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Pt and Pd electrocatalysts are active for the complex 8-electron borohydride oxidation reaction (BOR), but the completeness of the electrochemical reaction is compromised by the formation of byproducts, including unreacted H2. We probe how combining the two electrocatalysts might improve the overall BOR activity. Five catalyst layer compositions are compared by rotating disk electrode (RDE) voltammetry and as the anode in hydrogen-peroxide direct borohydride fuel cells (H2O2-DBFCs): Pt/C, Pd/C, a Pt/C + Pd/C mixture, and graded layers of Pt/C and Pd/C as Pt/C|Pd/C or Pd/C|Pt/C. The RDE results show distinct mechanistic pathways for Pt and Pd, electrodes, but that the mixtures and Pt/C|Pd/C graded electrodes lead to better BOR activity than Pt or Pd alone. Similarly, the graded anodes in H2O2-DBFC outperform the ones with pure Pt/C or Pd/C under several operational conditions due to synergy between Pt and Pd. The Pt and Pd appear to serve as cooperative electrocatalysts, with their combination leading to less deleterious H2 escape than cells with Pt-only electrodes, and higher electrochemical performance than cells with Pd-only electrodes. We conclude that catalyst layers with graded compositions are promising electrode architectures for DBFCs.

We study whether the borohydride oxidation reaction (BOR) on Pt is improved when the Pt is supported on tantalum oxyphosphate-Vulcan carbon (Pt/[TaOPO4/VC]). Pt on carbon (Pt/C) is unstable in the alkaline conditions at the fuel cell anode. The support is employed to improve stability, and mitigate poisoning of the Pt from BOR intermediates. BOR measurements on the Pt/[TaOPO4/VC] by rotating disk electrode (RDE) voltammetry show that the Pt/[TaOPO4/VC] is more poison-resistant than Pt/C when the NaBH4 concentration is high (0.10 M). The Pt/[TaOPO4/VC] is also incorporated at the anode of a hydrogen peroxide direct borohydride fuel cell (H2O2-DBFC). At NaBH4 anode concentrations of 0.1 M NaBH4, the DBFCs with Pt/[TaOPO4/VC] anodes have higher specific activity than those with Pt/C, particularly at 60oC.

Incorporation of short-side chain (SSC) ionomers in the catalyst layers (CL) of proton exchange membrane fuel cells (PEMFCs) can improve performance, particularly at low relative humidities. We attempt to understand this effect by comparing PEMFCs with cathode CLs containing Pt on carbon-black (CB) and either SSC Aquivion ionomer or a standard long-side-chain (LSC) Nafion ionomer at 50% and 100% RH. The CL microstructures are characterized for their micro- and mesoporosity. The CLs are formed into PEMFCs and probed with polarization curves, cyclic voltammetry, O2 gain, limiting current measurements, and electrochemical impedance spectroscopy. PEMFCs containing the SSC ionomer in the cathode CL have superior polarization curves compared to those containing the LSC ionomer in the mass transport region under all conditions. We find that the SSC ionomer imparts lower proton transport resistances, lower charge transfer resistance to the cathode near 0.60 V, and lower mass transport resistance at 0.40 V. We attribute some of the performance improvements to the superior proton conductivity of the SSC ionomer, and the remainder to the higher micropore volume in the SSC-containing CLs which can more effectively evaporate water to the gas phase, improving both the availability of catalyst sites for charge transfer and mesopores for gas transport.

The direct electrooxidation of sodium borohydride (NaBH4) provides a path to release the high energy of the 8-electron, multi-step borohydride oxidation reaction (BOR). In practice, no single electrocatalyst is known to effectively oxidize all steps of the reaction. We investigate whether more complete BOR is achieved using an anode with a mixed electrocatalyst of nanoparticulate Pt and/or Pd supported on carbon (noted Pt/C and Pd/C). Electrocatalysts are compared in a liquid flow-through hydrogen peroxide direct borohydride fuel cell (H2O2-DBFC) having single Pt/C or Pd/C electrocatalyst, a mixture, or a gradient of the two along the anode flow channel. The best performance and lowest impedance over a broad range of potentials comes from a graded catalyst in which the composition varies from Pd/C at the channel inlet to Pt/C at the outlet, suggesting that catalyst gradients might provide a path to more efficient fuel cells for flow-type reactant systems.

