First-Principles Investigation of the Formation of Pt Nanorafts on a MoC Support and Their Catalytic Activity for Oxygen Reduction Reaction.

We use first-principles calculations to study the formation of Pt nanorafts and their oxygen reduction reaction (ORR) catalytic activity on MoC. Due to the high Pt binding energy on C atoms, Pt forms sheet-like structures on the MoC surface instead of agglomerating into particles. We find that the disordered MoC surface carbon arrangement limits the Pt sheet growth, leading to the formation of 4-6 atom Pt nanorafts. The O-O repulsion between the O atoms on the MoC and O adsorbate enhances the ORR activity by weakening the O adsorption energy. We find a significant change from the usual scaling of the energies of the intermediates in the ORR pathway and a strong interaction between the nanoraft and water that lead to a high activity of the Pt nanorafts. Fundamentally, our work demonstrates that the activity of metal catalysts can be strongly affected by manipulation of the atomic arrangement of the supporting carbide surface.