Generation of Hydrous Oxide Species at Carbon-Supported, Finely Divided Platinum Surfaces

It has been pointed out recently that with regard to the electrocatalytic behavior of noble metal electrodes, the important species in a number of technologically important processes are submonolayer coverages of hydrous oxide species; these may inhibit certain reduction processes or accelerate certain oxidation reactions. It was demonstrated in the present work that such an oxide can be generated more readily on carbon-supported, as compared with platinum-supported, platinum black deposits. Thick films of the hydrous oxide formed on platinum were found to be relatively stable, e.g., they were resistant to reduction to potentials below that at which the normal monolayer oxide was reduced. Their inhibiting effect on the oxygen gas reduction processes was demonstrated. It is suggested that such species are produced at submonolayer coverages at active, adatom sites at much lower potentials where they enhance certain anodic processes, e.g., methanol oxidation, but inhibit certain cathodic processes, e.g., oxygen gas reduction. The latter reaction at potentials of interest in fuel cell work, 0.8 to 0.6 V (RHE), may be forced to occur at less active sites on the surface where incipient hydrous oxide formation is less likely to occur.