The high efficiency of fuel cells combined with the high energy of hydrogen can be used to create energy systems for long endurance vehicles. As the automotive sector has developed fuel cells for this purpose, the same technology might enable long endurance unmanned undersea vehicles (UUVs). This paper describes fuel cell technologies for long endurance UUVs and issues related to integrating hydrogen fuel cells into large UUVs. We also describe an Office of Naval Research program with the U.S. Naval Research Laboratory, Naval Surface Warfare Center Carderock Division, University of Hawaii, and General Motors (GM) to integrate an automotive fuel cell from GM into a UUV. Hydrogen and oxygen storage technologies are also discussed.

It has been postulated that, similar to a battery, the optimized use of an electrolyzer as a variable load may help regulate grid frequency and increase the penetration of renewable energy resources on the grid. The use of an electrolyzer in this way could provide an "ancillary service" to the grid that can be assigned a monetary value. This monetary value can be used to offset the cost of hydrogen production. The hydrogen in turn can be used in high value applications such as a transportation fuel. The Hawai'i Natural Energy Institute (HNEI) is conducting research to assess the technical potential and economic value of using an electrolyzer-based hydrogen production and storage system as a demand response tool for grid management. This presentation will describe the Hydrogen Energy System (HES) configuration, plans for operation in the field, and results of initial tests to determine the dynamic response of the electrolyzer and overall system.

3D-printing is being touted as a tool for prototyping and manufacturing metal fuel cell bipolar plate (BPP) designs as it may speed development and lower costs by avoiding costly tooling, plus the 3D parts can be made as a single piece without welding. We use the 3D-printing method of direct metal laser sintering (DMLS) to make 21 cm2 titanium-alloy BPPs with embedded flow channels. To minimize the contact resistance in an individual cell, the surface of each BPP is polished to the appropriate roughness and coated with a conductive corrosion barrier. The coated BPPs are assembled with the appropriate seals, catalyst coated membranes and gas diffusion layers into both a single-cell and a 40-cell stack and tested. The single-cell stack performs well compared to a standard, but the 40-cell fuel cell stack power is 400 W, or 20% less than expected due to inadequate flatness of several of the DMLS BPPs. This cell-to-cell mismatch leads to high contact resistance in several of the cells. DMLS clearly shows the benefit of being able to make complex flow fields and hollow parts with no welds and is useful for prototyping flow fields in single cells or short stacks. More work is needed toward reducing the weight and increasing the flatness of BPPs made by DMLS before they can be used in larger stacks.

Lithium-ion batteries are prone to failure at low temperatures and dendrite growth during charging is one suspect. We attempt to understand lithium dendrite growth by observing their number, initiation time and growth rate at ambient and sub-ambient temperatures: [?]10degC, 5degC, and 20degC using an in-situ optical microscopy cell (Li0|Li0). We find that while dendrites initiate quickly at [?]10degC, the cells at 5degC short-circuit most rapidly due in part to a favorable morphology at this temperature. The experimental approach has broad applicability to other electrochemical energy storage technologies where mass transport limitations are present at low temperatures, particularly Li-air, Li-S, and Zn-air batteries.

