Unveiling the role of carbon oxidation in irreversible degradation of atomically-dispersed FeN₄moieties for proton exchange membrane fuel cells

Nonprecious Fe-N-C catalysts containing atomically-dispersed FeN₄moieties are today the best candidates to replace platinum in proton exchange membrane fuel cell (PEMFC) cathodes. However, limited understanding of problematicoperandodegradation mechanisms in these catalysts largely impedes widespread commercialization. Recent experiments have shown that there exist durable and non-durable FeN₄sites in Fe-N-C catalysts for PEMFCs [J. Liet al.,Nat. Catal., 2021,4, 10-19]. Yet, the identification of which FeN₄sites are durable and which are not - and why - remains unclear. Using first-principles density functional theory (DFT) computations, we investigated the irreversible degradation of FeN₄catalysts at the atomic level, caused by Fe de-metalation and chemical oxidation of carbonviaa proposed new carbon oxidation pathway. Our computational results show that oxidation of surface carbon next to FeN₄moieties at interior sites is essentially reversible underoperandoelectrochemical conditions; whereas oxidation of carbon next to FeN₄moieties at the edge sites leads to accelerated Fe de-metalation, inducing irreversible degradation of FeN₄catalysts. From amongst six FeN₄moieties established experimentally, we identify three durable and three non-durable configurations. This work resolves the controversy as to which FeN₄moieties are durable under PEMFCoperandoconditions and provides a deeper understanding of the irreversible degradation mechanism of FeN₄catalysts in acidic media, furnishing a practical guide for rational design of FeN₄catalysts with long-term durability.