Charge redistribution in covalent organic frameworks via linkage conversion enables enhanced selective reduction of oxygen to H2O2

Abstract

The most employed strategies for adjusting the electrocatalytic activity and selectivity of covalent organic frameworks (COFs) in the oxygen reduction reaction involve modifying the number and placement of heteroatoms, degree of asymmetry, and molecular configuration of the building units. However, the utilization of linkage conversion, which can induce huge local structure change, has been rarely explored for achieving such goals. In this work, we present the successful conversion of imine linkages into nonsubstituted quinoline within thiazolo-[5,4-d]thiazole-based COFs via a Rh-catalyzed C–H activation strategy. This conversion resulted in improved performance in the oxygen reduction reaction, specifically the production of hydrogen peroxide with a selectivity of 61–69% in acid solution (pH = 3.1), a high production rate (106.3 mg L⁻¹ in 100 min), and good durability. Control experiments and theoretical calculations were conducted to investigate the underlying mechanisms, indicating that the active sites could be the quinoline nitrogen and thiazole nitrogen. Furthermore, an analysis of the electronic structure revealed that the enhanced performance following linkage conversion was attributed to an increase in in-plane π electron delocalization. This delocalization induced charge redistribution around the active sites, optimizing the adsorption of oxygen intermediates. Overall, the work paves novel pathways to fine-tune the oxygen reduction reaction performance of COFs linked by imine bonds.