2015-Sustainable Industrial Processing Summit
SIPS 2015 Volume 7: Ionic Liquids & Energy Production
| Editors: | Kongoli F, Gaune-Escard M, Mauntz M, Rubinstein J, Dodds H.L. |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2015 |
| Pages: | 310 pages |
| ISBN: | 978-1-987820-30-0 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Influence of the Second Coordination Sphere on the Standard Rate Constants of Charge Transfer for Nb(V)/Nb(IV) Chloride Complexes
Sergey Kuznetsov1; Anna Popova2;1INSTITUTE OF CHEMISTRY, KOLA SCIENCE CENTRE RAS, Apatity, Russian Federation; 2INSTITUTE OF CHEMISTRY, KOLA SCIENCE CENTRE OF RUSSIAN ACADEMY OF SCIENCES, Apatity, Russian Federation;
Type of Paper: Regular
Id Paper: 46
Topic: 13
Abstract:
The aim of the present work is the study of the second coordination sphere influence on the standard rate constants of charge transfer (ks) for the Nb(V)/Nb(IV) redox couple in chloride melts and the investigation of the working electrode nature on kinetics of the redox reaction.
Cyclic voltammetry was employed, using a VoltaLab-40 potentiostat with complementarily packaged software VoltaMaster 4, version 6. The potential scan rate varied between 5x10-2 and 2.0 V s-1.
The electrochemical redox process:
Nb(V) + e- = Nb(IV) (1)
in KCl-NbCl5 and CsCl-NbCl5 melts at 0.75 V s-1 up to 2.0 V s-1 was determined as quasi-reversible. For the NaCl-KCl (equimolar mixture)-NbCl5 melt even at a sweep rate 2.0 V s-1, the process (1) was reversible and the determination of ks could not be done.
The theory of determining the standard rate constants of charge transfer for the quasi-reversible redox processes, which are not complicated by the formation of insoluble product, was developed by Nicholson. The standard rate constants for the Nb(V)/Nb(IV) redox couple were calculated on the basis of cyclic voltammetry data.
The ks obtained in KCl-NbCl5 melt were higher than ks determined in CsCl-NbCl5 molten system. So, in alkali chloride melts, it was defined that ks (CsCl) < ks (KCl) < ks (NaCl-KCl. It was found that ks increased with increasing temperature and values of ks obtained at platinum electrode were higher than those at a glassy carbon electrode. The values of the standard rate constants testify that the redox process (1) proceeds quasi-reversibly.
Keywords:
chloride melts, niobium complexes, cyclic voltammetry, second coordination sphere, standard rate constantsReferences:
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