Enhanced hydrogen peroxide photosynthesis in covalent organic frameworks through induced asymmetric electron distribution

Covalent organic frameworks (COFs) can be used as photocatalysts for the direct photosynthesis of hydrogen peroxide (H2O2) from oxygen, water and sunlight. However, their highly symmetric structure can lead to weak adsorption of O2 and, therefore, unsatisfactory photocatalytic performance. Here we explore the local asymmetric electron distribution induced by Pauli and electron–electron repulsion in COFs to construct localized bonding sites for O2 species, which promotes photocatalytic H2O2 production. Experimental results and theoretical calculations reveal that TAPT–FTPB COFs (where TAPT is 1,3,5-tris-(4-aminophenyl) triazine and FTPB is 5-(5-formylthiophen-2-yl)thiophene-2-carbaldehyde) with an asymmetric electron distribution show strong O2 adsorption interaction and a record-breaking solar-to-chemical conversion efficiency of 1.22% for direct photosynthesis of H2O2 from oxygen and water, which is higher than in the photosynthesis of plants (~0.1%). A flow-type photocatalytic microreactor integrated with TAPT–FTPB COFs exhibits 100% sterilization efficiency for killing bacteria and 97.8% conversion for photocatalytic 2-thiophene methylamine coupling. This work reports a strategy for manipulating the local electron distribution in COFs, opening the door for research on the rational design of high-performance photocatalysis with a local asymmetric electron distribution. Covalent organic frameworks (COFs) are promising photocatalysts for the direct photosynthesis of H2O2, but their symmetric structure can lead to weak O2 adsorption. Now thiophene sulfur atoms are introduced into COFs to induce local asymmetric electron distributions, which enhance the O2 adsorption capacity and interaction of the COFs, promoting direct photosynthesis of H2O2.