Ingenmey, Johannes Carl Maria: Novel Methods for Molecular and Ionic Liquids : From Fundamentals to Applications as Electrolytes. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Johannes Carl Maria Ingenmey}},
title = {Novel Methods for Molecular and Ionic Liquids : From Fundamentals to Applications as Electrolytes},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = sep,

note = {The trend towards sustainable technologies and processes requires the development of suitable solvents and electrolytes. In this regard, next to traditional molecular solvents, ionic liquids (ILs) are regarded as promising candidates. During the last decades, the continually growing interest in these substances gave rise to a wealth of research directed at their use as designer solvents. Enabling the application-driven design of solvents requires a solid understanding of their dynamics and fundamental structure–property relationships. This thesis aims to contribute to this goal and to describe the development and application of various computational methods to research molecular and ionic liquids.
The first part of the thesis focuses on developing and testing the binary Quantum Cluster Equilibrium method as a general and highly efficient approach to model liquids. The bQCE method applies methods of statistical thermodynamics to quantum chemically optimized clusters in order to obtain a cluster-based model of liquids. In Chapters 3 and 4, the bQCE method is applied to a variety of binary solvent mixtures. Their mixing behaviors and thermodynamic functions can be reproduced with minimal computational effort. Based on these results, an approach is developed to calculate activity coefficients of binary mixtures based on cluster distributions. Furthermore, this thesis documents the extension of the bQCE method from binary to general multi-component mixtures, allowing its future application to complex systems such as solute salts in electrolytes.
The second part of the thesis contains three studies on proton transfer equilibria in ionic, pseudo-ionic, and molecular liquids. In Chapter 5, a computational approach to model proton transfer equilibria based on the bQCE method is developed and applied to a range of alkylammonium-based PILs. It is shown that several properties are affected by the reverse proton transfer reaction. An extreme example of that is explored in Chapter 6. Despite its low ionicity, the pseudo-PIL N-methylimidazolium acetate features a unexpectedly high proton conductivity. By means of ab initio molecular dynamics simulations the underlying mechanism can be explained as a chain transfer reaction resembling Grotthuss diffusion. Based on these results, quantum chemical calculations are performed to find potential candidates for PILs with high proton conductivities. In Chapter 7, the bQCE approach to proton transfer equilibria is applied to aqueous formic acid and acetic acid as case studies. The degree of dissociation can be predicted over the whole mixing range, thus allowing a molecular interpretation of the experimental conductivity maximum in both systems.
The final part of the thesis deals with ion pairing in ILs, which is thought to be a cause for low ionicity. This hypothesis is disputed, however, due to conflicting evidence. Chapter 8 provides a detailed review of experimental and theoretical findings regarding the nature of ion pairing in ILs and extends them by the analysis of ion pair dynamics in 1-butyl-3-methylimidazolium triflate. By the aid of ab initio molecular dynamics and static quantum chemistry, it can be shown that ion pairs are short-lived in this system and its ionicity can be explained by charge transfer between anion and cation. In their practical applications, however, ILs are often solvents for other compounds and discussions of ion pairing must involve not only the its constituent ions but also the solutes. Chapter 9 deals with the ion association of magnesium in an IL-based electrolyte. The coordination of the Mg2+ cation by the anions of the IL prevents its deposition on the electrode and thus reduces reversibility. In a combined experimental and theoretical study, quantum chemical calculations on ionic clusters show that the 18-crown-6 ether can displace the anions and prevent ion association.
In summary, the thesis aims to explore different theoretical approaches to model liquids and liquid phase phenomena. The presented methods are computationally efficient and can be applied to complex systems. In future studies, they can help to establish structure–property relationships for the rational design of novel solvents and electrolytes.},

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