Modification Of Anion Exchange Membranes By Grafting Side Chains Having Star Structures

Anion exchange membrane fuel cell（AEMFC）has advantages such as enhanced oxygen reduction via catalysis and use of non-precious metal catalysts,which attracted much attention from researchers.As the core component of AEMFC,the anion exchange membranes（AEMs）should possess several properties,including high ionic conductivity,low swelling ratio and high chemical stability.At present,preparation of AEMs with excellent comprehensive performance is urgently needed for the development of the AEMFC.In this thesis,polyphenylene ether（PPO）is used as the membrane material after bromination and 1-methylpyrrolidine（MPy）functions as the main quaternization agent.Simultaneously,the membrane materials are modified by crosslinking or side chain grafting using seven kinds of star molecules to investigate the effects of the structures on membrane performance:（1）Three kinds of star molecules are selected to directly crosslink the matrix materials.The results indicated that the introduction of star crosslinked structures improved the dimentional and chemical stabilities of the AEMs and reduced the swelling ratio of the membranes.However,the conductivity and stability of the obtained membranes are still needed to improve.（2）The structure of the star crosslinker was modified using a flexible long chain molecule containing a tertiary amine at both ends;the hydrophobic alkyl chains combining with the hydrophilic head groups are expected to form a micro-phase separation structure for high conductivity.Among the crosslinkers,the star structure molecule containing N atom in the center was confirmed to benefit the chemical stability of the AEMs against the attack of OH-ions.The results revealed that the conductivity of the prepared membrane of MPPO-H-10TAPA reached 65.21 mS cm^-1 at 80℃,and it can be maintained above 10 mS cm^-1 after soaking in lmol L^-1 KOH solution at 80℃ for about 580 h.（3）In addition,the quaternary pyrrolidine head groups could be protected by the flexibile side chains for a futher improved stability of the membrane.The results showed that the MPPO-10TBPA-P membrane retained the conductivity above 10 mS cm^-1 by soaking in 1 mol L^-1 KOH solution at 80℃ for approximately 700 h.