Unravelling the Stability Stressors of Atomically Dispersed Fe–N–C Oxygen Reduction Catalysts

Enhancing the catalytic stability of Fe–N–C catalysts for cathodic oxygen reduction in proton-exchange membrane fuel cells (PEMFCs) necessitates an in-depth understanding of their degradation mechanisms. This study identifies key stressors affecting the stability of Fe–N–C catalysts, specifically acidic environment, oxygen (O2), and reactive oxygen species (ROS). Through ex situ/operando experiments, we show that the oxidation of local carbon by acidic environment + O2 + ROS, along with the demetalation of catalytic FeNxCy sites by O2 or O2 + ROS, is the primary factor responsible for the initial fast degradation of Fe–N–C catalysts. The demetalation of FeNxCy sites, influenced by O2, in particular by O2 + ROS, leads to the subsequent gradual degradation of Fe–N–C. Notably, FeN4C12-type active sites are more susceptible to demetalation than FeN4C10-type sites in O2 or O2 + ROS. Our findings indicate that, besides constructing more stable FeNxCy sites, preventing local carbon oxidation and scavenging of ROS are all critical for maintaining the stability of Fe–N–C catalysts.