Physicochemical characterisation of aqueous solutions of tetra-alkyl-ammonium-sulfonic acid ionic liquid

Zwitterionic ionic liquids (ILs) exhibit excellent characteristics when employed as electrolytes in water electrolysis. A good example of these ILs is 3-triethylammonium-propanesulfonic acid tetrafluoroborate ionic liquid (TEA-PS.BF4 IL), which has great advantages like high efficiency and high current density when used as an electrolyte in water electrolysis. The excellent performance of TEA-PS.BF4 IL in relation to other electrolytes and its promising use in electrochemical and other applications is better understood through the physicochemical properties of TEA-PS.BF4 ionic liquid. Linear dependence between the density and IL molar concentration (0.001 M to 0.70 M) was observed; moreover, the viscosity did not change significantly at low concentrations but at high concentrations. In dilute aqueous solutions, TEA-PS.BF4 IL showed the behaviour predicted by the Kohlrausch law and it was possible to calculate the value of the diffusion coefficient of IL. The molar conductivity was calculated with the Nernst‐Haskell equation, the self-diffusion coefficients of ions at infinite dilution were calculated with the Nernst‐Einstein equation and the hydrodynamic radius of each ion was calculated with the Stokes-Einstein equation. Comparison of the TEA-PS.BF4 with other ILs showed that it has the highest diffusion coefficient (1.77 × 10‐ 9m2 s‐ 1).