(641d) 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 (MnO_x) catalyst with high electrochemical activity for both the ORR and the OER. Previous in-situ XAS studies on active MnO_x catalysts have detected the formation of a disordered MnO_x 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 MnO_x 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 ORR^2-6 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.

References

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