A mechanistic study of hydrogen spillover in MoO3 and carbon-based graphitic materials

We present a systematic study of the mechanisms of the hydrogen spillover process from a Pt-6 cluster onto a well-known hydrogen bronze material, MoO3, and several carbon-based materials, including a graphene sheet and single walled carbon nanotubes, using density functional theory (DFT). We show that initially hydrogen undergoes a sequential dissociative chemisorption upon interacting with the Pt-6 cluster. The threshold desorption energy of H atoms was identified. We then mapped out the energetics required for hydrogen atoms to flow onto the surfaces of the selected materials in the vicinity of the subnanometer Pt-6 particle and to diffuse to other sites of the substrates. Our results indicate that while the spillover of H atoms onto the MoO3 lattice can be greatly facilitated by the abundant H-bonding network, the process becomes energetically difficult on carbon-based materials via chemisorption since it requires C-H bond breaking. Spillover in the selected carbon-based materials could only become possible if 'cold' H atoms could come out of the saturated catalyst.