Getting insights into the edge effect of FeN4C catalysts on the electroreduction of CO to methane by density functional theory calculations

Abstract

Isolated FeN₄ atomically dispersed on graphene (FeN₄C) has emerged as a versatile catalyst for the electrochemical carbon monoxide reduction reaction (CORR). However, there is still a lack of underlying understanding of the impact of the local coordination environment of FeN₄ on CORR performance, particularly the intrinsic activity differences among various FeN₄ sites. Herein, by using density functional theory, we investigated the electrocatalytic performance of FeN₄ embedded in the interior, armchair- and zigzag-edges of carbon sheets for converting CO to valuable C1 products. The Gibbs free energy profile analyses along the possible reaction pathways identify that the armchair-edge FeN₄ site (FeN₄@A) exhibits the best catalytic activity and the highest CH₄-selectivity through the *CHO key intermediate with the lowest free energy change of 0.31 eV. The corresponding kinetic analyses also confirm that FeN₄@A possesses the fastest kinetic CORR activity with an activation barrier of 1.31 eV for the rate-determining step. In addition, the d-band center calculations suggest that the local environment of the FeN₄ site can regulate the overlap of the d-orbitals of the center Fe and the p-orbitals of coordination N atoms to change the position of the d-band center relative to the Fermi level, which significantly affects the catalytic activity of the FeN₄ site. The d-band center of FeN₄@A is very close to the Fermi level in energy, indicating that the armchair-edge of graphene favors the FeN₄ site to achieve the high CORR performance. These results provide insight into the relationship of electronic structure–catalytic activity of different-type FeN₄C catalysts, which may guide the design of novel electrode materials with improved performances for achieving efficient multi-intermediate electrocatalysis.