The electrochemistry of praseodymium was studied on liquid Zn film electrode in LiCl-KCl eutectic melts by transient electrochemical techniques. Cyclic voltammogram and square wave voltammogram showed that eight reduction peaks, corresponding to the formation of eight Pr-Zn intermetallic compounds, were observed at less negative potential values, which indicated the underpotential deposition of praseodymium occurs on liquid Zn film electrode. Thermodynamic properties on the formation for Pr-Zn intermetallic compounds, such as activities and relative partial molar Gibbs free energies of Pr in two-phase coexisting states as well as the standard Gibbs free energies of formation for Pr-Zn intermetallic compounds, were estimated using electromotive force (emf) measurement in the temperature range from 723 to 873 K. Electrochemical preparation of Pr-Zn alloys was executed by potentiostatic and galvanostatic electrolysis on Zn film electrode and liquid Zn pool electrode, respectively. X-ray diffraction (XRD) indicated that Pr-Zn alloy were comprised of different Pr-Zn intermetallics. The surface microstructures and micro-zone chemical analyses of Pr-Zn alloys were also characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results of SEM-EDS displayed that the distribution of Pr is non-homogeneous in Pr-Zn alloys.

The electrochemical reactions of Tb(III) were investigated on a W electrode, Bi pool electrode and Bi film electrode in eutectic LiCl–KCl by transient electrochemical techniques. The exchange current densities of the Tb(III)/Tb(0) redox couple were determined on W and Bi film electrodes at different temperatures by the linear polarization method. On both Bi electrodes, the redox potential of Tb(III)/Tb couple was observed at less negative potential values than that on the W electrode, which indicated underpotential deposition of Tb occurring on the both Bi electrodes. The result of cyclic voltammetry performed on the Bi pool electrode suggested that the electrochemical reaction of Tb(III) to Tbin liquid Bi was a quasi-reversible and diffusion-controlled process. From the cyclic voltammogram and square wave voltammogram of Tb(III) obtained on the Bi film electrode, three reduction signals corresponded to the formation of Tb–Bi intermetallic compounds. The thermodynamic data, such as the activities of Tb in Tb–Bi alloys and the standard Gibbs free energies of formation for different Tb–Bi intermetallic compounds, were estimated using open circuit chronopotentiometry in the temperature range from 673 to 873 K. Moreover, the electrochemical preparation of Tb–Bi alloys was conducted in LiCl–KCl–TbCl3 melts on a liquid Bi electrode by galvanostatic and potentiostatic electrolysis, respectively. The Tb–Bi alloys were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). XRD results showed that the Tb–Bi alloys were composed of the TbBi phase and TbBi, TbBi3/4 and TbBi3/5 phases, respectively.

The electrochemical behavior of Tb(III) in the LiCl-KCl eutectic melts was studied on Mo and Al electrodes by cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry in the temperature range of 773–873 K. On a Mo electrode, the reduction of Tb(III) was one-step electrochemical process. The diffusion coefficient of Tb(III) was determined by applying the Berzins and Delahay equation. The activation energy for diffusion of Tb(III) ions was found to be 30.5 kJ mol−1. The equilibrium potential of Tb(III)/Tb(0) redox couple was measured by open circuit chronopotentiometry, with subsequent calculation of the apparent standard potential, ETb(III)/Tb(0)*0, and the apparent Gibbs free energy of formation, ΔGf*0(TbCl3). The activity coefficients for Tb(III), γTb(III)γTb(III) was also determined from the difference of apparent and standard Gibbs free energies of formation, ΔGf*0(TbCl3)−ΔGf0(TbCl3,SC). On an Al electrode, the reduction potential of Tb(III)/Tb was observed at more positive potential values than that on Mo electrode, due to the formation of Al-Tb intermetallic compound when Tb(III) ions react with the Al substrate. The TbAl2 intermetallic compound characterized by XRD (X-ray diffraction) and SEM-EDS (scanning electron microscopy and energy dispersive spectrometer), was obtained in the LiCl-KCl melts containing Tb(III) by potentiostatic electrolysis at −1.8 V and −1.9 V (vs Ag/Ag+), respectively. The activity of Tb, in the Al phase, as well as the standard Gibbs free energy, enthalpy and entropy of formation for TbAl2 were estimated from the open circuit chronopotentiometric measurements.

The work concerned the electrochemical behaviors of Y(III) on W and Ni electrodes in molten LiCl-KCl salts by a series of electrochemical techniques. The electrochemical reaction of Y(III) to Y(0) proceeded in a one-step reduction process with the exchange of three electrons, Y(III)+3e−→Y(0). Compared with the cyclic voltammogram and square wave voltammogram obtained on W electrode, the reduction potential of Y(III) on Ni electrode was observed at less negative potential than the one of Y(III) to give pure Y metal on W electrode, which revealed the occurrence of underpotential deposition of Y(III) on Ni electrode. Electromotive force (emf) measurements were performed to calculate the relative partial molar Gibbs energies and activities of Y in Y-Ni alloys. The standard Gibbs energies of formation for different Y-Ni intermetallic compounds were also estimated. The different Y-Ni alloys were formed by potentiostatic electrolysis at different potentials and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). It was found that four intermetallic compounds, YNi5, Y2Ni7, YNi3 and YNi2, were selectively produced by controlling applied potential.