Effects of F- on the electrochemical properties and electrodeposition nucleation mechanism of Ce(III) in LiCl-KCl melts

Abstract

The purpose of this work is to systematically investigate the effect of F⁻ on the electrochemical properties and electrodeposition nucleation of Ce(III) in LiCl-KCl molten salt. Electrochemically reversible, three-electron transfer and diffusion-controlled Ce(III)/Ce redox reactions were still observed by using Cyclic voltammetry (CV), Square wave voltammetry (SWV), and Chronopotentiometry (CP) methods in the LiCl-KCl molten salt containing F⁻. With the addition of F⁻, a negative shift in peak and equilibrium potentials were observed, indicating that F⁻ could interact with Ce(III) via the coordination competition with Cl⁻. Also, F⁻ ions were found to decrease both the diffusion coefficient and exchange current density j₀ of Ce(III). In addition, the thermodynamic data of Ce(III)/Ce at multiple F⁻ concentrations were calculated theoretically, which showed that Ce(III) preferred to form [CeCl₅F]³⁻complexes in chlorine molten salts. Finally, the effect of F⁻ on the electrodeposition nucleation mechanism of Ce(III) at tungsten electrodes was studied. The results showed that the nucleation and growth mechanism shifted from instantaneous nucleation to between instantaneous and progressive nucleation with the addition of F⁻. The current research paves a new way for changing the nucleation mode of electrodeposition, which provides a new direction to retrieve the uranium dendrites during the electrorefining of spent nuclear fuel.