Patent Application
20050048352
This application claims the priority of Japanese Patent Application Number 2003-209731, filed on Aug. 29, 2003.
1. Field of the Invention
The present invention relates to a fuel-cell device utilizing surface-migration on solid oxide, and more particularly to a fuel-cell device utilizing surface-migration on solid oxide comprising a cathode layer and an anode layer formed a prescribed distance apart on one surface of a solid oxide substrate, wherein provisions are made to supply a fuel to the anode layer via a fuel supply layer formed thereon and to supply air to the cathode layer, thereby accomplishing a simple structure obviating the need to hermetically seal the fuel-cell device, and thus achieving a compact and thin construction while, at the same time, achieving lower operating temperature for power generation.
2. Description of the Related Art
Heretofore, fuel cells have been developed and commercially implemented as a low-pollution power generating means to replace traditional power generation such as thermal power generation, or as an electric energy source for electric vehicles that replaces the internal combustion engine which uses gasoline or the like as the fuel. For such fuel cells, much research effort has been expended to increase the efficiency and to reduce the cost.
Fuel cells can be classified into various types according to the method of power generation, one being the type of fuel cell that uses a solid electrolyte. As one example of the fuel cell that uses a solid electrolyte, a fuel cell is known that uses a calcined structure made of yttria(Y2O3)-doped stabilized zirconia as an oxygen ion conducting solid electrolyte layer. This type of fuel cell comprises a cathode layer formed on one surface of the solid electrolyte layer and an anode layer on the opposite surface thereof, and oxygen or an oxygen-containing gas is fed to the cathode layer, while a fuel gas such as methane is fed to the anode layer.
In this fuel cell, the oxygen (O2) fed to the cathode layer is converted into oxygen ions (O2−) at the boundary between the cathode layer and the solid electrolyte layer, and the oxygen ions are conducted through the solid electrolyte layer into the anode layer where the ions react with a fuel gas such as, for example, methane gas (CH4), fed to the anode layer, the end products of the reaction being water (H2O) and carbon dioxide (CO2). In this reaction process, as the oxygen ions release electrons, a potential difference occurs between the cathode layer and the anode layer. Here, when the cathode layer and the anode layer are electrically connected by a lead wire, the electrons in the anode layer flow into the cathode layer via the lead wire, and the fuel cell thus generates electricity. The operating temperature of this type of fuel cell is about 1000° C.
However, this type of fuel cell requires the provision of separate chambers, one being an oxygen or oxygen-containing gas supply chamber on the cathode layer side and the other a fuel gas supply chamber on the anode layer side; furthermore, as the fuel cell is exposed to oxidizing and reducing atmospheres at high temperatures, it has been difficult to increase the durability of the fuel cell.
On the other hand, there has been developed a fuel cell of the type that comprises a cathode layer and an anode layer formed on opposite surfaces of a solid electrolyte layer, and that generates an electromotive force between the cathode layer and the anode layer by placing the fuel cell in a mixed fuel gas consisting of a fuel gas, for example, a methane gas, and an oxygen gas. The principle of generating an electromotive force between the cathode layer and the anode layer is the same for this type of fuel cell as for the above-described separate-chamber type fuel cell but, as the whole fuel cell can be exposed to substantially the same atmosphere, the fuel cell can be constructed as a single-chamber type cell to which the mixed fuel gas is supplied, and this serves to increase the durability of the fuel cell.
However, in this single-chamber fuel cell also, as the fuel cell has to be operated at a high temperature of about 1000° C., there is the danger that the mixed fuel gas may explode. Here, if the oxygen concentration is reduced to a level lower than the ignitability limit to avoid such danger, there occurs the problem that carbonization of the fuel, such as methane, progresses and the cell performance degrades. In view of this, there is proposed, for example, in Japanese Unexamined Patent Publication No. 2003-92124, a single-chamber fuel-cell device that can use a mixed fuel gas whose oxygen concentration is adjusted so as to be able to prevent the progress of carbonization of the fuel, while at the same time, preventing the explosion of the mixed fuel gas.
The above proposed fuel-cell device is of the type that is constructed by housing individual fuel cells in a single chamber; on the other hand, an apparatus is proposed that does not require the provision of a special chamber, and that generates electricity by placing a solid electrolyte fuel cell in or near a flame and thereby holding the solid electrolyte fuel cell at its operating temperature.
