Conductive and stable ceramic materials and coatings for solid oxide fuel cell interconnects

Abstract

An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The present work involves conductive and stable ceramic materials and coatings for solid oxide fuel cell interconnects. Chapter 3 is concerned with a ceramic interconnect based on perovskite oxides for SOFCs. We report a dual-layer interconnect film for segmented-in-series (SIS) SOFCs comprising perovskite-type oxides, $Sr_{0.7}La_{0.2}TiO_3$ and $La_{0.8}Sr_{0.2}FeO_3$ . The interconnect film fabricated by a co-sintering process is not only dense but also highly conductive and stable under SOFC operating conditions. A flat-tubular SIS-SOFC fabricated using these interconnect films exhibits a power density of $340 mW cm^{-2}$ , which proves the feasibility of the dual-layer interconnect design. Chapter 4 deals with protective coatings based on spinel oxides for metallic interconnects. $Mn_{1.5}Co_{1.5}O_4$ (MCO) spinel oxides doped with Cu and Ni are synthesized and applied as protective coatings on a metallic interconnect. Doping of Cu and Ni into MCO improves sintering characteristics as well as electrical conductivity and thermal expansion match with the interconnect. The dense layers of Cu- and Ni-doped MCOs are fabricated on the interconnects by a slurry coating process. The Cu-doped MCO coating acts as an effective barrier to evaporation and migration of Cr-containing species from the interconnect. Chapter 5 is devoted to protective coatings based on perovskite-type rare-earth oxides for metallic interconnects. Perovskite-type $LaCoO_3$ , $La_{0.9}Ca_{0.1}CoO_3$ , and $LaMnO_3$ films are fabricated on the SOFC interconnects through “chemically assisted electrodeposition” of hydroxide coupled with thermal conversion of hydroxide to oxide. The electrodeposition parameters, such as solution pH, applied potential, solution composition, and deposition time, have a dominant influence on the composition, microstructure and adhesion of the perovskite oxide films. The fabricated films exhibit outstanding performance as a conductive protection coating for SOFC interconnects and current？collectors, and high stability during both continuous operation and repeated thermal cycling.