Positive Potential Pretreatment of TiO2 Photoanode Towards Efficient Charge Separation

Low charge separation efficiency ( η sep ) of TiO 2 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%, TiO 2 ) and 0.92   mA   cm −2 (vs. 0.32   mA   cm −2 , TiO 2 ) 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 TiO 2 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 Ti 3+ or oxygen vacancies.