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–Nx)‐containing catalysts are highly efficient for electrochemical reduction of CO2 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–Nx moieties toward CO2 reduction reaction (CO2RR) results in difficulties in regulating the CO2RR product selectivity on the M–Nx‐containing catalysts. Herein, by using fluorinated iron phthalocyanines with axial‐coordinated ligands (L–FePc–F) as an M–N4‐based model electrocatalyst for CO2RR, a correlation between the electronic structure and C2 selectivity of Fe–N4 is revealed and a comprehensive descriptor based on the Fe–CO π‐backbonding is proposed for guiding the regulation of M–N4 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 FEC2 of FePc–F) to 34% due to the strengthened Fe–CO π‐backbonding stemming from the elevated 3dxz/dyz orbital energy and enhanced electron‐donating ability of the Fe centers of Fe–N4. This work provides a strategy and mechanism insights on the regulation of the C2 selectivity of CO2RR on the Fe–N4 moieties, which may be inspiring for precise construction and regulation of the M–Nx‐containing catalysts for specific CO2RR products.