Characterization of La[sub 0.5]Ba[sub 0.5]CoO[sub 3−δ] as a SOFC Cathode Material

Abstract

This study reports the physical properties and electrochemical behavior of La(0.5)Ba(0.5)CoO(3-delta) (LBC), a perovskite material and a potential candidate for the solid oxide fuel cell (SOFC) cathode. LBC was synthesized by a solid-state route, and phase purity was checked by X-ray diffraction measurement. Thermogravimetric analysis of LBC was performed both in air and in argon atmosphere to observe its phase stability. Total conductivity, measured by a four-point dc polarization method, exhibited a pseudometallic-type behavior. Ionic conductivity was determined in air over a 650-775 degrees C temperature range by a dc polarization technique using electron-blocking electrodes. The high total conductivity, combined with a sufficiently high ionic conductivity (1.2x10(-3) S/cm at 650 degrees C), indicates that LBC possesses a certain degree of mixed ionic-electronic conducting nature. The oxygen reduction behavior of porous LBC electrodes on a gadolinium-doped ceria electrolyte was studied in a symmetrical cell configuration by impedance spectroscopy. The CO(2) tolerance and the high temperature stability of the cell were also investigated. Impedance spectra obtained at zero dc bias conditions consisted of two semicircular arcs, which indicate that the overall oxygen reduction comprises at least two distinct processes. The area specific resistance (ASR) for electrode polarization was determined over a wide range of temperatures (600-850 degrees C). The ASR value at 600 degrees C was determined to be 0.16 cm(2), which offers the promise of utilizing LBC as a cathode for low temperature SOFCs.