Magnetron sputtered bilayer composite (Mn, Co)₃O₄ coating to improve oxidation resistance and suppress elements diffusion for interconnects of solid oxide fuel cell

A dense and continuous (Mn, Co)₃O₄ spinel coating on the interconnect is critical to achieve a long-term stability of solid oxide fuel cell (SOFC). In this paper, a bilayer composite (Mn, Co)₃O₄ spinel coating is prepared by magnetron sputtering to suppress elements diffusion during the fabrication process and the following operation conditions. A thin (Mn, Co)₃O₄ layer with a thickness of 0.8 μm is deposited via reactive magnetron sputtering prior to the coating of the main MnCo layer using metallic magnetron sputtering. The inward diffusion of O and the outward diffusion of Cr are weakened significantly compared with the conventional single-layer MnCo coating. After annealing at 800 °C for 2 h, the diffusion depth of Cr in the composite coating is reduced by 45 % compared with the conventional MnCo coating. After oxidation of 1000 h at 750 °C, a thinner layer of thermally grown oxides (TGOs) in 0.4 μm is formed, whose thickness is only half of the conventional MnCo coating and 25 % of the bare steel. Compared with the bare steel, the composite coating manifests a denser microstructure and the oxidation rate decreases by 3.6 times at 650 °C and 5.4 times at 750 °C, respectively. The area specific resistance (ASR) of the steel with the composite coating is 28.8 mΩ·cm² at 750 °C, which drops by 51 % compared with the bare steel. The composite coating exhibits better oxidation resistance and electrical conductivity which can improve the durability of SOFC stacks evidently.