Research On The Preparation And Properties Of Mesoporous Silica/Sulfonated Polyimide Hybrid Proton Exchange Membranes

Direct methanol fuel cells (DMFCs) are one of green power sources, which canconvert chemical energy directly into electrical energy with fuel available and lowemission of pollutants. As a portable power, DMFCs have a wide range ofapplications in transportation, military, emergency rescue, communication and otherareas. Proton exchange membrane as one of the key components in DMFCs, play thedual role of conducting the proton and blocking the fuel and the oxidizer. At present,the most widely used and commercialized membranes are the Nafion perfluorinatedsulfonic acid polymer membranes developed by Dupont. Nafion membrane hasexcellent chemical and mechanical stability, as well as high proton conductivityunder low temperature and high humidity. However, Nafion membrane exhibits highcost, sharp decline in proton conductivity above80℃and high crossover ofmethanol, which limits its use in DMFCs. Therefore, it is strongly desired to developnew proton exchange membrane materials with lower cost and high performance.Organic-inorganic hybrid proton exchange membrane is one of the mostpromising materials because the inorganic component can increase the thermal andchemical stability, whereas the organic component can improve the flexibility of themembranes. So it becomes a research hotspot in recent years. In this paper, weselected the sulfonated polyimide as the polyelectrolyte matrix to fabricate theorganic-inorganic hybrid membranes with excellent thermal stability, chemicalproperties and high mechanical strength. The main content is divided into two parts:(1) We synthesized the silica sol with cetyltrimethylammonium bromide (CTAB) astemplate agent in acidic conditions by in situ self-assembly method, then the silicasols were blended with the sulfonated polyimides solution to prepare a series ofhybrid proton conducting membranes with different content of silica. Themesoporous structure of silica was in situ formed in the membrane by directlysolvent extraction of CTAB.(2) The organic-inorganic hybrid membranes were fabricated by the interaction between amine groups in APTES and sulfonic acidgroups in SPEEK. Meanwhile, The sulfonic acid groups of sulfonated polyimidesitself was used as a catalyst for sol–gel process of aminopropyltriethoxysilane(APTES) to form the crosslinked silica network. The thermal stability and hydrolyticstability of the composite membranes can be improved to some extent. But in theprocess, a certain amount of sulfonic acid was consumed, which may cause thereduction of the water-uptake and IEC, in turn will affect the proton conductivity. So,a certain amount of sulfonated mesoporous silica nanoparticles was alsoincorporated into the acid–base hybrid system by blending method. The sulfonic acidand the mesoporous structure of the silica can compensate for the reduction of thewater uptake and the IEC. Our research results indicated that the prepared compositeproton exchange membranes had a more excellent performance than the purepolyimide membranes. Their thermal stability, proton conductivity and methanolpermeability were improved significantly.