Phosphotungstic acid doped poly(vinyl alcohol)/poly(ether sulfone) blend composite membranes for direct methanol fuel cells

Abstract

Non-perfluorinated composite proton exchange membranes are prepared by solution casting for direct methanol fuel cell (DMFC) based on poly(vinyl alcohol) (PVA) and poly(ether sulfone) (PES) polymer blends and phosphotungstic acid (PWA) as proton conductive material. The homogenous structure of the blend membranes is confirmed by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) shows that the addition of PES and PWA to the PVA matrix improves membranes’ thermal stability. The water uptake and swelling degree of membranes are reduced with increasing PWA and decreasing PES contents in membranes. The ion exchange capacity (IEC) is improved by rising the percentage of PWA. However, the blend of two polymers has no effect on the IEC. The proton conductivity and the methanol permeability of membranes increase with the increase in the PWA and the PES contents. Addition of PWA and PES to the PVA matrix increases the tensile strength while the elongation at break increases by addition of PES content and decline in PWA content. Moreover, the performance of membrane electrode assembly using the highest selective membrane in the DMFC is investigated at 80 °C with 1 and 5 M methanol concentrations and oxygen at a pressure of 2 atm and compared with Nafion 117 membrane.