Structure And Performance Regulation Of Crosslinking Polynorbornene-based Alkaline Anion Exchange Membranes For Fuel Cell

As a new type of energy conversion device the polymer electrolyte fuel cell?PEFCs?acts as the equipment that directly converts chemical energy into electricity power,which can achieve rapid start,efficient transformation,flexible dismantling,with wide environment friendly fuel sources.The alkaline anion exchange membrane fuel cell?AAEMFC?,as one of the important branches in PEFCs,has became a hot topic in recent years owing to their virtue of flexible selection of fules,reasonable fabrication cost and low fuel crossover rate.The anion exchange membrane?AEM?is a significant part of the AAEMFC,strongly influencing the property and life-span of the fuel cell.Currently,there are two major challenges in exploiting high-performance AAEMs:low ion conductivity and insufficient long-term alkaline stability.Thus,the development of AEMs with excellent ionic conductivity and sufficient durability is urgently required.The key to developing high-performance AEMs lies in the regulation of the structure of AEM reasonably.Therefore,based on the principle that material properties depend on its molecular structure,and ring-opening metathesis polymerization?ROMP?and block copolymerization strategy,the hydrophilic/flexible long side chain type,conjugate/large steric hindrance group modified imidazole cation and post-functionalization hybrid multiple imidazolium cations comb type polynorbornene based AEMs were designed and fabricated in this essay.The thermomechanical and electrochemical properties of AEM were regulated by the differentiation configuration of polymer which was constructed by the self-crosslinking of epoxy groups,the self-assembling of flexible long side chains and the cross-linking of hybrid multiple imidazolium cations,with the aim to achieve the construction of new high-performance AEM membrane so as to satisfy the application requirements of AAEMFC.The detailed research works are summarized as follows:?1?To improve the ionic conductivity of the AEMs,molecular design was introduced in this chapter to construct the effective microphase separation structure by using the hydrophilic side-chain with block copolymerization and 6 carbon imidazolium spacer of polynorbornene based AEMs?r PNB-COO-Im-x AEMs,x=10,20,30 and 40?.The strategy of hydrophilic side chain and epoxy self-crosslinking were beneficial to construct high efficiency ion transport and improve the dimensional stability of AEMs.Different degree of microphase separation structure was observed in r PNB-COO-Im-30 and r PNB-COO-Im-40 AEMs,with high OH^-conductivity(60.4 and 69.2 cm^-1 m S at 80?,respectively).At the same time,a peak power density(P_max)of r PNB-COO-Im-30 was reached at 90.06 m W cm^-2 at 80?during the H₂/O₂ single cell test,which proved the practical availability of r PNB-COO-Im-30 in the fuel cell.Moreover,the prepared r PNB-COO-Im-x AEMs showed good thermal stability,however,the alkali resistance should be enhanced due to the inherent strong hydrophilic ester group in the lateral chain.?2?In consideration of the poor alkali resistance stability of the r PNB-COO-Im-x AEMs with strong hydrophilic ester side-chains,an ester free and flexible ether spacer long side chain was introduced to enhance the self-assembly process of the polymer chain segment by virtue of its rotatable and flexible side chain,which facilitated to constructe efficient and continuous conducting channels in this chapter.At the same time,the dimensional stability,alkali stability and ionic conductivity of the prepared ROMP polynorbornene based flexible ether spacer long side chain type AEMs?r PNB-O-Im-x,x=10,20,30 and 40?were regulated by epoxy self-crosslinking technique.As expected,distinct phase separated was observed in r PNB-O-Im-30 and 40 AEMs which guaranteed the OH^-conductivity,meanwhile r PNB-O-Im-x showed higher alkali resistance stability.In addition,a moderate cell AEM,which revealed a potential application in fuel cell.?3?In order to further investigate the effects of N1 substituents of2-methylimidazole on the functionalized norbornene AEMs?r PNB-RMIm-30 AEM,R=Me,i Pr,Bu,Bn and Dod?,N1 substituents with different steric hindrance and conjugation effects were designed and synthesized.The physical mechanical and electrochemical performance of the r PNB-RMIm-30 was regulated by the chemical structure and effect of the N1 substituent group,which the mechanism of OH^-conduction and alkaline environmental degradation of the different steric hindrance and conjugate effect of imidazole cation were futher explored.Results showed that the mechanical properties and alkaline stability of the r PNB-i Pr MIm-30 and r PNB-Bu MIm-30 AEMs were significantly enhanced,and the conductivity loss was17%and 14%,respectively.At the same time,an obvious micro phase separation was observed by the introduction of flexible N1-butyl substituent,thus the highest OH^-conductivity(51.5 m S cm^-1 at 80?)of r PNB-Bu MIm-30 AEM was achieved.Furthermore,the H₂/O₂ AAEMFC assembled by r PNB-Bu MIm-30 membrane gives rise to an optimistic peak power density of 205 m W cm^-2 at 60?.?4?Considering the excellent overall performance of organic and inorganic hybrid materials,the amphiphilic Bis-imidazole functionalized siloxane hybrid monomer was designed and synthesized,which was used as the functional monomer for post-functionalization of epoxy functionalized norbornene precursor polymer,and and 100)were regulated by the multiple imidazolium cations crosslinking strategy.The AEMs exhibited good thermal stability and mechanical properties.Among them,r PB-BIm PS-60 and r PB-BIm PS-80 AEMs hold good mechanical properties and strong alkaline stability,with a OH^-conductivity loss of 9.91%and 14.57%,respectively.Meanwhile,AFM and SAXS showed that the introduction of amphiphilic diimidazole-functionalized siloxane gave rise to a significant microphase separation.Futhermore,The AAEMFC using r PB-BIm PS-60 AEM yielded a peak power density of 240 m W cm^-2 at 60?.