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

Abstract

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–N₄ (S/Fe–poN₄–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–poN₄–C, with CO Faraday efficiency of 98.2% and turnover frequency of 4621.2 h⁻¹, superior to the S-free pyridine-type Fe–N₄ 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.