Single atomic Fe–N4 active sites and neighboring graphitic nitrogen for efficient and stable electrochemical CO2 reduction

Abstract

Single atomic Fe–N_x moieties have shown great performance in CO₂-to-CO conversion. However, understanding the structural descriptors that determine the activity of Fe–N_x remains vague, and promising strategies to enhance their catalytic activity are still not clear. Herein, we used a high-temperature pyrolysis strategy and post-synthesis acid treatment for the direct growth of a single Fe–N_x site adjacent to graphitic nitrogen for the electrochemical CO₂ reduction reaction. This strategy could significantly reduce the amount of pyridinic and pyrrolic N atoms, while graphitic N surrounding the Fe–N_x site predominantly increases. An experimental study combined with density functional theory revealed that the increase in the neighboring graphitic N decreases the number of electrons transferred between CO and the catalyst for FeN₄-2N-3 and FeN₄-4N-3, which results in the decrease of the adsorption strength of CO and the energy barrier for desorbing CO*. The as-synthesized Fe–N_x neighbored by graphitic nitrogen exhibited maximum faradaic efficiency of 91% at a lower overpotential of 390 mV. Due to the increase in the graphitic N, the catalysts perform efficiently for 35 h without any drop in current density.