Nafion–clay hybrids with a network structure

Burgaz, Engin, Lian, Huiqin, Alonso, Rafael Herrera, Estevez, Luis, Kelarakis, Antonios and Giannelis, Emmanuel P. (2009) Nafion–clay hybrids with a network structure. Polymer, 50 (11). pp. 2384-2392. ISSN 00323861

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Nafion–clay hybrid membranes with a unique microstructure were synthesized using a fundamentally
new approach. The new approach is based on depletion aggregation of suspended particles – a wellknown
phenomenon in colloids. For certain concentrations of clay and polymer, addition of Nafion
solution to clay suspensions in water leads to a gel. Using Cryo-TEM we show that the clay particles in the
hybrid gels form a network structure with an average cell size in the order of 500 nm. The hybrid gels are
subsequently cast to produce hybrid Nafion–clay membranes. Compared to pure Nafion the swelling of
the hybrid membranes in water and methanol is dramatically reduced while their selectivity (ratio of
conductivity over permeability) increases. The small decrease of ionic conductivity for the hybrid
membranes is more than compensated by the large decrease in methanol permeability. Lastly the hybrid
membranes are much stiffer and can withstand higher temperatures compared to pure Nafion. Both of
these characteristics are highly desirable for use in fuel cell applications, since a) they will allow the use
of a thinner membrane circumventing problems associated with the membrane resistance and b) enable
high temperature applications.

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