Here we demonstrate that the performance of TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced through oxygen vacancy doping. The ion irradiation is a simple method to introduce oxygen vacancies on the surface and into the interior of TiO2 for making oxygen-deficient titania (TiO2-x). The TiO2-x thin films exhibit obvious increase in the performance of photoelectrochemical water splitting under light irradiation. The photoconversion efficiency eta of the TiO2-x photoanode is 0.5-fold higher than that of the pristine TiO2 photoanode, which benefits from the introducing of oxygen vacancies produced by ion irradiation. While the irradiation-induced titanium vacancies act as trapping centers for charge carriers and decrease the photoelectrochemical performance of the samples. Positron annihilation spectroscopy (PAS) was used to study the type of the formed vacancies. Combining experimental with theoretical study, this study demonstrates that ion irradiation technique combing with thermal annealing could be an effective way to enhance the performance of photoanode for water splitting. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.