Characteristics of Mn-Co and Ni-Co metal powders mixed with oxides as cathode contact materials for SOFC

Manganese, cobalt and nickel metal powders are mixed with 10 wt% oxides: La0.6Sr0.4CoO3, La0.6Sr0.4Co0.2Fe0.8O3, La0.8Sr0.2MnO3 and MnCo2O4, to form ten compositions. Powder mixtures are studied as cathode contact materials in solid oxide fuel cell stacks. Electrical resistance is measured on samples of powder pellets and steel/powder/steel assemblies at 800 degrees C for over 10000 h. Microstructures are examined after measurements. For the powder pellets, Mn-Co (mole ratio 1:2) and Ni-Co (mole ratio 1:2) with MnCo2O4 exhibit minimum resistivity in the Mn-Co and Ni-Co series respectively. For the steel/powder/steel assemblies, Mn-Co (mole ratio 1:1) with La0.6Sr0.4CoO3 and Ni-Co (mole ratio 1:2) with La0.8Sr0.2MnO3 show close low values. Oxide scales grown on steel surfaces which contact powders with lanthanum-based perovskites are irregular and thinner. Other powders result in more regular and thicker oxide layers. The two forms of oxide structures are in accordance with the two trends of electrical resistance change observed in the assemblies. The addition of lanthanum-based perovskites reveals phenomenal effects on reducing the resistivity of powder mixtures and suppressing the growth of steel oxide scales. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.