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 (Cs 3 Cu 2 Br 5 ) 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 Cs 3 Cu 2 Br 5 NC. In situ X‐ray photoelectron spectroscopy and in situ kelvin probe force microscopy (KPFM) confirm that the Mn 2+ incorporation causes efficient electron–hole separation and extended charge lifetime in Mn‐doped Cs 3 Cu 2 Br 5 NC, which exhibits significantly raised selectively photocatalytic biomass conversion coupled with obviously enhanced H 2 O 2 evolution. With an external magnetic field, the spin‐polarized electrons in Mn‐doped Cs 3 Cu 2 Br 5 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.