Ab initio molecular dynamics study of H2 dissociation mechanisms on Cu13 and defective graphene-supported Cu13 clusters: active sites, energy barriers and adsorption states.

Abstract

Ab initio molecular dynamics calculations were performed to study H2 dissociation mechanisms on Cu13 and defective graphene-supported Cu13 clusters. The study reveals that seven types of corresponding dissociation processes are found on the two clusters. The average dissociation energy barriers are 0.51 eV on the Cu13 cluster and 0.12 eV on the defective graphene-supported Cu13 cluster, which are lowered by ~ 19% and ~ 81% compared with the pristine Cu(111) surface, respectively. Furthermore, compared with the pure Cu13 cluster, the average dissociation energy barrier on the defective graphene-supported Cu13 cluster is substantially reduced by about 76%. The preferred dissociation mechanisms on the two clusters are H2 located at a top-bridge site with the barrier heights of 0.30 eV on the Cu13 cluster and - 0.31 eV on the defective graphene-supported Cu13 cluster. Analysis of the H-Cu bond interactions in the transition states shows that the antibonding-orbital center shifts upwards on the defective graphene-supported Cu13 cluster compared with the one on the Cu13 cluster, which explains the reduction of the dissociation energy barrier. The average adsorption energy of dissociated H atoms is also greatly enhanced on the defective graphene-supported Cu13 cluster, about twice that on pure Cu13.