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Abstract
The all-vanadium redox flow cell is proposed as an alternative
energy storage system, utilising the vanadium (II)/vanadium(III) and
vanadium (IV)/(V) redox couples for the negative and positive half
cells, respectively.
Single redox flow cells with an active electrode area of up to
200 cm2 were constructed and their performance characteristics evaluated
employing various electrode and membrane materials. Of the
electrode materials evaluated graphite felt (RVG, Le-Carbone Lorraine)
was found to maximise the kinetics of the vanadium couples while
minimising 02 and H2 evolution reactions.
Two membranes, namely the anion (AMV) exchange and cation (CMV)
exchange (Asahi Glass Co., Japan) were evaluated and were found to
meet the resistivity and selectivity requirements for redox flow cell
applications.
Employing the graphite felt (RVG) electrode and either a cation
(CMV) or anion (AMV) exchange membrane excellent cell performance was
achieved. Using 2 M vanadium solutions coulombic efficiencies of
greater than 90% were achieved, voltage efficiencies ranged between
80%-85% while overall energy efficiencies of 76%-81% were obtained.
The average open circuit voltage under these conditions is 1.4 volts.
The high overall energy efficiency achieved for the single cells
together with the simplicity and inherent characteristics of the all vanadium
redox flow cell make it one of the most promising energy
storage systems currently under development.