Simulation of growth process of Pt-particles - first-principles calculations

First-principles calculations have been applied to investigate the interactions between Pt_n (n = 1 ~ 4) clusters and a graphene sheet as models of Pt/C fuel-cell catalytic electrodes. A Pt atom is stably adsorbed on the bridge site between two carbon atoms with the adsorption energy of about 2eV. For the case of Pt₂, both of the Pt atoms are adsorbed on the bridge site. For the case of Pt₃, the triangular cluster is more stable than the linear cluster. For the case of Pt₄, the tetrahedral cluster is more stable than the planar cluster. The adsorption energies on the surface without defects are 0.55 eV/adatom for Pt₂ and 0.05 eV/adatom for Pt₃. The interaction energy between the Pt cluster and the graphite surface per Pt atom becomes weaker as the number of Pt atoms increases. The adsorption energy for a Pt atom on the vacant site is 8.00 eV/adatom, which is stronger than the formation energy of a Pt-Pt bond (about 2 eV/bond) for small clusters.