(351b) Effect of Amine Groups Incorporation on Morphology and Transport Properties of Sulfonated Poly(styrene-isobutylene-styrene) Membranes for Fuel Cell Applications

The growing demand in the search for energy sources independent of fossil fuels, has generated a considerable interest in the use of fuel cells as an alternative energy source with low environmental impact and high electrical efficiency. Even with their advantages, fuel cells exhibit some severe limitations like high permeability to fuels and high cost. These limitations are associated with the composition of the proton exchange membrane (PEM) which is considered a key component on these devices. In order to overcome these downsides, PEMs based on aromatic polymers have been synthesized and used because of their availability and easy modification.

In this study, blend membranes based on sulfonated poly (styrene-isobutylene-styrene) (SIBS) with isopentylamine (IPA) were synthetized as a potential candidate for direct methanol fuel cell (DMFC) applications. Properties of the resulting membranes were determined as a function of critical parameters such as sulfonation level (57-93 mol%) and percentage of IPA incorporation (1, 3, and 5 wt.%). FTIR analysis proved that isopentylamine was successfully incorporated into the sulfonated polymer matrix and confirmed the interaction between the sulfonic and amine groups. That interaction is attributed to the hydrogen bonds formed with the presence of both groups inside the membranes which generatessignificant morphological changes in the nanostructure of the membranes that are evident through results of small angle x-ray scattering (SAXS) and atomic force microscopy (AFM).On the other hand, proton conductivity and methanol permeability were measured to analyze the transport properties of the membranes. The results suggest different transport mechanisms for proton and methanol in the membrane, since IPA incorporation showed different patterns in both properties for each sulfonation level. Methanol permeability seems to be related to the water content in the membrane while proton conductivity seems to be more sensitive to the morphological changes produced after the IPA incorporation and the interconnection between the ionics domains. The selectivity (proton conductivity over methanol permeability) of membranes revealed an optimum IPA incorporation between 3-5 wt.%, which depends onthe sulfonation level. The results also indicated that blended membranes show a better chemical stability compared to the sulfonated membranes.

Keywords: Amine-sulfonic groups interaction, Proton exchange membrane, Morphology, Transport properties, Direct methanol fuel cell.