Fuel cell

Abstract

To provide a fuel battery capable of generating electric power directly using organic material as fuel.SOLUTION: A fuel battery 1 includes a solid electrolyte 2 having oxide ion conductivity, an anode electrode 3 which is provided on one surface of the solid electrolyte 2 and supplied with a fuel 30 containing an organic material 31, and a cathode electrode 4 which is provided on the other surface of the solid electrolyte 2 and reduces oxygen gas to generate oxide ions. The fuel battery 1 satisfies at least one of Requirement A and Requirement B below. Requirement A: the fuel 30 further includes a reverse Boudoir reaction catalyst 32 that promotes a reverse Boudoir reaction for generating carbon monoxide from carbon and carbon dioxide. Requirement B: the anode electrode 3 has a reverse Boudoir reaction catalyst 32.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fuel cell.

Background Art

[0002] Conventionally, a fuel cell having a solid electrolyte having oxide ion conductivity, an anode electrode provided on one surface of the solid electrolyte to which fuel is supplied, and a cathode electrode provided on the other surface of the solid electrolyte to which oxygen gas is supplied is known.

[0003] For example, Patent Document 1 discloses a fuel cell that supplies a fuel gas containing carbon monoxide and hydrogen gas obtained by reforming a hydrocarbon to an anode electrode. Recently, fuel cells that directly supply hydrocarbons as fuel to the anode electrode have also been reported.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a conventionally known fuel cell, when an organic substance such as biomass is directly supplied as fuel to the anode electrode, carbon (C) is deposited on the anode electrode. The carbon deposited on the anode electrode inhibits the battery reaction. Note that Patent Document 1 described above describes a technique for suppressing carbon deposited by the Boudouard reaction (2CO → C + CO2) caused by carbon monoxide contained in the fuel gas generated by a reformer. However, since this technique is not related to a fuel cell that directly supplies an organic substance as fuel to the anode electrode, it is difficult to apply this type of fuel cell.

[0006] The present invention has been made in view of such problems, and aims to provide a fuel cell capable of generating electricity using an organic substance directly as a fuel.

Means for Solving the Problems

[0007] One aspect of the present invention is a solid electrolyte (2) having oxide ion conductivity, an anode electrode (3) provided on one surface of the solid electrolyte and supplied with a fuel (30) containing an organic substance (31), a cathode electrode (4) provided on the other surface of the solid electrolyte and reducing oxygen gas to generate oxide ions, and A fuel cell (1) that satisfies at least one of the following requirements: Requirement A: The fuel further includes a reverse Boudouard reaction catalyst (32) that promotes a reverse Boudouard reaction for generating carbon monoxide from carbon and carbon dioxide; and Requirement B: The anode electrode has the reverse Boudouard reaction catalyst. When the concentration of carbon monoxide generated at the anode electrode rises above the equilibrium point in the Boudouard equilibrium, the temperature of the fuel cell is raised to the temperature at which carbon monoxide is generated. When the concentration of carbon monoxide generated at the anode electrode drops below the equilibrium point in the Boudouard equilibrium, the temperature of the fuel cell is lowered to the equilibrium point at that concentration, and has a control unit for controlling the carbon monoxide concentration and the temperature. , a fuel cell (1) 。

Effects of the Invention

[0008] The fuel cell has the above configuration. Therefore, when an external load is connected between the anode electrode and the cathode electrode and the fuel cell is operated, at the cathode electrode, the cathode reaction of O2 + 4e - → 2O2 - occurs, and oxygen gas is reduced to generate oxide ions. At the anode electrode, carbon monoxide is generated from carbon and carbon dioxide derived from the organic substance by the catalytic action of the reverse water gas shift reaction catalyst (C + CO2 → 2CO). The generated carbon monoxide reacts with the oxide ions (O2 - ) that have moved through the solid electrolyte from the cathode electrode, and carbon dioxide is generated. That is, at the anode electrode, the anode reaction of 2CO + 2O2 - → 2CO2 + 4e - occurs. Thus, the fuel cell can generate electricity by utilizing the reaction of converting the organic substance to carbon monoxide at the anode electrode and then converting the carbon monoxide to carbon dioxide.

[0009] Therefore, according to the above fuel cell, a fuel cell capable of directly generating electricity using an organic substance as a fuel can be provided.

[0010] Note that the reference signs in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] (Embodiment 1) The fuel cell of Embodiment 1 will be described with reference to FIGS. 1 to 3. As illustrated in FIG. 1, the fuel cell 1 of the present embodiment has a solid electrolyte 2, an anode electrode 3 provided on one surface of the solid electrolyte 2, and a cathode electrode 4 provided on the other surface of the solid electrolyte 2. In FIG. 1, specifically, an example is shown in which the anode electrode 3, the solid electrolyte 2, and the cathode electrode 4 are laminated in this order and joined to each other to form a cell.

[0013] The fuel cell 1 may be flat plate-shaped or cylindrical. Further, the fuel cell 1 may have a shape such as a honeycomb shape. In FIG. 1, a flat plate-shaped fuel cell 1 is illustrated. Note that the cylindrical fuel cell 1 will be described later in Embodiment 2 and Embodiment 3. Also, the honeycomb-shaped fuel cell 1 will be described later in Embodiment 4. The fuel cell 1 can be configured in various support methods, such as an anode support type in which the anode electrode 3 also serves as a support, a cathode support type in which the cathode electrode 4 also serves as a support, a self-supporting film type in which the solid electrolyte 2 also serves as a support, and a metal support type in which a metal support (not shown) serves as a support.

