Electrolyte substrate for solid oxide fuel cell, single cell for solid oxide fuel cell, solid oxide fuel cell stack, and method for manufacturing electrolyte substrate for solid oxide fuel cell

Abstract

An electrolyte substrate 10 for a solid oxide fuel cell comprises: an electrolyte layer 20 including a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia; and a barrier layer 30 provided on at least one main surface of the electrolyte layer 20 and including a sintered body of Ce(X)O2 (X is any of Sm, Gd, and Y). When viewing a cross section in the thickness direction of the barrier layer 30, holes 40 are present within the interior of the barrier layer 30 and occupy an area ratio of 24-72% thereof.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte substrate for a solid oxide fuel cell, a single cell for a solid oxide fuel cell, a solid oxide fuel cell stack, and a method for manufacturing an electrolyte substrate for a solid oxide fuel cell. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) are fuel electrodes: H2 + O 2- →H2O+2e - , Air electrode: (1 / 2)O2+2e - →O 2- A solid oxide fuel cell is a device that extracts electrical energy through the reaction of the following: A solid oxide fuel cell is used in a stacked structure by stacking multiple single cells for solid oxide fuel cells, each of which has a fuel electrode and an air electrode provided on an electrolyte substrate for solid oxide fuel cells.

[0003] Patent Document 1 discloses a solid oxide fuel cell having a fuel electrode and an air electrode provided via an electrolyte membrane, characterized in that an intermediate layer of Ce(X)O2 (where X is any one of Sm, Gd, or Y) is provided between the electrolyte membrane of scandia-stabilized zirconia and the air electrode of La(Ni)FeO3.

[0004] Furthermore, Patent Document 1 discloses a method for manufacturing a solid oxide fuel cell, which comprises forming a fuel electrode on one side of a scandia-stabilized zirconia electrolyte membrane, applying a slurry of Ce(X)O2 (where X is any of Sm, Gd, or Y) to the other side, sintering the mixture to form an intermediate layer, and then providing a cathode of La(Ni)FeO3; and a method for manufacturing a solid oxide fuel cell, which comprises forming a scandia-stabilized zirconia electrolyte membrane on a fuel electrode, sintering the mixture, applying a slurry of Ce(X)O2 (where X is any of Sm, Gd, or Y) to the electrolyte membrane, sintering the mixture to form an intermediate layer, and then providing a cathode of La(Ni)FeO3. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3789380 Summary of the Invention [Problem to be solved by the invention]

[0006] According to Patent Document 1, by forming an intermediate layer of Ce(Sm)O2 or the like between the La(Ni)FeO3 air electrode and the zirconia-based electrolyte, it is possible to suppress the reaction between the La(Ni)FeO3 air electrode and the zirconia in the electrolyte during electrode sintering, thereby improving cell performance.

[0007] However, when the electrolyte layer and the barrier layer are co-sintered or when the barrier layer is subsequently baked onto the sintered electrolyte layer to form the intermediate layer (hereinafter referred to as the barrier layer) as described in Patent Document 1, cracks may occur in the electrolyte layer, the barrier layer, or both due to differences in thermal expansion or firing shrinkage between the materials. If such cracks occur, problems such as a decrease in the strength of the electrolyte layer, a decrease in the long-term reliability (durability) of the cell after electrode formation, and a decrease in power generation characteristics due to a decrease in the separation function between oxidant gas and fuel gas may occur.

[0008] The present invention has been made to solve the above problems, and aims to provide an electrolyte substrate for a solid oxide fuel cell that can reduce the difference in thermal expansion or firing contraction between the electrolyte layer and the barrier layer, thereby suppressing the occurrence of cracks. The present invention also aims to provide a unit cell for a solid oxide fuel cell that includes the electrolyte substrate, a solid oxide fuel cell stack in which a plurality of the unit cells are stacked, and a method for manufacturing the electrolyte substrate. [Means for solving the problem]

[0009] The electrolyte substrate for a solid oxide fuel cell according to the present invention comprises an electrolyte layer containing a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia, and a barrier layer provided on at least one main surface of the electrolyte layer and containing a sintered body of Ce(X)O2 (where X is any one of Sm, Gd, and Y), wherein, when viewed in a cross section along the thickness direction of the barrier layer, pores are present within the barrier layer in an area ratio of 24% to 72%.

[0010] The single cell for a solid oxide fuel cell according to the present invention comprises an air electrode, an anode, and an electrolyte substrate according to the present invention disposed between the air electrode and the anode, with a barrier layer of the electrolyte substrate disposed between the electrolyte layer of the electrolyte substrate and the air electrode.

[0011] The solid oxide fuel cell stack of the present invention is formed by stacking multiple cells each comprising a single cell of the present invention, a first interconnector arranged on the air electrode side of the single cell, and a second interconnector arranged on the fuel electrode side of the single cell.

