Wenhui Su

Synthesis and characterization of IT-electrolyte with perovskite structure La0.8Sr0.2Ga0.85Mg0.15O3−δ by glycine–nitrate combustion method

The intermediate-temperature electrolyte with perovskite-type La0.8Sr0.2Ga0.85Mg0.15O3-delta (LSGM) was synthesized using glycinenitrate combustion method. The formation process of the LSGM phase was investigated using DTA-TGA and XRD, and the thermal and electrical properties of the sintered samples were studied by thermal expansion and ac impedance technology. The research results show that the formation process of the LSGM phase suffered several different reaction stages. The perovskite phase was formed essentially at a sintering temperature of 1200 degreesC. The stable perovskite phase was formed completely after a sintering temperature of 1400 degreesC. The sinterability shows that the sintering temperature of the sample, which was synthesized by glycine-nitrate combustion method, is at least 100 degreesC lower than that of the conventional solid state method that was reported previously. The thermal expansion coefficient of the LSGM is somewhat higher than that of the YSZ. Impedance spectra indicate that the grain boundary resistance of the LSGM synthesized by glycine-nitrate combustion method is smaller. The conductivity of sample sintered at 1500 degreesC is higher than that at 1550 degreesC. The conductivity of a sample is 7.8X10(-2) S cm(-1) at 850 degreesC. The thermal analysis shows that the LSGM is relatively stable over an intermediate temperature range of 500-800 degreesC

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.

Enhanced high temperature thermoelectric characteristics of transition metals doped Ca3Co4O9+δ by cold high-pressure fabrication

A series of Fe, Mn, and Cu doped Ca(3)Co(4)O(9+delta) samples, Ca(3)(Co,M)(4)O(9+delta) (M=Fe, Mn, and Cu), were fabricated by cold high-pressure compacting technique. Their thermoelectric properties were investigated from room temperature up to 1000 K. The cold high-pressure compacting method is advantageous to increasing density and texture, in favor of the improvement of thermoelectric performance. The electrical transport measurements indicate that Fe/Mn substitutes for Co mainly in [CoO(2)] layers whereas the substitution of Cu for Co takes place in [Ca(2)CoO(3)] layers. The thermoelectric properties as well as electronic correlations depend not only on the substitution ion but also the Co site that is replaced. Thermopower can be well calculated by the carrier effective mass according to Boltzmann transport model, indicating that the electronic correlation plays a crucial role in the unusual thermoelectric characteristics of this system. From the changes in thermopower, resistivity, and thermal conductivity, thermoelectric performance of Ca(3)Co(4)O(9+delta) is efficiently improved by these transition metals doping. Fe doped samples possess the highest ZT values. Combining cold high-pressure technique, ZT of Ca(3)Co(3.9)Fe(0.1)O(9+delta) can reach similar to 0.4 at 1000 K, which is quite large among ceramic oxides, suggesting that Fe doped Ca(3)Co(4)O(9+delta) could be a promising candidate for thermoelectric applications at elevated temperatures.

High temperature thermoelectric characteristics of Ca0.9R0.1MnO3 (R=La,Pr,…,Yb)

Electron-doped perovskite manganite Ca0.9R0.1MnO3 (R=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) polycrystalline samples were prepared and their transport and thermoelectric properties were studied from room temperature to 1000 K. The transport behavior for all the samples is adiabatic small polaron hopping mechanism below 600 K but changes to metallic conductivity at higher temperature. Above 600 K, more 3d electrons of Mn3+ ions will occupy eg orbitals, resulting in the variation in thermoelectric power values. For all the samples, thermoelectric power is only determined by carrier concentration, but resistivity also rests with effective bandwidth. The size matching between Ca2+ and R3+ ions together with heavier R3+ doping can improve thermoelectric performance evidently. Combining these two factors, Ca0.9Dy0.1MnO3 and Ca0.9Yb0.1MnO3 reach ZT=0.2 at 1000 K, suggesting that they can be efficient high temperature n-type thermoelectric oxide materials.

Correlation between the Structural Distortions and Thermoelectric Characteristics in La(1-x)A(x)CoO(3) (A = Ca and Sr)

Detailed structures and thermoelectric (TE) properties are investigated for the perovskite La(1-x)Ca(x)CoO(3) and La(1-x)Sr(x)CoO(3) with 0 <or= x <or= 0.3. The monoclinic crystal structures for all samples are refined from powder X-ray diffraction, which reveals that the La(1-x)Sr(x)CoO(3) series has smaller global distortions but larger local distortions. The different structural distortions strongly influence the transport and TE properties in terms of resistivity, thermopower, thermal conductivity, bandwidth, and effective mass as well as electronic correlation. These results unambiguously demonstrate a close correlation between the structural distortions and TE characteristics in this family. Furthermore, a new approach is suggested to improve the TE performance by controlling the structure factors in such strongly correlated oxide systems. The effects of the spin-state transition of Co ions on the TE properties are also discussed.

Single intermedium-temperature SOFC prepared by glycine-nitrate process

A combustion synthesis method, the glycine-nitrate process, was used to prepare all nano-size materials used in a single intermedium-temperature solid-oxide fuel cell (IT-SOFC). Samaria-doped ceria (CeO2)(0.9)(SmO1.5)(0.1) (SDC) was used as electrolyte, La0.6Sr0.4Fe0.8Co0.2O3 (LSCF) with 50 wt% SDC was selected as the cathode, and a SDC-Ni composite powder was used as the anode. In this study, the performance of the SOFC was obtained from 250 to 750 degreesC. The highest open circuit voltage was about 0.95 V at 450 degreesC and the maximum power density of 0.104 W cm(-2) and a short circuit current density of 500 mA cm(-2) of the cell were achieved at 750 degreesC. The initial cell performance showed that, with a proper choice of synthesis process and technology, a SOFC using CeO2-based materials as electrolyte operating at IT-temperature is a realistic goal

Enhanced electron correlation in rare-earth doped Ca3Co4O9

Thermoelectric and thermodynamic properties of a series of Ca-site rare-earth R3+ doped Ca3Co4O9 were investigated. For a fixed doping level, with the reduction in R3+ radius, thermopower is found to gradually increase despite the carrier concentration remains unchanged. The scaling behavior between thermopower and electron specific heat coefficient reveals that the additional increase in thermopower originates from enhanced electron correlation which may be attributed to doping-induced chemical pressure.

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.

Lactate oxidation in pyrite suspension: a Fenton-like process in situ generating H2O2.

Pyrite is a common mineral at many mining sites. In this study, the mineral pyrite was studied as a Fenton-like reagent for environmental concerns. We selected lactate as a model target molecule to evaluate the Fenton-like catalytic efficiency of pyrite upon organic oxidation. A complete set of control experiments in both aerobic and anaerobic atmospheres unequivocally established that the pyrite in aqueous solution could spontaneously in situ generate (·)OH and H(2)O(2), serving as a Fenton-like reagent to catalyze the oxidation of lactate to pyruvate with no need for additional H(2)O(2). We called it the pyrite-only Fenton-like (PF) reagent. Monitoring concentration changes of lactate and pyruvate with the time indicated that the pyrite mediated the favorable pyruvate formation at pH 4.5, 60 °C, under air atmosphere. The PF reaction could be stimulated by visible light illumination. Under the optimum conditions, up to 50% of lactate was degraded within 10d. The results suggest that pyrite and its Fenton-like processes may be potentially practical in wastewater treatment.