金在低温燃料电池技术中的应用前景

金因其良好的物理化学性质和催化活性在低温燃料电池技术中具有很好的应用前景.本文就金在此方向的研究进展进行综述,包括:金催化剂选择氧化燃料电池氢燃料中的CO以及Pt-Au系电催化剂、Pd-Au系电催化剂、以金为主体的电催化剂的研究状况.同时简要介绍了低温燃料电池电催化剂的发展现状和金应用于电催化剂的基础.     

含纳米CeO2,Cu混合物添加剂润滑油摩擦学性能研究

本文中将纳米二氧化铈与铜粒子混合物应用于润滑油添加剂,使润滑油具有优良的减摩、抗磨性能.纳米二氧化铈与铜粒子用适当的表面活性剂进行表面改性处理,经表面改性的纳米粒子在润滑油中具有良好的分散、稳定性.采用透射电镜(TEM)观察与测量纳米二氧化铈、铜粒子的形貌和平均直径.应用四球摩擦磨损试验机测定添加纳米二氧化铈、铜粒子的润滑油的极压性能(PB)、磨痕直径(WSD)和摩擦因数(μ)等.研究结果表明,最佳的纳米二氧化铈、铜粒子的总添加量为0.6%左右、纳米二氧化铈、铜粒子的质量分数之比为1∶1.该润滑油具有最佳的的减摩、抗磨作用.文中还探讨了纳米二氧化铈、铜粒子混合物具有优良摩擦学性能的机理.     

纳米二氧化铈的研究现状

通过文献分析 ,阐述了纳米二氧化铈的制备方法 ,添加物对二氧化铈涂层性能的影响及不同基体上二氧化铈涂层的研究现状 ,指出了其中的不足 ,并对二氧化铈的研究进行了展望。     

含纳米CeO2，Cu混合物添加剂润滑油摩擦学性能研究

本文中将纳米二氧化铈与铜粒子混合物应用于润滑油添加剂，使润滑油具有优良的减摩、抗磨性能。纳米二氧化铈与铜粒子用适当的表面活性剂进行表面改性处理，经表面改性的纳米粒子在润滑油中具有良好的分散、稳定性。采用透射电镜（TEM）观察与测量纳米二氧化铈、铜粒子的形貌和平均直径。应用四球摩擦磨损试验机测定添加纳米二氧化铈、铜粒子的润滑油的极压性能（PB）、磨痕直径（WSD）和摩擦因数（μ）等。研究结果表明，最佳的纳米二氧化铈、铜粒子的总添加量为0．6％左右、纳米二氧化铈、铜粒子的质量分数之比为1：1，该润滑油具有最佳的的减摩、抗磨作用。文中还探讨了纳米二氧化铈、铜粒子混合物具有优良摩擦学性能的机理。     

纳米二氧化铈的研究现状

通过文献分析，阐述了纳米二氧化铈的制备方法，添加物对二氧化铈涂层性能的影响及不同基体上二氧化铈涂层的研究现状，指出了其中的不足，并对二氧化铈的研究进行了展望。     

铂金属催化剂的应用前景

燃料电池催化剂 铂合金广泛用于质子交换膜燃料电池，在电池的阴极上，使用添加锰、铁或铬的铂合金，与纯铂相比，可使电池电势提高25mV；在阳极上，Pt-Ru具有抗CO和CO2毒化的特性。 燃料电池的燃料处理器改进引人关注。很多水-气振荡反应器采用非铂族金属催化剂，美国新技术材料研究所的S. L. Swart及其同事则采用在独石上涂刷纳米级二氧化铈沉积铂的方法，使反应器在300℃以上的使用性能得到提高。 车用三元催化剂 美国的H. W. Jen及其同事研究了以Ce0.63Zr0.37O2为载体时，预处理条件对钯型和铑型催化剂储氧量(OSC)的影响。结…     

