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

Abstract

AbstractTiO2 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 ZnIn2S4 were introduced into an anodization‐annealed TiO2 film (TiO2 NT) to enhance the photoanode activity. The activity‐enhanced TiO2 photoanode (ZIS@TiO2 NT‐EA) was characterized by surface analyses and photoelectrochemical measurements. Mott‐Schottky measurement indicated that the introduction of titanium vacancies into the TiO2 NT changed its semiconductor type from n to p, and significantly reduced its apparent activation energy if compared with the TiO2 NT. In addition, after the ZnIn2S4 nanoparticles were loaded on the TiO2 NT‐EA film, the carrier concentration of the ZIS@TiO2 NT‐EA was nearly 12 times higher than the pristine TiO2 NT. Due to the higher carrier separation efficiency resulting from the formation of p‐n heterojunction between TiO2 and ZnIn2S4, the photocurrent density of the ZIS@TiO2 NT‐EA reached 3.89 mA cm−2 at 1.23 V (vs. RHE), nearly 3 times higher than that of the original TiO2 NT. Amazingly, the maximum applied bias photon‐to‐current efficiency (ABPE) value of the ZIS@TiO2 NT‐EA photoanode reached 2.15 % at 0.496 V (vs. RHE), which is very competitive if compared with all the reported TiO2 film electrodes in the PEC water splitting application. The incident photon‐to current efficiency (IPCE) of the ZIS@TiO2 NT‐EA photoanode was approximately 40.9% at 300 nm, which was about 3 times higher than that of the TiO2 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 TiO2 lattice and the formation of p‐n junction between the TiO2 and ZnIn2S4 on the PEC behaviour, as well as on the charge transfer resistance and separation efficiency of carriers.