Spin-State Reconfiguration in Single Mn Sites Directs Selective Two-Electron O2 Reduction to H2O2

Abstract Spin state strongly governs the pathway selectivity of photocatalytic oxygen reduction, dictating whether the reaction proceeds via the desired two electron (2e–) route to H2O2 or the competing four electron (4e–) pathway. Herein, this work reports a ligand-field symmetry-breaking strategy that enables controlled spin state switching, thereby steering the oxygen reduction pathway toward selective two electron H2O2 production. Specifically, symmetry breaking creates an asymmetric equatorial ligand field, triggering a deterministic spin state transition from intermediate spin to high spin on the Mn site. The resulting high-spin configuration features delocalized d-states and a downshifted d-band center, which collectively weaken *OOH adsorption to suppress premature O–O bond cleavage while preserving efficient O2 activation through spin polarized electron transfer. As a result, the optimized high spin catalyst delivers an exceptional H2O2 production rate of 5025 μmol·g–1·h–1 under simulated sunlight, representing a 2.3-fold enhancement over its intermediate spin (IS) counterpart. Furthermore, its activity is maintained under natural sunlight in ambient air, achieving a H2O2 production rate of 2662 μmol·g–1·h–1. This work establishes ligand field symmetry breaking as a precise and generalizable paradigm for spin state engineering in single atom catalysis, offering a direct route to overcome the selectivity efficiency compromise in photosynthesis of H2O2.