A Mixed Ionic and Electronic Conducting Dual‐Phase Membrane with High Oxygen Permeability

To combine good chemical stability and high oxygen permeability, a mixed ionic‐electronic conducting (MIEC) 75 wt % Ce_0.85Gd_0.1Cu_0.05O_2?δ‐25 wt % La_0.6Ca_0.4FeO_3?δ (CGCO‐LCF) dual‐phase membrane based on a MIEC–MIEC composite has been developed. Copper doping into Ce_0.9Gd_0.1O_2?δ (CGO) oxide enhances both ionic and electronic conductivity, which then leads to a change from ionic conduction to mixed conduction at elevated temperatures. For the first time we demonstrate that an intergranular film with 2–10 nm thickness containing Ce, Ca, Gd, La, and Fe has been formed between the CGCO grains in the CGCO‐LCF one‐pot dual‐phase membrane. A high oxygen permeation flux of 0.70 mL min^?1 cm^?2 is obtained by the CGCO‐LCF one‐pot dual‐phase membrane with 0.5 mm thickness at 950 °C using pure CO₂ as the sweep gas, and the membrane shows excellent stability in the presence of CO₂ even at lower temperatures (800 °C) during long‐term operation.     

Chemical Stability,Ionic Conductivity of BaCe0.9−xZrxSm0.10O3−α and Its Application to Ammonia Synthesis at Atmospheric Pressure

Dense ceramic samples BaCe_0.9?xZr_xSm_0.10O_3?α (x=0.10, 0.15, 0.20, 0.30) were obtained by heat‐treating the precursors prepared from a coprecipitation route. The phase structure, chemical stability and conduction behaviors of the ceramic samples have been investigated by X‐ray powder diffraction and alternating current impedance spectroscopy methods. All the ceramic samples displayed a single phase of orthorhombic perovskite. The samples with x≧0.20 were relatively stable after exposed to the flowing mixed gases: CO₂ +H₂O+N₂ at 873 K for 12 h. Among the samples tested, the sample with x=0.20 exhibited both adequate conductivity and better chemical stability. The contribution of different charged species for x=0.20 sample to the conduction in wet hydrogen atmosphere was investigated by means of gas concentration cells. It was found that the sample of x=0.20 was almost a pure ionic conductor, and the ionic conduction was contributed mainly by proton and partially by oxide ion in wet hydrogen atmosphere at 773–1073 K. The ammonia synthesis at atmospheric pressure in an electrolytic cell based on the sample of x=0.20 was successfully conducted and the peak ammonia formation rate achieved 2.67×10^?9 mol·s^?1·cm^?2 with direct current of 0.80 mA at 773 K.     

Chemical Stability and Electrical Property of BaCe0.7Zr0.2Nd0.1O3-α Ceramic

BaCe_0.7Zr_0.2Nd_0.1O_3?α ceramic was prepared by solid state reaction. Phase composition, surface and fracture morphologies of the material were characterized by using XRD and SEM, respectively. Chemical stability against carbon dioxide and water steam at the high temperature was tested. The conductivity and ionic transport number of the material were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air, respectively. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen‐air fuel cell was constructed, and the cell performance at the temperature from 500 to 900°C was examined. The results indicate that BaCe_0.7Zr_0.2Nd_0.1O_3?α was a single phase perovskite‐type orthorhombic system, with high density and good chemical stability in carbon dioxide and water steam atmospheres at the high temperature. The conductivity of the material in wet hydrogen and wet air was increased as the temperature rises. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 600°C, a mixed conductor of proton and electron with the protonic transport number of 0.973–0.955 from 700 to 900°C. In wet air, the material was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.002–0.003, and the oxide ionic transport numbers were 0.124–0.179. The fuel cell could work stably. At 900°C, the maximum short‐circuit current density and power output density were 156 mA·cm^?2 and 40 mW·cm^?2, respectively.     

BaCe0.8Ho0.2O3-a陶瓷的性质与应用

Ceramic BaCe0.8Ho0.2O3-α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600-1000 ℃ in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600-1000 ℃ was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600-900 ℃ in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 ℃. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01-0.09, and the oxide-ionic transport numbers were 0.27-0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 ℃, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 ℃, the maximum short-circuit current density and power output density were 346 mA/cm^2 and 80 mW/cm^2, respectively.     

