Durability of Cu/CeO₂ films under SOFC anode conditions: from elemental valence state to electrochemical performance

Solid oxide fuel cells (SOFCs) face significant oxidation and interdiffusion challenges under anode operating conditions. The development of thin protective coatings with uniform density, appropriate conductivity, and excellent chemical/mechanical compatibility is crucial for metallic interconnectors (MICs). However, research addressing service stability issues under the anode environments still remains limited. This work systematically investigates the long-term stability of two nano-scale coatings (CeO₂/AISI 441 and CeO₂/Cu/AISI 441) and an anode-coated Ni-GDC/CeO₂/Cu/AISI 441 system under an SOFC anode atmosphere (800 °C, 90% H₂/10% H₂O). The results demonstrate that increasing sputtering power, pressure, and deposition time significantly enhances both the grain size and crystallinity of CeO₂/Cu composite coatings. After 1000 h exposure at 800 °C to 90% H₂/10% H₂O, both CeO₂/AISI 441 and CeO₂/Cu/AISI 441 maintained excellent adhesion to the substrate, with interfacial oxide layers below 500 nm, indicating sufficient structural stability and long-term oxidation resistance under the anode serving conditions. The electrical conductivities of CeO₂/AISI 441 and CeO₂/Cu/AISI 441 systems reached approximately 8.07 S cm⁻¹ and 10.46 S cm⁻¹, respectively, both satisfying the conductivity requirements for SOFC stack operation, confirming that introducing a Cu interlayer between the ferritic stainless steel (FSS) substrate and CeO₂ film effectively enhances system conductivity. Furthermore, the Ni-GDC/CeO₂/Cu/AISI 441 system with an anode coating exhibited even lower resistivity, demonstrating that the CeO₂ coating not only shows excellent compatibility and interfacial stability with Ni-based anodes, but also maintains stable conductivity and effective protection under MIC/anode operating conditions.