贵金属在直接甲醇燃料电池催化剂的应用

电极催化剂是燃料电池组件中的关键,直接影响着电池性能及燃料电池的产业化进程。综述了直接甲醇燃料电池电极催化剂中贵金属的应用。从燃料电池的阳极催化剂和阴极催化剂2个方面阐述了应用贵金属的研究进展,并对其未来发展进行了展望。     

铈锆固溶体对贵金属整体样催化剂氧化性能的影响

采用共沉淀法制备了不同铈锆比的粉末铈锆固溶体,考察了铈锆比和铈锆固溶体负载量对浸渍法制备的颗粒状和整体样贵金属催化剂上C3H6(丙烯)氧化反应催化性能的影响,并运用XRD和TPD表征技术对催化剂的物化性能进行研究.结果表明,所制备的催化剂中均形成了铈锆固溶体,并且铈锆含量的增加能够提高催化剂对C3H6的吸附能力.当铈锆固溶体的负载量相同时,在氧化气氛和较低贵金属含量条件下、Ceo.6Zro.4O2的加入使催化剂在低温时具有最好的催化效果.但与Pt/A12O3相比,采用浸渍法添加铈锆固溶体降低了贵金属整体样催化剂的活性,且活性随着负载量的增加显著降低.     

燃料电池技术要论

叙述燃料电池的组成原理和结构材料以及该技术的开发意义和应用前景，还讨论贵金属电极催化剂在燃料电池中的作用。     

氮化硅──氧化镁──二氧化铈的无压烧结

对氧化硅－氧化镁－二氧化铈无压烧结的研究表明：MgO－CeO_2是一种非常有效的氮化硅助烧剂，MgO－CeO_2的含量及烧结工艺对氮化硅的致密化及机械性能有强烈的影响，本文讨论了这些影响规律，当氧化镁与氧化铈共存时，二氧化铈更容易与氮化硅颗粒表面的二氧化硅反应形成难熔的窗铈的玻璃相，无压烧结的氮化硅－氧化镁－二氧化铈陶瓷，其相对密度可超过98％，强度超过920MPa，这在目前的各种无压烧结的氮化硅材料中，是非常高的，Si－Mg－Ce－O－N系统在理论研究和实用上都有极大的价值。     

Ceramic materials containing rare earth oxides for solid oxide fuel cell

Materials for a solid oxide fuel cell were investigated aiming especially at low temperature operation of the cell. Although yttria-stabilized zirconia has been most popularly investigated as an electrolyte for the cell, the conductivity reaches the allowable level only around or higher than 1000 °C. The use of a ceria-based electrolyte, especially samaria doped ceria, significantly lowered the operation temperature of the cell due to its high oxide ion conductivity. The reduction of ceria with H₂ and resultant electronic conduction could be avoided by the coating of YSZ on to the anode side of the ceria. The ceria layer facing the air electrode is effective in reducing cathodic polarization. Ni-ceria cermet exhibited higher fuel electrode performance than Ni-YSZ cermet in lowering polarization.     

Relationship Between Particle and Plasma Properties and Coating Characteristics of Samaria-Doped Ceria Prepared by Atmospheric Plasma Spraying for Use in Solid Oxide Fuel Cells

Samaria-doped ceria (SDC) has become a promising material for the fabrication of high-performance, intermediate-temperature solid oxide fuel cells (SOFCs). In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were measured and correlated to the resulting microstructures of SDC coatings fabricated using atmospheric plasma spraying, a manufacturing technique with the capability of producing full cells in minutes. Plasmas containing argon, nitrogen and hydrogen led to particle surface temperatures higher than those in plasmas containing only argon and nitrogen. A threshold temperature for the successful deposition of SDC on porous stainless steel substrates was calculated to be 2570?°C. Coating porosity was found to be linked to average particle temperature, suggesting that plasma conditions leading to lower particle temperatures may be most suitable for fabricating porous SOFC electrode layers.     

