Study On Proton Exchange Membrane Of Sulfonated Polyimide Containing Imidazole Group For Fuel Cell

Proton exchange membrane(PEM)is an important component of proton exchange membrane fuel cell(PEMFC).It has the double effect of blocking fuel and electrolyte and acting as proton conduction medium.The Nafion membrane produced by Du Pont is a commercially available PEM due to its outstanding proton conductivity and chemical stability.However,the Nafion perfluorosulfonic acid membrane preparation process is complicated and expensive,which hinders its wide application in fuel cells.Sulfonated nonfluorinated polymer membranes have become the priority of PEM research because of their excellent proton conductivity,polymer structure design,good thermal stability and chemical stability.Sulfonated polyimide(SPI)is a good proton exchange membrane material because of its outstanding proton conductivity,mechanical properties and thermal stability,lower cost than Nafion,and environmental friendly non-fluorine materials.The results show that the sulfonated polymer containing imidazole group has excellent radical oxidative stability,and the sulfonated polymer membrane with ether bond has more excellent flexibility.In this article,a novel non-sulfonated diamine monomer containing imidazole group and ether bond,namely 2-(4’-(4-aminophenoxy)-[1,1’-biphenyl]-4-yl)-1H-benzoimidazol-6-amine(AABBI).SPI with different proportions was prepared by random copolymerization.SPI with better comprehensive performance was screened out and blended with sodium lignosulfonate(SLS)and sulfonated mesoporous silica(SMCM),respectively,to prepare SPI/SLS and SPI/SMCM proton exchange composite membranes.A new type of non-sulfonated diamine monomer containing imidazole group was synthesized,using the non-sulfonated diamine monomer with1,4,5,8-naphthalenetetracarboxylic dianhydride(NTDA)and commercially available sulfonated diamine monomer Random copolymerization of 2,2’-bissulfonic acid benzidine(BDSA),two SPIs were prepared under different diamine molar ratios(BDSA/AABBI=2/1,4/1).Through the characterization of the performance of the SPI proton exchange membrane,the membrane with the best comprehensive performance was screened out as the SPI(NTDABDSA/AABBI(2:1))proton exchange membrane.The ion exchange capacity of SPI(NTDA-BDSA/AABBI(2:1))membrane was 2.01 meq/g,the proton conductivity was 0.238 S/cm in the fully hydrated state at 90 ℃,and the tensile strength was 39 MPa,which was 1.46 times that of Nafion117 membrane.The complete dissolution time of SPI(NTDA-BDSA/AABBI(2:1))membrane with Fenton reagent at 80 ℃ was 580 min,and the hydrolytic stability at 80 ℃ was greater than 360 h.The results have shown that the addition of AABBI improves the radical oxidative stability,thermal stability,flexibility and hydrolytic stability of SPI membrane synthesized by BDSA,a commonly used commercially available monomer.A series of SPI/SLS(5%,10%,15%,20%)composite membranes were prepared by blending NTDA-BDSA/AABBI(2:1)with sodium lignosulfonate.The introduction of low-doping SLS improves the mechanical properties of SPI/SLS composite membranes.The tensile strength of the SPI/SLS-10%composite membrane was 55.0 MPa,which was 1.40 times that of the pure SPI membrane and 2.06 times that of the Nafion117 membrane.The introduction of SLS improved the IEC and moisture content of all SPI/SLS composite membranes.Due to the water absorption and self-swelling of SLS,the swelling in the thickness and plane directions of the SPI/SLS composite membrane increased,resulting in a decrease in dimensional stability.The anti-radical oxidation stability and hydrolytic stability of SLS were reduced at high doping levels(15 wt.%-20 wt.%).The increased hydroxyl and sulfonic acid groups of SLS increase the hydrophilic area of the SPI/SLS composite membrane.The hydrogen bond formed by the hydroxyl group and the sulfonic acid group on the SPI strengthens the proton jumping and increases the proton conduction rate.Among them,the proton conductivity of the SPI/SLS-20% composite membrane reached 0.299 S/cm at 90 °C,which was 1.26 times that of the pure SPI membrane.The best overall performance was the SPI/SLS-10% composite membrane.The proton conductivity of the SPI/SLS-10% composite membrane reached 0.282 S/cm at 90 °C,which was 1.18 times that of the pure SPI membrane.The tensile strength of SPI/SLS-10% composite membrane reached55.0 MPa,which was 1.40 times that of pure SPI membrane and 2.06 times that of Nafion117 membrane.Due to the water absorption and self-swelling of SLS,the swelling of the SPI/SLS-10% composite membrane in the thickness direction and the plane direction at room temperature increases,which reduces its dimensional stability.The hydrolytic stability of the SPI/SLS-10%composite membrane was the same as that of the pure SPI membrane,and the anti-radical oxidation stability was slightly lower than that of the pure SPI membrane.A series of SPI/SMCM composite membranes(2%,4%,6%,8%,10%)were prepared by blending SPI membrane NTDA-BDSA/AABBI(2:1)with sulfonated mesoporous silica.The introduction of low-doped SMCM improves the mechanical properties of the SPI/SMCM composite membrane.The tensile strength(46.2 MPa)of the SPI/SMCM-2% composite membrane was 1.18 times that of the pure SPI membrane and 1.73 times that of the Nafion117 membrane.The introduction of SMCM increases the moisture content of the SPI/SMCM composite membrane(2wt.%-10 wt.%).The introduction of SMCM leads to the formation of rigidity of the polymer chain,which leads to a decrease in the elongation at break of the SPI/SMCM composite membrane.The introduction of SMCM to form a support structure in the SPI/SMCM membrane inhibits the swelling in the thickness direction of the SPI/SMCM composite membrane(2wt.%-10 wt.%),and improves the dimensional stability of the composite membrane.The anti-radical oxidation stability and hydrolytic stability of SMCM are reduced when the amount of SMCM is high(8 wt.%-10 wt.%).The added sulfonic acid group of SMCM increases the hydrophilic area of the SPI/SMCM composite membrane,which makes proton-conducting ion cluster channels more and increases the proton conduction rate;at the same time,the introduction of SMCM can also form available protons in the hybrid membrane.The auxiliary channel of transmission improves the proton conductivity of the composite membrane.Among them,the proton conductivity of the SPI/SLS-20% composite membrane reached 0.330 S/cm at90°C,which was 1.39 times that of the pure SPI membrane.The best overall performance is the SPI/SMCM-4% composite membrane.The proton conductivity of the SPI/SMCM-4% composite membrane reached 0.259 S/cm at 90°C,which was 1.09 times that of the pure SPI membrane.The swelling of the thickness of the SPI/SMCM-4% composite membrane at room temperature was 0.63 times,which improved its dimensional stability.The tensile strength of SPI/SMCM-4% composite membrane was 37.1 MPa,which was 1.39 times that of Nafion membrane.The hydrolytic stability of the SPI/SMCM-4%composite membrane was the same as that of the pure SPI membrane,and the anti-radical oxidation stability was slightly lower than that of the pure SPI membrane.