Rotating disk electrode (RDE) voltammetry has been touted as a simple means for benchmarking the oxygen reduction reaction (ORR) activity of platinum-based electrocatalysts in proton exchange membrane fuel cells. In practice, the RDE methodology has been highly variable across laboratories, with up to 20% differences in values for the Pt electrochemical surface area and 10x differences in mass activity and area-specific activity reported from the same standard Pt/C electrocatalyst. We confirm that the same ORR activities can be replicated across laboratories when a detailed experimental protocol is followed. From our work and others', we conclude that dominant factors in the RDE experimental protocol include the ink formulation, electrocatalyst film quality and the electrochemical procedures. We make a recommendation for procedures for the reproducible characterization of Pt/C commercial catalysts, present simple metrics for researchers to use for a quick check of their results, and also propose new benchmark values for two Pt/C standards.

The performance degradation is probed for a proton exchange membrane fuel cell (PEMFC) exposed to 4 ppm HCl in air at cell voltages of 0.4, 0.5 and 0.6 V. While the steady-state cell current decreases by 90% for the cells held at 0.6 V, it only decreases by 17% when the cells are at 0.4 V. We hypothesize that Cl[?] poisoning is more pronounced at 0.6 V vs. 0.4 V due to increase in Cl[?] coverage of the Pt nanoparticle electrocatalysts as the cell voltage (and electrode potential) becomes more positive, implying chemisorption coupled to an electrostatic effect. Chloride coverage increases by ca. 30% as cell voltage increases from 0.4 to 0.6 V. Further losses are caused by a 12% decrease in Pt electrochemical surface area (ECSA) due to Pt dissolution to chloroplatinate ions, followed by growth and agglomeration of Pt nanoparticles.

The high rate capability and reversibility of lithium iron phosphate battery cathodes is attributed to the highly reversible transition between its LiFePO4 and FePO4 phases. Conflicting models exist for the phase transition mechanism, such as the shrinking or expanding core models, surface reaction limited model, and the single-phase kinetic model. A literature review suggests that the subscribed theories depend upon the experimental methods and also the geometry and size of the LiFePO4 particles. We study the electronic structure and disorder during the two-phase transition of commercial oval-shaped LiFePO4 particles using in situ XAS (X-ray absorption spectroscopy) with the Du XANES (X-ray absorption near edge structure) difference technique along with traditional EXAFS (extended X-ray absorption fine structure) to track the Debye-Waller (DW) factor. The Du XANES magnitude, |Du|, tracks changes in the electronic structure which does not follow a synchronous path with lithium content. The magnitude of the DW shows the degree of structural disorder reaches a maximum near the middle of the charge/discharge cycle. The combined |Du| and EXAFS results suggests the LiFePO4/FePO4 transition occurs through a "collective mosaic" or an unrelaxed "sequential" single-phase kinetic model.

The ORR on Pt in an alkaline electrolyte is studied for the impact of support effects. Platinum nanoparticles are supported on nanoscale tantalum oxyphosphate or tantalum oxide films on Vulcan carbon (VC) to make either Pt/[TaOPO4/VC] or Pt/[Ta2O5/VC] electrocatalysts, which were then characterized with BF-STEM. Their ORR activity was determined by RDE methodology in 0.10 M KOH electrolyte. The Pt mass activities of the Pt/[TaOPO4/VC] and Pt/[Ta2O5/VC] electrocatalysts are both approximately 250 mA mgPt[?]1 at 0.925 V, or about 2 x greater than that of a commercial Pt/VC electrocatalyst (120 mA mgPt[?]1), implying a substantial effect of the Ta-based support films.

The impedance response of LiCoO2|C battery cells is exploited to develop a single-frequency (500 Hz) diagnostic tool to detect overcharge abuse. The impedance data are reversible at all states-of-charge during normal charge/discharge operations (2.8-4.2 V), with little change in Z' or Z'' at 500 Hz even after 200 cycles. However, a single 4.6 V overcharge shows clear differentiation in the impedance values at 500 Hz, which is responsive to the cell passivation layers, with the Z' and Z'' first decreasing and then irreversibly increasing with cycling. Thus, this single-frequency impedance method provides a simple means of monitoring battery health.

