Rhenium Electrodeposition and Its Electrochemical Behavior in Molten KF-KBF₄-B₂O₃-KReO₄

The electrochemical behavior of rhenium ions in the molten KF-KBF₄-B₂O₃ salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF₄-B₂O₃ were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10^-5 cm²/s and 4.61 × 10^-5 cm²/s for R₁ and R_2, respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF₄-B₂O₃ at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO₄ and K₃ReO₅). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component.