Mechanism of Stationary Bulk CO Oxidation on Pt(111) Electrodes

Carbon monoxide oxidation at platinum electrodes in acid solutions presents a characteristic behavior depending on the presence or not of dissolved CO in the bulk of the solution. In the present paper, bulk CO electro-oxidation is studied on a Pt(111) electrode. A change of the (2 × 2)-3CO overlayer, formed by admitting CO at 0.05 V, into a (√19 × √19)-13CO structure was observed at around 0.4 V. These changes were monitored by in situ Fourier transform IR spectroscopy through the bands for on-top, 2-fold, and 3-fold bonded CO. If the solution is saturated with CO, oxidation of the CO adlayer formed at 0.05 V begins at ca. 0.4 V and presents a “quasistationary” behavior. This process involves weakly bonded CO. The presence of such species is rationalized in terms of the steep decrease of the desorption energy at high degrees of coverage, reported for CO adlayers on Pt(111) in UHV. When CO is adsorbed at high potentials (above 0.6 V), segregated adlayers of CO and H-bonded H2O are formed. The H-bonded H2O ...