Unraveling the potential-dependent degradation mechanism in Fe-N-C catalysts for oxygen reduction reaction

Abstract

Fe-N-C is hailed as the most promising candidate for replacing costly platinum-based catalysts for proton-exchange membrane fuel cells (PEMFCs) owing to their impressive catalytic activity and low cost. However, the durability of Fe-N-C catalysts remains a major challenge, primarily due to an insufficient understanding of their degradation mechanisms. In this study, we monitor the real-time changes in the electrode during the oxygen reduction reaction (ORR), shedding light on the potential-dependent degradation mechanisms inherent to Fe-N-C catalysts. Utilizing in-situ differential electrochemical mass spectroscopy, we identify three distinct potential regions with varying degrees of performance loss, notably observing carbon corrosion signals at low potentials. Theoretical calculations and fluorescence probe experiments corroborate that degradation mechanisms at high potentials are primarily driven by strong oxidative potentials that overcome the carbon oxidation energy barrier, whereas the degradation at low potentials is predominantly caused by the high concentrations of reactive oxygen species (ROS) generated during the ORR. The potential-dependent carbon corrosion consequently leads to a similar dependence of demetallation of active sites on the working potential. This study offers a comprehensive understanding of the intrinsic interrelations among various degradation mechanisms, thus paving the way for enhancing the durability of Fe-N-C catalysts in PEMFC applications.