Fe–N–C single atom catalysts for the electrochemical conversion of carbon, nitrogen and oxygen elements

Single atom catalysts (SACs) are constituted by isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and amorphous carbon. The thermal stability, electronic properties, and catalytic activities of the metal center can be controlled via manipulating the neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomical dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased. Furthermore, new possibilities are offered to easily control the selectivity of a given transformation process as well as to improve turnover frequencies and turnover numbers of target reactions. Among them, Fe–N–C single atom catalysts own special electronic structure, and have been widely used in many fields of electrocatalysis. This review aims to summarize the synthesis of Fe–N–C based on anchoring individual iron atoms on carbon/graphene. The spin-related properties of Fe–N–C catalysts are described, including the relation between spin and electron structure of Fe–N_x as well as the coupling between electronic structure of Fe–N_x and electronic (orbit) of CO₂, N₂ and O₂. Next, mechanistic investigations conducted to understand the specific behavior of Fe–N–C catalysts are highlighted, including C, N, O electro-reduction. Finally, some issues related to the future developments of Fe–N–C are put forward and corresponding feasible solutions are offered.