Electrochemical behaviors of Ce-metal (Bi, Sn, Zn) binary system on a solid electrode and liquid metal electrodes in molten LiCl-KCl salt

Abstract

One of the electrochemical properties of a liquid metal electrode is lowering the reduction potential of elements by forming the intermetallic compounds. Therefore, the liquid metal electrode is utilized in the electrowinning process of pyroprocessing, which is one of the reprocessing options with strength in light of nuclear non-proliferation. Cadmium metal has been considered as the candidate of liquid metal electrodes, but attempts to find other surrogate metals have been conducted because of its harmfulness and low vapor pressure. Hence, bismuth, tin, and zinc are selected as the surrogate liquid metal electrode to investigate the electrochemical properties of cerium on liquid metal electrodes in this study. First, the cerium-metal binary system on the solid tungsten electrode was utilized to investigate the cerium-metal intermetallic compounds, which are formed during the electrowinning process. The number of intermetallic compounds was confirmed from the oxidation peaks of cyclic voltammetry and the plateaus of open-circuit chronopotentiometry. The Gibbs free energy of formation of each intermetallic compound was used to determine the composition of each intermetallic compound. Subsequently, the electrochemical behaviors of cerium were investigated on the liquid metal electrodes. The high blank current was observed on the liquid bismuth electrode and the liquid tin electrode compared to the liquid zinc electrode from cyclic voltammetry results. The activity coefficient of cerium on the liquid bismuth, tin, and zinc electrodes was revealed to be lower than one on the liquid cadmium electrode. It was also found that the calculation of the exchange current density on the liquid metal electrode is feasible in the system with a low blank current, such as cerium on the liquid zinc electrode. This study provides a basic understanding of the liquid metal electrode system for the efficient electrowinning process.