Preparation And Characterization Of Polysulfone-based Hydroxide Exchange Membranes

As anion exchange membrane is the key component of hydroxide exchange membrane fuel cells (HEMFCs), the R&D of excellent anion exchange membrane with high conductivity good mechanical and chemical stability is the focus of nowadays HEMFCs researchs.Research ideas are mainly focused on the design of the polymer backbone and basic functional groups,that is,functional monomer polymerization to form block polymer and halomethylation of aromatic polymers followed by reactions with highly alkaline, stability, good basic quaternized groups to get functional polymers.In this thesis, polysulfone with excellent thermoplastic performance was chosen as the matrix,respectively,using homogeneous quaternized method, and developing urotropin,l-methylimidazole which has long branches chain with ether bond as new quaternary ammonium reagent methods, to prepare of high performance polysulfone-based anion exchange membrane.According to the problem of uniform reaction、low ion conductivity of Heterogenious membranes,a series of trimethylamine-functional polysulfone anion exchange membrane were successfully prepared through the homogeneous quaternization reaction of trimethylamine and chloromethylated polysulfone. Homogeneous and heterogeneous membrane have the ion exchange capacity of 0.52-1.13 mmol g-1 and 0.56-1.28 mmol g-1,respectively. Compared with the heterogeneous membrane, homogeneous quaternization membrane can achieve higher degree of quaternary ammonium, and therefore get more quaternary ammonium groups (IEC has an increase of approximately 10%) and higher water uptake about increase of 8.8%,the increase of hydroxide conductivity which were prepared by homogeneous method is much larger than that of IEC and water uptake.TEM indicates that homogeneous membranes possesses a better micro-phase separation structure.Although hydroxide conductivity of homogeneous polysulfone membranes have the improved conductivity in a certain degree, it can’t solve the problem of quaternary ammonium group drop at high temperature and alkaline solution. Hexaminium-functional polysulfone membranes(CPSF-QuOH) were synthesized by the reaction of CMPSF and hexamine as a new quaternary ammonium agent successfully.CPSF-QuOH membranes have been crosslinked partially because hexamine has four nitrogen active sites,therefore quaternization degree and degree of crosslinking can be confirmed according to 1HNMR integral area. CPSF-QuOH membrane have the ion exchange capacity of 1.39-2.23 mmol g-1, degree of crosslinking in the 7.6-21%, water uptake and the degree of swelling were maintained at 30% and 20%, conductivity increased from 18.2 mS cm-1 to 40 mS cm-1 at 30℃.The results show that CPSF-QuOH membranes have high hydroxide ion conductivity and good mechanical stability. CPSF-QuOH membranes have good thermal stability because of initial decomposition temperature up to 204℃ and good chemical stability which have 12.8% decline of hydroxide ion conductivity after tested under 1M KOH at 60℃ for seven days.In order to further improve the stability of the anion exchange membrane, imidazolium-functionalized PSFs with ether bond grafted side chain were synthesized successfully by the Williamson reaction of CMPSF and 1-(2-hydroxyethyl)-3-methyl imidazole chloride salt (EPSF-ImCl),and then EPSF-ImOH membranes with theoretical IEC 1.37-1.95mmol g-1 were prepared by the solution casting method. EPSF-ImOH 1.22 membranes have hydroxide ion conductivity of 27.4 mS cm-1 at 20℃ and 72 mS cm-1 at 60℃. which have theoretical IEC 1.95mmol g-1. EPSF-ImOH membranes have good thermal stability because of initial decomposition temperature up to 169℃ and good chemical stability which have approximately no decline of hydroxide ion conductivity after tested under 1M KOH at 80℃ for 144 hours.