Investigation of electrochemical kinetics for La(III)/La reaction in molten LiClKCl eutectic salt using potentiometric polarization

Although the activity coefficients and diffusion coefficients of LaCl₃ in molten LiClKCl salt have been extensively studied, the data on the electrochemical properties of La(III)/La reaction in the melt are very scarce. Among the few measurements, up to five orders of magnitude discrepancies for the reaction rate constant $k^0$ have been reported. In the present study, potentiodynamic polarization measurements at different LaCl₃ concentrations (1–6 wt%) and temperatures (723–823 K) are conducted to obtain accurate values of the exchange current density $i_0$ and charge transfer coefficient $\alpha$. The data are analyzed using non-simplified electrode kinetic equations through the optimization fitting procedures, and conventional Tafel and linear polarization (LP) methods. The concentration dependence of $i_0$ obtained from the optimization fitting method is examined, showing agreement with the theoretical correlation $i_0=nF{k}^0{c}^{(1-\alpha )}$. The corresponding values of $k^0$ are 1.76–3.22 × 10⁻⁵ cm s⁻¹ in 723–823 K.