Influence of Step and Island Edges on Local Adsorption Properties: Hydrogen Adsorption on Pt Monolayer Island Modified Ru(0001) Electrodes

The influence of steps and island edges on the local electronic structure of a (bi-) metallic single crystalline electrode surface and on the local, site-specific adsorption energy of adsorbed species, the so-called structural effects, was studied by periodic density functional theory based calculations, focusing on longer-range effects. Using hydrogen adsorption energies as a local probe, calculations were performed both for partly Pt monolayer covered planar Ru(0001) surfaces and for a stepped Ru(10 (19) over bar) surface decorated with a row of Pt atoms. The calculations demonstrate that the steps/island edges affect not only the nearest neighbor adsorption sites but also more distant ones with the extent depending on the particular structure. This longer-range effect is in excellent agreement with recent temperature-programmed desorption and spectroscopy experiments (Hartmann et al. Phys. Chem. Chem. Phys. 14, 10919, 2012). For the interaction of water molecules with partly Pt monolayer covered Ru(0001), similar trends as in the hydrogen adsorption have been found. In addition, hydrogen adsorption energies as a function of coverage have been used to derive the hydrogen coverage as a function of the electrode potential, exhibiting a broad range of stable hydrogen adsorption structures.