复合阳极Ni-Fe/Ce0.9Gd0.1O1.95在阴极支撑单电池的性能及其表征

为了提高固体氧化物燃料电池在中温条件下的电性能,探索了一种双金属阳极的阴极支撑单电池。单电池以La_0.6Sr_0.4CoO₃（LSC）-Ce_0.9Gd_0.1O_1.95（GDC）为阴极支撑体,旋涂了甘氨酸-硝酸盐法制备的La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ（LSGM）电解质及Sm_0.2Ce_0.8O_1.9（SDC）缓冲层,涂覆了由硬模板法和浸渍法结合制备的Ni-Fe/GDC双金属阳极。对制备材料进行了XRD和微观形貌分析,单电池电化学测试在800 ℃和750 ℃下,以氢气为燃料的最大功率密度达0.73 W/cm²和0.64 W/cm²,以甲烷为燃料时达0.41 W/cm²和0.40 W/cm²。测试后的SEM表明,阳极具有多孔的微观结构,金属颗粒均匀包覆蠕虫状GDC,保证了单电池具有较高的发电性能。     

Synthesis and oxygen transport characteristics of dense and porous cerium/gadolinium oxide materials: Interest in membrane reactors

Cerium/gadolinium oxide (CGO)-based ceramic ion conductive membranes (CICMs) have potential uses in catalytic membrane reactors (CMRs) and solid oxide fuel cells (SOFCs). A supercritical CO₂ aided sol–gel process allowed the synthesis of CGO materials with the composition Ce_0.9Gd_0.1O_1.95. The produced nanophase powders were non-agglomerated, with a controlled morphology, a high purity and a high specific surface area (>100 m²/g). The CGO cubic crystalline phase has been obtained at temperatures <300 °C, lower than those of conventional solid state chemistry routes. With respect to ionic oxygen transport, a high conductivity at intermediate temperature (2 × 10⁻² S cm⁻¹ at 600 °C), almost equivalent in dense and porous samples, has been obtained on sintered materials prepared from these powders. In relation to their porosity characteristics, a modelling approach successfully explained the high ionic oxygen transport of some specific porous samples. Future directions for preparing porous conductive ceramics well adapted to CMR or SOFC applications can be anticipated from this model.     

Comparative analysis of ceramic-carbonate nanocomposite fuel cells using composite GDC/NLC electrolyte with different perovskite structured cathode materials

A comparative analysis of perovskite structured cathode materials, La_0.65Sr_0.35MnO₃ (LSM), La_0.8Sr_0.2CoO₃ (LSC), La_0.6Sr_0.4FeO₃ (LSF) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF), was performed for a ceramic-carbonate nanocomposite fuel cell using composite electrolyte consisting of Gd_0.1Ce_0.9O_1.95 (GDC) and a eutectic mixture of Na₂CO₃ and Li₂CO₃. The compatibility of these nanocomposite electrode powder materials was investigated under air, CO₂ and air/CO₂ atmospheres at 550 °C. Microscopy measurements together with energy dispersive X-ray spectroscopy (EDS) elementary analysis revealed few spots with higher counts of manganese relative to lanthanum and strontium under pure CO₂ atmosphere. Furthermore, electrochemical impedance (EIS) analysis showed that LSC had the lowest resistance to oxygen reduction reaction (ORR) (14.12 Ω·cm²) followed by LSF (15.23 Ω·cm²), LSCF (19.38 Ω·cm²) and LSM (>300 Ω·cm²). In addition, low frequency EIS measurements (down to 50 µHz) revealed two additional semi-circles at frequencies around 1 Hz. These semicircles can yield additional information about electrochemical reactions in the device. Finally, a fuel cell was fabricated using GDC/NLC nanocomposite electrolyte and its composite with NiO and LSCF as anode and cathode, respectively. The cell produced an excellent power density of 1.06 W/cm² at 550 °C under fuel cell conditions.     

