Enhancing charge separation and collection in semiconducting photoelectrodes is a key issue in the area of photoelectrochemical water splitting. Herein we report that photoelectrochemical performance of rutile TiO2 nanowires arrays could be significantly enhanced by sequential treatment with hydrogen atmosphere and TiCl4 solution at elevated temperature. Hydrogen treatment increased the concentration of donors in rutile nanowires as revealed by Mott-Schottky measurements, but meanwhile increased charge recombination as evidenced by enhanced photoluminescence. Treatment with TiCl4 solution, by which rutile nanowires were modified with anatase nanoparticles, could reduce the charge recombination in hydrogen-treated TiO2 nanowires to a level even lower than pristine rutile nanowires, due to the formation of type II anatase-rutile heterojunction. Photoelectrochemical measurements in concentrated KOH solution showed that water splitting on rutile nanowire arrays was enhanced by a factor of similar to 1.63 after the sequential treatment with hydrogen and TiCl4 solution at a potential of 0.22 V vs. Ag/AgCl, more significantly than the enhancing factor of similar to 1.35 by hydrogen treatment only, which could be attributed to the synergistic effect of hydrogen and TiCl4 treatment that improved both electron transportation along TiO2 nanowires and charge separation in the orthogonal direction. (C) 2014 Elsevier Ltd. All rights reserved.