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Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction

Nature Catalysis volume 1, pages 711–719 (2018)Cite this article

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Abstract

Efficient catalysts for the anodic oxygen evolution reaction (OER) are critical for electrochemical H2 production. Their design requires structural knowledge of their catalytically active sites and state. Here, we track the atomic-scale structural evolution of well-defined CoOx(OH)y compounds into their catalytically active state during electrocatalytic operation through operando and surface-sensitive X-ray spectroscopy and surface voltammetry, supported by theoretical calculations. We find clear voltammetric evidence that electrochemically reducible near-surface Co3+–O sites play an organizing role for high OER activity. These sites invariably emerge independent of initial metal valency and coordination under catalytic OER conditions. Combining experiments and theory reveals the unified chemical structure motif as µ2-OH-bridged Co2+/3+ ion clusters formed on all three-dimensional cross-linked and layered CoOx(OH)y precursors and present in an oxidized form during the OER, as shown by operando X-ray spectroscopy. Together, the spectroscopic and electrochemical fingerprints offer a unified picture of our molecular understanding of the structure of catalytically active metal oxide OER sites.

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Fig. 1: Possible mechanisms of O–O bond formation.
Fig. 2: Structures of the selected cobalt oxides and cobalt oxyhydroxides.
Fig. 3: Morphological and structural integrity of CoOx(OH)y electrocatalysts.
Fig. 4: Ex situ and operando cobalt oxidation states at selected catalyst states.
Fig. 5: Ex situ and operando structural characterization at selected catalyst states.
Fig. 6: Near-surface oxygen chemistry in CoOx(OH)y before and after OER conditioning.
Fig. 7: Redox electrochemistry and OER catalytic activity of CoOx(OH)y in a neutral electrolyte.
Fig. 8: Correlation of near-surface chemistry with electrochemical reducibility and catalytic activity.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank S. Rudi, C. Spöri, H. N. Nong, Z. Pawolek, F. Dionigi, E. Hornberger and H. Schmies (Technische Universität Berlin), as well as I. Zaharieva, J. Heitkamp and D. González-Flores (Freie Universität Berlin) for contributing to data collection at the synchrotron radiation sources. We thank S. Carlsson (Max-Lab, Lund, Sweden), J. Drnec (ESRF, Grenoble, France), and M. Mertin and F. Schäfers (Helmholtz-Zentrum Berlin) for excellent technical support at the I811 beamline of Max-Lab, ID31 of ESRF and beamline KMC-1 of BESSY II, Berlin, respectively. We thank Max-Lab, ESRF and ANKA for allocation of the synchrotron radiation beamtime. We thank Höchstleistungsrechenzentrum Stuttgart for computational facilities. We thank R. Loukrakpam for recording transmission electron microscopy micrographs and selected-area electron diffraction patterns at the Zelmi of Technische Universität Berlin. Financial support from the German Federal Ministry of Education and Research through the projects 'MEOKATS' and 'CO2EKAT' is gratefully acknowledged. A.B. acknowledges financial support from the Berlin Graduate School of Natural Sciences and Engineering. T.E.J. thanks the Alexander-von-Humboldt foundation for financial support. P.S., T.R. and D.T. acknowledge financial support from DFG through priority programme SPP1613. P.C. and H.D. gratefully acknowledge financial support from DFG.

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  1. Arno Bergmann

    Present address: Department of Interface Science, Fritz-Haber-Institute of the Max-Planck-Society, Berlin, Germany

Authors and Affiliations

  1. The Electrochemical Energy, Catalysis and Materials Science Laboratory, Department of Chemistry, Technical University Berlin, Berlin, Germany

    Arno Bergmann, Manuel Gliech, Tobias Reier & Peter Strasser

  2. Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Berlin, Germany

    Travis E. Jones & Detre Teschner

  3. Department of Physics, Freie Universität Berlin, Berlin, Germany

    Elias Martinez Moreno, Petko Chernev & Holger Dau

  4. Department of Heterogeneous Reactions, Max-Planck-Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany

    Detre Teschner

  5. Ertl Center for Electrochemistry and Catalysis, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

    Peter Strasser

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Contributions

A.B. prepared all the samples, performed the electrochemical characterization, hard X-ray absorption spectroscopy at Max-Lab and HE-XRD experiments at ESRF, and analysed the data. E.M.M. and P.C. performed the hard X-ray absorption spectroscopy experiments at BESSY II and analysed the corresponding data, D.T. and A.B. performed the XPS and soft X-ray absorption spectroscopy experiments and analysed the data. T.E.J. performed the DFT calculations and wrote parts of the manuscript. M.G. performed the transmission electron microscopy. T.R. performed the scanning electron microscopy and assisted in the X-ray absorption spectroscopy at Max-Lab. A.B., H.D. and P.S. designed the research and experiments and wrote parts of the manuscript.

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Correspondence to Arno Bergmann, Holger Dau or Peter Strasser.

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Bergmann, A., Jones, T.E., Martinez Moreno, E. et al. Unified structural motifs of the catalytically active state of Co(oxyhydr)oxides during the electrochemical oxygen evolution reaction. Nat Catal 1, 711–719 (2018). https://doi.org/10.1038/s41929-018-0141-2

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