What determines the stability of Fe-N-C catalysts in HT-PEMFCs?

Fe-N-C catalysts are an attractive low-cost alternative to Pt for the oxygen reduction reaction (ORR) in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) as they are less sensitive to phosphate poisoning, but they suffer from poor stability and unclear degradation mechanisms. In this study, the activation and degradation mechanisms of HT-PEMFCs with several classes of Fe-N-Cs operating for 90 h are identified using a combination of operando electrochemical and post-mortem physical analysis. While simultaneous activation in terms of accelerated ORR processes takes place by acid redistribution, the degradation of the catalyst leads to drastic performance loss (-27%) within the first 24 h. Carbon corrosion has a lower impact and the strongest degradation is attributed to active site deactivation e.g. by transformation to inactive nanoparticles or by site loss. This study helps to understand the degradation of Fe-N-Cs in HT-PEMFC and points to the necessary and inevitable modification of single-atom catalysts.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.