Surface and Defect Engineering Coupling of Halide Double Perovskite Cs₂NaBiCl₆ for Efficient CO₂ Photoreduction

Abstract Non‐toxic halide double perovskite materials have many advantages of lead halide perovskite. Whereas, they usually exhibit poor stability and very low intrinsic photocatalytic CO₂ reduction activity due to the insufficient separation of photogenerated charges and the lack of active sites. In this work, stable chlorine‐deficient 3D hierarchical Cs₂NaBiCl₆ porous microspheres assembled by highly crystalline nanoflakes were prepared by a simple grinding method. An unprecedented CO yield of 30.22 µmol g⁻¹ h⁻¹ was achieved in the gas‐solid photocatalytic reduction of CO₂ without sacrificial agents, which is the highest value among lead‐free halide perovskite photocatalysts. Experimental results and density‐functional theory calculations show that the chlorine vacancy plays the triple role of suppressing photogenerated electron‐holes recombination, enhancing CO₂ adsorption, and significantly reducing the free energy barrier for the key intermediate COOH* generation. In comparison with the pristine Cs₂NaBiCl₆, coupling of surface and defect engineering of the hierarchical sample brings 12.34 times enhancement of CO₂ photoreduction activity. This work proposes a simple method to synthesize a chlorine‐vacancy rich 3D hierarchical lead‐free halide perovskite and offers a new design idea to substantially enhance the photocatalytic activity, opening a door for the prospective contribution of these materials to carbon neutralization.