The Zinc/Bromine Flow Battery: Fundamentals and Novel Materials for Technology Advancement

Abstract

Flow batteries are a promising solution for solving intermittency challenges and increasing uptake of renewable power sources such as wind and solar. In particular, zinc/bromine batteries are an attractive option for large-scale electrical energy storage due to their relatively low cost of primary electrolyte and high theoretical specific energy of 440 Wh kg-1. However, inefficient materials of construction hinder practical utilization of this capability and reduce power delivery. The work presented in this thesis aims to overcome these limitations by providing an understanding of the fundamental physical and electrochemical processes governing interactions within the bulk electrolyte and at the electrode–electrolyte interface. Suitable alternative materials to improve system performance are developed via electrochemical investigations, physical characterization and molecular modelling. It is shown that conventional chloride-based supporting electrolytes significantly influence the morphology of zinc electrodeposits generated. High chloride concentration causes removal of zinc from the bulk, causing coulombic losses in the system. It is shown that sulfates, phosphates or even a higher proportion of bromides, are potentially suitable alternatives. Single-halide type tetrahedral zinc complexes exist in conventional electrolytes, and a previously unreported Raman vibrational band at 220 cm-1 is assigned to the [ZnBr2Cl(H2O)]– complex. Ionic liquid additives are proven not to be merely spectators in the zinc half-cell, due to the effects of their chemical structures. Studies using hybrid ionic liquid mixtures indicate that each half-cell benefits from the use of different compounds. It is expected that the approaches and findings presented in this thesis contribute towards aiding and guiding the future search for novel materials to further improve Zn/Br battery technology.