Study On The Preparation And Properties Of Sulfonated Polyimide/SiO₂ Hybrid Proton Exchange Membranes

Proton exchange membranes are the most important part in proton exchange membrane fuel cells (PEMFC). The development of proton exchange membranes plays an important role in the industrialized process of PEMFC. Currently, Nafion membranes are the main commercial membrane materials used for PEMFC. However, Nafion has many flaws such as high cost, environment pollution, low proton conductivity at low humidity and high methanol crossover. These flaws limit the use of Nafion. Thus, the study on new proton exchange membranes is a major research subject.Organic-inorganic composite membranes own the merits of both organic membranes and inorganic membranes, so this method is very attractive and popular. In this paper, we chose sulfonated polyimides (SPI) as polymer matrix because of their good mechanical properties, high proton conductivity and low methanol permeability. A series of SPI/SiO₂ organic-inorganic composite membranes were prepared via in situ sol-gel process and blending process, respectively. The addition of SiO₂ improved the mechanical and thermal properties of the hybrid membranes. The hybrid membrane of SPIK-30-SiO₂ that was prepared via in situ sol-gel process showed the highest proton conductivity and the lowest methanol permeability. The hybrid membrane prepared by the blending method also showed affected properties. We found that the addition of s-SiO₂ also improved the thermal properties and proton conductivity of the membranes. But when the content of s-SiO₂ was higher than 7 wt%, the mechanical properties of the resulting membranes decreased and the proton conductivity was lower than that of the hybrid membranes with lower content s-SiO2. On the whole, the hybrid membrane with 3 wt% s-SiO₂ showed the excellent mechanical properties and high proton conductivity, and low methonal permeability.