The fuel cell used in this electric power generating apparatus comprises a zirconia solid electrolyte layer formed in a tubular structure, an anode layer as a fuel electrode formed on the outer circumference of the tubular structure, and a cathode layer as an air electrode formed on the inner circumference of the tubular structure. This solid electrolyte fuel cell is operated with the anode layer exposed to a reducing flame portion of a flame generated from a combustion apparatus to which the fuel gas is supplied. In this arrangement, radical components, etc., present in the reducing flame are utilized as the fuel, while air is supplied by convection or diffusion to the cathode layer inside the tubular structure, and the fuel cell thus generates electricity. Such a fuel-cell device is proposed, for example, in Japanese Unexamined Patent Publication No. 6-196176.
In any of the above proposed fuel-cell devices, the solid electrolyte layer functions as an oxygen ion conductor, and the oxygen ions conducted through the solid electrolyte layer react with fuel species to generate an electromotive force. On the other hand, in a paper by W. van Gool, entitled “THE POSSIBLE USE OF SURFACE MIGRATION IN FUEL CELLS AND HETEROGENEOUS CATALYSIS,” Philips Res. Repts 20, 81-93, 1965, a fuel cell is proposed that operates on the principle that an electromotive force can be generated by the two reactant species migrating over the surface of an insulating substrate and reacting with each other.
In this fuel cell, two electrodes are arranged in close proximity to each other on the same surface of an insulating substrate, and both electrodes are exposed to a mixed gas of oxygen and hydrogen. At one electrode, oxygen ions are formed by chemisorption and, at the other electrode, hydrogen ions are formed by chemisorption; then, the thus formed oxygen ions and hydrogen ions migrate over the surface of the insulating substrate and react with each other. It is claimed that, in this way, an electromotive force can be generated between the two electrodes.
The earlier described single-chamber fuel-cell device obviates the necessity of strictly separating the fuel and the air, as was the case with conventional solid electrolyte fuel-cell devices, but has to employ an explosion-proof, hermetically sealed construction. Further, to increase the electromotive force, a plurality of plate-like solid electrolyte fuel cells need to be stacked and, since they are operated at high temperatures, an interconnect material having high heat resistance and high electrical conductivity must be used to electrically connect the plurality of plate-like solid electrolyte fuel cells. As a result, the single-chamber fuel-cell device constructed from a stack of plate-like solid electrolyte fuel cells has the problem that the construction is not only large but also costly.
Furthermore, as the temperature is gradually raised to the high operating temperature in order to prevent cracking of the plate-like solid electrolyte fuel cells, this type of single-chamber fuel-cell device has had the problem that it requires a significant startup time and hence extra trouble to operate; that is, with this type of fuel-cell device, it has not been possible to generate electricity in a simple manner.
In contrast, the oxygen ion conducting solid electrolyte fuel-cell device formed in a tubular structure employs the fuel cell of the type that directly utilizes a flame; this type of fuel cell has the characteristic of being an open type, the solid electrolyte fuel cell not needing to be housed in a hermetically sealed container. As a result, this type of fuel cell can have a reduced startup time, is simple in structure, and is therefore advantageous when it comes to reducing the size, weight, and cost of the fuel cell, and it can be said that this fuel cell is a handy power plant. Further, as the flame is directly used, this type of fuel cell can be incorporated in a conventional combustion apparatus or an incinerator or the like, and is thus expected to be used as an electricity supply device.
However, in this type of fuel cell, as the anode layer is formed on the outer circumference of the tubular solid electrolyte layer, radical components due to the flame are not supplied, in particular, to the upper half of the anode layer, and effective use cannot be made of the entire surface of the anode layer formed on the outer circumference of the tubular solid electrolyte layer. This has degraded the power generation efficiency. There has also been the problem that, as the solid electrolyte fuel cell is directly heated by the flame, cracking tends to occur due to rapid changes in temperature, and the solid electrolyte fuel cell, if cracked, eventually disintegrates into pieces, resulting in an inability to generate electricity.
On the other hand, the earlier cited paper provides no more than a report that the proposed fuel cell can theoretically generate an electromotive force, and this type of fuel cell has not been implemented in practice for such reasons as: it has been difficult to form the two electrodes close enough together; an electrode material that can form a specific reactant species by selectively chemisorbing one of the reaction components is not easily found; the insulating substrate must have good desorption for the reaction product formed on its surface; and experiments must be performed outside the explosion range of the mixed gas.
