Preparation of porous Ni-YSZ cermet anodes for solid oxide fuel cells by high frequency induction heated sintering

Ni-YSZ cermet anodes for solid oxide fuel cells were successfully prepared by high frequency induction heated sintering, producing a uniformly porous microstructure without abnormal grain growth found in the conventional sintering method. All sintering processes commenced below 1150 °C and finished within 2 min. The rupture strength and electrical conductivity of the sample sintered by high frequency induction heated sintering without addition of a pore former were over 180 MPa and about 2000 S cm^− 1 at 800 °C, respectively.     

Phases in copper-stabilized zirconia solid oxide fuel cells anode material

Solid oxide fuel cells (SOFC) are emerging as an alternate source of energy. Anodes form one of the components of the fuel cells. Ni/Yttrium stabilized zirconia is a classic anode material for SOFC when hydrogen is used as the fuel source, but it is not that effective when methane is used as fuel source due to carbon deposition on the anode. Recently, copper stabilized zirconia has been investigated as anode material for SOFC for its self-cleaning properties. We have tried to investigate phases in copper stabilized zirconia for better understanding of its properties. Copper stabilized zirconia (CSZ) with different CuO loading was prepared by the solid-state reaction method. X-ray diffraction studies on these samples reveal only monoclinic zirconia phase in those samples loaded with less than 5 mol% of CuO. Traces of monoclinic CuO along with monoclinic ZrO₂ is observed in the samples when loading of CuO is between 5 and 20 mol%. Orthorhombic copper zirconium oxide and monoclinic zirconia phases were observed when CuO loading was greater than 20 mol%. Scanning and back-scattered electron micrographs reveal a clear two-phase structure only in the samples with greater than 20 mol% of CuO loading. Atomic force microscopy carried out on 33 mol% loaded zirconia shows a three-phase structure with flattened seven-fold-coordination of Zr⁴⁺ with oxygen.     

Progress in Ni-based anode materials for direct hydrocarbon solid oxide fuel cells

Ni-based anode materials of solid oxide fuel cells (SOFCs) are susceptible to carbon deposition and deactivation in direct hydrocarbon fuels, greatly limiting the commercialization. Extensive studies on finding new alternative anode materials have been developed; however, new problems such as low electrochemical performance and complex cell preparation process destroyed the further research passion of Ni-free anode materials. Considering the superior catalytic activity and mature technology of Ni-based anode materials, a large number of recent research results proved that it is still important and promising to solve the carbon coking of Ni-based anode materials. In this review, progress in four typically promising Ni-based anode materials free from carbon coking has been summarized, including the noble metals, ceria, Ba-containing oxides and titanium oxide. Correspondingly, the mechanisms that improve the carbon tolerance of Ni-based modified SOFCs anodes are clearly concluded, providing the materials and theoretical basis for the use of direct hydrocarbon SOFCs as early as possible.     

A review of anode materials development in solid oxide fuel cells

High temperature solid oxide fuel cell (SOFC) has prospect and potential to generate electricity from fossil fuels with high efficiency and very low greenhouse gas emissions as compared to traditional thermal power plants. In the last 10 years, there has been significant progress in the materials development and stack technologies in SOFC. The objective of this paper is to review the development of anode materials in SOFC from the viewpoint of materials microstructure and performance associated with the fabrication and optimization processes. Latest development and achievement in the Ni/Y₂O₃-ZrO₂ (Ni/YSZ) cermet anodes, alternative and conducting oxide anodes and anode-supported substrate materials are presented. Challenges and research trends based on the fundamental understanding of the materials science and engineering for the anode development for the commercially viable SOFC technologies are discussed.     

碳基燃料SOFC阳极材料研究进展

固体氧化物燃料电池(SOFCs)是一类可以将燃料气体的化学能以高效而环境友好的方式直接转化为电能的电化学反应器。最近的研究趋势是发展可以直接电化学氧化碳氢化合物燃料(如天然气)的电池,但是使用碳氢化合物作为燃料时,目前最常使用的镍-氧化钇稳定的氧化锆(Ni/YSZ)金属陶瓷阳极材料具有易积碳和硫中毒的缺点。因此,研究在燃料气氛下具有混合离子-电子电导的替代阳极材料显得尤为必要。综述了以碳基燃料工作的SOFCs阳极材料研究的一些进展,并展望本领域在未来的发展趋势。     

Synthesis and properties of dense nickel and cobalt zirconia cermet anodes for solid oxide fuel cells

Porous Ni/Zirconia cermets have been traditionally used as anodes in solid oxide fuel cell configurations. They show excellent catalytic activity towards hydrogen oxidation as well as a number of other attributes. However, they are prone to sintering during long term operation, thus causing a drop in the efficiency of the cell. This paper describes the fabrication and properties of a dense cermet which, we suggest, may act as an intermediate layer between the electrolyte and the porous anode and possibly reduce anode degradation. Co and Ni based cermet systems were investigated and a 30 vol % Co/zirconia system could be fabricated with less than 20% porosity after being sintered at 1300°C.     

