Dissociation-Chemisorption Pathways of H_2 Molecule on Graphene Activated by a Hydrogenated Mono-Vacancy V_(11)

摘要

Based on density functional theory, we investigate the interaction between a hydrogen molecule and a hydrogenated vacancy V_(11) in graphene surface. V_(11) is graphene mono-vacancy with two hydrogen atoms adsorbed at the edge of vacancy. The hydrogen molecule physisorbed on deformed V_(11) is shown to dissociate producing a known stable vacancy V211, in which two carbon atoms are mono-hydrogenated and another is di-hydrogenated at the edge of the vacancy. We observe that an energy barrier, which is a little above 0.5 eV, exists along all reaction pathways from V_(11) + H_2 to V211. There is a gradual change in the charge-transfer rate from a reacting hydrogen atom to the graphene surface, which reaches a common value of 0.19e per a hydrogen atom in the product. We also observed the energy barrier for a migrated hydrogen atom from the vacancy site to in-plane graphene site is around 2 eV. Since the reaction energy of H_2 on V_(11) is as large as 2.5 eV, the migration motion may be easily induced after the dissociative adsorption of H_2 on this defective graphene effectively enhancing dissociative adsorption of hydrogen molecules.