Thin Reinforced Ion-Exchange Membranes Containing Fluorine Moiety for All-Vanadium Redox Flow Battery

Abstract

In this work, we developed pore-filled ion-exchange membranes (PFIEMs) fabricated for the application to an all-vanadium redox flow battery (VRFB) by filling a hydrocarbon-based ionomer containing a fluorine moiety into the pores of a porous polyethylene (PE) substrate having excellent physical and chemical stabilities. The prepared PFIEMs were shown to possess superior tensile strength (i.e., 136.6 MPa for anion-exchange membrane; 129.9 MPa for cation-exchange membrane) and lower electrical resistance compared with commercial membranes by employing a thin porous PE substrate as a reinforcing material. In addition, by introducing a fluorine moiety into the filling ionomer along with the use of the porous PE substrate, the oxidation stability of the PFIEMs could be greatly improved, and the permeability of vanadium ions could also be significantly reduced. As a result of the evaluation of the charge–discharge performance in the VRFB, it was revealed that the higher the fluorine content in the PFIEMs was, the higher the current efficiency was. Moreover, the voltage efficiency of the PFIEMs was shown to be higher than those of the commercial membranes due to the lower electrical resistance. Consequently, both of the pore-filled anion- and cation-exchange membranes showed superior charge–discharge performances in the VRFB compared with those of hydrocarbon-based commercial membranes.

Thin-Reinforced Anion-Exchange Membranes with High Ionic Contents for Electrochemical Energy Conversion Processes

“…As the IEC increases, the membrane swelling elevates, which promotes the crossover of the vanadium ions, and thus, the CE decreases. In the case of the VE, it is greatly affected by the ER of the membrane, that is, as the IEC of the membrane increases, the ER decreases and the VE increases [40]. Since CE and VE have a trade-off relationship with each other, EE, which is determined by the product of the two efficiencies, could be optimized under specific conditions.…”

“…The unit cell was charged up to 1.9 V and then discharged to 0.8 V using an automatic battery cycler (WBCS 3000, Wonatech Corp., Seoul, Korea) and the applied current density was 20 mA/cm 2 . To evaluate the charge-discharge performance of the VRFBs employing different AEMs, coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were calculated using the following equations, respectively [40]:…”

“…In order to confirm the oxidation stability of the commercial membrane and the prepared AEMs, the Fenton oxidation test was carried out. The membrane sample was prepared at a size of 2 × 2 cm 2 , impregnated in the Fenton solution prepared by mixing 3 wt% of H 2 O 2 and 3 ppm of FeSO 4 , and maintained at 80 • C for 8 h [40]. The weight change was calculated by measuring the weights of the membrane at the initial stage and after the Fenton oxidation.…”

“…In addition, a vanadium oxidation stability test was also performed to ensure the chemical stability of the AEMs in the VRFB system. This is based on the principle that VO 2 + (V(V) species) is reduced to VO 2+ (V(IV) species) by the oxidation reaction of a membrane immersed in a VO 2 + /H 2 SO 4 solution [40]. For the measurement of vanadium oxidation stability, an AEM sample prepared in a constant size of 2 × 2 cm 2 was immersed in 20.0 mL of 0.1 M (VO 2 ) 2 SO 4 (0.1 M V(V) in 5 M H 2 SO 4 ) solution and maintained at 50 • C for 100 h [42].…”

High-Capacity Retention Thermally Reinforced Pore-Filled Anion Exchange Membrane for All-Vanadium Flow Batteries

“…Before deposition, the PTFE substrate was treated with catechol and polyethyleneimine (PEI) . Moon et al systematically investigated the influence of fluorine content on the electrochemical and physicochemical properties of the electrolyte polymer contained in the porous polyethylene (PE) substrate and its VRFB performance . Kim and Kang developed a high-performance PFAEM for dual application (alkaline direct liquid fuel cells and VRFBs) using a highly porous PTFE film substrate and N , N ′-dimethylaminoethyl methacrylate (DMAEMA) as the base monomer for polymer electrolytes .…”