Electrochemical Behavior of SmF₃ in Alkali Chloride Melts

Abstract

Electrochemical studies of the Sm(III)/Sm(II) redox couple 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 the Randles–Sevchik equation. 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 Sm(III)/Sm(II) redox couple were determined by cyclic voltammetry in all studied melts using the Nicholson’s equation, which is valid for quasi-reversible processes. The following series of the standard rate constants of charge transfer was found k s(CsCl) < k s(KCl) < k s(NaCl–KCl).

(Digital Presentation) Study of the Intervalence Charge Transfer in a 18NaCl+Na3SmF6 Model System By Quantum Chemical Methods

“…The following series of the standard rate constants of charge transfer rates (k s ) for the Sm(III)/Sm(II) redox couple in NaCl-KCl-SmF 3 , KCl-SmF 3 and CsCl-SmF 3 melts were obtained in our previous works (1,2). It was determined that k s (NaCl-KCl) > k s (KCl) > k s (CsCl) with corresponding values of charge transfer activation energies (Е а ) 128.3±9.0, 126.6±4.3, and 123.4±3.7 kJ/mol, respectively.…”

“…On the other hand, all the experimentally obtained values of Е а are very close to each other (the difference ~5%), in turn, this may indicate a small influence of OS cations on the electron transfer process. (1,2). In these works, was suggested an outer-sphere mechanism of electron transfer in samarium-containing melts.…”