Electrochemical Impedance Spectroscopy and Cyclic Voltammetry Methods for Monitoring SmCl3 Concentration in Molten Eutectic LiCl-KCl

Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm3+ over the concentration range. Equipped with Sm3+ diffusion coefficient, the Randles-Sevcik equation predicted Sm3+ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm3+ and Sm2+. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.