Chemical and morphological effects of blended sulfonated poly(styrene‐isobutylene‐styrene) and isopentylamine for direct methanol fuel cell applications

Abstract

AbstractIn this study, blend membranes based on a combination of sulfonated poly (styrene‐isobutylene‐styrene) (SIBS) with isopentylamine (IPA) were synthetized as potential candidates for direct methanol fuel cell (DMFC) applications. The impact of sulfonation level (57–93 mol%) and percentage of IPA incorporation (1, 3, and 5 wt%) were analyzed via different properties of the resulting membrane. FTIR analysis showed that IPA was successfully incorporated into the sulfonated polymer matrix and also confirmed the interaction between the sulfonic and amine groups. This interaction generates significant morphological changes in the nanostructure of the membranes that are evident through results of small angle x‐ray scattering and atomic force microscopy analysis. Proton conductivity and methanol permeability of the membranes were also analyzed. Proton conductivity was significantly enhanced with the incorporation of IPA at an optimum loading, creating additional paths for the conduction of protons through the membrane. It was also sensitive to the morphological changes produced after the IPA incorporation and the interconnection between the ionic domains. Methanol permeability increased slightly due to the additional water domains and the inability of the isopentyl groups of IPA to block the free‐volume in the membrane. Despite this, the selectivity (proton conductivity over methanol permeability) of the membranes was comparable to the state‐of‐the‐art Nafion®, especially at an optimum IPA incorporation of 3 wt%.