Lattice gas model for CO electrooxidation on Pt-Ru bimetallic surfaces

We propose a lattice gas model for the carbon monoxide oxidation on platinu m-ruthenium electrode surfaces. The kinetic model includes the main mechani stic "bifunctional" features as they are generally agreed upon in the liter ature. The CO stripping voltammetry is solved by dynamic Monte Carlo simula tions. For a randomly dispersed alloy of Ru and Pt, the model gives a satis factory semiquantitative agreement with the experimental CO stripping resul ts of Gasteiger ct al. [J. Phys. Chem. 1994, 98, 617]. It is shown how the bifunctional mechanism cannot operate if CO is not mobile on the surface, a nd a simple Tafel-type experiment with a low concentration of active Pt-Ru sites is suggested to check quantitatively the CO mobility rate. On a surfa ce with large Ru islands, the overpotential for CO oxidation increases, and two CO stripping peaks may appear if the CO mobility is sufficiently low. A mean-field model of the system reproduces the DMC results for high CO mob ility but breaks down for a system with large Ru islands and a comparativel y low CO surface diffusion constant.