Doping and Defect Structure of Mixed-conducting Ceramics for Gas Separation
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My main objective is to gain a firm understanding of the correlation between the defect chemistry and the properties of Ba-based perovskite structure proton-conducting ceramics, especially B-site doped BaCeO3, so as to allow the engineering of these compounds with the desired properties for the application in devices; develop membranes of mixed protonic-electronic conductors suitable for hydrogen separation from gas mixtures; and further advance hydrogen separation technology by gaining fundamental understanding about electrochemical separation mechanism. BZCY proton conductors with various compositions have been synthesized and characterized. The absence of low-angle supercell reflections indicates a random B-site cation distribution. The substitution of Zr led to a decrease in cell volume and an enhanced structural stability against reactions with CO2. The total conductivity for BZCY pellets increased with temperature increased and decreased as the zirconium content increased at each fixed temperature. Dense Ni-BZCY composite membranes have been successfully fabricated for evaluating hydrogen permeability and stability. Doping Zirconium in the B-site only slightly reduced the hydrogen permeation at high temperatures, but dramatically increased the chemical stability in CO2- and H2O-containing gases. Among the compositions studied, the Ni-BZCY7 exhibited both highest H2 permeation rate and good chemistry stability, thus having potential for practical applications.