Correlative operando microscopy of oxygen evolution electrocatalysts

J. Tyler Mefford (), Andrew R. Akbashev, Minkyung Kang, Cameron L. Bentley, William E. Gent, Haitao D. Deng, Daan Hein Alsem, Young-Sang Yu, Norman J. Salmon, David A. Shapiro, Patrick R. Unwin and William C. Chueh ()
Additional contact information
J. Tyler Mefford: Stanford University
Andrew R. Akbashev: Stanford University
Minkyung Kang: University of Warwick
Cameron L. Bentley: University of Warwick
William E. Gent: Stanford University
Haitao D. Deng: Stanford University
Daan Hein Alsem: Hummingbird Scientific
Young-Sang Yu: Lawrence Berkeley National Laboratory
Norman J. Salmon: Hummingbird Scientific
David A. Shapiro: Lawrence Berkeley National Laboratory
Patrick R. Unwin: University of Warwick
William C. Chueh: Stanford University

Nature, 2021, vol. 593, issue 7857, 67-73

Abstract: Abstract Transition metal (oxy)hydroxides are promising electrocatalysts for the oxygen evolution reaction1–3. 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.

Date: 2021
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DOI: 10.1038/s41586-021-03454-x

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