Preparation Of Multiimidazole Cationic Functionalized Benzonorbornadiene Triblock Copolymers And Its Self-crosslinked Alkaline Anion Exchange Membranes And Application Performance In Fuel Cell

The alkaline anion exchange membrane fuel cells(AAEMFCs)have been extensively studied because of their faster cathodic oxygen reduction kinetics under alkaline conditions and the use of non-precious metal catalysts.Anion exchange membrane(AEM)as an important part of AAEMFCs,plays a role of blocking fuel and oxidant,while conducting anions and water molecules.However,it is still a challenge to obtain a good alkaline stability and a high ion conductivity while maintaining a balance between high ion exchange capacity and dimensional stability.The ion conductivity is an important parameter of AEMs.The level of ion conductivity is related to ion exchange ablity,water content and ion exchange capacity(IEC).The alkaline stability is another important indicator to measure the application performance of the AEM,and the alkaline stability is related to the chemical structure of the polymer.In order to obtain AEM with high ion conductivity,good alkaline stability and better dimensional stability,two types of self-cross-linked multi-imidazolium functionalized triblock copolymer based on ring-opening metathesis polymerization(ROMP)type benzonorbornadiene were prerpared.The multi-imidazolium cations were introduced through the two side chains of the benzonorbornadiene derivative,and at the same time build a hydrophilic and hydrophobic micro phase separation through the block polymerization method and the design of the main chain and side chain hydrophilic/hydrophobic structure to improve the ion conductivity of AEMs.The all-carbon main chain structure and the self-crosslinking structure under alkaline conditions ensure the dimensional stability and alkali resistance stability of AEMs.The detail work as follows:(1)Several different halogenated benzonorbornadiene monomers were synthesized.1,2-dimethylimidazole was used to react with one of the dibromo halogenated benzonorbornadiene monomer(BenzoNBD-BisBr)to prepare a bisimidazolium cation functionalized benzonorbornadiene monomer(BenzoNBD-BisIm+Br-).Then,the BenzoNBD-BisIm+Br-monomer,epoxy group functionalized norbornene monomer(NB-MGE)and norbornene(NB)were triblock copolymerized through Grubbs’ 2nd catalyst to prepare a series of bisimidazolium cations functionalized tri block copolymer AEM rP(NB-MGE-b-BenzoNBD-BisIm+OH--b-NB)-x(x=10,20,30 and 40).The thermal performance,micro phase separation structure and performance of H2/O2 fuel cell cells of triblock copolymer AEM were studied.The thermal decomposition temperature of the prepared membrane was higher than 320℃,and a distinct micro phase separation structure was formed.Among them,the peak power density of AEM rP(NB-MGE-b-BenzoNBD-BisIm+OH--b-NB)-40 is as high as 189.1 mW cm-2.(2)By constructing micro-phase separation structure and introducing more cationic groups to further improve the ion conductivity of AEMs.Based on the above-synthesized BenzoNBD-BisIm+Br-monomer,BenzoNBD-Bis(Im+Br--Im+I-)monomer functionalized by tetraimidazolium cations with hydrophilic ether linkages and hydrophobic alkyl intervals was designed and synthesized in this section.Construction of hydrophilic and hydrophobic microphase separation structures by introducing hydrophilic ether bond spacers and hydrophobic alkyl spacers.Then,BenzoNBD-Bis(Im+Br--Im+I-)monomer,NB-MGE monomer and NB monomer were triblock copolymerized by Grubbs’ 3 rd catalyst to prepare a series of ROMP-type triblock copolymer rP[NB-MGE-b-BenzoNBD-Bis(Im+Br--Im+I-)-b-NB]-x(x=3.85,4.76,6.25 and 9.09).After alkalization treatment,a series of self-crosslinked AEM rP[NB-MGE-b-BenzoNBD-Bis(Im+OH--Im+OH-)-b-NB]-x(x=3.85,4.76,6.25 and 9.09).TEM,AFM and SAXS test results showed that the as-prepared AEMs exhibited a distinct micro-phase separation structure.The gel fraction analysis and the tensile test showed that the prepared AEMs have formed a certain cross-linked structure.At 80℃,the water absorption rate of AEM-9.09 was 52.00%,and the degree of swelling was 35.33%,indicating that the prepared AEM has a moderate water uptake rate and a low degree of swelling.When the IEC of AEM-9.09 is only 1.41 mmol g-1,the OH-conductivity of as-parpered AEM at 80℃ is as high as 100.74 mS cm-1.The as-prepared AEM showed good H2/O2 single-cell fuel cells performance.When the open circuit voltage was 1.01V,the peak power density of AEM-9.09 was 174.5 mW cm-2.