Effect of vanadium ion valence state on the deposition behaviour in molten salt electrolysis

The electrodeposition process of vanadium from LiCl–KCl base electrolytes was investigated by means of cyclic voltammetry, galvanostatic electrolyses and micro analytical analysis of the deposits. It is demonstrated that the valence state of the vanadium ions has a critical influence on the feasibility of performing a reproducible and stable coating process aiming to obtain compact vanadium films. When the electrolyte contained predominantly trivalent vanadium ions, the process was unstable and the deposit consisted of dendrites. In contrast, making use of a comproportionation reaction of metallic vanadium and VCl3 to divalent vanadium ions led to a stable deposition behaviour and allowed to obtain thick deposits with high current efficiencies. The disadvantageous behaviour of melts with mostly trivalent ions is explained by the fact that deposition is interfered by the reduction of trivalent to divalent ions under limiting current conditions. © 2018, Springer Science+Business Media B.V., part of Springer Nature.