Adsorption of bromide and iodide anions on a renewable liquid (Cd–Ga) electrode from acetonitrile solutions. Effect of (Cd–Ga)–solvent chemisorption interaction on the anion adsorption energy

Abstract The specific adsorption of bromide and iodide anions was studied at a (Cd–Ga)/acetonitrile (AN) interface from mixed solutions of [0.1 m M LiBr + 0.1 (1–m) M LiBF4] and [0.1 m M LiI + 0.1 (1–m) M LiBF4] at the following values of molar fraction m of the surface–active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The main experimental method was measurement of differential capacitance on a renewable liquid (Cd–Ga) electrode. The obtained experimental results can be described quantitatively by the Frumkin isotherm in a wide range of charge densities (σ). The adsorption parameters of halide anions (Hal−) were determined using regression analysis of two-dimensional pressure isotherms. It is shown that the adsorption energies (ΔGads) of Br− and I− at the (Cd–Ga)/AN interface practically coincide. It follows that the difference in the interaction energies of Br− and I− with (Cd–Ga) is equal to the difference of the solvation energies of these anions: (ΔG(Cd‐Ga)‐Br‐ − ΔG(Cd‐Ga)‐I‐)≈(ΔGAN‐Br‐ − ΔGAN‐I‐) and therefore ΔG(Cd-Ga)-I−