Publication Search Results

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  • (1989) Kazacos, Michael
    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.

  • (1988) Grossmith, F.P.
    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.

  • (1995) Pennisi, Paul

  • (1990) Hoong Ang, Chi Ping
    In this project, the selectivity and resistivity characteristics of various types of membrane separators were evaluated and the most suitable membrane for the Vanadium redox flow cell was chosen on the basis of overall cell efficiency and cost. The results from membrane evaluation tests indicated that the cation-exchange Selemion CMV membrane (Asahi Glass Co., Japan) has the characteristics required for viable Vanadium redox cell performance, giving energy efficiency of over 80% for a cell using activated FMI felt electrode. Even higher efficiencies of up to 88% have been achieved with these materials [124]. Initial tests have also shown very promising results with the Daramic polyethylene microporous separator with a nominal thickness of 0.16 mm. Due to the lower cost of microporous separators compared to ion exchange membranes, attempts were made to impart ion-selective capability to the Daramic microporous separators. Three different methods of treatments were tested and were found to be capable of imparting ion-selective characteristics to the microporous separators although further optimization of the treatment process is required. The problem of solvent transfer from one half-cell to the other half-cell during cycling of the Vanadium redox flow cell was investigated. It was found that by carefully adjusting the ionic strengths of the positive and negative electrolytes, the solvent transfer due to osmotic pressure effects can be minimized so that it is negligible during battery cycling. The fouling of the Selemion CMV membrane in the Vanadium electrolytes was also investigated.