Investigation of the charge transport kinetics and photoelectrochemical properties of CuInS2/R-TiO2 NTs heterostructures photoanode

It is significant to study the role of Ti3+ sites in heterojunction and its influence on charge transport kinetics for photoelectrochemical water splitting. Here, by using NaBH4 reduction treatment, Ti3+ self-doped reduced TiO2 nanotubes (R-TiO2 NTs) were obtained under mild conditions. CuInS2, a narrow bandgap semiconductor, was uniformly coated on R-TiO2 NTs to form a CuInS2/R-TiO2 NTs heterostructure photoelectrode through a simple one-step pulse electrodeposition method. The charge transfer and recombination process were characterized by the intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS). The results showed that the introduced Ti3+ sites formed an intermediate gap between the valence band and the conduction band. What's more, the heterojunction structure effectively enhanced the interface charge separation, which promoted the surface reaction kinetics. The electron transfer time of CuInS2/R-TiO2 NTs was about 0.28 ms, which was higher than that of the individually R-TiO2 NTs and CuInS2/TiO2 NTs alone. The electron lifetime was extended from 1.19 ms to 3.77 ms. Due to the reduction treatment and surface loading of CuInS2 nanoparticles, the carrier collection efficiency and the charge transfer efficiency of the CuInS2/R-TiO2 NTs were increased to 92.6% and 10.71%, respectively. This study sheds light on the charge transport kinetics of CuInS2/R-TiO2 NTs heterostructures for application in efficient PEC water splitting.