Covalent Organic Frameworks for Boosting H₂O₂ Photosynthesis via the Synergy of Multiple Charge Transfer Channels and...

Covalent organic frameworks (COFs) serve as one of the most promising candidates for hydrogen peroxide (H₂O₂) photosynthesis, while attaining high-performance COFs remains a formidable challenge due to the insufficient separation of photogenerated charges. Here, through the rational design of bicarbazole-based COFs (Cz-COFs), we showcase the first achievement in piezo-photocatalytic synthesis of H₂O₂ using COFs. Noteworthily, the ethenyl group-modified Cz-COFs (COF-DH-Eth) demonstrates a record-high yield of H₂O₂ (9212 μmol g^-1 h^-1) from air and pure water through piezo-photocatalysis, which is ca. 2.5 times higher than that of pristine Cz-COFs without ethenyl groups (COF-DH-H) under identical condition and COF-DH-Eth without ultrasonic treatment. The H₂O₂ production rate originates from the synergistic effect between an ultrasonication-induced polarized electric field and the spatially separated multiple charge transfer channels, which significantly promote the utilization of photogenerated electrons by directional transfer from bicarbazole groups to the ethenyl group-modified benzene rings. Several Cz-COFs and bifluorenylidene-based COFs (COF-BFTB-H) with similar twisted monomers exhibit obvious piezoelectric performance for promoting H₂O₂ generation, signifying that organic ligands with a twistable structure play a crucial role in creating broken symmetry structures, thereby establishing piezoelectric properties in COFs.