Dielectric properties OF 40SiO2–40P2O5–20ZrO2 /sulfonated styrene-ethylene-butylene-styrene hybrid membranes for proton exchange membrane fuel cells

Abstract

The dielectric spectra of a series of hybrid membranes prepared with sulfonated styrene-ethylene-butylene-styrene (sSEBS) as the polymeric matrix, and zirconia-modified phosphosilicate (40SiO2–40P2O5–20ZrO2), as inorganic filler through direct infiltration, was analysed. All the membranes displayed characteristic sSEBS spectra, consisting of three molecular relaxations: A non-cooperative (β) relaxation and two cooperatives (αEB, αPS) ones ascribed to the glass transition of the ethylene-butylene and the polystyrene blocks, respectively. As a result of the infiltration of the inorganic component (40SiO2–40P2O5–20ZrO2), the dielectric spectra were considerably modified. Accordingly, the formation of dynamic crosslinking (M-O-M′ bonds, with M = P, Si, Zr) difficulties the motion of the αEB process, thus shifting it towards higher temperatures. Moreover, a significant plasticisation effect was found at high temperatures, which facilitates the activation of the αPS process. Furthermore, the decreasing values of the fragility parameter, due to the infiltration of the inorganic filler, revealed that all hybrid membranes displayed an arrangement of molecular chains and a strong behaviour. Thus, higher resistance to sudden temperature changes is expected. The optimum infiltration time (τinf) is between 10 and 20 min since it provides acceptable values of electric permittivity, and the induced dynamic crosslinking brings the glass transitions of both blocks closer. Consequently, a complete characterisation of the molecular mobility by studying the spectrum of dielectric relaxations enables to fine-tune the membranes for an optimum design focused on its application in a proton exchange membrane fuel cell (PEMFC).