Preparation and characterization of $nafion^{TM}/polypyrrole$ composite membrane for direct methanol fuel cell

Abstract

Nano-sized polypyrrole particles were incorporated into the ionic clusters rather than non-polar backbone of Nafion in chemical in-situ polymerization by means of ion-dipole interaction between the sulfonate groups of Nafion and secondary ammonium groups of polypyrrole. The existence of the polypyrrole particles in the matrix was confirmed by color change, SEM, and TEM. The incorporation of polypyrrole particles into the clusters, where was the transport pathway, changed the morphology of Nafion matrix, as observed by SAXS and WAXD. In particular, the crystallite region of backbones as well as the cluster region of side chains was influenced by the existence of polypyrrole particles in the ionic clusters. The thermal property of the composite membrane was influenced by the morphological changes. As shown by DSC diagrams, the temperature of the polar cluster transition shifted to a higher value due to the restricted mobility of the clusters, whereas the melting temperature of the non-polar backbone crystallite shifted to a lower value due to the disruptive effect of swelled cluster. The composite membrane had a higher thermal stability than the Nafion membrane, as shown by TG diagrams. The methanol crossover was reduced more than the proton conductivity as a result of the invasion of polypyrrole particles. The existence of the polypyrrole particles in the ionic clusters also affected the transport properties of the composite membranes. Additionally, it was observed that transport phenomenon in the composite membranes was influenced by the equilibrium factor rather than the kinetic factor due to their structures. The optimization of performance was related to the distribution of polypyrrole particles over the cross section of the membrane, as observed by SEM and EPMA data. The content of the polypyrrole particles mainly increased in the surface rather than in the internal space by the polypyrrole content of 3.5 wt% in N/P 003. The proton conductivity of the com...