Advances in single-atom M–N–C catalysts propel next-generation fuel cell technologies

Proton exchange membrane fuel cells (PEMFCs) are widely regarded as a clean and efficient energy conversion technology, particularly for electric vehicles and portable power systems. However, their large-scale commercialization has been hindered by the high cost and limited durability of platinum-based catalysts used for the oxygen reduction reaction (ORR). In response, single-atom metal–nitrogen–carbon (M–N–C) catalysts have emerged as promising non-platinum group metal (non-PGM) alternatives due to their high metal utilization efficiency, tunable active sites, and low cost. Despite significant progress, challenges remain in enhancing their catalytic activity and long-term stability under acidic conditions typical of PEMFCs.

A recent review article published in Frontiers in Energy (2025) by researchers from Northwestern Polytechnical University, Fuzhou University, and Yulin Innovation Institute of Clean Energy provides a comprehensive overview of the latest strategies to enhance the performance of single-atom M–N–C catalysts for PEMFCs. The paper systematically explores mechanisms to improve both the intrinsic activity and the density of active sites in these catalysts, focusing on structural tuning, heteroatom doping, multi-metallic site construction, and carbon support engineering.

The study highlights that the ORR activity of M–N–C catalysts is highly dependent on the coordination environment of the central metal atom. Optimizing the number and type of nitrogen ligands (e.g., FeN₄, FeN₅) and introducing axial coordination or heteroatoms (such as S, P, B, O, and halogens) can significantly modulate the electronic structure, enhancing intermediate adsorption/desorption and promoting the desirable four-electron ORR pathway.

The review also emphasizes the role of dual- and multi-metallic active sites, which can create synergistic effects that facilitate O–O bond cleavage and improve reaction kinetics. In addition, advanced carbon support engineering—such as curvature control, edge defect introduction, and porous structure design—can enhance mass transport, expose more active sites, and prevent metal aggregation during high-temperature synthesis.

To increase the density of accessible active sites, the authors discuss strategies such as chelation-assisted synthesis, defect capture, cascade anchoring, spatial confinement using MOFs or COFs, and secondary atom doping. These methods help stabilize single metal atoms and prevent their agglomeration, leading to higher catalytic efficiency and durability.

This review provides a roadmap for the rational design of high-performance, low-cost M–N–C catalysts that could replace platinum in PEMFCs. By integrating structural, electronic, and morphological optimization strategies, the study offers practical insights for developing catalysts that meet the activity, stability, and scalability requirements for commercial fuel cell applications. These advancements are critical for accelerating the adoption of clean hydrogen energy technologies and achieving global decarbonization goals.