Synthesis And Properties Of Poly(Vinyl Alcohol)Homogeneous Anion Exchange Membrane

Alkaline exchange membrane fuel cell has attracted great attention in the field of fuel cells in past decade.The main reason is that it allows the use of non-precious metal catalysts,which is critical to reducing the cost of low temperature fuel cell.However,as one of the key components,anion exchange membrane still suffered from low conductivity and stability.To address the problems,this thesis develops a general stratedy to synehsize homogeouns anion exchange membrane through acetalation based on Polyvinyl alcohol?PVA?,and optimized the AEM performance via structure control.The main work of the thesis includes:1.A dialdehyde containing multiple cationic groups was synthesized with4-bromomethylbenzaldehyde and a diamine,and then grafted onto PVA mainchain to prepare a crosslinked PVA homogeneous membrane through acetalation.The long alkyl group between the ion exchange groups and the backbone can weaken the nucleophilic substitution on the a-carbon,so as to improve the alkaline stability.To increase the ionic conductivity of the membrane,multiple ion exchange groups on crosslinker were designed to increase the ion exchange capacity.The results showed that the as-prepared PVA-QBMB-MC-50%film had a conductivity of 89.10 mS cm^-1 at 80?,a swelling ratio of 10.57%and a water uptake of not more than 50%.The tensile strength of fully hydrated PVA-QBMB-MC-50%membrane was 8.82 MPa.However,the alkaline stability of membrane of PVA-QBMB-MC-50%was poor,after being immersed in80?,6 M NaOH solution for 7 days,the conductivity decreased by 81.7%.2.PVA homogeneous AEM was prepared by acetalization of4-imidazolecarboxaldehyde with PVA and then cross-linked with a binary halohydrarbon containing multiple cationic groups.Imidazole functional groups was adopted to enhance the alkaline stability,as well as the introduction of long alkyl chains to keep quaternary ammonium groups away from the arylene and electron withdrawing groups.The results showed that the as-prepared AEMs exhibited good comprehensive performance,the conductivity of PVA-IMI-MC-0.4 membane was as high as 141.60mS cm^-1 at 80?.However,water upatake and swelling ratio of the membrane needs further regulation.