Quantitative detection of hydroxyl radical–mediated degradation in Fe–N–C catalysts during the oxygen reduction reaction

This study provides direct quantitative evidence that hydroxyl radicals (•OH) play a significant role in the degradation of Fe–N–C catalysts during the oxygen reduction reaction (ORR) under specific electrochemical conditions. Using a radical trapping method with coumarin, we demonstrate that at 0.6 V, •OH is generated in proportion to H2O2 production and correlates strongly with the catalyst degradation rate. This finding offers the first experimental confirmation of the long-suspected •OH-driven degradation pathway in non-precious metal catalysts. In contrast, at 0.8 V, degradation occurs with negligible •OH formation, indicating alternative pathways such as oxidative Fe demetalation or nitrogen species modification. Post-degradation structural analyses support this scenario, revealing voltage-dependent changes in surface oxygen content, nitrogen speciation, and Fe–Nx site abundance. These results emphasize the importance of identifying radical-mediated contributions to catalyst instability and provide insights for improving the durability of Fe–N–C electrocatalysts.