Active Sites on Heterogeneous Single-Iron-Atom Electrocatalysts in CO2 Reduction Reaction

Nitrogen-coordinated single-metal-atom catalysts (Me–N–C) are promising candidates for CO2-to-CO electrocatalytic conversion. The nature of real active sites in this type of electrocatalyst, however, is not clear. In this Letter, we study the specific interactions between the reaction intermediates and a model single-iron-atom catalyst (Fe–N–C) by combining in situ infrared absorption spectroscopy and density functional theory (DFT) calculations. For the first time, we confirm that the Fe centers in Fe–N4 moieties hosted by the complete graphitic layer are poisoned by strongly adsorbed CO and should not be the real active sites for gaseous CO production. Further DFT calculation results suggest that the high CO selectivity and reaction rate may originate from Fe–N4 moieties embedded in a defective graphitic layer that have balanced binding energies of adsorbed COOH and CO species. These findings add significant new insights into the mechanisms of CO2 reduction on carbon-based single-atom electrocatalysts.