Study On The Mechanism Of Influence Of Cations And Main Chains On The Performance Of Anion Exchange Membranes

Anion exchange membranes(AEMs)is an important component of anion exchange membrane fuel cells,which plays the role of separating cathode and anode while conducting cations.An ideal AEMs should have high ionic conductivity and sufficient stability under alkaline conditions.However,there is no AEMs with comprehensive performance that fully meets the requirements of fuel cell applications.The anion exchange membrane is composed of a polymer backbones and cationic groups,both of which determine the physical and chemical properties of AEMs.However,how the cation and the polymer backbone affect the ionic conductivity and alkali resistance stability of AEMs has not been systematically and deeply studied.Aiming at the above problems,this paper studies the influence of two polymer backbone and seven cations on the performance of AEMs.The main research progress is as follows:1.A series of AEMs based on seven different cations and two different backbones were synthesized.The seven cations include trimethylamine(TMA),N,N-dimethylethylamine(DMEA),1-methylpyrrolidine(MPY),1-methylpiperidine(MPr D),1-methylimidazole(Me Im),N,N-dimethylaniline(DMAni),and N,N-dimethylbenzylamine(DMBA).The cations are grafted onto poly(vinylbenzyl chloride)(PVB)backbone or brominated poly(2,6-dimethyl-1,4-phenylene oxide)(BPPO)backbone,14 kinds of AEMs were prepared as PVB-TMA,PVB-DMEA,PVB-MPY,PVB-MPr D,PVB-Me Im,PVB-DMAni,PVB-DMBA,BPPO-TMA,BPPO-DMEA,BPPO-MPY,BPPO-MPr D,BPPO-Me Im,BPPO-DMAni and BPPO-DMBA AEMs.2.The ionic exchange capacity,water uptake,swelling degree and ionic conductivity of the above 14 kinds of AEMs were tested respectively,and the influence of ion exchange capacity and temperature on the performance of polyelectrolyte was analyzed.On the premise of the same ionic exchange capacity,discuss the influence of different cations on the performance of AEMs under the same main chain conditions and the influence of different main chains on the performance of AEMs under the same cation conditions.and the rules of action of cations and main chains on the performance of AEMs are summarized.3.Under the premise of the same ionic exchange capacity,the chemical stability of the above 14 kinds of AEMs in hot alkaline solution was tested.The effects of the main chain structure and cation types on the alkali resistance stability of polyelectrolytes are discussed respectively,and then the mechanism of action is obtained,which provides ideas for the subsequent structural design of AEMs.After the above research,the following conclusions are drawn:increasing the ion exchange capacity of AEMs or increasing the temperature can increase the water uptake,swelling degree and ionic conductivity of AEMs;Heterocycle cation-attached AEMs exhibit robust cationic stability,but the ionic conductivity of the membranes needs to be further improved;Aromatic cation attached AEMs exhibit superior OH~-conductivity but inferior cations stability;PVB-AEMs show excellent backbone stability,while BPPO-AEMs show higher OH~-conductivity and cation stability than those of the same cationic-grafted PVB-based AEMs.