Electrochemical cell and method for manufacturing same

Abstract

An electrochemical cell (1) according to the present invention is provided with an air electrode (2), a solid electrolyte layer (4), a fuel electrode (6), and a porous layer (8) in this order. The porous layer (8) comprises an alloy containing Cr and Fe, has a porosity of 15-50%, and has a pore diameter (average equivalent circle diameter) of 5-50 μm. The solid electrolyte layer (4) preferably contains stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce.

Description

Electrochemical cell and method of manufacturing the same

[0001] The present invention relates to an electrochemical cell, which may be a metal supported cell type solid oxide fuel cell or a solid oxide electrolysis cell, and to a method for manufacturing the same.

[0002] Known solid oxide electrochemical cells include solid oxide fuel cells and solid oxide electrolysis cells. Of these, solid oxide fuel cells include a three-layer power generation cell consisting of a solid electrolyte layer containing an oxygen-ion conductive solid oxide and a fuel electrode and a cathode arranged opposite each other on either side of the electrolyte layer. A fuel gas such as hydrogen is supplied to the fuel electrode, and an oxidizing gas such as air is supplied to the cathode, generating DC power based on an electrochemical reaction.

[0003] Among such fuel cells, metal-supported cell type solid oxide fuel cells have recently become known, in which a power generating cell is supported via an anode by a gas-permeable and electrically conductive metal support portion.

[0004] Patent Document 1 discloses a support structure for a metal support cell, which includes a metal support cell in which an electrolyte layer is fixed to a metal support layer via an electrode layer, and a metal frame surrounding the periphery of the metal support cell, wherein the electrolyte layer has compressive residual stress along the surface direction, the metal frame is sinter-bonded to the electrolyte layer, and the linear expansion coefficient of the metal frame is approximately the same as the linear expansion coefficient of the metal support layer.

[0005] Patent Document 2 discloses a metal support that is formed in a plate shape as a whole and has a plurality of through holes that penetrate from a front side surface on which an electrode layer is provided to a back side surface, the through holes having inclined through holes whose central axes are inclined with respect to the thickness direction. It also discloses an electrochemical element that is configured by providing an electrode layer, an electrolyte layer, and a counter electrode layer on the front side surface of the metal support.

[0006] Patent Document 3 discloses an electrochemical cell having a metal support, a cell unit including a solid electrolyte layer having oxygen ion conductivity, a first electrode laminated on one side of the solid electrolyte layer, and a second electrode laminated on the other side of the solid electrolyte layer, and a bonding layer bonding the metal support and the first electrode of the cell unit, wherein the bonding layer includes at least one of an alloy containing a metal support constituent element that is at least one metal element constituting the metal support and a first electrode constituent element that is at least one metal element constituting the first electrode, and a metal oxide containing the metal support constituent element and the first electrode constituent element.

[0007] Also, for example, known methods for forming a fuel electrode on a metal support include a baking method (e.g., a wet method in which baking treatment is applied at about 1100°C), a spray coating method (thermal spraying, aerosol deposition, aerosol gas deposition, powder jet deposition, particle jet deposition, cold spray, etc.), a PVD method (sputtering, pulsed laser deposition, etc.), a CVD method, etc.

[0008] JP 2020-21646 A JP 2021-163655 A JP 2023-3622 A

[0009] If the mechanical strength of the metal support (layer) is high, the strength of the metal-supported cell type solid oxide electrochemical cell will also be high, but considering the air permeability from one side to the other side and the electrochemical performance, the lower limit of the porosity is also limited. Furthermore, in order to manufacture an electrochemical cell by the sintering method, a metal plate that is air permeable in the thickness direction (cross-sectional direction) is used as a manufacturing material, and when an anode membrane and a solid electrolyte layer membrane are placed on this and this stack is heat-treated (co-sintered), shrinkage may occur, and the porosity may decrease, improving the strength of the metal support (layer), but the air permeability may decrease. From the viewpoint of the performance and structural stability of the resulting metal-supported cell type solid oxide electrochemical cell, it is preferable to form a metal support (layer) that has high strength and good air permeability by co-sintering.

