Electrochemical behavior of La(III) on the zinc-coated W electrode in LiCl-KCl eutectic

The electrochemical behaviors of La(III) on W and Zn-coated W electrodes was investigated, respectively, in the LiCl-KCl eutectic by cyclic voltammetry (CV) and open circuit chronopotentiometry (OCP). On an inert W electrode, the reduction of La(III) takes place at about −2.11 V in a single soluble-insoluble electrochemical step La(III)/La(0). In contrast, the electrochemical reduction of La(III) on a Zn-coated W electrode was observed at less cathodic potentials than at the inert W electrode. The potential shift was mainly caused by the formation of La-Zn intermetallic compounds, in which the activity of La was largely decreased compared to that in pure La metal. From CV results, six peaks corresponding to the formation of La-Zn intermetallic compounds were observed. By the OCP technique, eight plateaus corresponding to the co-existence of two phases of La-Zn intermetallic compound such as LaZn-LaZn2, LaZn2-LaZn4, LaZn4-LaZn5, LaZn5 -La3Zn22, La3Zn22-La2Zn17, La2Zn17-LaZn11, LaZn11-LaZn13 and LaZn13-Zn were observed. The formation energy of each La-Zn intermetallic compound, and the overall formation constant were estimated from OCP measurements at 723 K. X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) were employed to characterize the potentiostatic and galvanostatic electrolysis products. The presences of LaZn, LaZn2, LaZn5 and La2Zn17 in the electrolysis products were identified.