| With the increasing requirements on energy for global development, the demands on environmental protection and the raising price of crude-oil, hydrogen as a new energetic carrier is attractive for their clean, effective and portable nature. Coke-oven-gas (COG), the byproduct of the coal industry, is one of the most attractive hydrogen sources for their amounts and costs. However the traditional partial oxidation of COG to maximize the hydrogen-yields requires pure oxygen by high-cost cryogenic method. Mixed ionic-electronic conductor (MIEC) membrane with theoretically infinite perm-selectivity to oxygen allows integrating O2 separation, partial oxidation and reforming reaction in single reactor. The partial oxidation technology based on MIEC membranes provides the economic and environmental benefits with respect to conventional industrial processes.Although the high oxygen permeability have nearly only been found among perovskites containing cobalt, most cobalt-containing system express the drawback of low stability. Our studies showed that BaCo0.7Fe0.2Nb0.1O3-δ membrane possesses excellent permeability and preserves stability under working condition of reducing atmosphere. Therefore chemical properties of BaCo0.7Fe0.2Nb0.1O3-δ material, the reaction mechanism of COG reforming in BaCo0.7Fe0.2Nb0.1O3-δ membrane, and the composition optimization for material are investigated systematically in my dissertation.Compound BaCo0.7Fe0.2Nb0.1O3-δ is synthesized by conventional solid state reaction process. The stability, permeation performance, and electrical properties of BaCo0.7Fe0.2Nb0.1O3-δ compounds are investigated. Single cubic perovskite phase of compound powders is decomposed under reduced atmosphere, however BaCo0.7Fe0.2Nb0.1O3-δ membrane could maintain stable regarding the application under reducing atmosphere because of the protection by the penetrated oxygen from air-side. The chemical diffusion coefficient and oxygen-transfer coefficients of the material in oxygen -rich or -poor atmospheres is studied using the conductivity relaxation technique. The flow rate of sweeping gas would influence oxygen permeation of membrane. The oxygen permeation of the membrane would be decreased greatly when CO2 is introduced into the oxygen-lean side. The BaCo0.7Fe0.2Nb0.1O3-δ membrane coupled with catalyst bed performs well for hydrogen production through COG-reforming.The main reacting species in COG on membrane surface is H2. The oxygen flux of BaCo0.7Fe0.2Nb0.1O3-δ membrane reforming COG would be enhanced by the metal particle on reduction surface. The reaction pathway in practical membrane reactor reforming COG is that the absorbed-H2 is dissociated on metal surface; then the mediated species, H*, are migrated to the 'triphase boundary' and oxidized; finally the oxidized species, H2O, is reformed to H2 and CO by CH4 in catalyst-bed. Besides, the space charge at membrane/metal interface might influence on the oxidation process on membrane surface. The reaction mechanism on membrane surface provides guidance for design of membrane reactor and modification of membrane surface.BaCo0.7Fe0.3-xNbxO3-δ(x=0.080.14) compounds were synthesized by conventional solid state reaction process. The increase of niobium doping concentration in BaCo0.7Fe0.3-xNbxO3-δ(x=0.080.14) would improve the chemical stability of oxides significantly but influence the oxygen permeation of compounds little. The high performance of the high niobium content samples could not be contributed to the microstructure of membrane. We utilize experimental evaluation and computational modeling to realize the mechanism of niobium doping effects on the physical chemical properties of BaCo0.7Fe0.3-xNbxO3-δ compounds. The electronic structure, formation enthalpy, formation energy of oxygen vacancy, and oxygen conducting process in doped BaCoO3 are calculated from density functional theory. The niobium doping raises the formation energy of oxygen vacancy in perovskite, and improves the chemical stability of compounds. Ba-Nb-Ba opening is the more favorable channel for oxygen ion migration than Ba-Fe-Ba opening. The positive effects of niobium doping on oxygen conductivity would compensate its negative impacts on oxygen defects effectively. The BaCo1-xNbxO3-δ compositions were proposed according to our simulating results. And the experiments demonstrate BaCo1-xNbxO3-δ compounds possess excellent stability and permeability.La0.0.5Ba0.0.5(CoM)O3-δ(M=Co,Zn,Cu,Nb) compounds were synthesized by conventional solid state reaction process. Only undoped and Zn-doped compounds synthesize the pure perovskite structure. The substitution of Co by Zn in La0.0.5Ba0.0.5CoO3-δ improves mobility of oxygen ions in lattice significantly. The La0.0.5Ba0.0.5CoO3-δ and La0.0.5Ba0.0.5Co0.9Zn0.1O3-δ materials show better stability resisting CO2 and H2 than BaCo0.7Fe0.2Nb0.1O3-δ material. Computational modeling compares the electronic structure, formation energy of oxygen vacancy, and oxygen conducting process of La0.0.5Ba0.0.5CoO3 before and after Zn doping. The zinc doping can not reduce the formation energy of oxygen vacancy in perovskite, and also can not improve the chemical stability of compounds. However, Ba-Zn-La opening is the more favorable channel for oxygen ion migration than Ba-Co-La opening, therefore the mobility of oxygen ion in compounds is improved after zinc doping.
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