodes by Solution Processing for High Density Energy Storage.

An inexpensive, solution phase modification of flat carbon electrodes by electrochemical reactions of a 1,8-diaminonaphthalene derivative results in a 120- to 700-fold increase in capacity by formation of a 15-22 nm thick organic film. Modification of high surface area carbon electrodes with the same protocol resulted in a 12- to 82-fold increase in capacity. The modification layer contains 9-15% nitrogen present as -NH- redox centers that result in a large Faradaic component involving one H+ ion for each electron. The electrodes showed no capacity loss after prolonged cycling in 0.1 M H2SO4 and exhibited significantly higher charge density than similar reported electrodes based on graphene and polyaniline. Investigation of the deposition conditions revealed that N-doped oligomeric ribbons are formed both by diazonium ion reduction and diaminonaphthalene oxidation, and the 1,8 isomer is essential for the large capacity increases. The capacity increase has at least three contributions: increased microscopic surface area from ribbon formation, Faradaic reactions of nitrogen-containing redox centers, and changes in ribbon conductivity resulting from polaron formation. An aqueous fabrication process was developed which both increased capacity and improved stability and was amenable to industrial production. The high charge density, low-cost fabrication, and <25 nm thickness of the diaminonaphthalene-derived films should prove attractive toward practical application on both flat surfaces and in high surface area carbon electrodes.

High performance nanoporous carbon microsupercapacitors generated by a solvent-free MOF-CVD method

Micro power sources that support higher power capabilities, specific energies, and ultra-long cycling lifetimes are required for next generation microelectro-mechanical systems (MEMS) and miniaturized portable microdevices. We demonstrated a simple, solvent-free method to coat interdigitated gold electrodes with a conformal layer of nanoporous carbon. Initially the electrodes were coated with a film of ZnO via electrodeposition to serve as the zinc source. These films were exposed to 2-methylimidazole vapor to transform the ZnO into a metal organic framework (MOF) called ZIF-8. The thickness of the ZnO film and the duration of the MOF conversion process created ZIF-8 films with different morphologies, cross-sections and elemental compositions. The ZIF-8 films were then carbonized at 800 °C under a flowing environment of N2 gas to generate nanoporous carbon film electrodes for supercapacitors. The devices have superior capacitance retention, in addition to high power and energy densities. Our 16-electrode microsupercapacitor had a stack power of 232.8 W⋅cm−3, which could be attained even at a scan rate of 1000 V ⋅s−1, without rapid stack energy attenuation. The process of combining an inexpensive ZnO electrodeposition method with solvent-free MOF deposition and subsequent carbonization generates high surface area carbon electrodes with good electrochemical performance.

Bio-Derived Nanocarbons in Electrochemical Applications

Carbonaceous materials are well known and readily used in a broad range of applications. Owing to the well-developed porous structure and the presence of certain surface functional groups, these materials are commonly used as adsorbents for a wide range of contaminants from gaseous or liquids media. Currently, activated carbons are also widely used as the electrodes for electric double-layer capacitors because of their high surface area, chemical stability and acceptable price.This work is focused on the carbon materials obtained from biopolymers such as lignin, cellulose and chitosan as precursors. The carbonisation in nitrogen atmosphere followed by chemical activation in KOH was chosen as a synthesis method. The resulting carbon materials were characterised by well-developed surface area and microporous structure, beneficial for electric double-layer capacitors (EDLC) electrodes. In parallel, graphene-like materials obtained from graphite oxidation followed by thermal reduction were also synthesised.The main goal of performed research tasks was to compare the electrochemical properties of carbon materials applied as electrode materials in different energy storage systems - electrochemical capacitors and in hydrogen storage systems. The special example taken into the consideration were hybrid capacitors composed of a battery-type electrode and a high surface area carbon electrode. This kind of configuration allows merging the advantages and reduces the drawback of redox and capacitive based systems. Since the same electrode material can give different electrochemical response depending on the type of device in which they are employed, this work will report on the influence of the physicochemical properties of carbon-based electrodes of various origin on their electrochemical response in various energy storage systems.