Preparation and properties of Gd and Y co-doped ceria-based electrolytes for intermediate temperature solid oxide fuel cells

Co-doped ceria electrolytes of Ce_0.8Gd_0.2−xY_xO_1.9 (x = 0.0–0.20) fine powders were prepared with glycine–nitrate method. The results of X-ray diffraction showed that all powders crystallite calcined at 873 K were single phase with cubic fluorite structure. The average crystallite sizes calculated by the Scherrer formula were between 21 and 23 nm, which was in good agreement with the results of TEM and particle size distribution measurements. The thermal expansion curves of Ce_0.8Gd_0.2−xY_xO_1.9 were measured and the thermal expansion coefficients between 373 and 1123 K were calculated. The SEM results exhibited that electrolyte pellets sintered at 1523 K were dense, and the relative densities of these pellets were over 96%. The impedance spectra analysis of these electrolytes has been performed at 623–1023 K. The results showed that co-doped ceria exhibited higher ionic conductivity and lower activation energy than the singly doped ceria with the same dopant concentration at the temperature range of 773–1023 K, and the electrolytic domain boundary of co-doped ceria was smaller than that of singly doped ceria at 873–973 K. It suggested that co-doping with appropriate ratio gadolinium and yttrium could further improve the electrochemical performance of ceria-based electrolytes. These co-doped samples are ideal electrolyte materials of intermediate temperature solid oxide fuel cells.     

Mechanical Properties and Thermal Shock Resistance of HVOF Sprayed NiCrAlY Coatings Without and With Nano Ceria

NiCrAlY coatings without and with 0.2?wt.% nano ceria were prepared by high velocity oxygen fuel spraying. The microstructure, mechanical properties, and thermal shock resistance of as-sprayed coatings were investigated. The results showed that in the as-sprayed coatings, the number of un-melted particles was reduced drastically, the microstructure was refined and compact due to the refinement of sprayable powders. Both the hardness and adhesive strength of the NiCrAlY increased due to the refinement of microstructure and the decrease of the defects, such as pores and oxides, after adding nano ceria. The thermal cycle life of NiCrAlY coatings was improved by 15% after adding 0.2?wt.% nano ceria, which is attributed to the low content of spinel NiCr₂O₄ and high content of Cr₂O₃ in the thermal cycling, the refined and compact microstructure, and increased interfacial boundary.     

Gas phase deposition of diffusion barriers for metal substrates in solid oxide fuel cells

One way to improve the mechanical properties of solid oxide fuel cells is the development of metal supported designs. This type of SOFC offers improved thermal shock resistance, reduced temperature gradients due to the greater thermal conductivity of the metal, and lower operating temperatures. Switching from ceramic supports to metal supports also allows the uses of conventional metal joining and forming techniques and could significantly reduce the material and manufacture costs. However, one persistent problem needs to be solved: inter-diffusion of chemical elements contained in the metal substrates and in the anodes of SOFC leads to degradation, which is to be prevented by protective coatings. In order to address the issues of sintering and delamination for metal supported SOFC, the deposition of gadolinia doped ceria on metal substrates made of Crofer 22 APU has been done by electron beam evaporation and reactive spray deposition technique, as two direct deposition techniques that will not require a sintering step, respectively. Additionally, the effect of ion-assistance on layers made by electron beam evaporation was studied. Because metal supported fuel cells aim at low/intermediate operating temperatures, reducing the thickness of these protective coatings is crucial, since layer thickness is directly correlated to its ohmic resistance. A layer of nickel was applied by magnetron sputtering to prove the effectiveness of the deposited diffusion barrier layers.     

Properties and microstructure of NiO/SDC materials for SOFC anode applications

NiO/SDC composites and Ni/SDC cermets for solid oxide fuel cell （SOFC） anode applications were prepared from nickel oxide （NiO） and samada doped ceria （SDC） powders by the powder metallurgy process. The physical and mechanical properties, as well as the microstructure of the NiO/SDC composites and the Ni/SDC cermets were investigated. It is shown that the sintedng temperature of the NiO/SDC composites and NiO content plays an important role in determining the microstructure and properties of the NiO/SDC composites, which, in turn, influences the microstructure, electrical conductivity, and mechanical properties of the Ni/SDC cermets. The present study demonstrated that composition and tprocess parameters must be appropriately selected to optimize the microstructure and the properties of NiO/SDC materials for solid oxide fuel cell applications.     

