Study on the characteristics of the composite proton-conducting membrane based on PVdF copolymer matrix

Abstract

ABSTRACT

The goal of the research in this thesis is to extend the understanding of the physics involved in the electrochemical characteristics of the composite proton-conducting membrane based on the PVdF copolymer matrix. Through this study, I focused on the development of the composite membrane with quite inhibited methanol permeation, which is decisive for the application to direct methanol fuel cells (DMFC). Blends of vinylidene fluoride - hexafluoropropylene copolymer (P(VdF-co-HFP)) with perfluorosulfonic acid copolymer $(Nafion\circledR)$ were prepared with a variation of blend ratio, fabrication condition, and HFP content in the PVdF copolymer. The investigations of blend morphology were performed by means of small-angle x-ray scattering (SAXS), dielectric loss measurement, permeability test, differential-scanning calorimetry (DSC), uptake measurement, and scanning electron microscopy (SEM). The blend morphology could be controlled by the variation of fabrication condition, blend ratio, and HFP content in the PVdF copolymer. Proton conductivity of the blend showed a strong dependence on the blend morphology. Proton conductivity of the blend showed a strong dependence on the blend morphology. This dependence was explained by the pathway tortuosity (n parameter) and the hydration degree (water uptake) of the blends. As for the pathway tortuosity in the blends, the formability of hydrated ionic clusters in the Nafion domain, the interconnectivity of ionic clusters, and the crystallinity of PVdF copolymer phase were analyzed. So as to increase the number of proton sources, then to enhance the proton conductivity of the PVdF copolymer / Nafion blend, each blend film was coated with the Nafion solution to the composite membrane. Methanol permeability of the composite membrane was quite suppressed by the inhibited diffusion of methanol through the membrane. Moreover, proton conductance of the composite membrane could be enhanced around to...