An electrochemical study on the ionic conductivity of ceramic electrolyte La1-2SrxCo3-yMyO3-sigma oxide and its Pd/Ag compsites

Abstract

This thesis studied the electrochemical properties of the oxygen ceramic electrolytes of La1-xSrxCo1-yMyO3-d perovskite-type oxides that possess excellent electronic and oxygen anionic conductivity. Such mixed-conductivity is the essential property that the cathode material of solid oxide fuel cell (SOFC) and the electrochemical oxygen separation membrane must have. The oxides were synthesized via combustion of their metallo-organic precursors and then annealing of the resulting amorphous oxides at different temperature to attain desire perovskite structure. The study showed that crystal structure, temperature of measurement, composition of the oxides and oxygen content in the measurement atmosphere affect the ionic conductivity, which was obtained by applying AC impedance method. Among these factors, temperature has the most significant impact on the ionic conductivity, for instance La0.2Sr0.8CoO3-d (LSCO) exhibits O2- conductivity of 2.56 A' 10-3 S/cm at 900A?C but of only 1.23 A' 10-7S/cm at 400A?C. Moreover, the highest possible dopant content at site A of perovskite cell in terms of not scarifying stability of the resulting crystal structure has been investigated. Besides modifying composition of the oxides, an alloy Ag/Pd was incorporated into LSCO oxide to form a high-temperature stable metal-ceramic composite. The alloy phase enhances not only the structural integrity of the composite monolith fabricated but also ionic conductivity of the ceramic phase.