[0014] The solid electrolyte 2 has oxide ion conductivity. The solid electrolyte 2 serves as a separator that separates the anode electrode 3 and the cathode electrode 4 so that electrons do not flow between them, and only oxide ions can move inside the solid electrolyte 2. Specifically, the solid electrolyte 2 can be formed in a layered structure from a solid electrolyte having oxide ion conductivity. The solid electrolyte 2 is usually formed into a dense material to ensure gas tightness. As the solid electrolyte material constituting the solid electrolyte 2, for example, from the viewpoints of oxide ion conductivity, strength, thermal stability, etc., an oxide ion conductor composed of zirconium oxide-based oxides such as yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), etc. can be preferably used. As the solid electrolyte material constituting the solid electrolyte 2, yttria-stabilized zirconia, etc. are preferable from the viewpoints of oxide ion conductivity, mechanical stability, compatibility with other materials, and being chemically stable from an oxidizing atmosphere to a reducing atmosphere.

[0015] When the solid electrolyte 2 also serves as a support, the thickness of the solid electrolyte 2 can be, for example, 0.05 mm or more and 1 mm or less. When the solid electrolyte 2 does not also serve as a support, the thickness can be, for example, 0.001 mm or more and 0.01 mm or less.

[0016] The anode electrode 3 can contain one or more electronic conductors such as Ni, Ni alloys, Pt, Pt alloys, Co, Co alloys, Cu, Cu alloys, etc. Among these, from the viewpoints of electronic conductivity, catalytic action of the anodic reaction, cost, etc., preferably, Ni, Ni alloys, and more preferably, Ni. Further, the anode electrode 3 can contain one or more oxide ion conductors composed of zirconium oxide-based oxides such as yttria-stabilized zirconia, scandia-stabilized zirconia, etc. Among these, preferably, yttria-stabilized zirconia. Specifically, the anode electrode 3 can have a configuration containing, for example, Ni and yttria-stabilized zirconia. Also, from the viewpoint of improving gas diffusibility, etc., the anode electrode 3 can have a porous region containing pores 33 (not shown in FIG. 1). Also, from the viewpoint of anodic reactivity, etc., the anode electrode 3 can have a dense region denser than the above porous region. Note that the porosity of the anode electrode 3 can be, for example, 70% or more and 90% or less from the viewpoints of gas diffusibility, strength, etc.

[0017] In the anode electrode 3, the ratio of the electronic conductor to the oxide ion conductor can be, in terms of volume ratio, preferably, 10:90 to 90:10, more preferably, 20:80 to 80:20, and even more preferably, 30:70 to 70:30 from the viewpoints of the formability of the electronic conduction path and the oxide ion conduction path, the balance between electronic conductivity and oxide ion conductivity, etc.

[0018] The anode electrode 3 can be composed of multiple layers. The anode electrode 3 can have a configuration, for example, arranged in contact with the solid electrolyte 2, having a reaction layer (not shown) that mainly serves as the site of the anodic reaction and a gas diffusion layer (not shown) arranged in contact with the reaction layer to promote gas diffusion. According to this configuration, the anode electrode 3 can be functionally separated into a part that causes the anodic reaction and a part that promotes gas diffusion, making it easier to maintain the output. Note that the reaction layer can be formed denser than the gas diffusion layer (the gas diffusion layer can be formed more porous than the reaction layer).

[0019] When the anode electrode 3 also serves as a support, the thickness of the anode electrode 3 can be, for example, 0.05 mm or more and 0.5 mm or less. When the anode electrode 3 does not also serve as a support, the thickness can be, for example, 0.001 mm or more and 0.05 mm or less.

[0020] The cathode electrode 4 reduces oxygen gas to generate oxide ions. Specifically, an oxygen-containing gas 41 containing oxygen gas such as oxygen gas or air is supplied to the cathode electrode 4. Examples of the cathode electrode material include transition metal perovskite-type oxides such as lanthanum-strontium-cobalt-based oxides, lanthanum-strontium-cobalt-iron-based oxides, and lanthanum-strontium-manganese-iron-based oxides, or a mixture containing the above transition metal perovskite-type oxides and a ceria-based solid solution doped with one or more elements selected from Gd, Sm, Y, La, Nd, Yb, Ca, and Ho in ceria (CeO2). These can be used singly or in combination of two or more. Note that the cathode electrode 4 can be formed into a porous body containing pores (not shown) from the viewpoint of improving gas diffusibility. Further, the cathode electrode 4 can be composed of a plurality of layers.

[0021] When the cathode electrode 4 also serves as a support, the thickness of the cathode electrode 4 can be, for example, 0.05 mm or more and 0.5 mm or less. When the cathode electrode 4 does not also serve as a support, the thickness can be, for example, 0.001 mm or more and 0.05 mm or less.

[0022] Note that, although not shown in the drawings, the fuel cell 1 can have an intermediate layer between the solid electrolyte 2 and the cathode electrode 4. The intermediate layer is mainly a layer for suppressing the reaction between the solid electrolyte material and the cathode electrode material. Examples of the material of the intermediate layer include cerium oxide-based oxides such as ceria (CeO2) and ceria doped with one or more elements selected from Gd, Sm, Y, La, Nd, Yb, Ca, and Ho, such as ceria-based solid solutions. These can be used alone or in combination of two or more. As the ceria-based solid solution, specifically, CeO2 doped with Gd, CeO2 doped with Sm, etc. can be preferably used. The thickness of the intermediate layer can be, for example, 0.001 mm or more and 0.05 mm or less.

[0023] In the fuel cell 1, fuel 30 containing the organic substance 31 is supplied to the anode electrode 3. Examples of the organic substance 31 include plastics such as biomass and resin. From the viewpoints of contribution to a recycling-oriented society, reduction of greenhouse gas emissions, and contribution to the environment by waste treatment, preferably, organic wastes such as waste-based biomass, plastic waste, and food waste can be preferably used. These can be used alone or in combination of two or more. The organic substance 31 can be, for example, in a solid form. Note that the fuel 30 may also contain other reinforcing materials such as glass components.

