Atomically dispersed Fe³⁺ sites catalyze efficient CO₂ electroreduction to CO

Currently, the most active electrocatalysts for the conversion of CO₂ to CO are gold-based nanomaterials, whereas non-precious metal catalysts have shown low to modest activity. Here, we report a catalyst of dispersed single-atom iron sites that produces CO at an overpotential as low as 80 millivolts. Partial current density reaches 94 milliamperes per square centimeter at an overpotential of 340 millivolts. Operando x-ray absorption spectroscopy revealed the active sites to be discrete Fe³⁺ ions, coordinated to pyrrolic nitrogen (N) atoms of the N-doped carbon support, that maintain their +3 oxidation state during electrocatalysis, probably through electronic coupling to the conductive carbon support. Electrochemical data suggest that the Fe³⁺ sites derive their superior activity from faster CO₂ adsorption and weaker CO absorption than that of conventional Fe²⁺ sites.