Electrochemical Performance of Activated Carbon Based Electric Double Layer Capacitors Using 1-Ethyl-3-Methylimidazolium Dicyanamide Ionic Liquid and Its Gel Polymer Electrolyte

The supercapacitors have emerged as an important energy storage device as they can deliver a high specific power, long cycle life, and much higher charge-discharge rates than a battery. In particular, solid-state supercapacitors have gained worldwide attention as an emerging candidate for smart and efficient energy storage devices due to the increasing demand for miniaturized electronics. Electric double layer capacitors (EDLCs) are the most widely studied class of supercapacitors which physically stores charge by forming an electric double layer at the interfaces between the high surface area carbon electrode and the electrolyte. The conventional EDLCs using high surface area activated carbon electrodes and non-aqueous liquid electrolytes represent the current state of the art. The most common cause of failure of such devices is related to the electrolyte leakage. Most of the past work on EDLCs have been carried out using the liquid electrolytes (aqueous, organic and pure ionic liquid). The gel polymer electrolytes with high ionic mobility and good dimensional/mechanical stability, offer a viable substitute for the liquid electrolytes and they are being used for flexible and solid-state electrochemical energy storage devices. Here, we report the electrochemical performance of high surface area activated carbon based EDLCs using 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA) ionic liquid and its poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) gel counterpart as electrolytes. The gel electrolyte films were prepared by immobilizing the EMImDCA ionic liquid in PVdF-HFP copolymer matrix by solution casting method. The activated carbon electrodes were prepared by mixing the activated carbon powder with conductive additive (Super C65) and PVdF-HFP binder in a ratio of 8:1:1 (w/w/w), and then the mixture was drop-casted onto a flexible thin graphite sheet which serves as current collector. The solid-state EDLC cells were fabricated by sandwiching the gel electrolyte film between two identical activated carbon electrodes whereas EDLC cells with pure IL were fabricated by using fiberglass separator soaked with IL. The EDLC cells show highly capacitive behavior as evident from the cyclic voltammogram of the cells measured at a scan rate of 20 mV s-1 which is rectangular in shape (Fig 1a). However, gel electrolyte based solid-state cell shows slightly higher resistance, obvious from slight deviation from rectangular shape at both turning potential. Typical galvanostatic charge-discharge characteristic of the EDLC cells at current density of 5 mA cm-2is shown in Fig. 1b. The linear discharge characteristics of the cell further confirms the capacitive behavior of the cells due to formation of an electric double layer at the interfaces. The EDLC cell with pure IL shows specific capacitance of ~98 F g-1 whereas IL-gel based EDLC cell shows specific capacitance of ~86 F g-1, derived from charge-discharge curves at 5 mA cm-2. A comparative performance of the EDLC cells was carried our using the impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. This paper discusses the results of these comparative studies with pure IL and its PVdF-HFP gel electrolytes. Figure 1

High-Energy Electrochemical Capacitors Utilizing Chemically Reduced Graphite Oxide As Negative Electrode Material

