Anion Influence on Properties of Acidic Protic Ionic Liquids

Anion influence on the properties of acidic protic ionic liquidsHui Hou, Jürgen Giffin, Carsten KorteForschungszentrum Jülich GmbH, IEK-3Wilhelm-Johnen-Straße, 52428 Jülich, Germany Tel.: +49-2461-61-85360Fax: +49-2461-61-6695h.hou@fz-juelich.deAbstractTo run polymer electrolyte fuel cells (PEFCs) at an operating temperature above 100 °C, there is a growing need for new proton conducting membrane electrolytes that can be used when water activity is low. This would allow for a system setup without feed gas humidification and a more efficient cooling system. Nafion® membranes, as used for low temperature PEFCs (LT-PEFCs), suffer from drying effects that result in low proton conductivity. H3PO4-doped PBI membranes, as used in high temperature PEFCs (HT-PEFCs), will result in a low power density because of low O2 solubility, as well as a specific adsorption of H3PO4 species on the platinum redox catalyst. Proton-conducting ionic liquids (PILs) based on sulfonic acid derivatives may be used as alternative liquid electrolytes because they exhibit sufficient proton conductivity, electrochemical and thermal stability over a wide temperature range and, specifically, faster ORR kinetics compared to H3PO4 [1]. It was shown in a previous work by Wippermann et al. that the ORR limiting current density of the 2-sulfoethylammonium triflate with a strong acidic cation is significantly higher compared to H3PO4 in a high potential range [2]. However, the conductivity is about one order of magnitude lower. In this study, we investigate strong acidic PILs based on a 2-sulfoethylmethylammonium cation combined with various anions such as HSO¬4-, mesylate, tosylate, benzenesulfonate and triflate. Acidity influence of the anion on the ORR kinetics (oxygen diffusion coefficient and oxygen solubility), thermal and electrochemical stability, as well as conductivity, was measured at different temperatures for the neat PILs, as well as for various amounts of water. The measured values are compared to phosphoric acid and correlated to the anion properties to find an optimum.Literature:[1] Mitsushima, Shigenori, et al. Electrochimica Acta 55 (22), 6639-6644 (2010).[2] Wippermann, Klaus, et al. Journal of The Electrochemical Society 163.2, F25-F37 (2016)