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 k0 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 i0 and charge transfer coefficient α. 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 i0 obtained from the optimization fitting method is examined, showing agreement with the theoretical correlation i0=nFk0c(1−α). The corresponding values of k0 are 1.76-3.22 × 10−5 cm s−1 in 723-823 K.