Synthesis And Properties Of Modified Polyimide Proton Exchange Membrane

Recently,considerable attentions have been paid to proton exchange membrane fuel cells(PEMFCs)as a clean electric source for automobile,stationary,and portable power applications due to their lower weight,high efficiency,and low poison emission.Proton exchange membrane(PEM)is a critical component in PEMFC.Perfluorosulfonic acid(PFSA)ionomer membranes,e.g.Nafion?,Aciplex?,Flemion?are considered as state-of-the-art membrane for fuel cell applications due to their excellent chemical and physical stability along with high proton conductivity.However,complex synthetic procedure,low glass transition temperature,restricted operation temperature(<80°C),and high fuel crossover limit their application.Sulfonated polyimides membranes are one of the potential candidates for PEM application,due to their high thermal,chemical and mechanical stability,excellent film forming ability,strong resistance to fuel crossover and high proton conductivity.One of the main disadvantages of sulfonated polyimide(SPI)based membranes is their tendency of hydrolysis under the fuel cell operating conditions,which in turn deteriorates the mechanical properties of the membrane.Therefore,two SPIs containing imidazole groups were prepared to solve the above-mentioned problems of SPI.In order to further enhance the thermal stability,dimensional stability,hydrolysis stability,oxidation stability and proton conductivity of SPI,it was cross-linked and composite modified.To investigate the effect of sulfonation on the performance of proton exchange membranes,2,2-'benzidinedisulfonicacid(BDSA)and4,4'-diaminopurine-2,2'-disulfonicacid(DSDSA)reactedwith1,4,5,8-naphthalenetetracarboxylicdianhydride(NTDA),2-(4-aminophenyl)-5-aminobenzimidazole(DAPBI),respectively.A series of SPIs with different degrees of sulfonation were prepared.In view of the problem of poor hydrolysis stability of SPI,?-glycidyloxypropyltrimethoxysilane(KH-560)was used for cross-linking modification treatment to explore the effect of the amount of cross-linking agent on its properties.In order to further enhance the proton conductivity of proton exchange membrane,the proton exchange membrane was modified by PDA@CNTs to study the effect of PDA@CNTs doping amount on its performance.Using nuclear magnetic resonance spectroscopy(~1H NMR)and infrared spectroscopy(FT-IR)to characterize the material structure,~1H NMR indicated that BSPI and DSPI polymers were synthesized.FT-IR displayed successful preparation of cross-linked proton exchange membranes and composite proton exchange membranes.Through thermal weight loss analysis and mechanical properties test,all proton exchange membranes have good thermal and mechanical stability and can meet the requirements of fuel cells.For BSPI and DSPI membranes,as the degree of sulfonation increases,the size stability,hydrolysis stability and anti-radical oxidation stability of the proton exchange membrane decrease,while the proton conductivity increases with the increase of the degree of sulfonation.After cross-linking,the size stability,hydrolysis stability,and anti-radical oxidation resistance of the proton exchange membrane are improved.After composite modification,the dimensional stability,anti-free radical stability and proton conductivity of the composite membrane increased;the proton conductivity decreased with the increase of the amount of PDA@CNTs.