Analysis of Equilibrium Electrocapillary Curves at the Interface between Hydrophobic Ionic Liquid, Trioctylmethylammonium Bis(nonafluorobutanesulfonyl)amide, and Aqueous Lithium Chloride Solutions

Electrocapillary curves obtained under the thermodynamic equilibrium at the interface between trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide and aqueous lithium chloride have been analyzed to study the adsorption of Li+ and Cl− ions at the interface. The specific adsorption of Li+ and Cl− is negligible in almost the entire range of the polarized potential window. At the positive extreme where the excess surface charge density is greater than 3 μC·cm−2, the deviation of the experimental relative surface excesses of Li+ and Cl− from the Gouy’s theory was detected. This deviation suggests the coordination of adsorbed bis(nonafluorobutanesulfonyl)amide to Li+ in the aqueous side of the interface. The double layer capacitance on the ionic liquid side of the interface is deduced to be 125 μF·cm−2 at the potential of zero charge.