Understanding the ORR Electrocatalysis on Co–Mn Oxides
Wang Wang, Ershuai Liu, Youcheng Hu, Li Jiao, Praveen Kolla, Yucheng Liu, Meihua Tang, Jin Luo, Qiang Sun, Shengli Chen, Qingying Jia, Sanjeev Mukerjee
Abstract
The Co–Mn spinel oxides have attracted much research attention as a class of low-cost electrocatalysts toward the oxygen reduction reaction (ORR) owing to their promising performance in anion-exchange membrane fuel cells (AEMFCs). In this work, the nature of the active sites in a representative CoMn2O4 catalyst was investigated with the assistance of in situ X-ray absorption spectroscopy (XAS) within the ORR-relevant potential range. Our work revealed that the superior activity of the Co–Mn spinel oxides relates to the Mn2+/Mn3+ redox transition. The Mn2+/Mn3+-associated activity is largely affected by the operating potential window, i.e., an activity loss would be observed for Co–Mn spinel oxides operated at potential lower than 0.4 V (vs RHE). It is proposed that this irreversible activity decay is caused by the irreversible change of the Jahn–Teller (J–T) distortion during the Mn2+/Mn3+ transition.