Interplay between nanostructure and proton conductivity of Nafion-based nanocomposite membranes

An overview of the studies carried out on Nafion®-based nanocomposite membranes for application in proton exchange membrane fuel cells is reported here. The membranes are obtained either by: (a) dispersing in Nafion ceramic nanofillers, including single oxides (e.g., SiO2, HfO2) or “core-shell” inorganic particles (e.g., [(ZrO2)∙(SiO2)0.65], [(TiO2)∙(WO3)0.148]); or (b) neutralizing a Nafion membrane with an organic base such as triethylamine and doping with a variety of proton-conducting ionic liquids (e.g., TEATF, TMS, TPFBu). A comprehensive model is proposed to explain the effect of the nanocomposite materials on the nanostructure of the overall membrane and pays particular attention to the introduction of phase boundaries and the alteration of chain conformation in the Nafion host polymer. The structure of the nanocomposite membranes is investigated by vibrational spectroscopy, while the thermal and thermomechanical properties are studied with HR-TG, MDSC and DMA. The structural and mechanical information is combined with the electrical properties, as determined with BES, to achieve a detailed understanding of the factors that influence the proton conduction mechanism.