Direct Measurement of Vanadium Crossover in an Operating Vanadium Redox Flow Battery
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Measurements of Vanadium diffusion coefficients for transport across cation exchange membranes using dialysis cells have been reported in the literature. However, to date direct measurement of crossover coefficients in an operating Vanadium redox flow battery (VRB) cell have not been reported. Results are reported in this paper on experiments utilizing a special VRB cell which allows measurement of Vanadium ion transport across ion exchange membranes with and without the presence of current. The cell utilizes two additional flow regions which collect Vanadium ions which diffuse from the positive and negative half cells. The effects of the magnitude and direction of electrical current on transport can be measured directly with this cell. We observe that transport is greatly enhanced when the direction of the hydrogen ion flux is in the same direction as the density gradient driven vanadium flux and suppressed when the hydrogen ion flux is in the opposite direction. The cell has been used to of investigate the effects on transport of current densities up to 900 mA/cm(2).