Co-adsorption of water and hydroxyl on a Pt2Ru surface

Gradient-corrected periodic density functional theory calculations are performed to explain the mobility of surface-bonded hydroxyl on a Pt2Ru(1 1 1) surface in the presence of co-adsorbed water, as recently observed by Desai and Neurock [S.K. Desai, M. Neurock, Phys. Rev. B 68 (2003) 075420] in ab initio molecular dynamics calculations. The effect can to a large extent be explained by an energetic compensation effect: the loss in energy associated with transferring OH from a Ru site to a Pt site is compensated by a gain in energy with the associated transfer of H2O from the Pt to the Ru site. The calculated property of the Pt2Ru(1 1 1) surface would support the OH spillover mechanism suggested by Davies et al. [J.C. Davies, B.E. Hayden, D.J. Pegg, M.E. Rendall, Surf. Sci. 496 (2002) 110], at least in as far as it concerns OH spillover to Pt site neighboring a Ru site, and provides new insight into the classical bifunctional mechanism of CO electro-oxidation.