The influence of nano-silica on properties of sulfonated polystyrene-lignosulfonate membranes as proton exchange membranes for direct methanol fuel cell application

The membranes of sulfonated polystyrene, lignosulfonate and nano-silica (SPS-LS-SiO2) that contain different percentages of nano-silica (1%-5% [w/w]) were prepared and characterized for polymer electrolyte membrane fuel cell (PEMFC). Nano-silica is an inorganic compound with a surface area of 200 m(2)/g, and it has a hygroscopic property so that the presence of nano-silica in membrane can increase properties of membrane. The SPS-LS-SO2 membranes were prepared by casting polymer solution and membranes were characterized by functional groups analysis, water uptake, ion exchange capacity (IEC), proton conductivity, methanol permeability, thermal stability, mechanical properties, and surface morphology. The results show the increase of nano-silica composition in SPS-LS-SiO2 membranes, the IEC, water uptake, proton conductivity increase, but a pore size of membrane decreases. On the other hand, it can maintain the mechanical strength of membranes. The SPS-LS-SiO2 membranes with nano-silica composition of 2%-5% (w/w) have the same properties with Nafion (R) 117, especially in proton conductivity at the same treatment and measurement conditions, and its methanol permeability is about 28%-35% smaller than that of Nafion (R) 117 (2.09 x 10(-6) cm(2)/s), so this SPS-LS-SiO2 membrane could be used as a polymer electrolyte membrane for direct methanol fuel cell (DMFC) application.