Precise control of TiO2 overlayer on hematite nanorod arrays by ALD for the photoelectrochemical water splitting

The short lifetime of electron-hole pairs and high electron-hole recombination rate at surface states significantly limit the practical applications of hematite (alpha-Fe2O3) photoanodes in photoelectrochemical (PEC) water splitting. Surface modification with a TiO2 overlayer has been demonstrated to be an efficient way to improve the PEC performance. However, a fine control of the TiO2 overlayer and a deep understanding of the impact of the TiO2 overlayer with variable thickness on the PEC performance, to the best of our knowledge, has yet to be done. Here, a conformal ultrathin TiO2 overlayer is successfully deposited on hydrothermal grown one-dimensional hematite nanorod arrays by atomic layer deposition. The morphology and thickness of the TiO2 overlayer can be precisely controlled. The effect of the thickness of the TiO2 overlayer on the overall water splitting efficiency of hematite photoanodes under visible and UV light has been systematically investigated. The charge excitation and transfer mechanism at the semiconductor-electrolyte interface has also been studied.