Morphology of mesoscopic Rh and Pd nanoparticles under oxidizing conditions

The thermodynamic equilibrium shape of rhodium and palladium crystals are predicted under conditions from ultrahigh vacuum to high oxygen pressures using the Gibbs-Wulff construction. The analysis is based on data obtained from ab initio calculations for the adsorption of oxygen on the low-index (111), (100), and (110) surfaces, and the stepped (311), (211), and (331) surfaces. While the close-packed (111) facets dominate the shape in the low-coverage cases, the higher adsorption energies at the more open surfaces lead to a rounding of the crystallite. A linear correlation between the surface energies of the clean surfaces and the respective adsorption energies is found.