Preparation And Properties Of Proton Exchange Membrane Based On Metal Organic Framework/sulfonated Polyaryl Ether Nitrile

Nowadays,the world is facing two major problems of energy shortage and environmental pollution,and a variety of new energy sources have been developed.As a new type of energy source with environmental friendliness,proton exchange membrane fuel cells(PEMFCs)have been praised in practical application due to their high energy conversion efficiency and strong corrosion resistance.PEMFCs can directly convert the energy generated by the reaction of fuel and oxidizer into electricity without going through the Carnot cycle,so their energy conversion efficiency of PEMFCs is 2-3 times higher than that of traditional fossil energy sources.Besides,PEMFCs only produce water,carbon dioxide and other nonpolluting substances.Several countries have introduced relevant policies to support the development of PEMFCs technology,such as China,the United States,Japan,Germany,etc.As one of the core material of PEMFCs,proton exchange membranes(PEMs)mainly play the role of transferring protons and isolating the fuel.PEMs have been pursued in the direction of high proton conductivity,strong stability,and excellent alcohol resistance.Sulfonated polyarylene ether nitrile(SPEN)is a polyaryl ether polymer containing nitrile groups with excellent thermal stability,flame retardancy,radiation resistance and mechanical properties.The sulfonic acid groups in the side chain of SPEN can provide a jumping site for proton transfer,which endow SPEN with certain proton-conducting properties.With the advantages of low production cost and simple synthesis process,SPEN is the most promising materials to replace Nafion membrane.However,the degree of sulfonation should be strictly controlled during the synthesis process of SPEN.The proton conductivity of the PEMFCs was unsatisfied when the degree of sulfonation is low.And the high degree of sulfonation tends to cause swelling of the membrane,which has a serious impact on the dimensional stability and alcohol resistance of the membrane.Therefore,the study of novel structure of SPEN or doped filler modification is an effective way to solve such problems.Metal organic frameworks(MOFs)are organic-inorganic hybrid materials consisting of organic ligands and metal ions or clusters in coordination.They have been widely used in gas adsorption,sensors,magnetic materials and reaction catalysis by virtue of their large specific surface area,high porosity and diverse structures.MOFs contain a certain amount of hydrogen bonds and the pores inside the framework can be loaded with functional groups,which provide extra transport pathway for proton transfer.Therefore,MOFs have a certain potential for development in proton conduction applications.However,the proton transport channels inside the MOFs are uncontinuous,which results in low proton conductivity of majority MOFs.Moreover,the production cost of preparing pure MOFs membranes is expensive and the stability of membranes is not guaranteed.Therefore,in this paper,two composite PEMs were prepared by combining the advantages of MOFs with SPEN.We investigated the effects of MOFs on the working properties of SPEN composite proton exchange membranes such as thermal stability,proton conductivity,and alcohol resistance.The details are as follows.1.In this paper,MOF-801 with hydrophilicity and high proton conductivity was selected as the subject of the framework,and imidazole was loaded on the MOF-801structural skeleton by chemical coordination to assist in enhancing the proton conduction properties of the material.The synthesized Im-MOF-801 was subjected to a series of structural characterizations such as FT-IR,XRD and SEM to demonstrate the successful loading of imidazole.A series of SPEN@Im-MOF-801 composite membranes with different doping ratios were prepared by homogeneous mixing of Im-MOF-801 with SPEN by physical ultrasonic compounding method.The electrical,chemical and mechanical properties of the composite membranes were analyzed.The Im-MOF-801 enhanced the tensile strength and thermal stability of the composite membranes to a certain extent.The hydrogen bonding network formed by Im-MOF-801 and the additional imidazole proton donor promoted the transport of proton and reduced the methanol permeability,which greatly improved the relative selectivity of the composite membranes.2.Carbon nanotubes(CNTs)have high stiffness,excellent chemical stability and mechanical properties.Ui O-66-NH₂/CNT with 1-D moniliform nanostructure was designed and synthesized on the surface of CNTs by an in-situ synthesis method.A series of SPEN@Ui O-66-NH₂/CNT composite membranes with different addition ratios were prepared by blending Ui O-66-NH₂/CNT with SPEN.The SEM figures showed that no agglomeration occurred in Ui O-66-NH₂/CNT,which proved that the addition of CNTs effectively solved the MOF agglomeration problem.The parameters of the SPEN@Ui O-66-NH₂/CNT composite membranes such as swelling rate,tensile strength,proton conductivity,and methanol permeability were tested.The test results revealed that compared with pure SPEN membrane,the tensile strength of the SPEN@Ui O-66-NH₂/CNT composite membranes were increased by 65.5%-95.2%,which was mainly attributed to the presence of CNTs substantially enhanced the mechanical properties of the composite membranes.The high stiffness of Ui O-66-NH₂/CNT and its entanglement with the main chain of SPEN significantly reduced the swelling rate of the composite membranes.At 80°C,the proton conductivity of the composite membranes could reach 17.37×10^-2S cm^-1.And Ui O-66-NH₂/CNT effectively reduces the methanol permeation rate of the composite membranes.