Characterization of La_(2-x)Sr_xCoTiO_6 (0.6≤x≤1.0) series as new cathodes of solid oxide fuel cells

摘要

La_(2-x)Sr_xCoTiO_6 (0.6≤x≤1.0) compound series is prepared by Sr-substitution in the A-site of the perovskite by a modified Pechini procedure under air. Charge compensation as Sr~(2+) content increase occurs by CO~(2+) oxidation to CO~(3+). Reduced samples are obtained by further treatment under 5%H_2/Ar and characterized by Neutron Powder Diffraction. Upon redution, CO~(3+) to CO~(2+) reduction and oxygen vacancies creation are detected. Dependence of total conductivity with temperature and pO_2 exhibits a typical p-type semiconducting behaviour. Results show that the higher the Sr content, the higher holes (CO~(3+)) concentration and consequently, La_(2-x)Sr_xCoTiO_6 (x = 1.0) shows the highest conductivity (13.23 S/ cm at 1073 K in air). The negligible reactivity with YSZ, used as the electrolyte, of symmetrical cells under oxidant conditions and the moderate thermal expansion found by XRD point to their possible use as SOFC cathodes. Thus, La_(1.2)Sr_(0.8)CoTiO_6-based cathodes display polarization resistance of 0.9 Ω cm~2 at 1073 K in oxygen, only slightly above than the current state-of-the-art.