Preparation And Characterization Of High Temperature Proton Exchange Membranes Based On Poly(Aryl Ether Ketone)

It can simplify the water and thermal management system of fuel cells,improve the tolerance of Pt electrodes to CO and accelerate the electrode reaction rate to run proton exchange membrane fuel cells at elevated temperatures(100-200℃).As a key component of the high temperature proton exchange membrane fuel cell(HT-PEMFC),high temperature proton exchange membrane(HT-PEM)has received much attention.Phosphoric acid doped PBI membrane has been considered as the most promising HT-PEM because of its high proton conductivity under low relative humidity above 100 ℃.However,a high phosphoric acid content can not only bring a high proton conductivity,but also decrease the mechanical strength of the membranes.Therefore,many reports are focused on how to improve the dimensional stability and mechanical strength of phosphoric acid doped HT-PEM without sacrificing its proton conductivity.In this thesis,Poly(aryl ether ketone)(PAEK)was chosen as the matrix material to prepare phosphoric acid doped HT-PEM due to its excellent mechanical properties and thermal stability.A series of cross-linked PAEK membranes named as BPAEKx-y EAm/z DMIm(x is the bromination degree of BPAEK,y and z represent the molar ratio of EAm and DMIm to theCH2Br group in BPAEK,respectively)were fabricated by adding BPAEK with different bromination degrees as the matrix material and the copolymer of 2-(dimethylamino)ethyl methacrylate(EAm)and styrene(St)as the crosslinker.Meanwhile,1-decanyl-2-methylimidazole(DMIm)was grafted to improve membranes’proton conductivities.The results indicated that the cross-linking structure enhanced the dimensional stability and mechanical properties of membranes.The volume swelling rate and tensile strength at break at room temperature of BPAEK51.2-7.5 EAm/62.5 DMIm are 167.3%and 4.1 MPa,respectively,while that of BPAEK51.2-70 DMIm are 200.1%and 1.5 MPa,and the proton conductivity of BPAEK51.2-7.5 EAm/62.5 DMIm is 45.5 mS cm-1 at 180℃.In this work,a novel HT-PEM having a dual cross-linked structure were prepared based on brominated PAEK and P(VIm-DVB-St)copolymer.P(VIm-DVB-St)was synthesized by copolymerization of 1-vinylimidazole(Vlm),styrene(St)and p-divinylbenzene(DVB),DVB was added as the crosslinker.The introduction of imidazole groups endow the membrane with a good adsorption capacity of phosphoric acid,while the dual cross-linking structure enhances the mechanical properties of the membranes.Thereinto,the conductivity of BPAEK40.0-85 VIm is 117.3 mS cm-1 under anhydrous condition at 180℃,and the tensile strength at break reaches 7.2 MPa at room temperature.Fuel cell tests based on the BPAEK40.0-85 VIm shows a peak power density of 306.3 mW cm-2 at 200℃,and the voltage of the MEA remains stable after continuous operation for nearly 340 h at 160℃.A novel poly(aryl ether ketone)named as PAEK-DB which contains carbon-carbon double bonds in side chains was synthesized from 2,2’-diallyl bisphenol A and 4,4’-difluorobenzophenone.Semi-interpenetrating high temperature proton exchange membranes,denoted as BPAEK/PAEK-DB(x:y)(x:y is the mass ratio of BPAEK to PAEK-DB)were prepared by constructing the semi-interpenetrating polymer network(semi-IPN)via polymerization of carbon-carbon double bonds in PAEK-DB to make the linear quaternary ammoniated BPAEK to be intertwined.The effects of semi-IPN structure on the dimensional stability,proton conductivity and mechanical properties of membranes were investigated.The results show that the semi-interpenetrating structure can restrict the phosphoric acid doping of the membranes and thus decrease the membrane’s proton conductivity.However,the mechanical properties of the semi-IPN membranes are enhanced.For instance,the proton conductivities of semi-IPN membrane BPAEK/PAEK-DB(7:3)and BPAEK/PAEK-DB(7:3)N without semi-IPN structure are 93.2 mS cm-1 and 108.2 mS cm-1,and their tensile strength at break at room temperature are 4.3 MPa and 2.4 MPa,respectively.