Year: 2015
Type: dissertation
Abstract: The Zinc Bromide Redox Flow Battery (ZBB) has been proposed as a promising storage technology for intermediating renewable energy supplies (e.g., intermittent wind and solar) and the demands of the electricity grid. While the ZBB is nearing commercial reality, a number of known limitations face its widespread operation, namely the sequestration of volatile bromine on one half-cell, and complications regarding the electrodeposition of zinc at the other half-cell. In this thesis, the fundamental chemistry underlying the operation of the ZBB was studied in detail, applying insights and techniques from the growing research area of ionic liquids, via spectroscopic, structural, computational and voltammetric methods. Studies of the interactions between IL bromide salts and their polybromide addition products revealed design parameters for the targeted design of bromine sequestration agents (BSA), which are required for the safe sequestration of bromine during the operation of the ZBB. Through understanding of the self-assembly of bromide salts in solution, to the manner of which H…Br interactions influence the relative strength of association and structure of growing polybromides, it was found that weakly associating cations resulted in the preferential formation of higher polybromides. These insights were used to examine the potential of a weakly associated bromide salt for the sequestration of high-order polybromides in an all-IL system. A room temperature IL (RTIL) mixture was shown to be a robust solvent medium for the sequestration of high-order polybromides from large excesses of bromine. The growth of pentabromide to undecabromide anions were identified spectroscopically, while a [Br24]2- dianion ¬(the largest polybromide species reported to date) was isolated from one of these reaction mixtures. This finding has potential for increasingly energy dense electrolytes for future designs of bromine-containing redox cells. However, the application of some of the salts screened early in this thesis proved to be non-ideal for application as battery electrolytes due to the precipitation of bromozincate salts from the mixture of zinc bromide and IL bromide salts in water. This complexation of bromozincate species was shown to influence the voltammetry of the Zn/Zn(II) redox couple, demonstrating an unfavourable influence of complexation on the current magnitude, reversibility and cyclability of zinc deposition. Herein, ionic liquid cations with lower aliphatic character were shown to be favourable agents for use in an aqueous flow battery system due to their lessened influence on free zinc deposition. This thesis describes the approach, methodology and outcomes of new research designed to understand the chemistry underlying that of the ZBB. The work contained herein has contributed to zinc, bromine and polybromide chemistry on a fundamental level, as well as providing important information for the directed engineering of future battery electrolytes. Further outcomes include strengthening the targeted role of ionic liquids in synthetic polybromide chemistry and understanding the intricacies of zinc deposition from aqueous environments, as has been applied to ZBB test cells to yield improvements in operational efficiencies.
Author: Max E. Easton
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2237506153