Synthesis and Active Site Identification of Fe-N-C Single-Atom Catalysts for the Oxygen Reduction Reaction

Fe-N-C catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) are still inferior to the Pt catalysts. The major downsides of Fe-N-C are the low density and ambiguous structural identification of active sites. Fe-N-C single-atom catalysts (SACs) have shown great potential for maximizing the active site density and can serve as ideal platforms for investigating the nature of active sites. This review starts with a summary of the latest progress in the synthetic strategy for Fe-N-C SACs, followed by an introduction to the active site identification by atomic-resolution techniques and electrochemical analyses. Finally, the major challenges are highlighted, and the prospective directions are proposed to guide the development of high-performance Fe-N-C catalysts.