The Preparation Of Polysulfone-based Anion Exchange Membranes Functionalized By Imidazolium With Hydrophilic Side Group

Alkaline anion exchange membrane fuel cells（AEMFCs）have attracted more and more attention because of its characteristics of high oxidation kinetics and low cost in catalysts.Alkaline anion exchange membrane（AEM）is the core component of AEMFC and its performance directly affects the development of AEMFC.At present,low ion conductivity and poor alkali stability are two major problems restricting the development of AEMFC.In this paper,three modified imidazoles with ether-bonded side groups were designed and synthesized,and anion exchange membranes were prepared by introducing this modified imidazoles into polysulfone backbones to explore their effects on hydroxide conductivity and alkali stability.In addition,in the case of high IEC,the swelling of the membranes containing the hydrophilic side is too high and the alkali stability is poor.A hydrophobic crosslinked structure is introduced into the membranes,and the alkali stability of the membranes is expected to be improved by the structure of the cross-linking chain.The main contents are as follows:（1）Three modified imidazole with different hydrophilic side group,1-（4-（2-methoxy-ethoxy）butyl）-2-methyl-1H-imidazole（1）,1-（4-（2-（2-methoxyethoxy）ethoxy）-butyl）-2--methyl-1H-imidazole（2）and 2-methyl-1-（2,5,8,11-tetraoxapen-tadecanyl）-1H-imidazole（3）were designed and synthesized,and its structure was accurately characterized by NMR spectroscopy.NMR spectroscopy confirmed the successful synthesis of the three kinds of modified imidazole and pure product obtained.（2）Various imidazolium anion exchange membranes based polysulfone were prepared successfully,namely PSf-1,PSf-2,PSf-3 and PSf-Im.PSf-2 exhibited the highest hydroxide conductivity of 35.2 mS/cm（the IEC is 1.05 mmol/g）under similar IEC conditions at room temperature.After the three kinds of anion exchange membranes with 60%grafting degree of functional groups were soaked in 1mol/L KOH solution in 80 ^oC for 168 h,the conductivities decreased by 11%,16%and 21%,respectively and PSf-1 membrane exhibits the best alkali stability.In addition,as the length of the hydrophilic side groups increases,the elongation at break of the membrane gradually increases and the toughness enhances.（3）In order to further improve the alkali stability of the ether-bond-containing membrane,an polysulfone membrane PSf-ImOEG-CL with crosslinked structure was prepared with1,6-hexamethylenediamine as a cross-linking agent.The introduction of the cross-linked structure can effectively control the water content in the membrane and improve the dimensional stability of the membrane.When the IEC was 1.20 mmol g^-1,the conductivity decreased by less than 10%after immersed in 1 mol/L KOH solution 80 ^oC for 168 h.Under similar IEC conditions,cross-linked membranes are significantly more dimensionally and alkali-stable than uncrosslinked membranes.