The performance degradation of a proton exchange membrane fuel cell (PEMFC) is studied in the presence of HCl in the air stream. The cathode employing carbon-supported platinum nanoparticles (Pt/C) was exposed to 4 ppm HCl in air while the cell voltage was held at 0.6 V. The HCl poisoning results in generation of chloride and chloroplatinate ions on the surface of Pt/C catalyst as determined by a combination of electrochemical tests and ex-situ chlorine K-edge X-Ray absorption near-edge structure (XANES) spectroscopy. The chloride ions inhibit the oxygen reduction reaction (ORR) and likely affect the wetting properties of diffusion media/catalyst layer, while the chloroplatinate ions are responsible for enhanced platinum particle growth most likely due to platinum dissolution-redeposition. The chloride ions can cause corrosion of the Pt nanoparticles in the presence of aqueous HCl in air even if no potential is applied. Although the majority of chloride ions are desorbed from the Pt surface by hydrogen treatment of the cathode, they partially remain in the system and re-adsorb on platinum at cell voltages of 0.5-0.9 V. Chloride ions are removed from the system and fuel cell performance at 0.5[?]0.7 V is restored by multiple exposures to low potentials.

The thermal stability of a layered transition metal oxide with complete Al-substitution, Li1-xNi1/3Co1/3Al1/3O2 (NCA1/3), is studied in comparison to its better understood analogue, Li1-xNi1/3Co1/3Mn1/3O2 (NCM), to elucidate information critical to the safety of lithium-ion batteries. NCA1/3 and NCM have crystalline structures with the R-3m space group by high temperature synthesis from coprecipitate precursors. The specific capacities for NCA1/3 and NCM are 115 mAh/g and 180 mAh/g within 2.5-4.5 V. Thermogravimetric analysis coupled with mass spectrometry confirms the loss of oxygen at 271degC and 292degC for NCM and NCA1/3 delithiated to 4.4 V, respectively. The heat generation reaction of delithiated NCM is 91.7 J/g compared to 10.5 J/g for NCA1/3. The improved thermal stability offered by NCA1/3 is attributed to its low Li+ capacity due to the substitution of Al3+ for Mn4+ and its low heat of reaction due to the stability of the intermediate crystalline phases during delithiation and annealing.

Doped lithium copper-nickel mixed-metal oxides are prepared and studied as cathode materials for secondary Li-ion batteries. The compounds, Li2Cu0.5Ni0.4M0.1O2 (where M = Al, Ga), are made using solid state and micro-emulsion synthesis techniques. All compounds have a body-centered orthorhombic (Immm) crystal structure. The undoped compound has an initial discharge capacity of 270 mAh/g but exhibits poor capacity retention with cycling. The Al- and Ga-doped compounds made by solid-state synthesis have a higher discharge capacity than those made by micro-emulsion. Micro-emulsion processed compounds exhibit better cycleability and capacity retention upon charge/discharge suggesting a more stable crystal structure. Gallium doping improved the structural stability resulting in lowered irreversible capacity loss. Two reversible reaction mechanisms, lithium intercalation/de-intercalation and a displacement reaction are suggested to occur in the Li2Cu0.5Ni0.4M0.1O2 system.

Sulfur dioxide, , is a common impurity in air that is known to deactivate electrocatalysts for the oxygen reduction reaction (ORR) at proton exchange membrane fuel cell cathodes. The poisoning of a Vulcan-carbon-supported platinum cobalt alloy is compared to that of a standard platinum (Pt/VC) electrocatalyst using cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) methodology at controlled concentrations of S(IV) in an oxygen-free solution. The CV and RRDE measurements show that for electrodes with the same Pt loading, the is two times more active than the Pt/VC. Upon exposure to S(IV) solutions, the nanoparticle electrocatalysts are more poisoned than the Pt/VC ones, and their initial sulfur coverage is higher. The poisoning of both catalysts is accompanied by an increase in the amount of production, as adsorbed sulfur species inhibit the four-electron ORR. The electrocatalyst loses 80% activity in a 0.0001 M S(IV) compared to a 30% loss by the Pt/VC electrocatalysts. The adsorbed sulfur species are more easily removed from the than the Pt/VC by potential cycling, implying a weaker bonding between species and . We conclude that is more susceptible to poisoning by than Pt at a given Pt loading, but its activity is more easily recovered.

