Ab Initio Study of Stability and Site-Specific Oxygen Adsorption Energies of Pt Nanoparticles

We have employed ab initio calculations based on density functional theory in order to study stability and oxygen adsorption energies of Pt nanoparticles. For particles with sizes up to 200 atoms and various geometric shapes, we have explored the dependence of cohesive energies on atomic coordination number and on lattice strain effects. A simple empirical relation, which is consistent with the well-known Gibbs-Thomson relation, represents the cohesive energy over the range of considered sizes and shapes. For hemispherical cuboctahedral particles with 37 and 9:2 atoms, we have generated contour plots of the adsorption energy of atomic oxygen on all nanofacets. These plots furnish the known trend of strongly enhanced oxygen adsorption energies in comparison to extended surfaces. We found that the interplay of geometric effects, involving the periodic arrangement of surface atoms and edge effects on nanofacets, causes the high site-selectivity of Pt-oxygen interaction energies, with the largest adsorption energies found at the edges. Particle relaxation upon oxygen adsorption exhibits a significant influence on adsorption energies. The presented results provide a map of the peculiar site-selectivity of adsorption at Pt nanoparticles, which should be accounted for in building detailed models of reaction mechanisms and reactivity.