Ceria-based materials for solid oxide fuel cells

This paper is focused on the comparative analysis of data on electronic and ionic conduction in gadolinia-doped ceria (CGO) ceramics as well as on the electrochemical properties of various oxide electrodes in contact with ceria-based solid electrolytes. Properties of electrode materials, having thermal expansion compatible with that of doped ceria, are briefly reviewed. At temperatures below 1000 K, Ce_0.90Gd_0.10O_2– (CGO10) was found to possess a better stability at reduced oxygen pressures than Ce_0.80Gd_0.20O_2– (CGO20). Incorporation of small amounts of praseodymium oxide into Ce_0.80Gd_0.20O_2– leads to a slight improvement of the stability of CGO20 at intermediate temperatures, but the difference between electrolytic domain boundaries of the Pr-doped material and CGO10 is insignificant. Since interaction of ceria-based ceramis with electrode materials, such as lanthanum-strontium manganites, may result in the formation of low-conductive layers at the electrode/electrolyte interface, optimization of electrode fabrication conditions is needed. A good electrochemical activity in contact with CGO20 electrolyte was pointed out for electrodes of perovskite-type La_0.8Sr_0.2Fe_0.8Co_0.2O_3– and LaFe_0.5Ni_0.5O_3–, and LaCoO_3–/La₂Zr₂O₇ composites; surface modification of the electrode layers with praseodymium oxide results in considerable decrease of cathodic overpotentials. Using highly-dispersed ceria for the activation of SOFC anodes significantly improves the fuel cell performance.     

Functionally graded cathodes for solid oxide fuel cells

Functionally graded Solid Oxide Fuel Cell cathodes have been prepared from mixtures of strontium doped lanthanum manganite (LSM) and yttria stabilised zirconia (YSZ) using screen printing techniques. Samples were characterised using scanning electron microscopy, elemental dot mapping, and electrochemical impedance spectroscopy. Characterisation using AC impedance techniques showed that each cathode could be analysed in terms of a low frequency, mid frequency and high frequency response. Results showed that as the level of YSZ-LSM grading within the cathode increased, the polarisation resistance decreased. No region of the graded cathode should contain less than 20 wt% LSM to prevent an accompanying increase in series resistance.     

Materials for lower temperature solid oxide fuel cells

The solid oxide fuel cell (SOFC) continues to show great promise for the generation of electricity for an increasing range of applications. The present SOFC technology is based on an all-ceramic design, which eliminates the corrosion problems associated with fuel cells containing liquid electrolytes. To obtain good electrochemical performance with the currently used materials, this all-ceramic fuel cell operates at 1000°C. Despite a significant amount of research and several successful demonstrations at the 100 kW level, commercialisation of the technology is not as rapid as anticipated. This is, in part, due to the high operating temperatures required, necessitating the use of expensive materials. As a result of these problems, there has been an effort over the past few years to lower the SOFC operating temperature. This paper will address the issues concerning the development of new materials that can operate at lower temperatures. Many of these issues have been or are being addressed in the research performed at Argonne National Laboratory, and some recent results will be discussed.     

Oxide-ion conducting ceramics for solid oxide fuel cells

Realization of a solid oxide fuel cell (SOFC) operating at 700°C on a hydrocarbon fuel or gaseous H₂ is an outstanding technical target. For the past 25 years, efforts to achieve this goal have been based on yttria-stabilized zirconia as the electrolyte, a NiO + electrolyte composite as the anode, a porous La_0.85Sr_0.15MnO₃ (LSM) metallic perovskite as the cathode, and a La_1–x Sr _x CrO₃ ceramic as the interconnect material. This paper reviews progress in our laboratory on an alternate approach that would use a Sr- and Mg- doped LaGaO₃ perovskite as the electrolyte, a Sm-doped ceria (SDC) as the anode or as a buffer layer with a NiO + SDC composite as the anode, a mixed oxide-ion/electronic conductor (MIEC) as the cathode, and a stainless steel as the metallic interconnect.     