We synthesize, measure and use first principles density functional theory (DFT) calculations to study two Ru-based metal oxides, layered Li2RuO3 and rutile RuO2, in terms of their electrochemical performance as potential battery cathode materials. Despite being composed of identical constituent elements, and having the same local structure, the two compounds have very different voltage profiles and conductivities that can be traced back to differences in their long range structures. We find that three basic factors contribute to the superior cathode properties of Li2RuO3 in comparison to RuO2: a lower Ru/O ratio that raises the oxidation state of Ru, more localized electron states due to quasi-two-dimensionality, and strong Ru-Ru bonding in the metal oxide plane that shifts the electronic energy levels. The principles extracted from the comparison of these two materials can be generalized and used to help guide the search for superior cathode compounds

Lanthanum nickelate (LN, ) is a mixed ionic and electronic conductor with oxygen self-diffusion and surface exchange properties that predict that it will be a good cathode catalyst for solid oxide fuel cells. We show that LN performs poorly when used as a single-phase cathode in yttria-stabilized-zirconia-based air- dime cells at . Power densities up to are measured only when LN is used in a composite bilayer cathode. Parametric modeling shows that the kinetics of the LN-based cathodes is relatively poor, but their low ohmic resistance leads to their high power density.

The poisoning of the oxygen-reduction reaction (ORR) by adsorbed sulfur-containing species is quantified for platinum cobalt alloy fuel-cell materials using rotating ring disk electrode (RRDE) methodology. Electrodes of Pt3Co on Vulcan carbon (Pt3Co/VC) are contaminated by submersion in SO2-containing solutions. The initial sulfur coverage of the Pt is determined from the total charge consumed as the sulfur is oxidized from S0 at 0.05 V (vs. RHE) to water-soluble sulfate (SO42-) at > 1.3 V. Initial sulfur coverage (thS,i) is higher on Pt3Co/VC compared to Pt/VC electrodes for poisoning done in the same SO2-containing solution. Electrodes are then evaluated for their ORR activity. Significant (99.8%) loss in initial Pt mass activity is measured when approximately 54% of the Pt3Co/VC surface has adsorbed the sulfur-containing species. When 96% of the Pt surface is covered with sulfur, the reaction pathway of the ORR on the Pt/VC catalyst changes from a 4-electron to 2-electron process reaction for peroxide.

Three synthetic routes are evaluated to obtain highly dispersed platinum on tantalum oxide supported catalysts: a) deposition of platinum colloids on tantalum oxide followed by mechanical grinding with Vulcan carbon; b) deposition of tantalum oxide on Vulcan carbon, followed by the deposition of platinum colloids; and c) deposition of Pt colloids on Vulcan carbon, followed by deposition of tantalum oxide. Specific activities for oxygen reduction reaction at 0.9V are a factor of two higher for catalysts synthesized via preparation routes a and b compared to Pt/VC. In comparison, the activity of catalysts synthesized via route c is close to that of Pt/VC. Mass activities for the catalysts possessing high specific activities are lower than for Pt/VC due to their low electrochemically available platinum surface area.

A blend of Li2RuO3 and carbon-coated LiFePO4 is examined as a low impedance cathode for high power lithium-ion microbatteries. A lithium metal cell with a composite positive electrode of LiFePO4/C and Li2RuO3 showed a greater specific capacity and specific energy at 1C discharge than at C/5. A specific capacity of 145 mAh/g was observed for the blend of 40% Li2RuO3 and 60% LiFePO4/C when discharged at C/5, whereas 160 mAh/g was observed for 1C discharge rate. Discharge rates greater than 1C showed progressively decreased specific capacities.

