Preparation And Characteristics Of Polyethersulfone-based Anion Exchange Membranes Containing Multiple Long Side Chains

Alkaline anion exchange membrane fuel cells（AAEMFCs）have been considered as a new energy technology with the advantage of clean,efficiency and environmental friendliness.As one of the key components of the AAEMFCs,alkaline anion exchange membranes（AAEMs）play the roles of hydroxide conductor and fuel/oxidant separator,which directly influences the energy conversion efficiency and service life of the battery.However,AAEMs still have the problem of low conductivity of hydroxide,which limits the commercial application of AAEMFCs.The preparation of AAEMs with high ionic conductivity,good dimensional stability and excellent alkali stability is the main focus of current research.In this work,it is proposed to synthesize amino-substituted polyethersulfone based on amino-substituted phenolic monomers and then graft functionalized ionic liquids with alkyl chains onto the polymers.The polyethersulfone has multiple long side chains in one repeating unit.This structure will improve the local charge density and promote the microphase separation of membranes,which will be able to form the ion transport channels to improve the ionic conductivity.In this work,a series of imidazolium functionalized polyethersulfone-based anion exchange membranes（A-PES-ImOH）with different degree of functionalization and different length of the side chains were prepared.The results show that the ionic conductivity of A-PES-ImOH with butane side chains increases from 18.6 mS cm^-1 to 35.0 mS cm^-1 at 20 ℃ with the IEC increasing from 0.83 mmol g^-1 to 1.46 mmol g^-1,while their swelling ratio just increases from 5.7% to 15.9%.The A-PES-Im OH-30^-10 C exhibits higher ionic conductivity than the A-PES-ImOH-30,whose ionic conductivity reaches 46.6 mS cm^-1 at 20 ℃.However,due to the limitation of solubility,the ion exchange capacity（IEC）of the A-PES-ImOH is limited to a low level,and the overall characteristics of the membranes are limited.In order to improve the ionic conductivity of the membranes which was limited by the solubility,4-Methylmorpholine was used to prepare polyethersulfone-based anion exchange membranes（A-PES-MmOH）with higher IEC level.The ionic conductivity of A-PES-MmOH increases from 38.5 mS cm^-1 to 54.9 mS cm^-1 at 20 ℃ with the IEC increasing from 1.03 mmol g^-1 to 1.79 mmol g^-1.The conductivity of A-PES-MmOH-30 is up to 110.4 mS cm^-1 at 80 ℃ with a low swelling ratio of 33.5%.All the results show good ionic transport property and dimensional stability of the membranes.In order to further increase the local charge density in the membranes to improve the conductivity,the nanocomposites functionalized by 4-Methylmorpholine（Al₂O₃-Mm）were synthesized and doped in A-PES-MmOH.A series of composite anion exchange membranes（A-PES-MmOH-30/Al₂O₃-MmOH）with different mass ratio of Al₂O₃-Mm were prepared.The conductivity of the composite membranes showes a tendency to increase firstly and then decrease with the increasing of the nanoparticle content.When the mass ratio reaches 12 wt.%,the composite membrane showes the highest ionic conductivity of 62.9 mS cm^-1 at 20 ℃,showing better ionic conductivity than the A-PES-MmOH.