[0012] The method for manufacturing an electrolyte substrate for a solid oxide fuel cell according to the present invention comprises the steps of: preparing an unsintered substrate, in which an unsintered barrier layer containing a powder of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burn-off material is provided on at least one main surface of an unsintered electrolyte layer containing a powder of scandia-stabilized zirconia or yttria-stabilized zirconia, or on at least one main surface of an electrolyte layer containing a sintered compact of scandia-stabilized zirconia or yttria-stabilized zirconia; and firing the unsintered substrate at a temperature equal to or higher than the temperature at which the burn-off material is burned off. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an electrolyte substrate for a solid oxide fuel cell, which can reduce the difference in thermal expansion or firing contraction between the electrolyte layer and the barrier layer, thereby suppressing the occurrence of cracks. Furthermore, according to the present invention, it is possible to provide a unit cell for a solid oxide fuel cell including the electrolyte substrate, a solid oxide fuel cell stack in which a plurality of the unit cells are stacked, and a method for manufacturing the electrolyte substrate. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of an electrolyte substrate for a solid oxide fuel cell according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing another example of an electrolyte substrate for a solid oxide fuel cell according to the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of a process for producing a green sheet for an electrolyte layer. [Figure 4] FIG. 4 is a cross-sectional view schematically showing an example of a process for producing a green sheet for a barrier layer. [Figure 5] FIG. 5 is a cross-sectional view schematically showing an example of a process for producing a green substrate. [Figure 6] FIG. 6 is a cross-sectional view schematically showing another example of the steps for producing a green substrate. [Figure 7] FIG. 7 is a cross-sectional view schematically showing an example of a step of firing the green substrate. [Figure 8] FIG. 8 is a cross-sectional view schematically showing another example of the step of firing the green substrate. [Figure 9] FIG. 9 is a cross-sectional view that schematically shows an example of a single cell for a solid oxide fuel cell according to the present invention. [Figure 10] FIG. 10 is a cross-sectional view that schematically shows another example of a unit cell for a solid oxide fuel cell according to the present invention. [Figure 11] FIG. 11 is an exploded perspective view schematically showing an example of a solid oxide fuel cell stack according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes an electrolyte substrate for a solid oxide fuel cell, a single cell for a solid oxide fuel cell, a solid oxide fuel cell stack, and a method for manufacturing an electrolyte substrate for a solid oxide fuel cell according to the present invention. Note that the present invention is not limited to the following configurations, and can be modified as appropriate within the scope of the present invention. Furthermore, a combination of two or more of the individual desirable configurations of the present invention described below also constitutes the present invention.

[0016] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0017] [Electrolyte substrate for solid oxide fuel cells] The electrolyte substrate for a solid oxide fuel cell according to the present invention comprises an electrolyte layer containing a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia, and a barrier layer provided on at least one main surface of the electrolyte layer and containing a sintered body of Ce(X)O2 (where X is any one of Sm, Gd, and Y), wherein, when viewed in a cross section along the thickness direction of the barrier layer, pores are present within the barrier layer in an area ratio of 24% to 72%.

[0018] FIG. 1 is a cross-sectional view schematically showing an example of an electrolyte substrate for a solid oxide fuel cell according to the present invention.

[0019] The electrolyte substrate 10 for a solid oxide fuel cell shown in FIG. 1 includes an electrolyte layer 20 and barrier layers 30 provided on both main surfaces of the electrolyte layer 20 .

[0020] FIG. 2 is a cross-sectional view schematically showing another example of an electrolyte substrate for a solid oxide fuel cell according to the present invention.

[0021] The electrolyte substrate 10A for a solid oxide fuel cell shown in FIG. 2 includes an electrolyte layer 20 and a barrier layer 30 provided on one main surface of the electrolyte layer 20.

[0022] The electrolyte layer 20 includes a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia.

[0023] Examples of scandia-stabilized zirconia include Zr(Sc)O2 and Zr(Sc,M)O2 (wherein M is any one of Al2O3, CeO2, and Y2O3).

[0024] An example of yttria-stabilized zirconia is Zr(Y)O2.

[0025] The barrier layer 30 includes a sintered body of Ce(X)O2 (where X is any one of Sm, Gd, and Y). The barrier layer 30 provided on each main surface of the electrolyte layer 20 may be two or more layers, but is preferably one layer.

[0026] Similar to the intermediate layer described in Patent Document 1, the barrier layer 30 has the function of suppressing the reaction between the electrolyte layer 20 and the air electrode 50 (see FIGS. 9 and 10 described later).

[0027] As shown in FIGS. 1 and 2, pores 40 exist inside the barrier layer 30.

[0028] By forming pores 40 inside the barrier layer 30, the difference in thermal expansion or firing contraction between the electrolyte layer 20 and the barrier layer 30 is alleviated, and the occurrence of cracks can be suppressed.

[0029] On the other hand, when pores are formed inside the electrolyte layer 20, if the pores connect to each other and penetrate the electrolyte layer 20, the power generation performance will be deteriorated due to the loss of the ability to separate the oxidant gas and the fuel gas. Therefore, it is desirable to form pores 40 inside the barrier layer 30.