Sintering behavior of Ni/Y2O3-ZrO2cermet electrodes of solid oxide fuel cells

The sintering behavior of Ni/Y₂O₃-ZrO₂(YSZ) cermet electrode coating on 3 mol% Y₂O₃-ZrO₂electrolyte was studied under moist and dry hydrogen atmosphere at 1000°C for up to 2000 h. The sintering behavior of Ni/YSZ cermet electrodes was dominated by the agglomeration and grain growth of Ni particles in the cermets, which was critically related to the content of Ni and YSZ phases in the cermet. For pure Ni electrode coating, the sintering was substantial and cross plane cracks and isolated Ni island were formed after sintering at 1000°C for only 250 h. However with the addition of YSZ phase, the sintering of Ni/YSZ cermet anode coatings was significantly reduced. For the cermet composition of Ni (50 vol%)/YSZ (50 vol%), the change in the surface porosity and pore size distribution after sintering at 1000°C for 2000 h was very small. The microstructural stability of the Ni (50 vol%)/YSZ (50 vol%) cermet electrodes was also demonstrated by the performance stability tested under current load of 250 mAcm^–2at 1000°C for over 2500 h.     

碳基燃料固体氧化物燃料电池发展前景

以煤炭、石油、天然气为代表的化石燃料是中国乃至世界的主要能源资源,其平均发电效率低(30%左右),环境危害大,迫切需要改进。燃料电池是一种高效发电装置,将燃料的化学能直接转换为电能。在各种燃料电池中,固体氧化物燃料电池(SOFC)可以直接使用各种含碳燃料,很容易与现有能源资源供应系统兼容,一次发电效率高(50%～60%);SOFC采用全固态结构,长期稳定性好;不使用贵金属催化剂,成本低廉。SOFC尤其适用于分布式发电系统和动力电源系统。基于我国能源结构的现状和稀土资源优势,很有必要发展碳基燃料SOFC。在SOFC从示范运行逐步走向产业化应用的过程中,迫切需要进一步提高其长期稳定性并降低成本,所以今后的研究重点是碳基燃料SOFC关键材料和系统集成创新,解决其中的材料设计和制备、碳基燃料反应特性、电池构造、理论模拟、系统集成与运行过程中的基础科学和技术问题,为高效率、低成本、稳定可靠的碳基燃料SOFC系统产业化奠定基础。     

Synthesis and characterization of electrolyte-grade 10%Gd-doped ceria thin film/ceramic substrate structures for solid oxide fuel cells

In the present research, spray pyrolysis technique is employed to synthesize 10%Gd-doped ceria (GDC) thin films on ceramic substrates with an intention to use the "film/substrate" structure in solid oxide fuel cells. GDC films deposited on GDC substrate showed enhanced crystallite formation. In case of NiO-GDC composite substrate, the thickness of film was higher (~ 13 μm) as compared to the film thickness on GDC substrate (~ 2 μm). The relative density of the films deposited on both the substrates was of the order of 95%. The impedance measurements revealed that ionic conductivity of GDC/NiO-GDC structure was of the order of 0.10 S/cm at 500 °C, which is a desirable property for its prospective application.     

Materials and manufacturing technologies for solid oxide fuel cells

This article summarises recent developments in solid oxide fuel cell research regarding materials, processing and microstructure–property relationships. In the materials section, the various cell and stack materials are briefly described, i.e. electrolytes, electrodes, contact and protective layers, interconnects and sealing materials. The section on processing gives an overview of manufacturing technologies for cells including a view of different substrate materials and designs. Besides the widely used planar cell designs, the technologies for tubular designs are also described. In addition, the technologies are grouped with respect to the support, e.g. metal- or ceramic–metal (cermet anode substrate)-supported SOFCs. Finally, special emphasis is laid on the microstructure of functional layers which primarily govern the power output of the SOFC.     

Advanced synthesis of materials for intermediate-temperature solid oxide fuel cells

