Tailoring the Microstructure of B‐Cation Octahedra in Halide Double Perovskites for Efficient Selective CO2‐to‐CO Photoreduction

Abstract Solar‐driven CO 2 photoreduction using halide perovskites (HPs) has recently garnered significant attention; however, the conversion efficiency remains suboptimal for practical applications. Here, using Cs 2 AgBiBr 6 double perovskites as a model photocatalyst, the interplay between the coordination of octahedral B‐cation sites and photocatalytic performance are reported. The results reveal that modulating the microstructure of octahedra in Cs 2 AgBiBr 6 enables orbital rehybridization, resulting in an upshifted d‐band center and reduced effective masses, thereby improving the adsorption strength of intermediates, lowering reaction energy barriers, and promoting charge separation. Experimentally, it is demonstrated that the tailored Cs 2 AgBiBr 6 achieves selective CO 2 photoreduction toward CO without sacrificial agents, yielding a CO generation rate of 23.73 µmol g −1 h −1 with ≈100% selectivity, 13‐fold higher than pristine Cs 2 AgBiBr 6 and outperforms most reported HP‐based photocatalysts. This work highlights microstructure modulation in HPs as an effective strategy for efficient solar‐to‐fuel conversion.