Preparation And Properties Of Adamantyl Quaternary Phosphonium Cationic Alkaline Membranes

Anion exchange membrane fuel cell(AEMFCs)have attracted great attention owing to their independence on precious metal catalysts and effective oxygen reduction.However,as the key of the AEMFCs,anion exchange membranes(AEMs)still face a series of problems to be solved,such as low ion conductivity,poor alkali resistance.Therefore,the development of anion exchange membrane with excellent performance is a necessary prerequisite for the commercial use of AEMFCs.Based on these problems,in order to balance the ionic conductivity,alkali stability and dimensional stability of anion exchange membrane,the following exploration has been carried out:1.Preparation and properties of di(1-adamantane)n-butyl n-butyl amino-phosphonium hexafluorophosphate(DABAPP)functionalized polyphenylene ether(PPO)alkaline membranes.In order to improve the alkali stability of quaternary phosphonium cations,adamantane with high stability and large steric hindrance was selected as the substituent to synthesize DABAPP.It was loaded on the brominated polyphenylene ether with high stability and mechanical strength,and triethylamine was used to replace excess benzyl bromide to prepare PPO-DABAPP-x series anion exchange membranes.The prepared alkaline membranes have good mechanical properties,and the ionic conductivity of PPO-DABAPP-40% is32.4 mS/cm at 80 ℃.After soaking in 60 ℃ 2M KOH solution for 1200 h,the ionic conductivity remained about 71%,the alkali resistance was slightly insufficient.2.Preparation and properties of(4-hydroxyphenyl)di(1-adamantyl)n-butyl phosphonium bromide(HDABPB)functionalized polydichlorophosphazene(PDCP)alkaline membranes.The alkali stability of the anion exchange membrane decreased because of the introduction of triethylamine and benzyl loading structure.In order to improve the alkali stability of the membrane,HDABPB with large steric hindrance was synthesized and loaded on the PDCP skeleton with high stability and flexibility.A series of anion exchange membranes PDCPHDABPB-x were obtained by adjusting the substitution ratio.The ionic conductivity of PDCP-HDABPB-55% anion exchange membrane is 25.6mS/cm at 80 ℃,and the IEC is 0.59 mmol/g.After immersion in 2M KOH solution at 60 ℃ for 1200 h,the ionic conductivity remains 86% of its initial value.The alkali resistance of the membrane is improved,but the ionic conductivity and mechanical strength are low.3.Preparation and properties of PVA-quaternary phosphonium functionalized polyphosphazene blend crosslinked composite membrane(PVA-PHDABPB-x).In order to improve the ionic conductivity and dimensional stability of the alkaline membrane,the modification methods of blending and crosslinking were adopted,PVA-PHDABPB-x composite membrane was prepared by blending PDCP-HDABPB with PVA which was rich in hydrophilic hydroxyl group,and crosslinking with glutaraldehyde.The highest ionic conductivity is 41.2 mS/cm at 80 ℃.The ionic conductivity decreased by 12% after soaking for 1200 h in 2 M KOH at 60 °C.This series of anion exchange membranes have higher ionic conductivity,alkali stability and mechanical strength than PDCPHDABPB-x series membranes.