[0024] Here, the fuel cell 1 satisfies at least one of the following requirement A and requirement B. Requirement A: The fuel 30 further contains a reverse water-gas shift reaction catalyst 32 that promotes the reverse water-gas shift reaction (C + CO2 → 2CO) for generating carbon monoxide from carbon and carbon dioxide. Requirement B: The anode electrode 3 has a reverse water-gas shift reaction catalyst 32.

[0025] Examples of the reverse water-gas shift reaction catalyst 32 include, for example, Fe2O3, FeO, CuO, CoO, SnO2, NiO, etc. These can be used alone or in combination of two or more. The reverse water-gas shift reaction catalyst 32 can contain at least Fe2O3 from the viewpoints of catalytic reactivity, cost, etc.

[0026] When the fuel cell 1 satisfies requirement A, the reverse water-gas shift reaction catalyst 32 can exist in a state mixed with the organic matter 31, for example, as illustrated in FIG. 1. That is, the fuel 30 can be composed of a mixture of the organic matter 31 and the reverse water-gas shift reaction catalyst 32. Further, the reverse water-gas shift reaction catalyst 32 can exist in the form of particles and can exist in a state dispersed in the organic matter 31. According to these configurations, it is easy to exert the catalytic action by the reverse water-gas shift reaction catalyst 32 in the thickness direction of the fuel 30.

[0027] Regarding the case where the fuel cell 1 satisfies requirement A, the operation and effect of the fuel cell 1 will be described. When operating the fuel cell 1, an external load 5 is connected between the anode electrode 3 and the cathode electrode 4. The external load 5 consumes the electric power obtained by the power generation of the fuel cell 1. The operating temperature of the fuel cell 1 can be, for example, 600°C to 850°C. Further, a current collector 60 such as a Pt mesh is usually laminated on the anode electrode 3 and the cathode electrode 4 for current collection. Note that the anode electrode 3 and the cathode electrode 4 can be connected to the external load 5 via each current collector 60.

[0028] Fuel 30 containing the organic matter 31 and the reverse water-gas shift reaction catalyst 32 is introduced into the anode electrode 3 of the fuel cell 1. Further, an oxygen-containing gas 41 such as oxygen gas or air is introduced into the cathode electrode 4 of the fuel cell 1. At the cathode electrode 4, the cathode reaction of O2 + 4e - → 2O2 - occurs, and the oxygen gas is reduced to oxide ions (O2 -) is generated. At the anode electrode 3, carbon is deposited from the organic matter 31 (in FIG. 1, reference numeral 310 is the deposited carbon). Also, the organic matter 31 thermally decomposes at high temperature and gasifies, generating carbon dioxide. When requirement A is satisfied, carbon monoxide is generated from the carbon and carbon dioxide derived from the organic matter 31 by the catalytic action of the reverse water-gas shift reaction catalyst 32 in the fuel 30 (C + CO2 → 2CO). The generated carbon monoxide reacts with the oxide ions that have moved through the solid electrolyte 2 from the cathode electrode 4, generating carbon dioxide. That is, at the anode electrode 3, 2CO + 2O2 - → 2CO2 + 4e - The anode reaction occurs. In the fuel cell 1, carbon monoxide can also be obtained during the thermal decomposition process of the organic matter 31, but it can be automatically supplied from the carbon deposited from the organic matter 31 and the carbon dioxide generated by the thermal decomposition of the organic matter 31. That is, the fuel cell 1 can spontaneously proceed with the reaction while utilizing carbon monoxide and carbon dioxide that would otherwise be exhaust gases, and the carbon deposited on the anode electrode 3.

[0029] In this way, the fuel cell 1 can generate electricity by utilizing the reaction of converting the organic matter 31 into carbon monoxide at the anode electrode 3 and then converting that carbon monoxide into carbon dioxide. That is, the fuel cell 1 can directly use the organic matter 31 as fuel to generate electricity.

[0030] Next, the case of satisfying requirement B will be described. In this case, for example, as illustrated in FIG. 2, the anode electrode 3 can be configured to have a catalyst layer 320 containing the reverse water-gas shift reaction catalyst 32 on its surface. Also, for another example, as illustrated in FIG. 3, the anode electrode 3 has a large number of pores 33, and the reverse water-gas shift reaction catalyst 32 can be provided within the pores 33. Even when requirement B is satisfied, similar to the case of satisfying requirement A described above, due to the catalytic action of the reverse water-gas shift reaction catalyst 32 possessed by the anode electrode 3, at the anode electrode 3, the reverse water-gas shift reaction (C + CO2 → 2CO) and the anode reaction (2CO + 2O2 - → 2CO2 + 4e -) occurs, and the fuel cell 1 can generate electricity using the organic matter 31 as a direct fuel.

[0031] At this time, as illustrated in FIG. 2, when the anode electrode 3 has a catalyst layer 320 containing the reverse fermentation reaction catalyst 32 on its surface, there are the following advantages. The surface side of the anode electrode 3 is a location where carbon deposition by the organic matter 31 is likely to occur. Therefore, by laminating the catalyst layer 320 containing the reverse fermentation reaction catalyst 32 on the surface of the anode electrode 3, the contact between the organic matter 31 near the surface of the anode electrode 3 and the reverse fermentation reaction catalyst 32 possessed by the catalyst layer 320 is improved. Therefore, in this case, it becomes easier to react the organic matter 31 contained in the fuel 30 until the end, and it is possible to suppress the carbon deposition on the surface of the anode electrode 3 due to insufficient contact with the reverse fermentation reaction catalyst 32.

