Controlled Sn-Doping in TiO2 Nanowire Photoanodes with Enhanced Photoelectrochemical Conversion

We demonstrate for the first time the controlled Sn-doping in TiO2 nanowire (NW) arrays for photoelectrochemical (PEC) water splitting. Because of the low lattice mismatch between SnO2 and TiO2, Sn dopants are incorporated into TiO2 NWs by a one-pot hydrothermal synthesis with different ratios of SnCl4 and tetrabutyl titanate, and a high acidity of the reactant solution is critical to control the SnCl, hydrolysis rate. The obtained Sn-doped TiO2 (Sn/TiO2) NWs are single crystalline with a rutile structure, and the incorporation of Sn in TiO2 NWs is well controlled at a low level, that is, 1-2% of Sn/Ti ratio, to avoid phase separation or interface scattering. PEC measurement on Sn/TiO2 NW photoanodes with different Sn doping ratios shows that the photocurrent increases first with increased Sn doping level to >2.0 mA/cm(2) at 0 V vs Ag/AgCl under 100 mW/cm(2) simulated sunlight illumination up to similar to 100% enhancement compared to our best pristine TiO2 NW photoanodes and then decreases at higher Sn doping levels. Subsequent annealing of Sn/TiO2 NWs in H-2 further improves their photoactivity with an optimized photoconversion efficiency of similar to 1.2%. The incident-photon-to-current conversion efficiency shows that the photocurrent increase is mainly ascribed to the enhancement of photoactivity in the UV region, and the electrochemical impedance measurement reveals that the density of n-type charge carriers can be significantly increased by the Sn doping. These Sn/TiO2 NW photoanodes are highly stable in PEC conversion and thus can serve as a potential candidate for pure TiO2 materials in a variety of solar energy driven applications.