Oxidation of carbon monoxide on poly-oriented and single-crystalline platinum electrodes over a wide range of pH

The oxidative stripping of pre-adsorbed carbon monoxide has been studied on poly-oriented platinum, and on Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) single-crystal electrodes in phosphate buffer solutions as a function of pH, both stripping voltammetry and chronoamperometry. It was found that the stripping peak potential has a tendency to decrease as a function of pH until a pH of ca. 10-11, which is ascribed to a weaker adsorption of phosphate on platinum with increasing pH. Above a pH of ca. 11, the stripping peak appears to stay constant or increase, depending on the surface structure. We hypothesize that this may be due to the fact that above a pH of ca. 10-11, the main product of carbon monoxide oxidation is carbonate, which may be block active sites on the surface. By comparison with the stripping on the single-crystalline Pt, the stripping voltammetry on the poly-oriented Pt electrode appears as a convolution of the oxidation on the different facets. A similar conclusion is drawn for the chronoamperometry experiments, and it is suggested that this may be the main reason for the asymmetrical transients observed on the poly-oriented Pt electrodes, as well as on other strongly heterogeneous Pt electrodes that have been studied in the literature.