[0030] In order to mitigate the difference in firing shrinkage, if the shrinkage of the electrolyte layer 20 is greater than that of the barrier layer 30, it is effective to form pores 40 inside the barrier layer 30.

[0031] Regarding the reduction of the thermal expansion difference, when the thermal expansion coefficient of the electrolyte layer 20 is smaller than that of the barrier layer 30, it is effective to form pores 40 inside the barrier layer 30.

[0032] Furthermore, as will be shown in the examples described later, it has been found that the substrate strength improves as the number of voids 40 inside the barrier layer 30 increases. This is presumably due to the effect of reducing residual stress (i.e., tensile stress acting on the surface of the barrier layer 30) due to relaxation of the thermal expansion difference during firing, and the effect of the voids 40 stopping the propagation of cracks even if they occur.

[0033] On the other hand, if there are too many voids 40 inside the barrier layer 30, the barrier layer 30 becomes more likely to detach from the electrolyte layer 20. This is thought to be due to a decrease in the bonding area between the electrolyte layer 20 and the barrier layer 30, as well as a decrease in the strength of the barrier layer 30 itself.

[0034] For the above reasons, when viewing a cross section of the barrier layer 30 along its thickness direction, it is desirable that the area ratio of pores 40 within the barrier layer 30 be 24% or more and 72% or less. In other words, it is desirable that the pore area ratio within the barrier layer 30 be 24% or more and 72% or less.

[0035] The thickness of the barrier layer 30 is not particularly limited and may be the same as, greater than, or smaller than the thickness of the electrolyte layer 20. However, the higher the ratio of the thickness of the barrier layer 30 to the thickness of the electrolyte layer 20, the more likely cracks will occur, thereby enhancing the effectiveness of the pores 40. On the other hand, the higher the ratio of the thickness of the barrier layer 30 to the thickness of the electrolyte layer 20, the more likely power generation characteristics will deteriorate. Therefore, from the viewpoint of ensuring power generation characteristics, the ratio of the thickness of the barrier layer 30 to the thickness of the electrolyte layer 20 is preferably 20% or less. On the other hand, from the viewpoints of the strength of the barrier layer 30 itself, the adhesion between the barrier layer 30 and the electrolyte layer 20, and enabling the barrier layer 30 to exhibit its functions, the ratio of the thickness of the barrier layer 30 to the thickness of the electrolyte layer 20 may be, for example, 1% or more, but is preferably 5% or more, and more preferably 10% or more.

[0036] For example, the thickness of the barrier layer 30 is preferably 20 μm or less. On the other hand, the thickness of the barrier layer 30 may be 1 μm or more, but is preferably 5 μm or more, and more preferably 10 μm or more. When the thickness of the barrier layer 30 is within the above range, the thickness of the electrolyte layer 20 is preferably 80 μm or more and 120 μm or less. Furthermore, when the thickness of the barrier layer 30 is within the above range, the ratio of the thickness of the barrier layer 30 to the thickness of the electrolyte layer 20 is preferably within the above range.

[0037] In either case, when the barrier layer 30 is provided on both main surfaces of the electrolyte layer 20 as shown in FIG. 1, or when the barrier layer 30 is provided on one main surface of the electrolyte layer 20 as shown in FIG. 2, the thickness of the barrier layer 30 means the thickness of the barrier layer 30 provided on each main surface of the electrolyte layer 20 (the thickness of one layer).

[0038] Additionally, there are no particular limitations on the shape, size, etc. of the holes 40. The shapes of the holes 40 may be the same or different. Similarly, the sizes of the holes 40 may be the same or different.

[0039] For example, some of the pores 40 may be connected to each other, but if the pores 40 are connected to each other and penetrate the barrier layer 30, there is a risk of reaction between the electrolyte layer 20 and the air electrode 50 (see FIGS. 9 and 10 described below), and if a crack occurs, the pores 40 will not be able to sufficiently prevent the crack from progressing. Therefore, it is preferable that the pores 40 do not communicate with each other from one principal surface to the other principal surface opposing each other in the thickness direction of the barrier layer 30.

[0040] It is preferable that the pores 40 are uniformly dispersed inside the barrier layer 30. In other words, it is preferable that the pores 40 are not unevenly distributed inside the barrier layer 30.

[0041] 1, when the barrier layers 30 are provided on both main surfaces of the electrolyte layer 20, it is preferable that the thickness, pore area ratio, etc. of the barrier layers 30 are the same. Here, "the same" does not have to be exactly the same, but may be within a range of about 3%. By providing the barrier layers 30 symmetrically with respect to the electrolyte layer 20, warping and other problems during sintering can be suppressed.

[0042] Additionally, the shape, size, thickness, etc. of the electrolyte substrates 10 and 10A are not particularly limited.

