Self-hydrogenated shell promoting photocatalytic H evolution on anatase TiO.

As one of the most important photocatalysts, TiO has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H (H-H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.