Preparation via microemulsion method and proton conduction at intermediate-temperature of BaCe1−xYxO3−α

The ceramic powders of BaCe_1?xY_xO_3?α (x = 0.05, 0.10, 0.15, 0.20) have been prepared via a microemulsion method. Green compacts of the powders were sintered to densities higher than 95% of theoretical at the lower temperature (1500 °C). The obtained ceramics showed a single-phase of orthorhombic perovskite. The proton conduction was investigated by employing the techniques of AC impedance and electrochemical hydrogen permeation (hydrogen pumping) at 300–600 °C. It was found that the ceramics were almost pure proton conductors in wet hydrogen, and the highest proton conductivity was observed for x = 0.15 at 600 °C. Ammonia was synthesized successfully from nitrogen and hydrogen at atmospheric pressure in the electrolytic cell using BaCe_0.85Y_0.15O_3?α. The maximum rate of NH₃ formation was found to be 2.1 × 10^?9 mol s^?1 cm^?2 at 500 °C with an applied current of 0.75 mA.     

Remarkable Oxygen‐Evolution Activity of a Perovskite Oxide from the Ca2−xSrxFe2O6−δ Series

Herein in we report the unprecedented catalytic activity of an iron‐based oxygen‐deficient perovskite for the oxygen‐evolution reaction (OER). The systematic trends in OER activity as a function of composition, defect‐order, and electrical conductivity have been demonstrated, leading to a methodical increase in OER catalytic activity: Ca₂Fe₂O_6?δ<CaSrFe₂O_6?δ<Sr₂Fe₂O_6?δ. Sr₂Fe₂O_6?δ also has the highest electrical conductivity and a unique type of defect‐order. In conventional experiments using glassy carbon electrode, Sr₂Fe₂O_6?δ shows better OER activity than the current state of the art catalysts, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ and RuO₂. It also offers a high intrinsic electrical conductivity, which allows it to act as a catalyst without the need for glassy carbon electrode or carbon powder. Pure disks of this material exhibit an outstanding activity for OER, without any additives or need for electrode preparation.     

Ba1.03Ce0.8 Ho0.2O3-α固体电解质的制备和电性能

采用高温固相反应法制备了非化学计量组成的Ba1.03Ce0.8 Ho0.2O3-α 固体电解质,用XRD和SEM对其相组成和表面及断面形貌进行了表征。用气体浓差电池方法测定了材料在600～1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中的离子迁移数;用交流阻抗谱技术测定了它们在各实验气氛中的电导率。研究了材料的离子导电特性,并与BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α 的性能进行了比较。结果表明：该材料为单相钙钛矿型斜方晶结构。在600～1000 ℃温度范围内、干燥空气中,是氧离子与电子空穴的混合导体,氧离子迁移数为0.10～0.36;在湿润空气中,是质子、氧离子与电子空穴的混合导体,质子迁移数为0.11～0.01,氧离子迁移数为0.34～0.30;在湿润氢气气氛中,是纯质子导体,质子迁移数为1。在600～1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中,非化学计量组成材料(x = 1.03,0.97)的电导率高于化学计量组成材料(x = 1)的电导率,其中,Ba1.03Ce0.8 Ho0.2O3-α的电导率最高 (1000 ℃时、在干燥空气气氛中：3.92×10-2 S·cm-1;在湿润空气气氛中：3.46×10-2 S·cm-1;在湿润氢气气氛中：2.10×10-2 S·cm-1)。Ba1.03Ce0.8 Ho0.2O3-α材料的离子导电性优于BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α。     

