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.