[0010] An object of the present invention is to provide a metal-supported cell type electrochemical cell, typified by a metal-supported cell type solid oxide fuel cell and a metal-supported cell type solid oxide electrolysis cell, which comprises a metallic porous layer, a fuel electrode, a solid electrolyte layer, and a cathode, and which has excellent structural stability and electrochemical cell performance, and a method for producing the same.

[0011] The present inventors have found that when an electrochemical cell is manufactured using a porous metal plate produced by utilizing powder metallurgy technology, which porous metal plate is produced by pressure molding a composition containing alloy particles containing Cr and Fe and a pore-forming agent, and sintering the resulting thin-walled molded body, the porous metal plate being made of a connected structure of alloy particles and having a porosity of 50 to 80%, the porosity and pore diameter (average circle-equivalent diameter) in the porous layer are within specific ranges, thereby solving the above-mentioned problems.

[0012] The present invention provides the following: (1) An electrochemical cell comprising an air electrode, a solid electrolyte layer, an anode, and a porous layer in this order, wherein the porous layer is made of an alloy containing Cr and Fe, has a porosity of 15 to 50%, and has a pore diameter (average circle-equivalent diameter) of 5 to 50 μm. (2) The electrochemical cell according to (1) above, wherein the solid electrolyte layer contains stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce. (3) A method for producing the electrochemical cell according to (1) above, comprising the steps of: a first stack fabrication step of forming or placing an anode film on a surface of a porous metal plate having a porosity of 50 to 80% and made of a connected structure of alloy particle portions containing Cr and Fe, thereby fabricating a first stack; a second stack fabrication step of forming or placing a solid electrolyte layer film on the surface of the anode film, thereby fabricating a second stack; a first sintering step of heat-treating the second stack to co-sinter the anode film and the solid electrolyte layer film, thereby fabricating an integrated body (A) consisting of a porous layer derived from the porous metal plate, an anode, and a solid electrolyte layer; a third stack fabrication step of forming or placing a cathode film on a surface of the solid electrolyte layer, thereby fabricating a third stack; and a cathode fabrication step of heat-treating the third stack to bond the cathode film to the solid electrolyte layer. (4) The method for producing an electrochemical cell according to (3), wherein, after the first sintering step, a dispersion of electrolyte particles containing stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce and having an average particle size of 150 nm or less is applied to a surface of the solid electrolyte layer in the integrated product (A), followed by drying and further heat treatment to densify the solid electrolyte layer.

[0013] The electrochemical cell of the present invention has excellent structural stability and electrochemical cell performance. In particular, the porous layer corresponding to the gas-permeable metal support does not have a plurality of through-holes with a single flow path, but rather has voids extending nonlinearly to form multiple interconnected pores, providing a structure with excellent gas diffusivity, which is believed to result in excellent electrochemical cell performance. The electrochemical cell manufacturing method of the present invention uses a porous metal plate having a porosity of 50 to 80% and a connected structure of alloy particle portions containing Cr and Fe. This allows for efficient formation of a suitable porous layer, resulting in an electrochemical cell with excellent structural stability and electrochemical cell performance. Furthermore, when the solid electrolyte layer is densified using electrolyte particles with an average particle diameter of 150 nm or less, even better electrochemical cell performance can be obtained.

[0014] 1 is a schematic cross-sectional view showing an example of an electrochemical cell of the present invention. It is an enlarged image of a porous layer in an electrochemical cell of the present invention, and is an image taken by an optical microscope showing an example of an image for measuring the pore diameter (average circle equivalent diameter) in the porous layer. It is an SEM image showing an example of the surface of a porous metal plate used in manufacturing an electrochemical cell of the present invention. It is an enlarged image of FIG. 3. It is a schematic diagram showing an example of a connection structure of a plurality of alloy particle portions constituting a porous metal plate used in manufacturing an electrochemical cell of the present invention, and is an explanatory diagram showing a method for measuring the maximum diameter of each alloy particle portion. It is a graph showing the battery performance of electrochemical cells obtained when solid electrolyte layers were bonded at 1240°C in Examples 1 and 2. It is a graph showing the battery performance of electrochemical cells obtained when solid electrolyte layers were bonded at 1260°C in Examples 1 and 2.

