Author: Wendy PellPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
The zinc/bromine battery is a flowing electrolyte battery operating at ambient temperatures, and having both stationary and mobile applications. It is characterized by a flat voltage discharge profile, can be deeply discharged without adverse effects, and is made from low cost materials which can be recycled at the end of the battery's life. The electrochemically active materials are stored externally to the electrode assembly in two reservoirs, and are pumped to the electrodes during operation. The electrolyte typically includes aqueous zinc bromide and quaternary ammonium salts, such as methyl ethyl pyrrolidinium bromide (MEPBr) and methyl ethyl morpholinium bromide (MEMBr) which complex bromine and reduce self-discharge losses. Modification of the low temperature behaviour of the usual electrolyte, which freezes between $-$5 and 5$\sp\circ$C, is required if the battery is to perform successfully at low temperatures. This project identified electrochemical and physical chemical techniques to study zinc deposition and bromine production at glassy carbon electrodes as a method to gain quantitative and qualitative information from the electrolyte system. Electrochemical response, chemical species distribution, conductivity and phase change data were obtained for battery electrolytes at low temperatures and used to identify candidate electrolytes for low temperature applications. The effect of the quaternary ammonium bromide salt on zinc species distribution and zinc deposition has not previously been studied. Spectroscopic and electrochemical studies indicated that the distribution of zinc/bromine complexes in solutions, and zinc deposition at glassy carbon were unaffected by the addition of quaternary ammonium bromides. The distribution of zinc/bromine complexes was significantly affected by temperature and state-of-charge or concentration of the electrolyte. Several organic compounds, including propan-2-ol, ethylene dichloride, propylene glycol and ethylene glycol, were evaluated as additives to the aqueous electrolyte for low temperature applications using techniques of cyclic voltammetry, chronoamperometry, conductivity, and freezing point determination. Ethylene glycol was also selected on the basis of electrochemical and physical chemical data, to be tested in the single cell battery. Due to reduced conductivity of the electrolyte (higher solution resistance in the battery), the voltaic and energy efficiencies were expected to be lower than those of a standard electrolyte battery. Electrochemical experiments showed that neither bromide oxidation nor zinc cation reduction reactions were significantly affected by the presence of ethylene glycol. (Abstract shortened by UMI.).