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  Solid oxide fuel cell anodes and electrodes for other electrochemical devicesRelated Patent Categories: Chemistry: Electrical Current Producing Apparatus, Product, And Process, Fuel Cell, Subcombination Thereof Or Methods Of Operating, Catalytic Electrode Structure Or Composition, Having An Inorganic Matrix, Substrate Or SupportThe Patent Description & Claims data below is from USPTO Patent Application 20070172719. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] The present invention relates generally to the field of electrochemical devices, and more particularly but not exclusively to anode supported electrochemical cells and methods of fabrication. Materials and devices in accordance with the invention find advantageous use in solid oxide electrolyte electrochemical devices such as, for example, solid oxide fuel cells, electrolyzers, electrochemical sensors and the like. [0002] As a background to the invention, electrochemical devices based on solid oxide electrolytes have received, and continue to receive, significant attention. For example, solid state oxygen separation devices have received significant attention for the separation of pure oxygen from air. In addition, electrochemical fuel cell devices are believed to have significant potential for use as power sources. Fuel cell devices are known and used for the direct production of electricity from standard fuel materials including fossil fuels, hydrogen, and the like by converting chemical energy of a fuel into electrical energy. Fuel cells typically include a porous fuel electrode (also referred to as the "anode"), a porous air electrode (also referred to as the "cathode"), and a solid or liquid electrolyte therebetween. In operation, gaseous fuel materials are contacted, typically as a continuous stream, with the anode of the fuel cell system, while an oxidizing gas, for example air or oxygen, is allowed to pass in contact with the cathode of the system. Electrical energy is produced by electrochemical combination of the fuel with the oxidant. Because the fuel cells convert the chemical energy of the fuel directly into electricity without the intermediate thermal and mechanical energy step, their efficiency can be substantially higher than that of conventional methods of power generation. [0003] Solid oxide fuel cells (SOFCs) employing a dense ceramic electrolyte are currently considered as one of the most attractive technologies for electric power generation. In a typical SOFC, a solid electrolyte separates the porous metal-based anode from a porous metal or ceramic cathode. Due to its mechanical, electrical, chemical and thermal characteristics, yttria-stabilized zirconium oxide (YSZ) is currently the electrolyte material most commonly employed. At present, the anode in a typical SOFC is made of nickel-YSZ cermet, and the cathode is typically made of lanthanum manganites, lanthanum ferrites or lanthanum cobaltites. In such a fuel cell, an example of which is shown schematically in FIG. 1, the fuel flowing to the anode reacts with oxide ions to produce electrons and water. The oxygen reacts with the electrons on the cathode surface to form oxide ions that migrate through the electrolyte to the anode. The electrons flow from the anode through an external circuit and then to the cathode. The movement of oxygen ions through the electrolyte maintains overall electrical charge balance, and the flow of electrons in the external circuit provides useful power. Useful fuels for fuel cell power generation include, for example, hydrogen, carbon monoxide, methane and hydrazine. [0004] Because each individual electrochemical cell made of a single anode, a single electrolyte, and a single cathode generates an open circuit voltage of about one volt and each cell is subject to electrode activation polarization losses, electrical resistance losses, and ion mobility resistant losses which reduce its output to even lower voltages at a useful current, a fuel cell assembly comprising a plurality of fuel cell units electrically connected to each other to produce the desired voltage or current is required to generate commercially useful quantities of power. [0005] SOFCs typically operate at high temperatures, such as, for example, 650-1000.degree. C. This allows flexibility in fuel choice and results in suitable fuel-to-electricity and thermal efficiencies; however, high temperatures impose stringent requirements on the materials selection for components of the fuel cell or fuel cell assembly. High operating temperatures also result in large thermal swings when the fuel cell is shut down and allowed to approach room temperature, either intentionally or accidentally. Because the different materials of the fuel cell invariably react differently to thermal cycling, i.e. they exhibit different thermal expansion coefficients; this thermal cycling can cause undesirable stress and lead to fluid leaks