ON THE REACTION PATHWAY FOR METHANOL AND CARBON-MONOXIDE ELECTROOXIDATION ON PT-SN ALLOY VERSUS PT-RU ALLOY SURFACES

It has been observed in this work and previous studies that Pt3Sn allo y surfaces are very effective catalysts for CO electrooxidation, but n ot for methanol electrooxidation. Since COads is postulated to be an i ntermediate in methanol electrooxidation on Pt alloy surfaces, the rel ative inactivity of Pt3Sn for methanol oxidation appears paradoxical. We present an explanation for this apparent contradiction diction in t erms of a unique state of COads on this surface, which is not the same state of CO as occurs on either Pt-Ru or pure Pt surfaces. It is also not a state of COads which is produced by methanol dehydrogenation. T he state is unique in the sense that a significant fraction of COads i s oxidized at a much lower (<400 mV) potential than the rest of the CO ads, a phenomenon that does not occur on any other Pt and Pt-alloy sur faces examined in the same way. This CO state is only formed at high c overages by direct adsorption from dissolved CO and is not formed by t he dehydrogenation of methanol, since the multiple Pt atom sites neede d to dehydrogenate methanol are blocked by COads at low coverage. Copy right (C) 1996 Elsevier Science Ltd.