Properties of SPES/PWA/SiO2 Composite Proton Exchange Membranes

Novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica organic-inorganic composite membranes for application in direct methanol fuel cells (DMFCs) were prepared by doping SiO2 sol and PWA into SPES matrix. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy. energy dispersive X-ray spectroscopy (SEM-EDX), etc. Compared with the pure SPES membrane, SiO2 and PWA doping led to higher thermal stabilities, a higher glass transition temperature (T-g), and higher water uptake. At 20 degrees C and a fuel cell operating temperature of 80 degrees C, the tensile strength of all the composite membranes was lower than that of the SPES membrane. However, even when the content of SiO2 was as high as 20% (w), the composite membrane still possessed a higher strength than a Nafion 112 membrane. The morphology of the composite membranes indicated that SiO2 and PWA were uniformly distributed throughout the SPES matrix, which may facilitate proton transport. The proton conductivity of the composite membrane (SPES-P-S 15%: 15% (w) SiO2 and 6% (w) PWA) reached 0.034 S.cm(-1), which was similar to that of the Nafion 112 membrane at room temperature. However, methanol permeation through the SPES-P-S 15% composite membrane decreased dramatically and was only one. seventh that of the Nafion 112 membrane. This excellent selectivity of the SPES/PWA/SiO2 composite membrane points to its potential use as a promising electrolyte for DMFCs.