Solid-oxide fuel cells (SOFCs) technology has a substantial potential in the application of clean and efficient electric power generation. However, the widespread utilization of SOFCs has not been realized because the cost associated with cell fabrication, materials and maintenance is still too high. To increase its competitiveness, lowering the operation temperature to the intermediate range of around 500-800 °C is one of the main goals in current SOFCs research. A major challenge is the development of cell materials with acceptably low ohmic and polarization losses to maintain sufficiently high electrochemical activity at reduced temperatures. During the past few decades, tremendous progress has been made in the development of cell materials and stack design, which have been recently reviewed. SOFCs are fabricated from ceramic or cermet powders. The performances of SOFCs are also closely related to the ways in which the cell materials are processed. Therefore, the optimization of synthetic processes for such materials is of great importance. The conventional solid-phase reaction method of synthesizing SOFCs materials requires high calcination and sintering temperatures, which worsen their microstructure, consequently, their electrochemical properties. Various wet chemical routes have recently been developed to synthesize submicro- to nano-sized oxide powders. This paper provides a comprehensive review on the advanced synthesis of materials for intermediate-temperature SOFCs and their impact on fuel cell performance. Combustion, co-precipitation, hydrothermal, sol-gel and polymeric-complexing processes are thoroughly reviewed. In addition, the parameters relevant to each synthesis process are compared and discussed. The effect of different processes on the electrochemical performance of the materials is evaluated and optimization of the synthesis processes is discussed and some emerging synthetic techniques are also briefly presented.     

Electrophoretic deposition of YSZ powders for solid oxide fuel cells

The technological feasibility of applying Electrophoretic Deposition (EPD) to Solid Oxide Fuel Cells (SOFCs) has been studied. Here, EPD characteristic of SOFC composition material powders has been investigated from the viewpoint of DC and AC electrochemical experiments. An electrolyte of SOFCs required gas tight dense coating. Commercial YSZ (3–8 mol% yttria stabilized zirconias) powders, as for the electrolyte materials, and various organic solvents were used in this study. In the case of 8YSZ (Tosoh, TZ-8Y) dispersed n-propanol bath, the zeta potential of 8YSZ particle showed positive and grain size distribution showed less than 0.1 m. 8YSZ powder can be electrophoretically deposited onto the substrate because dispersed particle has charged and the charged particle acts as a migration onto the substrate by the potential gradient, and dense uniform coating was obtained less than 100 V/cm. On the other hand, as-deposited YSZ coating acts as a function of insulated layer. Potential gradient in the EPD bath has decreased because resistance of YSZ layer becomes higher than that of EPD bath with the progress of EPD under applied constant voltage. However, EPD bath characteristic itself does not change with the progress of EPD. It is suggested that the YSZ powder well dispersed EPD bath can be found by using 8YSZ and n-propanol.     

Electrophoretic deposition of electrolyte materials for solid oxide fuel cells

Electrophoretic deposition of electrolyte materials for solid oxide fuel cells, including La_0.8Sr_0.2Ga_0.875Mg_0.125O_3–x , yttria stabilized zirconia and (Ce_0.8Gd_0.2)O_1.9, was studied under various experimental conditions. The use of phosphate ester as a dispersant and poly (vinyl butyral) as a binder enabled high deposition rate and formation of crack-free, adherent deposits. Electrodeposition rates were quantified in experiments performed at constant current and constant voltage modes from suspensions in ethanol, isopropanol and mixed ethanol—isopropanol solvents. The microstructure of as prepared and sintered deposits was studied by electron microscopy. The bath composition was optimized to enable formation of dense deposits.     

中温固体氧化物燃料电池的Ag-YSB复合阴极

用草酸盐共沉淀法制备了Y0 25Bi0.75O1.5(YSB),用X-ray衍射方法考察了其成相温度,用交流阻抗法测试了其电导率.与Ag复合制成复合阴极,研究了烧结温度对复合阴极微结构的影响.同时以Sm0.2Ce0.8O1.9(SDC)为电解质,用交流阻抗法研究YSB含量对复合阴极界面阻抗的影响.用草酸盐共沉淀制备的YSB粉,其电导率比SDC大得多.Ag-YSB复合阴极疏松多孔,Ag-YSB与SDC的界面结合良好,形成了足够多的三相界面,降低了界面极化电阻.YSB有一个最佳添加量,电阻最小,即电极界面性能最高.YSB的过量添加损坏Ag相的连续性,降低氧的还原转化速度,使界面的电阻增大.     

Materials for high-temperature oxygen reduction in solid oxide fuel cells

Solid state ionic devices such as fuel cells and oxygen separation membranes require the adsorption of oxygen molecules, their dissociation into oxygen atoms, oxidation by charge exchange and entry of the resultant ion into the solid phase. The cathodes capable of sustaining these processes must themselves be stable in the high temperature environment of air with a significant water vapour content, and compatible chemically and mechanically with the contacting solid phase, normally an electrolyte. As charge transfer materials obviously a high electronic conductivity is imperative, and some degree of ionic conductivity can serve to delocalise the oxidation process, thus reducing polarisation. In the present review the evolution of these cathode materials and their present status will be presented.