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The Structure of the Electric Double Layer of the Protic Ionic Liquid [Dema][TfO] Analyzed by Atomic Force Spectroscopy. Int J Mol Sci 2021; 22:ijms222312653. [PMID: 34884462 PMCID: PMC8658030 DOI: 10.3390/ijms222312653] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 11/17/2021] [Accepted: 11/18/2021] [Indexed: 12/05/2022] Open
Abstract
Protic ionic liquids are promising electrolytes for fuel cell applications. They would allow for an increase in operation temperatures to more than 100 °C, facilitating water and heat management and, thus, increasing overall efficiency. As ionic liquids consist of bulky charged molecules, the structure of the electric double layer significantly differs from that of aqueous electrolytes. In order to elucidate the nanoscale structure of the electrolyte–electrode interface, we employ atomic force spectroscopy, in conjunction with theoretical modeling using molecular dynamics. Investigations of the low-acidic protic ionic liquid diethylmethylammonium triflate, in contact with a platinum (100) single crystal, reveal a layered structure consisting of alternating anion and cation layers at the interface, as already described for aprotic ionic liquids. The structured double layer depends on the applied electrode potential and extends several nanometers into the liquid, whereby the stiffness decreases with increasing distance from the interface. The presence of water distorts the layering, which, in turn, significantly changes the system’s electrochemical performance. Our results indicate that for low-acidic ionic liquids, a careful adjustment of the water content is needed in order to enhance the proton transport to and from the catalytic electrode.
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Abstract
This short overview describes the historical development of the physics and chemistry of organic solvents and solutions from the alchemist era until the present time based on some carefully selected examples that can be considered landmarks in the history of solution chemistry.
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Affiliation(s)
- Christian Reichardt
- Fachbereich Chemie, Philipps-Universität, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
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Rauber D, Philippi F, Kuttich B, Becker J, Kraus T, Hunt P, Welton T, Hempelmann R, Kay CWM. Curled cation structures accelerate the dynamics of ionic liquids. Phys Chem Chem Phys 2021; 23:21042-21064. [PMID: 34522943 DOI: 10.1039/d1cp02889h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ionic liquids are modern liquid materials with potential and actual implementation in many advanced technologies. They combine many favourable and modifiable properties but have a major inherent drawback compared to molecular liquids - slower dynamics. In previous studies we found that the dynamics of ionic liquids are significantly accelerated by the introduction of multiple ether side chains into the cations. However, the origin of the improved transport properties, whether as a result of the altered cation conformation or due to the absence of nanostructuring within the liquid as a result of the higher polarity of the ether chains, remained to be clarified. Therefore, we prepared two novel sets of methylammonium based ionic liquids; one set with three ether substituents and another set with three butyl side chains, in order to compare their dynamic properties and liquid structures. Using a range of anions, we show that the dynamics of the ether-substituted cations are systematically and distinctly accelerated. Liquefaction temperatures are lowered and fragilities increased, while at the same time cation-anion distances are slightly larger for the alkylated samples. Furthermore, pronounced liquid nanostructures were not observed. Molecular dynamics simulations demonstrate that the origin of the altered properties of the ether substituted ionic liquids is primarily due to a curled ether chain conformation, in contrast to the alkylated cations where the alkyl chains retain a linear conformation. Thus, the observed structure-property relations can be explained by changes in the geometric shape of the cations, rather than by the absence of a liquid nanostructure. Application of quantum chemical calculations to a simplified model system revealed that intramolecular hydrogen-bonding is responsible for approximately half of the stabilisation of the curled ether-cations, whereas the other half stems from non-specific long-range interactions. These findings give more detailed insights into the structure-property relations of ionic liquids and will guide the development of ionic liquids that do not suffer from slow dynamics.
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Affiliation(s)
- Daniel Rauber
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany.
| | - Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK
| | - Björn Kuttich
- INM-Leibniz Institute for New Materials, Campus D2.2, 66123, Saarbrücken, Germany
| | - Julian Becker
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK
| | - Tobias Kraus
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany. .,INM-Leibniz Institute for New Materials, Campus D2.2, 66123, Saarbrücken, Germany
| | - Patricia Hunt
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK.,School of Chemical and Physical Sciences, Victoria University of Wellington, New Zealand
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, UK
| | - Rolf Hempelmann
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany.
| | - Christopher W M Kay
- Department of Chemistry, Saarland University, Campus B2.2, 66123, Saarbrücken, Germany. .,London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK.
