Remote p-d orbital hybridization via first/second-layer coordination of Fe single atoms with heteroatoms for enhanced electrochemical CO₂-to-CO reduction

The electrochemical CO2 reduction reaction (CO2RR) to CO is closely correlated with appropriate sorption of *COOH and *CO species toward the electrode surface, and the proton transfer process that often competes with the hydrogen evolution reaction (HER). Herein, an unconventional p-d orbital hybridization induced by doping of S to the second coordination layer of atomically dispersed pyrrole-type Fe-N-4 (S/Fe-poN(4)-C) could not only modulate the binding strength between *COOH and pyrrole-type Fe single atoms but also facilitate the succedent desorption of *CO, effectively hindering the occurrence of the HER. An excellent CO2RR performance was achieved in an H-type cell over S/Fe-poN(4)-C, with CO Faraday efficiency of 98.2% and turnover frequency of 4621.2 h(-1), superior to the S-free pyridine-type Fe-N-4 catalyst and previously reported electrodes. In situ characterization techniques and theoretical calculations demonstrated that the constructed p-d orbital hybridization suitably balanced the adsorption of the *COOH intermediate by accelerating proton transfer and further desorption of *CO by optimizing the nitrogen coordination environment of the electrocatalyst, which could also stabilize the atomic Fe sites to avoid aggregation. The remote p-d orbital hybridization strategy offers an alternative approach for more precious regulation of both the electronic and coordination structure of the electrodes for highly selective CO2RR.