Considering the above problems, and noting that the type of fuel cell configuration in which the two electrodes are arranged side by side on one surface of an insulating substrate is suitable for reducing the thickness of the fuel cell, it is an object of the present invention to provide, based on the findings obtained during the development of solid electrolyte fuel cells, a fuel-cell device utilizing surface-migration on solid oxide in which a cathode layer and an anode layer are arranged parallel to each other on one surface of a solid oxide substrate, wherein provisions are made to supply air to the cathode layer and to supply a fluid fuel directly to the anode layer, thereby achieving reductions in the size and cost of the fuel-cell device while, at the same time, achieving lower operating temperature for power generation.
To solve the above-enumerated problems, the present invention provides a fuel-cell device utilizing surface-migration on solid oxide in which a cathode layer, to which air is supplied, and an anode layer, to which a fluid fuel is supplied, are arranged on one surface of a solid oxide substrate in such a manner as to oppose each other across a given surface region of the solid oxide substrate, wherein a fuel supply layer for supplying the fluid fuel to the surface region via the anode layer is provided in a contacting relationship with the anode layer.
The solid oxide substrate is selected from the group consisting of a glass substrate, a sintered alumina substrate, and samaria-doped ceria ceramic substrate, and the substrate may be formed on a reinforcing substrate, a semiconductor substrate, or a heat-exchange substrate.
The cathode layer and the anode layer are porous layers each formed in the shape of a strip. Alternatively, the cathode layer is a porous layer formed in the shape of a strip, and the anode layer is a metal powder filled layer formed in the shape of a strip or a metal plate formed in the shape of a strip.
The anode layer is formed from a material selected from the group consisting of rhenium, tungsten, nickel, molybdenum, and copper, while the cathode layer is formed from a material selected from the group consisting of samarium strontium cobaltite, lanthanum strontium cobaltite, and lanthanum strontium manganite.
The fuel supply layer is placed along the length of the anode layer in a contacting relationship with an upper surface or a side surface of the anode layer so that the fluid fuel permeates from one end of the fuel supply layer and is supplied to the surface region, wherein the fuel supply layer is formed from an inorganic powder filled material or an inorganic fiber aggregate.
Further, the fuel supply layer has, at least on an outer surface thereof, a cover layer for preventing the fluid fuel from scattering or evaporating, wherein when the fuel supply layer is placed in contacting relationship with the side surface of the anode layer, the cover layer covers the upper surface of the anode layer.
A plurality of cathode layers and a plurality of anode layers are formed on the solid oxide substrate, wherein the plurality of cathode layers extending from a common cathode layer and the plurality of anode layers extending from a common anode layer are arranged parallel to each other in interlocking comb-shaped patterns on the solid oxide substrate.
In a preferred mode, a plurality of common cathode layers and a plurality of common anode layers are provided, wherein the common cathode layers and the common anode layers are respectively connected together electrically and the common cathode layers and the common anode layers are connected in parallel, or the common cathode layers and the common anode layers are alternately connected electrically and the common cathode layers and the common anode layers are connected in series. In another preferred mode, the common cathode layers and the common anode layers are respectively connected together electrically, forming a plurality of parallel connection groups of the common cathode layers and the common anode layers, and the plurality of parallel connection groups are connected in series.
The fuel supply layer is placed between two adjacent ones of the anode layers in contacting relationship with side surfaces of the adjacent anode layers so that the fluid fuel permeates from one end of the fuel supply layer and is supplied to the surface region via each of the adjacent anode layers, wherein each of the cathode layers is disposed on either side of the anode layers opposite from the fuel supply layer in such a manner as to sandwich the surface region therebetween, and a cover layer is provided that covers the upper surfaces of the adjacent anode layers as well as the fuel supply layer placed between the anode layers.
Other features, objects and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings in which like reference characters designate like or corresponding parts throughout several views, and in which:
Embodiments of a fuel-cell device utilizing surface-migration on solid oxide according to the present invention will be described below with reference to the drawings. However, before proceeding to the description of the fuel-cell devices utilizing surface-migration on solid oxide of the embodiments according to the present invention, prior art solid electrolyte fuel-cell devices related to the fuel-cell devices utilizing surface-migration on solid oxide of the embodiments will be described in order to clarify the features and advantages of the respective embodiments.
