Morphologycal characterization of cobaltite mixed conductors for solid oxide fuel cell cathode

F. NAPOLITANO; L. BAQUE; E. SCERBO; C. AYALA; C. N. COTARO; E. DJURADO; C. ROSSIGNOL; H. TROIANI; M. GRANADA; A. SERQUIS; A. CANEIRO

Rosario, Argentina

Congreso; 10th Inter-American Congress on Electron Microscopy; 2009

CIASEM

Solid Oxide Fuel Cells (SOFCs) have being extensively investigated in recent years due totheir high performance and wide potential applications in power generation [1]. The principle ofoperation 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 ofLa1-xSrxMnO3-δ 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.[1,2] 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).[1] However, cathode overpotential becomes important at these temperatures,[1] decreasing the cell performance.In order to lower the cathode overpotential, most of research work only focuses on chemicalcomposition. In that sense, La1-xSrxCo1-yFeyO3-δ mixed conductors are good candidates for IT-SOFC cathodes because these materials present high ionic and electronic conductivity, and compatibility with Cerium Gadolinium Oxide (CGO) electrolytes [3] allowing a lower operation temperature.Nevertheless, previous studies have shown that the use of novel cathode morphologies, besidescomposition, could further improve cell performance [4 - 6].In this work, the morphology of La0.4Sr0.6Co0.8Fe0.2O3-δ (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 [6, 7] (several characteristic pore diameters were used), obtaining different microstructures depending on sintering conditions. Independently, LSCFO powders have been prepared by three different methods: an acetic acid-based chemical route [4, 8], a hexamethylenetetramine (HTMA) chemical route [4] and spray pyrolysis [9]. 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 and films 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. On one handsize distributions of several characteristic magnitudes (i.e. tube lengths and diameters, particle size, electrode thickness, etc) were measured. On the other hand the deposited films were qualitatively characterized according their surface roughness, porosity, layer homogeneity over entire cathode area, and electrode/electrolyte interface. Bright field TEM images were acquired for individual tube characterization.The correlation between the morphological characteristics of nanotubes, powders and films andthe synthesis parameters is discussed.