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Correlative operando microscopy of oxygen evolution electrocatalysts

Abstract

Transition metal (oxy)hydroxides are promising electrocatalysts for the oxygen evolution reaction1,2,3. The properties of these materials evolve dynamically and heterogeneously4 with applied voltage through ion insertion redox reactions, converting materials that are inactive under open circuit conditions into active electrocatalysts during operation5. The catalytic state is thus inherently far from equilibrium, which complicates its direct observation. Here, using a suite of correlative operando scanning probe and X-ray microscopy techniques, we establish a link between the oxygen evolution activity and the local operational chemical, physical and electronic nanoscale structure of single-crystalline β-Co(OH)2 platelet particles. At pre-catalytic voltages, the particles swell to form an α-CoO2H1.5·0.5H2O-like structure—produced through hydroxide intercalation—in which the oxidation state of cobalt is +2.5. Upon increasing the voltage to drive oxygen evolution, interlayer water and protons de-intercalate to form contracted β-CoOOH particles that contain Co3+ species. Although these transformations manifest heterogeneously through the bulk of the particles, the electrochemical current is primarily restricted to their edge facets. The observed Tafel behaviour is correlated with the local concentration of Co3+ at these reactive edge sites, demonstrating the link between bulk ion-insertion and surface catalytic activity.

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Fig. 1: Mass loading and scan-rate-dependent electrochemistry of β-Co(OH)2.
Fig. 2: SECCM of bulk redox transformations and OER activity of β-Co(OH)2 particles.
Fig. 3: Operando EC-AFM of a β-Co(OH)2 particle.
Fig. 4: Operando STXM of β-Co(OH)2 particles.
Fig. 5: Correlations between Co oxidation state at the edge of the particles and OER activity.

Data availability

The experimental data that support the findings of this study are available in ref. 31.

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Acknowledgements

J.T.M., A.R.A., W.E.G. and W.C.C. acknowledge funding provided by the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (contract no. DE-AC0276SF00515). C.L.B. acknowledges financial support from the Ramsay Memorial Fellowship Trust. Both M.K. and P.R.U. acknowledge support from Warwick-Monash Alliance Accelerator funding. Separately, P.R.U. acknowledges support from a Royal Society Wolfson Research Merit Award. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF)/Stanford Nano-fabrication Facility (SNF), supported by the National Science Foundation under award ECCS-1542152. D.H.A. and N.J.S. acknowledge support from the DOE Office of Basic Energy Sciences SBIR program under awards DE-SC-0007691 and DE-SC-0009573. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. We thank J. Lim, S. B. Kalirai, C. Baeumer, L. Zhang, Y.-L. Liang and C. E. D. Chidsey for discussions and assistance with the experiments.

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Contributions

J.T.M. and W.C.C. developed the concept of the experiments, J.T.M. performed the synthesis, STXM, UV–vis, EQCM, RDE, SEM and XRD experiments. A.R.A. performed the EC-AFM and TEM experiments. P.R.U., M.K. and C.L.B. designed and performed the SECCM experiments. W.E.G. wrote the principal components analysis and non-negative matrix factorization code for the STXM data analysis. H.D.D. performed the EC-AFM image alignment. D.H.A. and N.J.S. designed and fabricated the STXM cell. Y.-S.Y. and D.A.S. assisted with the STXM experiments. All authors contributed to the discussion of the results and writing of the manuscript.

Corresponding authors

Correspondence to J. Tyler Mefford or William C. Chueh.

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Competing interests

D.H.A. and N.J.S. are employed by Hummingbird Scientific, which designed and manufactured the STXM microfluidic liquid cell used in these experiments.

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Peer review information Nature thanks Shannon Boettcher, Marcel Risch and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Mefford, J.T., Akbashev, A.R., Kang, M. et al. Correlative operando microscopy of oxygen evolution electrocatalysts. Nature 593, 67–73 (2021). https://doi.org/10.1038/s41586-021-03454-x

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