Taking into account power needs for portable devices, the energy storage through electrochemical reactions seems to be a crucial technology, especially due to the growing technological advances requirements. Electrochemical capacitors have attracted great attention as promising energy storage devices because of their high power density and cycle life noticeably longer than batteries [i],[ii]. Recently, extensive works have been focused on enhancing both the energy and power density accompanied by reasonable cost of device production as well as its environment-friendly character. One of the approaches is idea initiated in 2001 [iii], of improving capacitors performance by merging advantages of capacitors and lithium-ion batteries. This procedure was aimed to increase the energy of the capacitor while maintaining the level of supplied power. Starting from 2001 till now in the literature we can find examples of different methods involving various electrode materials [iv],[v],[vi],[vii],[viii],[ix],[x]. Asymmetric supercapacitors composed of battery-type electrode and a high surface area carbon electrode [xi] combine the advantages and reduces the drawback of redox and capacitive based systems. Therefore, the asymmetric design offers the advantages of supercapacitors (power rate, cycle life) and batteries (energy density) [xii]. This work is focused on high-energy electrochemical capacitors utilizing chemically reduced graphite oxide (CRGO) as a negative electrode material and activated carbon (AC) with the well-developed surface area as a positive electrode material. For comparison, electrochemical characteristic of capacitors utilizing graphite negative electrode was also performed. The pre-lithiation process, made by electrochemical intercalation of lithium ions into graphite, has been chosen as the main method of negative electrode material preparing. Performed electrochemical measurements, i.e., cyclic voltammetry and galvanostatic charging/discharging presented improved energy efficiency compared with results for symmetric cells (i.e. AC/AC capacitor). All measurements were performed in the organic electrolyte to provide a wide range of operating voltage. In the case of the hybrid system energy density has been improved and exceed 90 Wh kg-1 accompanied by good power profile. Additionally, good cycle performance was also achieved. Chemically reduced graphite oxide (CRGO) displays excellent performance at current densities up to 8 A g-1and, therefore, it can be considered as a very promising material for high energy Lithium-ion capacitors (LICs). Moreover, for more detailed analysis, measurements in three-electrode cells were also conducted. Fig. 1 shows an example of cyclic voltammetry curves for two systems composed of activated carbon cathode and graphite or CRGO anode. For graphite anode, Faradaic reactions can be observed in very narrow working range (134 mV) comparing to the positive electrode (1266 mV). CRGO characteristics merge two mechanisms of lithium storage, namely, Faradaic and capacitive one. In result, the quite good proportion of working potentials between positive and negative electrodes (772 mV vs. 628 mV, respectively) can be seen. The intercalation of lithium ions into graphite material occurs relatively slowly, hence the difference in power between the electrochemical capacitors and lithium-ion batteries. The electrode with the slowest sweep of potential will determine the power of the device. In this case chemically reduced graphite oxide seems to be promising material as an anode in lithium ion capacitors due to the merged lithium insertion movement, that’s why the energy storage can take place comparatively fast, as in the positive electrode. Financial support from the project DEC-2013/09/D/ST5/03886 is gratefully acknowledged. Fig. 1. Comparison of working potentials positive and negative electrodes in hybrid systems AC/G(Li) and AC/CRGO(Li), obtained from cyclic voltammetry measurements. [i] A. Burke, J. Power Sources 91 (2000) 37 [ii] P. Simon, Y. Gogotsi, Nat. Mater. 7 (2008) 845 [iii] G.C. Amatucci, F. Badway, A.D. Pasquier, T. Zheng, J. Electrochem. Soc. 148 (2001) A930 [iv] D. Cericola, R. Kötz, Electrochimica Acta 72 (2012) 1 [v] W.J. Cao, J. Shih, J.P. Zheng, T. Doung, J. Power Sources 257 (2014) 388 [vi] S.R. Sivakkumar, A.G. Pandolfo, J. Appl. Electrochem. 44 (2014) 105 [vii] X. Sun, X. Zhang, H. Zhang, N. Xu, K. Wang, Y. Ma, J. Power Sources 270 (2014) 318 [viii] S. Dsoke, B. Fuchs, E. Gucciardi, M. Wohlfahrt-Mehrens, J. Power Sources 282 (2015) 385 [ix] J. Zhang, Z. Shi, J. Wang, J. Shi, J. Electroana. Chem. 747 (2015) 20 [x] K. Naoi, P.Simon, Electrochem. Soc. Interface 17 (1) (2008) 34 [xi] J.W. Long, D. Belanger, T. Brousse, W. Sugimoto, M.B. Sassin, O. Crosnier, MRS Bull. 36 (2011) 513 [xii] Z.J. Fan, J. Yan, T. Wei, L.J. Zhi, G.Q. Ning, T.Y. Li, F. Wei, Adv. Funct. Mater. 21 (2011) 2366 Figure 1

