Zhe Lü

Thermal and electrical properties of new cathode material Ba0.5Sr0.5Co0.8Fe0.2O3-delta for solid oxide fuel cells

A newly developed cathode material, Ba0.5Sr0.5Co0.8Fe0.2O3-delta, was synthesized and characterized. X-ray diffraction results identified it as a cubic perovskite structure. Thermogravimetric results showed that lattice oxygen loss was about 2% in weight between 50 and 1000 degrees C. Thermal expansion coefficient results in air and argon were extraordinarily high, with slope changes occurring at about 382 and 360 degrees C, respectively. Electrical conductivity values were sufficient for cathode application with the maximum of about 28.1 S cm(-1) at 500 degrees C in air and 17.3 S cm(-1) at 900 degrees C in N-2, correspondingly. Both thermal and electrical properties were closely associated with lattice oxygen behaviors and oxygen partial pressure. (c) 2005 The Electrochemical Society.

Mixed valence state and electrical conductivity of La1-xSrxCrO3

La1-xSrxCrO3 (x=0.0 similar to 0.5) samples were prepared by the sol-gel method. The crystal structures of La1-xSrxCrO3 at room temperature all are of the othorhombic perovskite GdFeO3-type. XPS analysis indicates that chromium ions are in mixed valence state. The introduction of Sr2+ into the lattice is compensated by the oxidation from Cr3+ to Cr6+ With x increasing, the amount of Cr6+ increases. The presence of the Cr6- is one of the key factors that affect the electric conductivity of La1-xSrxCrO3

Study on the properties of Al2O3-doped (ZrO2)0.92(Y2O3)0.08 electrolyte

Abstract Alumina (Al 2 O 3 ) is doped into cubic structured yttrium stabilized zirconia (ZrO 2 ) 0.92 (Y 2 O 3 ) 0.08 (YSZ) by a ceramic method. The influence caused by the access of Al 2 O 3 on the sintering behavior, mechanical and electrical properties of YSZ are studied, and the mechanism is analyzed. The experiments show that doping Al 2 O 3 to YSZ can significantly improve the sintering behavior by reducing sintering temperature. Impedance analysis shows that the electrical properties can be also improved by doping Al 2 O 3 because of the improvement of grain boundary conditions. YSZ doped with different amount of Al 2 O 3 have different grain boundary conductivities among which the highest value belongs to the specimen of YSZ doped with 4 wt% Al 2 O 3 . Pure YSZ and YSZ doped with 4 wt% Al 2 O 3 are used as the electrolytes to make SOFCs. The performance of SOFC with an Al 2 O 3 doped electrolyte is better than that with a pure YSZ one.

Nanostructured ( Ba , Sr ) ( Co , Fe ) O3 − δ Impregnated ( La , Sr ) MnO3 Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

A nanostructured cathode is fabricated by incorporating a mixed ionic and electronic conducting (MIEC) perovskite, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF), via ion impregnation into the most common, highly electronic conducting, and structurally stable La 0.8 Sr 0.2 MnO 3-δ (LSM) porous cathode skeleton. The introduction of nanosized MIEC BSCF particles significantly improves the electrocatalytic activity of the LSM for the oxygen reduction reaction of solid oxide fuel cells at an intermediate temperature range of 600-800°C. The electrode polarization resistance of a 1.8 mg cm -2 BSCF-impregnated LSM cathode is 0.18 Ω cm 2 at 800°C, which is ~12 times lower than that of pure LSM. A single cell with an yttria-stabilized zirconia (YSZ) electrolyte film and the nanostructured BSCF/LSM cathode exhibits maximum power densities of 1.21 and 0.32 W cm -2 at 800 and 650°C, respectively. The atomic force microscopy (AFM) studies of the electrode/electrolyte interface before and after polarization indicate that the impregnation of BSCF extends the three-phase boundary area for the oxygen reduction reaction from the electrode/electrolyte interface to the electrode bulk. The formation of a second phase was also observed by AFM for the BSCF-impregnated LSM after being heat-treated at 800°C though its phase could not be identified due to the extremely small amount of the second phase particles on the YSZ electrolyte surface. The initial structure and polarization performance stability of the nanostructured BSCF-impregnated LSM composite cathodes are also investigated.

Synthesis and luminescence of europium doped yttria nanophosphors via a sucrose-templated combustion method

Nanocrystalline Y2O3:Eu phosphors have been successfully synthesized by a novel combustion method using sucrose as a chelating agent and fuel. The sucrose hydrolysation and complexing mechanisms are discussed. X-ray diffraction analysis showed that the cubic phase can be formed at a low temperature of 400 °C, and transmission electron microscopy observations revealed that the phosphor particles were 30–50 nm annealed at 1000 °C. The post-treated Y2O3:Eu nanophosphors yield intense red emission at 610 nm, corresponding to the 5D0–7F2 transitions. The luminescence properties of the Y2O3:Eu particles were strongly affected by the annealing temperatures and the sucrose to metal ion ratios. This work demonstrates that the sucrose combustion process can be a quasi-universal medium for the preparation of nanoscale phosphors.