We have incorporated small Pt nanoparticles (1.7 {plus minus} 0.5 nm) stabilized with triphenylphosphine triphosphate (Pt-TPPTP) or triphenylphosphine oxide (Pt-TPPT-oxide) into composite polymer-Vulcan carbon thin films and measured the effects of the ligands on the ORR activity of the Pt nanoparticles using rotating disk electrochemistry (RDE). We measure ORR activities for TPPTP-stabilized particles of 0.21 A/mgPt at 0.9 V, which is less than the 0.25 A/mgPt that we measure for the "bare" Pt nanoparticle. However, when normalizing the ORR kinetic current for Pt microscopic surface area, the specific activity, is, for Pt-TPPTP is significantly higher than for the parent nanoparticles (0.41 mA/cm2real vs. 0.29 mA/cm2real), suggesting a kinetic enhancement of the ORR viz. a weakening of the Pt-O bond strength by the TPPTP ligand. Cyclic voltammetry also reveals a positive shift in Pt-oxide electrochemistry for Pt-TPPTP compared to that for bare Pt nanoparticles, which is consistent with the improved area-specific ORR kinetics.

Gold nanoparticles supported on hydrous tin-oxide (Au-SnOx) below 0.5V vs. RHE are active for the 4-electron oxygen reduction reaction (ORR) in acid electrolyte. In comparison, gold on Vulcan carbon (Au/VC) is inactive for ORR and generates mostly peroxide (i.e. 2-electron reduction) rather than water. These results indicate a significant support effect from SnOx which enhances the activity of the Au. This metal support interaction was studied in this work using in situ X-ray absorption spectroscopy (EXAFS and XANES) at the Au L3 and Sn K edges in an electrochemical cell. The results show that a bifunctional mechanism plays the dominant role in the ORR reaction on Au/SnOx. The O2 adsorbs and dissociates on the SnOx surface, and then is reduced on the Au either directly or after conversion to O[H] groups. Enhanced O[H] adsorption occurs at potentials above 1.2 V on the Au; this adsorption is enhanced through a ligand mechanism involving the SnO support, but this has no apparent effect on the ORR occurring at lower potentials

Nanostructured nickel tungsten carbide (Ni6W6C) and nickel molybdenum carbide (Ni6Mo6C) are well known hydrodesulfurization catalysts, that have been speculated to be useful as sulfur-tolerant proton exchange membrane fuel cell anode catalysts. We synthesized these compounds and evaluated their electrocatalytic activities for the hydrogen oxidation reaction (HOR) in sulfur-free electrolyte as well as electrolyte contaminated with 31 uM mercaptosuccinic acid (1 ppm sulfur) using a rotating disk electrode. The HOR activity of the carbides is higher than that reported elsewhere, but still is low when compared to platinum catalysts. The nanostructured catalysts corrode and show poor sulfur tolerance. Further development is needed to understand why these catalysts perform poorly in fuel cell environments.

Rotating ring disk (RRDE) methods are used to quantify the poisoning of the oxygen reduction reaction (ORR) at Pt/VC catalysts by adsorbed sulfur species. Coulometric analysis indicates that only S(0) is adsorbed on the Pt/VC surface. RRDE measurements show that the ORR activity decreases significantly as the sulfur coverage increases. Sulur coverage {greater than or equal to} 0.37, drastically changes both the activity and the reaction pathway of the ORR on the Pt/VC catalyst from a 4-electron to 2-electron process reaction. At high current densities, the Tafel slopes of the sulfur-poisoned electrodes increase, and the electrodes are no longer efficient for the ORR, as evident by the loss 95% mass activity with initial sulfur coverage of only 0.14. The decrease in activity due to the adsorbed sulfur is accompanied by an enhanced formation of hydrogen peroxide (up to 70% for initial sulfur coverage {greater than or equal to} 0.37).

