Synthesis And Characterization Of Novel Fluorinated Anion Exchange Membranes With Quaternary Guanidinium Groups

The vanadium redox flow battery, sometimes abbreviated as VRB, isa new type of energy storage technology. These years, more and moreattention has been paid on this system. Its development is still in thepreliminary stages of commercialization. One of the largest limitingfactors is battery diaphragm. At present, ion exchange membranes used inVRB are fully fluorinated cation exchange membrane, such as Nafionmembrane and Flemion membrane. They have good stability, but the highcost and low ion selectivity limit their application. Therefore, in recentyears, many researchers have been paid more and more attention on theanion exchange membranes which have low cost and good ion selectivity.In this test, with the aim to reduce the vanadium permeation inVRBs, a series of novel fluorinated poly （aryl ether oxadiazole）s were synthesized and fuctionalized with quaternary guanidinium group to getAEMs（GFPEO）. At first, fluorinated poly（aryl ether oxadiazole）s （FPEO）were synthesized and brominated with N-bromosuccinmide （NBS） bynucleophilic substitution reaction. The brominated fluorinated poly（arylether oxadiazole）s（BFPEO） were then functionalized with quaternaryguanidinium to get fluorinated anion exchange membranes（AEMs）withpendant quaternary guanidinium groups. The structure of resultingpolymers was characterized by FTIR and¹H-NMR spectroscopy.The properties of the AEMs were further investigated in terms ofIEC, solubility, thermal stability, electrolyte uptake and swelling ratio. Inaddition, the area resistance of GFPEO-1has a relatively low value of1.44.cm²which can be comparable with Nafion. Due to the Donnanexclusion effect, the permeation of vanadium ions across GFPEOmembranes can achieve2.1×10^-8cm.min^-1, which is much lower than thatof Nafion112. The self-discharge test also indicated that the AEMs had amuch slower OCV decay rate compared with Nafion112. Based on theabove results obtained from experiments, it can be concluded that theGFPEO membranes are promising for the application in VRBs.