Self-hydrogenated shell promoting photocatalytic H2 evolution on anatase TiO2

Abstract

As one of the most important photocatalysts, TiO₂ has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO₂ at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO₂ are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO₂ nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO₂ 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 TiO₂ interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H₂ (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.