In Situ Electrochemical Study of the Coexistence of Eu³⁺ and Eu²⁺ in Molten LiCl-KCl by Rotating Disc Electrode

Abstract

In this study, a graphite rotating disc electrode was successfully designed and applied to conduct electrochemical measurements under flow conditions in molten LiCl-KCl at 773 K. The concentration and diffusion coefficients of Eu3+ and Eu2+ in molten salt were quantitatively measured with this electrode by applying in situ cyclic voltammetry and chronoamperometry techniques. The initial concentration ratio of Eu3+/Eu2+ in LiCl-KCl-0.5 wt% EuCl3 was calculated to be 2.37. The calculated diffusion coefficients of Eu3+ and Eu2+ in the salt were 9.31 ± 0.06 × 10−5 cm2 s−1 and 9.65 ± 0.6 × 10−5 cm2 s−1, respectively. A decrease of the diffusion coefficient of Eu3+ and Eu2+ was observed at a higher concentration of EuCl3, which implies the enhanced Eu-Eu ion interaction. This electrode design is expected to be utilized for the concentration measurement of multivalent ions in a flowing molten salt.