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González-Veloso I, Figueiredo NM, Cordeiro MNDS. Unravelling the Interactions of Magnetic Ionic Liquids by Energy Decomposition Schemes: Towards a Transferable Polarizable Force Field. Molecules 2021; 26:molecules26185526. [PMID: 34576997 PMCID: PMC8466702 DOI: 10.3390/molecules26185526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 09/07/2021] [Accepted: 09/08/2021] [Indexed: 11/16/2022] Open
Abstract
This work aims at unravelling the interactions in magnetic ionic liquids (MILs) by applying Symmetry-Adapted Perturbation Theory (SAPT) calculations, as well as based on those to set-up a polarisable force field model for these liquids. The targeted MILs comprise two different cations, namely: 1-butyl-3-methylimidazolium ([Bmim]+) and 1-ethyl-3-methylimidazolium ([Emim]+), along with several metal halides anions such as [FeCl4]−, [FeBr4]−, [ZnCl3]− and [SnCl4]2− To begin with, DFT geometry optimisations of such MILs were performed, which in turn revealed that the metallic anions prefer to stay close to the region of the carbon atom between the nitrogen atoms in the imidazolium fragment. Then, a SAPT study was carried out to find the optimal separation of the monomers and the different contributions for their interaction energy. It was found that the main contribution to the interaction energy is the electrostatic interaction component, followed by the dispersion one in most of the cases. The SAPT results were compared with those obtained by employing the local energy decomposition scheme based on the DLPNO-CCSD(T) method, the latter showing slightly lower values for the interaction energy as well as an increase of the distance between the minima centres of mass. Finally, the calculated SAPT interaction energies were found to correlate well with the melting points experimentally measured for these MILs.
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Markiewicz R, Klimaszyk A, Jarek M, Taube M, Florczak P, Kempka M, Fojud Z, Jurga S. Influence of Alkyl Chain Length on Thermal Properties, Structure, and Self-Diffusion Coefficients of Alkyltriethylammonium-Based Ionic Liquids. Int J Mol Sci 2021; 22:5935. [PMID: 34073046 PMCID: PMC8198313 DOI: 10.3390/ijms22115935] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 05/24/2021] [Accepted: 05/25/2021] [Indexed: 12/13/2022] Open
Abstract
The application of ionic liquids (ILs) has grown enormously, from their use as simple solvents, catalysts, media in separation science, or electrolytes to that as task-specific, tunable molecular machines with appropriate properties. A thorough understanding of these properties and structure-property relationships is needed to fully exploit their potential, open new directions in IL-based research and, finally, properly implement the appropriate applications. In this work, we investigated the structure-properties relationships of a series of alkyltriethylammonium bis(trifluoromethanesulfonyl)imide [TEA-R][TFSI] ionic liquids in relation to their thermal behavior, structure organization, and self-diffusion coefficients in the bulk state using DSC, FT-IR, SAXS, and NMR diffusometry techniques. The phase transition temperatures were determined, indicating alkyl chain dependency. Fourier-transformed infrared spectroscopy studies revealed the structuration of the ionic liquids along with alkyl chain elongation. SAXS experiments clearly demonstrated the existence of polar/non-polar domains. The alkyl chain length influenced the expansion of the non-polar domains, leading to the expansion between cation heads in polar regions of the structured IL. 1H NMR self-diffusion coefficients indicated that alkyl chain elongation generally caused the lowering of the self-diffusion coefficients. Moreover, we show that the diffusion of anions and cations of ILs is similar, even though they vary in their size.
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Affiliation(s)
- Roksana Markiewicz
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
| | - Adam Klimaszyk
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
- Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego str. 2, 61-614 Poznań, Poland; (M.T.); (Z.F.)
| | - Marcin Jarek
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
| | - Michał Taube
- Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego str. 2, 61-614 Poznań, Poland; (M.T.); (Z.F.)
| | - Patryk Florczak
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
| | - Marek Kempka
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
- Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego str. 2, 61-614 Poznań, Poland; (M.T.); (Z.F.)
| | - Zbigniew Fojud
- Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego str. 2, 61-614 Poznań, Poland; (M.T.); (Z.F.)
| | - Stefan Jurga
- NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej str. 3, 61-614 Poznań, Poland; (M.J.); (P.F.); (M.K.); (S.J.)
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Koutsoukos S, Philippi F, Malaret F, Welton T. A review on machine learning algorithms for the ionic liquid chemical space. Chem Sci 2021; 12:6820-6843. [PMID: 34123314 PMCID: PMC8153233 DOI: 10.1039/d1sc01000j] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 04/28/2021] [Indexed: 01/05/2023] Open
Abstract
There are thousands of papers published every year investigating the properties and possible applications of ionic liquids. Industrial use of these exceptional fluids requires adequate understanding of their physical properties, in order to create the ionic liquid that will optimally suit the application. Computational property prediction arose from the urgent need to minimise the time and cost that would be required to experimentally test different combinations of ions. This review discusses the use of machine learning algorithms as property prediction tools for ionic liquids (either as standalone methods or in conjunction with molecular dynamics simulations), presents common problems of training datasets and proposes ways that could lead to more accurate and efficient models.
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Affiliation(s)
- Spyridon Koutsoukos
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Frederik Philippi
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
| | - Francisco Malaret
- Department of Chemical Engineering, Imperial College London South Kensington Campus London SW7 2AZ UK
| | - Tom Welton
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London White City Campus London W12 0BZ UK
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