Coordination structure of vanadium ion and its kinetic parameters in electrodeposition in molten salt

Abstract

The effect of fluoride ions on the coordination properties and kinetic parameters of vanadium ions in molten salts was investigated. The competitive coordination process of V(III) with Cl⁻ and F⁻ and its mechanism were investigated by combining electrochemical and spectroscopic techniques and ab initio molecular dynamics (AIMD) simulations. The electrochemical behavior of V(III) in melt LiCl-KCl-KF with various F/V molar ratios was studied by cyclic voltammetry, square wave voltammetry and open circuit potentiometry at 823 K. The morphology of V(III) in the molten salt was observed by Raman spectroscopy. Combining mathematical calculations and AIMD simulations, it is concluded that VCl₄F₂³⁻ is the most stable complex in the melt at 823 K. In addition, the diffusion coefficients of V(III) were calculated to be between 6.79×10⁻⁵ cm/s and 2.68×10⁻⁴ cm/s under various contents of KF. The kinetic mechanism of V(III) was studied by electrochemical impedance spectroscopy and the exchange current density i₀=1.27–2.89 A/cm², and the reaction rate constant k₀=1.69×10⁻⁶–3.84×10⁻⁶ cm/s. This work aims to provide a theoretical basis for the mechanistic study and process optimization of vanadium electrolysis from molten salts.

Keywords

molten salt / vanadium ion / coordination properties / kinetic parameters / electrodeposition

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