Kinetic and thermodynamic properties of La(III) on Molybdenum electrode in LiCl–KCl–LaCl₃ melts

The kinetic and thermodynamic properties of La(III) in LiCl–KCl–LaCl₃ melts on inert electrode (Mo) were investigated by different electrochemical methods. The reduction of La(III) into metallic La on the Mo electrode is a quasi-reversible process that can transfer three electrons in a single step. In the temperature range of 723–848 K, the diffusion coefficient and reaction activation energy of La(III) in LiCl–KCl–LaCl₃ melts were calculated using Cyclic voltammetry (CV) and Chronopotentiometry (CP). Moreover, relationships between the diffusion coefficient with temperature were formulated as follows: lnD₀ = − 3.32/T + 5.27 (CV) and lnD₀ = − 4.7/T − 5.89 (CP). The dependence of exchange current density of La(III)/La(0) on the experimental temperatures was constructed by Tafel (lnj₀ = − 2.04/T − 1.93) and Linear polarization (LP) (lnj₀ = − 2.74/T − 0.912). The apparent electrode potentials, Gibbs free energy, and activity coefficient of La(III)/La(0) were estimated using Open-circuit chronopotentiometry (OCP). Different LaCl₃ concentrations were added to LiCl–KCl melts, and the ion concentration of La(III) in the melts was determined using Normal Pulse Voltammetry (NPV). The obtained results had a relative error of less than 10% when compared to the ICP results. It shows that the results obtained by NPV detection are accurate and reliable.