Comparison of Membrane Performance for Vanadium Redox Flow Batteries

The vanadium redox flow battery (VRFB) is a promising solution for large-scale energy storage applications. VRFBs consist of positive and negative cells operating with VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox couples.  Ion diffusion across the membrane, known as crossover, is a problem that causes battery self-discharge. Electron Paramagnetic Resonance (EPR) is a sensitive technique with the ability to detect VO²⁺. By flowing battery electrolyte through the EPR cavity, the concentration of VO²⁺can be monitored. This method is used to characterize vanadium transport in VRFB membranes. Data from such experiments is useful in guiding membrane development as well comparing the performance of existing membranes. Cost, chemical stability, vanadium permeability, and ion conductivity are important factors to consider when developing and selecting an appropriate membrane for battery operation. The Sulfonated Diels-Alder Polyphenylene (SDAPP) membrane is a promising alternative membrane for VRFB applications. Characterization of SDAPP membranes with different ion exchange capacities (IEC) allows for a better understanding of the effect of sulfonation level on the transport properties of the membrane.