[0043] [Method of manufacturing an electrolyte substrate for solid oxide fuel cells] The method for manufacturing an electrolyte substrate for a solid oxide fuel cell according to the present invention comprises the steps of: preparing an unsintered substrate, in which an unsintered barrier layer containing a powder of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burn-off material is provided on at least one main surface of an unsintered electrolyte layer containing a powder of scandia-stabilized zirconia or yttria-stabilized zirconia, or on at least one main surface of an electrolyte layer containing a sintered compact of scandia-stabilized zirconia or yttria-stabilized zirconia; and firing the unsintered substrate at a temperature equal to or higher than the temperature at which the burn-off material is burned off.

[0044] In the step of preparing the green substrate, a green substrate may be prepared in which a green barrier layer containing a powder of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burnout material is provided on at least one main surface of a green electrolyte layer containing a powder of scandia-stabilized zirconia or yttria-stabilized zirconia. In this case, the barrier layer is formed by co-sintering with the electrolyte layer.

[0045] Examples of methods for forming an unsintered electrolyte layer include a method for preparing an electrolyte layer green sheet, a method for applying an electrolyte layer paste, etc. Examples of methods for forming an unsintered barrier layer include a method for preparing a barrier layer green sheet, a method for applying a barrier layer paste, etc.

[0046] For example, the process for producing the green substrate includes the steps of: preparing an unsintered electrolyte layer green sheet containing a powder of scandia-stabilized zirconia or yttria-stabilized zirconia; preparing an unsintered barrier layer green sheet containing a powder of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burn-off material; and laminating the electrolyte layer green sheet and the barrier layer green sheet.

[0047] Alternatively, in the step of preparing the green substrate, a green substrate may be prepared in which an electrolyte layer including a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia has an electrolyte layer including a sintered body and an green barrier layer including a powder of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burn-off material provided on at least one main surface thereof. In this case, the barrier layer is formed by post-baking the sintered electrolyte layer.

[0048] In the method for manufacturing an electrolyte substrate according to the present invention, voids are intentionally formed inside the barrier layer by incorporating a burn-off material (a material that is burned off during firing) into the barrier layer green sheet or the barrier layer paste in advance.

[0049] Examples of the burn-off material include resin beads, carbon, binders, and other organic substances. The burn-off material may be one type or two or more types. Among these, the burn-off material is preferably resin beads. By using resin beads as the burn-off material, the shape of the pores can be easily adjusted.

[0050] An example of a method for manufacturing the electrolyte substrate 10 shown in FIG. 1 or the electrolyte substrate 10A shown in FIG. 2 will be described below step by step with reference to the drawings.

[0051] FIG. 3 is a cross-sectional view schematically showing an example of a process for producing a green sheet for an electrolyte layer.

[0052] For example, an unsintered electrolyte layer green sheet 2s is produced by molding a ceramic slurry for the electrolyte layer. The electrolyte layer green sheet 2s contains a powder 5 of scandia-stabilized zirconia or yttria-stabilized zirconia.

[0053] The ceramic slurry for the electrolyte layer can be prepared by mixing, for example, a powder of scandia-stabilized zirconia or yttria-stabilized zirconia, a binder, a dispersant, an organic solvent, and the like.

[0054] FIG. 4 is a cross-sectional view schematically showing an example of a process for producing a green sheet for a barrier layer.

[0055] For example, an unfired barrier layer green sheet 3s is produced by molding a ceramic slurry for the barrier layer. The barrier layer green sheet 3s contains a powder 6 of Ce(X)O2 (where X is any one of Sm, Gd, and Y) and a burn-off material 4.

[0056] The ceramic slurry for the barrier layer can be prepared by mixing, for example, powder of Ce(X)O2 (where X is any of Sm, Gd, and Y), a burn-off material, a binder, a dispersant, an organic solvent, and the like.

[0057] FIG. 5 is a cross-sectional view schematically showing an example of a process for producing a green substrate.

[0058] As shown in Fig. 5, an unsintered substrate 1 is produced by laminating an electrolyte layer green sheet 2s and a barrier layer green sheet 3s. In the unsintered substrate 1 shown in Fig. 5, an unsintered barrier layer 3 is provided on both main surfaces of an unsintered electrolyte layer 2.

[0059] In the example shown in FIG. 5 , the green substrate 1 is fabricated by laminating one barrier layer green sheet 3s, three electrolyte layer green sheets 2s, and one barrier layer green sheet 3s in this order. The number of electrolyte layer green sheets 2s included in the green electrolyte layer 2 is not particularly limited and may be one or more. The number of barrier layer green sheets 3s included in the green barrier layer 3 provided on one main surface of the green electrolyte layer 2 is also not particularly limited and may be one or more. The number of barrier layer green sheets 3s included in the green barrier layer 3 provided on one main surface of the green electrolyte layer 2 may be the same as, more than, or less than the number of electrolyte layer green sheets 2s included in the green electrolyte layer 2. Similarly, the number of barrier layer green sheets 3s included in the green barrier layer 3 provided on the other main surface of the green electrolyte layer 2 is not particularly limited and may be one or more. The number of barrier layer green sheets 3s included in the unsintered barrier layer 3 provided on the other main surface of the unsintered electrolyte layer 2 may be the same as, more than, or less than the number of electrolyte layer green sheets 2s included in the unsintered electrolyte layer 2. Furthermore, the number of barrier layer green sheets 3s included in the unsintered barrier layer 3 provided on the other main surface of the unsintered electrolyte layer 2 may be the same as, more than, or less than the number of barrier layer green sheets 3s included in the unsintered barrier layer 3 provided on one main surface of the unsintered electrolyte layer 2.

