| Fuel cells are widely studied because of their advantages such as high efficiency,environmental friendliness and high specific energy.According to the different of membranes,fuel cells can be divided into proton exchange membrane fuel cells(PEMFCs)and anion exchange membrane fuel cells(AEMFCs).Compared with proton exchange membrane fuel cells,anion exchange membrane fuel cells have the following advantages:1)non-noble metal electrodes are used to reduce costs;2)fuel crossovers are reduced;3)oxidation kinetics are higher.For anion exchange membranes,it is required to have excellent mechanical properties,water management,electrochemical performance and alkaline stability.Increasing the number of functionalized cations can increase the anion exchange membrane electrochemical performance,but overdose of cations will lead to excessive swelling of the anion exchange membrane.In this paper,polynorbornene is selected as the main chain,and imidazolium ions are used as functional cations to prepare imidazolium functional anion exchange membranes.At the same time,in order to alleviate the problem of excessive swelling caused by excessive cations,multiple cations are introduced in the same side chain to reduce the grafting degree and reduce the influence of the side chain on the main chain.(1)The bis-imidazolium functionalized norbornene ionic liquid[NB-O-BisIm+][Br-]2 was synthesized by 5-Norbornene-2-methanol.The anion exchange membranes were obtained by the ring-opening metathesis polymerization of[NB-O-BisIm+][Br-]2 and epoxy functionalized norbornene derivative NB-O-MGE.The chemical structures of monomers and copolymers were characterized by 1H NRM and FTIR.The resulting anion exchange membrane has a high thermal stability(Td=250?),strength and anti-swelling properties.The SEM image shows that the anion exchange membrane has a dense structure,which is conducive to preventing fuel crossover when used in fuel cells.At the same time,the transmission electron microscopy(TEM)test results show a good microscopic phase separation structure and form ion channels in the membranes,which is benefited to ions conductivity.This nano-scale micro-phase separation structure and bis-imidazolium structure give the anion exchange membrane excellent conductivity and alkaline stability,The conductivity of rP(NB-MGE-b-[NB-O-BisIm+][OH-]2)-40 reaches 95×10-3 S cm-1 at 80?,and it still maintains a conductivity of more than 90%after soaking in 1 M NaOH solution at 60? for 250 hours.(2)In order to further increase the number of cations on the side chain,a multi-imidazolium functionalized polynorbornene-based anion exchange membrane was prepared.Two monomers 5-norbornene-2-methylenehexyl ether(NB-O-Hex)and 5-norbornene-2-methylene-[(6-Bromo)-hexyl]ether(NB-O-Br)were prepared by 5-Norbornene-2-methanol.The block copolymer was obtained through ring-opening metathesis polymerization of two monomers with Grubbs' 2nd catalyst.The copolymer was functionalized with 1-(6-chlorohexyl)-imidazole(6ClIm),an imidazole derivative containing active groups-Cl,and a kind of anion exchange membrane base on polynorbornene with multi-imidazadium functionalized in side chain was prepared.The chemical structures of the synthesized monomers and polymers were confirmed by 1H NRM.The obtained anion exchange membrane shows excellent thermal stability and ionic conductivity,and the ionic conductivity reached 28.9×10-3 S cm-1 and 73.36×10-3 S cm-1 at 30? and 80?,respectively. |
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