[0032] The catalyst layer 320 may be composed of the reverse fermentation reaction catalyst 32, or may contain, for example, the material of the anode electrode 3 (such as the above-described electron conductor or oxide ion conductor). In the latter case, the interfacial bonding property between the catalyst layer 320 and the surface of the anode electrode 3 can be improved. Further, the catalyst layer 320 preferably has surface irregularities. In this case, by increasing the surface area of the catalyst layer 320, it becomes easier to improve the contact between the organic matter 31 and the reverse fermentation reaction catalyst 32 contained in the catalyst layer 320. Therefore, in this case, it becomes easier to obtain the above-described effects.

[0033] Also, as illustrated in FIG. 3, when the anode electrode 3 has a large number of pores 33 and has a reverse Bouduard reaction catalyst 32 in the pores 33, there are the following advantages. The pores 33 of the anode electrode 3 are responsible for gas diffusion, but there is a risk that carbon may be deposited or residues of the organic substance 31 may intrude due to the organic substance 31 having poor contact with the reverse Bouduard reaction catalyst 32 there. In such a case, the pores 33 become clogged, the gas diffusibility of the anode electrode 3 decreases, and the output of the fuel cell 1 decreases. However, when the reverse Bouduard reaction catalyst 32 is present in the pores 33, the carbon and the residues of the organic substance 31 deposited in the pores 33 are eliminated by the reverse Bouduard reaction catalyst 32 present in the pores 33, and it becomes possible to suppress clogging of the pores 33. Therefore, in this case, it is advantageous for suppressing a decrease in the output of the fuel cell 1.

[0034] In FIG. 3, an example in which the reverse Bouduard reaction catalyst 32 is provided on the inner wall surface of the pores 33 is shown. In this case, specifically, the anode electrode 3 can be configured such that the reverse Bouduard reaction catalyst 32 is supported on the inner wall surface of the pores 33. The reverse Bouduard reaction catalyst 32 can contain a metal oxide having a melting point lower than the firing temperature when the anode electrode 3 is formed. Specifically, examples of the reverse Bouduard reaction catalyst 32 include Fe2O3, CuO, etc. These can be used alone or in combination of two or more. Note that the reverse Bouduard reaction catalyst 32 can exist in the form of a composite oxide, an alloy, or the like.

[0035] As a method for supporting the reverse Bouduard reaction catalyst 32 on the inner wall surface of the pores 33, for example, the following method can be exemplified. The surface of the pore-forming material used when making the anode electrode 3 have a porous structure is coated with the reverse Bouduard reaction catalyst 32. By burning out the pore-forming material during firing of the anode electrode 3, the reverse Bouduard reaction catalyst 32 can be left on the inner wall surface of the pores 33.

[0036] When the fuel cell 1 satisfies both of the above-described requirement A and requirement B, at the anode electrode 3, the reaction that converts the organic matter 31 into carbon monoxide and then changes the carbon monoxide into carbon dioxide can be made reliable, so that power generation by direct fueling of the organic matter 31 can be made more reliable.

[0037] (Embodiment 2) The fuel cell of Embodiment 2 will be described with reference to FIGS. 4 and 5. Among the reference numerals used after Embodiment 2, those identical to the reference numerals used in the previous embodiments represent the same components and the like as those in the previous embodiments unless otherwise specified.

[0038] As illustrated in FIG. 4, the fuel cell 1 of the present embodiment is a cylindrical fuel cell. Specifically, the fuel cell 1 of the present embodiment has a cylindrical anode electrode 3, a solid electrolyte 2 formed along the outer peripheral surface of the anode electrode 3, and a cathode electrode 4 formed along the outer peripheral surface of the solid electrolyte 2. An interconnector 6 is formed in the axial direction of the cylinder on a part of the outer peripheral surface of the anode electrode 3. Both circumferential ends of the solid electrolyte 2 are separated by the interconnector 6. An insulating layer 7 is formed between both circumferential ends of the cathode electrode 4 and the interconnector 6. Thereby, the current collection of the anode electrode 3 is performed without contacting the cathode electrode 4 via the interconnector 6. When operating the fuel cell 1, the external load 5 is electrically connected to the interconnector 6 and the cathode electrode 4. When a plurality of fuel cells 1 are connected in series, the interconnector 6 of one fuel cell 1 and the cathode electrode 4 of the other fuel cell 1 may be electrically connected.

[0039] In the fuel cell 1, any one of the anode electrode 3, the cathode electrode 4, and the solid electrolyte 2 can also serve as a support. Additionally, although not shown in the figure, the fuel cell 1 can also be configured such that the anode electrode 3, the solid electrolyte 2, and the cathode electrode 4 are sequentially formed on the outer peripheral surface of a cylindrical support made of a metal, a conductive ceramic, or the like that can permeate gas. In FIG. 4, an anode-supported fuel cell 1 in which the anode electrode 3 also serves as a support is illustrated.

[0040] As illustrated in FIG. 5, the fuel cell 1 of the present embodiment has a first fuel supply unit 11 configured to be able to extrude and supply fuel 30 to the anode electrode 3. When the fuel 30 supplied to the anode electrode 3 remains in the anode electrode 3 as it is, the battery characteristics depend on the supply amount of the fuel 30 and deteriorate over time as the available fuel 30 is exhausted. In contrast, since the fuel cell 1 of the present embodiment has the first fuel supply unit 11, when the available fuel 30 is exhausted, new fuel 30 can be extruded and supplied, and the fuel residue 201 can be extruded and discharged. Therefore, according to the fuel cell 1 of the present embodiment, the fuel 30 can be continuously supplied with high filling. In particular, when the fuel 30 has the organic substance 31 and the reverse fermentation reaction catalyst 32 (when requirement A is satisfied), the organic substance 31 and the reverse fermentation reaction catalyst 32 can be continuously supplied with high filling, which is advantageous for suppressing the deterioration of the battery characteristics over time.

