Site-Directing Sequential Doping: Sn/Sc Codoped SrTiO3 with Selective B-Site Occupation for Enhanced Photocatalytic Overall Water Splitting

Abstract

Photocatalytic overall water splitting (OWS) using particulate semiconductors represents a promising route for solar-to-hydrogen conversion. However, conventional doping strategies for SrTiO3 suffer from uncontrollable dopant sites, severe Ti3+ defect-induced carrier recombination, and inefficient charge separation, which severely limit its catalytic activity. Herein, a two-step molten-salt-assisted site-directing doping strategy is developed to achieve exclusive Ti-site (B-site) codoping of Sc and Sn in SrTiO3 (STO), overcoming uncontrollable dopant sites and severe Ti3+ defect-induced carrier recombination in conventional doping. Sc is first doped as a structure-directing agent, creating a favorable lattice microenvironment that guides subsequent Sn4+ to selectively occupy Ti sites rather than Sr sites. Different from conventional one-step and reverse-sequence doping that cause random Sn occupation and uncontrolled defect formation, the premodulation of Sc effectively neutralizes the intrinsic electron-rich lattice environment of STO, stabilizes tetravalent Sn, and realizes precise Ti-site doping. Density functional theory (DFT) calculations confirm that Sn/Sc codoping at Ti sites eliminates the adverse effects of oxygen vacancies (Ov) and Ti3+ defects by forming shallow defect levels near the band edges, which facilitate thermal ionization of carriers, increase free carrier concentration, and promote carrier separation efficiency. The optimized Sn/Sc-STO photocatalyst loaded with Rh/Cr2O3/CoOOH cocatalysts exhibits a remarkable hydrogen evolution rate of 646 μmol·h−1 and oxygen evolution rate of 240 μmol·h−1, which is 5.5 times higher than that of pure STO, with 93.8% activity retention after 12 h cycling. Mechanistic investigations reveal that Sn/Sc codoping selectively passivates harmful Ti3+ defects and enhances surface water adsorption. This work not only provides the first example of sequence-controlled site-selective B-site codoping in SrTiO3 but also establishes a coordinated strategy for defect engineering, lattice manipulation, and morphology regulation in perovskite-based photocatalysts.