| The alkaline anion exchange membrane fuel cells（AEMFCs）have gradually received people’s attention due to the advantages of high ionic conductivity,especially the use of non-noble metals during the last decades.AEMFCs not only have fast oxygen reduction kinetics,but also possess low methanol permeability.As the key component of alkaline anion exchange membrane fuel cells,anion exchange membranes（AEMs）have excellent thermal stability,mechanical strength and remarkable electrochemical properties.Polynorbornene has good mechanical strength,high chemical stability and low methanol permeability.The grafting of imidazole group on the side chain of polynorbornene can improve the ionic conductivity and enhance the alkaline resistance of anion exchange membranes.In this paper,contraposing the poor alkaline resistance,low ionic conductivity of anion exchange membranes and poor processing performance of polynorbornene,5-norbornene-2-epoxypropyl ether（NB-MGE）and the norbornene monomer with the imidazole group（[NB-Im][Br]）were designed and synthesized,the corresponding random copolymers were synthesized via ring-opening metathesis polymerization,which were used as polymer matrix to obtain corresponding anion exchange membrane with remarkable electrochemical properties.The block copolymers were synthesized to further improve the ionic conductivity of anion exchange membrane.The details are as follows:（1）A series of ROMP-type imidazolium-functionalized norbornene copolymers named rP（NB-MGE-co-[NB-Im][Br]）-x（x=6.6,12.4,19.2 and 25.6 mol%[NB-Im][Br]）were synthesized by copolymerization of 5-norbornene-2-epoxypropyl ether（NB-MGE）and 5-norbornene-2-carboxylate-1-hexyl-3-methyl-imidazolium bromine（[NB-Im][Br]）via ring-opening metathesis polymerization.The rP（NB-MGE-co-[NB-Im][Br]）-x was confirmed by 1H NMR and FT-IR.The Br-of rP（NB-MGE-co-[NB-Im][Br]）-x was replaced by OH-to obtain the corresponding anionexchangemembrane（rP（NB-MGE-co-[NB-Im][OH]）-x）inalkaline environment.The effects of imidazole group compositions on thermodynamic properties of polymer and electrochemical properties of anion exchange membrane were investigated.Anion exchange membrane possess low methanol permeability(3.52-5.77×10-7 cm2 s-1),excellent IEC and remarkable ionic conductivity.The rP（NB-MGE-co-[NB-Im][OH]）-25.6 achieves the best ionic exchange capacity(1.01×10-3 mol g-1)and ionic conductivity with 2.77×10-3 S cm-11 at 30 oC and 6.08×10-3 S cm-1 at 80 oC.A membrane electrode assembly（MEA）fabricated using rP（NB-MGE-co-[NB-Im][OH]）-25.6 was also tested in a direct methanol fuel cell,and a maximum open circuit voltage（OCV）of 0.705 V and a current density of 72.4mA cm-2 at a peak power density of 27.8 mW cm-2 were achieved.（2）In order to further improve ionic conductivity of anion exchange membrane,we designed and synthesized 5-norbornene-2-epoxypropyl ether（NB-MGE）,and copolymerized with the imidazolium-functionalized norbornene（[NB-Im][Br]）to afford diblock copolymers named rP（NB-MGE-b-[NB-Im][Br]）-y（y=8.6,15.4,22.1,29.4 mol%[NB-Im][Br]）.We prepared the corresponding anion exchange membrane（rP（NB-MGE-b-[NB-Im][OH]）-y）,the block copolymerization had been employed to produce ion clusters via micro-phase separation,which was conducive to the formation of ion channels.The rP（NB-MGE-b-[NB-Im][OH]）-29.4 achieves the best ionic exchange capacity(1.12×10-3 mol g-1)and ionic conductivity with 3.79×10-3 S cm-11 at 30 oC and 9.32×10-3 S cm-1 at 80 oC.A membrane electrode assembly（MEA）fabricated using rP（NB-MGE-b-[NB-Im][OH]）-29.4 was also tested in a direct methanol fuel cell,and a maximum open circuit voltage（OCV）of 0.85 V and a current density of 83.7 mA cm-2 at a peak power density of 44.6 mW cm-2 were achieved. |
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