[0060] FIG. 6 is a cross-sectional view schematically showing another example of the steps for producing a green substrate.

[0061] As shown in Fig. 6, an unsintered substrate 1A may be produced by laminating an electrolyte layer green sheet 2s and a barrier layer green sheet 3s. In the unsintered substrate 1A shown in Fig. 6, an unsintered barrier layer 3 is provided on one main surface of an unsintered electrolyte layer 2.

[0062] 6, the green substrate 1A is produced by laminating one barrier layer green sheet 3s and three electrolyte layer green sheets 2s in this order. The number of electrolyte layer green sheets 2s included in the green electrolyte layer 2 is not particularly limited and may be one or two or more. Furthermore, the number of barrier layer green sheets 3s included in the green barrier layer 3 provided on one main surface of the green electrolyte layer 2 is not particularly limited and may be one or two or more.

[0063] When forming the green electrolyte layer 2, stacking a plurality of electrolyte layer green sheets 2s makes it possible to easily control the thickness of the green electrolyte layer 2. Similarly, when forming the green barrier layer 3, stacking a plurality of barrier layer green sheets 3s makes it possible to easily control the thickness of the green barrier layer 3.

[0064] When producing the green substrate 1 or 1A, the electrolyte layer green sheet 2s and the barrier layer green sheet 3s may be laminated and then pressed together.

[0065] FIG. 7 is a cross-sectional view schematically showing an example of a step of firing the green substrate.

[0066] 5 is fired at a temperature equal to or higher than the temperature at which the burn-off material 4 is burned off, whereby the green substrate 1 is sintered to form the electrolyte layer 20 and the barrier layer 30, and the burn-off material 4 is burned off to form voids 40 inside the barrier layer 30. As a result, the electrolyte substrate 10 shown in FIG. 7 is produced.

[0067] FIG. 8 is a cross-sectional view schematically showing another example of the step of firing the green substrate.

[0068] 6 is fired at a temperature equal to or higher than the temperature at which the burn-off material 4 is burned off, whereby the green substrate 1A is sintered to form the electrolyte layer 20 and the barrier layer 30, and the burn-off material 4 is burned off to form voids 40 inside the barrier layer 30. As a result, the electrolyte substrate 10A shown in FIG. 8 is produced.

[0069] [Solid oxide fuel cell unit cell] A single cell for a solid oxide fuel cell according to the present invention comprises an air electrode, an anode, and an electrolyte substrate according to the present invention provided between the air electrode and the anode.

[0070] In the single cell for a solid oxide fuel cell according to the present invention, a barrier layer of the electrolyte substrate is disposed between the electrolyte layer of the electrolyte substrate and the air electrode, thereby suppressing a reaction between the electrolyte layer and the air electrode.

[0071] FIG. 9 is a cross-sectional view that schematically shows an example of a single cell for a solid oxide fuel cell according to the present invention.

[0072] The solid oxide fuel cell unit cell 100 shown in FIG. 9 includes an air electrode 50, an anode 60, and an electrolyte substrate 10 (see FIG. 1) disposed between the air electrode 50 and the anode 60.

[0073] 1, the electrolyte substrate 10 includes an electrolyte layer 20 and barrier layers 30 provided on both main surfaces of the electrolyte layer 20. Pores 40 exist inside the barrier layer 30.

[0074] FIG. 10 is a cross-sectional view that schematically shows another example of a unit cell for a solid oxide fuel cell according to the present invention.

[0075] The solid oxide fuel cell unit cell 100A shown in FIG. 10 includes an air electrode 50, an anode 60, and an electrolyte substrate 10A (see FIG. 2) provided between the air electrode 50 and the anode 60.

[0076] 2, the electrolyte substrate 10A includes an electrolyte layer 20 and a barrier layer 30 provided on one main surface of the electrolyte layer 20. Inside the barrier layer 30, pores 40 exist.

[0077] As shown in FIGS. 9 and 10, the barrier layer 30 of the electrolyte substrate 10 is disposed between the electrolyte layer 20 of the electrolyte substrate 10 and the air electrode 50 .

[0078] A known air electrode for a solid oxide fuel cell is used as the air electrode 50. Examples of materials for the air electrode 50 include La(Ni)FeO3, (La,Sr)CoO3, (La,Sr)FeO3, and (La,Sr)(Co,Fe)O3. If no barrier layer 30 is provided between the electrolyte layer 20 and the air electrode 50, high-temperature heat treatment causes the air electrode 50 to react with the electrolyte layer 20, producing an insulating layer such as SrZrO3 or La2Zr2O7.

