Direct Measurement of Vanadium Crossover in an Operating Vanadium Redox Flow Battery

Measurements of Vanadium diffusion coefficients for transportacross cation exchange membranes using dialysis cells have beenreported in the literature. However, to date direct measurement ofcrossover coefficients in an operating Vanadium redox flowbattery (VRB) cell have not been reported. Results are reported inthis paper on experiments utilizing a special VRB cell whichallows measurement of Vanadium ion transport across ionexchange membranes with and without the presence of current.The cell utilizes two additional flow regions which collectVanadium ions which diffuse from the positive and negative halfcells. The effects of the magnitude and direction of electricalcurrent on transport can be measured directly with this cell. Weobserve that transport is greatly enhanced when the direction of thehydrogen ion flux is in the same direction as the density gradientdriven vanadium flux and suppressed when the hydrogen ion fluxis in the opposite direction. The cell has been used to of investigatethe effects on transport of current densities up to 900 mA/cm2.