Stability/durability challenges of cathode catalysts for PEM fuel cells: experiments, mechanisms, and perspectives beyond three-electrode systems

The sluggish oxygen reduction reaction (ORR) determines the performance and lifetime of proton exchange membrane (PEM) fuel cells. Commercialized cathodic ORR catalysts are synthesized using platinum-group-metal (PGM)-based chemicals, which suffer from low geological reserves; hence, PGM-free catalysts are emerging as alternatives. However, PGM and PGM-free catalysts suffer from insufficient stability/durability. The stability/durability test protocols for ORR catalysts, especially for PGM-free catalysts, have not been well agreed—different groups use different stability/durability test protocols in their experiments, particularly in membrane electrode assembly (MEA) tests; some false comparison may be overlooked by researchers. However, a deep understanding of degradation mechanisms and the development of efficient strategies to improve stability/durability have become the research frontier in this field. In this regard, we herein discuss the key experimental factors influencing the accuracy of stability/durability tests in three-electrode systems and MEAs and discuss critical degradation mechanisms and material-based solutions to improve catalyst stability/durability. We hope this discussion will highlight the importance of stability/durability studies and promote PEM fuel cell development.