Fundamental studies and perceptions on the spillover mechanism for hydrogen storage

In this feature article, the atomic-scale understanding of the hydrogen spillover mechanism for hydrogen storage in metal-doped carbon materials and metal-organic frameworks is discussed by critically assessing recent computational and experimental studies. It is argued that the spillover mechanism involves: (a) the generation and desorption of mobile H atoms on the metal nanoparticles (b) the diffusion of H atoms in weakly-bound states on the support (c) the sticking and immobilization of H atoms at preferential locations of the receptor where barriers to sticking are decreased, and, (d) the Eley-Rideal recombination of the adsorbed H atoms with diffusing mobile H atoms to form H-2. The implications and open questions on the mechanism and effectiveness of hydrogen storage by spillover are critically assessed.