Specific adsorption of bromide and iodide ions from N-methyl formamide solutions with constant ionic strength on liquid ga electrode

Abstract

The differential capacitance curves were measured with an ac bridge in the Ga/[N-MF + 0.1 m M KBr + 0.1 (1 − m) M KClO₄] and Ga/[N-MF + 0.1 m M KI + 0.1 (1 − m) M KClO₄] systems at the following fractions m of surface-active anions: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with other solvents, N-methyl formamide (N-MF) enables one to realize the largest positive charges of Ga electrode, at which it remains ideally polarizable (up to 20 μ/cm²). The data on the specific adsorption of Br⁻ and I⁻ anions in the system can be quantitatively described by the Frumkin’s isotherm; to the first approximation, free energy of halide ion (Hal⁻) adsorption $\Delta G_{adsHal^{ - 1} }$ is a linear function of electrode charge. It is found that, in contrast to the Hg/N-MF interface, $\Delta G_{adsHal^{ - 1} }$ at the Ga/N-MF interface varies in the reverse order: Br^t— ∼ I⁻ < Cl⁻. From the measured results, we can conclude that the energy of metal-Hal⁻ interaction increases in series: $\Delta G_{M - Cl^ - } > \Delta G_{M - Br^ - } > \Delta G_{M - I^ - }$ and the difference $(\Delta G_{Ga - Hal_1^ - } - \Delta G_{Ga - Hal_2^ - } )$ is larger than the difference between the solvation energies of $Hal^ - (\Delta G_{S - Hal_1^ - } - \Delta G_{S - Hal_2^ - } )$.