Inducing exciton dissociation in covalent organic framework by local gradient ionic polarization for enhanced hydrogen peroxide photosynthesis

Covalent organic frameworks (COFs) have emerged as a thriving family in the realm of photocatalysis. However, the high exciton dissociation energy and lack of driving force for carrier transport cannot be disregarded. In this work, we proposed a strategy to enhance the built-in electric field of COFs by fabricating local ionic defect on the skeleton. Specifically, a series of metal-free TAPT-EFIB-X (X = 0, 10, 20, 40) with gradient ionic defect concentration were synthesized, which can evenly induce a reshuffling of the local electronic structure, charge distribution, and dipole polarization, thus promoting exciton dissociation and driving electronic transfer. Moreover, TAPT-EFIB-X were endowed with a cationic skeleton and a strong reduction center formed by bromine anions. Among them, TAPT-EFIB-20 achieves high hydrogen peroxide photosynthesis of 8323 μmol h −1 g cat −1 from O 2 and H 2 O. The results show that the strong electron-deficient feature of the TAPT-EFIB-20 promotes the directional distribution of electrons, and the polarization attenuates the spatial barrier effect resulted from the introduction of ionic groups. Subsequently the hybridized orbitals formed by N + and C atoms interact with the corresponding orbitals of adsorbed O 2 to promote the 2e - ORR, while the formation of the hole-rich sites facilitate the 4e - WOR pathway for efficient overall photocatalytic H 2 O 2 generation.