Integration of TiO2/ZnIn2S4 p‐n Heterojunction with Titanium Defects to Boost PEC Oxygen Production

Abstract TiO 2 is a widely used photoelectric conversion semiconductor material. However, due to its native defects, such as the selective absorption of ultraviolet light and high recombination rate of photogenerated carriers, it exhibits poor photoelectrochemical (PEC) water splitting performance. In this study, intrinsic defect titanium vacancy and semiconductor recombination agents ZnIn 2 S 4 were introduced into an anodization‐annealed TiO 2 film (TiO 2 NT) to enhance the photoanode activity. The activity‐enhanced TiO 2 photoanode (ZIS@TiO 2 NT‐EA) was characterized by surface analyses and photoelectrochemical measurements. Mott‐Schottky measurement indicated that the introduction of titanium vacancies into the TiO 2 NT changed its semiconductor type from n to p, and significantly reduced its apparent activation energy if compared with the TiO 2 NT. In addition, after the ZnIn 2 S 4 nanoparticles were loaded on the TiO 2 NT‐EA film, the carrier concentration of the ZIS@TiO 2 NT‐EA was nearly 12 times higher than the pristine TiO 2 NT. Due to the higher carrier separation efficiency resulting from the formation of p‐n heterojunction between TiO 2 and ZnIn 2 S 4 , the photocurrent density of the ZIS@TiO 2 NT‐EA reached 3.89 mA cm −2 at 1.23 V ( vs . RHE), nearly 3 times higher than that of the original TiO 2 NT. Amazingly, the maximum applied bias photon‐to‐current efficiency (ABPE) value of the ZIS@TiO 2 NT‐EA photoanode reached 2.15 % at 0.496 V ( vs . RHE), which is very competitive if compared with all the reported TiO 2 film electrodes in the PEC water splitting application. The incident photon‐to current efficiency (IPCE) of the ZIS@TiO 2 NT‐EA photoanode was approximately 40.9% at 300 nm, which was about 3 times higher than that of the TiO 2 NT (13.6%). To understand these impressive improvements in water splitting, further analyses were conducted on the effect of the increased titanium vacancy concentration in the TiO 2 lattice and the formation of p‐n junction between the TiO 2 and ZnIn 2 S 4 on the PEC behaviour, as well as on the charge transfer resistance and separation efficiency of carriers.