Exploring Durable Single-Atom Catalysts for Proton Exchange Membrane Fuel Cells

Exploring low-cost, highly active, and durable oxygen reduction catalysts is essential for the widespread use of proton exchange membrane fuel cells. Fe–N–C catalysts with nitrogen-coordinated single-atom (Fe–Nx) active sites are the most promising candidates due to their highest activity in acid media among platinum-group-metal-free catalysts. However, the application of Fe–N–C catalysts in realistic fuel cells is still hindered by the conundrum of insufficient stability. This review focuses on the understanding of the structure–stability relationship of Fe–N–C catalysts, which provides valuable guidance for the rational material design toward improved stability. The most significant achievements in recent years are the discovery of several site-specific degradation mechanisms and the identification of intrinsically stable active sites. The development of Fe-free single-atom catalysts is also discussed as an alternative solution.