A novel approach for gasification of carbon using a mixed conductor

“One-Pot” Solar Fuels

Oxygen Permeation Through Composite Oxide-Ion and Electronic Conductors

The electronic and ionic conduction behavior of Ru-doped SrTiO3 at high temperature was investigated. The conductivity increased significantly with increasing Ru content. SrTi0.80Ru0.20O3−δ exhibits fairly high conductivities, e.g., 3 S cm−1 at 1000°C, and 2 S cm−1 at 600°C. The conductivity had only a slight dependence on the partial pressure of oxygen over a wide range and was largely attributed to n-type electronic conduction. Ru-doped SrTiO3 showed mixed oxide-ionic and electronic conduction under reducing atmospheres. The mechanism of the electronic and ionic conduction is discussed.

Oxide ion and electron conduction in sintered oxides of the system Bi2O3-Pr6O11 have been studied. Two types of rhombohedral phase are formed in this system. Oxide ion conduction is predominant in the rhombohedralβ-phase present in the composition range less than 35 mol% Pr2O11/3. Electronic (hole) conduction appeared in addition to oxide ion conduction in another rhombohedral phase containing more than 40 mol% Pr2O11/3. This phase is of the LaOF-type which is a distorted defect fluoritetype structure. Electronic conduction in the LaOF-type phase is considered to be due to the change of oxidation state of praseodymium at high temperatures.

Inhibiting in situ phase transition in Ruddlesden-Popper perovskite via tailoring bond hybridization and its application in oxygen permeation

Mixed ion conductor shows oxide ion and electronic conduction simultaneously and expecting for application to oxygen separation membrane from air. Because of significant volume change depending on oxygen partial pressure, oxygen separation membrane using mixed ion conductor has disadvantage of narrow range of oxygen partial pressure resulting in the limited permeation rate. Therefore, increased oxide ion conductivity and mechanical strength have been required for mixed ion conducting membrane for oxygen separator. In our previous study, we found that Fe doped LaGaO3 shows reasonably high oxide ion conductivity and chemical stability. In particular, La0.7Sr0.3Ga0.6Fe0.4O3 (LSGF) shows largest oxide permeation rate from air to He. In this study, for further increase in oxygen permeation rate, effects of dopant to Ga site in LSGF was investigated. Application to CH4 partial oxidation was also studied. All LSGF sample was prepared with conventional solid state reaction method using oxide as source materials. Partial substitution was performed for Ga site in LSGF and dense sample without impurity phase was confirmed by XRD measurement. For oxygen permeation measurement, La0.6Sr0.4CoO3 catalyst was coated on the surface of LSGF disk (Φ17mm diameter, 0.5mm thickness) It was found that the oxygen permeation from air to He was sensitively influenced by dopant and the oxygen permeation rate was increased as the following order, Co>Al>In>Ni>Mn at 1273 K. On the other hand, in case of Ru and Ir which is easily reduced to metallic state decreased the oxygen permeation rate significantly. Therefore, it was found that addition of 10 mol % of Co or Al is effective for increasing oxygen permeation rate of LSGF. Effects of Co in LSGF was further studied from oxygen permeation rate and the highest oxygen permeation rate was achieved at 3 mol% in Ga site of LSGC. On this optimized composition, La0.7Sr0.3Ga0.57Fe0.4Co0.03O3, shows 225 μmol min-1 cm-2 at 1273 K and this value is almost 2.5 times larger than that of LSGF. Effects of small amount of Co on electrical conductivity in LSGF were also studied. Although LSGF shows high hole conduction like log(σ/Scm-1)=0.6, the conductivity was increased by Co doping, in particular, at lower temperature. In contrast, Al doping decreases total conductivity and so, increase in oxygen permeation rate could be assigned to the increased mobility of oxide ion in LSGF. Application of Co doped LSGF to CH4 partial oxidation was further studied. Although optimized amount of Co doped for Ga site in LSGF is 3 mol%, the membrane was broken when 3 mol% doped LSGF was used for oxygen membrane. 1% Co doped LSGF was applied for oxygen permeation membrane and it was found that amount of oxygen permeation rate was 1.5 times increased comparing with LSGF. In addition, no crack was formed in membrane. The amount of oxygen permeation was achieved 364μmol cm2 min-1 which is corresponded to 8.9ml/min cm2 at 1273K. In summary, this study reveals that doping small amount of Co to Ga site of LSGF is highly effective for increasing oxygen permeation rate without decreasing chemical stability.

