Concentration Dependence of VO²⁺Crossover of Nafion for Vanadium Redox Flow Batteries

The VO 2+ crossover, or permeability, through Nafion in a vanadium redox flow battery (VRFB) was monitored as a function of sulfuric acid concentration and VO 2+ concentration. A vanadium rich solution was flowed on one side of the membrane through a flow field while symmetrically on the other side a blank or vanadium deficit solution was flowed. The blank solution was flowed through an electron paramagnetic resonance (EPR) cavity and the VO 2+ concentration was determined from the intensity of the EPR signal. Concentration values were fit using a solution of Fick's law that allows for the effect of concentration change on the vanadium rich side. The fits resulted in permeability values of VO 2+ ions across the membrane. Viscosity measurements of many VO 2+ and H 2 SO 4 solutions were made at 30–60°C. These viscosity values were then used to determine the effect of the viscosity of the flowing solution on the permeability of the ion.