or structural breakdown. [0006] Even larger thermal swings might be experienced by portions of the fuel cell during fabrication. For example, it is common to form portions of a fuel cell via a process which entails sintering at high temperatures, for example 1000-1400.degree. C. In order to increase the overall efficiency of the fuel cell is it desirable to reduce the thickness of the electrolyte membrane. This is accomplished by co-sintering the thin (1-15 .mu.m) electrolyte with one of the electrodes as the primary support. Thermal expansion mismatches between the electrolyte and the electrode materials can result in undesirable stresses at material interfaces and/or the development of warping or camber when cooling from these high temperatures. Moreover, it is often desirable or necessary to utilize a series of thermal treatments to fully assembly a fuel cell. For example, an individual cell might be formed by first constructing an electrolyte-anode membrane in the first co-sintering operation. Then a cathode layer is applied to the electrolyte membrane and finished in a second co-sintering step. Alternately the cathode may be fired during the same sintering operation as the anode-electrolyte layers. [0007] Present efforts to develop commercially acceptable SOFCs that can be economically mass produced are hindered by the challenges presented by this thermal cycling and material property mismatch. For example, potential efficiencies to be gained through size reductions, for example by the construction of thin cells which utilize less materials and minimize gas diffusion distances, are offset by the need to overcome the challenges of thermal cycling. [0008] Accordingly, it is apparent that there is a continuing need for further developments in the field of SOFC technology. In particular, there is a need for further advancement in the development of materials and techniques that are practical and cost-effective yet can withstand the rigorous demands of manufacturing and use in advanced SOFC designs. The present invention addresses this need, and further provides related advantages. SUMMARY [0009] The present invention relates generally to systems and methods for forming electrochemical devices, and in particular supported electrolytes. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the embodiments disclosed herein are described briefly as follows. [0010] In one form of the present invention, a solid oxide fuel cell for electrochemically reacting a fuel gas with an oxidant gas to product a DC output voltage comprises a layer of ceramic ion conducting electrolyte defining first and second opposing surfaces; a conductive anode layer facing the first surface of the electrolyte layer; and a conductive cathode layer facing the second surface of the electrolyte layer; wherein at least a portion of the conductive anode layer contains between about 0.5% and 10% by weight silicon carbide. [0011] It is one object of the present invention to provide improved systems and methods for use in constructing electrochemical devices. [0012] Further objects, features, advantages, benefits, and further aspects of the present invention will become apparent from the drawings and description contained herein. BRIEF DESCRIPTION OF THE FIGURES [0013] Although the characteristic features of this invention will be particularly pointed out in the claims, the invention itself, and the manner in which it may be made and used, may be better understood by referring to the following description taken in connection with the accompanying figures forming a part hereof. [0014] FIG. 1 depicts a general schematic diagram showing the function of a solid oxide fuel cell. [0015] FIG. 2 is a schematic diagram of an embodiment of a fuel cell in accordance with the invention. [0016] FIG. 2A is a schematic diagram of an embodiment of a fuel cell unit including an interconnect in accordance with the invention. [0017] FIG. 3 is a schematic diagram of an embodiment of an electrochemical device of the invention. [0018] FIG. 4 is a schematic diagram of the roll lamination process used in the construction of anode-electrolyte bilayers. [0019] FIG. 5 is a scanning electron micrograph showing the microstructure of an anode-electrolyte bilayer with SiC particles in the bulk anode. [0020] FIG. 6 is a picture of an anode-electrolyte bilayer at room temperature after sintering illustrating the undesirable formation of camber. [0021] FIG. 7 is a picture of an anode-electrolyte bilayer at room temperature after sintering illustrating the reduction in camber with 1 wt % SiC in the bulk anode. Continue reading... Full patent description for Solid oxide fuel cell anodes and electrodes for other electrochemical devices Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Solid oxide fuel cell anodes and electrodes for other electrochemical devices patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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