Protective Co–Mn Spinel Coatings Prepared by Composite Electrodeposition for High-Temperature Service of Ferritic Stainless Steel

Chromium volatilization and interfacial oxidation are critical challenges limiting the long-term high-temperature service of ferritic stainless steel (FSS) interconnects in solid oxide fuel cells (SOFCs). In this study, a dense (Co,Mn) 3 O 4 spinel coating was fabricated on E-brite FSS substrates via a composite electrodeposition–thermal conversion approach conducted at 800 °C. A homogeneous single-phase spinel was formed with a stable Cr 2 O 3 interlayer that suppressed chromium volatilization and surface degradation. Microstructural and elemental analyses confirmed the structural integrity. After 500 h of oxidation at 800 °C, the coating remained stable without cracking or spallation. The area-specific resistance (ASR) decreased to 7.9 mΩ·cm 2 , an 80.7% reduction compared with the uncoated alloy (41.0 mΩ·cm 2 ), demonstrating improved electrical conductivity under prolonged exposure. This study provides a practical strategy that uses composite electrodeposition and thermal conversion to enhance both oxidation resistance and electrical performance of ferritic interconnects for intermediate-temperature SOFC applications.