Improved hydrogen sorption properties of Pd in protic and aprotic ionic liquids effected by superacid addition

The mixtures of selected protic and aprotic ionic liquids with their parent superacids were used as electrolytes in the process of hydrogen electrosorption in thin (ca. 0.5 µm) Pd films. The properties of ionic liquids and their mixtures with superacids were characterized with the use of electrochemical and physicochemical methods to show the perspectives of their potential utilization as electrolytes in hydride/protonic systems. Based on the electrochemical studies it was possible to estimate the minimum concentrations of the superacids in protic and aprotic ionic liquids which give maximum hydrogen absorption capacities in Pd (H/Pd). Unusual, previously unnoticed ‘two-step’ α→β phase transition was observed on the hydrogen electrosorption isotherm of Pd for the process of hydrogen absorption from the protic ionic liquids for some superacid concentrations. 1H NMR spectroscopy of the protic ionic liquids enables to discuss the relation between proton mobility and hydrogen electrosorption properties.