Activating *CO by Strengthening Fe–CO π‐Backbonding to Enhance Two‐Carbon Products Formation toward CO2 Electroreduction on Fe–N4 Sites

Abstract Many non‐precious metal‐nitrogen (M–N x )‐containing catalysts are highly efficient for electrochemical reduction of CO 2 to CO and yet encounter challenges in further converting CO to more valuable two‐carbon products (C2), such as ethanol and acetic acid. The ambiguous structure‐activity relationship of the M–N x moieties toward CO 2 reduction reaction (CO 2 RR) results in difficulties in regulating the CO 2 RR product selectivity on the M–N x ‐containing catalysts. Herein, by using fluorinated iron phthalocyanines with axial‐coordinated ligands (L–FePc–F) as an M–N 4 ‐based model electrocatalyst for CO 2 RR, a correlation between the electronic structure and C2 selectivity of Fe–N 4 is revealed and a comprehensive descriptor based on the Fe–CO π‐backbonding is proposed for guiding the regulation of M–N 4 toward higher C2 selectivity. Based on the regulation principle, the Br‐axial‐coordinated FePc–F (Br–FePc–F) remarkably increases the Faradic efficiency (FE) of C2 products from 0% (i.e., the FE C2 of FePc–F) to 34% due to the strengthened Fe–CO π‐backbonding stemming from the elevated 3 d xz / d yz orbital energy and enhanced electron‐donating ability of the Fe centers of Fe–N 4 . This work provides a strategy and mechanism insights on the regulation of the C2 selectivity of CO 2 RR on the Fe–N 4 moieties, which may be inspiring for precise construction and regulation of the M–N x ‐containing catalysts for specific CO 2 RR products.