A theoretical study of H surface and subsurface species on Pt(1 1 1)

Abstract

Adsorption of H at a coverage ranging up to 2 monolayers with occupation of fcc and hcp sites and insertion in subsurface sites of Pt(111) is studied with use of a DFT-based ab initio method. It is shown that no important repulsion between the adatoms grows up to 1 ML, justifying the usual wisdom that 1 H atom adsorbs per Pt surface atom. Beyond this coverage, the surface occupation of both the fcc and the hcp sites become disfavoured and H starts to occupy subsurface sites. Both occupation of octahedral and tetrahedral insertion sites were studied. It is concluded that configurations involving fcc surface sites associated with tetrahedral subsurface sites are favoured. The evolution of the Pt local density of states (LDOS) with the coverage is reported. It is shown that the presence of H in the subsurface decrease the surface Pt chemical reactivity. Finally, stability curves of the Pt–H system as a function of H2 pressure and temperature are given, showing that subsurface H is likely to be present under usual catalytic reaction conditions.