POTENTIAL DEPENDENCE OF CO(ADS) OXIDATION BY OH(ADS) ON PLATINUM ANODES - MOLECULAR-ORBITAL THEORY

An atom superposition and electron delocalization molecular orbital (ASED-MO) study has been made of the electrochemical oxidation of the CO poison on the Pt anodes that is generated during methanol fuel cell operation. The interaction of CO(ads) with the oxidant OH(ads) is shown to be productive only at high surface coverages, as high coverages activate CO(ads) by weakening its bond to the surface. The potential dependence of this reaction, modeled by shifting the metal valence band parametrically, has the wrong behavior for it to be the rate-limiting step. A rate-limiting step which has good qualitative agreement with measured apparent activation energies at different potentials is the generation of OH(ads) from H2O(ads), for which the activation energy barrier is calculated to decrease as the potential increases.