Unravelling the Stability Stressors of Atomically Dispersed Fe–N–C Oxygen Reduction Catalysts
Xiaohong Xie, Boyang Li, Pan Xu, Moulay Tahar Sougrati, Ricardo García‐Serres, David A. Cullen, A. Jeremy Kropf, Fan Xia, Miao Song, Sulay Saha, Yachao Zeng, Mark Engelhard, Mark Bowden, Hanguang Zhang, Litao Yan, Teresa Lemmon, Xiaohong S. Li, Ulises Martinez, Yingwen Cheng, Gang Wu, Piotr Zelenay, Vijay Ramani, Deborah J. Myers, Frédéric Jaouen, Lijun Yang, Guofeng Wang, Yuyan Shao
Abstract
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 (O 2 ), and reactive oxygen species (ROS). Through ex situ/operando experiments, we show that the oxidation of local carbon by acidic environment + O 2 + ROS, along with the demetalation of catalytic FeN x C y sites by O 2 or O 2 + ROS, is the primary factor responsible for the initial fast degradation of Fe–N–C catalysts. The demetalation of FeN x C y sites, influenced by O 2, in particular by O 2 + ROS, leads to the subsequent gradual degradation of Fe–N–C. Notably, FeN 4 C 12 -type active sites are more susceptible to demetalation than FeN 4 C 10 -type sites in O 2 or O 2 + ROS. Our findings indicate that, besides constructing more stable FeN x C y sites, preventing local carbon oxidation and scavenging of ROS are all critical for maintaining the stability of Fe–N–C catalysts.