Spectroelectrochemistry and Electrochemistry of Europium Ions in Alkali Chloride Melts

In order to investigate the redox equilibrium of europium ions in molten NaCl-2CsCl, UV-Vis absorption spectrophotometry measurements were performed for Eu2+ and Eu3+ in molten NaCl- 2CsCl at 923 K under simultaneous electrolytic control of their ratio. Molar absorptivities of EuCl3 and EuCl2 in NaCl-2CsCl at 923 K were determined to be (420±21) M −1cm−1 at 31200 cm−1 and (1130±56) M−1cm−1 at 30300 cm−1, respectively. The formal redox potential of the Eu2+/Eu3+ couple in NaCl-2CsCl melt at 923 K was determined to be (−0.941 ±0.004) V vs. Cl2/Cl− by electromotive force measurements on varying concentration ratios of Eu2+ and Eu3+, which were performed using a technique based on the combination of electrolysis and spectrophotometry. Cyclic voltammetry was also carried out in order to examine the characteristics of the voltammograms for the Eu2+/Eu3+ couple in NaCl-2CsCl melt. The formal redox potential of the Eu2+/Eu3+ couple determined by a spectroelectrochemical method agreed with that determined by cyclic voltammetry [(−0.946±0.008) V vs. Cl2/Cl−]. The effects of temperature on the redox potential of the Eu2+/Eu3+ couple in NaCl-2CsCl, NaCl-KCl, LiCl-KCl, and CsCl melts were studied by cyclic voltammetry in the range from 923 to 1123 K.