268598 In-Situ X-Ray Absorption Spectroscopy Investigation of a Bifunctional Manganese Oxide Catalyst with High Activities for the Oxygen Reduction and Evolution
The development of active catalytic materials for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the major challenges in energy conversion and storage technologies such as fuel cells, metal-air batteries, electrolysis cells, and solar fuel synthesis. To implement strategies for the rational design of catalysts for the ORR and the OER, it is important to improve our understanding of the chemical state and structure of active surfaces under reaction conditions. X-ray absorption spectroscopy (XAS) can be combined with electrochemistry to elucidate properties of catalytic materials in-situ. In our work, we perform in-situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for both the ORR and the OER. Previous in-situ XAS studies on active MnOx catalysts have detected the formation of a disordered MnOx with a structure similar to that of birnessite-MnO2 under OER conditions1 and have linked the presence of Mn (III) to high ORR activity in thermally prepared MnOx catalysts.2 Additionally, ex-situ spectroscopy and x-ray diffraction studies have identified a variety of Mn (III) and Mn (IV) oxides as materials with high catalytic activity for either the ORR2-6 or the OER.3,7-9 Our measurements confirmed that different catalytic surfaces form under the oxygen reduction and evolution conditions and identified a distorted Mn3O4structure as an active ORR phase and manganese (III, IV) mixed oxide as an active OER phase.
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