Preparation And Properties Of High-performance Polybenzimidazoles Anion Exchange Membrane Grafted With Hetero-cyclic Quaternary Ammonium Salts

Fuel cells,as energy conversion devices,have attracted tremendous interests form many researchers because of the outstanding advantages-environmentally friendly,high conversion efficiency,low operation temperature and the promising prospect of the ion exchange fuel cells.Although the development of Proton Exchange Membrane Fuel Cells?PEMFCs?is earlier than Anion Exchange Membrane Fuel Cells'?AEMFCs?,AEMFCs have been hot research in the field of fuel cells,on the strength of non-noble metal catalysts,simple water management system.As for the core component of AEMFCs,the low conductivity and poor stability restrict the development of AEMFCs.In order to improve the conductivity and chemical stability of the AEMs,the AEM,which were prepared by the polybenzimidazoles functionalized by hetero-cyclic quaternary ammonium salts,have been designed in this study.The details of this paper are described as follow:?1?In order to improve the alkaline stability of quaternary ammonium salts,two types of quaternary ammonium salt have been designed:N-heterocyclic quaternary ammonium salts and N-spirocyclic quaternary ammoniums salts.The synthesis of N-heterocyclic QAs?Br-Pip,Br-Pyr?were performed by successive quaternarization reactions between N-methylpiperidine,1-methyl pyrrolidine and 1,6-dibromohexane in THF solution.The synthesis of N-spirocyclic quaternary ammoniums?Br-ScPiz,Br-ScNPiz,Br-ScBiPip?were performed by successive quaternarization reactions between 1,3-di?piperidin-4-yl?propane,1-methylpiperazine,piperazine and 1,5-dibromopentane,1,6-dibromohexane in THF solution.By means of ¹H-NMR,the structure of QAs was characterized,so the structure of QAs was verified.?2?In order to improve the alkaline stability of polymer main chain,the polybenzimidazole?PBI?was synthesized by high temperature solution polymerization of DAB and isophthalic acid.Pip-PBI,Pyr-PBI functionalized by Br-Pip,Br-Pyr were synthesized.By means of ¹H-NMR,the structure of Pip-PBI,Pyr-PBI was characterized.The microphase separation of Pip-PBI was characterized,accidentally the scattering peaks demonstrates of ion cluster disappear in the range of small angle.The conductivity of Pip-PBI,Pyr-PBI go to 85.1 mS cm^-1?79.2mS cm^-11 respectively,which represents high level.To inspect of the alkaline stability and oxidation stability of Pip-PBI and Pyr-PBI,Pip-PBI and Pyr-PBI immersed in 1M NaOH.The remaining of conductivity of Pip-PBI and Pyr-PBI is 84%?67%respectively,after immersed in 1M NaOH 1500 h.The ion exchange membrane immersed in Fenton reagent,33 h later,the remaining of weight of Pyr-PBI ion exchange membrane is 76%,45 h later,the remaining of weight of Pip-PBI ion exchange membrane is 86%.Therefore,Pip-PBI ion exchange membrane,Pyr-PBI ion exchange membrane proposed relatively good conductivity and stability.?3?In order to improve the flexibility,solubility of the polymer main chain,the copolymer polybenzimidazole?CoPBI?was synthesized by high temperature solution polymerization of DAB,isophthalic acid and heptanediacid.In order to improve the alkaline stability of ion exchange membranes,the more stable N-spirocyclic quaternary ammoniums were synthesized.ScPiz-PBI?ScNPiz-PBI?ScBiPip-PBI,ScPiz-CoPBI?ScNPiz-CoPBI?ScBiPip-CoPBI functionalized by Br-ScPiz,Br-ScNPiz,Br-ScBiPip were synthesized.By means of ¹H-NMR,the structure of ScNPiz-PBI,ScBiPip-PBI was characterized.The microphase separation of ScBiPip-PBI,ScBiPip-CoPBI was characterized,accidentally the scattering peaks demonstrates of ion cluster disappear in the range of small angle.The OH^-conductivity of ScNPiz-PBI,ScBiPip-PBI goes to,50.6 mS cm^-1?54.1 mS cm^-1 respectively at 30°C,100.2 mS cm^-1?105 mS cm^-11 respectively at 80°C,which represents high level.The ion exchange membrane immersed in fenton reagent,41 h later,the remaining of weight of ScPiz-PBI,ScNPiz-PBI,ScBiPip-PBI ion exchange membrane is 7 above 90%.After immersing in the alkaline reagent,the degradation of ScNPiz-PBI ion exchange membrane is the fastest,600 h later,the remaining of conductivity is only 75%.ScPiz-PBI?ScBiPip-PBI ion exchange membrane degraded more slowly,150 h later,degradation tends to quietly,600 h,the remaining of conductivity is above 90%.Therefore,ScPiz-PBI?ScBiPip-PBI ion exchange membrane have very good prospects in the field of fuel cells.