Preparation And Performance Of New Imidazolium Anion Exchange Membranes For Alkaline Fuel Cells

As one of the core components of alkaline fuel cells(AFCs),anion exchange membranes still face some problems,such as low ion conductivity and poor alkali stability,which hinders the commercial application of alkaline fuel cells.In this thesis,three series of AEMs were designed and prepared to improve the hydroxide ion conductivity and alkali stability of imidazolium ions.The detailed research is as follows.1.Study on sterically hindered polybenzimidazolium anion exchange membrane.Using bibenzoyl as the starting material,after a simple three-step reaction,4'-hexyl-5'-octyl-[1,1',2',1"-terphenyl]-3',6'-dicarboxylic acid diethyl ester(HOTP)monomer with steric hindrance was synthesized and characterized.A series of novel polybenzimidazolium anion exchange membranes were prepared by copolymerization with different ratios of isophthalic acid and biphenyltetramine under microwave conditions and quaternization with iodo-n-butane.Some parameters including conductivity,water absorption,swelling ratio,ion exchange capacity and alkali stability for membrane materials have been tested.The results show that the IEC of mPBI-HOTP-20%-(n-Bu)polybenzimidazolium membrane is 1.98 mmol·g-1,and the ion conductivity is 35.35 mS·cm-1 at 80?.The alkali stability test of the membrane showed that after being immersed in 1 M NaOH solution at 60? for 1440 h,its ionic conductivity decreased by 11%and IEC decreased by 10%,showing better alkali resistance.2.Study on sterically hindered imidazolium functionalized PVC membrane.Using a simple one-step reaction,1-butyl-2-(2,6-dimethylphenyl)-4,5-diphenyl-1 H-imidazole(BPIM)was prepared and characterized.A series of PVC BPIM-x anion exchange membranes were prepared by reacting different percentages of BPIM with polyvinyl chloride.The ion conductivity of alkaline membranes has been greatly improved.At 30?,the OH-conductivity of PVC-BPIM-x series membranes is 34.45-39.67 mS·cm-1,while at 80?,the OH-conductivity of PVC-BPIM-x series membranes is in the range of 92.84 to 97.10 mS·cm-1.The alkali resistance test of the membrane showed that when PVC-BPIM-20%membrane was immersed in 1 M NaOH solution at 60? for 1320 h,the conductivity decreased by about 57.47%.3.Study on sterically hindered imidazolium functionalized polyvinyl alcohol membrane.The BPIM is quaternized with 1,5-dibromopentane to obtain BPIM-(CH2)5-Br,which is then grafted on a polyvinyl alcohol skeleton at a certain ratio and cross-linked.The obtained PVA-BPIM-(CH2)5-x membrane material has good thermal stability and tensile properties.The PVA-BPIM-(CH2)5-35%membrane has the largest ion conductivity at 80?,reaching 69.27 mS·cm-1.Alkali stability test of PVA-BPIM-(CH2)5-3 5%membrane was proceeded by immersing in 1 M NaOH aqueous solution at 60? for 720 h.The OH-conductivity was only reduced by nearly 15%,showing good alkali resistance stability.