Cathode Reduction of Ce(III) Ions in Fused 3LiCl–2KCl Eutectic

Abstract

The cathode reduction of Ce(III) ions to form a metal at an inert Mo electrode in the molten 3LiCl–2KCl eutectic is studied in a temperature range of 723–823 K by stationary and nonstationary electrochemical methods. In voltammograms, a single cathodic current peak is recorded at a potential of –3.19 ± 0.10 V, and an anodic current peak associated with the cathodic current peak is recorded at a potential of ‒3.10 ± 0.08 V vs. the chlorine reference electrode. Therefore, the reduction process occurs by the reaction Ce3+ + 3 $${\bar {e}}$$ → Ce. An analysis of cyclic voltammograms showed that the current peak potential of the Ce(III) ion reduction shifts to a negative range as the scan rate increases. At the same time, the current corresponding to the cathodic peak is directly proportional to the square root of the polarization rate in the entire potential range under study. An increase of the scan rate is shown to decrease the transfer coefficient (α), i.e., to increase in the irreversibility of the cathodic process. According to the theory of cyclic voltammetry, the cathode reduction of cerium ions is an irreversible process, which is single-stage and is controlled by the charge transfer rate. The temperature dependence of the apparent standard potential of the pair Ce(III)/Ce is measured by zero-current chronopotentiometry. The experimental values are described by linear equation $$E_{{{{{\text{Ce}}\left( {{\text{III}}} \right)} \mathord{\left/ {\vphantom {{{\text{Ce}}\left( {{\text{III}}} \right)} {{\text{Ce}}}}} \right. \kern-0em} {{\text{Ce}}}}}}^{{\text{*}}} = - \left( {{\text{3}}{\text{.455}} \pm {\text{0}}{\text{.010}}} \right)$$ + (6.1 ± 0.1) × 10–4T ± 0.009 V. The changes in the apparent standard Gibbs energy, the enthalpy, and the entropy of the reaction of formation of cerium thrichloride from the elements in the molten 3LiCl–KCl eutectic and the activity coefficient of CeCl3 are calculated.