Electrochemical Behavior of the SmF₃ in Alkali Chloride Melts

Abstract

Electrochemical studies of the redox couple Sm(III)/Sm(II) were carried out in NaCl-KCl, KCl, and CsCl melts in a temperature range of 973-1173 K by cyclic voltammetry. Diffusion coefficients (D) of Sm(III) in these melts were determined using Randels–Shevchik equation. The diffusion coefficients decrease with a change in the composition of the second coordination sphere from sodium to cesium. It is associated with a decrease in the counter-polarizing effect during the transition from Na to Cs, which in turn causes a decrease the metal–ligand bond length in the complexes. The standard rate constants of charge transfer (k s) of the redox couple Sm(III)/Sm(II) were determined by cyclic voltammetry in the all studied melts using the Nicholson’s equation, which is valid for quasi-reversible processes. The following series of the standard charge transfer constants was found k s(CsCl)<k s(KCl)<k s(NaCl–KCl).