Surface polaron states on single-crystal rutile TiO 2 nanorod arrays enhancing charge separation and transfer.

Polaron states on TiO2 photoanodes provide an important electron transfer pathway at the electrode-electrolyte interface. Here, we electrochemically doped single-crystal rutile TiO2 nanorod arrays with exposed (110) facets to produce surface polaron states, Ti3+-OH, which greatly contributed to charge separation and transfer. Our results experimentally clarified the previously confused understanding of the origin of improved photoelectrochemical (PEC) water splitting performance and verified that the enhanced PEC effects mainly arise from surface polaron states instead of grain boundary passivation.