Preparation And Properties Of Poly(aryl Indole) Based Anion Exchange Membrane

With the environmental pollution and depletion of traditional energy,alkaline ion exchange membrane fuel cells have attracted much attention due to the high efficiency and environmental friendliness.However,alkaline ion exchange membranes,one of the important components of fuel cells,still face great challenges such as poor dimensional stability,low ionic conductivity and poor alkali stability.Therefore,the development of alkaline ion exchange membranes with good alkali resistance and high ion transport properties remains one of the major targets for alkaline fuel cell applications.In this thesis,the branched poly（ether ether ketone）ionic exchange membranes were synthesized by introducing branched structure,improving the dimensional stability of the membranes.And the aryl ether-free poly（aryl indole）polymers were synthesized in order to improve alkali resistant of the membrane.The introduction of the comb-like side chains improved the microphase separation structure of the membrane and constructed the connected ion channel,improving the ionic conductivity of the membrane.Novel branched poly（ether ether ketone）based anion exchange membranes were prepared by the copolymerization of phloroglucinol,methylhydroquinone and4,4’-difluorobenzophenone and following functionalization.The effects of the branched polymer structures on the membrane’s properties were investigated.The swelling ratios of all the membranes were kept below 15%at room temperature and had good dimensional stability at elevated temperatures.The branching degree had almost no effect on the dimensional change,but played a great role in tuning the nanophase separation structure.The BPEEK-3-Pip-53 membrane showed the best performances and the ionic conductivity was 43mS cm^-1 at 60°C.After immersed for 336 hours in a 1 mol L^-1 KOH aqueous solution at60°C,its ionic conductivity and ion exchange capacity were 75%and 83%of the initial values,respectively,showing good alkali stability.Because the poly（ether ether ketone）backbone which contained aryl ether bonds,it was easily degraded by hydroxide attack,in order to further improve the alkali resistance of the membrane,the poly（aryl indole）polymers without aryl ether bond were synthesized by super acid catalyzed reaction through indole-2,3-dione and biphenyl,and then through the reaction by the amide with 2,3-epoxypropyl trimethyl ammonium chloride.A novel quaternized poly（aryl indole）anion exchange membrane was successfully prepared.Since the aryl ether bond was not contained,it was effectively reduced that the attack of the hydroxide chain on the main chain skeleton of the membrane,improving the alkali resistance of the membrane.Immersed in the alkaline solution of 1 mol L^-1 KOH aqueous solution for 672 hours at 80°C,the ionic conductivity and ion exchange capacity for membranes reached 84%and 89%of before that,respectively.This proved the membrane had good alkali resistance.The performance of the fuel cell was tested at 80°C.The fuel cell established the open circuit voltage of 0.97 V and the maximum power density was up to 68 mW cm^-2 when the current density was 150 mA cm^-2.In order to further increase the ionic conductivity of the membrane and improve the alkali resistance,the aryl ether-free poly（aryl indole）polymer was grafted with the long chains containing 1-bromohexyl-N-methylpiperidinium and 1-bromo-n-hexane to form a comb structure.The comb-like poly（aryl indole）based anion exchange membranes were prepared.The migration of the flexible long chains,the steric hindrance of the hexyl alkyl chain and the stable N-methylpiperidinium favored the membranes to exhibit superior performance.The PBN-100Pip membrane had the ionic conductivity of 54 mS cm^-1 at 20°C and 108 mS cm^-1 at 80°C.The PBN-Pip membranes had good alkali stability.After treatment for 1000 hours in 1 mol L^-1 KOH aqueous solution at 80°C,the ionic conductivity and ion exchange capacity of PBN-100Pip membrane were not reduced.There was no cation loss in the ¹H NMR spectrum of the membrane before and after the comparison treatment.The fuel cell performance was tested.The single fuel cell of PBN-100Pip membrane had the open circuit voltage of 1.02 V and the maximum power density of 404 mW cm^-2 at current density of 960 mA cm^-2 at 80°C.It indicates that PBN-Pip membrane has good development potential and prospects in the application of fuel cell.