Distinctly Improved Photocurrent and Stability in
TiO<sub>2</sub> Nanotube Arrays by Ladder Band Structure
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Abstract
Introducing a ternary
interlayer into binary heterostructures to
construct a ladder band structure provides a promising way for photoelectrochemical
water splitting. Here, we design and fabricate a sandwich structure
on TiO<sub>2</sub> nanotubes using CdS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub> as the interlayer to obtain
a matching band alignment. The photoelectrochemical (PEC) properties
of composite photoanodes are optimized by the order of sensitization
and elements ratio, wherein the TiO<sub>2</sub>/CdS/CdS<sub>0.5</sub>Se<sub>0.5</sub>/CdSe photoanode shows a significantly enhanced photocurrent
of 14.78 mA cm<sup>–2</sup> at −0.2 V vs SCE, exhibiting
a nearly 15-fold enhancement, over 1 order of magnitude. The quantum
efficiency apparently increases to 40% at a range of 400–520
nm, resulting from the fact that a sensitizing layer with a matching
band alignment can facilitate the separation of photogenerated electron–hole
pairs and also extend the absorption range to the visible region due
to its narrow bandgaps. Furthermore, its stability was distinctly
improved by coating MoS<sub>2</sub> on the surface of the TiO<sub>2</sub>/CdS/CdS<sub>0.5</sub>Se<sub>0.5</sub>/CdSe photoanode. Our
findings provide a novel route toward developing a highly efficient
photoelectrode for water splitting