The container 4 is provided with a supply pipe 5 for supplying the mixed fuel gas containing oxygen and a fuel such as methane and an exhaust pipe 6 for ejecting the exhaust gas. Vacant spaces in the container 4, where the mixed fuel gas and the exhaust gas flow, i.e., the areas in the container 4 other than the area occupied by the fuel cells, are filled with the fillers 7 and 8, and a suitable gap is provided therebetween, thereby preventing the mixed fuel gas from igniting even when a mixed fuel gas within the ignitability limit is contained therein when the fuel-cell device is operated.
The basic structure of the fuel-cell device shown in
Next, the embodiments of the fuel-cell device utilizing surface-migration on solid oxide according to the present invention will be described with reference to FIGS. 1 to 8, but before proceeding to the detailed description of the embodiments of the fuel-cell device utilizing surface-migration on solid oxide according to the present invention, the reason that has led to the adoption of the fuel cell structure characterizing the embodiments will be described first.
An oxygen ion conducting solid electrolyte fuel-cell device that directly utilizes a flame, such as described previously, has been developed as a fuel-cell device that can be used as a handy power plant without requiring a hermetically sealed structure. In this type of solid electrolyte fuel-cell device, unlike the fuel-cell device that uses separate chambers according to the prior art, the oxygen to be fed to the cathode layer and the fuel to be fed to the anode layer can be reliably separated despite its open type construction, but since the solid electrolyte layer is formed in the shape of a tube, the flame has not been applied efficiently to the anode layer formed on the outer circumference of the solid electrolyte layer, and therefore, its power generation efficiency has been low.
It can therefore be understood that, to increase the power generation efficiency of the solid electrolyte fuel-cell device, the fuel should be supplied uniformly over the entire surface of the anode layer. To increase the power generation efficiency, in the fuel-cell device utilizing surface-migration on solid oxide of each embodiment of the present invention, a fluid fuel relatively easy to handle is employed as the fuel, and a fuel supply layer is provided that allows the fluid fuel to permeate therethrough so as to be fed uniformly over the entire surface of the anode layer. A fuel that easily permeates through the fuel supply layer is suitable for use as the fluid fuel, examples including hydrogen, vapor-phase hydrocarbons, etc. in the case of a gaseous fuel, and liquid-phase hydrocarbons, alcohol, ketone, ester, ether, etc. in the case of a liquid fuel.
On the other hand, attempts have been made to increase the power generation performance of the oxygen ion conducting solid electrolyte fuel-cell devices of the single chamber type shown in
The anode layer of each fuel cell is formed from a ceramic having electrical conductivity or a metal having oxidation resistance to the mixed fuel gas supplied at the operating temperature of the fuel cell; here, it has been proposed to increase the power generation performance by adding a transition metal or its oxide to the anode layer, the transition metal being selected from the group consisting of rhodium (Rh), platinum (Pt), ruthenium (Ru), palladium (Pd), rhenium (Re), and iridium (Ir).
When contributions, etc. of such metals or their oxides to the power generation performance, when added in the anode layer, were examined, it was confirmed that any of these transition metals or their oxides have a catalyst activation effect in the oxidation-reduction reaction occurring between the fuel gas and the oxygen. It has thus been found that, when the anode layer of the oxygen ion conducting solid electrolyte fuel cell is formed from any of these transition metals, the oxidation-reduction reaction can be sufficiently induced between the fuel gas and the oxygen, and an electromotive force can be generated between the cathode layer and the anode layer.
Therefore, based on this finding, it has been decided to form the anode layer of the oxygen ion conducting solid electrolyte fuel cell from a transition metal selected from the group consisting of rhodium (Rh), platinum (Pt), ruthenium (Ru), palladium (Pd), rhenium (Re), and iridium (Ir). Further, as it is required that the anode layer formed from such a transition metal be permeable to the fluid fuel supplied, it has been found that the anode layer should be formed from a porous layer or a layer filled with powder particles.
Here, taking rhenium (Re) as an example, the anode layer can be formed on the solid electrolyte layer by sputtering or evaporating a rhenium metal; here, as a rhenium powder with a purity of 99.995% and a grain size of 100 to 325 mesh (manufactured by Aldrich) is commercially available, this rhenium powder can be conveniently used, as-is, as the anode layer. In particular, the rhenium powder has the property that its electrical conductivity is high even in a powder state; therefore, the rhenium powder is advantageous because the internal resistance of the anode layer itself can be reduced even if the rhenium metal powder is used, as-is, as the anode layer.
