Electrochemical evaluation of reference electrode for LiF-CaF2-LaF3 melt and electrochemical studies on Ni electrode

Abstract

Reference electrode is considered to be very important in studies of the recovery of lanthanum (La) from fluorinated molten salt electrolysis. Undoubtedly, the search for economically stable reference electrodes is crucial. Herein, a Ni/NiF₂ reference electrode encapsulated in corundum material that can be used for electrochemical studies in LiF-CaF₂ melt is proposed. The performance of Ni/NiF₂ reference electrode in LiF-CaF₂ melt at 1113 K, such as stability and repeatability, is verified by the cyclic voltammetry (CV) method. Moreover, the electrochemical test results obtained with Ni/NiF₂ reference electrode and Pt quasi-reference electrode (QRE) were compared and analyzed. The diffusion coefficient of La(III) ions on the W electrode was calculated to be 7.72 × 10⁻⁵ cm² s⁻¹ using the Ni/NiF₂ reference electrode. Furthermore, the electrochemical behavior of La(III) on active Ni electrode was further investigated using a Ni/NiF₂ reference electrode, and La was successfully extracted on the Ni electrode. The results indicate that the Ni/NiF₂ reference electrode is extremely stable in LiF-CaF₂ melt, which opens a new possibility for reference electrode in fluoride salts.