Analysis of Ion Crossover in Membranes in All-Vanadium Redox Flow Batteries

Abstract

The full integration of renewable energy sources in a grid system requires robust energy storage capabilities. Redox flow batteries (RFBs) are viable candidates to be utilized as energy storage since they are scalable and decouple energy storage from power generation. All-vanadium redox flow batteries (VRFBs) belong to this family and are very promising 1, 2. However, in order to achieve the Department of Energy short term capital cost target of $250/kWh 3, cost reduction and performance improvement are required. Among the different components of VRFBs, the ion-exchange membrane significantly affects both voltage and coulombic efficiencies and is a topic of active research in the field. The ideal membrane needs to have very high protonic conductivity and low permeability for electroactive vanadium species. Several experimental and modeling approaches have been developed to better understand and quantify the transport mechanism through these ion-exchange membranes 4-8, and specifically in VRFB systems 9, 10. However, a comprehensive and systematic experimental study on ion crossover is presently lacking in the literature. In this talk, we will report results for direct measurement of species crossover through multiple VRFB ion exchange membranes. A unique set-up utilizing UV-Vis spectrometry has been designed and implemented to quantify species crossover in an operating VRFB with and without the presence of an electric field. Experimental data depending on ion exchange membrane equivalent weight, reinforcement, and pretreatment history will be reported. The results of this study should be useful to optimize the VRFB performance and reduce the total cost. Fig.1 : The crossover measurement of different ion-exchange membranes for VRFB applications (a) Semi-natural log plot used to determine permeability (b) Image of solution at the end of experiment for different membrane types