Ab-initio First Principle Investigations of Molybdenum Carbide Supported Pt Catalyst

Platinum nanorafts on molybdenum carbide support have been found to be an excellent electrocatalyst for the oxygen reduction reaction (ORR) and show enhanced performance in proton exchange membrane fuel cells (PEMFCs). We use first-principles psuedopotential plane-wave calculations to describe the formation of Pt nano rafts and their ORR catalytic activity on β-Mo₂C. Our simulations demonstrates that Pt adsorbs strongly on the C atom of the β-Mo₂C surface with the adsorption energy of 7.18 eV that is larger than the values found for other absorption sites on the β-Mo₂C surface. Subsequent addition of Pt atoms on the β-Mo₂C surface reduces the adsorption energy to 5.90 eV. This is still significantly higher than the cohesive energy of bulk Pt (5.3 eV). As a result, Pt prefer to forms a sheet-like structure on the β-Mo₂C support instead of agglomerating into particles, leading to the formation of catalytically active and stable Pt nanorafts, in agreement with the experimental reports. Our calculations also show that the adsorption and dissociation of oxygen is slightly more difficult on Pt nanorafts than on the bare Pt surface, as indicated by the higher dissociative O adsorption energy. The dissociative O adsorption energy of the-Mo₂C supported Pt is closer to the peak of the volcano curve than that for the unsupported Pt surface. Thus, the Pt nano rafts on β-Mo₂C are found to be catalytically more active for ORR than the Pt nanoparticles.