Copper-based electrodes for IT-SOFC

Copper and gadolinium doped ceria (GDC) anode supported fuel cells were co-sintered at relatively low temperature (900 °C) and successfully tested in the intermediate temperature (IT) range. The GDC electrolyte densification was promoted by a compressive strain induced by increasing the anodic thickness and was evaluated by SEM investigation. Instead of more commonly used La_0.8Sr_0.2Fe_0.6Co_0.4O_3-δ, strontium and copper-doped lanthanum ferrite La_0.8Sr_0.2Fe_0.8Cu_0.2O_3-δ (LSFCu) mixed with 30 wt% GDC (LSFCu-GDC) was employed as cathodic material. Preliminary tests on Cu-GDC/GDC/LSFCu-GDC single cells showed promising results at temperature as low as 650 °C using hydrogen as fuel.     

Electrochemical performance of Nd1.93Sr0.07CuO4 nanofiber as cathode material for SOFC

Nd_1.93Sr_0.07CuO₄ nanofibers are prepared by electrospinning technique followed by a simple thermal treatment. The morphology and phase evolution of as-obtained fibers are characterized by TG-DTA, XRD, FT-IR and SEM, respectively. Typical ceramic fiber diameter is 100–200 nm, with length exceeding tens of microns. Rapid heating the nanofiber cathode at 1000 °C for 15 min results in homogeneous porous microstructure and good contact with the CGO electrolyte. EIS analysis of the nanofiber electrode gives a polarization resistance of 0.26 Ω cm² at 700 °C in air, two times smaller than that from the powder cathode with the same composition. The excellent electrochemical performance can be attributed to the well constructed microstructure of the fiber cathode, which can promote surface oxygen diffusion or adsorption processes on the cathode.     

Performance of anode-supported solid oxide fuel cell using novel ceria electrolyte

The potential of a novel co-doped ceria material Sm_0.075Nd_0.075Ce_0.85O_2−δ as an electrolyte was investigated under fuel cell operating conditions. Conventional colloidal processing was used to deposit a dense layer of Sm_0.075Nd_0.075Ce_0.85O_2−δ (thickness 10 μm) over a porous Ni-gadolinia doped ceria anode. The current-voltage performance of the cell was measured at intermediate temperatures with 90 cm³ min⁻¹ of air and wet hydrogen flowing on cathode and anode sides, respectively. At 650 °C, the maximum power density of the cell reached an exceptionally high value of 1.43 W cm⁻², with an area specific resistance of 0.105 Ω cm². Impedance measurements show that the power density decrease with decrease in temperature is mainly due to the increase in electrode resistance. The results confirm that Sm_0.075Nd_0.075Ce_0.85O_2−δ is a promising alternative electrolyte for intermediate temperature solid oxide fuel cells.     

Physical and electrochemical characterization of Bi2O3-doped scandia stabilized zirconia

Electrolytes based on Sc₂O₃–ZrO₂ exhibit the highest ionic conductivity of zirconia based systems, however, stabilization of the electrochemical properties at operational temperatures, 600–1000 °C, are needed before implementation into SOFCs. Trace additions of Bi₂O₃ are a known sintering aid for zirconia systems. Crystal structures, electrical properties and long-term stability of Bi₂O₃-doped 10ScSZ systems were investigated. The addition of more than 1.0 mol% Bi₂O₃ resulted in suppression of the rhombohedral to cubic phase transformation at 600 °C and cubic phase stabilization at room temperature. The ionic conductivity of 10ScSZ was also improved by Bi₂O₃ additions. A maximum conductivity of 0.034 S cm⁻¹ at 700 °C was observed in 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C. No phase change was observed in 10ScSZ after annealing at 1000 °C. A certain amount of monoclinic phase, and dramatic conductivity decrease, were observed in Bi₂O₃-doped samples sintered below 1200 °C after annealing. However, 10ScSZ and 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C show no significant conductivity degradation with annealing. Samples with more than 1 mol% Bi₂O₃ and sintered above 1300 °C resulted in good ionic conductivity and stability.     

中温固体氧化物燃料电池阴极材料La_(0.7)Sr_(0.2)Co_(0.1)CuO_(3-σ)的制备与表征

用柠檬酸络合法制备超细的钙钛矿型结构的固体氧化物燃料电池阴极材料La_(0.7)Sr_(0.2)Co_(0.1)CuO_(3-σ)(LSCC).选用合适的反应条件和煅烧温度制得所需要的材料后,用DSC-TG、XRD、SEM等对粉体进行物相测定和形貌观察;选用不同温度煅烧前驱体,得到不同比表面积的粉体材料,通过半干法工艺成型LSCC阴极材料并测试它在不同温度条件下的电性能.结果表明,溶胶凝胶-高温自燃烧法能制备出超细纯相的LSCC阴极材料,且该阴极材料在中温条件下使用具有良好的导电性能(不低于150 S/cm)和输出功率(0.85 W/cm~2)和较低的活化能(112.1 kJ/mol).     

