Spinel Coatings for Solid Oxide Fuel Cell interconnects and Crystal Structure of Cu-Mn-O

Abstract

<p>Long-term stability and chromium (Cr) contamination are two major concerns for application of chromium-bearing metallic materials as interconnects of solid oxide fuel cells (SOFCs) at intermediate temperature (~800°C). Copper-manganese (Cu-Mn) and cobalt-manganese (Co-Mn) spinel can be promising coating materials for the metallic interconnects as they show high electrical conductivities. The first objective of this research is to develop an economical and convenient method through which the spinel coatings can be applied to the metallic substrates. The investigations on the crystal structure of CuᵪMn₃₋ᵪO₄ spinel, e.g., structure symmetry and cation distributions, have always been controversial, which hinders the total understanding of the detailed structure of the material. In order to resolve the inconsistency, in-situ neutron and X-ray diffraction were employed to determine the structure of the spinel.</p> <p>A novel method was developed to obtain high quality manganese coating without any additives (sulphur or selenium compounds). Cu-Mn and Co-Mn spinel coatings were applied to metallic coupons by electrodeposition and subsequent annealing. The method is convenient and easy to control. The performance testing showed that the area specific resistances (ASRs) of the coated samples (0.003 Ω•cm²) are much lower than that of the uncoated UNS 430 (0.189 Ω•cm²) after oxidation at 750°C for 1500 hours. Moreover, both spinel coatings can effectively suppress the outward diffusion of Cr, which resulted in reduction of Cr contamination significantly. The oxidation studies of Cu-Mn coating revealed the transformation mechanisms of Cu-Mn coating to the spinel. In-situ neutron and X-ray diffraction analysis clarified the crystal symmetry of CuᵪMn₃₋ᵪO₄ spinel and CuMnO₂ at high temperatures. Rietveld refinement revealed the cation distribution of Cu and Mn ions on tetrahedral and octrahedral sites of CuᵪMn₃₋ᵪO₄ spinel, which was compared to values in the literatures.