Intervalence Charge Transfer of the Nb(V)/Nb(IV) Redox Couple in Alkali Chloride Melts: Experiment and Quantum-Chemical Calculations

Self Cite

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).

Section: Resultsmentioning

confidence: 99%

Electrochemical Behavior of SmF₃ in Alkali Chloride Melts

Stulov

Kuznetsov

2021

Self Cite

“…The electrochemical behavior of niobium was investigated in melts of different composition and with utilization of different working electrode. [36][37][38][39][40][41][42][43] To the best of our knowledge, the usage of working electrode made from carbopyroceram has not been previously reported. In the present study, the electrochemical behavior of niobium in chloride-fluoride melt with utilization of working electrode from carbopyroceram was investigated.…”

mentioning

confidence: 99%

Electrodeposition of Niobium Coatings on the Cryogyroscope Rotor

Okunev¹,

Dubrovskii²,

Kuznetsov³

2023

The discharge process of Nb(IV) complexes to Nb was studied by cyclic voltammetry. A galvanostatic electrolysis with the cathodic current density of 1.5•10-2 A cm-2 in the NaCl–KCl–NaF–K2NbF7 melt in contact with Nb anode was used for deposition of niobium coatings on the cryogyroscope rotor at a temperature 1023 K and a process time of 8 to 12 hours. The coatings were continuous and smooth due to the special design of the cathode. The rotation speed of the stirrer was set to 35 rpm and did not change in all experiments. Such conditions made it possible to obtain coatings with the thickness up to 150 μm. The main characteristics of the niobium coatings such as purity, roughness, nonsphericity, and superconductivity were investigated.

“…[6][7][8] The electrochemical behavior of niobium in chloride-fluoride and fluoride melts has been the subject of numerous works. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Electrochemical studies showed that in these melts the electroreduction of Nb(V) complexes to the metal consists of two stages:…”

mentioning

confidence: 99%

Anodic Processes during the Electrowinning of Niobium from Chloride-Fluoride Melts and the Influence of Oxide Ions on Them

Kuznetsov¹

2022

Self Cite

Anodic processes were studied in chloride-fluoride and fluoride melts by voltammetry and gas chromatography mass spectrometry method. It was found that the reason for the occurrence of the anodic effect during the electrolysis of the KCl-KF-K2NbF7 melt is the formation of the compound CxFy on the electrode surface, which has electrical insulating properties. Influence of oxide ions on the anodic processes in the KCl-KF-K2NbF7 melt was investigated. It was determined that oxide ions and oxofluoride complexes of niobium oxidize at a glassy carbon electrode at more negative potentials than fluoride ions. The anodic effect in the chloride-fluoride melt containing oxide ions and oxofluoride complexes of niobium can be reached if the anodic current density will be higher than the limiting current density of electrooxidation of oxide ions and niobium oxofluoride complexes.