[0041] The first fuel supply unit 11 is not particularly limited as long as it can extrude and supply the fuel 30 to the anode electrode 3, and various methods can be adopted in consideration of the form of the fuel cell 1. In FIG. 5, the first fuel supply unit 11 is configured to extrude and discharge the fuel residue 201 of the fuel 30 filled (held) in the cylinder of the cylindrical anode electrode 3 with the piston member 110, and to extrude and supply new fuel 30 into the anode electrode 3 with the piston member 110. An example is shown. Specifically, the piston member 110 is formed in a columnar shape having a circular cross section with a diameter corresponding to the inner diameter of the cylinder of the cylindrical anode electrode 3. Further, the piston member 110 can be configured to move forward and backward in the axial direction of the cylinder within the cylindrical anode electrode 3. Note that the oxygen-containing gas 41 may be supplied to the outside (outer circumference) of the cathode electrode 4.

[0042] As described in the above-described Embodiment 1, in the case of the flat fuel cell 1, although not shown, the first fuel supply unit 11, for example, scrapes off the fuel residue 201 of the fuel 30 held on the surface of the anode electrode 3 with a blade member, and new fuel 30 can be configured to be extruded and supplied to the surface of the anode electrode 3 in a layer or the like with the blade member. Other configurations and operational effects are the same as those of Embodiment 1.

[0043] (Embodiment 3) The fuel cell of Embodiment 3 will be described with reference to FIGS. 6 and 7. As illustrated in FIG. 6, the fuel cell 1 of the present embodiment is a cylindrical fuel cell, similar to the fuel cell 1 of Embodiment 2. The basic cell configurations such as the anode electrode 3, the solid electrolyte 2, and the cathode electrode 4 are the same as those of Embodiment 2.

[0044] As illustrated in FIGS. 6 and 7, the fuel cell 1 of the present embodiment is configured to be able to supply a porous body 121 holding fuel 30 therein to the anode electrode 3, and has a second fuel supply unit 12 configured to be able to take out the porous body 121 after the use of the fuel 30. Since the fuel cell 1 of the present embodiment has the second fuel supply unit 12, when the power generation effect by the fuel 30 decreases, the used fuel 301 can be taken out together with the porous body 121 and exchanged with a porous body 121 holding new fuel 30, thereby recovering the decreased power generation effect. Further, in the fuel cell 1 of the present embodiment, by supplying the porous body 121 holding new fuel 30 in a cartridge type, the deposited carbon 32 excessively accumulated due to insufficient contact (unreacted) with the reverse water-gas shift reaction catalyst 32, the reverse water-gas shift reaction catalyst 32, the fuel residue 201, impurities, etc. can be efficiently recovered.

[0045] As the material of the porous body 121, various materials can be applied as long as the material itself of the porous body 121 has electronic conductivity and does not react (does not contribute to the reaction) with the anode electrode 3 or the fuel 30. The porous body 121 can contain, for example, alumina, mullite, magnesium oxide, etc.

[0046] Further, in FIG. 7, an example is shown in which the second fuel supply unit 12 is configured to supply a cylindrical porous body 121 filled (held) with fuel 30 therein into the cylinder of the cylindrical anode electrode 3 and be able to take out the used fuel 30 together with the porous body 121 from the anode electrode 3. That is, the fuel 30 is stored in the porous body 121 serving as an outer shell. The porous body 121 can be formed in a cylindrical shape having, for example, an outer cylinder diameter corresponding to the inner cylinder diameter of the cylindrical anode electrode 3 so as to be disposed in contact with the anode electrode 3. Further, the porous body 121 can be configured to be able to move forward and backward in the axial direction of the cylinder within the cylindrical anode electrode 3. Other configurations and operational effects are the same as those in Embodiment 1 and Embodiment 2.

[0047] (Embodiment 4) The fuel cell of Embodiment 4 will be described with reference to FIGS. 8 and 9. As illustrated in FIG. 8, the fuel cell 1 of this embodiment is a honeycomb-shaped fuel cell. Specifically, the fuel cell 1 of this embodiment includes a honeycomb-shaped solid electrolyte 2 in which a plurality of channels 21 extending in the honeycomb axial direction are formed, an anode electrode 3 formed in a layer on the inner wall surface of one of the adjacent channels 21, and a cathode electrode 4 formed in a layer on the inner wall surface of the other of the adjacent channels 21. Note that FIG. 8 shows only a part of the plurality of channels 21 included in the fuel cell 1.

[0048] Specifically, the solid electrolyte 2 can be configured in a honeycomb shape from a solid electrolyte 2 having oxide ion conductivity. More specifically, the solid electrolyte 2 can have a channel structure in which adjacent channels 21 are arranged with a partition wall 210 therebetween. In the honeycomb-shaped solid electrolyte 2, when viewed from the Z-axis direction, which is the axial direction, the plurality of channels 21 can be arranged in the X-axis direction and the Y-axis direction, which are two mutually perpendicular directions. The anode electrode 3 is provided on one surface of the partition wall 210 in the solid electrolyte 2, and the cathode electrode 4 is provided on the other surface of the partition wall 210 in the solid electrolyte 2. The channels 21 in which the anode electrode 3 is formed and the channels 21 in which the cathode electrode 4 is formed can be arranged alternately. Note that FIG. 8 shows an example in which the cross-sectional shape of the channel 21 is a rectangular shape, but alternatively, the cross-sectional shape of the channel 21 may be a polygonal shape such as a hexagonal shape or an octagonal shape, a circular shape, or the like. Also, channels 21 having different cross-sectional shapes may be combined.

[0049] The fuel cell 1 of this embodiment is an example in which the honeycomb-shaped solid electrolyte 2 also serves as a support. Although not shown, the fuel cell 1 can also be configured such that either the anode electrode 3 or the cathode electrode 4 serves as a support.