Influence of microstructure and applied current on the electrical conductivity of SmBaCo2O5+d cathode in solid oxide fuel cell

In this study, the electrical conductivity of SmBaCo₂O_5+d (SBCO) is measured and analyzed with respect to the microstructure of the analyzed samples. The microstructure is influenced by the sintering temperature and by the precise composition of the composite cathode. Difference in the electrical conductivity at different applied current is investigated. The value of the electrical conductivity of SBCO sintered at 1150 °C was about 1024 S/cm at 600 °C, which was the highest compared to other samples sintered at lower temperatures. The electrical conductivities of porous microstructural SBCO sintered at 1150 °C with an addition of 10 wt% carbon black and of a composite cathode comprised of SBCO and Ce_0.9Gd_0.1O₂ (CGO91) at a ratio of 1.9:0.1 were 256 and 525 S/cm at 600 °C. The electrical conductivities of SBCO samples increase when relatively low currents are applied. This trend can be observed at all pure SBCO and samples mixed with carbon black. However, these properties are not found in composite cathodes comprised of SBCO and CGO91.     

Gd1-xSrxCoO3-δ系阴极材料粉体的GNP法合成及表征

采用甘氨酸-硝酸盐(GNP)法合成了GdSrCoO3-δ及Gd1-xSrxCoO3-δ(x=0.1～0.5),用TG-DTA、XRD、SEM等对产物形成过程及微结构进行了表征.钙钛矿的结构随着x的增大而转变为对称性更高的晶系,当x=0.4时由正交晶系转变为立方晶系,并给出了晶系转变的XRD证据.     

Preparation and electrochemical properties of strontium doped Pr2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Pr_2−xSr_xNiO₄ (PSNO, x = 0.3, 0.5 and 0.8) cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC) were synthesized by a glycine-nitrate process using Pr₆O₁₁, Ni(NO₃)₂·6H₂O and SrCO₃ powders as raw materials. Phase structure of the synthesized powders was characterized by X-ray diffraction analysis (XRD). Microstructure of the sintered PSNO samples was observed and thermal expansion coefficient (TEC) and electrical conductivity were investigated. Electrochemical impedance spectroscopy (EIS) measurement of the PSNO materials on Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte was carried out, and single cells based on the PSNO cathodes were also assembled and their performances were tested. The results show that the synthesized PSNO powders have pure K₂NiF₄-type structure and the PSNO materials are chemically stable with Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte. The sintered PSNO samples have porous and fine microstructure with pore size smaller than 1 μm. Average thermal expansion coefficient of the PSNO materials is about 12–13 × 10⁻⁶ K⁻¹ at 200–800 °C and the electrical conductivity is in the range of 70–120 Scm⁻¹ at 800 °C. Area specific resistance (ASR) of the Pr_2−xSr_xNiO₄ materials on SCO electrolyte is 0.407 Ωcm², 0.126 Ωcm² and 0.112 Ωcm² for x = 0.3, 0.5 and 0.8 at 800 °C, respectively. Maximum open circuit voltage (OCV) and power density of the single NiO-SCO/SCO/PSNO cells are 0.75 V and 298 mWcm⁻² at 700 °C, respectively, which indicates that Pr_2−xSr_xNiO₄ may be a potential cathode material for IT-SOFC.     

Synthesis and electrochemical properties of layered perovskite substituted with heterogeneous lanthanides for intermediate temperature-operating solid oxide fuel cell

In this study, phase synthesis and electrochemical properties of Sm_1-xNd_xBa_0.5Sr_0.5Co₂O_5+d (x = 0–0.9) oxide systems where neodymium and samarium were replaced at the A-site of SmBa_0.5Sr_0.5Co₂O_5+d layered perovskite are investigated for use as cathode materials in Intermediate Temperature-operating Solid Oxide Fuel Cells (IT-SOFCs).The structure of Sm_1-xNd_xBa_0.5Sr_0.5Co₂O_5+d (x = 0–0.9) oxide systems can exist in either an orthorhombic (x = 0–0.4) or tetragonal (x = 0.5–0.9) form. The maximum electrical conductivities in Sm_1-xNd_xBa_0.5Sr_0.5Co₂O_5+d (x = 0–0.9) oxide systems were obtained from Sm_0.2Nd_0.8Ba_0.5Sr_0.5Co₂O_5+d (SNBSCO8) and their values are 1280 and 280 Scm^?1 at 50 °C and 900 °C, respectively. The area specific resistances (ASRs) of SBSCO are 3.019, 0.611, and 0.092 Ωcm² at 500, 600, and 700 °C, respectively. However, SNBSCO8 single phase gives the lowest ASRs of 1.751, 0.244 and 0.044 Ωcm² at the same temperatures tested. SNBSCO8 is thus a promising candidate cathode material for IT-SOFC applications.     

Synthesis of La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte via ethylene glycol route and its characterizations for IT-SOFC

Strontium and magnesium doped lanthanum gallate (La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ), known as LSGM, was first prepared via ethylene glycol method. This route of preparation showed improved electrical conductivity, better surface area and high density. X-ray diffraction patterns of LSGM sintered at different temperatures indicated that pure LSGM phase was formed after sintering at 1400 °C. X-ray Rietveld refinement confirmed the formation of pure perovskite orthorhombic phase of the LSGM. The sintered sample showed 99% relative density. Scanning electron microscopic study of LSGM also depicted fairly densed grain morphology. X-ray photoelectron spectroscopy measurement confirmed the stability of the sintered sample in air and the existence of constituent elements in their characteristic valence states. A surface without porosity was observed in BET measurement. Average thermal expansion coefficient was found to be 9.78×10⁻⁶/°C in the measured temperature range (RT–1000 °C). The frequency dependent electrical conductivity of the sample was measured in the temperature range 400–800 °C. Total electrical conductivity of the LSGM pellet was found to be 0.056 S cm⁻¹ at 800 °C.