Development of hybrid polymer electrolyte membranes based on the semi-interpenetrating network concept

Hybrid inorganic/organic polymer electrolyte membranes for potential fuel cell applications are prepared by centrifugal casting from solutions of sulfonated polyetheretherketone (SPEEK) (DS 64%) and polyethoxysiloxane (PEOS) in dimethylacetamide, following the concept of a semi-interpenetrating network. The in situ transformation of PEOS into SiO2 occurs in a "water free" process. The morphology of the films obtained is controlled by the phase segregation process, determined by the rate of evaporation of the solvent and by the transformation of PEOS into SiO2-particles. The latter process is influenced by the presence of a catalyst. Moreover, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole is added to the mixture to enhance the interaction between SPEEK and PEOS and to influence the membrane morphology. The size and size-distribution of the SiO2 particles formed in the organic matrix are examined by means of transmission electron microscopy. The TEM investigations show a strongly reduced particle size when N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole is added to the mixture. Proton conductivity measurements are performed on the membranes by impedance spectroscopy in an open set-up that allows measurements along the longitudinal direction of the sample. All the samples show a plateau in impedance at medium frequencies that represents the proton conducting process. Nafion((R)) 115 is measured in the same set-up for comparison.