Preparation and characterization of La_1.75Y_0.25Mo_2-xAl_xO_9- as solid electrolyte for intermediate temperatures SOFC

Yttrium and aluminium co-substitutions on lanthanum molybdate ceramics with the nominal formula La1.75Y0.25Mo2-xAlxO9-delta (LYMA, x = 0, 0.1, 0.2, 0.3 and 0.4) were synthesized by citric acid-nitrate combustion method and used for preparation of solid electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Phase composition, structure, conductivity and electrical properties of LYMA have been investigated as a function of aluminium content by X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy, respectively. Experimental results showed that the substitution of La and Mo with appropriate amounts of Y and Al can effectively stabilize the beta-form of La2Mo2O9 at room temperature and inhibit its phase transition to alpha-form. The LYMA synthesized by combustion method exhibited a better sinterability where relative density of the samples sintered at 950 degrees C for 4 h was higher than 95%TD. The performance of the LYMA electrolyte was found to be related to Al-content. The La1.75Y0.25Mo1.8Al0.2O8.7 exhibited high oxide ion conductivity (sigma = 42mS/cm at 800 degrees C) and low electrical activation energy (E-a = 1.18 eV). These preliminary results indicate that the LYMA is a promising electrolyte for IT-SOFCs.