Preparation And Property Of Proton Exchange Membrane Containing Polyhedral Oligomeric Silsesquioxane Block Copolymer

Proton exchange membrane fuel cell（PEMFC）is one of the most promising sustainable power source.As the core component,proton exchange membrane（PEM）plays the role of transporting protons and isolation of cathode and anode,which has a great influence on fuel cell performance.Nafion is the most widely used commercialized PEM due to the high proton conductivity under low temperature,good chemical stability and mechanical property.However,significant reduction of proton conductivity beyond 80 oC or under low humidity（< 50%）and high cost may limit its industrial application.Therefore,the goal of the next generation of PEM is maintaining high proton conductivity under high temperatures or low humidity.Compared to random copolymer,ionic block copolymer has been recoginized as the most promising candidates in PEM for its special microphase separation morphology and the tunable hydrophilic ionic phase domain.The structure of microphase and ion domain connectivity are affected by the distrubtuion of ionic groups of block copolymer,which play a great influence on proton conductivity under high temperature or low humidity.Therefore,ionic block copolymer with complex topology may achieve demaned ion domain microstructure,which facilating higher proton conductivity.The tunable ionic distribution and connectivity of the ion domain morphology may be effectiveto solve the reduction of proton conductivity of PEM under high temperature or low humidity.Polyhedral oligomeric silsesquioxane（POSS）containing block copolymer has great potential in designing novel ordered nanostructures due to its functionality and well-defined self-assembly behavior.POSS as inorganic filler has been incorporated into PEMs has already achieved enhanced proton conductivity,physical and chemical durability and mechanical properties.The main motivation of this study is to design sulfonated star-shaped POSS containing block copolymers and to investigate their morphology-property relationship for PEM applications.POSS as core is used macroinitiator to polymerize methyl methacrylate as the inner block and styrene as the outside block.The polystyrene block was sulfonated subsequently to afford novel PEMs.The copolymer with different block length and SPS distribtuion may be tuned by synthesistechnique.The relationship between structure,microstructure and proton conductivity property was studied.Two blends were prepared by introducing PVDF and GO into POSS-PMMA-SPS copolymer matrix.The main research contains the following context:（1）POSS as initiator,two different block proportion of star block copolymer of POSS-（PHEMA-b-PS）and POSS-（PMMA-b-PS）₈ ware synthesised by the method of ATRP.The structure of the copolymer was determined by FTIR,¹H NMR and GPCs respectively.The polymers were POSS-（PHEMA84-b-PS78）₈,POSS-（PHEMA73-b-PS64）₈,POSS-(PMMA₁₆-b-PS₂₀₀)₈ and POSS-(PMMA₂₆-b-PS₁₅₆)₈。（2）Preparation of sulfonated PEM was studied by two methods of the sulfonation in solution and sulfonation in membrane.The ion exchange capacity,proton conductivity and the water absorption and swelling rate by two sulfonation methode are studied.It is found that two POSS-（PHEMA-b-SPS）₈ membrances have high IEC and proton conductivity under sulfonation in solution techique.Because of-OH in PHEMA block,the PEM exhibits a poor solubitlity which may become the main obstale for PEM applications.（3）FTIR,¹HNMR,GPC and XPS was to determine the molecule structure of the two star block copolymer.And b POSS-(PMMA₁₆-b-SPS₂₀₀)₈ and POSS-(PMMA₂₆-b-SPS₁₅₆)₈ was obtained by conbination of.Two PEMs were prepared by sulfonation in solution techique.Under low relative humidities（RHs）,the PEM with longer SPS block exhibites higher proton conductivity than the PEM with shorter SPS block when compared at same hydration number（λ）conditions,which was attributed to the better connected hydrophilic domains of the former;The transmission electron microscopy（TEM）and atomic force microscope（AFM）analysis may illustrate the reason of that.which was found with a long chain of SPS segment of PEM for proton conduction connected to two of the microfacies of morphology;Low field nuclear magnetic resonance analyzer was to determine the distribution state of different PEM of weakly bound water（T2）,it was found that longer SPS corresponding higher content of weakly bound water to increase its proton conduction plays an important role.（4）Blend proton exchange membrane was prepared by blending polyhedral oligomeric silsesquioxane（POSS）containing star-shaped block copolymer POSS-(PMMA₂₆-b-SPS₁₅₆)₈ with polyvinylidene fluoride（PVDF）.The effect of PVDF content on the properties of blend membrane was investigated,ion exchange capacity（IEC）,proton conductivity and water uptake,swelling rate and spin-spin Relaxation time（T2）of the blend PEM are studied.The results show that IEC,water uptake and swelling rate decreases with adding PVDF amount in blend membrane.Blend proton exchange membrane shows higher dimensional stability.The Proton conductivity of blend PEM shows a continuous increasing with adding different ratio of PVDF.The dependence of proton conductivity on relative humidity was reduced owing to adding PVDF.It was found that proton conductivity of 50% PVDF blend membrane is higher about one order of magnitude than pure copolymer membranein 30% RH at 80℃.The reason of proton conductivity been enhancing at low RH is investigated by comparing T2 relaxation time of different binding water via low field NMR.（5）Blend proton exchange membrane with polyhedral oligomeric silsesquioxane（POSS）star block copoly-mergraphene oxide（GO）/polyhedral oligomeric silsesquioxane-（poly-methyl methacrylate-block-polystyrene）(POSS-(PMMA₂₆-b-SPS₁₅₆)₈)was prepared by the blending method.The effect of GO content on the properties of blendmembrane was investigated by testing ion exchange capacity（IEC）,proton conductivity and water uptake and swelling rate.The ion exchange capacity IEC of the blend membrane increases with adding GO,while water uptake and swelling rate reduces.The blend membrane shows higher dimensional stability in the determination of temperature range.The decline of the conductivity of pure polymer membranes owing to water loss in 80 ℃ can be improved by adding GO.In the meantime proton conductivity of proton exchange membrane can been improved.It was found that the proton conductivity of the blend proton exchange membrane with GO 0.3wt% content is approximately 3.2 times bigger than the pure polymer membranes in 100 RH % at 80℃.