Hydrogen diffusion into Pd(1 0 0) subsurface: Role of co-adsorbed bicomponent species on surface

Abstract

This work examines the inherent features of co-adsorbed bicomponent species affecting microscopic mechanism of hydrogen diffusion from metal surface into its subsurface. The O + H O2 + H and OH + H were chose to separately cover on proper Pd(100) surface with unique adsorption configurations and varying coverages. The climbing image nudged elastic band (CI-NEB) method was employed to comprehensively investigate all available minimum energy pathways of hydrogen diffusion. The quantum results show that bicomponent species would change electronic structures of Pd(100) surface and then significantly affect the basic peculiarities of all diffusion routes in aspects of energy barriers adsorption and chemisorption sites. On base of total energies the lowest forward diffusion barriers of 0.082 0.125 and 0.154 eV were obtained corresponding to O + H O2 + H and OH + H adsorbates at 0.5 ML coverages of O O2 and OH respectively. Notably the O + H adsorbates demonstrate the best performance in facilitating hydrogen diffusion. Additionally the O2 + H are most conducive to reducing the forward barriers at 0.25 ML coverages of O O2 and OH. For each type of bicomponent species studied O O2 and OH severally predominate the impacts on changing Pd(100) electronic structure and then promoting diffusion process.