Positive potential pretreatment of TiO2 photoanode towards efficient charge separation

Low charge separation efficiency (η_sep) of TiO₂ impedes its applications of photoelectrochemical (PEC) water splitting. A positive potential pretreatment approach has been developed to construct a surface polarization with −OH groups at a potential of 1.48 V_RHE. When the pretreatment time of 6 h is used, the η_sep and photocurrent density (J_ph) reach up to 54 % (vs. 24 %, TiO₂) and 0.92 mA cm⁻² (vs. 0.32 mA cm⁻², TiO₂) under AM 1.5 G illumination, respectively. The photovoltage can be increased from 0.17 V to 0.52 V. When the pretreatment time is extended to 22 h, a higher J_ph of 1.57 mA cm⁻² and η_sep of 87 % can be obtained. Furthermore, the positive potential pretreated TiO₂ possesses excellent PEC stability. The PEC improvements can be attributed to the surface polarization with the −OH groups and favorable surface states of Ti-OH, but not to the formation of Ti³⁺ or oxygen vacancies.