Renewable energy demand places fuel cells at the forefront of the development of energy conversion devices. High-efficiency polymer electrolyte membrane fuel cells, such as direct methanol fuel cells and hydrogen-air fuel cells require platinum-based alloy anode electrodes such as PtRu, PtRuOs, and PtRuOsIr mixed-metal alloys.  In an operando fuel cell condition, water molecules, CO molecules, and ionomer functional groups are co-adsorbed on platinum-based alloy surfaces in the presence an electric field. Here, we initiate the study for these concurrent effects by examining the coadsorption of CO and water molecules on Pt and the above Pt-based alloys using density functional theory. The efficiency of the anode catalyst is associated with the weakening of the C-metal bond for the adsorbed CO in the above conditions. For direct methanol fuel cells, Ru and Os surface atoms activate water, thus providing –OH groups to react with the absorbed CO and producing CO<sub>2</sub>. It is observed that the presence of Ru and Os surface atoms attract water molecules, thus enhancing the production of the –OH groups.  Increased hydration weakens the C-O bond and strengthens the C-Pt bond for CO adsorbed on pure Pt as verified by changes in the C-O and C-Pt stretching frequencies and corresponding bond lengths. These changes are in agreement with the observed upshift of the Fermi level of the Pt surfaces due to hydration, and is indicative of increased 2π* back donation to the CO, which weakens the C-O bond and strengthens the C-Pt bond.

Carbon monoxide and water coadsorption on platinum and platinum-based mixed-metal anode catalysts for polymer electrolyte membrane fuel cells

255th National Meeting (2018)

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