[0015] The electrochemical cell of the present invention comprises an air electrode, a solid electrolyte layer, an anode, and a porous layer in this order, and the porous layer is made of an alloy containing Cr and Fe, and is characterized by having a porosity of 15 to 50%, and a pore diameter (average circle-equivalent diameter) of 5 to 50 μm. Figure 1 shows an example of the electrochemical cell of the present invention, and shows an electrochemical cell 1 comprising an air electrode 2, a solid electrolyte layer 4, an anode 6, and a porous layer 8 in this order.

[0016] The constituent material of the air electrode 2 is not particularly limited, and may be any material contained in air electrodes disposed in known solid oxide fuel cells and solid oxide electrolysis cells, such as (Ba, Sr)(Fe, Co)O ３ , (La,Sr)CoO ３ , (La,Sr)(Fe,Co)O ３ , (Sm,Sr)(Fe,Co)O ３ In the present invention, the perovskite oxide may be one or more selected from the group consisting of (Ba, Sr)(Fe, Co)O ３ The air electrode 2 may also contain a solid electrolyte (described later) that can form a solid electrolyte layer.

[0017] The thickness of the air electrode 2 is preferably 5 to 100 μm.

[0018] The constituent material of the solid electrolyte layer 4 is not particularly limited, and may be an oxygen ion-conducting electrolyte contained in a solid electrolyte layer disposed in a known solid oxide fuel cell or solid oxide electrolysis cell. Examples of the constituent material include stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce (e.g., scandia-stabilized zirconia, yttria-stabilized zirconia, scandia-ceria-co-stabilized zirconia, scandia-yttria-co-stabilized zirconia, ytterbia-stabilized zirconia), and fluorite-type oxides having oxide ion conductivity. In the present invention, the stabilized zirconia is preferred from the viewpoint of thermal and chemical stability. In this specification, "stabilized zirconia" refers to zirconia in which a rare earth element oxide is solid-solved, and also includes partially stabilized zirconia.

[0019] The thickness of the solid electrolyte layer 4 is preferably 1 to 50 μm.

[0020] The constituent material of the anode 6 is not particularly limited and may be one contained in anodes arranged in known solid oxide fuel cells and solid oxide electrolysis cells, and may be one or more selected from electronic conductors such as metal Ni, Ni alloys, metal Cu, Cu alloys, metal Co, and Co alloys, metal Pt, and Pt alloys. In the present invention, metal Ni and Ni alloys are preferred. The anode 6 may also contain a solid electrolyte (described above) capable of forming a solid electrolyte layer.

[0021] The thickness of the fuel electrode 6 is preferably 5 to 100 μm.

[0022] The porous layer 8 is made of an alloy containing Cr and Fe, and this alloy may further contain, in addition to Cr and Fe, Mn, Ni, Ti, Cu, Zr, Si, Al, Mo, etc. The alloy is preferably ferritic stainless steel (such as SUS430).

[0023] The porous layer 8 is preferably an alloy skeleton having a three-dimensional mesh structure with voids, and does not have multiple through-holes of a single flow path inside, but rather the voids extend discontinuously from one side (e.g., the fuel electrode 6 side) to the other side (e.g., the surface side of the porous layer 8) to form communicating holes of multiple paths.

[0024] The porosity of the porous layer 8 is 15 to 50%, and preferably 25 to 50%. The pore diameter (average equivalent circle diameter) is 5 to 50 μm, and preferably 15 to 50 μm. Since the porosity and pore diameter (average equivalent circle diameter) of the porous layer 8 are within the above ranges, the electrochemical cell of the present invention is excellent in structural stability and electrochemical cell performance.

[0025] In the present invention, the porosity is determined by photographing a cross section of the electrochemical cell of the present invention using an optical microscope or the like, binarizing the obtained image, and calculating the area ratio of voids per predetermined area using image analysis software.

[0026] In the present invention, the pore diameter (average circle-equivalent diameter) is an average value obtained by photographing a cross section of the electrochemical cell of the present invention using an optical microscope or the like, setting arbitrary measurement target portions within the obtained image (e.g., FIG. 2 ), measuring the areas of 100 or more void portions within the measurement target portions, calculating the diameter of a perfect circle corresponding to each area, and calculating the average value based on the calculated values.

[0027] The thickness of the porous layer 8 is preferably 100 to 1500 μm.

[0028] The electrochemical cell of the present invention may be housed in a frame.

