The influence of hydrothermal treatment on TiO2 nanostructure films transformed from titanates and their photoelectrochemical water splitting properties

Anatase non-stoichiometric TiO2 nanostructure films transformed from titanates were fabricated using the alkaline hydrothermal method at different treatment durations. The field emission scanning electron microscopy (FESEM) images demonstrated the morphological change of TiO2 from nanosheets to nanowires. The X-ray diffraction (XRD) patterns confirmed the anatase phase for TiO2 nanostructures. The UV–vis-NIR measurement indicated the decline in visible light absorption with increasing treatment duration. For the photoelectrochemical (PEC) measurement, four hours hydrothermal synthesis TiO2 annealed in air at 500 °C for 90 min showed the optimal photocurrent response with the maximum photocurrent density of 149.1µA/cm2 at 0.8 V vs. Ag/AgCl, which is attributed to the narrow bandgap (3.22 eV), improved carrier density (4.806×1018 cm−3) and longest lifetime of carriers (3.2 ms). Thus, nanosheet morphology was found to be more superior than nanowire morphology and a relatively short hydrothermal treatment duration was beneficial to PEC water splitting properties. In addition, for superior PEC performance, appropriate nanosheet density and surface area are necessary. The results demonstrated that TiO2 nanostructures transformed from titanates could be used for PEC application and the PEC characteristics could be tuned and modified for better water splitting performance.