Dissociative adsorption of H2 molecules on steric graphene surface: Ab initio MD study based on DFT

Recently, carbon materials have attracted considerable attention with their strong potential for hydrogen storage. In the present study, the possibility for dissociative adsorption of hydrogen on the surface of graphene is investigated by using ab initio molecular dynamics (MDs) based on density functional theory. The orientation of a H2 molecule with respect to a modeled graphene surface (perpendicular or parallel) is taken into account in this investigation, and the differences between results obtained with different values of the incident energy are discussed. The adsorption processes of hydrogen molecules are simulated by focusing on electron transfer between H and C atoms, in which dissociation and adsorption of H2 are found to be promoted above the steric graphene structure due to pronounced electron transfer at the impact point. The local steric structure forms sp3 hybridized molecular orbitals, which results in increased electron density and acts as a catalytic agent inducing cleavage of the H–H bond. In MD simulations, an excess incident energy of 6.00 eV (579 kJ/mol) is required to promote the reaction, although the activation energy is evaluated as 3.33 eV (321 kJ/mol) by static electronic structure computation. This result is obtained by taking both the motion of molecules as well as electron transfer into account and assuming that chemical reactions do not always progress along the ideal reaction pathway in actual systems.