We report the demonstration of electrochemical doping as a simple and effective strategy to induce in situ homo-species for improving the photoelectrochemical (PEC) performance of WO3 film by passivating the trap states. To observe the effect of applied potential on the photoelectrochemical performance of WO3 nanoparticles films, various applied potentials are employed for the electrochemical doping treatment. In comparison to pristine WO3 and the WO3 that have been annealed in Ar gas, the electrochemical doping WO3 shows remarkably improved photoelectrochemical performance. The optimized WO3 film yields a photocurrent density of 1.30 mA/cm(2) (vs. Ag/AgCl), which is 2.33 times higher than that of pristine WO3 film. The results of intensity-modulated photocurrent spectroscopy (IMPS) and electrochemical impedance spectra (EIS) demonstrate that the electrochemcial doping accelerates the electron transport with trap-state passivation so as to improve the separation of photo generated electrons and holes. This approach brings new opportunities for the development of PEC water splitting with superior performance. (C) 2016 Elsevier Ltd. All rights reserved.