Investigating the electronic structure of ionic liquids: a combined eperimental and computational study
File(s)
Author(s)
Fogarty, Richard
Type
Thesis
Abstract
Ionic liquids (ILs) are promising materials for a broad range of applications:
electrolytes in batteries and supercapacitors, materials for gas separation and
solvents for catalysis. However, realisation of the full potential of ILs is hindered
by a lack of understanding in how varying IL composition (the identity of the ions)
affects physical properties. Multiple key IL properties are determined by
electronic structure, including reactivity, electrochemical window and interactions
with light. Therefore understanding IL electronic structure is an essential step
towards the rational design of ILs. The ability of small model systems to capture bulk IL electronic structure is
investigated by combining ab initio calculations with X-ray spectroscopy
(Chapter 4). Single ions surrounded by a (computationally cheap) solvent
continuum model are demonstrated to be capable of capturing bulk IL electronic
structure. Chapter 4 also contains an investigation into how intermolecular
interactions affect the electronic structure of ions in ILs, with particular focus on
molecular orbital (MO) energies.
Water will be present at significant concentrations in many IL applications,
therefore it is important to understand the effects of water on IL properties. The
effects of water on IL electronic structure are investigated by combining
photoelectron spectroscopy with calculations (Chapter 5). Water significantly
stabilises anionic MOs, which is rationalised in terms of dielectric constants.
Interactions in IL:water mixtures are investigated using a range of computational
methodologies, including natural bond orbital (NBO) and atoms in molecules
(AIM) analyses.
Charge distribution, often represented by atomic charges, is an important aspect
of IL electronic structure. However, different methods for calculating atomic
charges lead to qualitatively different charge distributions. Chapter 6 focuses on
determining the most suitable charge assignment method by using results from
X-ray spectroscopy to validate calculated charges.
electrolytes in batteries and supercapacitors, materials for gas separation and
solvents for catalysis. However, realisation of the full potential of ILs is hindered
by a lack of understanding in how varying IL composition (the identity of the ions)
affects physical properties. Multiple key IL properties are determined by
electronic structure, including reactivity, electrochemical window and interactions
with light. Therefore understanding IL electronic structure is an essential step
towards the rational design of ILs. The ability of small model systems to capture bulk IL electronic structure is
investigated by combining ab initio calculations with X-ray spectroscopy
(Chapter 4). Single ions surrounded by a (computationally cheap) solvent
continuum model are demonstrated to be capable of capturing bulk IL electronic
structure. Chapter 4 also contains an investigation into how intermolecular
interactions affect the electronic structure of ions in ILs, with particular focus on
molecular orbital (MO) energies.
Water will be present at significant concentrations in many IL applications,
therefore it is important to understand the effects of water on IL properties. The
effects of water on IL electronic structure are investigated by combining
photoelectron spectroscopy with calculations (Chapter 5). Water significantly
stabilises anionic MOs, which is rationalised in terms of dielectric constants.
Interactions in IL:water mixtures are investigated using a range of computational
methodologies, including natural bond orbital (NBO) and atoms in molecules
(AIM) analyses.
Charge distribution, often represented by atomic charges, is an important aspect
of IL electronic structure. However, different methods for calculating atomic
charges lead to qualitatively different charge distributions. Chapter 6 focuses on
determining the most suitable charge assignment method by using results from
X-ray spectroscopy to validate calculated charges.
Version
Open Access
Date Issued
2017-08
Date Awarded
2018-03
Advisor
Hunt, Patricia
Lovelock, Kevin
Welton, Tom
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)