The oxygen reduction reaction (ORR) at proton exchange membrane fuel cell (PEMFC) cathodes requires a relatively large amount of Pt to catalyze. Our goal is to reduce the Pt loading in PEMFC cathodes using catalysts modified by metal support interactions (MSIs), an approach commonly used in heterogeneous catalysis. We illustrate the benefits of MSIs by showing that the activity of Pt is improved by supporting it on hydrous tantalum phosphate. More dramatically, oxygen reduction on Au in changed from a 2- to 4-electron reaction simply by supporting the metal on hydrous tin oxide. The changes to the catalysis of Pt and Au are attributed to electronic and chemical effects imparted by the supports.

Rotating disk electrode (RDE) methods are used to quantify the poisoning of the oxygen reduction reaction (ORR) at Pt catalysts for PEMFCs by SO2. With the addition of 50 ppm of SO2, the Pt loses 17% of its mass activity, however its Tafel slope remains unchanged. With 200 ppm SO2, the catalyst activity drops by 52% and its Tafel slope changes from 129 to 186 mV dec-1 at potentials <0.83 V. Levich-Koutecky analysis shows significant deviation from mass-transport controlled kinetics at high concentrations (200 ppm) of SO2, even at high overpotentials, demonstrating poisoning of the Platinum/Vulcan Carbon (Pt/VC) catalysts. The analyses show that SO2 poisoning of Pt at higher potentials (> 0.85 V) is mainly due to blocking of Pt sites by adsorbed SO2, and is more severe at lower potentials (< 0.83 V) due to stronger adsorption that alters the electronic state of the Pt.

We describe the preparation of a manganese oxide polymorph in which the solid-pore architecture of the material is controllably varied. All gels derived from a sol-gel synthesis and annealed to crystallize in the 2x2 tunnel structure of cryptomelane , but exhibit markedly different final pore structures based on how the pore fluid is removed from the wet gel. The mesoporous structure of the initial gel is maintained by removing pore fluid under conditions where the capillary forces that result from extraction are either low (to form an ambigel) or nonexistent (to form an aerogel). These nanoscale mesoporous materials have higher capacities at high cycling rates than can be obtained for bulk cryptomelane. Finite-diffusion processes describe the electrochemical association of with the networked, nanoscale crystallites. Controlling both the pore and solid architecture on the nanoscale offers a strategy for the design of new battery and charge-storage materials. (c)2000 The Electrochemical Society

The poisoning effect of and in air is compared for phosphoric-acid-doped polybenzimidazole (PBI) membrane and perfluorosulfonic acid (Nafion) proton exchange membrane fuel cells (PEMFCs). The cathodes of PBI PEMFCs are about 70 times more resistant to 1 ppm of or than the Nafion PEMFCs. The PBI PEMFCs only lose in cell performance when exposed to 1 ppm of or and have 5.2 and 7.1% losses with 5 and 10 ppm over 24 h, respectively. Purging the poisoned PBI cells with neat air leads to complete performance recovery.

The vulcanized carbon (VC) used to support nanoscale catalysts in fuel cells contains organosulfur that poisons the upon heating in the absence of water. We have previously shown that in the art of making fuel-cell electrodes (which includes water and heat), surface-sited organosulfur in the VC is catalytically oxidized to innocuous sulfate when it contacts . When the carbon surface is desulfurized, electroactive electrodes can be fabricated without water and at temperatures that would otherwise poison when mixed with standard VC. The subsurface organosulfur in VC does not migrate over time to the desulfurized carbon surface under ambient conditions to deactivate supported . Electroactive sulfur-content carbon electrodes can now be made using nonaqueous protocols. Low-sulfur-content carbon supports should reduce performance losses in fuel cells. (c)2000 The Electrochemical Society