H ₂ O Deprotonation Promotes Hole Transfer at the Anatase TiO ₂ (001)/Water Interface: First-Principles Molecular Dynamics

Photocatalytic water splitting represents a promising approach for solar energy utilization, but its performance is primarily constrained by the sluggish water oxidation reaction, where the hole transfer at the solid/liquid interface plays a significant role. Despite extensive experimental and theoretical efforts, the hole trapping mechanism of TiO₂, a widely used photocatalyst, in the aqueous environment is still controversial. Here, using first-principles molecular dynamic simulations, we establish the hole trapping sites and the hole transfer mechanisms at the anatase TiO₂(001)/water interface. Both molecular and dissociative H₂O adsorptions are considered. We demonstrate that the holes at the adsorbed H₂O and HO^- species are unstable and migrate spontaneously to TiO₂, whereas the deprotonated O^2- ions can be oxidized and retain the holes forming stable structures. Further, bulk water facilitates hole localization at the TiO₂/water interface, and in turn, the trapped holes regulate the interfacial water configuration. These findings provide fundamental insights into the photocatalytic performance and interfacial charge separation.