Ag2O–Bi2O3 composites: synthesis, characterization and high efficient photocatalytic activities

Ag2O nanoparticle modified α-Bi2O3 composite photocatalysts were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy. XRD patterns confirmed that the composites consist of cubic phase Ag2O and monoclinic α-Bi2O3 phase. The Ag2O loading was greatly increased due to the rough surface of the acid etched Bi2O3 microrods. Photocatalytic activity of the Ag2O–Bi2O3 composites was evaluated using the degradation of methyl orange (MO). The correlation between the Ag2O content and photocatalytic activity was estimated. The composite with Ag to Bi ratio of 3 : 1 as raw material showed the highest visible light activity and the enhancement mechanism was attributed to the separation of photoinduced electron and holes by the carrier transfer.

Properties of nonstoichiometric Pr0.6−xSr0.4MnO3 as the cathodes of SOFCs

A series of samples Pr0.6-xSr0.4MnO3 (x = 0, 0.01, 0.05, 0.1, 0.15, 0.2) were synthesized by a solid state reaction method. Pr deficiency at the A site has a great effect on the properties of Pr0.6-xSr0.4MnO3 as the cathode of SOFCs (solid oxide fuel cells). Compared to the commonly used La0.6Sr0.4MnO3 and La0.55Sr0.4MnO3 cathode, Pr0.6-xSr0.4MnO3 is better in the properties of conductivity, overpotential and impedance. In all the samples, the one with x = 0.05, Pr0.55Sr0.4MnO3, revealed the best performance in the measured temperature range

Characterization of YSZ electrolyte membrane tubes prepared by a vacuum casting method

Abstract Eight mol% YSZ electrolyte membrane tubes with a thickness of 0.2 mm were made using a vacuum casting method. The sintered densities, microstructure and electrical conductivity of the YSZ electrolyte membrane tubes were studied using the Archimedes water immersion technique, SEM and complex impedance, respectively. The sintering temperature corresponding to optimal sinterability for the YSZ electrolyte membrane tubes was determined. The research results show that vacuum casting is a simple way of preparing YSZ electrolyte membrane tubes with high density and high electrical conductivity. YSZ electrolyte membrane tubes with a relative density of 98.1% and 254 mm in length are fabricated using this method. The range of sintering temperatures is 190–200°C lower than that of the conventional slip casting. The densification and the electrical conductivity of the samples increase gradually with the increase of the sintering temperature. The density and electrical conductivity of the samples reach an optimum value at a sintered temperature of 1600°C for 2 h. As the sintering temperatures are raised further, both the density and the electrical conductivity of the samples decrease.

A study on PrMnO3-based perovskite oxides used in SOFC cathodes

Two series of samples Pr1-xSrxMnO3 (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and Pr0.6-ySr0.4MnO3 (y=0, 0.01, 0.05, 0.1, 0.15, 0.2) were synthesized by a solid state reaction method. In the former series, the sample with x=0.4 exhibited the highest conductivity in the range of experimental temperature. Pr deficiency at the A site has a great effect on the properties of Pr0.6-ySr0.4MnO3 as a cathode of solid oxide fuel cells. Compared to the commonly used La0.6Sr0.4MnO3 cathode, Pr0.6-ySr0.4MnO3 has better properties of electrical conductivity, overpotential and impedance. Of all the samples, it is revealed that the one with y=0.05, Pr0.55Sr0.4MnO3 has the best performance in the measured temperature range

Anode-Supported Micro-SOFC Stacks Operated under Single-Chamber Conditions

A micro solid oxide fuel cell (SOFC) stack with two series-wound single fuel cells was fabricated and operated successfully under single-chamber conditions. In this stack, the single cells were based on Ni/yttria-stabilized zirconia (YSZ) anode-supported YSZ membrane and were arranged with an anode-facing-cathode configuration in diluted methane and oxygen mixture gas between 600 and 750 degrees C. The performances of the stack were affected by the flow rate, gas composition, and furnace temperature. The effects of the narrow path between two cells on the electrodes and cells were discussed in detail, according to the open-circuit voltages (OCVs) and impedance spectra of each cell. At 700 degrees C, the maximum OCV of the whole stack was larger than 2.0 V at CH4/O-2=1.75 and 2, while the maximum power output of stack was about 371 mW at CH4/O-2=1 with a mass specific power of 552 mW/g. The performance indicates that such microstacks have potential for portable applications. (c) 2007 The Electrochemical Society.