The effect of low concentrations of CO on H2 adsorption and activation on Pt/C: Part 2—In the presence of H2O vapor

CO affects H₂ activation on supported Pt in the catalyst layers of a PEMFC and significantly degrades overall fuel cell performance. This paper establishes a more fundamental understanding of the effect of humidity on CO poisoning of Pt/C at typical fuel cell conditions (80 °C, 2 atm). In this work, direct measurements of hydrogen surface concentration on Pt/C were performed utilizing an H₂-D₂ switch with Ar purge (HDSAP). The presence of water vapor decreased the rate of CO adsorption on Pt, but had very little effect on the resulting CO surface coverage on Pt_S (θ_CO) at steady-state. The steady-state θ_COs at 80 °C for Pt exposed to H₂ (PH₂=1 atm) and a mixture of H₂/H₂O (1 atm H₂, 10%RH) were 0.70 and 0.66 ML, respectively. Furthermore, total strongly bound surface hydrogen measured after exposure to H₂/H₂O was, surprisingly, the sum of the exchangeable surface hydrogen contributed by each component, even in the presence of CO. In the absence of any evidence for strong chemisorption of H₂O on the carbon support with/without Pt, this additive nature and seemingly lack of interaction from the co-adsorption of H₂ and H₂O on Pt may be explained by the repulsion of strongly adsorbed H₂O to the stepped-terrace interface at high coverages of surface hydrogen.