Structurally Locked\nHigh-Crystalline Covalent Triazine\nFrameworks Enable Remarkable Overall Photosynthesis of Hydrogen Peroxide

The development of green and efficient hydrogen peroxide\n(H<sub>2</sub>O<sub>2</sub>) production is of great interest but remains\nchallenging. Herein, we develop a new and simple strategy via locking\nthe coplanarity in highly crystalline covalent triazine frameworks\n(CTFs) to remarkably boost direct photosynthesis of H<sub>2</sub>O<sub>2</sub> from oxygen and water. The exfoliated ultrathin 2D-CTF nanosheets\nexhibit excellent photocatalytic H<sub>2</sub>O<sub>2</sub> evolution\nwith an ultrahigh solar-to-chemical efficiency of 0.91% and a superb\napparent quantum yield of 16.8% at 420 nm, surpassing all previous\nCTFs and most of the metal-free photocatalysts ever reported. Our\ndetailed experimental and theoretical studies reveal that the spatially\nlocked structure in the crystalline CTF photocatalyst can not only\ngreatly enhance the separation and transfer of photoexcited charge-carriers\nfor promoting H<sub>2</sub>O<sub>2</sub> photogeneration but also\nalter the local electronic structures that unexpectedly turn water\noxidation from a four-electron route to a two-electron pathway, resulting\nin a 100% atom utilization efficiency. This work provides valuable\ninsights into the designed synthesis of highly efficient metal-free\nphotocatalysts and precise control over photocatalytic reaction pathways\nin organic materials.