Manipulating the Spin State of Perovskite Cs ₃ Bi ₂ Br ₉ by Co‐Doped for Efficient Photocatalytic CO ₂ Reduction

The photocatalytic conversion of CO₂ into the renewable fuels is a promising strategy to address energy and environmental challenges, however, its limited application is mainly attributed to the inefficient charge separation and lack of active sites in conventional catalysts. Here, a spin-polarization strategy using Co²⁺ doping in lead-free perovskite Cs₃Bi₂Br₉ (CBB) synergized with an external magnetic field (MF), is reported to achieve highly efficient CO₂ reduction. The optimized Co-doped CBB (0.2CBB) exhibited a 2.6-fold enhancement in CO production rate (35.04 µmolg^-1h^-1) compared to the pristine CBB, with further improvement to 86.56 µmolg^-1h^-1 under 200 mT MF. Advanced characterizations together with the density functional theory calculations further revealed that the Co doping introduces spin-polarized electrons, suppresses charge recombination, and elongates the carrier lifetime (6.68 ns vs 5.20 ns in CBB). The Zeeman effect under MF activates the additional spin-polarized carriers, while the Co sites lower the energy barrier for ^*COOH intermediate formation (ΔG = -0.59 vs -0.38 eV in CBB), as confirmed by the in situ FT-IR and Gibbs free energy analysis. This work pioneers the integration of spin manipulation and MF-assisted catalysis in perovskites, offering a novel pathway for the design of high-performance photocatalytic systems.