Construction of a Rh-doped SrTiO₃/g-C₃N₄ p–n heterojunction for enhanced photoelectrochemical performance

Semiconductor photoelectrochemical (PEC) technology, capable of generating hydrogen energy from water and solar energy, has emerged as a promising solution to address environmental and energy challenges. Rhodium-doped strontium titanate (Rh doped SrTiO₃, RST) is regarded as a highly promising photocathode material for PEC systems. Nevertheless, the PEC performance of RST is hindered by inefficient carrier separation and poor charge transfer properties. In this paper, a hybrid RST/g-C₃N₄ heterojunction sample was prepared by a simple method. The pure RST sample possesses the ability to absorb visible light and exhibit p-type semiconductor characteristics with a negative photocurrent value of -6.2 μA cm^-2, and can be used as a photocathode material in PEC systems. The enhanced PEC performance with larger photocurrent values can be observed in the heterojunction samples. A photocurrent value of -26.5 μA cm^-2 was achieved in the optimized heterojunction, which is 4.3 times higher than the RST sample. This enhanced PEC performance can be attributed to the formation of a p-n junction between RST and g-C₃N₄ in composite samples. The p-n junction with built-in electric field and good band alignment will facilitate the more efficient separation and transfer of carriers, leading to enhanced PEC performance.