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Volume 206, 2018
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Molecular scale structure and dynamics at an ionic liquid/electrode interface

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Abstract

After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion–ion correlations dominating the liquid bulk structure. The relaxation dynamics of the interfacial structure upon charging/discharging were studied by impedance spectroscopy and time resolved X-ray reflectivity experiments with sub-millisecond resolution. The analysis revealed three relaxation processes of vastly different characteristic time scales: a 2 ms scale interface-normal ion transport, a 100 ms scale molecular reorientation, and a minute scale lateral ordering within the first layer.

Graphical abstract: Molecular scale structure and dynamics at an ionic liquid/electrode interface

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Publication details

The article was received on 15 May 2017, accepted on 27 Jun 2017 and first published on 27 Jun 2017


Article type: Paper
DOI: 10.1039/C7FD00171A
Citation: Faraday Discuss., 2018,206, 141-157
  • Open access: Creative Commons BY license
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    Molecular scale structure and dynamics at an ionic liquid/electrode interface

    P. Reichert, K. S. Kjær, T. Brandt van Driel, J. Mars, J. W. Ochsmann, D. Pontoni, M. Deutsch, M. M. Nielsen and M. Mezger, Faraday Discuss., 2018, 206, 141
    DOI: 10.1039/C7FD00171A

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