Preparation And Properties Of Semi-crosslinked, Semi-hyperbranched Sulfonated Polyimide Composite Proton Exchange Membranes

Proton exchange membrane fuel cell (PEMFC) is an electrochemical device that transforms directly chemical energy of fuels into electrical energy through an electrochemical reaction. PEMFC has many advantages, such as low environmental pollution, low noise, long life, low temperature, high specific energy, etc., and it will have a very broad application prospects in portable power and mobile power supply. The proton exchange membrane (PEM) is a core component of proton exchange membrane fuel cell. PEM plays two roles:(1) as the electrolyte to provide hydrogen ion transmission channel; (2) to barrier anode electrode and cathode electrode. Currently, the most widely used proton exchange membrane is perfluorinated sulfonic acid membrane (Nafion(?)) developed by DuPont. It has excellent thermal stability, chemical stability and high proton conductivity under the condition of high humidity. However, it is expensive and has low proton conductivity at high temperatures or low humidity conditions, which limits its wide application in the PEMFC. Therefore, the study of high-performance, low-cost proton exchange membrane is very important.Sulfonated polyimide is regarded as a kind of proton exchange membrane material that has a wide application prospect. Its main advantages include good proton conduction ability, mechanical properties, thermal stability and relatively low cost. However, sulfonated polyimide membrane suffers from hydrolysis in water, which seriously affects the life of fuel cell. In order to improve the hydrolytic stability of sulfonated polyimide membrane, researchers have tried a variety of modified methods, wherein the organic-inorganic hybrid is a commonly method, because organic-inorganic composite membranes own the merits of both inorganic component and organic component. Therefore, the organic-inorganic hybrid proton exchange membrane has got more and more attention.Based on the above analysis, we design and prepare semi- hyperbranched, semi-crosslinked sulfonated polyimide composite proton exchange membrane using sulfonated polyimide as the backbone material and polysulfone as support material. The membrane fabrication involves polycondensation reaction between anhydride terminated sulfonated polyimide with ammoniated silica. This thesis includes the following contents. First, acid anhydride-terminated polyimide is synthesized. Second, ammoniated silica as "Bx type-based monomer", directly polymerizes with anhydride terminated sulfonated polyimides. Finally, the support material polysulfone is added to prepare composite proton exchange membrane. The free volume by formed semi-hyperbranched structure and ammoniated silica can effectively improve the water content of composite membrane, afurther improve the proton conductivity of composite membranes, while semi-crosslinked structure and the presence of the support material polysulfone enhance the oxidative stability to extend the life of composite membrane. The results show that, at 30℃, start time of dissolution and complete dissolution time of SPI/SiO2-10-PSf (Silica content is 10%) composite membrane in Fenton are 14h and 37h longer than SPI/PSf composite membrane. At 60℃, proton conductivity of SPI/SiO2-10-PSf composite membrane is 0.162S·cm-1, higher than of Nafion115 (0.124S· cm-1). SPI/SiO2-10-PSf composite membrane has good comprehensive performance, which is expected to replace Nafion membrane, used in proton exchange membrane fuel cell.