Electrolytes for redox flow battery systems
Date
2010-03
Authors
Modiba, Portia
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Electrochemical behaviour of Ce, Fe, Cr,V and Mn in the presence of DTPA, EDTA, EDDS,
NTA ligands were investigated by using cyclic voltammetry, a rotating disc electrode and
electrochemical impedance spectroscopy for use in redox flow battery (RFB) systems. RFB is
currently used for energy storage, the vanadium, which is used in most of the RFB’s, however
suffers from species crossover and sluggish reactions, which limit the lifetime of the battery.
These various ligands and metal complexes mentioned above where all examined to identify
the suitable and favoured electrolyte that can be used for a RFB system.
Kinetic parameters such as potential, limiting current, transfer coefficient, diffusion
coefficients, and rate constants were studied. RDE experiments confirmed that the parameters
measured by CV are similar under hydrodynamic conditions and can be used to determine the
kinetic parameters of the redox couples. The use of DTPA as a ligand for complexation of
Ce(IV) gave more favourable results compared to other ligand with various metal complexes
used in this study [1-3]. The results of kinetic studies of Ce(IV)–DTPA complex shows
promise as an electrolyte for a redox flow battery.
The separation of V(IV)/(V), Fe (III)/(IV),Cr(III)/(IV),Mn (III)/(IV) and Ce(III)/(IV) with
various ligands (EDTA, EDDS, NTA and DTPA) were also investigated using capillary
electrophoresis. To understand the speciation of these metal complexes as used in this study
and particularly the vanadium, for the reason that it has a complicated (V) oxidation state. The
charge/discharge performance of all electrolytes used in this work was determined and a high
voltage achieved when Ce-DTPA was used, and it is compared to that of the vanadium
electrolyte currently in use. This was evaluated with systems studied previously. Therefore,
Ce-DTPA will be a suitable electrolyte for redox flow battery systems.
Description
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010.
Keywords
Electrolytes, Redox flow battery, Cyclic voltammetry, Dissertations -- Chemistry, Theses -- Chemistry