LAUSR

Abstract We report facile and effective surface-functionalization of TiO 2 nanotubes array (NTs) via a TiCl 3 -mediated solution treatment and its effects on the charge transport and transfer properties for photoelectrochemical (PEC) water-oxidation. TiO 2 NTs with ∼5 μm length were prepared by hydrothermal-etching a TiO 2 nanorods array. Subsequently, TiO 2 NTs were treated with an aqueous TiCl 3 solution at 80 °C to generate surface oxygen vacancies and to deposit a TiO 2 nano-branch layer on the side-walls of TiO 2 NTs, and these modifications were confirmed by X-ray photoelectron spectroscopy and transmission electron microscopy. Through electrochemical impedance spectroscopy analysis, we found that the TiCl 3 -mediated surface-functionalization of TiO 2 NTs significantly improves the charge carrier transport and transfer properties, owing to the increase in the charge carrier density (due to the generation of surface oxygen vacancies) and surface roughness (due to the formation of nano-branches), respectively. The TiCl 3 treatment considerably improves the incident photon-to-current conversion efficiency (IPCE) and photocurrent density of TiO 2 NTs (especially at low-bias potentials) during the PEC water-oxidation, and the treated material demonstrates a maximum IPCE of ∼93% and a photocurrent density of ∼2.25 mA/cm 2 at 1.23 V versus the reversible hydrogen electrode.