Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C₂H₄ Production from CO₂

Electrocatalytic carbon dioxide reduction reaction (CO₂RR) to produce ethylene (C₂H₄) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C₂H₄ production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp³ N hybridization is beneficial to CO₂ capture, but CO₂RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp³ N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp³ N density, strong CO₂ capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO₂ to C₂H₄ with a Faraday efficiency up to 19.1 %, which is stand out in all reported metal-free COF electrocatalysts. In addition, a series of imine-linked COFs are synthesized and combined with DFT calculations to demonstrate the critical role of sp³ N in enhancing the kinetics of CO₂RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.