Preparation And Performance Of Anion-Exchange Membranes Based On The Novel Polyphosphazene-bearing Crown Ether Units

As one of the key components in alkaline anion exchange membrane fuel cells,alkaline anion exchange membranes(AEMs)play an important role for transmission of OH-,cutting off the direct contact between the fuel and oxidizer in fuel cell operation.The majority of AEMs have been researched based on polymer carrying quaternary phosphonium,quaternary ammonium or imidazolium cationic groups.However,the low ionic conductivity and poor alkaline stability of these cationic polymer electrolytes are major challenges.For these reasons,it is necessary to look for other cationic groups to improve the alkali resistance and ionic conductivity of AEMs.In this paper,based on the advantages of chemical modification and high load density of polyphosphazene backbone,and strong coordination stability between alkaline metal cation and crown ether,three different types of novel polyphosphazene-based polymers carrying pendant crown ether groups were synthesized and characterized.All the three types of membranes were immersed in 30? 2 M KOH solution for 800 h,and show very good alkali stability,which has no obvious decrease in OH-conductivity and IEC during the whole testing period.The main research contents are as follows.1.Preparation and performance of serial PHCME-POH-x membranes.The crown ether monomer HCME was synthesized through Williamson synthetic methods with glycerol and pentaerythritol as raw materials.Polyphosphazene was chosen as polymer backbone.Nucleophilic substitution was employed for the preparation of polyphosphazene-based membrane bearing HCME and 1-pentanol.The prepared PHCME-POH membranes was obtained after accomplishing potassium ion-exchange.The IEC of the PHCME-POH-45 is 1.53 mmol g-1 at 25?,and conductivity is 40.6 mS cm-1 at 80?.2.Preparation and performance of PPACE-POH-x membranes.The crown ether monomer PACE was synthesized via 4-steped reactions with triethanolamine and tetraethylene glycol as raw materials.Semilar the HCME series,the corresponding polyphosphazene-based membrane bearing PACE and 1-pentanol were prepared.after accomplishing potassium ion-exchange,the IEC of PPACE-POH-45 is 1.32 mmol g-1 at 25?,and conductivity values is 42.6 mS cm-1 at 80?.3.Preparation and performance of PPACEP-PVA-x cross-linked membranes.To obtain high OH-conductivity and good mechanical properties,a kind of novel cross-linked membranes PPACEP-PVA were prepared by tuning the feeding mass ratio of the PPACEP and PVA.The optimized performances are obtained when the mass ratio between PPACEP and PVA is 0.4:0.6.The highest conductivity values of the PPACEP-PVA-40 is 79.6 mS cm-1 at 80?.These results indicate that these membranes may be candidate materials for anion exchange membranes in fuel cells application.