Active Site Engineering in Fe-N-C for Efficient Oxygen Reduction.

Developing efficient and stable oxygen reduction reaction (ORR) catalysts is crucial for fuel cell applications. Non-noble metal iron-nitrogen-carbon (Fe-N-C) catalysts, characterized by low cost, high stability, and tunable electronic structure, represent a promising alternative to Pt-based catalysts. Significant progress in improving the ORR performance of Fe-N-C has been achieved through strategies such as support regulation, defect engineering, and composite structure construction. Recently, active site engineering has emerged as a pivotal approach for optimizing catalytic performance by precisely tuning the coordination environment and electronic structure of Fe active centers. This review systematically summarizes the latest advances in the active site engineering of Fe-N-C ORR catalysts, covering single-atom FeNx sites, heteroatom-doped FeNx sites, dual-atom active sites, and single-atom/cluster composite sites. The design concepts, functional mechanisms, and performance enhancement strategies for these active sites are comprehensively discussed. Finally, the key challenges and future research directions in this field are presented, aiming to provide informative principles for the rational design of advanced Fe-N-C-based ORR catalysts.