Dual-electric-field synergy in a Cs2AgBiBr6/Bi3TiNbO9 all-perovskite S-scheme heterojunction for efficient CO2 photoreduction

Photocatalytic CO 2 reduction is primarily limited by inefficient charge separation and insufficient thermodynamic driving force. To address these intertwined challenges, this study constructs a novel S-scheme heterojunction by integrating the ferroelectric layered perovskite Bi 3 TiNbO 9 with the lead-free double perovskite Cs 2 AgBiBr 6 , which synergistically couples an interfacial built-in electric field with an intrinsic ferroelectric polarization field. This dual-electric-field design facilitates the efficient separation and directional migration of photogenerated charge carriers while preserving strong redox capability, thereby simultaneously overcoming both kinetic and thermodynamic limitations. The developed heterojunction exhibits outstanding CO 2 photoreduction performance, delivering a CO yield of 42.6 μmol g −1  h −1 , which is 6.7 and 26.6 times higher than those of the individual Cs 2 AgBiBr 6 and Bi 3 TiNbO 9 components, respectively. Moreover, it demonstrates excellent stability, retaining 89.3% of its initial activity after 48 h of continuous operation. Comprehensive characterization and theoretical calculations collectively confirm: (i) the successful construction of an intimate S-scheme heterojunction; (ii) the presence of a ferroelectric polarization field; and (iii) a significantly reduced energy barrier for COOH* formation, which promotes CO 2 reduction. The integration of ferroelectric effects with S-scheme heterojunction engineering presented in this work provides a promising strategy for developing efficient solar energy conversion systems.