Kinetic Mechanism of La³⁺ Reaction in LiCl-KCl-LaCl₃ Molten Salt System

In this paper, the reaction kinetic mechanism of La³⁺ was studied in the LiCl-KCl eutectic salt at various temperatures. First, the diffusion coefficient of La³⁺(D) measured by cyclic voltammetry(CV) increases from 3.06×10^-5 cm²/s to 6.08×10^-5 cm²/s with the temperature ranging from 723 K to 873 K, and the activation energy of La³⁺ diffusion(ED) in the molten salts is 34.51 kJ/mol calculated by the Arrhenius equation. Subsequently, the kinetic parameters of La³⁺ on the W electrode were studied by the electrochemical impedance spectroscopy(EIS). In the temperature range of 723-873 K, the exchange current density(i₀) is measured to be 0.48-1.39 A/cm², and the reaction rate constant(k₀) is determined as 2.04×10^-4-5.90×10^-4 cm/s. Moreover, the corresponding reaction activation energy(Ea) is found to be 35.04 kJ/mol. The Nyquist plots and the fitted circuit diagrams explored the reaction kinetic mechanism of La³⁺ on a W electrode. It was illustrated that the electrochemical reduction rate of La³⁺ in the LiCl-KCl eutectic salt is controlled by diffusion and charge transfer, and it is positively correlated with temperature.