Anchoring of Pt and PtRu to carbon nanofibers studied by density functional theory calculations

PtRu particles supported on carbon nanofibers have been reported to have higher activity as anode catalysts in proton exchange membrane fuel cells than conventional catalysts. In the present work, density functional theory calculations are used to investigate the metal-carbon interface for different crystal facets of mono-metallic Pt and the PtRu alloy. The carbon side is modeled by graphene sheets with either zigzag or armchair termination. The strongest metal-carbon interaction is predicted for a (1 1 1) facet attached to a zigzag edge. The anchoring of the PtRu metal is found to have pronounced effects on the surface composition of the alloy. Whereas the bare surface is rich in Pt, the interface with carbon favors the stoichiometric bulk composition. Core level binding energies of carbon, platinum and ruthenium are found to provide valuable signatures of the interface and give means to interpret future high resolution photoemission core level spectroscopy experiments.