Electrochemical behavior of zirconium ions regulated by fluoride ions revisited

This work investigates the influence of fluoride ions on the electrochemical behavior and coordination properties of zirconium ions under different molar ratios of fluoride ions to zirconium ions, utilizing a combination of electrochemical and spectroscopic methods. The electrochemical properties of zirconium ions were examined at different fluoride ion contents within NaCl-KCl-ZrCl 4 and NaCl-KCl-K 2 ZrF 6 molten salt systems using cyclic voltammetry (CV), square wave voltammetry (SWV), and the chronopotentiometry (CP). Additionally, the samples underwent analysis through raman spectroscopy. The results demonstrate that zirconium ions reduction behavior is highly sensitive to fluoride ion content, which directly affects their reduction path, while the overall reduction trend remains consistent. Meanwhile, the coordination structure of zirconium ions with anions in molten salts has been modified. As fluoride ions are introduced, the Cl − ions present in the original ZrCl 6 2− complex are progressively replaced, giving rise to new coordination ions (ZrCl x F y n − ). When fluoride ions accumulate to a specific concentration, the formed coordination ions (ZrF x 2− ) have stronger stability to support them avoiding the formation of intermediate valence zirconium ions and be reduced to metallic zirconium via one step. Ultimately, electrodeposition experiments were conducted using fluoride ion and zirconium ion electrolytes at various molar ratios. The findings indicated that the current efficiency enhanced as the concentration of fluoride ions increased, and the volume of cathode deposits also rose with the addition of fluoride ions.