A solid oxide fuel cell based on Sr- and Mg-doped LaGaO3 electrolyte:: the role of a rare-earth oxide buffer

In this paper we review a systematic study on the properties of the superior oxide-ion conductor Sr- and Mg-doped LaGaO3 (LSGM) and its performance in a single fuel cell. The conductivity of the oxygen-deficient perovskite phase was shown to be purely ionic over a wide range of oxygen partial pressures 10(-22)less than or equal to Po(2)less than or equal to 1 atm. The highest values of the oxide-ion conductivity, sigma(o)=0.17, 0.08 and 0.03 S/cm, were found for La0.8Sr0.2Ga0.83Mg0.17O2.815 at 800, 700 and 600 degrees C, respectively; they remained stable over a weeklong test. The reactivity of Ni and LSGM suggested use of a thin interlayer at the anode-electrolyte interface to prevent formation of lanthanum nickelates; Ce0.8Sm0.2O1.9 (SDC) was selected for the interlayer. The peak power density of the interlayered cell is 100 mW/cm(2) higher than that of the standard cell without the interlayer. This improvement is due to a significant reduction of the anode overpotential; the overpotential of the cathode La0.6Sr0.4CoO3-delta (LSCo) remained unchanged. Comparison of the peak power density in this study and with that of a previous study, also with a 500-mu m-thick electrolyte, indicates a factor of two improvement, i.e, from 270 mW/cm(2) to 550 mW/cm2 at 800 degrees C. The excellent cell performance showed that an LSGM-based SOFC operating at temperatures T(op)less than or equal to 800 degrees C is a realistic goal. (C) 2000 Published by Elsevier Science S.A. All rights reserved.