CO Desorption Rate Dependence on CO Partial Pressure over Platinum Fuel Cell Catalysts

Carbon monoxide adsorption on high area platinum fuel cell catalysts was investigated. Isotopic exchange experiments were performed to determine the exchange rate (k) of CO under different partial pressures of CO (p_CO) in argon. A linear dependence of ln(k) with ln(p_CO) was observed. This pressure dependence of the rate of exchange is explained by considering a change in surface coverage of CO with different CO pressures and a subsequent reduction in the CO binding energy as demonstrated by Density Functional Theory (DFT) calculations. High Pressure Scanning Tunneling Microscopy (HP STM) studies on the Pt(111) surface have also displayed a pressure dependency of the coverage consistent with this data. The relevance of these observations to the Polymer Electrolyte Membrane Fuel Cell (PEMFC) anode reaction is discussed.