Surface and Subsurface Oxygen on Platinum in a Perchloric Acid Solution

Abstract

The oxidation of polycrystalline platinum in perchloric acid is studied by cyclic voltammetry at a potential scan rate of 0.1 V s^–1 in various potential cycling ranges. The earlier model for the formation of a barrier layer of strong complexes consisting of subsurface oxygen O_ss, platinum atoms, and anions adsorbed on the latter is shown to correctly describe experimental results on the platinum oxidation in sulfuric and perchloric acids. The regularities in these acids are on the whole similar. A weaker adsorption of perchlorate anions as compared with bisulfate facilitates chemisorption of oxygen at 0.7–0.85 V and hinders exchange by sites Pt ⇔ O at 0.85–1.35 V. A prolonged potential cycling with a cathodic limit of 0.27 V and low anodic limits leads to the accumulation of surface complexes O_ss–Pt _n –ClO₄, which hinder both the oxygen chemisorption and the exchange Pt ⇔ O below 1 V. At more positive potentials, the complexes are destroyed and oxygen penetrates into subsurface platinum layers.