Polaron Delocalization Regulating Oxygen Reduction Selectivity and Directional Charge Transfer for Enhanced Dark Photocatalytic H2O2 Synthesis

Dark photocatalysis decouples light harvesting from catalysis via photogenerated charge storage, enabling H 2 O 2 production under intermittent illumination. However, increasing electron-storage capacity alone does not ensure efficient dark-state H 2 O 2 production, and how stored electronic states influence oxygen reduction reaction (ORR) remains unclear. Here, we show that polaron delocalization contributes to multi-electron ORR selectivity in poly(heptazine imide) (PHI), allowing dark photocatalytic H 2 O 2 synthesis. Sulfonated PHI (S-HPHI) delivers a 2.5-fold higher H 2 O 2 yield (588.9 μmol g –1 ) than protonated PHI (HPHI, 237.3 μmol g –1 ) despite comparable net photo-contributed electron-storage capacities (1441–1752 μmol e – g –1 ). This enhancement is consistent with the higher electron utilization efficiency toward H 2 O 2 formation (81.7% for S-HPHI versus 27.1% for HPHI), enabled by sulfonation-induced polaron delocalization. Combined experimental and theoretical analyses reveal that sulfonation promotes polaron delocalization and disperses structural relaxation during photocharging. These changes are consistent with reduced electron self-trapping and facilitated directional electron transfer to adsorbed O 2 , which may contribute to suppressing O–O bond cleavage in proton-coupled electron transfer steps. This favors enhanced selectivity toward H 2 O 2 formation even at high stored-electron densities. These findings highlight polaron delocalization as an important factor contributing to improved reaction selectivity in dark photocatalysis.