Preparation And Characterization Of SP/UiO-66-NH₂ Composite Membrane

Proton exchange membrane fuel cells（PEMFCs）are power generation devices that convert chemical energy into electrical energy.They have attracted much attention due to their advantages of high energy conversion efficiency,light pollution,fast startup speed and portability.Proton exchange membrane（PEM）is the core component of PEMFCs,which mainly plays the role of blocking the cathode and anode and conducting protons.At present,the Nafion series membranes produced by Du Pont are widely used.The Nafion membrane takes C-F as the main chain and hydrophilic-SO₃H as the branch chain.The main chain and branch chain are linked by oxygen.The proton in-SO₃H combines with water molecules to form hydrated proton to complete proton conduction.The efficiency of proton conduction depends on the amount of hydrophilic-SO₃H,and too much-SO₃H will absorb excess water and cause excessive swelling of the membrane,thereby destroying the water transport channels in the membrane.Moreover,it is expensive and difficult to synthesize.Therefore,the development of PEM with high conductivity,anti-swelling,low price and easy synthesis has become one of the important topics in the field of PEMFCs.Sulfonated poly（ether ether ketone）（SPEEK,SP）is one of the sulfonated polyaryl ether ketones.SPEEK is easy to synthesize,inexpensive,and environmentally friendly.It has a similar structure to Nafion and its comprehensive properties are not inferior to Nafion.However,it has the same disadvantages as Nafion,the conductivity is lower at low sulfonation degree,and the swelling degree of membrane is high at high sulfonation degree.Therefore,the trade-off between conductivity and mechanical properties is an urgent problem to be solved for SPEEK composite membranes.Metal-organic frameworks（MOFs）are a class of crystalline porous materials that are self-assembled by metal ions/metal clusters and organic ligands.As a new type of inorganic-organic hybrid material,MOFs has the characteristics of large pores and designable structure.However,MOFs are difficult to use directly as PEMs.It can be compounded with polymers and interact with the sulfonic acid group in the polymer SPEEK after modification to build an ordered proton transfer channel,which can not only improve the conductivity,but also overcome the shortcomings of SPEEK’s easy swelling in water and improve its dimensional stability.In this paper,SP/Ui O-66-NH₂composite membranes were prepared with Zr MOFs material Ui O-66（terephthalic acid as ligand）as filler,modified by amination（Ui O-66-NH₂）and combined with SPEEK.The effects of Ui O-66-NH₂on the properties of the composite membranes were studied.At the same time,SP/Ui O-66 composite membranes were prepared for comparison.Its main conclusions are as follows:1)Firstly,SPEEK was prepared by sulfonation method,and Zr MOFs material Uio-66was synthesized with terephthalic acid as ligand.Ui O-66 was introduced into SPEEK to prepare organic-inorganic composite membrane SP/Ui O-66.The amount of Ui O-66 was optimized,and the hydrogen bond network formed between an appropriate amount of Ui O-66 and SPEEK promoted the proton conductivity of the composite membrane.The prepared composite membrane has high thermal stability.However,the introduction of Ui O-66 increased the water uptake and swelling degree of the composite membrane,which affected its dimensional stability;2)To balance conductivity and dimensional stability,Ui O-66-NH₂was synthesized by modifying Ui O-66,and Ui O-66-NH₂and SPEEK were introduced to prepare organic-inorganic composite membrane SP/Ui O-66-NH₂.Due to the strong acid-base interaction between the amino group of Ui O-66-NH₂and the sulfonate group of SPEEK,the dispersion of Ui O-66-NH₂in the composite membrane is promoted.The introduction of Ui O-66-NH₂improves the thermal stability of the composite membrane,and all membranes are relatively stable within 200℃.The introduction of Ui O-66-NH₂not only improved the conductivity but had little effect on the water uptake and swelling degree of the membrane;The conductivity results showed that the addition of Ui O-66 increases the conductivity(0.28 S·cm^-1)of SP/Ui O-66-1.0 composite membrane to 1.16 times that of SPEEK(0.24 S·cm^-1)at 98%RH,the addition of Ui O-66-NH₂increased the conductivity(0.34 S·cm^-1)of SP/Ui O-66-NH₂-1.0 composite membrane to 1.42 times that of SPEEK(0.24 S·cm^-1).Amino groups not only provide proton hopping sites,but also interact with the sulfonate group of SPEEK to build an ordered proton transport channel to improve the conductivity of the composite membrane.This study provides basic experimental data for the development and application of such low-temperature,humidified PEMs.