Degradation Characteristics of Electric Double-Layer Capacitors Consisting of High Surface Area Carbon Electrodes with Organic Electrolyte Solutions

Aging characteristics of electric double-layer capacitors (EDLCs) comprising high surface area carbon electrodes with organic electrolyte solutions have been examined under high-voltage (high cell-potential) and high-temperature cycling conditions. The influences of the electrolyte components on decreasing the capacitance were investigated for cells using different electrolyte compositions. The use of acetonitrile (AN) as the electrolyte solvent in the cell led to higher cycling capacitance than those using alkyl carbonate solvents, such as propylene carbonate or ethylene carbonate mixed with dimethyl carbonate, under moderate cycling conditions. However, when the cycling was done with a higher operating voltage (>3.5V), significant capacitance degradation was observed for the cells using AN-based electrolytes. The EDLC cells using carbonate-based electrolytes showed moderate degradation behavior even at higher operating voltages. With respect to the electrolytic salt, cells using LiBF4 generally showed lower durability than cells using tetraethylammonium salt, TEABF4, especially at high operating voltages (>3.5V). The mechanism of the decreasing capacitance with repeated cycle is discussed.

Immobilization and electrochemical properties of ruthenium and iridium complexes on carbon electrodes

We report the synthesis and surface immobilization of two new pyrene-appended molecular metal complexes: a ruthenium tris(bipyridyl) complex (1) and a bipyridyl complex of [Cp*Ir] (2) (Cp* = pentamethylcyclopentadienyl). X-ray photoelectron spectroscopy confirmed successful immobilization on high surface area carbon electrodes, with the expected elemental ratios for the desired compounds. Electrochemical data collected in acetonitrile solution revealed a reversible reduction of 1 near −1.4 V, and reduction of 2 near −0.75 V. The noncovalent immobilization, driven by association of the appended pyrene groups with the surface, was sufficiently stable to enable studies of the molecular electrochemistry. Electroactive surface coverage of 1 was diminished by only 27% over three hours soaking in electrolyte solution as measured by cyclic voltammetry. The electrochemical response of 2 resembled its soluble analogues, and suggested that ligand exchange occurred on the surface. Together, the results demonstrate that noncovalent immobilization routes are suitable for obtaining fundamental understanding of immobilized metal complexes and their reductive electrochemical properties.

High Surface Area Carbon Electrodes for Bromine Reactions in H2-Br2 Fuel Cells

In a hydrogen-bromine (H2-Br2) fuel cell, the Br2 reactions don't require precious metal catalysts, hence porous carbon gas diffusion media (GDM) are widely used as electrodes. However, the specific surface areas of the commercial carbon gas diffusion electrodes (GDEs) are quite low and need to be enhanced. In order to improve the active surface area of carbon GDEs, a study was conducted to grow multi-walled carbon nanotubes (MWCNTs) directly on the carbon electrode fiber surface. Both constant and pulse current electrodeposition techniques were used to deposit Co nanoparticles to catalyze the MWCNT growth. The MWCNTs were grown in the presence of a mixture of acetylene, argon, and hydrogen gases using the chemical vapor deposition process. Based on the results obtained from SEM, TEM, and EDX analysis, MWCNT growth following the tip model was confirmed. The results from the multi-step chronoamperometry study have shown that the synthesized carbon GDEs with MWCNTs have 7 to 50 times higher active surface area than that of a plain GDE. The performance of a single layer of the best MWCNT GDE measured in a H2-Br2 fuel cell was found to be equal or slightly higher compared to that obtained using a three-layer plain carbon electrode.

