Influence of the Conductivity and Viscosity of Protic Ionic Liquids Electrolytes on the Pseudocapacitance of RuO2 Electrodes

Several new protic ionic liquids (PILs) were prepared by mixing trifluoroacetic acid (TFA) with various heterocyclic amines using different base:acid ratios (1:1 and 1:2). Their specific conductivities have been measured by electrochemical impedance spectroscopy and were found ranging from 0.71 to 9.07 mS center dot cm(-1) at 27.0 degrees C. In all cases, the conductivity of a given ionic liquid increased with a higher proportion of acid (1:2 ratio) which is explained mainly a smaller viscosity obtained in these conditions. Indeed, in most PILs, the dynamic viscosity (10.3-484 cp at 27.0 T) is decreased by a higher acid proportion. Both parameters were used to construct a Walden plot in order to evaluate the quality of these protic ionic liquids (PILs) and compare them with common room temperature (RT) molten salts. The physicochernical properties of the PILs were then compared with the specific capacitance values obtained with a thermally prepared RuO2 electrode in these ionic liquid electrolytes. This work brings evidence that pseudocapacitance is involved in the energy storage mechanism of the PILs studied here and shows that PILs could eventually be used as electrolytes in metal oxide-based supercapacitors.