[0029] The electrochemical cell manufacturing method of the present invention sequentially includes a first stack-fabricating step of forming or placing an anode film on the surface of a porous metal plate having a porosity of 50 to 80%, the porous metal plate comprising a connected structure of alloy particle portions containing Cr and Fe, to fabricate a first stack; a second stack-fabricating step of forming or placing a solid electrolyte layer film on the surface of the anode film to fabricate a second stack; a first sintering step of heat-treating the second stack and co-sintering the anode film and the solid electrolyte layer film to fabricate an integrated product (A) comprising a porous layer derived from the porous metal plate, an anode, and a solid electrolyte layer; a third stack-fabricating step of forming or placing a cathode film on the surface of the solid electrolyte layer to fabricate a third stack; and a cathode-forming step of heat-treating the third stack to bond the cathode film to the solid electrolyte layer.

[0030] The first stack fabrication step according to the present invention is a step of fabricating a first stack by forming or placing an anode membrane on the surface of a porous metal plate having a porosity of 50 to 80% and consisting of a connected structure of alloy particle portions containing Cr and Fe. The porous metal plate is preferably an article having a porosity of 50 to 80% obtained using powder metallurgy technology using alloy particles containing Cr and Fe as one of the manufacturing raw materials. The alloy particle portion is made of an alloy containing Cr and Fe, and this alloy may further contain Mn, Ni, Ti, Cu, Zr, Si, Al, Mo, etc. in addition to Cr and Fe. The alloy is preferably ferritic stainless steel (e.g., SUS430). Various types of stabilized zirconia are widely used in the solid electrolyte layer of electrochemical cells. Among stainless steels, the thermal expansion coefficient of ferritic stainless steel is close to that of stabilized zirconia. Therefore, when a porous metal plate is co-sintered to bond an anode and a solid electrolyte layer containing stabilized zirconia in this order, problems such as thermal shock are suppressed.

[0031] The shape of the porous metal plate is not particularly limited and may be either a flat plate or a curved plate. From the viewpoints of productivity of the electrochemical cell and structural stability of the formed electrochemical cell, the lower limit of the thickness is usually 0.1 mm and the upper limit is usually 1.5 mm, preferably 1.2 mm.

[0032] As shown in the typical example of Figure 3, the porous metal plate preferably has a plurality of nonlinear interconnecting holes extending from one side to the other side, providing breathability. As shown in the enlarged view of Figure 4, not all alloy particle portions are the same size, but alloy particle portions of various sizes form a connected structure, and the alloy particle portions are connected together, typically with a maximum diameter of 1 μm or more measured from their overall shape. The porous metal plate used in the present invention is not limited to this form, and all alloy particle portions may be the same size. Furthermore, the connection state between adjacent alloy particle portions may be either regular or irregular, but as can be seen from these typical examples, it is usually irregular.

[0033] The porosity of the porous metal plate is 50 to 80%, preferably 60 to 80%, and more preferably 70 to 80%, because when co-sintering is performed in the first sintering step, a porous layer with suitable pores can be formed and an integrated body (A) consisting of the porous layer, the fuel electrode, and the solid electrolyte layer can be efficiently formed. The porosity of this porous metal plate can be measured in accordance with JIS Z 2501.

[0034] In the porous metal plate, for example, when the thickness is 0.1 mm or more, the porosity can be ensured if the average value of the maximum diameter of the alloy particle portions measured from the outlines of at least 20 alloy particle portions is preferably 1 to 20 μm, more preferably 1 to 10 μm.

[0035] 5 is an explanatory diagram showing a method for measuring the maximum diameter of a plurality of connected alloy particle portions 10. The method involves photographing the surface or interior of a porous metal plate with an electron microscope, drawing an outline of each alloy particle portion from the obtained image, and measuring its maximum diameter. Figure 5 shows that the maximum diameters of four alloy particle portions 10 are r1, r2, r3, and r4, respectively. Using this measurement method, for example, the maximum diameters of 20 or more alloy particle portions are measured, and then the average value is calculated. If the average value is within the above-mentioned preferred average value range, the electrochemical cell obtained by the present invention will have a strength suitable for manufacturing.

