Architecting smart “umbrella” Bi2S3/rGO-modified TiO2 nanorod array structures at the nanoscale for efficient photoelectrocatalysis under visible light

Abstract

Photoelectrochemical water splitting to produce hydrogen under visible light has received intensive research interest but encounters significant scientific challenges. Sulphides have higher conduction band positions for H⁺ reduction and better sunlight absorption compared to oxides. CdS is the best candidate material, but its fatal toxicity from Cd makes it impossible to use for practical applications. Bi₂S₃ is non-toxic and has high absorption. However, Bi₂S₃ sensitized-TiO₂ photoanodes have never been studied under visible light. In addition, although surface heterojunction using graphene as an electron mediator on an array structure has been studied to improve electron–hole separation, the achieved photoconversion efficiency is still low. Herein, for the first time, by physically architecting a nanostructure with delicately tailored chemistry, we demonstrate a novel “umbrella” hybrid (Bi₂S₃/rGO)₅/TiO₂ nanorod array (NR) structure, in which the multi-layered Bi₂S₃/rGO umbrella cover not only significantly enhances the light absorption efficiency, but also by electrically connecting with Bi₂S₃-modified TiO₂ NRs creates a stepwise band-edge structure to accelerate the photo-generated electrons transport rate from Bi₂S₃ to TiO₂ through rGO while generating a higher resistance to inhibit charge back recombination. This nanostructure achieves considerably higher efficiency than all various control structures under visible light by ∼4–5 times. This work not only demonstrates an innovative approach to construct a smart architecture at the nanoscale for an efficient practical water splitting device, but also offers scientific insights.