Preparation And Characterization Of Crosslinked Anion Exchange Membranes Based On Poly(Phenylene Oxide)

Anion exchange membranes(AEMs)are the key components of alkaline polymer electrolyte fuel cells(APEFCs).The membrane performance determines the efficiency and lifetime of the APEFCs.The primary requirements of the AEMs for the APEFCs include:high ionic conductivity;good mechanical properties and superior stability in alkaline medium at elevated temperatures.Currently,it is a challenge to endow the prepared AEMs possessing superior properties and satisfying all of the requirements simultaneously.In this work,the polyphenylene oxide(PPO)is used as polymer membrane material.After bromination,the polymer was functionalized by using triethylamine(TEA)as the functional reagent.The quaternary ammonium functionalized polymer was crosslinked with different crosslinking reagents for enhanced properties of the AEMs.Several crosslinkers including p-xylenediamine(PXD),1,3-diaminopropane(DAP),1,6diaminohexan(DAH)and 4,4-methylenedianiline(MDA)were chosen to crosslink the quaternary ammonium functionalized PPO,respectively.The properties of the crosslinked membranes were investigated compared to non-crosslinked membranes,the crosslinked membranes exhibited better mechanical properties,dimensional stabilities and chemical stabilities.For example,The MDA crosslinked membranes having a crosslinking degree of 15%exhibit a tensile strength at break of 25.3 MPa at room temperature and its volume swelling is only 68.2%.Hybrid membranes containing organic and inorganic segments were prepared hybrid by doping N,N-dimethyl-3-(trimethoxysilyl)-1-propanamine(TPMS)in the polymer.After hydrolysis,TPMS formed Si-O-Si crosslinking structure between polymer chains.Because of the quaternary ammonium(QA)containing crosslinker,this hybrid membrane exhibits acceptable conductivity.The QAPPO/5Si membrane exhibited an anion conductivity of 41.5 mS cm-1 at 80℃ and the tensile strength at break of 9.7 MPa at room temperature.In order to improve chemical stability of the membranes,aminopropyltrimethoxysilane(APMS)and trimethyl[3-(trimethoxysilyl)-propyl]-ammonium chloride(TPAC)were used as crosslinking reagents to perform the polymer crosslinking.In this case,QA groups were dispersed randomly in the crosslinking structure.The APMS and TPAC co-crosslinked membranes exhibited high conductivities as well as good mechanical and chemical stability.The conductivity of QAPPO-10APMS-20TPAC reached 34.8 mS cm-1 at 80℃.After soaking in 1 mol L-1 KOH at 80℃ for 200 hours,its conductivity still reached 25.7 mS cm-1 at 80℃(73%of the pristine conductivity is retained).