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

Abstract

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 VCl 3 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.

Electrodeposition of titanium–vanadium alloys from chloride-based molten salts: influence of electrolyte chemistry and deposition potential on composition, morphology and microstructure

“…and dissolution (R3) of the insoluble product K 2 TiCl 6 [32], whereas V 2+ /V 3+ (O2/R2) and Ti 2+ /Ti 3+ (R1/O1) seem to be reversible reactions as was also observed in the singleelement systems [28,26].…”

“…As recently demonstrated, coherent high-quality vanadium coatings can be deposited from LiCl-KCl containing divalent vanadium ions [26]. The present study builds on the latter investigations and forms the next step towards the development of an electrodeposition process for Ti-Al-V alloys, in particular the most important and widely established titanium alloy Ti-6Al-4V [27].…”

“…-VCl 3 -V (ES 3). Based on this and according to our previous work [26], vanadium metal reacted by comproportionation with the trivalent vanadium ions (Eq. 1) showing that the potential E QRE is mainly determined by the electrode potential of the…”

“…The base electrolyte consisting of a eutectic mixture of LiCl (Alfa Aesar, ultra dry, 99.9%) and KCl (Alfa Aesar, ultra dry, 99.95%) was enriched with TiCl 2 (Sigma-Aldrich, 99.98% anhydrous) and VCl 3 (Alfa Aesar, 99.0%). Metallic titanium (Alfa Aesar, 99.8%) or vanadium (Alfa Aesar, 99.5%) was added to the LiCl-KCl-VCl 3 -TiCl 2 electrolyte in most experiments to generate and stabilize the divalent valence state of the vanadium ions by comproportionation [26]. An overview of the investigated systems is given in Table 1.…”

“…− 1180 mV vs. Cl 2 /Cl − , i.e., a bit more negative due to the presence of titanium ions than that of the (LiCl-KCl) (eut.) -VCl 3 (ES 1, investigated in a previous study [26]) which is ca. − 1000 mV vs. Cl 2 /Cl − .…”