We explore the new concept for a ceramics membrane reactor including the investigation of the nickel-based catalysts for methane conversion into synthesis gas and the exploitation of an oxide ionic and electronic mixed conductor. When Ca0.8Sr0.2Ti1−xFe x O3−α exhibiting the ionic and electronic mixed conduction was used as a support material of Ni based catalyst, coke formation over the catalyst under the methane conversion with air or carbon dioxide was strongly depended on the iron (III) ion contents, x. From the relationship between the amount of carbon deposited on the catalyst and the mixed conduction in support oxide materials, it was suggested that the self-migration of lattice oxygen inside the support regulated by the balance between the oxide ionic and electronic conductivities played an important role to prevent from accumulating the deposited carbon over the catalysts. In addition, we demonstrated the methane conversion into synthesis gas at 1173 K with one component ceramics membrane reactor constructed with the same type of perovskite-type oxide for both the catalyst supported and mixed conductor.

Determination of electronic and ionic conductivity in mixed ionic conductors: HiTEC and in-situ impedance spectroscopy analysis of isovalent and aliovalent doped BaTiO3

Electrical conduction in sintered oxides of the system Bi2O3-Tb2O3.5 has been investigated. Oxide ion conduction was observed in the rhombohedral (low temperature) phase and the f c c (high temperature) phase present in the composition range less than 20mol% Tb2O3.5. The fcc phase could be stabilized at lower temperatures by adding more than 30 mol % Tb2O3.5. In addition to oxide ion conduction, appreciable electronic conduction appeared in this composition range. The oxide ion transport number of this phase decreased with increasing content of Tb2O3.5 and the specimens having 40–50 mol % Tb2O3.5 showed mixed conduction where electrical conduction was comparably contributed by oxide ions and electrons. Electronic conduction in the fee phase was considered to be due to the change in valence of terbium at high temperatures.

Conductivity, dielectric and piezoelectric properties of SrBi4Ti4O15

Oxide Ion Conduction in Solid Solutions Ln1-xSrxCoO3-δ(Ln = La, Pr, Nd)

Effects of rock-salt layer on electronic and oxide ionic mixed conductivity in strontium titanate, SrO(SrTiO 3) n ( n = 1, 2, ∞)

Design of one-component ceramic membrane-reactor for natural gas conversion

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σo ) and electronic conductivity (σe ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σe but inadequate σo . It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2 , however, limits its use in practical applications. Here, the perovskite oxide Bi0.15 Sr0.85 Co0.8 Fe0.2 O3- δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo among the highest for known MIECs, but also high CO2 tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO2 . The combination of high oxide transport properties and CO2 tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.

Replacement of divalent ions by monovalent ions in decreases the electrical conductivity of LSGM and increases the activation energy to 1.42 eV. Substitution of La by substantial amounts of up to 50 atom % of Pr in LSGM yields new mixed oxide ion and electronic conductors. Substitution of 50 atom % Pr for La in the In-analog of LSGM, does not increase the electrical conductivity. Among the investigated oxides, exhibits the lowest activation energy of 0.44 eV and the highest electrical conductivity of at 200°C. Oxygen partial pressure dependence of the electrical conductivity reveals that LSIM and Pr-substituted LSIM perovskites are mixed oxide ion and p-type electronic conductors at high oxygen partial pressures. The electronic conductivity increases with increasing Pr content in LSIM. Open-circuit voltage measurements employing as separator in the galvanic cell show that the average transference number for oxide ion conduction is 0.78-0.90 in the temperature range 450-650°C. Powder X-ray diffraction data reveal that LSIM and Pr-substituted LSIM perovskites are not stable at low oxygen partial pressures of about while Pr-substituted LSGM retains the cubic perovskite structure. Accordingly, the new materials reported here may find application as electrode materials for solid oxide fuel cells and oxygen sensors. © 2001 The Electrochemical Society. All rights reserved.