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Kilchert F, Lorenz M, Schammer M, Nürnberg P, Schönhoff M, Latz A, Horstmann B. A volume-based description of transport in incompressible liquid electrolytes and its application to ionic liquids. Phys Chem Chem Phys 2023; 25:25965-25978. [PMID: 37646123 DOI: 10.1039/d2cp04423d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
Transference numbers play an important role in understanding the dynamics of electrolytes and assessing their performance in batteries. Unfortunately, these transport parameters are difficult to measure in highly concentrated liquid electrolytes such as ionic liquids. Also, the interpretation of their sign and magnitude has provoked an ongoing debate in the literature further complicated by the use of different languages. In this work, we highlight the role of the reference frame for the interpretation of transport parameters using our novel thermodynamically consistent theory for highly correlated electrolytes. We argue that local volume conservation is a key principle in incompressible liquid electrolytes and use the volume-based drift velocity as a reference. We apply our general framework to electrophoretic NMR experiments. For ionic liquid based electrolytes, we find that the results of the eNMR measurements can be best described using this volume-based description. This highlights the limitations of the widely used center-of-mass reference frame which for example forms the basis for molecular dynamics simulations - a standard tool for the theoretical calculation of transport parameters. It shows that the assumption of local momentum conservation is incorrect in those systems on the macroscopic scale.
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Affiliation(s)
- Franziska Kilchert
- German Aerospace Center, Wilhelm-Runge-Straße 10, 89081 Ulm, Germany.
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
| | - Martin Lorenz
- University of Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Max Schammer
- German Aerospace Center, Wilhelm-Runge-Straße 10, 89081 Ulm, Germany.
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
| | - Pinchas Nürnberg
- University of Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Monika Schönhoff
- University of Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Arnulf Latz
- German Aerospace Center, Wilhelm-Runge-Straße 10, 89081 Ulm, Germany.
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
- Ulm University, Albert-Einstein-Allee 47, 89081 Ulm, Germany
| | - Birger Horstmann
- German Aerospace Center, Wilhelm-Runge-Straße 10, 89081 Ulm, Germany.
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
- Ulm University, Albert-Einstein-Allee 47, 89081 Ulm, Germany
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Lorenz M, Kilchert F, Nürnberg P, Schammer M, Latz A, Horstmann B, Schönhoff M. Local Volume Conservation in Concentrated Electrolytes Is Governing Charge Transport in Electric Fields. J Phys Chem Lett 2022; 13:8761-8767. [PMID: 36102654 DOI: 10.1021/acs.jpclett.2c02398] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
While ion transport processes in concentrated electrolytes, e.g., based on ionic liquids (IL), are a subject of intense research, the role of conservation laws and reference frames is still a matter of debate. Employing electrophoretic NMR, we show that momentum conservation, a typical prerequisite in molecular dynamics (MD) simulations, is not governing ion transport. Involving density measurements to determine molar volumes of distinct ion species, we propose that conservation of local molar species volumes is the governing constraint for ion transport. The experimentally quantified net volume flux is found to be zero, implying a nonzero local momentum flux, as tested in pure ILs and IL-based electrolytes for a broad variety of concentrations and chemical compositions. This constraint is consistent with incompressibility, but not with a local application of momentum conservation. The constraint affects the calculation of transference numbers as well as comparisons of MD results to experimental findings.
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Affiliation(s)
- Martin Lorenz
- Institute of Physical Chemistry, University of Münster, Corrensstrasse 28/30, 48149 Münster, Germany
| | - Franziska Kilchert
- German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
| | - Pinchas Nürnberg
- Institute of Physical Chemistry, University of Münster, Corrensstrasse 28/30, 48149 Münster, Germany
| | - Max Schammer
- German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
| | - Arnulf Latz
- German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
- Universität Ulm, Albert-Einstein-Allee 47, 89081 Ulm, Germany
| | - Birger Horstmann
- German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
- Helmholtz Institute Ulm, Helmholtzstraße 11, 89081 Ulm, Germany
- Universität Ulm, Albert-Einstein-Allee 47, 89081 Ulm, Germany
| | - Monika Schönhoff
- Institute of Physical Chemistry, University of Münster, Corrensstrasse 28/30, 48149 Münster, Germany
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