Facile construction TiO2/ZnIn2S4/Zn0.4Ca0.6In2S4 ternary hetero-structure photo-anode with enhanced photo-electrochemical water-splitting performance

Abstract

Constructing hetero-junction on TiO2 is an effective way to overcome the fast charge recombination and slow charge transfer kinetics, but how to design the junction is still a significant challenge in photo-electrochemical (PEC) water splitting. In this study, a considerable improvement in PEC performance for TiO2 nanotubes was achieved following the introduction of a ternary hetero-junction through depositing ZnIn2S4 (ZIS) and Zn0.6Ca0.4In2S4 (ZCIS) in sequence via a facile hydrothermal method (TiO2/ZIS/ZCIS). The optimized photo-anode exhibited a photocurrent density of 1.07 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), to be 3.96 and 1.25 times enhanced compared to that of TiO2 and TiO2/ZIS, respectively. Meanwhile, the incident photon-to-current conversion efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) of TiO2/ZIS/ZCIS were also increased in contrast with its counterparts. The merits of appropriate band alignment of TiO2, ZIS, and ZCIS and fewer interface defects built an internal electric field among the ternary hetero-junction, leading to an enhanced conductivity and efficient interface charge separation. These results were supported by a series of photo-electrochemical measurements. Among others, the shortened average lifetime of photo-generated electron-hole pairs from 1.51 (TiO2) to 1.17 ns (TiO2/ZIS/ZCIS) according to time-resolved photoluminescence reveals that the charge carriers generated in TiO2 would have an additional decay pathway in the hetero-structure, which benefits for the charge separation. Our strategy could be extended to many low-efficiency semiconductors for the design and synthesis of effective photo-anodes in PEC water splitting.