title: First principles study of oxygen adsorption on Se-modified Ru nanoparticles.
abstract: We present here the results of our density-functional-theory-based calculations of the electronic and geometric structures and energetics of  Se and O adsorption on Ru 93- and 105-atom nanoparticles. These studies have been inspired by the fact that Se/Ru nanoparticles are considered promising electrocatalysts for the oxygen reduction reaction (ORR) on direct methanol fuel cell cathodes and the oxygen binding energy is a descriptor for the catalyst activity toward this reaction. We find the character of chemical bonding of Se on a flat nanoparticle facet to be ionic, similar to that obtained earlier for the Se/Ru(0001) surface, while in the case of a low-coordinated Ru configuration there is an indication of some covalent contribution to the bonding leading to an increase in Se binding energy. Se and O co-adsorbed on the flat facet both accept electronic charge from Ru, whereas the adsorption on low-coordinated sites causes more complicated valence charge redistribution. The Se modification of the Ru particles leads to weakening of the oxygen bonding to the particles. However, overall, O binding energies are found to be higher for the particles than for Se/Ru(0001). The high reactivity of the Se/Ru nanoparticles found in this work is not favorable for ORR. We thus expect that larger particles with well-developed flat facets will be more efficient ORR catalysts than small nanoparticles with a large fraction of under-coordinated adsorption sites.
authors.affiliation: Physics Department, University of Central Florida, Orlando, FL, USA. Sebastian.z.b@gmail.com
authors.forename: Sebastian
authors.initials: S
authors.lastname: Zuluaga
authors.forename: Sergey
authors.initials: S
authors.lastname: Stolbov