Hydrogen adsorption on palladium, a comparative theoretical study of different surfaces

The interaction of atomic hydrogen with the Pd(111), Pd(100) and Pd(110) surfaces is studied by ab-initio density functional calculations within the generalized gradient approximation (GGA). For the three surfaces, we have determined the preferred adsorption sites, the adsorption structures, the work function changes and the surface diffusion barrier, including relaxation effects. This comparative study allows some common features to be seen, in particular in the adsorption energies and geometries for both surface and subsurface H-atoms, and some significant differences such as the surface diffusion and the dispersion of the H-induced surface state, The origin of these differences is explained by a detailed analysis of the electronic structures of both clean and hydrogen-covered surfaces. Our study leads to an interesting correlation between the hydrogen diffusion barrier and the surface roughness since it plays an important part in the catalytic activity of the respective surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.