A time effect in the early stages of a surface oxidation of a Pt(111) plane in alkaline solution

Abstract

A time effect in the early stages of surface oxidation of a Pt(111) plane in 0.1 M NaOH solution was studied by examining the reduction parts of the j/E profile recorded after holding the potential for various times at several values at the end of anodic-going sweeps. The processes associated with the two peaks, which appear in the anodic part of the voltammogram, are assigned to the early stages of a surface oxidation. Two OHad states are suggested based on the existence of reversibly or weakly bound OHad species and irreversibly or strongly bound OHad species. The reversibly bound OHad species are involved in the normal structure of the butterfly peak, while the irreversibly adsorbed OHad species can be obtained only by the slow diffusion of a part of the initially electrosorbed OH species from sites with low to sites with higher binding energies. The irreversibly reduced OHad species cannot be completely removed from the surface causing, therefore, some permanent transformation of the initial state of the surface. This kind of species was not detected in the area of the second oxidation peak. The phenomena observed in the reduction part of the j/E profile induced by a time effect in the second peak could be associated with a place-exchange mechanism between oxygen containing species, whatever they are, and the platinum surface