Mechanism of Hydrogen Spillover on WO3(001) and Formation of HxWO3 (x = 0.125, 0.25, 0.375, and 0.5)

Hydrogen spillover onto the WO3(001) surface and further into the bulk in the presence of a platinum catalyst was investigated by density functional theory calculations. The diffusion pathways are designed based on the energetic preference of hydrogen adsorption. Atomic H migrates from a platinum catalyst, where it is adsorbed upon H2 dissociative chemisorption, to terminal oxygen on WO3 (001) surface, followed by migration to in-plane oxygen and then diffusion across the surface or insertion in the lattice. We first theoretically corroborated the role of water in facilitating the hydrogen spillover process. The otherwise prohibitively high activation barriers were considerably reduced with the participation of water, which agrees well with experimental facts. The high mobility of H inside the WO3 lattice was also identified with low calculated diffusion barriers for several selected migration pathways. Finally, the effects of hydrogen concentration and electronic structures of HxWO3 were investigated. Th...