[0079] The air electrode 50 may be provided over the entirety of one of the main surfaces of the electrolyte substrate 10 or 10A, or may be provided over a portion thereof.

[0080] A known fuel electrode for a solid oxide fuel cell is used as the fuel electrode 60. Examples of materials for the fuel electrode 60 include Ni, Ni / ScSZ (scandia-stabilized zirconia) cermet, Ni / YSZ (yttria-stabilized zirconia) cermet, and Ni / CeO cermet.

[0081] The fuel electrode 60 may be provided over the entirety of the other main surface of the electrolyte substrate 10 or 10A, or may be provided over a portion thereof.

[0082] The single cell for a solid oxide fuel cell according to the present invention can be manufactured by forming an air electrode on one main surface of the electrolyte substrate for a solid oxide fuel cell according to the present invention and forming a fuel electrode on the other main surface.

[0083] First, a binder and a solvent are added to a powder of the material constituting the air electrode, and a dispersant, etc. are further added as needed, to prepare a slurry for the air electrode. A binder and a solvent are added to a powder of the material constituting the anode, and a dispersant, etc. are further added as needed, to prepare a slurry for the anode. The slurry for the air electrode is applied to one main surface of the electrolyte substrate, and the slurry for the anode is applied to the other main surface of the electrolyte substrate, each to a predetermined thickness, and the coating is dried to form green layers for the air electrode and the anode. The green layers for the air electrode and the anode are then fired to form the air electrode and the anode. Firing conditions, such as the firing temperature, can be determined appropriately depending on the types of materials for the air electrode and the anode, etc.

[0084] When the unit cell according to the present invention is incorporated into a solid oxide fuel cell, an oxidant gas flow path is required for supplying an oxidant gas such as air or oxygen gas to the air electrode, and a fuel gas flow path is required for supplying a fuel gas such as hydrogen gas, carbon monoxide gas, or hydrocarbon gas to the fuel electrode. A solid oxide fuel cell stack in which a plurality of such unit cells according to the present invention are stacked, each cell having an oxidant gas flow path and a fuel gas flow path and further having an electrically conductive path, also constitutes one aspect of the present invention.

[0085] [Solid oxide fuel cell stack] The solid oxide fuel cell stack of the present invention is formed by stacking multiple cells each comprising a single cell of the present invention, a first interconnector arranged on the air electrode side of the single cell, and a second interconnector arranged on the fuel electrode side of the single cell.

[0086] In the solid oxide fuel cell stack according to the present invention, a plurality of unit cells are stacked via interconnectors (also called separators). That is, each of the unit cells is sandwiched between a pair of interconnectors. The interconnectors electrically connect the unit cells and also supply gas to each electrode.

[0087] FIG. 11 is an exploded perspective view schematically showing an example of a solid oxide fuel cell stack according to the present invention.

[0088] In the solid oxide fuel cell stack 200 shown in Fig. 11, cells 110 each including a unit cell 100 (see Fig. 9), a first interconnector 210 disposed on the air electrode 50 side of the unit cell 100, and a second interconnector 220 disposed on the fuel electrode 60 side of the unit cell 100 are stacked in two stages in the Z direction. The number of stacked cells 110 is not particularly limited. In the solid oxide fuel cell stack 200, only the unit cells 100 shown in Fig. 9 may be stacked, only the unit cells 100A shown in Fig. 10 may be stacked, or both the unit cells 100 shown in Fig. 9 and the unit cells 100A shown in Fig. 10 may be stacked.

[0089] The solid oxide fuel cell stack 200 is provided with an oxidant gas manifold 230 and a fuel gas manifold 240, which are through-holes. The oxidant gas manifold 230 extends in the X direction, and the fuel gas manifold 240 extends in the Y direction.

[0090] An oxidizing gas flow field 250 is provided on the main surface of the first interconnector 210 facing the air electrode 50. The oxidizing gas flow field 250 extends in the Y direction.

[0091] A fuel gas flow channel 260 is provided on the main surface of the second interconnector 220 facing the fuel electrode 60. The fuel gas flow channel 260 extends in the X direction.

[0092] The constituent material of the first interconnector 210 and the second interconnector 220 may be an insulating material such as a ceramic material, or a conductive material such as a metal material.

[0093] The constituent materials of the first interconnector 210 and the second interconnector 220 may be the same as or different from each other.

[0094] When the constituent materials of the first interconnector 210 and the second interconnector 220 are insulating materials, the first interconnector 210 and the second interconnector 220 may be, for example, a sintered body of partially stabilized zirconia.

[0095] When the constituent material of the first interconnector 210 is an insulating material, the first interconnector 210 is preferably provided with at least one through conductor that penetrates in the thickness direction, connects to the air electrode 50, and is exposed on the main surface opposite the air electrode 50. In this case, the air electrode 50 can be led out of the first interconnector 210 via the through conductor.