Investigation of double-layer and pseudocapacitance of surface-modified ionic liquid-functionalized graphene oxide

Electrochemical capacitors (supercapacitors) have received considerable attention as promising energy storage devices for applications including transportation, load leveling, and personal electronic devices. Common features among electrochemical capacitors are high power density and cycle life, and although they may differ with respect to electrode material, many electrochemical capacitors employ some type of high surface area carbon electrode. With the emergence of graphene (a single atom thick layer of carbon), some recent attention has focused on using this material as a supercapacitor electrode with generally promising results. In this paper, we present imidazolium-functionalized graphene oxide supercapacitor electrodes. We compare these materials to unmodified graphene oxide. Our results indicate that the functionalized graphene oxide materials exhibit higher capacity than unmodified graphene oxide, leading us to conclude that these materials may be suitable for supercapacitor electrodes. In addition, we show that the functionalized graphene oxide materials exhibit a mix of double-layer and pseudocapacitance, which ultimately could further enhance material capacity.

Design and Testing of Supercapacitors for High Temperature Operation

Supercapacitors combine efficient energy storage and delivery of power under high pulse current conditions, while retaining a high capacitance and low equivalent series resistance (ESR) during extended cycling. A high specific power is achieved via charge storage at a high surface area electrode/electrolyte interface, supported by a very low cell-level ESR. Another advantage of this type of electrochemical storage is the relatively wide operating range of the technology. This is due to the nature of the charge storage mechanism, which is dominated by non-Faradaic processes. Concerns over solid electrolyte interphase stability and ionic electrode diffusivity at wide temperature limits (associated with lithium ion batteries) are not present. Commercially available supercapacitors are typically limited in operation to ~-40 C to +65ºC. These limits are fixed by the liquid range of the non-aqueous acetonitrile solvent used in most supercapacitor electrolytes. Propylene carbonate possesses a wider liquid range, but limits low temperature power delivery due to its higher viscosity. Wider temperature operation is of interest for numerous applications, such as energy storage for remote distributed sensing and electric vehicle power trains. Previous work in wide temperature supercapacitors has demonstrated that operation to <-70ºC is possible, through the proper design and use of solvent blends (which extend the melting point of the electrolyte solution).1-4Primary concerns include preventing precipitation of the salt onto the high surface area carbon electrodes and maintaining a sufficiently low ESR. This is achieved by designing high dielectric/low viscosity solvent blends. Higher temperature operation is limited in large part by the boiling point of traditional non-aqueous solvents, as well as increased decomposition rates. 5-6Supercapacitors for elevated temperature operation have been designed and tested to +160ºC, as part of ongoing efforts to develop wider temperature energy storage technologies. To enable operation at these temperatures, ionic liquids have been utilized as the electrolyte. New electrode formulations, designed for long duration elevated temperature exposure, have also been designed and tested. Initial test data over several thousand cycles will be presented. ACKNOWLEDGEMENT The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration (NASA). M.S. Ding, K. Xu, J.P. Zheng and T.R. Jow, J. Power Sources, 138, 340 (2004). Y. Korneblitt, A. Kajdos, W.C. West, M.C. Smart, E.J. Brandon, A. Kvit, J. Jagiello, G. Yushin, Adv. Ener. Mater. 22, 1655 (2012). W.C. West, M.C. Smart, E.J. Brandon, L.D. Whitcanack and G.A. Plett, J. Electrochem. Soc., 155, 716 (2008). E.J. Brandon, W.C. West, M.C. Smart, L.D. Whitcanack and G.A. Plett, J. Power Sources, 170, 225 (2007). T. Sato, G. Masuda and K. Takagi, Electrochim. Acta., 49, 3603 (2004). R.S. Borges, A.L.M. Reddy, M.-T. F. Rodrigues, H. Gullapalli, K. Balakrishnan, G.G. Silva and P.N. Ajayan, Sci. Rep., 3, 2572 (2013).

