Amphiphilic nanocomposite proton conducting membrane

Abstract

The major issues limiting the application of Proton Exchange Membrane Fuel Cell (PEMFC) based on perfluorinated membrane (Nafion) is its inefficiency to perform at high temperature and low humidity. The high cost of Nafion which is due to the complicated production process, the swelling problems, and the environmental hazards associated with its disposal are some of the major technology drawbacks. Through the incorporation of nano zeolite as the host material, the proton conductivity may be enhanced because of its moderate proton conductivity, mechanical stability and hydrophilic feature at high temperature. Organosulfonic acid groups (sulfonate –SO- 3) are functionalized onto the surface of nano zeolite to further increase the proton conductivities of the bare zeolite, increase the cationic site density in the hydrophilic domains that enlarge hydrophilic domains in the membranes at high temperature. Well alignment of channel structures by the direct chemical bonding between the organosulfonic acid groups and zeolite eases proton and water transport, which consequently produce novel temperature tolerant proton conducting membrane for fuel cells. The synthesized functionalized nanocomposite has proton conductivity in the range of 1x10-3 S/cm with great properties in mechanical strength, hydrophilic features and chemical stability at high temperature operation. Proton conductivities of zeolites in the operating temperature range of 24-100 °C were enhanced significantly to higher values (about 1-3 orders of magnitude) by loading of sulfonic acids onto the surface of zeolite. Proton conductivities were correlated with the concentration of sulfonic acid groups and increased as follows: sulfonated polystyrene-zeolite composite > propylsulfonic acid functionalized ZSM-5 > phenylsulfonic acid functionalized ZSM-5 > zeolite ZSM-5 which is in line with the ion-exchange capacity and water uptake test.