Feasibility of magnetron sputtered nano-cerium oxide thin films for solid oxide fuel cells interconnector: Microstructure evolution under the anode side

Abstract

Given the significant oxidation challenges and reciprocal diffusion reactions that occur under the operating conditions of solid oxide fuel cells (SOFC) anodes, it is crucial to develop thin protective coatings that possess a dense structure, appropriate conductivity, good chemical and mechanical compatibility for metallic interconnectors (MIC). Except for the mainly studied cathode environments, the fuel streams during the real stack operation will also inevitably confront the MIC with oxidation and interfacial reaction issues, giving a potential contribution to the overall stack degradation. However, there is relatively little research on these service stability issues induced by the anode operating atmospheres. This research emphasizes the continuity of sputtered CeO_x coatings of different thicknesses during the initial oxidation phase and seeks to optimize the coating thickness. By varying the sputtering powers, CeO_x coatings with thicknesses of 110, 380, and 600 nm are deposited on laboratory-made ferritic stainless steel (AMIC 21). The chemical states of the sputtered Ce ions, the microstructure evolution, and the interfacial reaction mechanism for the CeO_x-coated MIC are successively explored under a simulated anode environment. After isothermal exposure to SOFC anode-reducing atmosphere (90%H₂/10%H₂O) at 800°C for 50–300 h, the CeO_x coatings exhibit good structural stability with uniform grains tightly arranged on the surface. The interfacial reaction layers detected for the CeO_x-coated AMIC 21 samples are less than 1.6 µm after exposure for 300 h, indicating the effectiveness of CeO_x coatings for SOFC interconnector application.