Abstract
? 2022 Elsevier B.V.MnO2 has been studied as the catalyst for oxygen reduction reaction (ORR) in neutral due to its considerably good performance and low cost. Although many studies focus on activity enhancement, little attention has been paid to the activity degradation of MnO2. In this study, we first probe the mechanism of ORR activity decay of MnO2 catalyst in neutral. Electrochemical measurements showed the apparent activity degradation of MnO2 in both short-term and long-time stability tests. After chronoamperometry test, surface amorphization was observed on the catalyst, while no significant amorphization occurred for the absence of ORR catalysis. The activity decay and surface amorphization of MnO2 catalyst are due to the disproportionation reaction of Mn3+ ions in neutral. Mn3+ ions involved in ORR catalysis disproportionate to generate soluble Mn2+ ions, resulting in the surface amorphization together with the change of the highly ORR-active Mn3+/Mn4+ redox to the low ORR-active Mn2+/Mn3+ redox. This study clarifies the activity decay mechanism of MnO2 for ORR in neutral media and provides theoretical support for improving and stabilizing the catalytic activity of MnO2 in the future.
NSTL
Elsevier