Abstract
The proton exchange membrane is widely used in vanadium redox flow battery as electrolyte separator and proton conductors. In this paper, two commercial proton exchange membranes, Nafion and 3Mion, have been investigated. High frequency resistance and water and acid uptake of the PEMs are measured after equilibration in sulfuric acid of different concentrations. The conductivity of the membrane is correlated to water content and water activity inside the membrane. The membrane conductivity of membranes equilibrated in a vanadium/sulfuric acid solution was also measured and compared to the internal resistance of an operating battery with the same vanadium and acid concentrations. The comparison result shows that membrane resistance is the major component of battery internal resistance.