Bilayer Micro-Mesoporous Membrane Assembly Offering Lower Pressure Drop to Realize High Energy Efficient Vanadium Redox Flow Battery

Abstract

The ion exchange membrane (IEM) is a critical component that determines the performance and economic viability of the Vanadium Redox Flow Battery (VRFB). Optimizing the thickness of IEM is essential for the success of the flow battery. The interplay of the crossover rate, water transport, and membrane resistance determines the battery's energy efficiency (E.E.). In this study, we have replaced thicker NafionTM-117 with ∼50 μm thick NafionTM-212 membrane coupled with ∼25 μm thick porous polypropylene membrane (PPM, i.e., Celgard®-3401) to mitigate vanadium crossover without compromising on the performance of the VRFB. At 100 mA cm−2 current densities, E.E. of NafionTM-212 + PPM based cell was improved by 4% compared to NafionTM-212 based cell. Similarly, at 250 mA cm−2 rate, EE of NafionTM-212 + PPM based VRFB stood at 6% improvement compared to NafionTM-212 based VRFB. There is a significant improvement in the discharge capacity from 19.8 to 21.4 Ah l−1, 14.1 to 18.6 Ah l−1, 12.2 to 16.1 Ah l−1, and 10.5 to 14.1 Ah l−1 at 100, 150, 200, and 250 mA cm−2 current densities, respectively. These results show that the combination of NafionTM-212 and PPM could significantly save the capacity and E.E. of VRFB.