Using the rhenium in the powder state has the advantage that the specific surface area increases, increasing the number of points at which the powder particles contact each other. In the case of other transition metals as well, the catalytic activity can be enhanced because the contact condition of particle surfaces improves and the specific surface area increases; therefore, it has been confirmed that not only rhenium but other transition metals can also be used in a powder state to form the anode layer.
In the case of the transition metals other than rhenium, a porous anode layer can be easily formed by preparing a metal powder in the form of a paste and sintering the paste, but in the case of the rhenium metal powder, it is known that when it is heated, for example, in the atmosphere, if the temperature exceeds about 400° C., its weight decreases, and also that when it is heated in a nitrogen atmosphere, if the temperature exceeds about 418° C., its weight decreases. As a result, if the rhenium metal powder is prepared in the form of a paste and the paste is sintered, the rhenium metal vaporizes and the anode layer cannot be formed; therefore, it can be understood that the rhenium metal should be used in a powder form.
It will be recalled that, in the case of the oxygen ion conducting type solid electrolyte fuel cells of the prior art, the operating temperature for power generation was about 1000° C.; on the other hand, when the anode layer is formed from the rhenium metal, it can be understood from the above property of the rhenium metal that the fuel cell should be operated for power generation at temperatures of about 300° C. or lower, considering variations in heat balance, and preferably at temperatures of about 200° C. or lower. This means that the operating temperature for power generation can be reduced in the case of the solid electrolyte fuel cell whose anode layer is formed from a rhenium metal powder. For the transition metals other than rhenium, it was confirmed that an electromotive force occurs between the cathode layer and the anode layer at 300° C. or lower or even at room temperature.
Considering the above findings, and based on the previously described surface-utilizing type fuel cell structure comprising fuel cells formed on an insulating substrate surface and capable of achieving a thin fuel cell construction, the embodiments of the present invention are each directed to the provision of a fuel-cell device utilizing surface-migration on solid oxide which uses a solid oxide substrate as the substrate, and in which the cathode layer, which directly contacts air, and the anode layer, to which a fluid fuel is directly supplied from the fuel supply layer, are arranged in parallel and in close proximity to each other on one surface of the solid oxide substrate and an electromotive force is generated between the cathode layer and the anode layer.
This configuration obviates the need to place the fuel cells in an explosive atmosphere of the mixed gas and also the need to house them in a hermetically sealed chamber. Further, as the cathode layer can be maintained in an oxygen-rich condition, and the anode layer in a fuel-rich condition, the catalytic activity of each layer can be enhanced. Moreover, when a transition metal such as rhenium is used for the anode layer, the operating temperature for power generation can be reduced compared with the prior art fuel cells, and it becomes possible to generate electricity even at room temperature.
When the fuel-cell device is constructed employing the above structure that supplies the fluid fuel to the entire surface of the anode layer formed from a transition metal, the power generation operating temperature of the fuel-cell device can be reduced; as a result, there is no need to take into account possible cracking of the solid layer due to thermal history, nor is it necessary to provide a hermetically sealed construction, and an inexpensive and handy fuel-cell device can thus be achieved. When the power generation operating temperature is lowered, it becomes easier to use a fluid fuel such as hydrogen, vapor-phase hydrocarbons, liquid-phase hydrocarbons, alcohol, ketone, ester, ether, etc. as the fuel for the fuel-cell device.
Next, a first embodiment of a fuel-cell device utilizing surface-migration on solid oxide according to the present invention, which is constructed based on the above-stated reason, will be shown in
In the fuel-cell device utilizing surface-migration on solid oxide, strip-shaped anode layers (fuel electrodes) 31 and 32 are formed in parallel and in close proximity to the respective sides of a strip-shaped cathode layer (air electrode) 2 on one surface (in
Fuel supply layers 111 and 112, each formed from an inorganic powder filled material or an inorganic fiber aggregate, are placed on the upper surfaces of the respective anode layers 31 and 32. The fuel supply layers 111 and 112 are provided to supply a fluid fuel directly to the entire surfaces of the respective anode layers; the fluid fuel is fed through one end of each fuel supply layer, permeates through the fuel supply layer while being diffused therein, and is supplied to the anode layer.
