Effect of plasma-sprayed NiFe₂O₄ coatings on the corrosion behavior of Ni-Fe-Co-Cu alloy anode in KF-NaF-AlF₃ electrolyte for aluminum electrolysis

A nickel ferrite (NiFe₂O₄) coating was deposited onto a Ni-Fe-Co-Cu (NFCC) alloy anode via plasma spraying, followed by a high-temperature pre-oxidation treatment to densify the coating and seal surface porosity. Electrolysis experiments were conducted at 850 °C in a NaF-KF-AlF₃ molten salt electrolyte (CR=1.40) with a current density of 0.75 A/cm² using both uncoated (NFCC) and a coated version alloy anode referred to as NFCC-SL (sprayed and oxidized NiFe₂O₄ layer). The pre-formed NiFe₂O₄ layer effectively prevented the direct diffusion of the alloy substrate, suppressing dissolution and enhancing corrosion resistance. Additionally, the coating enabled horizontal diffusion of Ni and Fe during electrolysis, promoting the formation of a secondary NiFe₂O₄ layer. As a result, the impurity content in the produced aluminum was significantly reduced. The combined barrier effect of the sprayed and regenerated oxide layers demonstrates this coating's potential for improving non-carbon anode performance in aluminum electrolysis.