Analysis of Reaction Kinetics for Carbon Monoxide and Carbon Dioxide on Polycrystalline Platinum Relative to Fuel Cell Operation

Polymer electrolyte fuel cells operate at high efficiencies using pure H 2 fuel. H 2 produced by reforming hydrocarbons or alcohols contains CO and CO 2 (CO x ) impurities which readily adsorb onto anode Pt electrocatalysts, reducing the efficiency for H 2 electrooxidation. A CO x inventory model is useful for describing the behavior of adsorbed CO on Pt electrocatalyst surfaces. The model compares three fluxes: (1) direct adsorption of CO, (2) the electroreduction of CO 2, and (3) electrooxidation of adsorbed CO. The fluxes of CO 2 electroreduction and CO electrooxidation were measured electrochemically on polycrystalline Pt electrodes (surface roughness = 30−100) in 1 N H 2 SO 4 between 23 and 66 °C. This study concludes that, under polymer electrolyte fuel cell conditions, CO tolerance is achieved when the flux of CO electrooxidation balances the combined adsorption fluxes from both CO and CO 2 . Furthermore, under most conditions, CO adsorption will generally exceed the fluxes of CO 2 electroreduction.