Computer Molecular Simulation Study Of SPEEK/PVDF-g-PSSA Composite Proton Exchange Membrane

As the best way to utilize hydrogen energy,fuel cell has been widely used in military,automobile,home power supply,mobile equipment and other fields in 21 Century.Proton exchange membrane is one of the important components of fuel cell,and its research is developing rapidly both at home and abroad.Sulfonated poly(ether ether ketone)(SPEEK)has become the preferred material for proton exchange membrane because of its high proton conductivity,excellent mechanical properties,low cost and high lifetime.In order to overcome the problem of the decrease of fuel barrier and thermal stability in SPEEK sulfonated film with increasing sulfonation degree,this study uses the computer molecular simulation to study the microstructure and dynamic properties for composite film of SPEEK and graft copolymers of polyvinylidene fluoride(PVDF)backbone with poly(styrene sulfonic acid)(PVDF-g-PSSA).On this basis,the effects of sulfonation degree,grafting condition,blending ratio,temperature and water content on proton transfer in the composite membrane system were investigated.Firstly,the effects of sulfonation degree,grafting condition and blending ratio on the morphology,structure and compatibility of SPEEK/PVDF-g-PSSA and SPEEK/PVDF composite films were investigated by means of dissipative particle dynamics(DPD)simulation.By analyzing the mesoscopic morphology,density distribution and isopycnic surface of the composite films under different conditions,we found that the compatibility of SPEEK and PVDF-g-PSSA in the composite films improved greatly with the increase of sulfonation degree,when the sulfonation degree increases to more than 50%,the PVDF-g-PVDF phase distributes uniformly in the SPEEK phase;the mesoscopic structure of composite membranes compared before and after grafting,we found that the density fluctuations of all components decreased significantly after the grafting,grafting part PSSA added links incompatible SPEEK and PVDF,forming a network of hydrophilic channels in the system;in addition,the 90/10 blend system can form a more hydrophilic channel for proton transport.Furthermore,the evolution of blending process of different blending ratio system was analyzed.It was found that the formation of PVDF clusters in 90/10 blends takes longer time,and the size and dispersity of the blends are better.The effects of blending ratio,temperature and water content on the proton conductivity of SPEEK/PVDF-g-PSSA composite membranes were investigated by molecular dynamics(MD)simulation.By analyzing the radial distribution function of different blending ratio system,we found that the composite film with 90/10 ratio can form more compact and more regular proton transfer channel;according to the calculation results of proton conductivity,the conductivity of composite membrane is slightly lower than that of pure SPEEK,and the influence of compatibility on proton conductivity is verified;the results at different temperatures show that the proton conductivity of the composite films continues to rise as the temperature increases,and the overall trends are in agreement with the experimental results.In addition,it was observed that with increasing the water content,the number of water clusters and proton conductivities first increase rapidly.When the water content reaches saturation(?_m=20),the calculated proton conductivity is 105 mS/cm,which was coincident with the results of experiment(96 mS/cm).With the water content increases to greater than the saturation value,the distance between sulfur atoms increases,proton conductivity tends to be stable.