Synthesis and characterization of sulfonated poly (arylene ether sulfone)/silicotungstic acid composite membranes for fuel cells

Abstract

A series of composite membranes based on sulfonated poly (arylene ether sulfone) (SPAES) embedded with powdered silicotungstic acid (STA) was synthesized. SPAES was synthesized by direct aromatic nucleophilic polymerization and then solution blended with STA. Fourier-transform infrared spectroscopy analysis showed that the sulfonic acid groups on the polymer backbone interacted with the tungstic oxide in STA. The composite membranes exhibited a low Heteropolyacid extraction after treatment with water at 60 °C for 24 h. The composite membranes were characterized for water uptake, ion-exchange capacity (IEC), hydrolytic stability, proton conductivity and thermal stability in order to evaluate the suitability of these membranes for fuel cells. The proton conductivity of the membranes increased with increasing STA content. With an increase in the STA content, the conductivity of the composite membranes at 30 °C increased from 0.079 to 0.109 S cm−1, whereas the parent membrane exhibits a proton conductivity of 0.073 S cm−1. The composite membranes not only had good proton conductivity but also showed excellent thermal stability and mechanical strength. This study shows that the composite membranes based on SPAES and STA can be viable candidates for electrolyte membranes. The influence of the dispersed silicotungstic acid (STA) on the membrane properties was studied. The proton conductivities of the composite membranes are higher than the parent SPAES membrane. Even though IEC and water uptake of the composite membranes decreased with increase in STA content, the proton conductivities and hydrolytic stabilities were increased. The acidity of the sulfonic acid group increased with the incorporation of STA. As the composite membranes showed negligible STA extraction, most of the STA retained in the polymer and this increases the efficiency of the membrane.