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Abstract
The work presented herein focuses on the utilisation and improved understanding of thermoelectrochemistry in the areas of measurement, and the processes and interactions involved.
First an experimental solution was developed consisting of an experimental apparatus, temperature controller and measurement programs that performed some processing of the data. This was capable of the rapid testing of the thermoelectrochemical performance of a wide variety of systems in conditions similar to real world applications.
Then lithium|Li[Tf2N] in tetraglyme was studied. The thermoelectrochemical performance and physicochemical properties were evaluated. These systems were found to have high Seebeck coefficients due to the significant ordering of the glyme around the lithium cation. Importantly, it was determined that an excess of free glyme was required for a large power output.
Subsequently a series of glymes were analysed as solvents for Li[Tf2N]. Only slight differences in the Seebeck coefficients of the systems were observed in the dilute electrolyte cases. This similarity was attributed to comparable entropic contributions from lithium being solvated by a large, coordinating glyme and solvated by several less coordinating ligands. In the ‘solvate ionic liquid’ cases significant differences in the Seebeck coefficients were observed. Additionally, comparisons were made between the Seebeck coefficients, Kamlet-Taft solvent parameters and NMR chemical shifts of the solutions.
On considering lithium intercalation materials as electrodes, it was discovered that the Seebeck coefficient of an asymmetric cell displays a non-linear dependence on the Seebeck coefficients of the individual electrodes which precludes determination of the absolute Seebeck coefficient of an electrode by isothermal measurements of an asymmetric cell. These electrodes were shown to be capable of being charged using heat and subsequently discharged when returned to isothermal conditions. This facilitates a potential application where a device can be powered and charged by body heat, and then run off this stored energy when not worn.
The final system studied was corannulene. It was found that corannulene has a large Seebeck coefficient when in an electrolyte with a small concentration of lithium ions. This was attributed to the lithium cation preferentially interacting with one side of the corannulene anion, preventing the bowl-to-bowl inversion.