When the cathode layers and the anode layers are arranged in parallel and in close proximity to each other on the surface of the solid oxide substrate 1, ion conducting surface regions are formed between the cathode layer and its adjacent anode layers, thus forming fuel cells C1 and C2. As these fuel cells are placed in an open air space, the cathode layer 2 is in an oxygen-rich condition, so that oxygen ions are formed there and supplied to the surface regions on the substrate 1. On the other hand, the fuel is supplied from the fuel supply layers 111 and 112 to the respective anode layers 31 and 32, where the fuel is activated to form fuel species which react with the oxygen ions that migrated over the surface regions. With this reaction, an electromotive force is generated between the cathode layer and the respective anode layers.
In
This structure prevents the fluid fuel from leaking or evaporating from the fuel supply layers, and enhances the fuel-rich condition of each anode layer while ensuring the oxygen-rich condition of the cathode layer, as the air can be clearly separated from the fluid fuel. It also becomes possible to forcefully blow air to the cathode layer so that the cathode layer can be effectively exposed to the air. When air is blown in this way, reaction products can also be removed forcefully, and the power generation efficiency improves.
In each of the fuel-cell devices utilizing surface-migration on solid oxide described above, the fuel supply layers are formed at least on the upper surfaces of the respective anode layers; on the other hand, a fourth embodiment shown in
As shown in
This structure serves to reduce the number of fuel supply layers, while ensuring effective supply of the fluid fuel. Further, as the fuel supply layers are arranged on the same plane as the anode layers in contacting relationship with their sides, the thickness of the fuel-cell device can be further reduced, making it easier to stack a plurality of fuel-cell devices.
As in the third embodiment shown in
In the fuel-cell devices utilizing surface-migration on solid oxide of the embodiments described above, not only a calcined alumina ceramic plate and a glass substrate, for example, but also a solid electrolyte substrate formed from a material selected from among the known materials listed below can be adopted for use as the solid oxide substrate.
For the anode layers formed on the solid oxide substrate, use is made of a metal such as tungsten (W) or nickel (Ni) or of a transition metal selected from the group consisting of rhodium (Rh), platinum (Pt), ruthenium (Ru), palladium (Pd), rhenium (Re), and iridium (Ir), as earlier described. These metals are used in the powdered or powder particle state to directly form the layers, or sintered into a porous structure. When constructing the anode layers by using an iron-nickel-chromium alloy, metal plates made of this alloy may be used directly as the anode layers.
The cathode layers arranged in parallel to the anode layers on the surface of the solid oxide substrate can be constructed using, for example, samarium strontium cobaltite or other known material such as lanthanum manganite doped with an element, for example, strontium (Sr), from group III of the periodic table (for example, lanthanum strontium manganite) or a lanthanum gallium oxide or cobalt oxide compound doped with such an element (for example, lanthanum strontium cobaltite).
While the cathode layers and anode layers of the fuel-cell devices utilizing surface-migration on solid oxide of the above embodiments are both formed from porous materials, it is preferable to form the surface of the solid oxide substrate as smooth as possible, because the surface regions over which the oxygen ions migrate need to be formed on the surface. Accordingly, it will be advantageous to form the solid oxide substrate as a compact structure.
In the case of the fuel-cell devices utilizing surface-migration on solid oxide of the above embodiments, as the operating temperature for power generation can be lowered, the fuel-cell devices need not be operated at high temperatures, unlike the prior art solid electrolyte fuel-cell devices; as a result, the temperature change during power generation is mild, and there is no need to take into account possible cracking of the substrate even when the conventional closely compacted structure is employed for the substrate.
The fuel cells utilizing surface-migration on solid oxide according to the above embodiments are fabricated, for example, in the following manner. First, a paste for forming the cathode layers is applied over one surface of a flat plate-like solid oxide substrate in a pattern of strips each having a prescribed width, and then the paste is calcined into a porous structure. A plurality of strip-shaped cathode layers spaced at prescribed intervals are thus formed on the solid oxide substrate. When forming the cathode layers, calcination may not be performed, depending on the material of the solid oxide substrate; in that case, the cathode layers formed in advance by calcining the paste or by using a plate-like material may be simply placed on the solid oxide substrate.
