Efficient Charge Transfer and Effective Active Sites in Lead‐Free Halide Double Perovskite S‐Scheme Heterojunctions for Photocatalytic H2 Evolution

Abstract The practical application of lead‐free double perovskite Cs 2 AgBiBr 6 in photocatalytic H 2 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 Cs 2 AgBiBr 6 with enriched Br‐vacancies and WO 3 nanorods (V Br ‐Cs 2 AgBiBr 6 /WO 3 ) obtaining excellent visible‐light responsive photocatalytic H 2 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 Cs 2 AgBiBr 6 (022) surfaces introduced by atom thermal vibration provide effective active sites for hydrogen evolution. The optimized V Br ‐Cs 2 AgBiBr 6 /WO 3 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 ‐Cs 2 AgBiBr 6 (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 ‐Cs 2 AgBiBr 6 /WO 3 S‐scheme heterojunctions, which emerges a new strategy in the applications of perovskite‐based photocatalysts.