Abstract
In this project the preparation of the electrolyte for the all
vanadium redox flow battery was investigated using both chemical and
electrolytic reduction of ^O,- powder. Oxalic acid and SO^ reduction
were found to be unsuitable as only the V(IV) state could be produced
directly. With suspended powder hydrolysis, however, vanadium
sulphate of any oxidation state, in this case 50% V(IV) plus 50%
V(III) in sulphuric acid can readily be prepared from V^O^ powder,
thus allowing a significant reduction in the cost of the vanadium
battery electrolyte.
Results from conductivity and electrolyte stability tests at
elevated temperature have led to modification of the electrolyte
composition for the vanadium redox cell, from the 2 M V plus 2 M
H^SO^, originally employed, to the use of 3 M H^SO^, much higher
energy efficiencies and greater electrolyte stability was demonstrated
with the 3 M H^SO^ supporting electrolyte.
Spectroscopy and electrolyte conductivity have been demonstrated
as suitable techniques for state-of-charge monitoring.
A number of electrode materials were also evaluated and a Toray
graphite bonded to a carbon plastic electrode was selected for further
prototype development. Energy efficiencies of between 83 and 86% were
obtained for a current density of 30 mA/cm for a temperature range 5
to 45'C, and between 0 and 100% state-of-charge.
A wide range of construction materials was tested for long term
stability in the vanadium redox electrolyte.