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

Spin state strongly governs the pathway selectivity of photocatalytic oxygen reduction, dictating whether the reaction proceeds via the desired two electron (2e – ) route to H 2 O 2 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 H 2 O 2 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 O 2 activation through spin polarized electron transfer. As a result, the optimized high spin catalyst delivers an exceptional H 2 O 2 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 H 2 O 2 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 H 2 O 2 .