When using a transition metal powder to form the anode layers, strips of transition metal powder are formed on the solid oxide substrate on which the cathode layers have been formed; more specifically, each strip of metal powder is formed on the substrate surface between the respective cathode layers with a prescribed spacing provided relative to each cathode layer. In this case, the metal powder may be prepared, for example, in the form of a paste, and the paste may be applied in a strip-like pattern and then dried to form the strip-shaped anode layers. Alternatively, metal layers preformed in a porous structure, or metal plates themselves, may be arranged as the anode layers.
When the strip-shaped cathode layers and anode layers have been formed on the same surface of the solid oxide substrate as described above, the fuel supply layers, for example, unwoven fabrics, having the same width as the anode layers, in the case of the fuel-cell device utilizing surface-migration on solid oxide shown in
A metal mesh that functions as an extraction electrode as well as a reinforcing member may be embedded in or fixed to the upper surface of each cathode layer. In the case of the embedding method, the material (paste) for forming each layer is applied over the solid electrolyte layer, and the metal mesh is embedded in the thus applied material, which is then calcined. In the case of the fixing method, the metal mesh is not completely embedded in each layer material but may be fixed on a surface of it, followed by calcining.
For the metal mesh used here, a material that has excellent heat resistance, and that well matches the thermal expansion coefficient of the cathode layer which the metal mesh is to be embedded in or fixed to, is suitable. Specific examples include a platinum metal and a platinum-containing metal alloy formed in the shape of a mesh. Alternatively, stainless steel of SUS 300 series (304, 316, etc.) or SUS 400 series (430, etc.) may be used; these materials are advantageous in terms of cost.
Instead of using the metal mesh, metal wires may be embedded in or fixed to the cathode layer. The metal wires are formed using the same metal material as that used for the metal mesh, and the number of wires and the configuration of the wire arrangement are not limited to any particular number or configuration.
The metal mesh or metal wires embedded in or fixed to the cathode layer serve to reinforce the structure so that the solid oxide substrate, if cracked, will not disintegrate into pieces; furthermore, the metal mesh or the metal wires act to electrically connect the cracked portions, and function as a current collecting electrode.
When the metal mesh or the metal wires are embedded in the cathode layer, the power generation performance of the fuel cell does not drop even if cracking occurs in the substrate, and the fuel cell can continue to generate electricity.
On the other hand, when the anode layers are formed from transition metal powder particles, the anode layers need not necessarily be provided with a metal mesh or metal wires, as the anode layers themselves flexibly deform because the powder particles accommodate the cracking of the solid oxide substrate. Accordingly, when each anode layer is formed from powder particles, the effective area of the anode layer is maintained even if cracking occurs in the solid oxide substrate, and the durability of the fuel-cell device utilizing surface-migration on solid oxide can thus be enhanced.
The structures of the fuel-cell devices utilizing surface-migration on solid oxide according to the first to fourth embodiments have been described above, each embodiment dealing with the case where the cathode layers and the anode layers, which together constitute individual fuel cells, are formed in interlocking comb-shaped patterns on a single solid oxide substrate, to construct one fuel-cell device. Next, referring to
In
Next, in the configuration of
With this method of connection, the electromotive force to be induced between the lead wires L1 and L2 can be increased, while retaining the power generation capacity of the fuel-cell device utilizing surface-migration on solid oxide shown in
Examples of the fuel-cell devices utilizing surface-migration on solid oxide of the embodiments described above will be shown below.
A solid electrolyte substrate of samaria-doped ceria (SDC, Sm0.2Ce0.8O1.9 ceramic) was used as the solid oxide substrate. A strip of sintered SSC-SDC containing 50% by weight of Sm0.5Sr0.5Co0.3 was placed as a cathode layer on one surface of the ceramic substrate. A strip of rhenium metal powder was applied on the same surface to form an anode layer by providing a spacing of about 0.5 mm or less relative to the cathode layer. Then, ethanol-impregnated gauze was placed in contact with the anode layer.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of about 1.0 V and a short-circuit current of about 41 μA were obtained.
An anode layer was formed by applying a rhenium metal powder in a raised strip pattern on a ceramic substrate made of specular polished alumina, and a strip-shaped SSC plate was placed as a cathode layer by providing a spacing of about 0.1 mm or less relative to the anode layer. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.87 V was obtained, and the short-circuit current at this time was about 33 μA.
An anode layer was formed by applying a tungsten metal powder in a raised strip pattern on a ceramic substrate made of specular polished alumina, and a strip-shaped SSC plate was placed as a cathode layer by providing a spacing of about 0.1 mm or less relative to the anode layer. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.69 V was obtained, and the short-circuit current at this time was about 0.9 μA.
