Structural, Thermal and Electrical Properties of Ce-Doped SrMnO3

The Sr_1-xCe_xMnO_1- system (0 x 0.5) was investigated with respect to its structural, thermal and electrical properties. Although un-doped SrMnO₃ has the perovskite structure above 1400°C, the structure is unstable at room temperature. However, partial substitution of Ce for Sr in SrMnO₃ stabilizes the perovskite structure down to room temperature. Single phase perovskite is obtained for 0.1 x 0.3 in Sr_1-xCe_xMnO_1-, and it remains stable even following heat treatment at 800°C for 100 h. The dependence of the electrical conductivity on temperature was measured from room temperature to 1000°C in air. Ce doping dramatically enhanced the electrical conductivity of SrMnO₃. Sr_0.7Ce_0.3MnO_1- exhibits a higher conductivity (290 S · cm^-1 at 1000°C) than that of La_0.8Sr_0.2MnO₃ (LSM, about 175 S · cm^-1) and remains n-type over the whole range of temperature examined. The thermal expansion coefficients in the system were nearly constant with values ranging between 1.24 × 10^-6 and 1.01 × 10^-6 cm/cm · K for temperatures of 50°C to 1000°C.     

溶胶-凝胶法在纳米La1-xMxCrO3粉料制备中的应用

掺杂二价碱土金属的铬酸镧是目前研究最深入和应用效果最好的固体氧化物燃料电池(SOFC)的连接材料,它几乎占整个SOFC制造成本的一半。制备工艺有固相法、溶胶-凝胶法、化学共沉淀法、联氨法和水热法等。本文综述了溶胶-凝胶法及用该方法制备La1-xMxCrO3(M=Sr,Ca)材料的现状。     

自蔓延高温合成技术法合成La0.7Sr0.3MnO3过程的热力学分析

通过热力学计算研究自蔓延高温合成技术合成La0.7Sr0.3MnO3反应机制。结果表明：对于Mn，La2O3，SrCO3，NaClO4组成的自蔓延高温合成La0.7Sr0.3Mn0.3反应体系，理论上Mn粉优先与La2O3反应生成LaMnO3，低温下Mn粉优先与O2反应生成少量MnOx，大部分剩余的Mn粉高温（〉1417K）下优先与O2反应生成SrMnO3；同时，少量低温（〈1417K）时形成的MnOx与SrCO3反应生成SrMnO3。高温下，SrMnO3与LaMnO3反应生成La0.7Sr0.3MnO3，这是SHS法合成La0.7Sr0.3MnO3的主要途径。另外，当温度大于1235K时，少量La2O3与SrCO3反应生成La2SrOx，La2SrOx再与LaMnO3反应生成La0.7Sr0.3Mn0.3。     

Preparation of thin film YSZ electrolyte by using electrostatic spray deposition

Yttria-stabilized zirconia (YSZ) thin film was successfully deposited onto Ni–YSZ anode disk by the electrostatic spray deposition (ESD) technique. To deposit a dense YSZ thin film onto porous Ni–YSZ substrate, the influence of process parameter variables were examined. The relationship between process parameters and morphologies of YSZ films coated by ESD was investigated by means of SEM photography and X-ray diffraction (XRD). The result showed that dense YSZ film of average 10–15 μm thickness was deposited on the porous Ni–YSZ substrate with temperature of 400 °C, the precursor solution concentration of 0.05 M, nozzle-to-substrate distance of 30 mm, applied electric field of 18 kV, and deposition time of 90 min.     

Fabrication and evaluation of solid-oxide fuel cell anodes employing reaction-sintered yttria-stabilized zirconia

This paper reports on the fabrication and performance of solid-oxide fuel cell (SOFC) anodes utilizing yttria reaction-sintered zirconia (YRSZ). Through the reaction-sintering process, the technical-grade YSZ commonly used in the Ni-YSZ anode cermet is replaced with lower-cost ZrO₂ and Y₂O₃ materials. When sintered in the presence of nickel oxide, ZrO₂ and Y₂O₃ form cubic-phase YSZ at temperatures characteristic of SOFC processing (1400-1550 °C). Reaction sintering enables the formation of YSZ during cell fabrication, reducing SOFC anode raw-materials cost and the number of SOFC-fabrication processes. This paper reports the results of a broad range of characterization and performance measurements to evaluate the YRSZ material, including (1) crystal structure, (2) morphology, (3) pore-size distribution, (4) electronic resistivity, (5) fracture strength, (6) gas transport and catalytic activity, and (7) electrochemical performance. Material properties and performance are found to be comparable to or better than equivalent materials fabricated by conventional processes.     

