钙钛矿型中温固体电解质La0.9Sr0.1Ga0.8Mg0.2O3-δ的制备

以硝酸盐为前驱体合成了具有钙钛矿结构的中温固体电解质La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM)。用XRD和SEM分析了样品钙钛矿相的形成过程和显微结构,用直流四电极法测试了电解质的氧离子电导率。研究结果表明:经1 450℃煅烧6 h后得到LSGM单相结构,800℃时的电导率为6.8×10-2S.cm-1,高于同温下钇稳定氧化锆(YSZ)样品的电导率,表明LSGM更适合做中温固体氧化物燃料电池(SOFC)的电解质材料。     

Infiltrated La0.5Ba0.5CoO3-δ in La0.8Sr0.2Ga0.8Mg0.2O2.8 scaffolds as cathode material for IT-SOFC

The electrochemical response of infiltrated La_0.5Ba_0.5CoO_3-δ (LBC) in porous La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 (LSGM) has been investigated. The thermal expansion coefficient (TEC) of the resulting electrode was measured, obtaining α?=?12.5?×?10^?6 K^?1, a value similar to that of LSGM. The polarization resistance (Rp) and the processes involved in the oxygen reduction reaction (ORR) for the new electrode were studied and analyzed through complex impedance spectroscopy measurements as a function of temperature and oxygen partial pressure (pO₂), using a symmetrical cell. The value of Rp for the infiltrated LBC turned out to be lower than that measured for an electrode prepared with a composite LBC-LSGM (1:1?wt%) by an order of magnitude, for the temperature range 750?°C ≤ T?≤?900?°C, and about 5 times lower for the temperature range 450?°C≤ T?≤?650?°C. At 600?°C, the LBC infiltrated cathode exhibits a polarization resistance R_p =?0.22?Ω?cm², in air. The complex impedance spectra show two processes, one identified as low frequency (LF),with a characteristic frequency of 10?Hz, and the other as intermediate frequency (IF), with a range between 0.05 and 2000?Hz. The LF process could be associated to the diffusion of oxygen in the gas phase through the pores of the electrode. Its resistance, R_LF =?0.01?Ωc?m²_, was found to be independent of the temperature and half of that obtained for the LBC composite cathode. On the other hand, the IF process is related to charge transfer at the electrode surface and the electrode-electrolyte interface. The LBC cobaltite infiltrated in the LSGM scaffolds offers an adequate thermal expansion coefficient and good electrocatalytic activity for the ORR.     

Study on Properties of LSGM Electrolyte Made by Tape Casting Method and Applications in SOFC

Solid oxide fuel cell is attracting more attention in recent years for its lower pollution emission and high energy convert efficiency. La0.9Sr0.1Ga0.8Mg0.2O3-δ is a new kind of electrolyte for intermediate temperature SOFC. In this paper, La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) was prepared by solid state reaction method and formed by tape casting process to make a planar electrolyte. The appropriate amount of the dispersive was obtained by viscosity test. The densities of sintered samples increase with the increasing sintering temperature. It was found that the relative density of electrolyte can approach the value of 95% by the isostatic pressing treatment of the green tape. The average thermal expansion coefficient of the LSGM is 11.4×10-6/℃ at temperature range (200～1200 ℃). Measurements of the current-voltage and power-current characteristics of the H2-Air cell show that the open-circuit voltage is 1.067 V at 800 ℃, peak current density is 0.56 A·cm-2 and the maximum power output is 0.147 W·cm-2.     

