Electrochemical Behavior of Titanium Complexes in the KCl-KF Melt with Additions of Alkaline Earth Metal Cations

Abstract

The goal of the present investigation was to study of Mg2+, Ca2+, Sr2+ and Ва2+ strongly polarizing cations influence on the standard rate constants of charge transfer (ks ) for the redox couple Ti(IV)/Ti(III) in the KCl-KF(10 wt.%)-K2TiF6 melt.Electrochemical studies were carried out in the temperature range of 1073-1173 K by cyclic voltammetry. Voltammetric curves were recorded at a glassy carbon electrode vs. a glassy carbon quasi-reference electrode. The sweep rate (v) varied from 0.1 up to 2.0 V s-1. The electrochemical redox process Ti(IV)+e-↔Ti(III) was classified as quasi-reversible at a sweep rate 1.0 V s-1≤ν≤2.0 V s-1.The values of k s were calculated by using the Nicholson’s method [1]. It was shown that k s increase with increasing the temperature. It is due to the number of particles capable of overcoming the potential barrier increases [2].Addition of alkaline earth metal cations resulted in increasing of ks up to the certain ratio of Me2+/Ti(IV) for all alkaline earth metal cations. It was determined the linear dependence of ks on ionic potential of alkaline earth metal cations.The activation energies of the charge transfer in the case of strongly polarizing cations addition were calculated. It was shown that values of the activation energy for molten systems with strongly polarizing cations are considerably less than activation energy of the initial melt and decrease with increasing of ionic potential.It was determined that the k s for the redox couple Ti(IV)/Ti(III) in the KCl-KF(10 wt.%)-K2TiF6 melt (for all systems) are less than k s in the NaCl-KCl based melt [3].