Catalytic methanol decomposition pathways on a platinum electrode

Through a combination of potential steps (chronoamperometry) and fast potential sweeps (cyclic voltammetry), temporal advancements involved in methanol decomposition-indicated by the decomposition charges-were referred to the extent of CO poisoning. In a broad potential range, especially at short times, there is an excess of charge above that needed for simple methanol dehydrogenation to surface CO. This indicates that there exist some efficient methanol decomposition pathways that lead to the formation of products other than CO, namely carbon dioxide, but also formic acid and/or formaldehyde. Because the formation of CO2 was not observed by others below the electrode potential of 0.35 V vs RHE (cf. infrared studies reported in J. Phys. Chem. B 1997, 101, 7542), we believe that, at low potentials, methanol dehydrogenation to formic acid and/or formaldehyde accounts for the excess oxidation charge. The formation of the dissolved products along with surface CO confirms the applicability of a dual-path mechanism for methanol oxidation on platinum. We also successfully modeled the mechanism of methanol decomposition using a three-term rate equation. The modeling allowed us to estimate the rates of the elementary reaction channels involved in methanol decomposition without the complication of CO poisoning effects. We believe that the results reported in this paper lead to an advanced understanding of the methanol decomposition processes on a polycrystalline platinum electrode, especially at short reaction times. Information about such short-time methanol decomposition events was missing from the previous studies of this important electrocatalytic system.