Electrochemical Behaviour of LaCl₃ in LiCl-KCl Eutectic Melt

The electrochemical behaviour of lanthanum ion in LiCl-KCl-LaCl3 molten electrolyte was studied at an inert tungsten electrode in the temperature range of 698-798 K employing various electrochemical techniques such as cyclic voltammetry, chronopotentiometry, square wave voltammetry, etc. Reduction of LaCl3 to La was found to be a three electron transfer, single-step quasireversible process. Important kinetic and thermodynamic properties like charge transfer coefficient, diffusion coefficient, and apparent electrode potential of La3+|La redox couple were determined. The kinetics of the reduction process was investigated by Nicholson method and Matsuda-Ayabe criteria. The exchange current density of the reduction process was calculated at various temperatures and concentrations of LaCl3, and the electrode kinetics was further investigated. The heterogeneous rate constant of La3+|La redox couple was estimated to be 3.34 x 10-4 cm s-1 at 773 K. The discrepancy in the values of the exchange current density and heterogeneous rate constant has been addressed.