Micro-modulation of linkers of covalent organic frameworks as catalysts for 2e− oxygen reduction reaction

Covalent organic frameworks (COFs) are attractive as metal-free catalysts for the 2e− oxygen reduction reaction (ORR) towing to their tunable skeletons and porosities. However, the specific roles of their properties, such as crystallinity, porosity, dipole moment, and binding ability to reactants, in the catalytic performance are still unknown. In this work, we adopted a linker engineering strategy to reveal the crucial factors in determining the catalytic performance. The properties of the COFs were systematically engineered by altering the substituent groups in the linkers. The optimized Br-COF achieved a maximum selectivity of 86.2%, and a mass activity of 32.0 A g−1, which were 112% and 174% higher than those from unmodified COF, respectively. The experimental and theoretical results revealed that the reductive ability of the COFs exerted the most prominent effect on their catalytic activity and confirmed that the easy formation of an OOH* intermediate contributed to the high activity.