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 FeN_xC_y sites by O₂ or O₂ + ROS, is the primary factor responsible for the initial fast degradation of Fe-N-C catalysts. The demetalation of FeN_xC_y 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 FeN_xC_y sites, preventing local carbon oxidation and scavenging of ROS are all critical for maintaining the stability of Fe-N-C catalysts.