Zirconium has a large number of properties that make it very attractive for different applications in several activity fields (nuclear, pyrotechnics, armament …). This article is devoted to the study of zir conium electrochemical behavior and crystallization phenomena on silver electrode in the LiF NaF eutectic mixture in the 690 900 C temperature range, using cyclic voltammetry, square wave vol tammetry and chronoamperometry. The result showed that Zr(IV) is reduced into Zr in a simple step exchanging four electrons and that zirconium nucleation is progressive whatever the temperature and the overvoltage. Nuclei growth takes place in all three dimensions and is limited by diffusion of Zr(IV) ions. The influence of overvoltage on the zirconium nucleation rate was also studied.
In this work, a detailed electrochemical study of the molten LiF-NaF-CrF2 system is provided on Ag electrode in the 750 °C–900 °C temperature range. The first part was dedicated to the electrochemical study, by cyclic and square wave voltammetries, allowing the determination of thermodynamic and physico-chemical data such as CrF2/Cr standard potential, diffusion coefficient, activity coefficient, transfer energy and nucleation overvoltage. The influence of Li2O addition on the electrochemical reduction pathway of dissolved CrF2 on a silver electrode was investigated. The results showed that an increase of Li2O activity in the solution causes CrF2 disproportionation into solid chromium oxide and metallic Cr.
The vanadium redox flow battery (VRFB) has been receiving great attention in recent years as one of the most viable energy storage technologies for large-scale applications. However, higher concentrations of vanadium species are required in the H 2 O-H 2 SO 4 electrolyte in order to improve the VRFB energy density. This might lead to unwanted precipitation of vanadium compounds, whose nature has not been accurately characterized yet. For this purpose, this study reports the preparation of V (II) ,V (III) ,V (IV) and V (V) supersaturated solutions in a 5 M H 2 SO 4 -H 2 O electrolyte by an electrolytic method, from the only vanadium sulfate compound commercially available (VOSO 4 ). The precipitates obtained by ageing of the stirred solutions are representative of the solids that may form in a VRFB operated with such supersaturated solutions. The solid phases are identified using thermogravimetric analysis, X-ray diffraction and SEM. We report that dissolved V (II) ,V (III) and V (IV) species precipitate as crystals of VSO 4 ,V 2 (SO 4 ) 3 and VOSO 4 hydrates and not in their anhydrous form; conversely V (V) precipitates as an amorphous V 2 O 5 oxide partially hydrated. The measured hydration degrees (respectively 1.5, 9, 3 and 0.26 mol of H 2 O per mol of compound) might significantly affect the overall engineering of VRFB operating with high vanadium concentrations.
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