Novel composite ZnO/TiO2 thin film photoanodes for enhanced visible-light-driven photoelectrochemical water splitting activity

Visible-light-driven photoelectrochemical water splitting activity has been achieved on heterojunction ZnO/TiO2 thin films for the first time using facile RF magnetron sputtering technique. In this study, post-deposition annealed ZnO/TiO2 films with a series thickness of about 30 nm (60, 95, and 120 nm) were tested as a future photoanodes. Here, the post-deposition annealing treatment at 673 K was mainly aimed to promote the close electronic interaction between energy levels of ZnO and TiO2 in the composite ZnO/TiO2. We find that annealing treatment induced a well connection between anatase TiO2 (101) and ZnO (002) facets, which is a determinant factor for the solar water splitting. Here, the PEC ability of the ZnO/TiO2 heterostructure was tested and achieved under visible light (λ = 532 nm). As a result, remarkable photocurrents were achieved. From linear sweep voltammagrams (I-V), there is no saturation of photocurrents at higher potentials suggests that spatial charge carrier separation. In addition, amperometric I-t curves revealed that photoanodes were relatively stable during the photo-oxidation process. As evidenced from I-V and I-t studies, the ZnO/TiO2-120 nm photoanodes exhibited a quite remarkable photocurrents, which is about ten times higher than that of thinner (ZnO/TiO2-60 nm) films. Comprehensively, the salient visible light response and sharp photocurrents suggested that composite ZnO/TiO2 in thin film form are productive photoanodes for efficient PEC water splitting activity and stability.