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

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_xSe_1-x 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.