Coinage and Pt-group metal surfaces stability

Abstract

Coinable (Cu, Ni, Ag, Au) and Pt-group metals (Pt, Pd, Ir, Rh) are face centered cubic (fcc) transition metals used in catalysis as active phases, usually in the form of nanoparticles. These nanoparticles mostly expose most stable surfaces, which are the main responsible of the interaction with reagents. Here we studied, by Density Functional Theory (DFT) calculations using slab models, the surface stability, in terms of surface energy, relaxation, degree of compression, and coordination number. The most stable surfaces studied are those with higher degree of compression and lowest Miller index, such as (111), (011), and (001) surfaces, which a priori are the most stable ones. Results were obtained, comparing and commenting two levels of computation, either using the Perdew-Burke-Ernzerhof (PBE) or the Tao-Perdew-Staroverov-Scuseria (TPSS) exchange-correlation functionals. The results suggest that the surface energy shows the typically parabolic dependence on the d band occupation in transition metals. It is also found that (111) surface is the most stable one because of its higher degree of compression, lower energy relaxation and surface energy. Furthermore, TPSS functional gives better surface energies with higher accuracies yet the data are more difficult to obtain. In contrast, semi-empirical methods can only be used for qualitative studies as they are just good giving trends of surface energy