[0050] In the fuel cell 1 of the present embodiment, fuel 30 is introduced into the channel 21 in which the anode electrode 3 is formed on the inner wall surface, so that the fuel 30 is supplied to the anode electrode 3. Further, the fuel 30 is held in the channel 21. Note that oxygen-containing gas 41 is introduced into the channel 21 in which the cathode electrode 4 is formed on the inner wall surface, so that oxygen gas from the oxygen-containing gas 41 is supplied to the cathode electrode 4.

[0051] Similar to the fuel cell 1 of the second embodiment, the fuel cell 1 of the present embodiment has a first fuel supply unit 11 configured to be able to extrude and supply fuel 30 to the anode electrode 3, as illustrated in FIG. 9. Since the fuel cell 1 of the present embodiment has the first fuel supply unit 11, when the available fuel 30 runs out, new fuel 30 can be extruded and supplied, and the fuel residue 201 can be extruded and discharged. Therefore, according to the fuel cell 1 of the present embodiment 4, fuel 30 can be continuously supplied with high filling. In particular, when the fuel 30 has the organic substance 31 and the reverse fermentation reaction catalyst 32 (when requirement A is satisfied), the organic substance 31 and the reverse fermentation reaction catalyst 32 can be continuously supplied with high filling, which is advantageous for suppressing the deterioration of the battery characteristics over time.

[0052] Specifically, in FIG. 9, the first fuel supply unit 11 is configured to be able to extrude and discharge the fuel residue 201 of the fuel 30 filled (held) in the channel 21 with the piston member 110, and extrude and supply new fuel 30 into the channel 21 with the piston member 110. In the present embodiment, the fuel 30 can be extruded and supplied to the anode electrode 3 in this way. Specifically, the piston member 110 can have a cross-sectional shape adapted to the cross-section of the channel 21. In FIG. 9, a piston member 110 having a square cross-sectional shape is illustrated. Other configurations and operational effects are the same as those of the first to third embodiments.

[0053] (Embodiment 5) The fuel cell of Embodiment 5 will be described with reference to FIGS. 10 and 11. When the concentration of carbon monoxide generated at the anode electrode 3 of the fuel cell 1 of this embodiment rises above the equilibrium point in the Boudouard equilibrium, the temperature of the fuel cell 1 is raised to the temperature at which carbon monoxide is generated. When the concentration of carbon monoxide generated at the anode electrode 3 drops below the equilibrium point in the Boudouard equilibrium, the control unit (not shown) controls the carbon monoxide concentration and the temperature by lowering the temperature of the fuel cell 1 to the equilibrium point at that concentration.

[0054] The cell configuration of the fuel cell 1 in the fuel cell 1 of this embodiment may be any of the cell configurations of the fuel cells 1 of Embodiments 1 to 4. FIG. 10 shows, for example, a Boudouard equilibrium diagram when the equilibrium between CO and CO2 is maintained using Fe2O3 as a catalyst. As shown in this Boudouard equilibrium diagram, when the CO concentration rises excessively compared to when it is in the equilibrium state due to the reverse Boudouard reaction (C + CO2 → 2CO), it may reach a concentration at which the decomposition of CO occurs. Therefore, in this case, the control unit raises the temperature of the fuel cell 1 to the temperature at which carbon monoxide is generated, specifically, the temperature of the equilibrium point at the increased CO concentration, to suppress the decomposition of CO. On the other hand, when CO is consumed by the anodic reaction (2CO + 2O2 - → 2CO2 + 4e - ), the CO concentration decreases compared to when it is in the equilibrium state. Therefore, in this case, the control unit lowers the temperature of the fuel cell 1 to the temperature of the equilibrium point at the CO concentration after consumption to suppress the increase in power consumption. Therefore, according to the fuel cell 1 of this embodiment, a fuel cell 1 capable of suppressing the decomposition of CO due to the anode atmosphere and the increase in power consumption due to excessive heating can be obtained.

[0055] The control unit can be configured to control the temperature rise of the fuel cell 1 such that the CO concentration is preferably within ±10%, more preferably within ±8%, and even more preferably within ±5% with respect to the curve of the Pourbaix equilibrium diagram. Similarly, the control unit can be configured to control the temperature drop of the fuel cell 1 such that the CO concentration is preferably within ±10%, more preferably within ±8%, and even more preferably within ±5% with respect to the curve of the Pourbaix equilibrium diagram. Specifically, the control unit can be composed of an ECU (Electronic Control Unit). Further, the control unit can be configured to be able to acquire the temperature (cell temperature) of the fuel cell 1 detected by the temperature detection unit. Specifically, the temperature detection unit can be composed of a temperature sensor. Further, the control unit can be configured to be able to acquire the CO concentration in the anode electrode 3 detected by the CO concentration detection unit. Specifically, the CO concentration detection unit can be composed of a CO concentration sensor. Further, the control unit can be configured to be able to adjust the temperature of the fuel cell 1 by the temperature adjustment unit. Specifically, the temperature adjustment unit can be composed of a heater or the like. Further, the control unit can be configured to be able to acquire information regarding the Pourbaix equilibrium diagram pre-stored in a storage device or the like.

[0056] Using FIG. 11, an example of the control by the fuel cell 1 of the present embodiment will be described more specifically with reference to a flowchart. In the following, a case will be described in which, when the temperature of the fuel cell 1 rises, control is performed so that the CO concentration falls within ±5% with respect to the curve of the Pourbaix equilibrium diagram, and when the temperature of the fuel cell 1 drops, control (feedback control) is performed so that the CO concentration falls within ±5% with respect to the curve of the Pourbaix equilibrium diagram.

