Fuel cell and method for manufacturing the same

Abstract

The purpose of the present invention is to reduce the cost of a fuel battery by increasing the yield of a fuel battery cell when the surface area thereof is increased, the yield being increased by suppressing a decrease in output power caused by foreign substances present in a base when a thin film solid electrolyte layer is formed. In the fuel battery cell according to the present invention, a membrane electrode assembly including a lower electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and an upper electrode layer is formed on a support substrate, the interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than the interface between the lower electrode layer and the solid electrolyte layer, and the film thickness of the second solid electrolyte layer is such that the leakage current between the first solid electrolyte layer and the second solid electrolyte layer is less than an allowable value even when the output voltage of the fuel battery cell is generated (see FIG. 5).

Description

Technical Field

[0001] The present invention relates to a solid oxide fuel cell in which a solid electrolyte layer is formed by a film-forming process.

Background Art

[0002] As background art in this technical field, there are JP 2016-115506 A (Patent Document 1) and Journal of Power Sources 194 (2009) 119-129 (Non-Patent Document 1).

[0003] Non-Patent Document 1 describes a cell technology for forming an anode layer, a solid electrolyte layer, and a cathode layer of a fuel cell membrane by a thin film forming process. By thinning the solid electrolyte, the ionic conductivity can be improved and the power generation efficiency can be improved. The ionic conductivity of the solid electrolyte exhibits an activated type temperature dependence. Therefore, the ionic conductivity is large at high temperatures and small at low temperatures. By thinning the solid electrolyte, a sufficiently large ionic conductivity can be obtained even at low temperatures, and practical power generation efficiency can be realized. As the solid electrolyte layer, for example, YSZ (Yttria Stabilized Zirconia), which is zirconia doped with yttria or the like, is often used. This is because it has excellent chemical stability and has the advantage of having little current due to electrons and holes that cause internal leakage current in the fuel cell. By using a porous electrode as the anode layer and the cathode layer, the three-phase interface where gas, electrode, and solid electrolyte are in contact with each other can be increased, and the power loss due to polarization resistance generated at the electrode interface can be suppressed.

[0004] By thinning the solid electrolyte layer, the output power per unit area can be improved. However, due to the thinning, leakage current in the solid electrolyte layer between the anode layer and the cathode becomes a problem. When a uniform solid electrolyte layer can be formed, for example, when YSZ is used for the solid electrolyte layer, it can be thinned to 100 nanometers or less. In reality, due to foreign substances present on the substrate before forming the solid electrolyte layer, extremely thin portions are formed in the solid electrolyte layer, often resulting in an increase in leakage current between the anode layer and the cathode.

[0005] In the case of a fuel cell stack manufactured using a green sheet as disclosed in Patent Document 1, a solid electrolyte layer with a thickness of several tens of micrometers is used, while in a fuel cell stack in which the solid electrolyte layer is formed by thin film deposition, the solid electrolyte layer is thinned to about 1 micrometer or less. Therefore, it is essential to suppress the influence of foreign substances. Quality Although it is not a measure against foreign substances present on the substrate before forming the solid electrolyte layer, Non-Patent Document 2 discloses a technique for filling voids formed in the solid electrolyte layer. Voids formed in the solid electrolyte layer (YSZ layer) formed on the anode layer are filled by depositing alumina by atomic layer deposition (ALD method), and then a part of the alumina is removed by etch-back, followed by additional deposition of the solid electrolyte layer (YSZ layer).

[0006]

Prior Art Documents

Patent Documents

Patent Document 1

[0007]

Patent Document 1

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Non - Patent Literature 2 In the method described in [Non - Patent Literature], although the voids formed in the solid electrolyte can be filled, the influence of foreign substances present on the substrate before forming the solid electrolyte layer cannot be suppressed. In a fuel cell, since the electrodes need to diffuse gas, they need to be formed porous. Therefore, when forming the solid electrolyte layer, it is formed on the porous electrode. Since the porous electrode has a structure in which granular electrode materials are aggregated, the frequency of generation of foreign substances during formation is extremely high compared to a flat and dense electrode. When foreign substances of a size that cannot be ignored compared to the film thickness of the solid electrolyte layer are present on the underlying porous electrode, the film thickness of the solid electrolyte layer is extremely thin in the foreign substance part, and in extreme cases, holes are formed in the solid electrolyte layer. As a result, during the operation of the fuel cell, leakage of electron current and hole current occurs between the anode layer and the cathode through the thin solid electrolyte layer in the foreign substance part, reducing the output power of the fuel cell. Also, when holes are formed in the solid electrolyte layer, the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side diffuse into each other through the holes in the solid electrolyte layer, also reducing the output power of the fuel cell.

