Performance of PVDF supported silica immobilized phosphotungstic acid membrane (Si-PWA/PVDF) in direct methanol fuel cell

PVDF supported silica-immobilized phosphotungstic acid membrane (Si-PWA/PVDF) was synthesized by impregnation of silica immobilized phosphotungstic acid particles in porous PVDF film. Pore size distribution as well as stability of membrane in oxidative environment was determined using Fenton's reagent test. Stability of membrane against leaching of PWA which provides ion exchanging capacity was also determined and found to be adequate. Properties which affect performance of membrane in DMFC like water uptake, methanol cross-over and proton conductivity were measured. Water uptake of the membrane increased from 30.3% to 37.9% as the temperature was increased from 25 °C to 80 °C. The proton conductivity of the membrane increased from 4.3 mS cm⁻¹ to 20 mS cm⁻¹ with increase in the temperature from 25 °C to 80 °C. Methanol uptake of the Si-PWA/PVDF membrane was low compared to Nafion membrane and changed by very small amount with increase in temperature. Effect of operating parameters on performance of direct methanol fuel cell (DMFC) with the synthesized Si-PWA/PVDF was determined. DMFC performance improved on increasing temperature. As the temperature was increased from 25 °C to 60 °C, open circuit voltage (OCV) increased from 0.685 V at 0.815 V and the peak power density increased from 21.4 mW cm⁻² to 44.0 mW cm⁻². Maximum peak power density was obtained with 1 M methanol concentration and 60% relative humidity. Peak power density decreased with further increase in both methanol concentration and relative humidity.