Abstract
To prevent Cr poisoning of the cathode and to retain high conductivity during solid oxide fuel cell (SOFC) operation, Cu or La doped Co-Mn coatings on a metallic interconnect is deposited and followed by oxidation at 750 °C. Microstructure and composition of coatings after preparation and oxidation is analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). High energy micro arc alloying process, a low cost technique, is used to prepare Cu or La doped Co-Mn coatings with the metallurgical bond. When coatings oxidized at 750 °C in air for 20 h and 100 h, Co3O4 is the main oxide on the surface of Co-38Mn-2La and Co-40Mn coatings, and (Co,Mn)3O4 spinel continues to grow with extended oxidation time. The outmost scales of Co-33Mn-17Cu are mainly composed of cubic MnCo2O4 spinel with Mn2O3 after oxidation for 20 h and 100 h. The average thickness of oxide coatings is about 60–70 μm after oxidation for 100 h, except that Co-40Mn oxide coatings are a little thicker. Area-specific resistance of Cu/La doped Co-Mn coatings are lower than that of Co-40Mn coating. (Mn,Co)3O4/MnCo2O4 spinel layer is efficient at blocking the outward diffusion of chromium and iron.
Highlights
Co-Mn-based spinel coatings and conversion coatings are the potential candidates for metallic interconnect coating materials of solid oxide fuel cell (SOFC) [1,2,3,4,5]
The granular appearance is not found after Co-38Mn-2La coating oxidized for 100 h
Rapid cation diffusion can be caused in the mono-oxide such as CoO and MnO, but the continuous (Co,Mn)3 O4 spinel oxide layer causes a significant reduction in the oxide rate and cation diffusion
Summary
Co-Mn-based spinel coatings and conversion coatings are the potential candidates for metallic interconnect coating materials of solid oxide fuel cell (SOFC) [1,2,3,4,5]. The high energy micro arc alloying process (HEMAA) [6,7,8] is a low cost technique to produce metallurgically bonded coatings. It is economically attractive for coating preparation to significantly reduce the cost of SOFC. In previous study [9], the Cr/La alloying layer is successively obtained on 430 stainless steel (SS) surface by HEMAA using metallic Cr electrode and metallic La electrode, respectively. The result shows that a good protective perovskite coating with an acceptable electrical contact resistance forms on the substrate steel after coating is thermally grown
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