Abstract
Heteropoly acids were investigated to determine their activity as non-Pt oxygen reduction reaction (ORR) catalysts in polymer electrolyte membrane fuel cell cathodes (PEMFCs). Polarization curves, cyclic voltammetry, and impedance spectroscopy results determined that, of the HPAs tested, only Mo based HPAs are active for the ORR and that V substitutions can improve the activity. Power densities of 67mW at 0.2V were obtained using H5PMo10V2O40. The catalysts must first be reduced insitu before the HPA can reduce oxygen. The reduction potentials of the HPAs in the fuel cell environment were determined by cyclic voltammetry and provide an explanation for why no activity is seen above 0.55V. Impedance spectroscopy confirmed that V substitutions increase catalytic activity. The potential at which the HPA can be reduced by 4 electrons has been determined to be the limiting factor when using these catalysts for ORR in PEMFCs.
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