Electron-Withdrawing Group in Covalent Organic Frameworks Induced Separated Redox Centers Toward Enhanced Overall H2O2 Photosynthesis in Pure Water

Abstract

Conventional hydrogen peroxide (H2O2) production is energy-intensive and environmentally burdensome. Photocatalytic synthesis using covalent organic frameworks (COFs) offers a sustainable alternative. This work introduces sulfone groups into COFs via [4+2] imine/alkene annulation to enhance photocatalytic H2O2 production from water and oxygen under visible light irradiation. The sulfone-modified S-PT-PB-COF achieves a remarkable H2O2 generation rate of 4794 μmol g-1 h-1, which is 2.2 times higher than that of the unmodified PT-PB-COF and significantly outperforms other control COFs (PB-PB-COF, S-PB-PB-COF). Comprehensive characterizations confirm the successful incorporation of sulfones in the COF structure. The sulfone group enhances the photocatalytic performance of COFs by improving charge separation and reducing recombination, as evidenced by photoelectrochemical and time-resolved fluorescence data. The presence of sulfone in COFs also significantly lowers the energy barrier (0.63 eV) for the rate-determining *OO formation step in the oxygen reduction reaction (ORR), as revealed by density functional theory calculations. Furthermore, sulfone introduction creates spatially separated redox centers for efficient water oxidation and ORR. Quenching experiments and in situ DRIFT spectroscopy confirm a two-step, 1e- ORR pathway involving ·O2- intermediates. This study demonstrates sulfone functionalization as an effective strategy for designing high-performance COF photocatalysts for sustainable H2O2 synthesis.