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Increased Stability of PFSA Proton Exchange Membranes Under Fuel Cell Operation by the Decomposition of Peroxide Catalyzed by Heteropoly Acids.
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2006
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Catalytic MembraneChemical EngineeringFuel Cell ElectrochemistryEngineeringMembrane TechnologyProton-exchange MembranePolymer MembranesFuel Cell OperationCatalysisChemistryHeteropoly AcidsStable HpasPolymer MembranePeroxide CatalyzedElectrochemistry
Proton exchange membranes were cast from mixtures of the 3M perfluorinated sulfonic acid ionomer, with side chain -O-(CF2) 4-SO3H, and various heteropoly acids (HPAs) at a 10 or 20 wt% doping level. The membrane electrode assemblies (MEAs) prepared from these membranes were subjected to a fuel cell testing protocols involving incubation to steady state, temperature challenge, accelerated testing, and post mortem analysis. The cell temperature was varied from 70 - 100 ºC under relatively dry conditions, 70 ºC dewpoint, to avoid leaching of the HPA. The most important finding from this study was that the more stable HPAs, H4SiW12O40, α-H3P2W18O62, and H6P2W21O71 reduce the rate of F- release threefold and improve the performance of the MEA dramatically under these conditions. For HPAs that possibly rearrange in peroxide or at elevated temperatures, H3PW12O40, H6CoW12O40, H5SiAlW11O39, H6As2W21O69, and H21B3W39O162, the results were mixed as fragments of these molecules possibly interfere with the fuel cell electrochemistry.