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Role of Nanoscale Inhomogeneities in Co2FeO4 Catalysts during the Oxygen Evolution Reaction

MPS-Authors
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Haase,  Felix
Interface Science, Fritz Haber Institute, Max Planck Society;

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Schmidt,  Franz
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Max Planck Institute for Chemical Energy Conversion;

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Herzog,  Antonia
Interface Science, Fritz Haber Institute, Max Planck Society;

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Jeon,  Hyosang
Interface Science, Fritz Haber Institute, Max Planck Society;

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Frandsen,  Wiebke
Interface Science, Fritz Haber Institute, Max Planck Society;

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Timoshenko,  Janis
Interface Science, Fritz Haber Institute, Max Planck Society;

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Lunkenbein,  Thomas
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Bergmann,  Arno
Interface Science, Fritz Haber Institute, Max Planck Society;

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Schlögl,  Robert
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Max Planck Institute for Chemical Energy Conversion;

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Roldan Cuenya,  Beatriz
Interface Science, Fritz Haber Institute, Max Planck Society;

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Citation

Haase, F., Rabe, A., Schmidt, F., Herzog, A., Jeon, H., Frandsen, W., et al. (2022). Role of Nanoscale Inhomogeneities in Co2FeO4 Catalysts during the Oxygen Evolution Reaction. Journal of the American Chemical Society, 144(27), 12007-12019. doi:10.1021/jacs.2c00850.


Cite as: http://hdl.handle.net/21.11116/0000-000A-8142-9
Abstract
Spinel-type catalysts are promising anode materials for the alkaline oxygen evolution reaction (OER), exhibiting low overpotentials and providing long-term stability. In this study, we compared two structurally equal Co2FeO4 spinels with nominally identical stoichiometry and substantially different OER activities. In particular, one of the samples, characterized by a metastable precatalyst state, was found to quickly achieve its steady-state optimum operation, while the other, which was initially closer to the ideal crystallographic spinel structure, never reached such a state and required 168 mV higher potential to achieve 1 mA/cm2. In addition, the enhanced OER activity was accompanied by a larger resistance to corrosion. More specifically, using various ex situ, quasi in situ, and operando methods, we could identify a correlation between the catalytic activity and compositional inhomogeneities resulting in an X-ray amorphous Co2+-rich minority phase linking the crystalline spinel domains in the as-prepared state. Operando X-ray absorption spectroscopy revealed that these Co-rich domains transform during OER to structurally different Co3+-rich domains. These domains appear to be crucial for enhancing OER kinetics while exhibiting distinctly different redox properties. Our work emphasizes the necessity of the operando methodology to gain fundamental insight into the activity-determining properties of OER catalysts and presents a promising catalyst concept in which a stable, crystalline structure hosts the disordered and active catalyst phase.