Photoelectrochemical Water Splitting with Rutile TiO2 Nanowires Array: Synergistic Effect of Hydrogen Treatment and Surface Modification with Anatase Nanoparticles

•We designed PEC photoanode of TiO2 NWs in view of both the carrier collection and charge separation process.•Rutile TiO2 NW was first annealed in hydrogen gas and followed by TiCl4 treatment to form heterojunctions of rutile TiO2 NWs decorated with anatase TiO2 nanoparticles.•PEC performance of the A/R heterojunctions photoanode was strongly enhanced due to both the improved conductivity from hydrogen treatment and the increased charge separation of heterostructures from TiCl4 treatment.

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 ∼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 ∼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.

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