Proving the Availability of Ni–Fe Anode for Electro-Reduction of Solid V 2 O 3 in Molten Fluoride Salts

The availability of casting Ni–Fe alloy as inert anode for direct electro-reduction of V 2 O 3 in molten Na 3 AlF 6 -K 3 AlF 6 -AlF 3 was investigated. The electrochemical oxidation behavior of anode as well as microstructural evolutions of formed oxide scale were systematically studied. The electrochemical characterization and reaction mechanism of the cathode oxide were also investigated to evaluate the influence of alloy anode on cathodic reduction process. The in situ formed three-layered oxide scale is compact and coherent, which is composed of an outermost Fe 2 O 3 + FeAl 2 O 4 skin layer, a Fe 2 O 3 middle layer and a FeAl 2 O 4 inner layer. The skin layer has a continuous, smooth structure and shows electrochemical activity. The Fe 2 O 3 layer with a compact structure prevents inward diffusion of electrolyte and outward migration of metal cations. The innermost FeAl 2 O 4 layer shows a loose structure and functions as a buffer layer to improve the peeling resistance of oxide scale. With the continuous extension of polarization time, the inner FeAl 2 O 4 layer is slowly oxidized and becomes thinner, simultaneously, the dense Fe 2 O 3 layer becomes thicker. Ultimately, metal vanadium product with fine rod-like particles can be obtained and the oxygen content in the metal vanadium is below 0.3 mass% within electrolyzing time of 2 h. The corresponding current efficiency is around 63%.