Study On Structure And Performance Of Proton Exchange Membrane Compounded By Nano Silicon Dioxide

Perfluorosulfonated acid membrane (i.e. Nation membrane) still plays a leading role in commercially available membranes for its excellent property, but the weakness in high temperature property is a key factor of blocking its development. Nowadays, Nafion/SiO₂ composite membrane via in-situ synthesis can improve the high temperature property effectively. But there are many problems regarding in-siu synthesizing of Nafion/SiO₂ composite membrane, which also affects the improvement of the properties of the composite membrane and hinders the enhancement of composite membrane properties. In the paper, based on the former researches, the influence on Nafion/SiO₂ composite membrane characters to the membrane properties were discussed. Physical property, electrochemical performance and single cell performance of the composite membrane were also studied, the mircostructure model of Nafion/SiO₂ composite membrane was designed,the performance of Nafion/SiO₂ composite membrane was analysed in theory. To reduce the cost of proton exchange membrane, the feasibility of Nafion/SiO₂/PTFE composite membrane in high-temperature fuel cell applications was also investigated. Initial research results are as follows:(1) The tensile strength of Nafion/SiO₂ composite membrane is lower than that of Nafion membrane, which was ascribed to the strength reduction of Nafion membrane after soaking in alcohol. Further, the appropriate time of immersing in alcohol is within 30 min. After soaking in alcohol ,the surface water of membrane will affect the distribute of Si,So before immersing in the mixed solution of TEOS and alcohol,blotting the moisture of the Nafion membrane surface can improve the gradient distribution situation of SiO₂ effectivly. The SiO₂ which adhere at the surface of membrane or unstable can be removed during the cleaning process.(2) The highest T_g of Nafion1135/SiO₂ composite membrane is 189℃, while, the T_g of Nafion1135 membrane is 130℃. the water content of Nafion1135/SiO₂ composite membrane is higher than that of nation. When temperature is 100℃, the water content of Nafion1135/SiO₂ composite membrane is 34.8%, while the nafion membrane's is 26.5%;when When temperature is 100℃, relatively humidity is 60%,the dehydration rate of Nafion1135 membrane is 45.26%,whie the 10% Nafion1135/SiO₂ composite membrane 's is 32.16%;at relatively humidity 60% ,the water absorption of dry Nafion1135/SiO₂ composite is seven times of that of Nafion1135 membrane. when the cell temperature is 110℃,the Nafion membrane can not work stable,the curve of cell present a violent shock shape,but the Nafion/SiO₂ composite membrane can work stably at current density 600mA/cm² and vlotage 0.6V.This means that the Nafion/SiO₂ composite membranehas better high temperature resistant ability.(3) FT-IR and NMR shows that the nano structure of SiO₂ has hydrophilic group (Si-OH) and this nano structure is primarily joined together and half joined together network. Small-angel X-ray and TEM. shows that SiO₂ distribute in the Nafion group , some part of SiO₂ present in crystalline state, the diameter of particles is between 5-10nm, the mircostructure model of Nafion/SiO₂ composite membrane was designed,the performance of Nafion/SiO₂ composite membrane was analysed in theory..(4) The Nafion/SiO₂/PTFE composite membrane prepared by vacume impregnation has a high resin loading. The stretch strength of Nafion/SiO₂/PTFE and the cross-section conductivity is comparative with the Nafion/PTFE composite membrane,while the stretch strength is higher than Nafion membrane with the same thickness, in additionally,the Nafion/SiO_/PTFE composite membrane has a good water uptake property. TG-DSC indicated that dehydrate rate of the Nafion/SiO₂/PTFE membrane between 30-120℃is lower than Nafion/PTFE composite membrane ,which indicates that Nafion/SiO₂/PTFE has a bright future in high temperature fuel cells.