Influence of magnesium cations on the electrochemical behavior of the Ti(IV)/Ti(III) redox couple in alkali chloride fluoride melt: Experimental and quantum-chemical studies

Abstract

The influence of Mg 2+ cations on the charge transfer kinetics of the redox couple Ti(IV)/Ti(III) was studied by cyclic voltammetry. The standard rate constants of charge transfer (ks) for the redox couple Ti(IV)/Ti(III) in the NaCl-KCl (equimolar mixture) .-NaF(10 wt.%)-K2TiF6 melt upon the addition of Mg 2+ cations into the initial melt were calculated based on the Nicholson's equation. The temperature dependence of ks for molten salt system with additions of Mg 2+ cations was determined and the activation energy of charge transfer was calculated. Based on the experimental data and the quantum chemical analysis of the frontier molecular orbitals in the MgTiF6 + 12MgCl2 system, a mechanism for electrochemical charge transfer was proposed. The geometric structure of the transition state was shown to be not intermediate between the initial and final states of the system. This approach can be recommended as a tool for verifying hypotheses related to the mechanism of electrochemical electron transfer.