Electrochemical Performance of Nanostructured Cobaltite Mixed Conductors for Solid-Oxide Fuel Cell Cathodes

L. BAQUÉ; F. NAPOLITANO; A. SERQUIS; A. CANEIRO

Hilton Sydney, Australia

Conferencia; IUMRS-ICEM08 Symposium F: Materials for Fuel Cells, the Hydrogen Economy and Sustainable Technologies; 2008

IUMRS

La1-xSrxCo1-yFeyO3-d oxides are good candidates for solid oxide fuel cell (SOFC) cathodes because these materials present high ionic and electronic conductivity, and compatibility with Cerium Gadolinium Oxide (CGO) electrolytes allowing a lower operation temperature. Previous studies have shown that microstructure strongly influences on polarization resistance, besides composition. In that sense, the use of new cathode microstructures could further improve cell performance. In this work, the microstructure of La0.4Sr0.6Co0.8Fe0.2O3-d (LSCFO) powders, nanotubes and films were characterized. In addition, cathode polarization resistance and possible limiting mechanisms of cathode reaction were studied. LSCFO nanotubes were prepared by a porous polycarbonate membrane mold approach, obtaining different microstructures depending on sintering conditions. Independently, LSCFO powders have been synthesized by an acetic acid-based and hexamethylenetetramine (HTMA) routes. Two different inks were prepared with powder synthesized by each chemical route, and then deposited onto Ce0.9Gd0.1O1.95 ceramic substrates by spin and dip-coating. The structure, morphology and composition of the powders, nanotubes and films were characterized by X-ray diffraction, transmission and scanning microscopy, and energy dispersive spectroscopy, respectively. The grain size and strain were analyzed by Rietveld method. Impedance spectroscopy spectra were recorded on cathode films at 400-700 C under oxygen partial pressures ranging from 10-3 to 1 atm. We found that nanotubes, powders and films microstructure is mainly determined by synthesis parameters. Furthermore, the electrochemical properties of LSFC cathodes films strongly depend on the microstructure and cathode polarization resistance can be decreased to values as low as 0.05 ohmcm2 at 600C and 0.7 ohmcm2 at 450 C.