A solid oxide fuel cell based on Sr- and Mg-doped LaGaO 3 electrolyte: the role of a rare-earth oxide buffer

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In this paper we review a systematic study on the properties of the superior oxide-ion conductor Sr- and Mg-doped LaGaO 3 (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≤ P O 2 ≤1 atm. The highest values of the oxide-ion conductivity, σ o=0.17, 0.08 and 0.03 S/cm, were found for La 0.8Sr 0.2Ga 0.83Mg 0.17O 2.815 at 800, 700 and 600°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; Ce 0.8Sm 0.2O 1.9 (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 La 0.6Sr 0.4CoO 3− δ (LSCo) remained unchanged. Comparison of the peak power density in this study and with that of a previous study, also with a 500-μm-thick electrolyte, indicates a factor of two improvement, i.e. from 270 mW/cm 2 to 550 mW/cm 2 at 800°C. The excellent cell performance showed that an LSGM-based SOFC operating at temperatures T op≤800°C is a realistic goal.