Electrochemical behavior of Ln0.6Sr0.4Co0.2Fe0.8O3−δ (Ln=Ce, Gd, Sm, Dy) materials used as cathode of IT-SOFC

The perovskite-type compounds Ln_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (Ln=Ce, Sm, Gd, Dy) used as the cathodes of intermediate temperature solid oxide fuel cell (IT-SOFC) were studied. The cells consisted of anode supported Sm-doped-ceria electrolyte bi-layer and cathode with 0.65 cm² effective area. Open-circuit voltage (OCV), V–I and P–I curves of the cells were measured over a temperature range from 400 to 800 °C, using H₂–3%H₂O as fuel and air as oxidant. Polarization potential of electrodes were measured with asymmetry three-electrode method during cell discharging. The results indicated that, Dy-SCF material cathode behaved with high catalytic activity for oxygen dissociation at low temperatures. For each cell with a particular cathode, there was a transition temperature, at which OCV of the cell reached the highest value. When temperature was higher than the transition temperature, OCV of the cell increases with decreasing temperature, whereas as temperature was lower than that, OCV decreased with lowering temperature.     

EMF measurements on gadolinia doped ceria

An experimental set up was built to measure the EMF, which is generated out of the oxygen partial pressure gradient, across the faces of solid electrolyte samples. The results obtained from this work show that ceria-gadolinia mixed oxide, of composition Ce_0·825Gd_0·175O_1·913, behaves in a manner quite satisfactory for use as an oxygen ion conducting material in fuel cells. This is especially true at relatively low temperatures (as low as 600°C) and with oxygen partial pressure down to 10⁻⁵ atm. The oxygen mean ionic transport number was shown to be almost unity at the above mentioned temperature and oxygen partial pressure.     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na_0.4Ni_0.2Ti_0.8O₂ were ca. 7×10³ S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm⁻¹ K⁻¹ at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na_0.4Ni_0.2Ti_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

甘油水蒸汽重整制氢Ni/Ce0.9Gd0.1O1.95催化剂的研究

采用浸渍法和共沉淀法制备了Ni质量分数10%的10%Ni/Ce_0.9Gd_0.1O_1.95催化剂,通过X射线衍射、N₂物理吸附与H₂脉冲化学吸附、H₂程序升温还原等技术表征了催化剂的结构和性质,并考察了其催化甘油水蒸汽重整制氢反应性能。结果表明,浸渍法制备的10%Ni/Ce_0.9Gd_0.1O_1.95-S催化剂的活性最佳,该催化剂上Ni晶粒小、分散度高,形成氧空穴使得催化剂抗积炭能力大大提高,所以活性、氢气选择性较高,稳定性也较好。同时考察了水与甘油物质的量比和泵流速对甘油重整反应性能的影响,发现在水与甘油物质的量比为24:1,泵流速为0.06 mL·min^-1的条件下,甘油几乎完全转化,氢气选择性也非常高,而且反应10 h没有失活。     

Ferroelectricity in Li2B4O7 single crystal

It has been found that Li₂B₄O₇ crystal shows ferroelectric activity in the c-direction in the temperature range from room temperature to 100°C. The values of spontaneous polarization and coercive field at 25°C estimated from the shown D-E hysteresis loop are 1.44 μC/cm² and 2.5 kV/cm, respectively. With increasing temperature above 100°C, the ferroelectric hysteresis loop was reduced into a line-shape with high conducting behavior. The reason is believed that a high ionic conductivity of Li₂B₄O₇ make a sample into a leak capacitor.     

