New proton conducting polymer membranes based on EPDM and branched HPBS

In this study, research was undertaken to obtain new proton conducting polymer blends based on hydrogenated poly(butadiene–styrene) (70/30) block copolymer (S-HPBS) and ethylene–propylene diene monomer (EPDM), in order to utilize them as membranes in polymer electrolyte membrane fuel cells (PEMFC). Blends become conducting by a sulfonation reaction, in heterogeneous phase, which inserts single bondSO3H groups into the macromolecular chain. As is known, there exists a direct relationship between the level of sulfonation and proton conductivity. Sulfonation results, however, in a simultaneous and direct loss of membrane stability, and this latter fact constitutes a very important limitation. Hence we decided to prepare membranes based on both polymers, incorporating, however, an additional component, i.e. polypropylene (PP) polymer with excellent mechanical and processing properties. First, all membranes were characterized from a structural point of view through techniques, such as: FT-IR, DSC, DMA, dynamic crystallization and complex impedance analysis. Then, we selected one membrane among all the blends studied, with the aim of determining its qualities as a membrane in a direct methanol fuel cell (DMFC). To this purpose we analyzed polarization curves and water and methanol crossover. The obtained membranes present good perspectives especially regarding the methanol permeability and physical stability, though the values of conductivity and power density need to be improved.