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

摘要

CO affects H_2 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 ℃, 2atm). In this work, direct measurements of hydrogen surface concentration on Pt/C were performed utilizing an H_2-D_2 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 (#co) at steady-state. The steady-state 鑏(co)S at 80℃ for Pt exposed to H_2 (P_h_2 = 1 atm) and a mixture of H_2/H_2O (1 atm H_2,10%RH) were 0.70 and 0.66 ML, respectively. Furthermore, total strongly bound surface hydrogen measured after exposure to H_2/H_2O 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 H_2O on the carbon support with/without Pt, this additive nature and seemingly lack of interaction from the co-adsorption of H_2 and H_2O on Pt may be explained by the repulsion of strongly adsorbed H_2O to the stepped-terrace interface at high coverages of surface hydrogen.