Electrochemistry of terbium in the eutectic LiCl–KCl

The electrochemical behaviour of terbium at a tungsten electrode, in the eutectic LiCl–KCl molten was investigated in the temperature range 673–823 K, by means of cyclic voltammetry, chronopotentiometry and chronoamperometry. It was found that during cathodic polarization, deposition of metallic Tb from the chloride mixture onto the tungsten surface proceeds in a single step, and electrocrystallization plays an important role in the whole process. Experimental current–time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei whatever the applied overpotential. From chronopotentiometric measurements, the diffusion coefficient of the Tb(III) ions was determined by applying the Sand equation and modifying the immersion dept of the working electrode in stages. The validity of the Arrhenius law was also verified and the activation energy for diffusion was found to be 33.4 ± 1.5 kJ mol−1.The standard apparent potential value of the Tb(III)/Tb(0) system has been determined by potentiometry at several temperatures, and the activity coefficient of Tb(III) in the molten chloride media based on a pure supercool reference state has also been calculated.