Magnetic Mn‐Incorporated Cs₃Cu₂Br₅ Nanocrystals for Spin‐Polarized Enhanced Photocatalytic Biomass Conversion Coupled with H₂O₂ Evolution

Abstract Copper‐based halide perovskite, as an ideal alternative to lead‐based halide perovskite, has attracted much attention in many applications owing to its earth‐abundant element, non‐toxicity, and excellent optical properties. In this report, magnetic Mn‐incorporated lead‐free copper halide perovskite (Cs₃Cu₂Br₅) nanocrystal (NC) is for the first time designed and prepared using a one‐pot hot‐injection route, resulting in a new emission band at ≈540 nm accompanied with self‐trapped exciton (STE) emission centered at ≈445 nm from Cs₃Cu₂Br₅ NC. In situ X‐ray photoelectron spectroscopy and in situ kelvin probe force microscopy (KPFM) confirm that the Mn²⁺ incorporation causes efficient electron–hole separation and extended charge lifetime in Mn‐doped Cs₃Cu₂Br₅ NC, which exhibits significantly raised selectively photocatalytic biomass conversion coupled with obviously enhanced H₂O₂ evolution. With an external magnetic field, the spin‐polarized electrons in Mn‐doped Cs₃Cu₂Br₅ NC arouses reduced charge recombination and more available electrons/holes for surface redox reaction, further raising the photocatalytic performance. This is confirmed by in situ steady‐state/transient‐state photoluminescence (PL) spectroscopy, in situ transient photocurrent measurement, and in situ electrochemical impedance spectroscopy with external magnetic field. In situ electron paramagnetic resonance (EPR) spectra reveal the radical‐involved reaction pathway for biomass conversion. This research exhibits the great potential of spin‐polarization‐enhanced photocatalysis by an external magnetic field without additional energy consumption.