表面修饰对镧锶钴铁阴极材料电化学性能的影响

通过柠檬酸-EDTA络合法制备固体氧化物燃料电池阴极材料La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF)粉体。以Sm_0.2Ce_0.8O_1.9(SDC)为电解质,制备了LSCF/SDC/LSCF对称电极。采用浸渍法在LSCF/SDC/LSCF两侧浸渍La(NO₃)₃、Ni(NO₃)₂、Fe(NO₃)₃混合溶液,850℃烧结后得到表面修饰后的阴极材料。研究了浸渍烧结后表面修饰阴极材料的物相结构特征、电化学交流阻抗、电化学催化活性及单电池输出性能。结果表明:通过浸渍法在LSCF阴极表面形成了与LSCF结构相似的La_0.62Sr_0.38Ni_0.03Co_0.19Fe_0.78O_3-δ(LSNCF)固溶体,在表面产生的纳米颗粒提升了阴极材料对O2的吸附解离能力,并表现出较低的极化阻抗,在800℃时LSNCF阴极材料的极化面电阻为0.083Ω·cm²,在800℃连续工作7 200 min后,LSNCF阴极材料对称电池极化阻抗为0.117Ω·cm²。以Ni-SDC为阳极,SDC为电解质,LSNCF为阴极组装阳极支撑单电池,在750℃时最大功率密度为693 m W/cm²。     

Effect of γ-alumina crystallinity on the state of rhodium during high-temperature treatments in oxygen and hydrogen

Rhodium catalysts, supported on six γ-Al₂O₃ supports with different crystallinities, were exposed to sequential treatments in hydrogen at 500°C, in oxygen at 760°C, in hydrogen at 500°C and at 760°C, respectively. Samples were characterized by X-ray diffraction and hydrogen chemisorption at various stages in the sequential treatment. Based on the characterization results, it is concluded that the formation of crystalline Rh₂O₃ is a function of γ-Al₂O₃ crystallinity; formation of crystalline Rh₂O₃ increased with increasing crystallinity of γ-Al₂O₃ during treatment in oxygen at 760°C. The crystalline Rh₂O₃ formed during treatment in oxygen at 760°C was reduced to Rh metal by hydrogen at 500°C, but most of the Rh did not adsorb hydrogen at room temperature. Subsequent treatment in hydrogen at 760°C increased the hydrogen adsorption capacity by as much as a factor of three. X-ray line broadening measurements showed that oxygen treatment of reduced Rh/γ-Al₂O₃ at 760°C followed by hydrogen reduction at 500°C resulted in significant increases in Rh crystal size; further treatment in hydrogen at 760°C resulted in additional sintering of Rh.     

Solid state protonic conductor NH4PO3–(NH4)2Mn(PO3)4 for intermediate temperature fuel cells

A new proton-conductive composite of NH₄PO₃–(NH₄)₂Mn(PO₃)₄ was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH₄)₂Mn(PO₃)₄ was stable as a supporting matrix for NH₄PO₃. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH₄PO₃ in both dry and wet atmospheres. A conductivity of 7 mS cm⁻¹ was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10²–10⁵ Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte. Fuel cells using 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm² was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells.     

YSZ thin films deposited by spin-coating for IT-SOFCs

Dense and crack-free yttria stabilized zirconia (YSZ) thin films were fabricated using a spin-coating technique for intermediate temperature solid oxide fuel cells (IT-SOFCs). The film thickness was greatly affected by spinning speed and coating cycles. The morphology of the films was investigated with scanning electron microscope. With cathodes consisting of yttria-stabilized bismuth oxide and sliver, anodes of samaria-doped ceria and nickel, the supported YSZ films were characterized as electrolytes for single cells with humidified hydrogen as fuel and stationary air as oxidant. Open circuit voltage was 1.08 V at 700 °C, close to the theoretical value and power density was 535 mW/cm² at 750 °C and 400 mW/cm² at 700 °C. Impedance analysis indicates that the performances of the SOFCs are determined essentially by the interfacial resistances, suggesting that optimizing the electrode materials are especially important for IT-SOFCs.     

Slip-Cast Ce0.8Sm0.2O1.9 Cone-Shaped SOFC

Cone-shaped Sm-doped CeO₂ (Ce_0.8Sm_0.2O_1.9, SDC) electrolyte cylinders have been fabricated using the slip-casting technique. A single solid oxide fuel cell has been prepared by applying a Sm_0.5Sr_0.5CoO₃ cathode on the outside of the cylinders and a NiO–SDC (7:3 wt%) anode on the inside. The open circuit voltage of the cell was 0.93 V at 400°C, and a maximum power density of about 300 mW/cm² at 700°C was obtained with humidified hydrogen (3% H₂O) as the fuel and ambient air as the oxidant. Impedance results showed that the performance of the cell was mainly influenced by the ohmic resistance of the electrolyte.     

