CATALYTIC EFFECT OF RUTHENIUM IN RUTHENIUM-PLATINUM ALLOYS ON THE ELECTROOXIDATION OF METHANOL - MOLECULAR-ORBITAL THEORY

An atom superposition and electron delocalization molecular orbital (ASED-MO) study has been made of the catalytic effect of Ru alloyed into Pt electrodes on the oxidation of the adsorbed CO poison that is generated during methanol fuel cell operation. Using cluster models of the Pt(lll) surface, the Ru in Pt(111) alloy surface, and the Ru(0001) surface, it is found that the H2O adsorption energy to surface atoms increases in the order Pt in Pt(lll) < Ru in Pt(lll) < Ru in Ru(0001). An inverse relationship is found for OH activation energies: the stronger the adsorption, the more easily the reaction H2O(ads) --> OH(ads) + H(ads) takes place. The values and potential dependencies of these activation energies are consistent with OH(ads) being the oxidizing species that removes the CO(ads) poison. Both the Pt and the alloy surfaces are calculated to have increasing activation energies with increasing potential for the CO(ads) oxidation step. In both cases high coverage of coadsorbed CO, OH, or other species will. activate CO(ads) and OH(ads) by weakening their chemisorption bond strengths.