Entropy-engineered spinel oxide coatings to enhance oxidation resistance and electrical performance of solid oxide fuel cell interconnectors

• Entropy stabilized coating for SOFC application has been demonstrated. • The High-Entropy system can promote formation of single-phase spinel oxide. • The complex spinel coating can provide effective oxidation protection. • The complex spinel coating can exhibit low ASR value. • The complex spinel coating can prevent Cr evaporation effectively. This study investigates spinel oxide coatings derived from medium- to high-entropy alloy systems for solid oxide fuel cell interconnect applications. Alloy coatings of Fe-Mn-Co, Fe-Mn-Co-Cu, and Fe-Mn-Co-Cu-Ni are deposited on SUS430 stainless steel substrates utilizing a magnetron sputtering system and subjected to isothermal oxidation at 650 °C. Microstructural and phase analyses reveal the anomalous formation of hematite layers and Cr-Fe mixed oxide structures in Fe-Mn-Co and Fe-Mn-Co-Cu coatings, which indicates greater Fe diffusion at the substrate/coating interface during the early stage of oxidation comparing to that of Fe-Mn-Co-Cu-Ni coating. Theoretical calculations confirm that the hematite and Cr-Fe oxides significantly increase the area specific resistance of Fe-Mn-Co and Fe-Mn-Co-Cu coated steels at 650 °C. Notably, the Fe-Mn-Co-Cu-Ni coating can exhibit superior electrical conductivity, and resistances to oxidation and Cr-evaporation. This study demonstrates that entropy-engineered composition can promote the formation of single phase spinel, enhance phase stability, and can potentially be beneficial for long-term performance of solid oxide fuel cell as coating material for interconnects.