Chronoamperometric determination of the diffusion coefficient in molten chlorides

Abstract

In this study, a method based on chronoamperometry (CA) with a simple unshielded microwire electrode and macroelectrode was used to estimate the diffusion coefficient (D) of the electroactive species in molten chlorides without any knowledge of its concentration. Theoretically evaluated CA response ratios of the two electrodes were fitted to the values obtained from digital simulations and experiments within a measurement time of 1 s, and the D value was determined as a fitting parameter. Theoretical and experimental analyses of the CA response under pure diffusion-controlled conditions confirmed the applicability of the proposed method for the determination of D for any electroactive species, regardless of its reaction kinetics characteristics. The D values of Eu3+ and Cr2+ in molten LiCl-KCl at 450 degree celsius, which were determined from the CA of their reduction reactions and validated by simulations of the microwire electrode CA response, were consistent with previously reported values. However, the D of Cr2+ could not be accurately determined from the CA of its oxidation, possibly owing to the additional chronoamperometric current generated by the dissolution of the Au electrode. Therefore, the prevention of side reactions is vital for the accurate estimation of D. The proposed method could facilitate future research on molten salts and their properties.