| Anion exchange membrane(AEM) is an important component which assembles into fuel cell,its performance can largely determine the working performance and life of fuel cell.However,low ionic conductivity and poor alkaline resistance are two major obstacles that hinder the development and application of AEM.Improving the ion conductivity of AEM can be achieved by increasing the IEC and constructing ion transport channels.Generally,high IEC will bring about the swelling and the dilution of ion concentration.Therefore,the construction of ion transport channels has become one of the hottest research topics in the field.The main chains without ether bonds and strong electrophilic groups can effectively avoid the attack from OH’ under alkaline conditions,which leads to good chemical stability.On the other hand,what follows is the large swelling and low ionic conductivity.In order to solve the above problems,the design and regulation of the structures of membranes are carried out in this paper.(1)Aliphatic backbone containing pendant pentafluorophenyl groups was synthesized by a superacid catalyzed polyhydroxyalkylation reaction to improve the hydrophobicity of the polymer.The side chain was grafted with 2,4,6-tri(dimethylaminomethyl)phenol that has multifunctional sites.During the process of casting membranes,crosslinking reaction and quaternization occured simultaneously by adding the crosslinking agent with two quaternary ammonium groups.The characterization results indicate that the local high concentration of ionic groups on the side chain and the fluorine-containing backbone result in obvious hydrophilicity difference between them,which could availably promote the formation of microphase separation structures.The high hydrophobicity of the fluorine-containing backbone and the crosslinking structure effectively limit the swelling behavior of the membrane.Among them,the CPFBP-TQA-100 membrane has the best comprehensive performance with a swelling ratio lower than 25%at 80℃.After being soaked in a 2 M NaOH solution at 80℃ for 500 h,it still retains more than 70%of ionic conductivity with good alkaline stability.Novel backbone structure provides valuable preference for the design of AEMs.(2)Considering that the all-carbon backbone structure without heteroatoms is not easy to degrade under alkaline conditions.While the aromatic backbone containing rotatable ether bonds makes it more flexible.which is conducive to the self-assembly of polymer chains.With the aim of ensuring the good alkaline stability and improving ionic conductivity of the membranes simultaneously,we attemptted to combine the superiorities of above mentioned polymer backbone structures.The partially fluorinated aromatic block and the aliphatic segment grafted with the ionic liquid are regarded as the hydrophobic segment and the hydrophilic segment,respectively.The block structure is helpful to the aggregation of ion clusters in the membranes and definite microphase separation structure is constructed.The functionalized segment contains no heteroatoms,which can ensure the good alkali stability of the backbone.FPAE-PVBC-QA-20 with the IEC of 1.51 meq g-1 achieves the ionic conductivity of 87.8 mS cm-1 at 80℃,and the swelling ratio was only 22.9%.Meanwhile,the ionic conductivity of the membrane remains 74.5%after being tested in a 2 M NaOH solution at 80℃ for 500 h.The single cell power density is 131.7 mW cm-2,which is expected to be used in fuel cells. |
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