An Axially Fluorine-Coordinated Ni Single-Atom Catalyst for Highly Efficient CO2 Electrocatalytic Reduction

Abstract

Electrochemical CO2-to-CO reduction stores renewable electricity in chemical feedstocks, but is limited by CO2's kinetic inertness and the competing HER. SACs with M–N4 motifs provide well-defined active sites and high atom utilization; tuning their local coordination environment, especially via axial ligands, boosts activity and selectivity. Although O, Cl, and Br axial coordination has been explored, fluorine coordination in Ni-based SACs remains unclear. We report a fluorine-modified Ni SAC (NiNFC) via one-step pyrolysis, achieving a peak FECO of 99.0% at −0.74 V vs RHE and sustaining FECO > 90% from −0.64 to −0.94 V. NiNFC operates stably for 105 h in an H-type cell, with improved CO2RR selectivity and activity versus fluorine-free NiNC. Spectroscopy, electrochemistry, in situ ATR-SEIRAS, and DFT calculations indicate that fluorine-induced modulation at Ni–N4 sites facilitates *COOH formation, accelerating CO2-to-CO conversion. These results illuminate fluorine-assisted coordination engineering for efficient, durable SACs.