Magnetic-Field-Assisted Photocatalytic H2O2 Production From Ambient Air via Spin-Matching-Mediated Dual Charge Transfer.

Abstract

Photocatalytic H2O2 synthesis from ambient air is promising but constrained by spin-forbidden O2 activation, unidirectional charge injection, and inefficient O2 mass transport. We introduce a spin-matching-enabled dual-channel cooperative charge delocalization strategy based on a Fe ions and an N,N'-di(4-benzoic acid)-3,4,9,10-tetracarboxylic acid diimide ligand (Fe-PDI). The polymer contains mixed-valence Fe(II)/Fe(III) sites and adopts an intermediate-spin configuration with a singly occupied axial dz 2 orbital. Experimental and computational results support a dual-channel Fe-O2 interaction involving O2-to-Fe σ donation and Fe-to-O2 π back-donation with spin-aligned electrons filling the O2 antibonding orbitals, which converts conventional localized unidirectional injection into bidirectional cooperative delocalization. This interaction alleviates spin-forbidden O2 activation through a spin-correlated •O2 - intermediate while preserving the O─O bond, promotes selective protonation to *OOH, and enhances O2 surface diffusion and H2O2 desorption. Consequently, with benzylamine as a hole scavenger, Fe-PDI achieves H2O2 production rates of 19.17 and 23.26 mmol g-1 h-1 without and with an applied magnetic field, respectively, surpassing most reported photocatalytic systems. This work establishes a spin-charge-transport synergistic paradigm, offering a generalizable route for spin-state engineering in single-site catalysis.