[0036] In the first stack fabrication step according to the present invention, an anode film is formed or placed on the surface of a porous metal plate to fabricate a first stack. When forming an anode film on the surface of a porous metal plate, an anode-forming slurry may be applied or printed (e.g., by screen printing) to a predetermined position on the porous metal plate, and the coating may then be dried. When placing an anode film on the surface of a porous metal plate, an anode-forming slurry may be separately applied to the surface of, for example, a release film, and dried to obtain an anode film, which may then be placed on the predetermined position on the porous metal plate. The thickness of the anode film is not particularly limited, but is preferably 5 to 300 μm.

[0037] The slurry for forming the fuel electrode can contain a solid electrolyte such as stabilized zirconia, metal oxides such as nickel oxide and strontium titanate, particles of precious metals such as metal Pt and Pt alloys, a binder, a dispersion medium, and the like.

[0038] In the second stack fabrication step according to the present invention, a solid electrolyte layer film is formed or placed on the surface of the anode film in the first stack to fabricate the second stack. When forming a solid electrolyte layer film on the surface of the anode film, a solid electrolyte layer forming slurry may be applied or printed (e.g., by screen printing) to a predetermined position on the anode film, and the coating may then be dried. When placing a solid electrolyte layer film on the surface of the anode film, a solid electrolyte layer forming slurry may be separately applied to the surface of, for example, a release film, and dried, to obtain a solid electrolyte layer film, which may then be placed on the predetermined position on the anode film. The thickness of the solid electrolyte layer film is not particularly limited, but is preferably 1 to 150 μm.

[0039] The solid electrolyte layer-forming slurry preferably contains particles of stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce as the solid electrolyte. Examples of stabilized zirconia include scandia-stabilized zirconia, yttria-stabilized zirconia, scandia-ceria co-stabilized zirconia, scandia-yttria co-stabilized zirconia, ytterbia-stabilized zirconia, Gd-doped ceria, Sm-doped ceria, and La-doped ceria. The stabilized zirconia contained in the solid electrolyte layer-forming slurry may be one type or two or more types. The average particle size of the stabilized zirconia particles is preferably 0.5 to 20 μm.

[0040] The solid electrolyte layer forming slurry may further contain particles made of metal oxides such as nickel oxide and iron oxide, a binder, a dispersion medium, and the like.

[0041] In the first sintering step according to the present invention, the second stack is heat-treated to co-sinter the anode membrane and the solid electrolyte layer membrane, producing an integrated body (A) consisting of a porous layer derived from the porous metal plate, an anode, and a solid electrolyte layer. The heat treatment conditions for the second stack are not particularly limited. The atmosphere may be a hydrogen gas atmosphere, an inert gas atmosphere, a low oxygen partial pressure atmosphere, or the like. Reduced pressure conditions may also be used. The heat treatment temperature is preferably 900°C or higher, more preferably 1100°C or higher, with the upper limit temperature usually being 1400°C. The second stack may also be heat-treated while being pressurized in the thickness direction.

[0042] As described above, the first sintering step provides an integrated product (A) consisting of the porous layer, the anode, and the solid electrolyte layer. The heat treatment of the second stack shrinks the porous metal plate (usually 15 to 25% in the width direction) and reduces the porosity of the porous layer, resulting in an integrated product (A) with excellent mechanical strength.

[0043] In the electrochemical cell manufacturing method of the present invention, the integrated product (A) obtained in the first sintering step can be subjected to the third stack fabrication step, and in order to further densify the solid electrolyte layer in the integrated product (A), after the first sintering step, a dispersion of electrolyte particles containing stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce and having an average particle size of 150 nm or less can be applied to the surface of the solid electrolyte layer in the integrated product (A), dried, and further heat-treated. Hereinafter, this method will be described as a "densification step."

[0044] The electrolyte particles used in the densification step may be made of one or more materials, and the material may be the same as or different from the stabilized zirconia contained in the solid electrolyte layer-forming slurry that can be used in the second stack fabrication step. In the present invention, the solid electrolyte layer preferably contains at least one material selected from the group consisting of (S1) stabilized zirconia particles consisting of 3.0 to 10.0 mol % scandium oxide, 0 to 2.0 mol % cerium oxide, and 88.0 to 97.0 mol % zirconium oxide, (S2) stabilized zirconia particles consisting of 0.5 to 15.0 mol % yttrium oxide and 85.0 to 99.5 mol % zirconium oxide, and (S3) stabilized zirconia particles consisting of 0.5 to 15.0 mol % ytterbium oxide and 85.0 to 99.5 mol % zirconium oxide.

