Positive potential pretreatment of TiO2 photoanode towards efficient charge separation

Low charge separation efficiency (ηsep) 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 VRHE. When the pretreatment time of 6 h is used, the ηsep and photocurrent density (Jph) 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 Jph of 1.57 mA cm−2 and ηsep 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. [Display omitted] •A positive potential pretreatment method is developed to construct TiO2 surface polarization with −OH groups.•A higher photocurrent and charge separation efficiency of 1.57 mA cm−2 and 87 % are obtained, respectively.•Positive potential pretreated TiO2 shows an excellent stability, which greatly vary from the electrochemical reduced TiO2.