Ionic Conduction in Ba0.95Ce0.8Ho0.2O3-α

Ba0.95Ce0.8Ho0.2O3-a was prepared by high temperature solid-state reaction. X-ray diffraction （XRD） pattern showed that the material was of a single perovskite-type orthorhombic phase. Using the material as solid electrolyte and porous platinum as electrodes, the measurements of ionic transport number and conductivity of Ba0.95Ce0.8Ho0.2O3-a were performed by gas concentration cell and ac impedance spectroscopy methods in the temperature range of 600---1000 ℃in wet hydrogen, dry and wet air respectively. Ionic conduction of the material was investigated and compared with that of BaCe0.8Ho0.2O3-a. The results indicated that Ba0.95Ce0.8Ho0.2O3-a was a pure protonic conductor with the protonic transport number of 1 during 600---700℃ in wet hydrogen, a mixed conductor of protons and electrons with the protonic transport number of 0.97--0.93 in 800---1000 ℃. But BaCe0.8Ho0.2O3-a was almost a pure protonic conductor with the protonic transport number of 1 in 600---900 ℃ and 0.99 at 1000 ℃ in wet hydrogen. In dry air and in the temperature range of 600---1000 ℃, they were both mixed conductors of oxide ions and electronic holes, and the oxide-ionic transport numbers were 0.24--0.33 and 0.17--0.30 respectively. In wet air and in the temperature range of 600---1000 ℃, they were both mixed conductors of protons, oxide ions and electronic holes, the protonic transport numbers were 0.11--0.00 and 0.09--0.01 respectively, and the oxide-ionic transport numbers were 0.41--0.33 and 0.27--0.30 respectively. Protonic conductivity of Ba0.95Ce0.8Ho0.2O3-a in both wet hydrogen and wet air was higher than that of BaCe0.8Ho0.2O3-a in 600--- 800 ℃, but lower in 900--1000 ℃. Oxide-ionic conductivity of the material was higher than that of BaCe0.8Ho0.2O3-a in both dry air and wet air in 600---1000 ℃.     

A Bifunctional Perovskite Catalyst for Oxygen Reduction and Evolution

La_0.3(Ba_0.5Sr_0.5)_0.7Co_0.8Fe_0.2O_3?δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm‐scale rhombohedral LaCoO₃ cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A‐site cations with La³⁺ and local stress on Co‐site sub‐lattice with the cubic perovskite structure.     

Hydrogen Production by Water Dissociation in Surface‐Modified BaCoxFeyZr1−x−yO3−δ Hollow‐Fiber Membrane Reactor with Improved Oxygen Permeation

A porous perovskite BaCo_xFe_yZr_0.9?x?yPd_0.1O_3?δ (BCFZ‐Pd) coating was deposited onto the outer surface of a BaCo_xFe_yZr_1?x?yO_3?δ (BCFZ) perovskite hollow‐fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ‐Pd porous layer on the outer surface of a dense BCFZ hollow‐fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ‐Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH₄ onto the permeation side of the membrane. The blank BCFZ membrane and surface‐modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H₂ min^?1 cm^?2 at 950 °C after depositing a BCFZ‐Pd porous layer onto the BCFZ membrane.     

Ionic Conduction and Application of Ba1.03Ce0.8Tm0.2O3−α Ceramic

Ba_1.03Ce_0.8Tm_0.2O_3?α ceramic with orthorhombic perovskite structure was prepared by conventional solid‐state reaction. The conductivity and ionic transport number of Ba_1.03Ce_0.8Tm_0.2O_3?α were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen‐air fuel cell was constructed, and the cell performance was examined at 500–900°C. The results indicate that the specimen is a pure ionic conductor with the ionic transport number of 1 at 500–900°C in wet hydrogen. In wet air, the specimen is a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers are 0.071–0.018, and the oxide ionic transport numbers are 0.273–0.365. The conductivities of Ba_1.03Ce_0.8Tm_0.2O_3?α under wet hydrogen, wet air or fuel cell atmosphere are higher than those of Ba_1.03Ce_0.8RE_0.2O_3?α (RE?Y, Eu, Ho) reported previously by us. The fuel cell can work stably. At 900°C, the maximum power output density is 122.7 mW·cm^?2, which is higher than that of our previous cell using Ba_1.03Ce_0.8RE_0.2O_3?α (RE?Y, Eu, Ho) as electrolyte.     

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13-δon the Catalytic Activity for Methane Combustion

A series of mixed oxides Sr₄Fe_6?xCo_xO_13?δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr₄Fe₅CoO_13?δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr₄Fe₅CoO_13?δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr₄Fe₆O₁₃, which was confirmed by TGA and XPS.     