[0045] The average particle size of the electrolyte particles is preferably 50 to 150 nm, more preferably 60 to 120 nm. This average particle size is a volume-average particle size measured using a laser diffraction method, and specifically, is the particle size at which the cumulative frequency is 50% in the volume-based particle size distribution.

[0046] The dispersion medium for the electrolyte particle dispersion is not particularly limited as long as it does not easily cause the electrolyte particles to settle. In the present invention, alcohol is preferred, and ethanol is particularly preferred. The concentration of the electrolyte particles in the dispersion is preferably 0.01 to 20% by mass, more preferably 0.01 to 1% by mass.

[0047] The method of applying the electrolyte particle dispersion to the solid electrolyte layer of the integrated product (A) is not particularly limited. Examples include a method of spraying or dropping the electrolyte particle dispersion onto the surface of the solid electrolyte layer. The electrolyte particle dispersion used is not limited to one type, and multiple types of dispersions with different electrolyte particle concentrations can be used. For example, a method of sequentially contacting the electrolyte particle dispersions starting from the lowest concentration can be applied.

[0048] The amount of electrolyte particles to be added to the solid electrolyte layer of the integrated product (A) is appropriately determined depending on the surface area or thickness of the solid electrolyte layer.

[0049] In the densification step, when the electrolyte particle dispersion is applied and then dried, a portion of the electrolyte particles fills the voids in the solid electrolyte layer of the integrated product (A), and the integrated product (A) is subjected to heat treatment in this state. The heat treatment conditions are not particularly limited. The atmosphere may be a hydrogen gas atmosphere, an inert gas atmosphere, a low oxygen partial pressure atmosphere, or the like. Reduced pressure conditions may also be used. The heat treatment temperature is preferably 900°C or higher, more preferably 1000°C or higher, and the upper limit temperature is usually 1300°C. The integrated product (A) may also be heat-treated while being pressed in the thickness direction.

[0050] Next, in the third stack fabrication step according to the present invention, a cathode membrane is formed or placed on the surface of the solid electrolyte layer to fabricate a third stack. To form the cathode membrane on the surface of the solid electrolyte layer, a cathode-forming slurry containing a cathode-forming material may be applied or printed (e.g., by screen printing) to a predetermined position on the solid electrolyte layer, followed by drying the coating. Alternatively, to place the cathode membrane on the surface of the solid electrolyte layer, a cathode-forming slurry may be applied separately to the surface of a release film or the like, followed by drying the resulting cathode membrane. Alternatively, a molded article made of a cathode-forming material, both of which are solid components, may be placed on a predetermined position on the solid electrolyte layer. The thickness of the cathode membrane is not particularly limited, but is preferably 5 to 300 μm.

[0051] The cathode material is (Ba, Sr) (Fe, Co) O ３ , (La,Sr)CoO ３ , (La,Sr)(Fe,Co)O ３ , (Sm,Sr)(Fe,Co)O ３ The cathode-forming slurry may further contain a binder, a dispersion medium, etc.

[0052] Thereafter, in the cathode formation step according to the present invention, the third stack is heat-treated to bond the cathode membrane to the solid electrolyte layer, thereby obtaining an electrochemical cell. The conditions for the heat treatment of the third stack are not particularly limited. The atmosphere may be an oxidizing gas atmosphere such as air or oxygen. Reduced pressure conditions may also be used. The heat treatment temperature is preferably 500°C or higher, more preferably 700°C or higher, with the upper limit temperature usually being 1200°C. The third stack may also be heat-treated while being pressurized in the thickness direction.

[0053] The electrochemical cell obtained by the present invention realizes efficient electrochemical reactions both as a solid oxide fuel cell and as a solid oxide electrolysis cell.

