Performance of PEMFC with new polyvinyl-ionic liquids based membranes as electrolytes

Polymer Electrolyte Membrane Fuel Cells (PEMFC) represent a key technology for sustainable energy production due to their high efficiency and low environmental impact. The use of task specific protic ionic liquids as electrolytes is gaining interest due to their high conductivity and thermal and electrochemical stability under anhydrous conditions. Ionic liquids with the imidazolium cation exhibit a high electrochemical stability, besides sulfonic groups can be incorporated to the cation as side chains acting as carriers in order to facilitate the proton transport. Moreover suitable anions such as Tf2N and OTf provide high ionic conductivity. In this work, two different types of membranes based on protic ionic liquids have been tested in PEMFC under anhydrous conditions i) Nafion membranes impregnated with the protic ionic liquids 1-methyl-3-(4-sulfobutyl)-imidazolium bis(trifluoromethylsulfonyl)-imide ([HSO3-BMIm][NTf2]) and 1-butyl-3-(4-sulfobutyl)-imidazolium trifluoromethanesulfonate ([HSO3-BBIm][OTf]) and, ii) membranes based on the polymerization of the specifically designed ionic liquid 1-(4-sulfobutyl)-3-vinylimidazolium trifluoromethanesulfonate ([HSO3-BVIm][OTf]). The influence of different operation variables such as cell temperature, gas humidity and membrane thickness on the performance of the PEMFC has been analyzed, and the resistance exerted by the electrolyte was determined using electrical impedance spectroscopy. Nafion membranes impregnated with [HSO3-BBIm][OTf] achieve current densities of 217 mA/cm2 under anhydrous conditions at 25 °C whereas [HSO3-BVIm][OTf] polymerized electrolytes provide current densities of 154 mA/cm2 at the same conditions. This is the first report that describes the application of designed polymerized protic ionic liquids membranes for fuel cells. Although some improvements in terms of thermal and mechanical stability should be achieved, this first approach presents a promising electrolyte with challenging characteristics.