Quaternized Graphene Oxide-Based Supercapacitor Electrode

Electrochemical capacitors (supercapacitors) have received considerable attention as promising energy storage devices for applications including transportation, load leveling, and personal electronic devices. Common features among electrochemical capacitors are high power density and cycle life, and although they may differ with respect to electrode material, most electrochemical capacitors employ some type of high surface area carbon electrode. With the emergence of graphene (a single atom thick layer of carbon), some recent attention has focused on using this material as a supercapacitor electrode with generally promising results. In this paper, we present novel quaternized graphene oxide-based supercapacitor electrodes. We compare these materials to unmodified graphene oxide. Our results indicate the functionalized graphene oxide materials exhibit higher capacity than unmodified graphene oxide, leading us to conclude that these materials may be suitable for supercapacitor electrodes. In addition, we show that the functionalized graphene oxide materials exhibit a mix of double-layer and pseudocapacitance, which ultimately could further enhance material capacity.

Development of High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 fuel Cells

The H2-Br2 system is considered as one of the viable options for large scale electrical energy storage due to faster H2 and Br2 reaction kinetics, low cost, and high round-trip efficiency. Since the bromine reactions in this fuel cell system do not need any precious metal catalysts, plain porous carbon paper can be used as an electrode material. However, these porous carbon electrodes have low surface area and hence multiple electrode layers are employed to improve the active surface area. While the active surface area is enhanced by using multiple electrode layers, it could lead to mass transport limited performance at higher current densities. To overcome this problem, porous carbon electrodes with multi-wall carbon nanotubes grown directly on their surface were developed. The cross section of a carbon nanotube based electrode is shown in Figure 1. In this presentation, we will discuss the synthesis and characterization of carbon nanotube based electrodes as well as their durability and actual performance in a H2-Br2 fuel cell. Also, the advantages of these carbon nanotube based electrodes over conventional porous carbon electrodes will be highlighted. Acknowledgements This work was funded by NSF through grant number EFRI-1038234 and DOE/ARPA-E under award number DE-AR0000262. References Haley Kreutzer, Venkata Yarlagadda, and Trung Van Nguyen, J. Electrochem Soc., 159(7), F331 (2012).Venkata Yarlagadda and Trung Van Nguyen, J. Electrochem. Soc., 160(6), F535 (2013).Cheng Wang, Mahesh Waje, Xin Wang, Jason M. Tang, Robert C. Haddon, and Yushan Yan, Nano Letters, 4(2), 345 (2004).Chunyu Du, Baorong Wang, and Xinqun Cheng, J. Power Sources, 187, 505 (2009).Venkata Yarlagadda and Trung Nguyen, ECS Transactions, 58(36), 25 (2014). Figure 1

Infrared Spectroscopy During Electrocatalytic Turnover Reveals the Ni-L Active Site State During H2 Oxidation by a NiFe Hydrogenase.

A novel in situ IR spectroscopic approach is demonstrated for the characterization of hydrogenase during catalytic turnover. E. coli hydrogenase 1 (Hyd-1) is adsorbed on a high surface-area carbon electrode and subjected to the same electrochemical control and efficient supply of substrate as in protein film electrochemistry during spectral acquisition. The spectra reveal that the active site state known as Ni-L, observed in other NiFe hydrogenases only under illumination or at cryogenic temperatures, can be generated reversibly in the dark at ambient temperature under both turnover and non-turnover conditions. The observation that Ni-L is present at all potentials during turnover under H2 suggests that the final steps in the catalytic cycle of H2 oxidation by Hyd-1 involve sequential proton and electron transfer via Ni-L. A broadly applicable IR spectroscopic technique is presented for addressing electrode-adsorbed redox enzymes under fast catalytic turnover.

High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 Fuel Cells

The H2-Br2 system is considered as one of the viable options for large scale electrical energy storage due to faster H2 and Br2 reaction kinetics, low cost, and high round-trip efficiency. In order to improve the performance of the H2-Br2 fuel cell, carbon electrodes with high active surface area are needed. A preliminary study was conducted to synthesize and characterize the carbon nanotube based electrodes. Based on the results obtained from SEM, TEM, and EDX analysis, multi-wall carbon nanotube growth is confirmed. Also, the results from the multi-step chronoamperometry study have shown that the active areas of carbon nanotube electrodes are significantly higher than a plain carbon electrode.

High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 fuel Cells

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