Proton Reservoir in Covalent Organic Framework Compensating Oxygen Reduction Reaction Enhances Hydrogen Peroxide Photosynthesis

Abstract The water oxidation reaction (WOR) with sluggish kinetics usually fails to adequately furnish protons to oxygen reduction reaction (ORR), which ultimately constrains the overall efficiency of photocatalytic synthesis of H ₂ O ₂ , particularly in the absence of sacrificial agents. Herein, a class of hydroxyl groups (─OH) functionalized covalent organic framework (COF) is reported as a proton reservoir to compensate ORR for greatly improving the efficiency of H ₂ O ₂ photosynthesis. It has been demonstrated that the incorporation of ─OH into the TFBP‐DHBD (TFBP: 1,2,4,5‐tetrakis‐(4‐formylphenyl)benzene, DHBD: 3,3′‐dihydroxybenzidine) COF can achieve a 3.3 times higher H ₂ O ₂ photosynthetic activity than that of TFBP‐BD (BD: benzidine) COF without ─OH groups. Isotope labeling experiments and in situ infrared spectroscopy analysis demonstrate that the proton reservoir can donate protons for ORR and subsequently regain the released protons from WOR. Theoretical calculations further confirm that the ─OH functionalized COF provides the protons for the formation of *OOH intermediate and reduces its energy barrier, thereby facilitating the photosynthesis of H ₂ O ₂ . A novel COF loaded with Al ₂ O ₃ spheres‐based streamlined microreactor is built that can simultaneously achieve production of H ₂ O ₂ and elimination of bacteria over 1.3 × 10 ⁴ CFU mL ⁻¹ , superior to the reported continuous flow photocatalytic reactors.