Preparation And Properties Of Functionalized RGO Crosslinked Polysulfone-based Anion Exchange Membranes

In recent years,anion exchange membranes?AEMs?have attracted much attention and at the same time a series of significant progress have been made in this field.AEMs can be applied to the electrochemical storage device and energy conversion systems such as fuel cells,redox flow batteries,and electrodialysis devices.However,there still exist a series of issues such as low ion conductivity and long-term chemically stability under alkaline condition for AEMs,which seriously hinders the development of practically useful AEM fuel cells.Introducing more ionic conductive groups in polymer-based AEMs can improve the ion exchange capacity and further overcome the disadvantage of low ion conductivity for AEMs.However,the excessive swelling of AEMs caused by exorbitant IEC value may reduce the dimensional stability of membranes.Constructing cross-linking structure in AEMs is a popular way to optimize the trade-off between dimensional stability and ion conductivity.Inorganic fillers can significantly affect the characteristics of composite AEMs in properties such as anion conductivity,mechanical property and alkaline resistance,etc.Therefore,the structure design and performance study of AEMs are very important.Herein,we try to combine the advantages of inorganic fillers and cross-linking strategies to construct novel anion exchange membranes with excellent performance.This thesis includes the following two parts:In the first part,we prepared highly ion conductive quaternized polysulfone?QPSU?-based AEMs?CQPSU-X-rGO?cross-linked by reduced graphene oxide functionalized with different-chain length small molecules.The cross-linked QPSU AEMs?CQPSU-n?with organic small molecules as cross-linkers were also prepared to serve as control samples.As compared with AEMs cross-linked by short-chain cross-linkers,the cross-linked membranes with elastic long-chain cross-linkers?PTMHDA?and their modified rGO?LrGO?have higher ion conductivity due to the generation of more quaternary ammonium groups and nanophase separated morphology.Especially,the functionalized rGO-cross-linked composite membranes?CQPSU-X-LrGO and CQPSU-X-SrGO?exhibited better conductivity and chemical stability compared with cross-linked polymer membranes?t-CQPSU-n and p-CQPSU-n?with small molecule cross-linkers.The highest ion conductivity was achieved for rGO-cross-linked AEMs(CQPSU-2%-LrGO,?^-_OH=139.7 mS/cm at 80 ^oC)owing to the increasing IECs and uniform nanophase separation formed during the cross-lingking process.Thus,the functionalized rGO was demonstrated to be a potential cross-linker and filler for preparing cross-linked AEMs with improved properties.In the second part,we proposed a facile strategy to construct reduced graphene oxide?rGO?cross-linked polysulfone-based AEMs with improved properties.rGO was non-covalently modified with pyrene-containing tertiary amine small molecule and polymer via?-?interactions.The as-prepared functionalized rGO?TrGO and PrGO?as both cross-linkers and fillers to fabricate quaternized polysulfone?QPSU?-based AEMs?CQPSU-X-TrGO and CQPSU-X-PrGO?for the first time.The cross-linked membranes can tighten the internal packing structure,and enhance the alkaline resistance,ion conductivity and oxidative stability of AEMs.Furthermore,the hydrophilicity and flexibility of the CQPSU-X-PrGO membranes were significantly improved as compared with that of CQPSU-X-TrGO membranes.PrGO-cross-linked membranes(CQPSU-2%-PrGO,?^-_OH=117.7 mS/cm)displayed higher ionic conductivities at 80 ^oC than TrGO-crosslinked membranes(CQPSU-1%-TrGO,?^-_OH=87.2 mS/cm).The remarkable nanophase separation can be observed in the CQPSU-X-PrGO membranes by TEM.This feasible strategy can be efficiently used to prepare new type of cross-linked organic-inorganic nanohybrid AEMs with excellent chemical stability and high ionic conductivity.