1,000-hour life testing of 10-cell planar solid oxide electrolysis cell stacks at 650 °C: Effects of bipolar plate coatings on degradation suppression

Corrosion of ferritic stainless steel bipolar plates in solid oxide electrolysis cells (SOECs) causes Cr volatilization and interfacial degradation, compromising long-term durability. In this study, Co-rich electroplated coatings were applied to both the air- and fuel-electrode sides of the bipolar plates, and their corrosion-mitigation performance was evaluated using a 10-cell SOEC stack. The final coating was Co-rich with minimal Ni content (∼3 wt%). After 1000 h at 650 °C, coated regions formed maintained structural integrity: compact Co₃O₄ spinel on the air side and metallic Co on the fuel side. These layers effectively suppressed Cr poisoning and preserved interfacial integrity under both atmospheres. Uncoated plates developed porous, unstable Cr–Mn protective layer, resulting in SrCrO₄ formation on the air electrode and steam-induced corrosion on the fuel side, accelerating cell degradation. Cells near coated plates showed minimal voltage degradation (−10 mV/kh) versus rapid degradation (390 mV/kh) near uncoated plates. While intermediate-temperature operation can suppress electrode chemical degradation, it cannot prevent fuel-side metal corrosion under humid conditions. These findings highlight the critical importance of Cr-blocking coatings, particularly on the fuel side, for mitigating corrosion-induced degradation and enhancing SOEC stack longevity.