Redox behaviour of cerium oxychloride in molten MgCl2-NaCl-KCl eutectic

The electrochemical behaviour of cerium oxychloride in MgCl₂-NaCl-KCl ternary eutectic was investigated by cyclic voltammetry at 823 K. The cyclic voltammogram of UO₂Cl₂-CeOCl in MgCl₂-NaCl-KCl eutectic shows two peaks during the cathodic sweep as well as anodic sweep. The reduction of UO₂²⁺ is by a single step two-electron transfer and that of CeO⁺ is by a single step one-electron transfer. The reduction of CeO⁺ was found to be quasi-reversible.The reduction potentials of UO₂²⁺/UO₂ and CeO⁺/CeO versus Ag(I)/Ag reference electrode at 823 K are 0.103 and −0.299 V, respectively. The diffusion coefficient of CeO⁺ at 823 K is in the range of (1.7-1.9) × 10⁻⁵ cm² s⁻¹. The cyclic voltammogram for 0.015 mol% CeOCl shows an additional peak during the anodic sweep at −0.056 V, which is being attributed to monolayer dissolution of CeO at the glassy carbon working electrode. Electrochemical impedance data of 0.015 mol% CeOCl in MgCl₂-NaCl-KCl eutectic at the open circuit potential was fitted to a Randles cell from which the heterogeneous rate constant was estimated. X-ray photoelectron spectroscopy was used to confirm that the oxidation state of cerium in the eutectic is +3.