Efficient Charge Transfer and Effective Active Sites in Lead-Free Halide Double Perovskite S-Scheme Heterojunctions...

The practical application of lead-free double perovskite Cs₂ AgBiBr₆ in photocatalytic H₂ evolution is still restricted due to the low activity and poor stability. The rational design of lead-free halide double perovskites heterojunctions with efficient charge transfer and effective active sites is a potential route to achieve the ideal prospect. Herein, in this work an S-scheme heterojunction of Cs₂ AgBiBr₆ with enriched Br-vacancies and WO₃ nanorods (V_Br -Cs₂ AgBiBr₆ /WO₃ ) obtaining excellent visible-light responsive photocatalytic H₂ evolution performance and durable stability is reported. The S-scheme heterojunction driven by the unaligned Fermi levels of these two semiconductors ensures the efficient charge transfer at the interface, and density functional theory calculations reveal the enriched Br vacancies on Cs₂ AgBiBr₆ (022) surfaces introduced by atom thermal vibration provide effective active sites for hydrogen evolution. The optimized V_Br -Cs₂ AgBiBr₆ /WO₃ S-scheme photocatalyst exhibits the photocatalytic hydrogen evolution rate of 364.89 µmol g^-1 h^-1 which is 4.9-fold of bare V_Br -Cs₂ AgBiBr₆ (74.44 µmol g^-1 h^-1 ) and presents long-term stability of 12 h continuous photocatalytic reaction. This work provides deep insights into the photocatalytic mechanism of V_Br -Cs₂ AgBiBr₆ /WO₃ S-scheme heterojunctions, which emerges a new strategy in the applications of perovskite-based photocatalysts.