Metal–nitrogen–carbon catalysts towards acidic ORR in PEMFC: fundamentals, durability challenges, and improvement strategies

Metal-Nitrogen-Carbon (M-N-C) materials are the most promising Platinum-group-metal (PGM)-free catalysts in replacing the high-cost and scarce Pt catalysts in proton exchange membrane fuel cells (PEMFCs). However, while striking improvement of M-N-C catalysts has been reached in activity, the headache degradation problems hinder their real-world application. Herein, we present a comprehensive overview of the durability of the M-N-C catalyst for oxygen reaction reduction (ORR). The fundamental understanding and identification of the ORR performance of M-N-C catalysts are discussed. Meanwhile, the standard methods to evaluate and predict the ORR performance of the PGM-free catalysts are suggested. We mainly introduce the durability challenges of the M-N-C catalyst and explain the inactivation mechanism in detail. The proposed solution and useful strategies to alleviate catalyst degradation are systematically summarized to overcome the durability bottlenecks.