Study on the chemical stability of the anion exchange membrane of grafting dimethylaminoethyl methacrylate

A kind of anion exchange membrane (AEM) was prepared by radiation-induced grafting of dimethylaminoethyl methacrylate (DMAEMA) into ethylene-tetrafluoroethylene (ETFE) membrane and subsequent protonation. For the purpose of long cycle life of vanadium redox battery (VRB), the chemical stability of the resulting AEM was evaluated firstly in the vanadium (V) solution, which is used as the positive half cell electrolyte in VRB. It was found that the AEM had slight weight loss after soaking in 1.5 M vanadium (V) solution for 90 days and 0.1 M V(V) solution for 540 days. The increase of permeability of V(IV) ion after 540 days soaking in 0.1 M V(V) solution for the prepared AEM was 41% which was relatively lower than that of other commercial membranes. Further evaluation on the degradation mechanism of the resulting AEM was carried out in 3% H2O2 aqueous solution at 60 °C. Micro-FTIR, TGA and XPS analyses of the AEM before and after degradation in H2O2 aqueous solution confirmed the absence of –NH+(CH3)2 group in the degraded membrane. UV and 1H NMR analyses of the degradation products proved that C–O bond of ester group in the poly(methacryloxyethyl dimethyl ammonium chloride) grafts of the AEM was vulnerable to be attacked by hydroxyl radicals in H2O2 aqueous solution.

► ETFE-g-PMAOEDMAC membrane had slight weight loss after soaking in 1.5 M vanadium (V) solution for 90 days and 0.1 M V(V) solution for 540 days.
► The increase of permeability of V(IV) ion after 540 days soaking in 0.1 M V(V) solution for the prepared AEM was 41% which was relatively lower than that of other commercial membranes.
► The change of the permeability of V(IV) ion and FTIR of the AEM after 540 days soaking in 0.1 M V(V) solution indicated that the resulting AEM suffered degradation during the period of soaking, but its chemical stability was better than other commercial membranes.
► The C–O bond of ester group in PMAOEDMAC was vulnerable to be attacked by hydroxyl radicals in H2O2 solution.
► N,N-dimethylethanolamine and its oxidation products were produced during the degradation process.