Nafion/sulfonated poly(arylene ether sulfone) composite membrane for fuel cell

Abstract

In this thesis, we prepared composite membranes consisting Nafion and poly(arylene ether sulfone). Poly(arylene ether sulfone)s varied degree of sulfonation were coated onto the surface of Nafion as a methanol barrier layer and solution blend of Nafion and PSSf were prepared. The aim of this work is reducing methanol crossover by obstructing the ionic clusters of Nafion membrane related to the methanol crossover. To reduce methanol crossover, this work focused on the development of the phase separated composite membrane. Sulfonated poly(arylene ether sulfone)s were successfully synthesized by direct polymerization using nucleophilic substitution condensation polymerization. FT-IR and NMR data confirmed that the sulfonate groups were quantitatively introduced. Thermal stability, glass transition temperature, decomposition temperature, ion exchange capacity, proton conductivity, and water uptake were investigated. The properties of prepared membranes were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The modified Nafion membranes by coating of sulfonated poly(arylene ether sulfone) showed phase separated morphology. The degree of phase separation could be controlled by variation of the condition of Nafion and the degree of sulfonation of poly(arylene ether sulfone). The penetration depth, the size, and number of Nafion domain were also varied. Solution blend of Nafion and sulfonated poly(arylene ether sulfone) was used to improve affinity between two polymers. The cross-sections of solution blend also showed phase separated morphology. The degree of phase separation and the phase separation mechanism could be controlled by varing the blend ratio and the degree of sulfonation of poly(arylene ether sulfone). These complex morphologies can be applied for reducing methanol crossover in DMFC. Phase separated top layer with PSSf matrix can reduce the methanol crossover and phase separated bottom layer with Nafion matrix...