Controlled Sn-Doping in
TiO<sub>2</sub> Nanowire Photoanodes
with Enhanced Photoelectrochemical Conversion
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Abstract
We demonstrate for the first time the controlled Sn-doping
in TiO<sub>2</sub> nanowire (NW) arrays for photoelectrochemical (PEC)
water
splitting. Because of the low lattice mismatch between SnO<sub>2</sub> and TiO<sub>2</sub>, Sn dopants are incorporated into TiO<sub>2</sub> NWs by a one-pot hydrothermal synthesis with different ratios of
SnCl<sub>4</sub> and tetrabutyl titanate, and a high acidity of the
reactant solution is critical to control the SnCl<sub>4</sub> hydrolysis
rate. The obtained Sn-doped TiO<sub>2</sub> (Sn/TiO<sub>2</sub>) NWs
are single crystalline with a rutile structure, and the incorporation
of Sn in TiO<sub>2</sub> 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/TiO<sub>2</sub> NW photoanodes with
different Sn doping ratios shows that the photocurrent increases first
with increased Sn doping level to >2.0 mA/cm<sup>2</sup> at 0 V
vs
Ag/AgCl under 100 mW/cm<sup>2</sup> simulated sunlight illumination
up to ∼100% enhancement compared to our best pristine TiO<sub>2</sub> NW photoanodes and then decreases at higher Sn doping levels.
Subsequent annealing of Sn/TiO<sub>2</sub> NWs in H<sub>2</sub> further
improves their photoactivity with an optimized photoconversion efficiency
of ∼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/TiO<sub>2</sub> NW photoanodes are highly stable in PEC conversion and thus can
serve as a potential candidate for pure TiO<sub>2</sub> materials
in a variety of solar energy driven applications