Kinetics of asphaltenes conversion during hydrotreating of Maya crude

The kinetics of asphaltene conversion was studied during the hydrotreating of Maya heavy crude oil. Experimental tests were conducted in a pilot plant at the following reaction conditions: total pressure of 70–100 kg/cm², liquid hourly space-velocity (LHSV) of 0.33–1.5 h⁻¹, and reaction temperature of 380–420 °C at a constant hydrogen-to-oil ratio of 5000 ft³/bbl. A commercial NiMo/Al₂O₃ catalyst was used in all experiments. Asphaltenes were precipitated from Maya crude and from hydrotreated products in a Parr Batch Reactor at 25 kg/cm² and 60 °C with n-heptane as solvent. Asphaltene hydrocracking data were used to estimate reaction orders and activation energy using a power-law model, and the average absolute error between experimental and calculated concentrations of asphaltenes was found to be less than 5%.     

Enhanced electrochemical performance of garnet-based solid-state lithium metal battery with modified anodic and cathodic interfaces

Due to high ionic conductivity and wide electrochemical window, the garnet solid electrolyte is considered as the most promising candidate electrolyte for solid-state lithium metal batteries. However, the high contact impedance between metallic lithium and the garnet solid electrolyte surface seriously hampers its further application. In this work, a Li-(ZnO)_x anode is prepared by the reaction of zinc oxide with metallic lithium and in situ coated on the surface of Li_6.8La₃Zr_1.8Ta_0.2O₁₂(LLZTO). The anode can be perfectly bound to the surface of LLZTO solid electrolyte, and the anode/electrolyte interfacial resistance was reduced from 2319 to 33.75 Ω·cm². The Li-(ZnO)_0.15|LLZTO|Li-(ZnO)_0.15 symmetric battery exhibits a stable Li striping/plating process during charge-discharging at a constant current density of 0.1 mA·cm^-2 for 100 h at room temperature. Moreover, a Li-(ZnO)_0.15|LLZTO-SPE|LFP full battery, comprised of a polyethylene oxide-based solid polymer electrolyte (SPE) film as an interlayer between LiFePO₄ (LFP) cathode and LLZTO solid electrolyte, presents an excellent performance at 60 ℃. The discharge capacity of the full battery reaches 140 mA·h·g^-1 at 0.1 C and the capacity attenuation is less than 3% after 50 cycles.     

Thin Yttrium-Stabilized Zirconia Electrolyte Solid Oxide Fuel Cells by Centrifugal Casting

A centrifugal casting technique was developed for depositing thin 8-mol%-yttrium-stabilized zirconia (YSZ) electrolyte layers on porous NiO-YSZ anode substrates. After the bilayers were cosintered at 1400°C, dense pinhole-free YSZ coatings with thicknesses of ∼25 μm were obtained, while the Ni-YSZ retained porosity. After La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF)-Ce_0.9Gd_0.1O_1.95 (GDC) or La_0.8Sr_0.2MnO₃ (LSM)-YSZ cathodes were deposited, single SOFCs produced near-theoretical open-circuit voltages and power densities of ∼1 W/cm² at 800°C. Impedance spectra measured during cell tests showed that polarization resistances accounted for ∼70%–80% of the total cell resistance.     