[0057] As illustrated in FIG. 11, control by the control unit is started (S1). Next, the control unit acquires the cell temperature t of the fuel cell 1 detected by the temperature detection unit (S2). Next, the control unit derives the CO equilibrium concentration Mt at the temperature t based on the Pourbaix equilibrium diagram (S3). Next, the control unit acquires the CO concentration Ma in the anode electrode 3 detected by the CO concentration detection unit (S4).

[0058] Next, as a result of the control unit comparing the CO concentration Ma and the CO equilibrium concentration Mt (S5), if the CO concentration Ma is greater than the CO equilibrium concentration Mt, it proceeds to Yes. Then, the control unit determines whether Ma - Mt > 5% is satisfied (S6). If Ma - Mt > 5% is satisfied, it proceeds to Yes, and the control unit determines the target of the cell temperature based on the Pourbaix equilibrium diagram (S7). If Ma - Mt > 5% is not satisfied, it proceeds to No, the control by the control unit ends, and it returns to Start (S8, S1). Next, the control unit performs temperature increase control on the temperature of the fuel cell 1 via the temperature adjustment unit (S9). Next, the control unit determines whether Ma - Mt > 5% is satisfied (S10). If Ma - Mt > 5% is not satisfied, it proceeds to No, the control by the control unit ends, and it returns to Start (S11, S1). If Ma - Mt > 5% is satisfied, it proceeds to Yes, and the control unit determines the target of the cell temperature again based on the Pourbaix equilibrium diagram (S7).

[0059] Also, as a result of the control unit comparing the CO concentration Ma and the CO equilibrium concentration Mt (S5), if the CO concentration Ma is not greater than the CO equilibrium concentration Mt, it proceeds to No. Then, the control unit determines whether Mt - Ma > 5% is satisfied (S12). If Mt - Ma > 5% is satisfied, it proceeds to Yes, and the control unit determines the target of the cell temperature based on the Pourbaix equilibrium diagram (S13). If Mt - Ma > 5% is not satisfied, it proceeds to No, the control by the control unit ends, and it returns to Start (S14, S1). Next, the control unit performs temperature decrease control on the temperature of the fuel cell 1 via the temperature adjustment unit (S15). Next, the control unit determines whether Mt - Ma > 5% is satisfied (S16). If Mt - Ma > 5% is not satisfied, it proceeds to No, the control by the control unit ends, and it returns to Start (S17, S1). If Mt - Ma > 5% is satisfied, it proceeds to Yes, and the control unit determines the target of the cell temperature again based on the Pourbaix equilibrium diagram (S13).

[0060] (Experimental Example 1) - Fabrication of Fuel Cell - An anode electrode made of Ni-8YSZ cermet, a dense solid electrolyte layer made of 8YSZ (thickness 0.01 mm), an intermediate layer made of Sm-doped CeO2 (thickness 0.01 mm), and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 A single cell in which a porous cathode electrode made of O3 (LSCF) (thickness 0.05 mm) is laminated in this order was prepared. Note that 8YSZ is yttria-stabilized zirconia containing 8 mol% of Y2O3. Also, the anode electrode has a two-layer structure consisting of a porous layer (thickness 0.5 mm) and a dense layer (thickness 0.02 mm). Note that the dense layer is in contact with the solid electrolyte layer. For the formation of the porous layer of the anode electrode, a material obtained by mixing NiO and 8YSZ at a weight ratio of 1:1 and adding 5 wt% of polymethyl methacrylate (PMMA) as a pore-forming agent was used. Also, for the formation of the dense layer of the anode electrode, a material obtained by mixing NiO and 8YSZ at a weight ratio of 1:1 without the above pore-forming agent was used.

[0061] Also, as organic substances, cellulose (manufactured by Wako Chemicals), lignin (manufactured by Tokyo Chemical Industry), polyurethane (manufactured by Negami Chemical Industry), PET (polyethylene terephthalate) (manufactured by Sigma-Aldrich, containing about 30 mass% of glass component as a reinforcing material), and soy-derived protein (manufactured by Wako Chemicals) were prepared. Note that only PET was repeatedly pulverized at 2 minutes / cycle using a blender (manufactured by Osaka Chemical Co., Ltd. "WB-1"). Also, Fe2O3 powder was prepared as a reverse Bouduard reaction catalyst. By mixing 0.2 g of each organic substance and 0.2 g of Fe2O3 powder, each model fuel composed of a mixture of a predetermined organic substance and a reverse Bouduard reaction catalyst was prepared. The model fuel is in a solid state.

[0062] The fuel cell of Sample 1 used cellulose as the organic matter of the model fuel, the fuel cell of Sample 2 used lignin, the fuel cell of Sample 3 used polyurethane, the fuel cell of Sample 4 used PET, and the fuel cell of Sample 5 used protein. Then, as shown in FIG. 12, a platinum mesh 91 to which a platinum wire 92 was connected was laminated on the surfaces of the anode electrode 3 and the cathode electrode 4 of the fuel cell 1. A predetermined model fuel 301 was supplied to the anode electrode 3, and air was supplied as the oxygen-containing gas 41 to the cathode electrode 4, and a power generation test was conducted batchwise at 800°C. The electrode area was 0.5 cm 2 was used. Also, the model fuel 301 was placed in a tubular body 93 made of alumina and supplied by bringing it into contact with the anode electrode 3. Also, the oxygen-containing gas 41 was supplied to the cathode electrode 4 from the inside of the inner tube of a double tube 94 made of alumina and discharged through the outer tube of the double tube 94.

