Effect of heat treatment on WO3-loaded TiO2 nanotubes for hydrogen generation via enhanced water splitting

We determined the optimum phase structure of WO₃-loaded TiO₂ nanotubes (WTNs) for hydrogen generation via photoelectrochemical (PEC) water splitting by controlling the annealing temperature. The surface morphology of WTNs was closely related to crystal growth and phase transformation. The nanotubular structure completely collapsed at 700 °C due to the anatase–rutile phase transformation. In PEC studies, high-crystallinity anatase-phase WTNs exhibited a higher photocurrent density (2.4 mA/cm²) than WTNs of amorphous or polycrystalline (anatase+rutile) phases. This can mainly be attributed to better charge carrier separation and transportation in PEC water splitting by providing an effective way to address recombination losses.