Hydrogen Diffusion on Graphene Surface: The Effects of Neighboring Adsorbate and Quantum Tunneling

We study the diffusion of atomic hydrogen (H) on graphene surface using first-principles calculations, with focus on the effects of H aggregation state and quantum tunneling. Compared to the diffusion of an isolated H, the presence of a neighboring H is shown to have significant effects on the energy pathways of diffusion. Depending on the starting and the destination configuration, the diffusion of single atomic H that leads to the transition between H dimer structures can be either greatly facilitated or inhibited. Based on first-principles calculations and the transfer matrix method, quantum tunneling of H across diffusion barriers is studied, which is found to be dominant at low temperatures and continues to play a nontrivial role at temperatures up to ∼600 K