[0096] When the constituent material of the second interconnector 220 is an insulating material, the second interconnector 220 is preferably provided with at least one through conductor that penetrates in the thickness direction, is connected to the anode 60, and is exposed on the main surface opposite to the anode 60. In this case, the anode 60 can be led out of the second interconnector 220 via the through conductor.

[0097] The constituent material of the through conductors provided in the first interconnector 210 and the second interconnector 220 is preferably an alloy of silver and palladium, or platinum.

[0098] The constituent material of the through conductor provided in the first interconnector 210 and the constituent material of the through conductor provided in the second interconnector 220 may be the same as or different from each other. [Example]

[0099] Hereinafter, examples will be given that more specifically disclose the electrolyte substrate for a solid oxide fuel cell according to the present invention, but the present invention is not limited to these examples.

[0100] [Preparation of green sheets for electrolyte layer] A slurry was prepared by mixing powder of scandia-stabilized zirconia, Zr(Sc)O2 (hereinafter referred to as ScSZ), a dispersant, a polyvinyl butyral binder, a plasticizer, and a toluene / ethanol solvent, and then the viscosity was adjusted by degassing under reduced pressure. The slurry was applied to a carrier film using a doctor blade and dried to produce a green sheet for the electrolyte layer.

[0101] [Preparation of green sheets for barrier layers] Ce(Sm)O2 (hereafter referred to as SDC) powder and resin beads (burn-off material) for pore formation were mixed in a specified ratio, and a dispersant, polyvinyl butyral binder, plasticizer, and toluene / ethanol solvent were added and mixed to create a slurry, which was then degassed under reduced pressure to adjust the viscosity. The slurry was coated onto a carrier film using a doctor blade and dried to create a green sheet for the barrier layer.

[0102] [Preparation of electrolyte substrate] The green sheets were stacked in the order of SDC / ScSZ / SDC, then isostatically pressed at 100 MPa and cut to the specified size to obtain a green sheet pressed body (unsintered substrate).Then, the organic components were burned off using a batch-type sintering furnace, and the substrate was sintered at a top temperature of 1350°C to obtain an electrolyte substrate of 50 mm x 40 mm.

[0103] [Cross-section observation of electrolyte substrate] The resulting 50mm x 40mm electrolyte substrate was cut into 5mm square pieces using a grinder, then solidified with a thermosetting resin to prepare a polishing specimen. The polishing specimen was finally polished with a 3μm diamond slurry to expose a smooth substrate cross section. Five fields of view were randomly selected using a scanning electron microscope (SEM) at 2000x magnification to reveal the interface between the entire thickness of the barrier layer (SDC layer) and the electrolyte layer (ScSZ layer). The presence or absence of cracks was confirmed, and backscattered electron images were taken.

[0104] In each of the electrolyte layer (ScSZ layer) and the barrier layer (SDC layer), if even one crack was found within the observation field, it was judged as "cracked."

[0105] The thicknesses of the electrolyte layer (ScSZ layer) and the barrier layer (SDC layer) were also measured using the scale of the images. The results are shown in Tables 1 and 2. The thickness of the barrier layer shown in Table 2 is the thickness of one barrier layer provided on one main surface of the electrolyte layer.

[0106] [Measurement of pore area ratio] The backscattered electron image was imported into image analysis software (WinROOF2018) and analyzed using the following procedure. (1) Convert a color image into a gray image. (2) A grayscale detection threshold is determined for the gray image so that holes can be distinguished from other areas, and areas below (above) the set threshold are detected. (3) Calculate the pore area ratio from the total pore area and the total area of the barrier layer according to the following formula: Pore area ratio (%) = 100 x total pore area / total barrier layer area

[0107] [Measurement of three-point bending strength] A three-point bending test of the electrolyte substrate was carried out using an autograph (AGS-5KNX) under the following test conditions: Distance between fulcrums: 20mm Test speed: 5mm / min

[0108] The maximum load until the electrolyte substrate was broken was measured, and the three-point bending strength was calculated according to the following formula. σ=3PL / (2bh 2 ) where σ is the three-point bending strength, P is the maximum load, L is the distance between supports, b is the sample width, and h is the sample thickness. Ten measurements were taken, and the average value of the three-point bending strengths was calculated.

[0109] The evaluation results for each sample are shown in Tables 1 and 2. The three-point bending strength values shown in Table 2 are relative values when the three-point bending strength of Sample No. 2 is set to 1.00.

[0110] [Table 1]

[0111] [Table 2]

[0112] In Tables 1 and 2, samples marked with * are comparative examples outside the scope of the present invention.

[0113] From Table 1, it was confirmed that, when the pore area ratio in the barrier layer is the same, the thicker the barrier layer, the more likely cracks are to occur. This is thought to be because the thicker the barrier layer, the greater the effect of the difference in thermal expansion or contraction between the electrolyte layer and the barrier layer that occurs during firing.

