Preparation and characterization of strontium and magnesium doped lanthanum gallates as the electrolyte for IT-SOFC

Abstract

LSGM (La 1 − x Sr x Ga 1 − y Mg y O 3 − δ ) powders of four different compositions ( x, y = 0.1 or 0.2) (a symbolic system such as LSGM9191 for x = 0.1 and y = 0.1 or LSGM9182 for x = 0.1 and y = 0.2 is used hereafter) were synthesized using the GNP (glycine nitrate process) as the electrolyte material of the intermediate temperature solid oxide fuel cell (IT-SOFC). They were then calcined at 1000 °C for 2 h, compacted into a disc or a rod, and sintered at 1400 °C for 4 h in preparation for structural, electrical and thermomechanical characterizations. The reactivity of the LSGM with the cathode material of LSM (La 0.85Sr 0.15MnO 3) or with the anode material of Ni–YSZ was analyzed by sintering an LSGM/LSM, LSGM/NiO or LSGM/YSZ powder mixture at 1400 °C for 4 h and then searching for possible reaction products in its XRD pattern. The sinters of LSGM9191, LSGM9182 and LSGM8282 consisted of a single LSGM phase. On the other hand, the sinter of LSGM8291 contained the second phases of LaSrGa 3O 7 and LaSrGaO 4 as well in addition to the main LSGM phase. The electrical conductivity of LSGM8282 (0.105 S cm −1 at 800 °C) turned out to be the highest among those of the four LSGMs and more than twice as high as that of YSZ (∼0.045 S cm −1). The linear thermal expansion coefficient was measured to be 12.1 × 10 −6 K −1 for LSGM8282 which was very close to that of LSM (11.7 × 10 −6 K −1). The phase stability of LSGM8282 in contact with LSM was fairly good. LSGM8282, however, reacted quite extensively with Ni–YSZ.