Tuning Polybenzimidazole Membrane by Immobilizing a Novel IonicLiquid with Superior Oxygen Reduction Reaction Kinetics

Protic ionic liquid (PIL) is a promising nonaqueouselectrolyte alternative to replacing phosphoric acid for fuel cellsoperating at temperatures above 100 degrees C. In this study, the physicaland electrochemical properties of stoichiometric and nonstoichio-metric PILs are investigated focusing on their acid/base ratio. Thestudy involves a series of PILs, generically indicated asN,N-diethyl-3-sulfopropane-1-ammonium trifluoromethanesulfonate([DESPA+][TfO-]), varying from an excess of the proton acceptor(N,N-diethyl-3-aminopropane-1-sulfonic acid) to an excess of theproton donor (trifluoromethanesulfonic acid, TfOH). Comparedto a state-of-the-art electrolyte, i.e., concentrated phosphoric acid,the nonstoichiometric [DESPA+][TfO-] shows superior oxygen reduction reaction kinetics on the investigated Pt catalysts andoxygen permeation ability (DO2middotcO2). [DESPA+][TfO-] with a base-to-acid molar ratio of 1:2 achieves a current density similar to 10 timeslarger than that of concentrated phosphoric acid at 110 degrees C and 0.8 V. Membranes including polybenzimidazole as a host polymerand stoichiometric and nonstoichiometric [DESPA+][TfO-] as the conductive electrolyte exhibit promising properties in terms ofthermal stability and conductivity. At 120 degrees C and 40% relative humidity, conductivities of 2 and 16 mS cm-1are achieved by themembranes employing stoichiometric and excess acid [DESPA+][TfO-], respectively

Automated summary

This study investigates the physical and electrochemical properties of stoichiometric and nonstoichiometric protic ionic liquids (PILs). The nonstoichiometric PILs show superior oxygen reduction reaction kinetics and oxygen permeation ability compared to concentrated phosphoric acid. Membranes with PILs as the conductive electrolyte exhibit promising properties in terms of thermal stability and conductivity.