Electrochemically induced Ti3+ self-doping of TiO2 nanotube arrays for improved photoelectrochemical water splitting

We report a facile electrochemical reduction method to synthesize Ti3+-self-doped TiO2 nanotube arrays (TNTs), where the effects of reduction duration and potential on the photoelectrochemical performance were systematically investigated. The X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra confirmed the presence of Ti3+ in the TNTs. Under the optimum reduction condition, the Ti3+-self-doped TNTs exhibited remarkably enhanced photocurrent density and photoconversion efficiency, which were nearly 3.1 and 1.75 times that of pristine TNTs, respectively. The enhancement of PEC performance is due to the improved electrical conductivity, accelerated charge transfer rate at the TNTs/electrolyte interface, as well as the improved visible light response, which is elucidated by electrochemical impedance spectra, Mott–Schottky, and UV–Vis diffuse reflection spectra.