Molecular scale structure and dynamics at an ionic liquid/electrode interface. (29th September 2017)

• Record Type: Journal Article
• Authors: Reichert, Peter; Kjær, Kasper Skov; Brandt van Driel, Tim; Mars, Julian; Ochsmann, Jannis Walther; Pontoni, Diego; Deutsch, Moshe; Nielsen, Martin Meedom; Mezger, Markus
• Is Part Of: Faraday discussions. Volume 206(2018)
• Page Start: 141
• Page End: 157
• Publication Date: 2017-09-29
• Subjects: Chemistry -- Periodicals; Metallurgy -- Periodicals; Electrochemistry -- Periodicals; 540
• DOI: 10.1039/c7fd00171a
• Languages: English
• ISSNs: 1359-6640

Abstract

Abstract : The structural arrangement and dynamics of ions near the IL/electrode interface during charging and discharging was studied by a combination of time resolved X-ray reflectivity and impedance spectroscopy. 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.