Modulating Local Electronegativity in Covalent Organic Frameworks for Host-Guest Oxygen Reduction

Developing high-performance metal-free electrocatalysts for the oxygen reduction reaction remains a major challenge in sustainable energy conversion. Herein, we report a host-guest chemistry strategy based on metal-free covalent organic frameworks (COFs) to significantly enhance the catalytic performance. Unlike conventional COFs that focus primarily on linkage chemistry or heteroatom doping, our approach explicitly leverages molecular-level design to create tailored binding pockets within the COFs pores, enabling high selectivity and strong interactions with O₂. A series of fluorene-based COF hosts with systematically tuned electronegativity are designed and synthesized to strengthen molecular recognition and binding toward oxygen via tailored electronic and structural environments. The optimized material achieves a remarkable half-wave potential (E_1/2, vs. RHE) of 0.78 V, among the highest reported metal-free COF-based catalysts. This exceptional performance originates from enhanced host-guest recognition, which effectively facilitates O₂ adsorption while optimizing the stabilization and subsequent dissociation of key reaction intermediates on the active site. Through a combination of in situ characterization and theoretical calculations, these host-guest interactions promote the optimized adsorption of intermediates and accelerate reaction kinetics. This study provides a new paradigm for the design of high-efficiency metal-free electrocatalysts through precise molecular recognition, opening avenues for advanced catalytic systems beyond conventional approaches.