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

doi:10.1039/c7fd00171a

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

Department of Physics - at Bar-Ilan University

Research output: Contribution to journal › Article › peer-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 language	English
Pages (from-to)	141-157
Number of pages	17
Journal	Faraday Discussions
Volume	206
DOIs	https://doi.org/10.1039/c7fd00171a
State	Published - 14 Dec 2017

Bibliographical note

Publisher Copyright:
© 2017 The Royal Society of Chemistry.

Funding

The expert advice and assistance of Veijo Honkimäki at beamline ID15, ESRF, is gratefully acknowledged. This work was supported by the German-Israeli Foundation for Scientic Research and Development (No. 2306-2310.14/2011). PR and JM are recipients of a fellowship funded through the Excellence Initiative (DFG/ GSC 266). KSK, TBvD, and MMN acknowledge support from the Danish National Research Foundation, the Danish Strategic Research Council through the project ‘ReLiable’, and from DANSCATT. Open Access funding provided by the Max Planck Society.

Funders	Funder number
DANSCATT
Danish Strategic Research Council
Excellence Initiative
Deutsche Forschungsgemeinschaft	/ GSC 266
Danmarks Grundforskningsfond
German-Israeli Foundation for Scientific Research and Development	2306-2310.14/2011

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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.",

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AU - Kjær, Kasper Skov

AU - Brandt Van Driel, Tim

AU - Mars, Julian

AU - Ochsmann, Jannis Walther

AU - Pontoni, Diego

AU - Deutsch, Moshe

AU - Nielsen, Martin Meedom

AU - Mezger, Markus

PY - 2017/12/14

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

Abstract

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