Regulation of charge carrier transportation in D–π–A type covalent organic frameworks for promoting photocatalytic H 2 O 2 production

Covalent Organic Frameworks (COFs) with diverse conjugated structures are extensively utilized as promising photocatalysts for hydrogen peroxide (H₂O₂) production. However, the current applications are constrained by the rapid recombination of photogenerated carriers and the slow reaction kinetics. To address these issues, in this study, we design and prepare four COF photocatalysts with a distinct donor-π-acceptor (D-π-A) structure to regulate the photogenerated charge carrier transportation. Significantly, Tf-TAPT-COF containing triazine units shows the most elevated rate of H₂O₂ evolution. This is primarily attributed to the electron-withdrawing capacity of N centers in COFs following the order: triazine > pyrimidine > pyridine > benzene, leading to the enhanced transportation of electrons along the π-bridge from the donor to the acceptor. In the absence of a sacrificial agent, the photocatalytic H₂O₂ production of Tf-TAPT-COF can reach 2700 μmol g^-1 h^-1, surpassing most of the similar photocatalysts reported previously. A series of experimental characterization studies and theoretical calculations indicate that increasing the number of N atoms in the N-heterocycles of COFs can enhance the transportation of photogenerated carriers along the π-bridge. It enables COFs to facilitate the oxygen reduction reaction (ORR) via both π-bridges and acceptor dual sites, and the water oxidation reaction (WOR) occurs on the donor, thereby significantly improving their activity in photocatalytic H₂O₂ production. This research provides a promising approach for the regulation of charge carrier transportation in COFs and the performance improvement in full photosynthesis of H₂O₂ based on COFs.