Tunable Catalytic Vertex Wall Chemistry in Metal-free Covalent Organic Frameworks for Enhanced Oxygen Reduction

Metal-free covalent organic frameworks (COFs) have emerged as promising catalysts for the oxygen reduction reaction (ORR) because of their unique structural properties and notable stability. To enhance both catalytic activity and selectivity, a variety of linkers and linkages have been investigated in efforts to precisely engineer COFs. However, the impact of vertex structures within COFs on ORR catalysis remains largely underexplored. Here, to modulate COF catalytic performance, we introduce tunable catalytic vertex wall chemistry by introducing diverse triazine and thiophene units. The catalytic vertex wall approach allows the fine-tuning of electronic surface states, leading to improved intermediate adsorption characteristics and accelerated ORR activity. Remarkably, the engineered COF achieved a half-wave potential of 0.76 V, surpassing COFs modified by linker or linkage strategies. Theoretical calculations suggest that this enhanced activity arises from the strong binding affinity of OOH* intermediates to carbon atoms adjacent to the thiophene vertex, facilitating OOH* reduction to a O₂ molecule, which is the rate-limiting step of the ORR. These findings reveal the pivotal role of vertex wall engineering in conjugated COF frameworks, and offer critical insights to advance COFs design toward superior ORR performance.