Mo Deposition and Dissolution in DES with the Use of Fluoride Salts

Abstract

The dissolution and deposition behavior of molybdenum in a deep eutectic solvent was examined to assess the possibility of molybdenum electrorefining. When added to the ethaline, MoCl5 exhibited electrochemically irreversible behavior and appeared to be reduced via a two-electron reaction. However, Mo metal deposition was not observed, even after an extended period at high cathodic overpotentials. Deposition of molybdenum from ethaline at 80 °C was enabled by adding fluoride ions to the liquid to alter the speciation of the metal complex. Fluoride changed the electrochemical behavior of Mo in solution determined by cyclic voltammetry. Mo was successfully deposited from ethaline onto a nickel substrate at constant potential in the presence of fluoride ions, as confirmed analytically. The impact of fluoride ions on the anodic dissolution of molybdenum in ethaline was also found to not significantly hinder the dissolution process. Thus, both dissolution and deposition of molybdenum are possible in a DES, opening the way for possible development of a Mo electrorefining process.