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Resonant anomalous X-ray reflectivity for revealing ion distributions near electrodes

Nature Reviews Physics volume 4, page 743 (2022)Cite this article

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A Publisher Correction to this article was published on 03 November 2022

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Energy storage devices, such as batteries, consist of an electrolyte sandwiched between two charged electrodes through which current can pass. The metal ion organization at the electrode–electrolyte interface, commonly referred to as the electric double layer, determines the efficiency and stability of the device. There are two major challenges with experimentally characterizing the metal ion distribution at the interface. First, it is difficult to observe metal ions without interference from their counterions. Many classical electrochemical techniques, like cyclic voltammetry, can measure the total charge on the electrode but cannot decouple the contributions from the individual ions. Second, ion behaviour in the few-nanometre region of the electrolyte–electrode interface can greatly differ from the bulk, but the experimental signal is dominated by the bulk. Resonant anomalous X-ray reflectivity (RAXR) is an interface-specific technique that can address both of these issues. X-ray reflectivity (XR) uses the penetrating capability of X-rays through the bulk solution to reveal structural information at the interface. Resonant anomalous scattering occurs near an element’s X-ray absorption edge energy, which in turn reveals the element’s coverage and location.

In general, measuring RAXR requires a synchrotron X-ray source. Reflected X-ray signals tend to be small, meaning a beam with high brilliance (flux over area) is necessary to obtain enough signal. A monochromator is needed to vary the incoming beam energy. These requirements are readily met by modern synchrotrons. In principle, any element with an accessible X-ray absorption edge energy can be measured by RAXR. Modern synchrotrons can readily access ~10–100 keV beam energies, depending on the specific hardware and optics.

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Acknowledgements

The author thanks A. Uysal and S. S. Lee for their assistance and guidance. This project is funded by the US Department of Energy, Office of Basic Science, Division of Chemical Sciences, Geosciences, and Biosciences Early Career Research programme under contract DE-AC02-06CH11357 to UChicago, Argonne, LLC as operator of Argonne National Laboratory.

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  1. Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL, USA

    Amanda J. Carr

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  1. Amanda J. Carr
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Correspondence to Amanda J. Carr.

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Carr, A.J. Resonant anomalous X-ray reflectivity for revealing ion distributions near electrodes. Nat Rev Phys 4, 743 (2022). https://doi.org/10.1038/s42254-022-00519-2

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  • DOI: https://doi.org/10.1038/s42254-022-00519-2

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