固体氧化物燃料电池双钙钛矿陶瓷阳极缺陷结构设计与性能调控

研究了固体氧化物燃料电池Sr₂Fe Mo_0.6Mg_0.25Al_0.15O₆ (SFMMA)双钙钛矿阳极的晶体缺陷结构、热膨胀性能、电荷传输特性、氧化还原稳定性以及电化学性能。结果表明:SFMMA室温下为I 4/m四方结构,400℃时材料转变为F m 3 m立方结构。SFMMA材料的实际晶体结构式为Sr₂(Fe_0.75Mg_0.25)(Mo_0.6Fe_0.25Al_0.15)O6-δ,材料晶格中含有大量反位缺陷FeB’以及—Fe_B—O—Fe_B’—键,有利于氧空位的形成及氧离子的迁移扩散。SFMMA的热膨胀系数在25~400℃和400~900℃范围内分别为13.0×10^–6K^–1和17.6×10^–6K^–1,在氢气气氛下600~900℃温度范围内电导率超过35 S·cm^–1,并且具有较快的氧表面交换特性以及非常优异的氧化还原循环结构稳定性。在900,850,800℃和750℃时,湿润H₂(3%H₂O,50 m L/min)气氛中,SFMMA/La_0.4Ce_0.6O₂(LDC)/La_0.8Sr_0.2Ga_0.8Mg_0.2O₃(LSGM)/LDC/SFMMA对称半电池面比电阻分别为0.096,0.142,0.239Ω·cm²和0.447Ω·cm²。以SFMMA为阳极组装电解质支撑型单电池SFMMA/LDC/LSGM (300μm)/Pr Ba_0.5Sr_0.5Co_1.5Fe_0.5O₅+δ,850℃时电池最大功率密度可达886 m W·cm^–2。     

Performance of microchannel reactor combined with combustor for methanol steam reforming

The microchannel reactor with combustor for methanol steam reforming was fabricated to produce hydrogen for onboard proton exchange membrane (PEM) fuel cell device. A commercial copper-containing catalyst (Cu/ZnO/Al₂O₃) and Pt/ZrO₂ were used as a catalyst for methanol steam reforming and combustion reaction, respectively. It was found that catalyst layer with zirconia sol solution in microchannel showed no crack on the surface of catalyst layer and an excellent adherence to stainless steel microchannel even after reaction. The temperature of combustor could be controlled between 200 and 300 °C depending on the methanol feed rate. The hydrogen flow of 3.9 l h⁻¹ hydrogen was obtained with the reforming feed flow rate of 3.65 ml h⁻¹ at 270 °C.     

Monodispersed gold nanoparticles supported on γ-Al2O3 for enhancement of low-temperature catalytic oxidation of CO

Monodispersed nano-Au/γ-Al₂O₃ catalysts for low-temperature oxidation of CO have been prepared via a modified colloidal deposition route, which involves the deposition of dodecanethiolate self-assembled monolayer (SAM)-protected gold nanoparticles (C₁₂ nano-Au) in hexane on γ-Al₂O₃ at room temperature. The diameter of the gold nanoparticles deposited on the support is 2.5 ± 0.8 nm after thermal treatment, and their valence states comprise both the metallic and oxidized states. It is found that the thermal treatment temperature affects significantly the catalytic activity of the catalysts in the processing steps. The catalyst treated at 190 °C exhibits considerably higher activity as compared to catalysts treated at 165 and 250 °C. A 2.0-wt.% nano-Au/γ-Al₂O₃ catalyst treated at 190 °C for 15 h maintains the catalytic activity at nearly 100% CO oxidation for at least 800 h at 15 °C, at least 600 h at 0 °C, and even longer than 450 h at −5 °C. Evidently, the catalysts obtained using this preparation route show high catalytic activity, particularly at low temperatures, and a good long-term stability.     

Polyetherimide Adhesive

High-temperature adhesives which can be adhered at adhesive temperatures lower than those of conventional polyimide adhesives were investigated. Polyetherimide (PEI), developed by General Electric Co., is one such promising low curing temperature adhesive because it melts at temperatures lower than those used for conventional polyimides. Lap shear adhesive strength was investigated in a 75 μm-thick PEI film using steel test pieces. 350 kgf/cm² was achieved after curing for 1 hour at 270°C and 150 kgf/cm² was achieved at the test temperature of 200°C. PEI adhesive dissolved by N, N-dimethylformamide exhibited a high adhesive strength of 240 kgf/cm² after curing for 2 hours at 200°C. In addition, it was found that PEI could be used at much lower adhesive pressures than those of conventional polyimide adhesives.