High-Performance PBI-EMIM-DCA Membrane for Enhanced Efficiency and Longevity in Vanadium Redox Flow Batteries

Abstract

In vanadium redox flow batteries (VRFBs), vanadium ion crossover contributes to performance degradation and a reduced system lifespan. Polybenzimidazole (PBI) membranes have been proposed as an effective solution to minimize ion crossover. In this study, PBI was used to achieve low vanadium ion permeability, while the addition of 1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA) created microstructures in the polymer, increasing ion pathways. Furthermore, a 10 mu m thin PBI-EMIM-DCA 45 wt % (PED 45) membrane was fabricated to minimize membrane resistance. PED 45 exhibits a vanadium ion permeability of 1.4 x 10-8 cm2 min-1 and a proton selectivity of 34.2 x 107 mS min cm-3. This results in 71- and 22-fold lower permeability compared to Nafion N115 and Fumatech FAP-450 membranes, respectively, while providing 4- and 14-fold higher proton selectivity, respectively. PED 45 demonstrates a Coulombic efficiency (CE) of up to 99.6% and an energy efficiency (EE) of 77.8% at a current density of 100 mA cm-2. Its self-discharge (SD) times are 6-9 times longer than those of other membranes, and its long-term stability shows over 5% higher efficiency across 100 cycles. PED 45 has proven to be a high-performance membrane for VRFB applications.