A continuing challenge in proton-exchange-membrane fuel cell research is identifying materials that deliver good performance at elevated temperatures (T > 100oC), where catalyst poisoning is reduced. It is well known that perfluoronated ionomers, such as Nafion, exhibit low ionic conductivities above 100oC due to membrane dehydration. This results in poor fuel cell performance, thereby essentially limiting the operation range of those materials to below 100oC. One strategy that has been proposed in the literature to overcome this limitation is to saturate Nafion with a proton-conducting ionic liquid. Ionic liquids are typically organic salts with low melting points, and in many cases, the materials possess very high ionic conductivities and negligible vapor pressures. Since ionic liquids do not have appreciable vapor pressures above 100oC, it may be possible to take advantage of the high proton conductivities of the ionic liquid to prepare Nafion-based membranes that function at elevated temperatures. In this work, we extend this general strategy by doping the protic ionic liquid, 1-methylimidazolium bis(trifluoromethylsulfonyl)imide in Nafion membranes that have been neutralized with imidazole. Membrane performance is assessed through temperature-dependent ionic conductivity measurements. In addition, the thermal and mechanical properties of the membranes are characterized to better understand how the ionic liquid affects the Nafion membrane. Molecular-level interactions among the various components of the ionic-liquid-saturated membranes are investigated with vibrational spectroscopy.

Investigation Nafion membranes neutralized with imidazole and saturated with 1-methylimidazolium bis(trifluoromethylsulfonyl)imide

247th National Meeting (2014)

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