Effective pathway for hydrogen atom adsorption on graphene

We investigate and discuss the interaction of a hydrogen atom (H) with graphene based on the density functional theory (DFT). Our calculation results show that reconstructions of carbon atoms play an important role in the H adsorption on graphene. When constituent carbon atoms are held rigid, endothermic H adsorption is about 0.2 eV, and the activation barrier is 0.3 eV for H adsorption, due to the strong pi-bonding network of the hexagonal carbon. On the other hand, when carbon atoms are allowed to relax, the carbon atom directly below the H atom moves 0.33 Angstrom upward towards the gas phase, and an sp(3)-like geometry is formed between the H and carbon atoms of graphene. This relaxation stabilizes the hydrogen-carbon interaction, and the exothermic hydrogen adsorption on the graphene has a binding energy of 0.67 eV. We also show that the effective pathway for H adsorption on graphene, which gives an activation barrier for the H adsorption on graphene of 0.18 eV.