Effect of the oxidation state of gold on the complete oxidation of isobutane on Au/CeO2 catalysts

Catalysts of highly dispersed gold supported on ceria were prepared by deposition precipitation method. Au is dispersed as Au⁰, Au⁺ and Au³⁺ species on ceria. The content of Au⁺ and Au³⁺ was highest on catalyst prepared on uncalcined ceria, which possess least ordered surface. It is inferred that oxygen vacancy on disordered ceria surface is essential for the preparation of highly dispersed gold catalysts and in stabilizing monolayer surface Au⁺ clusters while cationic vacancies are sites for substitutional Au³⁺. Au/CeO₂ catalysts showed low-temperature isobutane oxidation activity with maximum conversion at 150–180°C. Ex-situ XPS results demonstrated that the low temperature isobutane oxidation activity was closely related to the content of Au⁺ which we interpreted as surface gold oxide formed under reaction conditions. Isobutane oxidation activity associated with ceria at temperature above 300°C was enhanced by substitutional Au³⁺.     

氧化铈对CaO-Al_2O_3-SiO_2系微晶玻璃烧结和性能的影响

采用烧结法制备添加氧化铈的CaO-Al2O3-SiO2系微晶玻璃材料,并对其进行差热分析(DTA)、X射线衍射分析、扫描电镜(SEM)观察和性能测试。结果表明:添加少量氧化铈能够降低玻璃的玻璃转变温度和析晶峰值温度,促进玻璃粉体的烧结致密化,但氧化铈加入量过多将会阻止玻璃的烧结和晶化;氧化铈的最佳添加量(质量分数)为5%;随着氧化铈含量的增加,样品的介电常数呈"N"字形变化,而样品的介电损耗则表现为先减小后稍微增加的变化趋势。样品的热膨胀系数随氧化铈含量的增加基本呈下降趋势。添加5%氧化铈的样品在925℃烧结后,其相对密度达99.1%,其介电常数、介电损耗和热膨胀系数分别为6.7、0.09%和3.42×10-6K-1。     

Reducibility of ceria–lanthana mixed oxides under temperature programmed hydrogen and inert gas flow conditions

The present paper deals with the preparation and characterization of La/Ce mixed oxides, with La molar contents of 20, 36 and 57%. We carry out the study of the structural, textural and redox properties of the mixed oxides, comparing our results with those for pure ceria. For this aim we use temperature programmed reduction (TPR), temperature programmed desorption (TPD), nitrogen physisorption at 77 K, X-ray diffraction and high resolution electron microscopy. The mixed oxides are more easy to reduce in a flow of hydrogen than ceria. Moreover, in an inert gas flow they release oxygen in higher amounts and at lower temperatures than pure CeO₂. The textural stability of the mixed oxides is also improved by incorporation of lanthana. All these properties make the ceria–lanthana mixed oxides interesting alternative candidates to substitute ceria in three-way catalyst formulations.     

Crystallization of amorphous ceria solid solutions

Next-generation micro-solid oxide fuel cells for portable devices require nanocrystalline thin film electrolytes in order to allow fuel cell fabrication on chips at low operating temperatures and with high fuel cell power outputs. In this study amorphous gadolinia-doped ceria (Ce_0.8Gd_0.2O_1.9−x) thin film electrolytes were fabricated by spray pyrolysis and their crystallization to nanocrystalline microstructures was investigated by means of X-ray diffraction and transmission electron microscopy. At temperatures higher than 500 °C the amorphous films crystallize to a biphasic ceramic that is amorphous and nanocrystalline. The driving force for the crystallization is the reduction of the free enthalpy resulting from the transformation of amorphous into crystalline material. Self-limited grain growth kinetics prevail for the nanocrystalline grains where stable microstructures are established after short dwell times. A transition to classical curvature-driven grain growth kinetics occurs when the fully crystalline state is reached for average grain sizes larger than 140 nm and annealing temperatures higher than 1100 °C.