Assessment of layered La2-x(Sr,Ba)xCuO4-δ oxides as potential cathode materials for SOFCs

In this paper, selected layered cuprates with La_2-x(Sr,Ba)_xCuO_4-δ formula are evaluated as candidate cathode materials for Solid Oxide Fuel Cells. Two synthesis routes, a typical solid state reaction and a sol-gel method yield well-crystallized La_1.5Sr_0.5CuO_4-δ, La_1.6Ba_0.4CuO_4-δ and La_1.5Sr_0.3Ba_0.2CuO_4-δ materials having tetragonal I4/mmm space group, but differing in morphology of the powder. Fine powders obtained using sol-gel route seem to be more suitable for preparation of the porous cathode layers having good adhesion on the solid electrolyte, but powders obtained after the solid state route can be also successfully utilized. Investigations of structural and transport properties, the oxygen nonstoichiometry and its change with temperature, thermal expansion, as well as chemical and thermal stability are systematically performed, to evaluate and compare basic physicochemical properties of the oxides. At room temperature the average valence state of copper is found to be in 2.2–2.35 range, indicating oxygen deficiency in all of the compounds, which further increases with temperature. The conducted high-temperature X-ray diffraction tests reveal moderate, but anisotropic thermal expansion of La_2-x(Sr,Ba)_xCuO_4-δ, with higher expansion at temperatures above 400 °C occurring along a-axis, due to the oxygen release. However, the corresponding chemical expansion effect is small and the materials possess moderate thermal expansion in the whole studied temperature range. All compounds show relatively high electrical conductivity at the elevated temperatures, related to the Cu²⁺/Cu³⁺ charge transfer, with the highest values recorded for La_1.5Sr_0.5CuO_4-δ. Comprehensive studies of chemical stability of the selected La_1.5Sr_0.5CuO_4-δ material with La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ solid electrolyte revealed complex behavior, with stability being dependent apart from temperature, also on morphology of the powders. A model describing such behavior is presented. While it is possible to minimize reactivity and characterize electrochemical properties of the La_1.5Sr_0.5CuO_4-δ-based cathode layer, usage of the buffer layer is indispensable to maintain full stability. It is shown that mutual chemical compatibility of La_1.5Sr_0.5CuO_4-δ and commonly used La_0.4Ce_0.6O_2-δ buffer layer material is excellent, with no reactivity even at 1000 °C for prolonged time. Laboratory-scale fuel cell with the La_1.5Sr_0.5CuO_4-δ cathode sintered at the optimized temperature is able to deliver 0.16 W cm^?2 at 800 °C while fueled with wet hydrogen.     

Contribution of electron precession to the study of perovskites displaying small symmetry departures from the ideal cubic ABO3 perovskite: applications to the LaGaO3 and LSGM perovskites

Electron microscopy and electron diffraction are well adapted to the study of the fine‐grained, faulted pure and doped LaGaO₃ and LSGM perovskites in which the latter is useful for fuel cell components. Because these perovskites display small symmetry departures from an ideal cubic ABO₃ perovskite, many conventional electron diffraction patterns look similar and cannot be indexed without ambiguity. Electron precession can easily overcome this difficulty mainly because the intensity of the diffracted beams on the precession patterns is integrated over a large deviation domain around the exact Bragg condition. This integrated intensity can be trusted and taken into account to identify the ‘ideal’ symmetry of the precession patterns (the symmetry which takes into account both the position and the intensity of the diffracted beams). In the present case of the LaGaO₃ and LSGM perovskites, the determination of the ‘ideal’ symmetry of the precession patterns is based on the observation of weak ‘superlattice’ reflections typical of the symmetry departures. It allows an easy and sure identification of any zone axes as well as the correct attribution of hkl indices to each of the diffracted beams. Examples of applications of this analysis to the characterizations of twins and to the identification of the space groups are given. This contribution of electron precession can be easily extended to any other perovskites or to any crystals displaying small symmetry departures.     

