Specific adsorption of Cl-, Br-, and I- ions on liquid In-Ga electrode from dimethyl formamide solutions with a constant ionic strength

The differential capacitance curves were measured with an ac bridge in the (In-Ga)/[DMF + 0.1m M LiCl + 0.1(1-m) M LiClO4], (In-Ga)/[DMF + 0.1m M LiBr + 0.1(1-m) M LiClO4], and (In-Ga)/[DMF + 0.1m M LiI + 0.1(1-m) M LiClO4] (DMF is dimethyl formamide) systems at the following fractions m of surface-active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The data on the specific adsorption of Cl-, Br-, and I- anions in these systems can be quantitatively described by the Frumkin's isotherm. The free energy of Cl-, Br-, and I- adsorption (Delta G (ads)) is a quadratic function of electrode charge. It is found that, at the (In-Ga)/DMF interface, as well as at the Ga/DMF interface, Delta G (ads) varies in the series I- < Br- < Cl-. An analysis indicates conclusively that the series of surface activity of halide ions is reversed when we pass from the Hg/DMF and Bi/DMF interfaces to the Ga/DMF and (In-Ga)/DMF interfaces. A change of the solvent in the transition from (In-Ga)/N-methyl formamide interface to the (In-Ga)/dimethyl formamide interface is also accompanied by the transition from the common to the reversed series of surface activity of halide ions.