Protic Ionic Liquids Based on a Super-Strong Acid: Bulk and Electrochemical Properties

摘要

Protic ionic liquids were synthesized by simple neutralization reactions of a super-strong acid, bis(trifluoromethanesulfonyl) amide acid (H[NTf_2]), with a range of amines, resulting in a wide variation in the ΔpK_a of the constituent acid and bases. Bulk physicochemical and electrochemical properties of the PILs were studied with an emphasis on thermal stability and temperature dependencies of density, viscosity and conductivity, and electrochemical activity. Thermogravimetric analysis revealed that thermal stability strongly depends on the ΔpK_a of the constituent acid and the base. However, density, viscosity and conductivity at different temperatures by and large depend on the structure of amines rather than the ΔpK_a. Walden plots indicate that all of these salts are good PILs. Cyclic voltammetry analyses inferred that the PIL with the highest ΔpK_a value exhibited a very low electrochemical activity as apparent from the open circuit voltage of 0.60 V vs. RHE at 150 °C for oxygen reduction reaction.