Electroreduction Mechanism of Lanthanum Ions at a Nickel Electrode in a Chloride Melt

Abstract—Various electrochemical methods, such as cyclic voltammetry, chronopotentiometry, open-circuit chronopotentiometry (on/off curves), and square wave voltammetry are used to study the electrochemical behavior of lanthanum ions at a nickel electrode in the equimolar potassium and sodium chloride melt at 973 K. The cyclic voltammetry curve demonstrates several reduction waves in the cathode branch and their corresponding oxidation waves in the anode branch. The first wave A corresponds to potentials of –(0.0–0.1) V related to the reduction of Ni²⁺ ions. The second wave B is observed at potentials of –1.72 to –1.77 V and related to the electroreduction of \({\text{LaCl}}_{6}^{{3 - }}\) ions at the nickel electrode with a certain depolarization with the formation of lanthanum and nickel La_xNi_y intermetallics. The appearance of the third wave C at potentials of –2.9 to –2.13 V is related to the electrodeposition of \({\text{LaCl}}_{6}^{{3 - }}\) chloride complexes at the La_xNi_y intermetallics with the formation of metallic lanthanum. Based on the data obtained, we show that, the nickel electrode reacts with deposited lanthanum and causes a substantial depolarization of the electroreduction of chloride complex during the electroreduction of lanthanum chloride complex in the KCl–NaCl melt at 973 K; the formation of intermetallics with the Ni electrode also takes place.