Boosting H2O2 Photosynthesis by Accumulating Photo-electrons on Carbonyl Active Site of Polyimide Covalent Organic Frameworks

The low trapping efficiency of photogenerated electrons by the targeted reduction site seriously restricts the kinetics of H2O2 photosynthesis via two-electron oxygen reduction reaction. Here, two polyimide covalent organic frameworks (PT-COF and PB-COF) possessing carbonyl groups with different electron-trapping capacity are elaborately designed. PB-COF with electron-rich carbonyl site presents 4.22 times improvement in H2O2 formation rate up to 2044 μmol g-1 h-1, and exhibits outstanding stability after 120h continuous opearting. Meanwhile, solar to-chemical energy efficiency is 0.68%, representing one of advanced polymer based photocatalysts. We demonstrated electronic structure of the carbonyl active center is modulated by tuning electron attraction capability of the donor unit via increased the built-in electric field to accelerate charge separation and directional transfer. The electron-rich carbonyl site is identified to boosted H2O2 photosynthesis activity via reducing the *OOH binding energy. Our work offers a tailoring electron density of pre-designable active site strategy for enhanced solar-to-chemical energy conversion.