Benzothiophene-Based Covalent Organic Framework for H2O2 Electrosynthesis: The Critical Role of Conjugated Structure

Covalent organic frameworks (COFs), as a class of emerging porous crystalline polymers with high specific surface areas and tunable framework structures, exhibit great potential in oxygen reduction reaction (ORR). Herein, we synthesize a series of benzothiophene-based COFs with varying benzene ring counts in the linkers and employ these materials to unveil the correlation between conjugated structure and the selectivity toward H2O2 electro-synthesis. Experimental results display that the highest H2O2 selectivity (~90%) is offered by the benzothiophene-based COF bearing one benzene ring in the linker, exhibiting a negative correlation with the number of benzene rings in the linker. Theoretical calculations reveal that variations in the number of benzene rings modulated the adsorption strengths and sites of key reaction intermediates, thereby altering 2e- ORR pathway. The decrease in benzene ring count enable the dominant pathway for 2e- ORR become the H2O2 formation through the nucleophilic attack of the active *O2- species, which originates from the electron transfer of 3O2, on the carbon atom near the sulfur atom of the thiophene ring. This work highlights the importance of appropriate linkers and provides valuable insights for devising metal-free COF electrocatalysts.