Unravelling the role of hydrogen peroxide in pH-dependent ORR performance of Mn-N-C catalysts

Although the Mn-N-C catalyst has low toxicity and high durability, its intense pH-dependent ORR activity is perplexing and prevents its commercial use in PEMFCs. Herein, we have developed a novel understanding of the role of hydrogen peroxide in the pH-dependent activity and stability of Mn-N-C catalysts. Instead of nitrogen protonation, the strong pH effects of ORR activity are caused by the much faster kinetics of the H 2 O 2 reduction reaction in alkaline medium than in acid, due to the lower dissociation energy of the HO-OH bond in alkaline environment. Regarding durability, the deactivation induced by H 2 O 2 demonstrates a strong pH dependence, primarily due to the differing intensities of reactive oxygen species at different pH values. Correspondingly, isopropanol effectively reduces Fenton reagents and increases the acid resistance of Mn-N-C sites. The present research provides a mechanistic understanding of pH effects and paves the way for the creation of more efficient catalysts.