[0114] As can be seen from Table 2, when the pore area ratio in the barrier layer was 24% or more, no cracks were observed in either the electrolyte layer or the barrier layer. On the other hand, when the pore area ratio in the barrier layer was less than 24%, it is believed that the difference in thermal expansion or contraction between the electrolyte layer and the barrier layer that occurs during firing was not sufficiently alleviated.

[0115] Table 2 confirms that, for a given barrier layer thickness, the three-point bending strength improves as the void area ratio in the barrier layer increases. This is thought to be due to the effect of reducing residual stress (i.e., tensile stress on the surface of the barrier layer) caused by easing the thermal expansion difference during firing, and the effect of the voids stopping the propagation of cracks even if they occur.

[0116] Table 2 shows that when the void area ratio in the barrier layer is 77%, friction between the substrates that occurs during normal handling causes the barrier layer to detach from the electrolyte layer and break down into powder. This is thought to be due to a decrease in the bonding area between the barrier layer and electrolyte layer, as well as a decrease in the strength of the barrier layer itself. If this phenomenon occurs before the formation of the air electrode, the effect of suppressing the reaction between the air electrode and the electrolyte layer will be reduced. Furthermore, if this phenomenon occurs after the formation of the air electrode, the reaction field will be reduced, resulting in a decrease in battery performance.

[0117] From the above results, it is considered that the appropriate pore area ratio in the barrier layer is in the range of 24% or more and 72% or less. [Explanation of symbols]

[0118] 1, 1A Unsintered substrate 2 Unsintered electrolyte layer 2s Green sheet for electrolyte layer 3 Unsintered barrier layer 3s Barrier layer green sheet 4. Burned wood 5. Scandia-stabilized zirconia or yttria-stabilized zirconia powder 6 Ce(X)O2 powder 10, 10A Electrolyte substrate for solid oxide fuel cells 20 Electrolyte layer 30 Barrier Layer 40 vacancies 50 Air electrode 60 Fuel electrode 100, 100A Single Cell for Solid Oxide Fuel Cells 110 cells 200 Solid Oxide Fuel Cell Stack 210 First Interconnector 220 Second Interconnector 230 Oxidant gas manifold 240 Fuel Gas Manifold 250 Oxidant gas flow path 260 Fuel gas flow path

Claims

1. an electrolyte layer including a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia; provided on both main surfaces of the electrolyte layer, and ２ (wherein X is any one of Sm, Gd, and Y), and a barrier layer including a sintered body of An electrolyte substrate for a solid oxide fuel cell, wherein, when viewed in a cross section along the thickness direction of the barrier layer, pores exist within the barrier layer in an area ratio of 24% or more and 72% or less.

2. The electrolyte substrate according to claim 1 , wherein the ratio of the thickness of the barrier layer to the thickness of the electrolyte layer is 20% or less.

3. 3. The electrolyte substrate according to claim 1, wherein the barrier layer has a thickness of 20 [mu]m or less.

4. 3. The electrolyte substrate according to claim 1, wherein the thickness of the barrier layer and the area ratio of the pores present inside the barrier layer are the same on both main surfaces of the electrolyte layer.

5. 3. The electrolyte substrate according to claim 1, wherein the area ratio of pores present inside the barrier layer is 24% or more and 33% or less, or 67% or more and 72% or less.

6. an air electrode; a fuel electrode; the electrolyte substrate according to claim 1 or 2, which is provided between the air electrode and the fuel electrode; A single cell for a solid oxide fuel cell, wherein a barrier layer of the electrolyte substrate is disposed between the electrolyte layer of the electrolyte substrate and the air electrode.

7. A solid oxide fuel cell stack comprising a plurality of stacked cells, each cell comprising the unit cell according to claim 6, a first interconnector disposed on the air electrode side of the unit cell, and a second interconnector disposed on the fuel electrode side of the unit cell.

8. Ce(X)O is applied to both main surfaces of an unsintered electrolyte layer containing a powder of scandia-stabilized zirconia or yttria-stabilized zirconia, or to both main surfaces of an electrolyte layer containing a sintered body of scandia-stabilized zirconia or yttria-stabilized zirconia. ２ (wherein X is any one of Sm, Gd, and Y) powder and a green barrier layer comprising a burnt-out material; and firing the green substrate at a temperature equal to or higher than the temperature at which the burn-off material is burned off.

9. The step of preparing the green substrate includes: preparing an unsintered electrolyte layer green sheet containing scandia-stabilized zirconia or yttria-stabilized zirconia powder; Ce(X)O ２ (wherein X is any one of Sm, Gd, and Y) powder and a burnt-out material; The method for manufacturing an electrolyte substrate according to claim 8 , further comprising: a step of laminating the electrolyte layer green sheet and the barrier layer green sheet.

10. The method for manufacturing an electrolyte substrate according to claim 8 or 9, wherein the burn-off material is resin beads.

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