(155b) Synthesis and Transportation Characteristic of Poly (aryl ether oxadiazole) Amphoteric Ion Exchange Membrane for Redox Flow Batteries: Experimental and Molecular Dynamics Simulation

Authors: 
Pan, J., Tsinghua University
Li, X., Tsinghua University
Xie, X. F., Tsinghua University
LI, W., Tsinghua University
Wang, S., Tsinghua University
Zhang, P., Neotrident.Com

    All vanadium redox flow battery (VFB), a novel large-scale energy storage device, has drawnmore and more attention in recent years, and be considered as the potential technology in new energy generations application. Ion exchange membrane for redox flow battery applications provides conductive channel and prevents the crossover of different vanadium ions between positive and negative electrolytes. Currently the main membrane employed in VFBs is perfluorosulfonic acid cation exchange membrane (Nafion® series), it owns high ion conductivity and stability, however suffers from poor ionic selectivity. The positive exchange groups can prevent vanadium ions crossover because of the Donnan effect. However, the ionic conductivity of anion exchange membrane (AEM) is much less than that of cation exchange membrane (CEM), resulting the poor charging and discharging performance of VFB. Amphoteric ion exchange membrane (AIEM), with both cation and anion exchange groups in the membrane matrix, is endowed with excellent properties in conductivity and crossover-resistance.

In this study, a new route for synthesis of a novel amphoteric ion exchange membrane has beendeveloped. Compounds with amino-group and sulfonic group is employed as functionalized reagent, and poly (aryl ether oxadiazoles) as basic copolymer, a series of poly (aryl ether oxadiazole) amphoteric ion exchange membrane (AIEM-x) are synthesized and tested by GPC, NMR, FTIR, vanadium permeability and ion conductivity. Molecular dynamics simulation of AIEM-x is analyzed based on the first-principle. The experimental and simulation results indicate that the 2-aminoethanesulfonic acid branch structure in AIEM-x has both cation and anion group, and the groups can attract each other and become an ion cluster when membrane-forming. Electron cloud density of the ion cluster part in the membrane grows significantly, so the ion clusters turn into ionic transportation channels and reduce the resistance of the ions transport though the membrane, so the ion conductivity improves. Because of using of 2-aminoethanesulfonic acid, the functionalization of cation and anion exchange groups is one-step reaction and in mild condition, besides it is low in cost and high in productivity. The poly (aryl ether oxadiazole) amphoteric ion exchange membrane shows a good characteristics in ion conductivity, mechanical and heat stability, acid-resistance, is a promising membrane applied in the redox flow batteries.