Preparation and characterization of the SPEEK/PVA/Silica hybrid membrane for direct methanol fuel cell (DMFC)

The SPEEK-PVA-Silica hybrid membranes are prepared by solution casting method. The physical, chemical and electrical properties of the polymer membranes are studied by FESEM, FTIR, XRD, DSC, TGA, DMA, water and methanol uptake capacity, Ion Exchange Capacity (IEC), Degree of Sulfonation (DS), hydration number (lambda), void volume fraction (%), methanol permeability and proton conductivity. The void volume fraction and density of the polymer membrane increases with increase in the silica content of the membrane which decreases glass transition temperature. At 30 degrees C, the maximum proton conductivity is found for SPS-3 membrane (3.8 x 10(-2) S/cm) which is much higher than recast SPEEK membrane (2.9 x 10(-2) S/cm). The proton conductivity of the polymer membrane is dominated by free water facilitated vehicular mechanism. The improvement of the conductivity of the proton in the silica filled polymer membrane at medium to higher temperature is due to the strong interaction between the silica and water resulting in a reduction in the loss of evaporation of water as well as an improvement in the bound water content of the polymer channel, which is regulated by the Grotthuss mechanism. The reduction of methanol permeability and increment in membrane selectivity clearly confirms that the silica filled polymer have excellent methanol blocking capacity which is beneficial for direct methanol fuel cell design.