A novel amphoteric ion exchange membrane synthesized by radiation-induced grafting α-methylstyrene and N,N-dimethylaminoethyl methacrylate for vanadium redox flow battery application

A novel amphoteric ion exchange membrane (AIEM) was synthesized by radiation-induced grafting α-methyl styrene (AMS) and dimethylaminoethyl methacrylate (DMAEMA) into poly(vinylidenedifluoride) (PVDF) films, followed by sulfonation and protonation processes. The monomer AMS could be co-grafted successfully with DMAEMA in the presence of AlCl3 although it was difficult for AMS to be grafted solely into PVDF films. The grafting yield (GY) increased with absorbed dose up to about 40 kGy. It was found that the ratio of DMAEMA to AMS in the poly(DMAEMA-co-AMS) grafts changed slightly with various monomer ratio of DMAEMA to AMS in the feed by elemental analysis. The Micro-FTIR and XPS analyzes testified that the AIEM had been prepared as designed. The AIEM with a GY of 40% showed similar conductivity, higher IEC and lower permeability of vanadium ions compared with Nafion117 membrane. The vanadium redox flow battery (VRFB) assembled with the AIEM of 41.1% GY maintained an open circuit voltage higher than 1.4 V after placed for 60 h, which was much longer than that with the Nafion117 membrane. Therefore, it is expected to be excellent candidate for the application of VRFB.

► AMS can be co-grafted into PVDF film with DMAEMA in the presence of AlCl3.
► The AIEM had a permeability of vanadium ions 10 times lower than that of Nafion117.
► The chemical stability of the AIEM showed better when St was substituted by AMS.
► The OCV of VRFB with the AIEM showed better performance than that with Nafion117.