Preparation of ETFE-based anion exchange membrane to reduce permeability of vanadium ions in vanadium redox battery

Using γ-radiation technique, dimethylaminoethyl methacrylate (DMAEMA) was grafted onto ethylene–tetrafluoroethylene (ETFE) membrane (ETFE-g-PDMAEMA), and then ETFE-g-PDMAEMA membrane was protonized to prepare anion exchange membrane, while PDMAEMA grafted onto ETFE membrane was changed into poly(methacryloxyethyl dimethyl ammonium chloride) (PMAOEDMAC) (denoted as ETFE-g-PMAOEDMAC anion exchange membrane (AEM)). Micro-FTIR spectra testified that PDMAEMA was successfully grafted onto ETFE membrane. Water uptake and ion exchange capacity (IEC) of the AEM increased with grafting yield (GY), while area resistance decreased. At 40% GY, the AEM showed higher IEC and lower area resistance than Nafion117 membrane. In particular, the AEM had very low permeability of vanadium ions just as expected due to coulomb repulsion between the cation groups of the AEM and vanadium ions. Permeability of vanadium ions through the AEM with 40% GY has been reduced to 1/20 to 1/40 of that through Nafion117 membrane, which is favorable to reduce crossover of vanadium ions in vanadium redox battery (VRB). Finally, the open circuit voltage measurement showed that the VRB assembled with the AEM could maintain voltage for more than 50 h, which was much longer than that with Nafion117 membrane. The improved properties as well as the low cost suggest that the AEM can be good candidate for the VRB.