SrNb0.1Co0.7Fe0.2O3−δ Perovskite as a Next‐Generation Electrocatalyst for Oxygen Evolution in Alkaline Solution

The perovskite SrNb_0.1Co_0.7Fe_0.2O_3?δ (SNCF) is a promising OER electrocatalyst for the oxygen evolution reaction (OER), with remarkable activity and stability in alkaline solutions. This catalyst exhibits a higher intrinsic OER activity, a smaller Tafel slope and better stability than the state‐of‐the‐art precious‐metal IrO₂ catalyst and the well‐known BSCF perovskite. The mass activity and stability are further improved by ball milling. Several factors including the optimized e_g orbital filling, good ionic and charge transfer abilities, as well as high OH^? adsorption and O₂ desorption capabilities possibly contribute to the excellent OER activity.     

Ceramic Filter Balls Loaded with α-Fe2O3 and Their Application to NH3-N Wastewater Treatment

Hydrolysis reaction of Fe(NO₃)₃ at a high temperature in the presence of urea as the homogeneous precipitant was studied. With the prepared ceramic filter balls loaded with α-Fe₂O₃ after high temperature calcination, the loading of α-Fe₂O₃ on the porous ceramic filter balls from Fe(NO₃)₃ solutions of different concentrations and mechanical stability of the loaded α-Fe₂O₃ were studied. The product was characterized using XRD and SEM. Adsorption experiments were conducted to evaluate the performance of the product in adsorbing NH₃-N. It turned out that the specific surface area of the ceramic filter balls loaded with α-Fe₂O₃ had increased to 36.5387 m²/g from original 4.6127 m²/g. When the concentration of Fe(NO₃)₃ was 0.40 mol/L, the loading of α-Fe₂O₃ on the ceramic filter balls accounted for 8.4% of the total mass of the adsorbent and α-Fe₂O₃ was adsorbed on the filter balls very well. The adsorption isotherm of NH₃-N on the ceramic filter ball adsorbent loaded with α-Fe₂O₃ was of Langmuir type. The saturated adsorption capacity was 3.33 mg/L, and the adsorption constant K was 0.1873. NH₃-N was adsorbed by α-Fe₂O₃ more easily, which was a kind of specific adsorption.     

Preparation and characterization of ceria-Based electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFC)

Solid-oxide fuel cells (SOFCs) can be used for clean, efficient and environment-friendly energy conversion with a variety of fuels at high temperature (1273 K). The high temperature operation accelerates unwanted reactions and creates materials challenges; so, intermediate-temperature SOFCs (IT-SOFCs) have been developed. Reduction of the operating temperature (between 873–1073 K) requires solid electrolyte materials with higher conductivities. In this study, partially substituted ceria as solid electrolyte is experimented systematically for use in solid oxide fuel cells operating below 1073 K (intermediate temperature range). Nine compositions namely, CeO₂, Ce_0.95Gd_0.05O_2-δ (CGO9505), Ce_0.90Gd_0.10O_2-δ (CGO9010), Ce_0.85Gd_0.15O_2-δ (CGO8515), Ce_0.80Gd_0.20O_2-δ (CGO8020), Ce_0.95Sm_0.05O_2-δ (SDC9505), Ce_0.90Sm_0.10O_2-δ (SDC9010), Ce_0.85Sm_0.15O_2-δ (SDC8515) and Ce_0.80Sm_0.20O_2-δ (SDC8020) were synthesized by Glycine Nitrate (GN) combustion technique and investigated. The physical properties and the other relevant features of the data obtained are analyzed with a view to use these alternate electrolyte materials in IT-SOFC.     

