Design,Synthesis And Properties Of Anion Exchange Membranes With Phase Separation Structure

Ion exchange membrane is an important part of the vanadium redox flow battery(VRFB).In this paper,a series of novel anion exchange membranes(AEM)with phase separation structure have been designed and synthesized from the perspective of molecular structure design,and their ion conductivity,water absorption and swelling ratio,thermal stability,mechanical properties and other properties have been studied to explore the relationship between polymer structure and properties,and provide important technical accumulation for the research and development of AEM.The main content is:(1)A novel bisphenol monomer bearing eight electron rich phenyl rings was synthesized and polymerized with various amount of 4,4'-dihydroxydiphenylsulfone and 4,4'-difluorobenzophenone to give locally dense and selective sites in macromolecules for chloromethylation,followed with quaternization.The effects of content and concentration of quaternary ammonium groups on the water absorption,swelling rate,thermal stability,mechanical properties and ion conductivity of the membrane were studied.The SAXS was used to characterize the internal microphase separation of the membrane.It was found that an obvious ion cluster structure was formed inside the membrane.(2)We designed and synthesized a new type of bisphenol monomer bearing eight benzylmethyl groups at the outer edge of the molecule,which after condensation polymerization with various amounts of 4,4'-dihydroxydiphenyl-sulfone and 4,4'-difluorobenzophenone yielded novel poly(arylene ether)s(mPAEs)with densely located benzylmethyl groups.Then followed with bromination,quaternization,and film formation,a novel type of anion exchange membrane(QA-mPAEs)containing dense quaternary ammonium group in the hydrophilic segment was obtained.The prepared anion exchange membranes of QA-mPAEs series have relatively high ion conductivity.Among them,the QA-mPAE-40(IEC = 2.32 mmol g-1)has an ion conductivity of 33.5 mS cm-1 at 80 ?.The oxidative stability test showed that the QA-mPAEs series AEM has good stability in the VO2+ solution with strong oxidation.The current efficiency and energy efficiency of vanadiun redox flow battery with QA-mPAE-30(IEC = 1.95 mmol g-1)were higher than that of Nafion N212 at the same current density of 40 mA cm-2.By comparing the performance of the two series of anion exchange membranes,it is found that the bromomethylation route is relatively easier to control and has a higher degree of functionalization than the chloromethylation route.What's more,local high density cationic groups in the anion exchange membrane are favorable for the formation of hydrophilic-hydrophobic microphase separation structures.Under certain EEC conditions,the anion exchange membrane with phase separation structure can effectively improve the basic physical and chemical properties of the membrane,which is beneficial to its application in VBFBs.