Modulating N-Heterocyclic Microenvironment in β-Ketoenamine Covalent Organic Frameworks to Boost Overall Photosynthesis of HO.

Covalent Organic Frameworks (COFs) have emerged as promising platforms for photocatalytic synthesis of hydrogen peroxide (HO) due to their tunable chemical compositions and efficient catalytic functionalities. Inspired by the role of the microenvironment in enzyme catalysis, this study introduces various N-heterocyclic species into β-ketoenamine COFs (N-COFs, where N represents the number of nitrogen atoms in the N-heterocycle) to regulate the microenvironment around catalytic sites on acceptor-donor-acceptor (A-D-A) COFs foroverall HO photosynthesis in pure water. The N-COFs exhibit distinct HO photosynthetic rates following the number of nitrogen atoms sequence of N-COF > N-COF > N-COF > N-COF, with N-COF with triazine structure showing the highest HO generation rate (4881 µmol h g) and the decent solar-to-chemical conversion (SCC) efficiency (0.413%), surpassing many existing COF-based catalysts. In situ characterization and theoretical calculations support the experimental results, revealing that N-heterocyclic species promote the photosynthesis of HO through both an indirect stepwise single-electron oxygen reduction reaction (1e ORR) mechanism and a direct two-electron water oxidation (2e WOR) pathway. This study advances the design paradigm of photocatalysts by modulating the microenvironment within A-D-A COFs, paving the way for the development of more efficient and robust photocatalytic systems for the overall photosynthesis of HO.