EDTA溶胶-凝胶法制备LSGM8282和LSGMF5及其性能比较

采用EDTA络合溶胶-凝胶法合成了中温固体氧化物燃料电池的电解质LSGM8282(La0.8Sr0.2Ga0.8-Mg0.2O3-δ)和LSGMF5(La0.8Sr0.2 Ga0.8Mg0.15Fe0.05O3-δ),比较了LSGM8282和LSGMF5的比表面积、交流阻抗谱、电导率、密度、XRD和FT-IR等,研究了Fe掺杂对LSGM8282性能的影响.结果表明,Fe掺杂使LSGM8282离子的电导率由3.62×10-2S/cm提高到5.21×10-2S/cm,致密度由95.13%提高到97.93%.由此可见,Fe的掺杂使LSGM8282的各种性能均得到一定提升,LSGMF5比LSGM8282更适合作中温SOFC电解质材料.     

La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-α)的柠檬酸盐法制备和表征

采用柠檬酸盐法制备了　Ｌａ０．９Ｓｒ０．１Ｇａ０．８Ｍｇ０．２Ｏ３－α（ＬＳＧＭ）粉体材料．ＴＧ和　ＤＴＡ分析表明,凝胶在２６５～３０９℃下分解为相应的氧化物．ＸＲＤ测试表明,凝胶在１３００℃以上煅烧时,转变为简单立方钙钛矿结构的纯相产物．１４５０℃下烧结体的相对密度为８８％,其复阻抗特性表明产物中没有明显的晶界过程,且在８００℃下的电导率为 ２.１×１０－２Ｓｃｍ－１,活化能为０．９８ｅＶ．     

La0.9Sr0.1Ga0.8M0.2O3-δ (M = Mn, Co, Ni, Cu or Zn): Transition metal-substituted derivatives of lanthanum-strontium-galliummagnesium (LSGM) perovskite oxide ion conductor

Perovskite oxides of the general formula, La_0.9Sr_0.1Ga_0.8M_0.2O_3-δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities (σ R∼ 10⁻² S/cm at 800°C) comparable to that of the best perovskite oxide ion conductor, La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) (σ ∼ 8 × 10⁻² S/cm at 800°C). While M = Mn, Co, Ni, Cu members appear to be mixed conductors with a variable electronic contribution to the conductivity, especially at high oxygen partial pressures (pO₂ ≥1 atm), arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting a conductivity (σ ∼ 1.5 × 10⁻² S/cm at 800°C) that is slightly lower than that of LSGM. The lower conductivity of the M = Zn(II) derivative could be due to the preference of Zn(II) for a tetrahedral oxygen coordination.     

掺杂LaGaO3中温固体氧化物燃料电池电解质

叙述了掺杂LaGaO3(LSGM)作为优良的中温SOFC电解质的研究现状.在800℃左右,10-16≤PO2≤105Pa氧分压范围内,LSGM几乎是单纯的氧离子导体,具有较高的电导率,σ大于或等于0.1S/cm,而且长期保持稳定.在LSGM中掺杂少量低价金属阳离子,可望提高LSGM的电导率.LSGM存在的主要问题是Ga的蒸发.LSGM粉末的制备方法主要有3种:固态反应法、尿素法和Sol-gel法.     

Limiting current oxygen sensor based on La0.8Sr0.2Ga0.8Mg0.2O3−δ as both dense diffusion barrier and solid electrolyte

La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) was synthesized by a high temperature solid-state reaction. The crystal structure, relative density and electrical conductivity were measured with XRD, Archimedes method, and Van Der Pauw DC four-probe method. A limiting current oxygen sensor based on LSGM as both solid electrolyte and dense diffusion barrier was prepared by a Pt paste bonding method. The results show that LSGM has pure perovskite structure (cubic symmetry with space group of Pm-3m (No.221)), high density (relative density is 97.6%) and electrical conductivity (0.18 S∙cm⁻¹ at 1073 K). The sensor works optimally over temperature range of 973‒1123 K and oxygen concentration of 1.92%‒21%. The operating voltage ranges from 0.67 to 0.98 V. The limiting current is in proportion to oxygen concentration. The sensor has the highest sensitivity at 1123 K and low measurement error of less than 4%.