Ab Initio Molecular Dynamics Study of H Dissociation Mechanisms on Cu and Defective Graphene-supported Cu Clusters: Active Sites, Energy Barriers and Adsorption States.

Ab initio molecular dynamics calculations were performed to study H dissociation mechanisms on Cu and defective graphene-supported Cu 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 Cu cluster and 0.12 eV on the defective graphene-supported Cu cluster, which are lowered by ~19 % and ~81 % compared with the pristine Cu(111) surface, respectively. Furthermore, compared with the pure Cu cluster, the average dissociation energy barrier on the defective graphene-supported Cu cluster is substantially reduced by about 76 %. The preferred dissociation mechanisms on the two clusters are H located at a top-bridge site with the barrier heights of 0.30 eV on the Cu cluster and -0.31 eV on the defective graphene-supported Cu cluster Analysis of the H-Cu bond interactions in the transition states shows that the antibonding-orbital center shifts upward on the defective graphene-supported Cu cluster compared with the one on the Cu 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 Cu cluster, about twice that on the Cu cluster.