| Sulfonated poly?aryl ether nitrile?is the most promising alternative to Nafion membrane in the field of proton exchange membrane for fuel cells.It possesses good heat resistance,chemical resistance,insulation,flame retardancy,radiation resistance and mechanical properties.Furthermore,it's preparation process is simple and production cost is low.However,when the degree of sulfonation of sulfonated poly?aryl ether nitrile?is low,the distance between sulfonated groups is relatively far,and the hydrophilic channel is narrow or even discontinuous,which seriously hinders the transmission of H+.When the degree of sulfonation is high,the membrane is prone to serious swelling,which reduces the dimentional stability of the membrane.Deformation will lose strength and increase the methanol permeability of the membrane.These shortcomings seriously limit the application of sulfonated poly?aryl ether nitrile?membranes in the field of proton exchange membranes for fuel cells.Therefore,the development of new structure of sulfonated poly?aryl ether nitrile?has become one of the research hotspots in recent years.In this paper,novel sulfonated poly?aryl ether nitrile?membranes with good methanol resistance and dimensional stability were prepared by controlling the cross-linking reaction of different active functional groups in the molecular chain.The cross-linking reaction mechanism,cross-linking structure and comprehensive properties of the membranes were studied systematically.The structure,composition and properties of the best cross-linking sulfonated poly?aryl ether nitrile?were determined.Subsequently,by using the special proton conductivity of functional nanoparticles,the composite proton exchange membrane was prepared by introducing functional particles into the cross-linked sulfonated poly?aryl ether nitrile?polymer.The interaction mechanism between functional nanoparticles and poly?aryl ether nitrile?was analyzed.The specific research contents are as follows:1.The crosslinkable double bond groups were introduced into the molecular chain of sulfonated poly?aryl ether nitrile?.The self-crosslinking of sulfonated poly?aryl ether nitrile?was realized by controlling the crosslinking temperature.The results show that the thermal stability and mechanical properties of the membranes can be improved to a certain extent by controling the microstructure of the cross-linked network.More importantly,the sulfonated poly?aryl ether nitrile?membranes exhibit excellent dimensional stability,and the dimensional stability will gradually increase with the degree of cross-linking.In addition,the methanol permeability of the sulfonated poly?aryl ether nitrile?membrane decreases greatly after crosslinking,which greatly improves the selectivity of the membrane.The polymer membrane with 60%sulfonate group and 30%side chain double bond has the highest selectivity in all membranes,which is 2.6×105S·s·cm-3,about 5.8 times that of Nafion 117.2.The nitrile group was introduced into the side chain of sulfonated poly?aryl ether nitrile?by grafting.The content of nitrile group in the molecular chain of sulfonated poly?aryl ether nitrile?was effectively increased and the interaction between the molecular chains of sulfonated poly?aryl ether nitrile?was enhanced.The dimensional stability and methanol resistance of sulfonated poly?aryl ether nitrile?membranes were improved by controlling the degree of sulfonation and crosslinking.The results show that the introduction of nitrile groups can effectively increase the entanglement between molecular chains,greatly improve the dimensional stability and methanol resistance of the membranes without significantly reducing the proton conductivity.Among all the side-chain nitrile membranes,the polymer membranes with 60%sulfonate group and 30%side-chain nitrile group had the highest selectivity of 5.37×105 S·s·cm-3,about 11.9times that of Nafion 117.3.The end-crosslinking sulfonated poly?aryl ether nitrile?membranes were prepared by introducing cross-linkable nitrile groups into the end of sulfonated poly?aryl ether nitrile?by end-capping technique.The experimental results show that the entanglement between the molecular chains is tighter due to the introduction of nitrile groups only at the end,which leads to the further improvement of the methanol resistance and dimensional stability,and shortens the distance between the sulfonic groups in the molecular chains.Obviously,it has better comprehensive performance.The sulfonated poly?aryl ether nitrile?membrane with 50%sulfonic group had the highest selectivity,which is 14.3×105 S·s·cm-3,about 31.8 times that of Nafion 117.4.Aiming at the problem that the cross-linking reaction will reduce the proton conductivity to a certain extent.the functional nanoparticles?titanium dioxide?were introduced into the end crosslinked sulfonated poly?aryl ether nitrile?.The proton conductivity of the sulfonated poly?aryl ether nitrile?was improved by using the good proton conductivity of the nanoparticles.The experimental results show that the addition of functional nanoparticles not only improves the proton conductivity,but also further increases the dimensional stability and methanol resistance of the cross-linked membrane.All the experimental results show that functional nanoparticles can greatly enhance the comprehensive properties of crosslinked membranes.5.Novel functional nano-particle?UiO-66-NH2?was designed to prepare UiO-66-NH2/sulfonated poly?aryl ether nitrile?covalent-ion cross-linked composite membranes by using the high proton conductivity and surface amino reactivity of UiO-66-NH2.Thus simplify the preparation method of high-performance cross-linked sulfonated poly?aryl ether nitrile?composite membranes.The experimental results show that this method is simple and feasible,which can effectively improve the dimensional stability and methanol resistance of the membrane.All membranes showed excellent comprehensive properties. |
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