[0054] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0055] Example 1 Nickel oxide powder and scandia-stabilized zirconia powder were mixed in a mass ratio of 60:40. The resulting mixed powder was mixed with dibutyl phthalate, an acrylic binder, and a mixed solvent of toluene and 2-propanol using a ball mill to prepare a slurry for forming an anode. This slurry for forming an anode was then subjected to sheet forming to produce a preliminary anode sheet. This preliminary anode sheet was then placed on the surface of a porous metal plate (thickness: 1 mm) made of SUS430 stainless steel, consisting of a connected structure of alloy particles, with a porosity of 71% and an average maximum diameter of 8 μm measured from the outline of the alloy particles. This sheet was then hot-pressed and pressure-bonded. Degreasing was then performed for 0.5 hours at 850°C in an argon gas atmosphere to obtain a first stack consisting of a porous metal plate and a degreased anode layer. Next, to adjust the thickness of the anode, a separately prepared slurry was screen-printed on the surface of the degreased anode layer. The screen printing slurry was prepared by mixing nickel oxide powder and scandia-stabilized zirconia powder in a mass ratio of 60:40, and then mixing the resulting mixed powder with a mixed solution of ethyl cellulose diluted with terpineol using a ball mill. Subsequently, a slurry for forming an electrolyte layer was screen-printed on the surface of the screen-printed anode to form a film, thereby obtaining a second stack. The electrolyte layer forming slurry was prepared by mixing scandia-stabilized zirconia powder with a mixed solution of ethyl cellulose diluted with terpineol using a ball mill. Next, while pressurizing the second stack, the second stack was subjected to heat treatment (co-sintering) in a hydrogen gas atmosphere at 1150°C for 1 hour, and then under reduced pressure in an argon gas atmosphere at 1240°C and 1260°C for 3 hours each, thereby bonding the solid electrolyte layer to the anode and obtaining an integrated product (hereinafter referred to as "integrated product A1") consisting of a porous layer derived from the porous metal plate, the anode, and the solid electrolyte layer. Then, (Ba, Sr)(Co, Fe)O was deposited on the surface of the solid electrolyte layer of the integrated product A1. ３ and (Ce, Gd)O ２ A cathode membrane (thickness: 0.12 mm) made of a mixed powder (mass ratio 7:3) of the above was placed on the cathode membrane to prepare a third stack.

[0056] Next, platinum current collecting layers with a diameter of 6 mm were formed on the surfaces of the cathode membrane and the porous layer of the third stack, respectively. Two platinum wires were connected to each of these platinum current collecting layers. Pure hydrogen was then circulated through the pores of the porous layer to the anode, and air was circulated through the cathode membrane. Heat treatment was then performed at 750 °C for 1 hour to bond the cathode membrane to the solid electrolyte layer, forming an cathode. Two electrochemical cells (one with the solid electrolyte layer bonded at 1240 °C and one with the solid electrolyte layer bonded at 1260 °C) were obtained, each with excellent mechanical strength and a stable layer structure. Subsequently, the open circuit voltage (OCV) of each electrochemical cell was measured at 750 °C while maintaining the same gas flow conditions to evaluate battery performance. The current flowing through the external circuit was also measured when the terminal voltage was varied from the open circuit voltage to 0.3 V.

[0057] In the electrochemical cell in which the solid electrolyte layer was bonded at 1240°C, the cross section of the porous layer was photographed with an optical microscope, the obtained image was binarized, and the area ratio of voids in the porous layer per predetermined area (porosity) was calculated using image analysis software, which was 26%. In addition, the porosity of the electrochemical cell in which the solid electrolyte layer was bonded at 1260°C was 16%.

[0058] Furthermore, a cross section of the porous layer was photographed using an optical microscope, and an arbitrary measurement target portion was set within the obtained image. The areas of 100 or more voids within the voids were measured, and the diameter of a perfect circle corresponding to each area was calculated. An average value (pore diameter) was calculated based on each calculated value, and the average value was 38 μm for the electrochemical cell in which the solid electrolyte layers were bonded at 1240°C, and 38 μm for the electrochemical cell in which the solid electrolyte layers were bonded at 1260°C.