3D reconstruction of SOFC anodes using a focused ion beam lift-out technique

Improvements to electrode performance are essential to accelerate the commercialisation of SOFC technology. A key metric of performance for SOFC electrodes is the length and distribution of three or triple phase boundaries (TPBs) which provide an indication of electrochemical performance. Techniques that can be used to characterise TPB length are highly valuable; with an increasing knowledge of electrode microstructures, electrochemical performance can be optimised. One such technique for electrode characterisation uses focused ion beams (FIB) to sequentially mill and image an electrode surface, obtaining a sequence of 2D images that may be reconstructed in a 3D space. In this paper we present a technique to maximise the quality of the raw data obtained via ex-situ characterisation of electrode micro-sections based on FIB lift-out. With improved raw data, we have been able to conduct semi-automated image analysis to extract key microstructural information, including the length and distribution of TPBs.Reconstructions have been carried out using both single and dual beam instruments; two reconstructions of Ni-YSZ anode structures are presented here.     

Placement of reference electrode in solid electrolyte cells

The placement of reference electrodes in solid state ionic conductors is not as flexible as in liquid state electrochemistry. This is in particular a problem when material from the gas phase is involved, as in solid oxide fuel cell. Many of the arrangements used are problematic: either they produce results that are very sensitive to electrode placement, change the potential distribution, do not provide a uniform current density and overpotential at the electrode or require delicate patterns liable to fail. We here present a new approach suitable for thin layer SOFC. It includes a calibration procedure derived from numerical simulations in combination with experiments. This allows the use of the common three-electrode arrangement on thin solid electrolyte (SEs) where the reference electrode is placed side by side with the working electrode, on an extension of the thin layer SE. This is so despite the sensitivity of that arrangement to both misalignment of the electrodes and to a difference in the impedance of the two current carrying electrodes. The misalignment tolerated, with the present method, may exceed the SE thickness. The allowed misalignment increases with the electrode/SE impedance ratio. The method copes also with the difference in the electrode impedance. Two special configurations are discussed in which the calibration is not required. However, these require a more accurate preparation technique of the cell.     

Status and prospects of intermediate temperature solid oxide fuel cells

Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commercial applications, but it still faces many problems which hamper large-scale commercial applications of SOFC. To reduce the cost of SOFC, intermediate temperature solid oxide fuel cell （IT-SOFC） is presently under rapid development. The status of IT-SOFC was reviewed with emphasis on discussion of their component materials. 2008 University of Science and Technology Beijing. All rights reserved.     

Development of high strength ferritic steel for interconnect application in SOFCs

High-Cr ferritic model steels containing various additions of the refractory elements Nb and/or W were studied with respect to oxidation behaviour (hot) tensile properties, creep behaviour and high-temperature electrical conductivity of the surface oxide scales. Whereas W additions of around 2 wt.% had hardly any effect on the oxidation rates at 800 and 900 °C, Nb additions of 1% led to a substantially enhanced growth rate of the protective surface oxide scale. It was found that this adverse effect can be alleviated by suitable Si additions. This is related to the incorporation of Si and Nb into Laves phase precipitates which also contribute to increased creep and hot tensile strength. The dispersion of Laves phase precipitates was greatly refined by combined additions of Nb and W. The high-temperature electrical conductivity of the surface oxide scales was similar to that of the Nb/W-free alloys. Thus the combined additions of Nb, W and Si resulted in an alloy with oxidation resistance, ASR contribution and thermal expansion comparable to the commercial alloy Crofer 22 APU, but with creep strength far greater than that of Crofer 22 APU.