Simulation of anodic Pt oxide growth

Abstract

A microscopic model of the growth of the thin anodic oxide film on Pt is presented. The slow step is migration of a Pt atom from the metal lattice to become a Pt(II) species. Pt(II) species can then rapidly diffuse across the surface. Sites of different types, e.g. terrace atoms or step atoms, have different reactivity, dependent on their number and type of bonds. Monte Carlo simulations are used to predict the kinetics and the surface reconstruction. The treatment of the structures of the oxide and metal is oversimplified by the assumption that they both have simple cubic unit cells with identical lattice parameters. The model predicts correctly the observed direct logarithmic growth law for potential step transients, without any change in behavior at full monolayer coverage. For cyclic voltammetry, it predicts an anodic peak on the first cycle, and plateau behavior for subsequent cycles. The reversible component is found, and interpreted in terms of a reversible reconstruction aided by the rapid surface diffusion. The height distributions predicted by this model agree with recent structural measurements, but the exact topography of the surface after multiple cycles is not reproduced.