Nature of CO Adsorption during H 2 Oxidation in Relation to Modeling for CO Poisoning of a Fuel Cell Anode

To understand the polarization loss due to poisoning by of a porous Pt anode under various conditions, poisoning losses have been measured in a half‐cell in the temperature range 110°–190°C in 100 weight percent for various mixtures of , , and gases. At a fixed current density, the poisoning loss, , was observed to vary linearly with ln . Deviation from linearity was observed at lower temperatures and higher current densities for high ratios. Considering only the linear portions, it has been possible to derive a general relationship for with temperature, concentration, and current density. The surface coverage by was calculated at various temperatures and was found to bear a linear relationship with ln . From the experimental Temkin isotherms, a general adsorption relationship has been obtained. The standard free energies for adsorption were calculated and were found to vary from −14.5 to −12.1 kcal/mol in the temperature range 130°–190°C. The standard entropy for adsorption was calculated to be −39 cal/mol K. Interpretations of the data indicate that adsorption occurs through 1:1 replacement of H by through the process of selective site poisoning. Under conditions where a nonlinearity in the poisoning relationship occurs, molecules undergo some orientation, favored by the increasing positive charges on the Pt surface.