Ion Exchange Membranes for Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRBs) offer a scalable, long lasting, highly efficient means of energy storage. VRBs use different oxidation states of vanadium, V³⁺/V²⁺ in the negative and V⁴⁺ /V⁵⁺ in the positive half-cell, for chemical reactions that generate electrical energy. In a VRB an ion exchange membrane separates the two half cells, and also allows the diffusion of H⁺ ions between solutions to complete the oxidation/reduction reactions. The study of ion exchange membranes is important because the membrane controls the VRB’s internal resistance and effects the tendency of undesirable crossover. In this work we study the effect of different treatments on a commercial membrane (3M825EW), and how those treatments impact the membrane’s conductivity, water uptake, permeability, density and porosity as they are exposed to various concentrations of sulfuric acid and vanadium solutions. The purpose of these tests is to help us further our understanding of what features of ion exchange membranes control the resistance and crossover and to determine if the treatments improve the performance of the membrane. The observations made from these characterization techniques are that the conductivity is affected by the acid and vanadium concentration, the water uptake is inversely related to the acid concentration, and the proton mobility decreases as the water uptake decreases.