Stability and Performance Evaluation of Ion-Exchange Membranes for Vanadium Redox Flow Battery

Abstract

The performance of vanadium redox flow battery (VRFB) is highly dependent on the efficiency of the membrane. Generally, anion exchange membranes and cation exchange membranes can be applied in the VRFB. In this paperwork, AMI-7001S anion exchange membrane and CMI-7000S cation exchange membranes were tested for their suitability in the VRFB application. Both of the membranes were originally used for electrocoat and water treatment system. In order to study the behavior of the membranes in the VRFB, several tests were performed. This includes VO2+ ion permeability, ionic conductivity, ion selectivity, chemical stability and single cell performance. The results obtained were compared to Nafion 117 which is a proton exchange membrane. This membrane is one of the most established membranes for VRFB. From the experiment, it can be summarized that the membranes are unsuitable to be used in VRFB. This is due to the low ion selectivity, poor chemical stability and high resistance.

Ex-Situ Evaluation of Commercial Polymer Membranes for Vanadium Redox Flow Batteries (VRFBs)

“…Vanadium crossover represents the diffusion of vanadium ions across the membrane, leading to coulombic efficiency (CE) drop, capacity decay and OCV decline in VRFB charge/discharge cycling. In order to determine the diffusion coefficients of the VO 2+ ions penetrating through the selected membranes, a two-half diffusion cell (PermeGear, Inc., Hellertown, PA, USA) was employed [ 25 ]. The tested membrane was sandwiched between the two half diffusion cells and a pair of rubber gaskets.…”

“…The crossovers of VO 2+ ions across the selected membranes were compared and their diffusion coefficients of vanadium ions were calculated using Sun’s approach [ 25 , 37 ] by Equation (1): where V B is the volume of solution on the deficiency side (mL); C A and C B are the concentration of VOSO 4 on the enrichment side and deficiency side (mol∙mL −1 ), respectively; A is the effective area of the membrane (cm 2 ); D is the diffusion coefficients of VO 2+ (cm 2 ∙s −1 ); L is the thickness of the membrane (cm); t is the testing time (s).…”

“…The crossovers of VO 2+ ions across the selected membranes were compared and their diffusion coefficients of vanadium ions were calculated using Sun's approach [25,37] by Equation (1):…”

“…Membrane degradation in VRFB is believed to be caused by the oxidation reaction with V 5+ , although the mechanism of this decay is still not fully understood [9,[25][26][27]. Therefore, beside the visual observation of colour changes in soaking solutions as well as the tested membranes, the variation of VO 2+ ion concentration in the soaking solutions was monitored by UV-Vis spectrophotometry, which in turn provided additional indication of the membrane degradation rate.…”

“…Therefore, considerable efforts have been devoted to investigating hydrocarbon-based materials as an alternative solution to PFSA-based membranes driven by cost-effective mass production in the marketplace [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. It is thought that hydrocarbon-based anion exchange membranes (AEMs) could suppress vanadium permeability due to the Donnan exclusion effect [ 12 ]; however, their chemical and mechanical stability in VRFB operational conditions and lackluster ionic conductivity make their viability questionable [ 24 , 25 ]. Hydrocarbon-based membranes were primarily developed for fuel cell applications; as such, there are limited publications about the use of commercial AEMs in VRFBs.…”