Solid oxide membrane-assisted electrolytic reduction of Cr₂O₃ in molten CaCl₂

Solid oxide membrane-assisted electrolytic reduction of solid Cr₂O₃ to Cr in molten CaCl₂ was performed using a sintered porous Cr₂O₃ cathode paired with an yttria-stabilized zirconia (YSZ) tube anode containing carbon-saturated liquid copper alloy. Analyses of the reduction mechanism, ion migration behavior, and effects of cathode pellet porosity and particle size on the electrolysis products and reduction rate revealed that the cathode microstructure and electrolytic conditions were key factors influencing the electrolysis process. Optimal results were obtained when the cathode was characterized by high porosity and a small particle size because this combination of features contributed to ion migration. Good electrochemical activation was observed when cathode pellets prepared by 4 MPa molding followed by 2 h of sintering at 1150°C were applied. The electrode reduction process (Cr³⁺ → Cr²⁺ → Cr) was promoted by high electrode voltages, and Cr metal was efficiently formed. The proposed method appears to be well suited for electrolytic Cr production because it does not require expensive pre-electrolysis techniques or generate harmful by-products.