CuFe2O4/CuO bilayer protective coating deposited onto SUS430 interconnects by ultrasonic sprayed for solid oxide fuel cells

The standard solid oxide fuel cells (SOFCs) interconnects are ferritic stainless steels such as SUS430. However, these steels present serious issues such as chromium poisoning and oxidation of ferritic stainless steel interconnects. Here, we report a CuFe 2 O 4 /CuO bilayer protective coating deposited on SUS430 interconnects via ultrasonic spray deposition, a scalable and conformal surface engineering technique. The bilayer architecture combines a conductive CuFe 2 O 4 spinel inner layer and a CuO outer diffusion barrier to synergistically suppress chromium migration and oxidation reaction while maintaining low electrical resistance. The coating exhibits uniform coverage, strong adhesion, and excellent structural stability after extended exposure at 800 °C. Compared to bare and single-layer CuFe 2 O 4 -coated steels, the bilayer coating significantly inhibits Cr 2 O 3 scale formation, limiting its thickness to ∼3 μm after 1000 h. Long-term oxidation tests over 1000 h show a marked reduction in the parabolic oxidation rate constant, corresponding to a protection factor of 86.6%. Notably, the bilayer coating achieves low area-specific resistance, with values of 2.4 mΩ cm 2 after 100 h and below 7.6 mΩ cm 2 after 1000 h at 800 °C. Electrochemical impedance spectroscopy on symmetrical cells confirms that the bilayer coated interconnect effectively mitigates chromium-induced degradation of the oxygen reduction reaction, preserving cathode activity and interfacial stability. This work establishes the CuFe 2 O 4 /CuO bilayer, as a robust and scalable engineered solution for durable, high-performance SOFC interconnects.