The Effect of Chemical Etching by HF Solution on the Photocatalytic Activity of Visible Light-responsive TiO₂ Thin Films for Solar Water Splitting

The effect of chemical etching by HF solution on the photoelectrochemical performance and photocatalytic activity of visible light-responsive TiO₂ (Vis-TiO₂) thin films prepared by a radio-frequency magnetron sputtering method has been investigated. It was found that Vis-TiO₂ thin films treated with HF solution (HF-Vis-TiO₂) exhibit a remarkable enhancement of the photoelectrochemical performance not only under UV but also visible light irradiation as compared to untreated Vis-TiO₂. The incident photon to current conversion efficiencies reached 66 and 9.4% under UV (λ = 360 nm) and visible light (λ = 420 nm), respectively. The HF-Vis-TiO₂ thin films have a larger surface area and higher donor density than Vis-TiO₂, indicating that the remarkable increase in the photocurrent may be due to the short diffusion length of the photoformed holes in reaching the solid–liquid interface as well as to the high conductivity. Moreover, the HF-Vis-TiO₂ thin films were found to act as efficient photocatalysts for the decomposition of water with the separate evolution of H₂ and O₂ from H₂O under visible or sunlight irradiation.