Distinctly Improved Photocurrent and Stability in TiO₂ Nanotube Arrays by Ladder Band Structure

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 TiO₂ nanotubes using CdS_<i>x</i>Se_1–<i>x</i> 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 TiO₂/CdS/CdS_0.5Se_0.5/CdSe photoanode shows a significantly enhanced photocurrent of 14.78 mA cm^–2 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 MoS₂ on the surface of the TiO₂/CdS/CdS_0.5Se_0.5/CdSe photoanode. Our findings provide a novel route toward developing a highly efficient photoelectrode for water splitting