High-temperature superconductor materials for contact layers in solid oxide fuel cells: II. Chemical properties at operating temperatures

The chemical reactivity between superconducting ceramic materials (YBa2Cu3O 7-x, Bi2Sr2CaCu2O8+x and Bi2Sr2CuO6+x and the cathode material of solid oxi de fuel cells (La0.65Sr0.3MnO3) was investigated by long-term annealing exp eriments of pressed powder mixtures lasting two weeks at 850 degreesC. The chemical properties at the operating temperature of a solid oxide fuel cell revealed that all three superconducting materials reacted with La0.65Sr0.3 MnO3 and underwent changes in Volume and density after annealing. The chemi cal compatibility between the superconductors and interconnect material, a ferritic steel (X 10 CrAl 18), was investigated using screen-printed thick layers of Bi2Sr2CuO6+x on steel substrates. The formation of undesirable pr oducts, especially SrCrO4, due to diffusion processes across the interface was confirmed by investigations of metallographic cross-sections. Efforts t o stop the interfacial reaction by introducing a thin CuO barrier layer bet ween the superconductor and steel did not solve the problem. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All lights reserved.