Distinct oxygen reduction pathways for solar H₂O₂ production by regulating unsaturated bonds in covalent organic...

Photocatalytic H₂O₂ generation via the two-electron oxygen reduction reaction (2e^- ORR) is a highly sustainable approach, capable of proceeding via either a one-step or two-step 2e^- ORR route. Nonetheless, precise regulation of the 2e^- ORR pathways still remains a formidable challenge. Herein, for the first time, we modulate the 2e^- ORR pathway through unsaturated bond control in covalent organic frameworks (COFs). We synthesize a pair of isostructural COFs distinguished only by their unsaturated bonds. The alkyne-containing TY-COF favors the two-step 2e^- ORR route, whereas the alkene-containing TE-COF follows the one-step 2e^- ORR route. Without any sacrificial agents in O₂, the TY-COF and TE-COF display impressive H₂O₂ production rates of 6455 and 4804 μmol g^-1 h^-1, respectively. Further theoretical results reveal that the regulation of unsaturated bonds alters the electron-hole distribution along the COF skeletons, prompting the reorganization of the catalytic centers for ORR (the benzene ring in TY-COFs and the triazine in TE-COFs), which leads to divergent ORR pathways. Additionally, free-standing TY-COF and TE-COF membranes, fabricated via the interfacial polymerization method, are also able to drive H₂O₂ photosynthesis. The present work offers a new strategy and valuable inspiration for modulating 2e^- ORR pathways via strategic architectural engineering of COFs.