Electrochemistry and Electrocrystallization of Gadolinium on Mo Substrate in LiCl–KCl Eutectic Salts

Abstract

The electrochemistry of GdCl3 in LiCl-KCl eutectic salt was studied in the temperature range 683-813 K by using Mo working electrode. The Gd(III)/Gd(0) redox reaction was evaluated with respect to its major thermodynamic, kinetic and initial electrocrystallization properties. According to cyclic voltammetry and square wave voltammetry, the reduction of Gd(III) ions to Gd(0) metal is a one-step three-electron reaction. The equilibrium potentials of Gd(III)/Gd(0), determined by open-circuit chronopotentiometry, were also used to estimate the activity coefficients of GdCl3, γ. Sand's equation was used to determine the diffusion coefficients of Gd(III) ions. The exchange current density was determined by linear polarization of Mo electrode coated with gadoliniummetal. The reaction rate constant determined by convolutive voltammetry shows that Gd(III)/Gd(0) redox system is quasi-reversible per Matsuda-Ayabe criteria. The nucleation mechanisms of gadolinium metal deposited on a Mo substrate were predicted by using Scharifker-Hill model, and tested for the first time by scanning electron microscopy (SEM) studies of the electrode surface. The SEM studies confirmed that for the low initial concentration of GdCl3 gadolinium nucleates and grows progressively, while for higher GdCl3 concentrations the related mechanism is instantaneous. © 2014 The Electrochemical Society. All rights reserved.