Hydrocarbon Membrane for Vanadium Redox Flow Batteries

With the expanding need for large electrical energy storage systems in connection with renewable energy sources, flow batteries, have been enormously considered due to their high flexibility in upgrade and low cost associated with scale-up. Of all the flow batteries, vanadium redox flow battery (VRFB) use of same element in both half-cell solutions that overcomes the inherent issue of cross contamination by diffusion of different ions across the membrane. Together with the absence of any toxic emissions, the vanadium redox flow battery has demonstrated its uniqueness in terms of safety and long life cycle. Typical charge-discharge reactions of a VRFB involve two vanadium redox couples, V(II)/V(III) and V(IV)/V(V), in the negative and positive half-cells, respectively. In a fashion similar to most batteries, electrons are transferred between the two electrodes through the external circuit during the charge and discharge processes. In a VRFB, the ion exchange membrane is a key component as an ionic conductor and separator: it not only provides an ionic conduction pathway between the two electrolytes but also prevents mixing of the negative and positive electrolytes. The crossover of ions through the membrane, with the diffusion of vanadium ions from one half-cell to the other due to the concentration gradients between the two electrolytes, will result in self-discharge and thus the loss of the chemical energy.

In this study, in order to improve membrane selectivity, hydrocarbon based polymer membranes were synthesized and fabricated for VRFBs. Sulfonated polysulfone membranes (PATS-XX) were characterized in terms of ionic conductivity and permeability with degree of sulfonation. PATS-35 exhibited the ionic conductivity of 0.06 S/cm, which showed 40% lower permeability than Nafion 115 membrane. VRFB cell with PATS-35 exhibited higher coulombic and energy efficiency than that with nafion 115 membrane. The results of VRFBs with blended PATS-xx membrane will be discussed and compared with that with Nafion membrane.