Morphological Characterization of Cobaltite Mixed Conductors for Solid Oxide Fuel Cells Cathodes

FEDERICO NAPOLITANO; LAURA BAQUÉ; ERNESTO SCERBO; CAROLINA AYALA; NICOLÁS COTARO; ELISABETH DJURADO; CECILE ROSSIGNOL; HORACIO TROIANI; MARA GRANADA; ADRIANA SERQUIS; ALBERTO CANEIRO

Rosario

Congreso; 10mo Congreso Interamericano de Microscopía Electrónica (CIASEM 2009) y 1er Congreso de la Sociedad Argentina de Microscopía (SAMIC 2009); 2009

Asociación Argentina de Microscopía - Comité Interamericano de Sociedades de Microscopía Electrónica

Solid Oxide Fuel Cells (SOFCs) have being extensively investigated in recent years dueto their high performance and wide potential applications in power generation. The principle of operation of this kind of fuel cells involves reduction of O2 in the cathode, oxygen ions (O2-) diffusion through the electrolyte, and fuel oxidation in the anode. Conventional SOFCs consist of La1-xSrxMnO3-d cathode, yttria-stabilized zirconia (YSZ) electrolyte and Ni-Gadolinium doped ceria anode.The high temperatures (up to 1000ºC) needed for operation (i.e.to allow oxygen ions conduction through conventional electrolytes), require high cost interconnecting materials.The employment of new electrolyte materials (like gadolinium doped ceria and lanthanum gallate) lows the operation temperature to the 500 - 700ºC range in the so-called intermediate temperature SOFC (IT-SOFC). However, cathode overpotential becomes important at these temperatures,decreasing the cell performance.In order to lower the cathode overpotential, most of research work only focuses on chemical composition. In that sense, La1-xSrxCo1-yFeyO3-d; mixed conductors are good candidates for IT-SOFC cathodes because thesematerials present high ionic and electronic conductivity, and compatibility with Cerium Gadolinium Oxide (CGO)electrolytes allowing a lower operation temperature. Nevertheless, previous studies have shown that the useof novel cathode morphologies, besides composition, could further improve cell performance . In this work, the morphology of La0.4Sr0.6Co0.8Fe0.2O3-d; (LSCFO) cathodes prepared by different techniques was study as a function of the synthesis parameters. LSCFO nanotubes were prepared by a porous polycarbonate membrane mold approach (several characteristic pore diameters were used), obtaining different microstructures dependingon sintering conditions. Independently, LSCFO powders have been prepared by three different methods: an acetic acid-based chemical route, an hexamethylenetetramine (HTMA) chemical route and spray pyrolysis. Three different inks were prepared with powders synthesized by each chemical route, and then deposited onto Ce0.9Gd0.1O1.95 ceramic substrates by spin and dip-coating. The morphology and composition of the powders, nanotubes andfilms were characterized by transmission (TEM) and scanning electron microscopy (SEM), and energy dispersive spectroscopy, respectively.SEM images were used for quantitative and qualitative analysis for all structures: size distributions of several characteristic magnitudes, surfaces roughness, deposited layer homogeneity over entire cathode area and cross section for electrode/electrolyte interface analysis and electrode thickness measurement.Bright field TEM images were acquired for individual tube morphological characterization.The correlation between the morphology of nanotubes, powders and films and the synthesis parameters is discussed.