(A) study on Nafion/sulfonated Poly(aryl ether ketone) composite membrane for direct methanol fuel cell

Abstract

DMFC systems are based on polymer electrolyte in the form of PEMFC. It offers simple and compact design as the methanol is fed directly into the fuel cell. In order to improve the performance of the DMFC, it is necessary to eliminate or, at least, to reduce the loss of fuel cross the cell, usually termed "methanol crossover". In this thesis, we prepared Nafion/sulfonated poly(aryl ether ketone) composite membrane by blending two materials. The blend ratios of sPAEK and Nafion 117 were 2 : 1, 3 : 1, 5 : 1 and 7 : 1. The objective of this work is reducing methanol crossover and retaining proton conductivity. To reduce methanol crossover, this work focused on the development of the phase separated composite membrane. Sulfonated poly(aryl ether ketone)(sPAEK) was successfully synthesized. FT-IR data confirmed that the sulfonate group and ketone group were introduced. To check thermal stability, glass transition temperature and decomposition temperature were investigated. They showed sPAEK had good thermal properties. Ion exchange capacity, proton conductivity, methanol permeability and water uptake of sPAEK were also investigated. The membranes blended by Nafion117 and sPAEK showed phase separated morphology since they were immiscible. Due to the differences of specific gravity, solvent concentration profile and viscosity difference of blend solution, there existed distribution of the Nafion117 domain size as well as the Nafion117 volume fraction along the thickness direction of the blend membranes. Bigger Nafion117 domains were found in positions close to the substrate. The volume fraction of the Nafion117 domain was also higher in the position near the substrate. Mechanical properties such as stress at break, yield stress, Young``s modulus and Elongation at break were observed. The sPAEK had better mechanical properties than Nafion117. The mechanical properties increased with increasing sPAEK content. Proton conductivity and methanol permeability of the blend mem...