Study On Fluorinated Sulfonated Polyarylethernitrile And Its Proton Exchange Composite Membrane

Proton exchange membrane fuel cell（PEMFC）is the fifth generation of new fuel cell developed after alkaline fuel cell,phosphate fuel cell,molten carbonate fuel cell and solid oxide fuel cell.Compared with the previous four generations of fuel cells,PEMFC is widely used in chlor-alkali industry,aviation,shipping,automobile and other fields because of its advantages such as faster startup speed,lower startup temperature,higher energy density,more fuel sources,green combustion products,and no danger of electrolyte leakage.Proton exchange membrane（PEM）is an important part of proton exchange membrane fuel cell.It not only plays the role of isolating fuel and oxidant to prevent their direct reaction,but also plays the role of electrolyte.It conducts protons and insulates electrons.It is a functional polymer membrane with selective permeability.At present,the performance and price of proton exchange membranes limit the wide range of promotion and development of such fuel cells.Although Nafion membranes that have been successfully commercialized have good physical and chemical properties,it is difficult to solve the problems such as complex process,high cost and fuel permeation.Therefore,the research on alternative materials of Nafion membranes is the focus of current research.As a kind of special engineering plastics,poly（aryl ether nitrile）has the advantages of high strength,high modulus,easy processing and low price.Through molecular design,specific groups can be introduced into the structure,so that poly（aryl ether nitrile）has specific functionality.In this paper,a series of fluorinated sulfonated poly（aryl ether nitrile）named PEN（A_xF_yS_z）with different fluorine content were synthesized by molecular design using bisphenol A,hexafluorobisphenol A,and potassium 2,5-dihydroxybenzenesulfonate and2,6-difluorobenzonitrile,as the main raw materials and adjusting the monomer ratio of bisphenol A and hexafluorobisphenol A.The successful synthesis of the target product can be determined through analysis of infrared spectroscopy and nuclear magnetic resonance spectroscopy.The performance tests of PEN（A_xF_yS_z）series proton exchange membranes showed that the mechanical properties and thermal stability of the polymers were improved with the increase of fluorine content;However,the decrease in hydrophilicity leads to a decrease in both water absorption and swelling rates of the membrane-Although the introduction of-CF₃ group can reduce the ion exchange capacity（IEC）of the membrane due to its hydrophobicity,it can form a two-phase separation interface with the hydrophilic-SO₃H group,serving as a proton transport channel to accelerate the transport of protons.At the same time,because it is a strong electron absorbing group,it can promote the dissociation of the-SO₃H group and accelerate the proton jump rate,so the proton conductivity of the membrane also gradually increases.The proton exchange membrane with the best comprehensive performance is PEN(A₀F_0.3S_0.7)proton exchange membrane,with a T_5%temperature of 339℃,tensile strength of 48.6 MPa,and IEC of 1.83 mmol/g;Proton conductivity reaches 9.5×10^-2S/cm,1.2 times that of Nafion 117 proton membrane.A series of PEN/SLS-（5wt%,10wt%,15wt%,20wt%）binary proton composite membranes were prepared by blending PEN(A₀F_0.3S_0.7)proton exchange membrane with the best comprehensive performance as the matrix（referred to as PEN）and sodium lignosulfonate（SLS）.The successful preparation of PEN/SLS series binary proton exchange membranes can be confirmed by the infrared spectra of binary proton composite membranes.The results of testing its various properties show that SLS and PEN have good compatibility.With the increase of SLS doping content,both T_5%and T_10%of the composite membrane decrease.The tensile strength,elastic modulus,and elongation at break of the composite membrane first increase and then decrease.The hydrophilicity gradually increases.The water absorption and swelling first increase and then decrease.The IEC and proton conductivity also increase and then decrease.The proton membrane with the best comprehensive performance is a PEN/SLS-15wt%ternary proton composite membrane,with a T_5%temperature of 269℃,a tensile strength of 57.5MPa,and an elongation at break of 13.4%.The water absorption rate reaches 12.1%,and the swelling rate reaches 6.7%.The ion exchange capacity reaches 2.11mmol/g,and the proton conductivity reaches 17.1×10^-2S/cm at 25℃,2.06 times that of Nafion 117 proton membrane,and 1.79 times that of PEN(A₀F_0.3S_0.7)proton membrane without SLS doping at the same temperature.A series of ternary proton composite membranes of PEN/SLS/TiO₂-（2wt%,4wt%,6wt%,8wt%）were prepared by blending PEN/SLS-15wt%proton exchange membrane with the best comprehensive performance as the matrix（referred to as PEN/SLS）and nano-TiO₂.The various properties of the composite membrane were tested and the results showed that with the increase of nano-TiO₂ doping content,the T_5%and T_10%of the composite membrane decreased,the tensile strength,elastic modulus,and elongation at break first increased and then decreased,and the hydrophilicity gradually increased.The water absorption and swelling rates,IEC,and proton conductivity first increased and then decreased.The proton membrane with the best comprehensive performance is a PEN/SLS/TiO₂-4wt%ternary proton composite membrane,with a T_5%temperature of 273℃,a tensile strength of 64MPa,an elongation at break of 17.6%,a water absorption of 12.8%,and a swelling rate of 7.7%.IEC reaches 2.20mmol/g,proton conductivity reaches 21.4×10^-2S/cm at 25℃,2.6 times that of Nafion 117 proton membrane,and 1.2 times that of PEN/SLS-15wt%proton membrane without doped nano-TiO₂ at the same temperature.