An anode layer was formed by applying a rhenium metal powder in a raised strip pattern on a glass substrate made of a prepared slide, and a strip-shaped SSC plate was placed as a cathode layer by providing a spacing of about 0.1 mm or less relative to the anode layer. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.43 V was obtained, and the short-circuit current at this time was about 12 μA.
A metal plate of an iron-nickel-chromium alloy, or more specifically, a cutter blade, was placed as an anode layer on a ceramic substrate made of specular polished alumina, and a strip-shaped SSC plate was placed as a cathode layer by providing a spacing of about 0.1 mm or less relative to the anode layer. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.3 V was obtained, and the short-circuit current at this time was about 0.7 to 1.1 μA.
A cathode layer was formed by printing and calcining SSC in the form of a strip on an SDC substrate, and a rhenium metal powder was applied in a raised pattern to form an anode layer by the side of the cathode layer by providing a spacing of about 0.4 mm therebetween. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.83 V was obtained, and the short-circuit current at this time was about 90 μA.
SSC printed and calcined in the form of a bar was placed on a ceramic substrate made of specular polished alumina, and a rhenium metal powder was applied in a raised bar pattern to form an anode layer by the side of the SSC by providing a spacing of about 0.4 mm therebetween. The opposing electrodes were about 3 cm in length. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.83 V was obtained, and the short-circuit current at this time was about 70 μA.
A cathode layer formed by printing and calcining SSC in the form of a bar was placed on a ceramic substrate made of specular polished alumina, and a metal plate, i.e., a cutter blade, was placed as an anode layer by the side of the cathode layer by providing a spacing of about 0.4 mm therebetween. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.78 V was obtained, and the short-circuit current at this time was about 0.7 μA.
A cathode layer formed by printing and calcining SSC in the form of a bar was placed on a ceramic substrate made of specular polished alumina, and a nickel metal powder was applied in a raised bar pattern to form an anode layer by the side of the cathode layer by providing a spacing of about 0.1 mm or less therebetween. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.64 V was obtained, and the short-circuit current at this time was about 1.1 μA.
A cathode layer formed by printing and calcining SSC in the form of a bar was placed on a ceramic substrate made of specular polished alumina, and a tungsten metal powder was applied in a raised bar pattern to form an anode layer by the side of the cathode layer by providing a spacing of about 0.1 mm or less therebetween. Then, gauze dampened with ethanol was placed on the side of the anode layer opposite from the cathode layer, to impregnate the anode layer with the ethanol.
When test leads were connected to the cathode layer and the anode layer at room temperature, an open circuit voltage of 0.66 V was obtained, and the short-circuit current at this time was about 1.4 μA.
Two SSC plates, each printed and calcined in the form of a bar, were placed on an SDC substrate to form two cathode layers. A rhenium metal powder was applied in a raised bar pattern to form two anode layers extending in parallel to the respective cathode layers and spaced about 0.4 mm apart from the respective cathode layers. The cathode layer and the anode layer formed on the inner side were electrically connected together by a rhenium metal powder, thereby connecting the two fuel cells in series. Then, gauze dampened with ethanol was placed on the side of each anode layer opposite from its associated cathode layer, to impregnate the anode layer with the ethanol.
When, at room temperature, test leads were connected to the cathode layer and the anode layer located on the outer side, an open circuit voltage of 1.27 V was obtained, and the short-circuit current at this time was about 23 μA.
As described above, according to the present invention, the cathode layers and the anode layers are arranged in parallel and in close proximity to each other on a plate-like solid oxide substrate, and the cathode layers are exposed to the air in the atmosphere, while the anode layers are arranged each contacting a fuel supply layer so that a fluid fuel is supplied directly to the anode layers; as a result, an oxygen-rich condition can be easily maintained at the cathode layers, and a fuel-rich condition at the anode layers, by employing a simple structure that does not require a special hermetically sealed construction, thus achieving reductions in the size and cost of the fuel-cell device utilizing surface-migration on solid oxide.
Further, by selecting and using a material having high catalytic activity for the anode layers to which the fluid fuel is directly supplied, a fuel-cell device utilizing surface-migration on solid oxide can be achieved that can reduce the operating temperature for power generation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-209731 | Aug 2003 | JP | national |
