Molecular Dynamics Simulations of Surface Oxidation on Pt(111) and Pt/PtCo/Pt3Co(111)

Classical molecular dynamics simulations of surface oxidation in the presence of atomic oxygen and water are performed on Pt(111) and Pt/PtCo/Pt3Co(111) to determine the surface evolution during the oxidation process. On the basis of density functional theory calculations, the model considers electrostatic interactions between the adsorbates and the two topmost layers of the surface as a function of oxygen coverage and it is able to reproduce the main features of the oxidation phenomena observed experimentally. The results indicate that oxygen and water induce changes in the structure and local composition of the near-surface layers which may affect the activity and stability of the catalyst. Such changes are strongly dependent on the amount of adsorbed oxygen, and include oxygen absorption in the subsurface layers at high coverages, and significant atomic buckling and surface reconstruction. In the Pt-skin alloy surface, migration of cobalt atoms to the surface is accompanied by atomic buckling and detachment. The reverse “reduction” process is also simulated by gradually removing the electrostatic interactions between the top layers and adsorbates.