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

Peter Reichert, Kasper Skov Kjær, Tim Brandt Van Driel, Julian Mars, Jannis Walther Ochsmann, Diego Pontoni, Moshe Deutsch, Martin Meedom Nielsen, Markus Mezger

Research output: Contribution to journalArticlepeer-review

59 Scopus citations

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.

Original languageEnglish
Pages (from-to)141-157
Number of pages17
JournalFaraday Discussions
Volume206
DOIs
StatePublished - 14 Dec 2017

Bibliographical note

Publisher Copyright:
© 2017 The Royal Society of Chemistry.

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