Bifunctional In³⁺ Doping toward Defect Engineering in SrTiO₃ for Solar Water Splitting

Defect engineering in SrTiO₃ crystals plays a pivotal role in achieving efficient overall solar water splitting, as evidenced by the influence of Al³⁺ ions. However, the uneven structural relaxation caused by Al³⁺ ions has been overlooked, significantly affecting the defect state and catalytic activity. When an Al₂O₃ crucible is used, optimizing this defect engineering presents a significant challenge. In this study, we introduced In³⁺ into the SrTiO₃ crystal to achieve favorable photocatalytic performance. Notably, In³⁺ stabilizes at the B sites of SrTiO₃, outcompeting Al³⁺, demonstrating a bifunctional effect by simultaneously regulating the concentration of defect charges and mitigating the negative impact of Al³⁺ on structural relaxation, leading to shallow-state defects. Additionally, the incorporation of In³⁺ ions effectively prevents the precipitation of perovskite Sr²⁺. Carrier behavior studies and density functional theory (DFT) calculations provide substantial evidence of the underlying modulating mechanism. Consequently, the optimized In³⁺-doped SrTiO₃ exhibits impressive gas evolution rates of 1.40 mmol·h^-1 H₂ and 0.69 mmol·h^-1 O₂ under full-spectrum light irradiation, corresponding to a promising apparent quantum yield (AQY) of 82.36% at 365 nm and a solar-to-hydrogen (STH) efficiency of 0.54%. Such enhanced activity could be attributed to the effective incorporation of In³⁺ ions, which improves the structural stability of the perovskite SrTiO₃ lattice.