Generation of nanoflowers and nanoneedles on Co-based layered perovskite of IT-SOFC cathode affecting electrical conductivities

In this study, the unusual microstructure and electrical properties of SmBa_0.5Sr_0.5Co₂O_5+d (SBSCO) layered perovskite cathodes with dense and porous microstructures were analyzed by changing the applied current. Unique nanostructure shapes were observed when a high current was applied to a cathode with both dense and porous microstructures of the same chemical composition for electrical conductivity measurement. Nanoflower and nanoneedles, which are types of nanoseeds, were discovered. The nanoneedles were found on the entire surface of the SBSCO cathode, whereas nanoflowers were only present on part of the cathode surface. Results from an Energy Dispersive Spectrometer (EDS) analysis revealed that the nanoneedles generated on the SBSCO matrix had a chemical composition of SmBaCo₂O_5+d (SBCO). The electrical conductivity of the porous cathode with SBCO nanoneedles (nanoneedle cathode) was 238 S/cm at 700 °C under decreasing temperature in an air atmosphere (Air Down) during the experiment. In comparison, the electrical conductivity of the porous cathode without nanoneedles (normal cathode) was 136 S/cm at the same experiment condition (700 °C, Air Down). This indicates that the electrical conductivity of the nanoneedle cathode was significantly higher than that of the normal cathode.