DFT Study of the Hydrogen Spillover Mechanism on Pt-Doped Graphite

The mechanism of hydrogen storage by atomic hydrogen spillover on a Pt-doped graphite (0001) surface was studied by means of density functional theory. The coronene molecule and a Pt-4 cluster were used as primary models for the carbon surface and the metal nanoparticles, respectively. It was found that H-2 dissociates spontaneously on a Pt Cluster, but the dissociated H atoms have to overcome excessively large energy barriers (>60 kcal/mol) to migrate from Pt to the graphite surface. H atoms on a graphite (0001) surface can be either chemisorbed or physisorbed. The transition from the chemisorbed to the physisorbed state happens at sufficiently high rates. In the physisorbed state, H atom diffusion is essentially free of energy barriers. Physisorbed H atoms readsorb selectively adjacent to other chemisorbed H atoms, Our results indicate that H atom migration from a transition metal to the graphite surface is rate-limiting in the overall spillover process. The implications of the findings are discussed.