Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt:Ru alloy anodes, allowing a greater percentage of O2 to oxidize adsorbed CO to CO2. With an anode feed of H2, 2% O2, and up to 100 ppm CO, the Pt + Ru filter anode performed better at 70°C than the Pt:Ru alloy. The oxygen in the anode feed stream was found to form a hydroxyl species within the filter. The reaction of these hydroxyl groups with adsorbed CO was the primary means of CO oxidation within the filter. Because of the resulting proton formation, the Ru filter must be placed in front of and adjacent to the Pt anode and must contain Nafion in order to provide the ionic pathways for proton conduction, and hence achieve the maximum benefit of the filter.
Journal of the Electrochemical Society, 2002, pages A862-A867.
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Publisher's link: http://dx.doi.org/10.1149/1.1479726