[0059] Example 2 The surface of the solid electrolyte layer in the integrated product A1 produced in Example 1 was measured using a laser diffraction / scattering particle size distribution analyzer "LA-960V2" (model name) manufactured by Horiba, Ltd., to determine the 50% frequency diameter D of the volume diameter. ５０A dispersion of scandia-stabilized zirconia nanoparticles with a particle size of 85 nm (dispersion medium: ethanol, nanoparticle concentration: 0.134 wt%) was added dropwise five times (amount added per drop: 100 μL). An ethanol dispersion of these nanoparticles with a nanoparticle concentration of 0.670 wt% was then added dropwise five times (amount added per drop: 100 μL). The ethanol dispersion medium was then removed. The mixture was then heat-treated at 1200°C for 3 hours in a 20% hydrogen / argon balance atmosphere to obtain a densified solid electrolyte layer. This procedure yielded an integrated product (hereinafter referred to as "integrated product A2") with a densified solid electrolyte layer containing nanoparticles. Thereafter, in the same manner as for the integrated product A1 in Example 1, an air electrode was formed by bonding an air electrode membrane to the densified solid electrolyte layer of the integrated product A2, and two types of electrochemical cells (an electrochemical cell in which the solid electrolyte layer was bonded at 1240° C. and an electrochemical cell in which the solid electrolyte layer was bonded at 1260° C.) each having excellent mechanical strength and a stable layer structure were obtained. Thereafter, battery performance evaluation was performed in the same manner as in Example 1.

[0060] The evaluation results of the battery performance (current-voltage characteristics) of the four types of electrochemical cells obtained in Examples 1 and 2 above are shown in the graphs of FIG. 6 (electrochemical cells of Examples 1 and 2 in which the solid electrolyte layers were joined at 1240° C.) and FIG. 7 (electrochemical cells of Examples 1 and 2 in which the solid electrolyte layers were joined at 1260° C.).

[0061] From FIG. 6, the open circuit voltages (OCVs) of the electrochemical cells of Examples 1 and 2 were 0.875 V and 0.978 V, respectively, and the extracted power densities were 0.367 W / cm. ２ and 0.621 W / cm ２ Compared with the electrochemical cell of Example 1, the circuit voltage at 750°C in the electrochemical cell of Example 2 was improved by 0.103 V, and the maximum power density was 0.254 W / cm ２ 7, the circuit voltage at 750°C of the electrochemical cell of Example 2 was improved by 0.186 V and the maximum power density was 0.318 W / cm compared to the electrochemical cell of Example 1. ２ Improvement was confirmed.

[0062] The electrochemical cell of the present invention is suitable as a metal supported cell type solid oxide fuel cell or a metal supported cell type solid oxide electrolysis cell in which the solid electrolyte layer contains stabilized zirconia or the like.

[0063] 1: Electrochemical cell 2: Air electrode 4: Solid electrolyte layer 6: Fuel electrode 8: Porous layer 10: Alloy particle portion

Claims

1. An electrochemical cell comprising an air electrode, a solid electrolyte layer, a fuel electrode, and a porous layer in this order, characterized in that the porous layer is made of an alloy containing Cr and Fe, has a porosity of 15 to 50%, and has a pore diameter (average circle equivalent diameter) of 5 to 50 μm.

2. The electrochemical cell according to claim 1, wherein the solid electrolyte layer contains stabilized zirconia containing at least one stabilizing element selected from the group consisting of Sc, Y, Yb and Ce.

3. A method for producing an electrochemical cell according to claim 1 or 2, comprising the steps of: a first stack fabrication step of forming or placing a film for anode on the surface of a porous metal plate having a porosity of 50 to 80%, the film being made of a connected structure of alloy particles containing Cr and Fe, to fabricate a first stack; a second stack fabrication step of forming or placing a film for a solid electrolyte layer on the surface of the film for anode, to fabricate a second stack; a first sintering step of heat-treating the second stack and co-sintering the film for anode and the film for solid electrolyte layer to fabricate an integrated body (A) consisting of a porous layer derived from the porous metal plate, anode and solid electrolyte layer; a third stack fabrication step of forming or placing a film for cathode on the surface of the solid electrolyte layer to fabricate a third stack; and a cathode formation step of heat-treating the third stack and bonding the film for cathode to the solid electrolyte layer.

4. The method for manufacturing an electrochemical cell according to claim 3, further comprising the steps of: applying, to a surface of the solid electrolyte layer in the integrated body (A) after the first sintering step, a dispersion liquid of electrolyte particles containing stabilized zirconia containing at least one stabilizing element selected from Sc, Y, Yb, and Ce and having an average particle size of 150 nm or less; drying the dispersion liquid; and further heat treating the solid electrolyte layer to densify the solid electrolyte layer.

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