Thesis
Capacitive hysteresis studies of imidazolium triflate Ionic Liquids
University of Iowa
Master of Science (MS), University of Iowa
Spring 2021
DOI: 10.17077/etd.005929
Abstract
A comprehensive understanding of the electrochemical double layer (EDL) structure at the solid-liquid interface and its charge transfer processes can advance their use in heterogeneous electrocatalysis and energy storage devices such as batteries, electrochemical double-layer capacitors (EDLCs) or commonly known as ‘supercapacitors’. To increase the energy densities of such devices, Ionic Liquids (ILs) are promising replacements for traditional electrochemical solvents owing to their wide electrochemical stability windows. Moreover, ILs' non-volatility, non-flammability, and high thermal stability are added advantages. The processes of energy storage and delivery of supercapacitors are related to the EDL structure developed when the system is charged. However, the understanding of the IL EDL structure is still emerging as the interfacial structure formed by the IL near the electrode when potentials are applied is still unknown. Structural information on the electrochemical double layer may be obtained via capacitance measurements, as interfacial capacitance describes the variation of charge density at the interface with respect to the applied potential. Applying such tests to IL EDL systems, we find that IL systems’ capacitance-potential curves exhibit a wide variety of shapes, such as bell-shaped, camel-shaped, U-shaped, or featureless responses, even for the same chemical system.
Because the capacitance-potential curvature can be significantly affected by experimental parameters such as potential scan direction, potential range probed, the data acquisition protocol, potential perturbation rate, and electrochemical technique used, this thesis focuses on evaluating the capacitance changes arising from these different experimental parameters. It, therefore, provides a basis for the systematic collection of reproducible capacitance data.
We also take steps toward the design of IL supercapacitors. In making such designs, it is critical to understand both the energy-related properties of the IL system (i.e., capacitance and energy density) and its mass transport properties (i.e., viscosity, ionic conductivity, diffusion coefficients, etc.). As physicochemical properties of ILs can be tuned via combinations of cations and anions, it is crucial to explore the relationship of physicochemical properties of ILs to the molecular structure. Therefore, in this thesis, we investigate the variation of charge behavior and transport properties of ILs containing a range of imidazolium cations with varying alkyl tail lengths.
The electrochemical studies described in this thesis demonstrate systematic methods in collecting reproducible capacitance data and suggest a basis for the energy and transport properties of ILs in designing EDLCs.
Details
- Title: Subtitle
- Capacitive hysteresis studies of imidazolium triflate Ionic Liquids
- Creators
- Niroodha Rathnamaali Pitawela
- Contributors
- Scott K Shaw (Advisor)Mark A Arnold (Committee Member)Elizabeth A Stone (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2021
- DOI
- 10.17077/etd.005929
- Publisher
- University of Iowa
- Number of pages
- xv, 124 pages
- Copyright
- Copyright 2021 Niroodha Rathnamaali Pitawela
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 100-114)
- Public Abstract (ETD)
Fast-charging energy storage and delivery systems are the need of the hour. Batteries are well known as good energy storage devices, yet they deliver energy slowly compared to capacitors. Hence, capacitors are alternative energy storage systems to batteries if their energy storage ability is improved. However, an understanding of the mechanism of action of these processes (i.e., energy storage/release) is still underway.
An interface, a boundary separating two phases of matter, each of which may be solid, liquid, or gas, is where these processes occur. Some of the other common processes such as corrosion, catalysis, evaporation of liquids, adsorption of gases on metals, and lubrication often occur at interfaces on a daily basis even without our notice. The speed of energy storage and release is governed by how molecules arrange at the boundary of liquid electrolyte and solid electrode, and the microscopic dimensions of such 'boundaries' make these studies more complicated. Improved knowledge on interfaces would create a breakthrough in advancing such technology. My research focuses on studying the boundary between the solid and the liquid using electrochemistry.
The solvent-free liquid salts known as Ionic Liquids have attracted much attention to use in capacitors and batteries. I study how molecules of a pure liquid salt behave near a solid metal electrode. My results aim to provide a way of collecting experimental data with minimum variability even under varied experimental conditions. These results will help scientists to collect reproducible experimental data with better comparisons, leading to reliable chargeable devices.
One key parameter in optimizing the performance of such devices is the amount of energy storage provided by different salt systems, and my results provide the basis for such a comparison.
- Academic Unit
- Chemistry
- Record Identifier
- 9984096974402771
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