Phase equilibrium and electrical conductivity of SrCo0.8Fe0.2O3−δ

The phase diagram of the SrCo_0.8Fe_0.2O_3−δ compound has been determined at high temperatures (823?T?1223 K) and in the oxygen partial pressure range (10⁻⁵?pO₂?1 atm) by thermogravimetric measurements of the equilibrium pO₂, high temperature X-ray diffraction and electrical conductivity measurements. The cubic perovskite phase SrCo_0.8Fe_0.2O_3−δ is stable in a broad range of oxygen content, while the orthorhombic brownmillerite phase SrCo_0.8Fe_0.2O_2.5 stabilizes within a small range around 3−δ=2.5 at temperatures below 1073 K. Equilibrium pO₂ measurements under isothermal conditions show chemical hysteresis at the perovskite to brownmillerite transition. The hysteresis loop decreases its amplitude in pO₂ with decreasing temperature. This behavior is discussed considering the evolution from coherent intergrowth interfaces with elastic strain energy to incoherent interfaces without elastic strain energy as T decreases. The thermodynamic quantities h_O2^oxide and s_O2^oxide for the perovskite phase decrease when increasing the oxygen defects concentration. The electrical conductivity (σ) of the cubic phase exhibits a thermally activated behavior at high temperature. The variation of σ with the oxygen content is non-linear and the activation energy varies from 0.4 to 0.28 eV as the oxygen content increases from 2.4 to 2.6. These results are interpreted in the frame of the small polaron model.     

Tuning Magnetic Properties of CeO2 by Fe Doping via an Electrochemical Deposition Route

Herein Ce_1?xFe_xO_2?δ nanocomposites were investigated for dilute magnetic semiconductor (DMS) properties. Ce_1?xFe_xO_2?δ nanospheres and porous nanostructures with high surface areas have been successfully prepared by electrochemical deposition at room temperature and atmospheric pressure. The structures and morphologies of Ce_1?xFe_xO_2?δ deposits were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption–desorption techniques. The magnetic properties of the prepared Ce_1?xFe_xO_2?δ nanospheres and porous nanostructures were studied, and they showed room‐temperature ferromagnetism and giant magnetic moments. In addition, the effects of morphologies and compositions on the magnetic properties of Ce_1?xFe_xO_2?δ deposits were studied.     

A novel cathode material BaCe0.4Sm0.2Co0.4O3−δ for proton conducting solid oxide fuel cell

A novel cathode material BaCe_0.4Sm_0.2Co_0.4O_3−δ composed of two phases BaCe_1−x(Sm/Co)_xO_3−δ and BaCo_1-x(Sm/Ce)_xO_3−δ was prepared in situ via the citric–nitrate route and its performance as cathode material for proton conducting solid oxide fuel cell (SOFC-H) was characterized. BaCe_0.4Sm_0.2Co_0.4O_3−δ exhibited simultaneous protonic, electronic, and oxygen ionic conduction in air, leading to a good electrode performance. The polarization resistance of the novel cathode material in symmetrical cell was 0.36 Ω cm² with Pt as the current collector at 700 °C in wet air. The electrode performance can be further improved through microstructure optimization. It also showed good thermal expansion compatibility with BaCe_0.8Sm_0.2O_3−δ electrolyte over a 100 h duration test. BaCe_0.4Sm_0.2Co_0.4O_3−δ is a promising cathode material for SOFC-H.     

Promising membrane materials based on strontium titanate

Electroconductivity of SrTi_1?x Fe _x O_3?δ(x = 0–0.5) specimens was studied by four-probe method. An opportunity was studied to produce hydrogen by high-temperature electrochemical conversion using SrTi_0.5Fe_0.5O_3?δ as the membrane material of the best conductivity. The effective ambipolar conductivity values calculated for SrTi_0.5Fe_0.5O_3?δ from the leakage experiment were found different from the ambipolar conductivity values calculated by the four-probe data processing because ambipolar conductivity corresponds to bulk transfer of complex oxide particles, taking no surface phenomena into account.     

MnTaO2N: Polar LiNbO3‐type Oxynitride with a Helical Spin Order

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO₂N are reported. High‐pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high‐density structure containing middle‐to‐late transition metals. Synchrotron X‐ray and neutron diffraction studies revealed that MnTaO₂N adopts the LiNbO₃‐type structure, with a random distribution of O^2? and N^3? anions. MnTaO₂N with an “orbital‐inactive” Mn²⁺ ion (d⁵; S=5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] (δ≈0.3), which is different from the conventional G‐type order observed in other orbital‐inactive perovskite oxides and LiNbO₃‐type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO₄N₂ octahedral network combined with the mixed O^2?/N^3? species that results in a distribution of (super)‐superexchange interactions.