Valence state and defect modulation in reduced Sr-site deficient Pt/Sr0.95Ti0.9Cr0.1O3-δ perovskite for enhanced photocatalytic hydrogen production

• A-site deficiency tunes the band structure and promotes hydrogen evolution. • Cr 4+ is identified in Sr 0.95 Ti 0.9 Cr 0.1 O 3-δ , revealing new oxidation-state behavior. • Valence states tuning of active elements is explored for efficient photocatalyst design. As the global energy landscape shifts to a green hydrogen economy, efficient and stable visible-light photocatalysts are increasingly central to optimizing solar-to-hydrogen conversion. Here, a Sr-site-deficient perovskite photocatalyst (R-Pt/Sr 0.95 Ti 0.9 Cr 0.1 O 3-δ ) was synthesised by a solid-state method, followed by Pt impregnation and hydrogen reduction post treatment. The introduction of A-site deficiency effectively tunes the band structure and facilitates hydrogen evolution, doubling activity compared to stoichiometric analogs. Besides, A-site deficiency reduces overall cation charge and promotes Cr 4+ formation. Through spectroscopy and thermal analysis, Cr 4+ was identified in the Sr 0.95 Ti 0.9 Cr 0.1 O 3-δ perovskite, revealing unexplored oxidation state dynamics. Upon reduction, Cr 4+ converts to Cr 3+ , creating oxygen vacancies and eliminating hole-trap sites. The resulting synergistic active sites greatly boost photocatalytic hydrogen evolution. Specifically, the R-Pt/Sr 0.95 Ti 0.9 Cr 0.1 O 3-δ achieved 120.46 μmol/g cat /h under full spectrum and 68.66 μmol/g cat /h under visible light (λ ≥ 420 nm), representing twice and 5 times enhancements relative to stoichiometric R-Pt/SrTi 0.9 Cr 0.1 O 3-δ and unreduced Pt/Sr 0.95 Ti 0.9 Cr 0.1 O 3-δ in visible light separately. This work demonstrates that combining A-site engineering and valence-state modulation provide a helpful strategy for designing high-performance visible-light photocatalysts.