Bifunctional\nIn<sup>3+</sup> Doping toward Defect\nEngineering in SrTiO<sub>3</sub> for Solar Water Splitting

Defect engineering in SrTiO<sub>3</sub> crystals plays\na pivotal\nrole in achieving efficient overall solar water splitting, as evidenced\nby the influence of Al<sup>3+</sup> ions. However, the uneven structural\nrelaxation caused by Al<sup>3+</sup> ions has been overlooked, significantly\naffecting the defect state and catalytic activity. When an Al<sub>2</sub>O<sub>3</sub> crucible is used, optimizing this defect engineering\npresents a significant challenge. In this study, we introduced In<sup>3+</sup> into the SrTiO<sub>3</sub> crystal to achieve favorable\nphotocatalytic performance. Notably, In<sup>3+</sup> stabilizes at\nthe B sites of SrTiO<sub>3</sub>, outcompeting Al<sup>3+</sup>, demonstrating\na bifunctional effect by simultaneously regulating the concentration\nof defect charges and mitigating the negative impact of Al<sup>3+</sup> on structural relaxation, leading to shallow-state defects. Additionally,\nthe incorporation of In<sup>3+</sup> ions effectively prevents the\nprecipitation of perovskite Sr<sup>2+</sup>. Carrier behavior studies\nand density functional theory (DFT) calculations provide substantial\nevidence of the underlying modulating mechanism. Consequently, the\noptimized In<sup>3+</sup>-doped SrTiO<sub>3</sub> exhibits impressive\ngas evolution rates of 1.40 mmol·h<sup>–1</sup> H<sub>2</sub> and 0.69 mmol·h<sup>–1</sup> O<sub>2</sub> under\nfull-spectrum light irradiation, corresponding to a promising apparent\nquantum yield (AQY) of 82.36% at 365 nm and a solar-to-hydrogen (STH)\nefficiency of 0.54%. Such enhanced activity could be attributed to\nthe effective incorporation of In<sup>3+</sup> ions, which improves\nthe structural stability of the perovskite SrTiO<sub>3</sub> lattice.