[0063] FIG. 13 shows the power generation test results of the fuel cell single cells of the fuel cells of each sample. In the graph of FIG. 13, the horizontal axis represents the current density (A·cm -2 ), the left vertical axis of the graph represents the cell voltage (V), and the right vertical axis of the graph represents the power density (W·cm -2 ). In FIG. 13, the downward-sloping line is the cell voltage, and the upward-sloping curve is the power density. Also, FIG. 13 also shows the characteristics (flow type: a system in which gas is continuously supplied) when the supply of the model fuel was stopped and hydrogen gas was supplied instead, and Fe2O3 of the reverse water-gas shift reaction catalyst was reduced to FeO. Also, FIG. 14 shows the relationship between the temperature (°C) (horizontal axis) during cell operation of the fuel cell of Sample 1 in Experimental Example 1 (organic matter used: cellulose) and the concentration (%) of the gas generated at the anode electrode (vertical axis), compared with the case where there was no Fe2O3 powder and the case where the Fe2O3 powder was changed to NiO powder.

[0064] Anode reaction (2CO + 2O2 - →2CO2 + 4e - ) and cathode reaction (O2 + 4e - →2O2 -) Due to the potential difference, the fuel cell of each sample has a high theoretical electromotive force of 1.33 V. As shown in Fig. 13, although the fuel cell of each sample has a cell voltage lower than the theoretical electromotive force due to the loss called overvoltage, an output is obtained, and it was confirmed that power can be generated using an organic substance directly as fuel. When comparing the fuel cells of each sample, when PET is used as the organic substance, an output as high as 0.6 W·cm -2 was obtained. This is an output level comparable to that of a hydrogen-oxygen fuel cell. Also, in the fuel cell of each sample, CO required for the anodic reaction can be obtained even during the pyrolysis process of the organic substance, and it can be automatically supplied by the carbon component of the organic substance and CO2 generated by pyrolysis. That is, it can be seen that CO2 does not need to be supplied as fuel. The catalytic Fe2O3 can generate CO2 while changing to Fe3O4 or FeO due to the change in valence. In this way, the fuel cell of each sample can proceed with the reaction spontaneously to some extent while using CO2, CO, which would originally be exhaust gas, and C deposited on the electrode as fuel. Although there is concern that Fe2O3 will turn into FeO when reduced by the influence of fuel, FeO can react with oxide ions and be oxidized, and as a result, it can return to Fe2O3 (2FeO + O2 - →Fe2O3 + 2e - ). Also, according to Fig. 14, Fe2O3 can generate more CO than NiO in the temperature range of 600°C to 800°C, and it was confirmed that it is suitable as the reverse water-gas shift reaction catalyst of the present disclosure.

[0065] (Experimental Example 2) In the production of the fuel cell of Sample 1 in Experimental Example 1 (organic matter in the fuel: cellulose, metal oxide in the fuel: Fe2O3), fuel cells of Samples 6 to 9 were produced in the same manner except that CuO, SnO2, CoO, or NiO was used as the metal oxide in the fuel. Further, in the production of the fuel cell of Sample 1, a fuel cell of Sample 10 was produced in the same manner except that Fe2O3 was not mixed in the fuel. Then, for the fuel cells of Sample 1 and Samples 6 to 10, a power generation test similar to that in Experimental Example 1 was conducted, and the relationship between the cell operation time and the cell voltage was measured. The results are shown in Fig. 15.

[0066] According to Fig. 15, it can be seen that when Fe2O3 and CuO are used as the metal oxide, the obtained cell voltage is high and it is easy to suppress the decrease in the cell voltage. Also, when Fe2O3, CuO, CoO, and SnO2 are used, it was confirmed that the time until the cell voltage becomes zero can be extended compared to the case where these metal oxides are not used. On the other hand, when NiO is used, the cell voltage decreases in a very short time. At the anode electrode, the gas (such as CO) obtained by thermal decomposition of the organic matter of the sample also contributes to the anodic reaction, but it can only serve as a fuel for power generation for a very short time. When an appropriate metal oxide catalyst such as Fe2O3 or CuO is used, the reaction gas CO increases due to the reverse water-gas shift reaction, and the power generation time can be extended.

[0067] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications can be made without departing from the gist thereof. Also, the respective configurations shown in the embodiments and experimental examples can be arbitrarily combined with each other.

Explanation of Reference Numerals

[0068] 1 Fuel cell 2 Solid electrolyte 3 Anode electrode 30 Fuel 31 Organic matter 32 Reverse water-gas shift reaction catalyst

Claims

1. A solid electrolyte (2) having oxide ion conductivity, An anode electrode (3) provided on one surface of the solid electrolyte and supplied with a fuel (30) containing an organic substance (31), A cathode electrode (4) provided on the other surface of the solid electrolyte and reducing oxygen gas to generate oxide ions, and a fuel cell (1) having the same, Requirement A: The fuel further contains a reverse water-gas shift reaction catalyst (32) that promotes the reverse water-gas shift reaction for generating carbon monoxide from carbon and carbon dioxide, and requirement B: The anode electrode has the reverse water-gas shift reaction catalyst, and at least one of them is satisfied, When the concentration of carbon monoxide generated at the anode electrode rises above the equilibrium point in the water-gas equilibrium, the temperature of the fuel cell is raised to the temperature at which carbon monoxide is generated, When the concentration of carbon monoxide generated at the anode electrode drops below the equilibrium point in the water-gas equilibrium, the temperature of the fuel cell is lowered to the equilibrium point at that concentration, and a control unit for controlling the carbon monoxide concentration and the temperature is provided, Fuel cell (1).

2. Having a first fuel supply unit (11) configured to extrude and supply the fuel to the anode electrode, The fuel cell according to claim 1.

3. Having a second fuel supply unit (12) configured to supply a porous body (121) holding the fuel inside to the anode electrode and configured to be able to take out the porous body after use of the fuel, The fuel cell according to claim 1.

4. The anode electrode has a catalyst layer (320) containing the reverse water-gas shift reaction catalyst on its surface, The fuel cell according to any one of claims 1 to 3.

5. The anode electrode has a large number of pores (33), The reverse fermentation reaction catalyst is present in the pores. The fuel cell according to any one of claims 1 to 4.

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