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Atomic-scale insights into surface species of electrocatalysts in three dimensions


The topmost atomic layers of electrocatalysts determine the mechanism and kinetics of reactions in many important industrial processes, such as water splitting, chlor-electrolysis or fuel cells. Optimizing the performance of electrocatalysts requires a detailed understanding of surface-state changes during the catalytic process, ideally at the atomic scale. Here, we use atom probe tomography to reveal the three-dimensional structure of the first few atomic layers of electrochemically grown iridium oxide, an efficient electrocatalyst for the oxygen evolution reaction. We unveil the formation of confined, non-stoichiometric Ir–O species during oxygen evolution. These species gradually transform to IrO2, providing improved stability but also a decrease in activity. Additionally, electrochemical growth of oxide in deuterated solutions allowed us to trace hydroxy-groups and water molecules present in the regions of the oxide layer that are favourable for the oxygen evolution and iridium dissolution reactions. Overall, we demonstrate how tomography with near-atomic resolution advances the understanding of complex relationships between surface structure, surface state and function in electrocatalysis.

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Fig. 1: Activity and stability of electrochemically formed Ir oxides and their surface electronic state.
Fig. 2: Schematic of the sample and edge-on surface oxide morphology of Ir after exposure to anodic oxidation for 69 h.
Fig. 3: APT data of as-deposited Ir film and Ir oxides formed by anodic oxidation for 4 h, 69 h and 120 h.
Fig. 4: Schematic representation of the gradual changes observed during anodic polarization of Ir under OER conditions.

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T.L. and O.K. acknowledge the Alexander von Humboldt Foundation. S.Z. and C.S thank the German Science Foundation within the Priority Programme SPP 1613 (DFG SCHE 634/12-2).

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Authors and Affiliations



K.J.J.M. and B.G. initiated the project. O.K. prepared Ir oxide films, performed the electrochemical and XPS measurements and carried out data analysis. T.L. prepared the APT and TEM samples, conducted the APT experiment and analysed the APT data. S.Z. carried out the TEM experiment. T.L, O.K., B.G., S.C., D.R. and K.J.J.M. wrote the paper. All authors discussed the results and their interpretation.

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Correspondence to B. Gault or K. J. J. Mayrhofer.

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Supplementary Notes 1–6, Supplementary Figures 1–8, Supplementary Table 1, Supplementary References

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Li, T., Kasian, O., Cherevko, S. et al. Atomic-scale insights into surface species of electrocatalysts in three dimensions. Nat Catal 1, 300–305 (2018).

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