Specific adsorption of bromide and iodide ions on liquid Ga electrode from 0.1m M LiBr + 0.1(1 − m) M LiClO₄ and 0.1m M LiI + 0.1(1 − m) M LiClO₄ mixed solutions in dimethyl formamide

Abstract

The differential capacitance curves were measured with an ac bridge in the Ga/[DMF + 0.1m M LiBr + 0.1(1 − m) M LiClO₄] and Ga/[DMF + 0.1m M LiI + 0.1(1 − m) M LiClO₄] 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. Dimethyl formamide (DMF), as well as N-methyl formamide (N-MF), enables one to realize considerable positive charges of Ga electrode, at which it remains ideally polarizable (up to 11 μC/cm²). The data on the specific adsorption of Br⁻ and I⁻ anions in these systems can be quantitatively described by the Frumkin’s isotherm. The free energy of Br⁻ and I⁻ adsorption ΔG _ads is a quadratic function of electrode charge. It is found that, at the Ga/DMF interface, ΔG _ads varies in the series I⁻ < Br⁻ < Cl⁻. It is shown that the series of surface activity of halide ions is reversed when we pass from Hg/DMF and Bi/DMF interfaces to Ga/DMF interface. In contrast to the Ga/N-MF interface, where the values of ΔG _ads for Br⁻ and I⁻ were almost equal and an increase in ΔG _ads for Cl⁻ was rather small, at the Ga/DMF interface, ΔG _ads increases significantly in the series I⁻ < Br⁻ < Cl⁻.