Homostructured rutile TiO2 nanotree arrays thin film electrodes with nitrogen doping for enhanced photoelectrochemical performance

Homostructured rutile TiO2 nanotree arrays thin films with nitrogen doping were synthesized on FTO glass substrates via a two-step hydrothermal method. The crystal structure and morphology of nanotree arrays thin films were characterized by means of X-ray diffractometer and field-emission scanning electron microscopy. Furthermore, the optical and photoelectrochemical performance of nitrogen doped TiO2 nanotree arrays thin films was analyzed respectively using diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, linear sweep voltammetry, transient photocurrent and Mott-Schottky measurements. The results showed that nitrogen doping significantly affected the morphology of branched nanostructure, electron energy band structure, electron transportation and charge carrier recombination at the surface and interface of nanotrees. Optimized photoelectrochemical performance was achieved with relatively lower electron transport resistance and higher photocurrent density by the TiO2 nanotree arrays thin film with N/Ti molar ratio of 1, which can be mainly attributed to the formation of appropriate branched nanostructure to improve photoexcited electrons rate and new localized mid-gap states energy levels due to the nitrogen doping.