Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C 2 H 4 Production from CO 2 .

Electrocatalytic carbon dioxide reduction reaction (CO 2 RR) to produce ethylene (C 2 H 4 ) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C 2 H 4 production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp 3 N hybridization is beneficial to CO 2 capture, but CO 2 RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp 3 N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp 3 N density, strong CO 2 capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO 2 to C 2 H 4 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 sp 3 N in enhancing the kinetics of CO 2 RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.