[0010] The present invention has been made in view of the above - mentioned problems, and aims to suppress the decrease in output power due to foreign substances present on the substrate during the formation of the thin - film solid electrolyte layer, increase the yield when the area of the fuel cell is increased, and reduce the cost of the fuel cell.

Means for Solving the Problems

[0011] The fuel cell according to the present invention has a membrane electrode assembly formed of a lower electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and an upper electrode layer on a support substrate. The interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than the interface between the lower electrode layer and the solid electrolyte layer. The second solid electrolyte layer has a film thickness such that the leakage current between the first solid electrolyte layer and the second solid electrolyte layer is less than the allowable value even when the output voltage of the fuel cell is generated.

Advantages of the Invention

[0012] According to the fuel cell of the present invention, it is possible to provide a solid oxide fuel cell having a large output power per unit area, capable of increasing the area, and capable of operating at a low temperature. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, members having the same function are denoted by the same or related reference numerals, and repeated explanations thereof are omitted. In addition, when there are a plurality of similar members (parts), symbols may be added to the general reference numerals to indicate individual or specific parts. Further, in the following embodiments, the description of the same or similar parts is not repeated in principle unless particularly necessary.

[0015] In the following embodiments, the X direction, the Y direction, and the Z direction are used as directions for explanation. The X direction and the Y direction are orthogonal to each other and constitute the horizontal plane, and the Z direction is the vertical direction with respect to the horizontal plane.

[0016] In the drawings used in the embodiments, hatching may be omitted even for cross-sectional views in order to make the drawings easier to view. Also, hatching may be added even for plan views in order to make the drawings easier to view.

[0017] In cross-sectional views and plan views, the size of each part does not correspond to the actual device, and in order to make the drawings easier to understand, specific parts may be relatively enlarged. Also, even when the cross-sectional view and the plan view correspond to each other, specific parts may be relatively enlarged in order to make the drawings easier to understand.

[0018] <Output Power Improvement per Projection Area on the Substrate and Low Temperature of the Operating Temperature by a Thin Film Process Type Fuel Cell> FIG. 1 is a diagram showing a general structure of a fuel cell having a thinned solid electrolyte layer. In order to increase the power generation efficiency and realize low-temperature operation, it is necessary to thin the solid electrolyte layer constituting the membrane electrode assembly for the fuel cell. For this purpose, a thin-film process type fuel cell that forms the solid electrolyte layer in a film-forming process is optimal. When all of the anode electrode layer, the solid electrolyte layer, and the cathode electrode layer are thinned, the mechanical strength of the membrane electrode assembly for the fuel cell becomes weak, but it can be compensated by substrate support as shown in FIG. 1. As the substrate, for example, an anodized alumina substrate (AAO substrate) 4 as shown in FIG. 1 can be used. In FIG. 1, a first solid electrolyte layer 101 is formed on a lower electrode layer 20 formed on a first AAO substrate 4, and an upper electrode layer 10 is formed thereon. The first AAO substrate 4 can supply a fuel gas or an oxidant gas to the lower electrode layer 20 from the back surface through the first pores 51. The upper electrode layer 10 and the lower electrode layer 20 can be formed in a porous manner.

[0019] <Embodiment 1: Configuration of Fuel Cell> FIG. 2 is a schematic diagram showing a configuration example of a fuel cell module using a thin-film process type SOFC (Solid Oxide Fuel Cell) according to Embodiment 1 of the present invention. The gas flow paths in the module are separated into a flow path for the fuel gas and a flow path for a gas containing oxygen gas (for example, air, the same applies hereinafter). The flow path for the fuel gas includes a fuel inlet, a fuel chamber, and a fuel outlet. The flow path for the air includes an air inlet, an air chamber, and an air outlet. The fuel gas and the air are shielded by the shielding plate in FIG. 2 so as not to mix in the module. Wiring is drawn from the anode electrode and the cathode electrode of the fuel cell through a connector and connected to an external load.

[0020] FIG. 3 is a view of the shielding plate seen from the fuel cell side. The fuel cell is mounted on the shielding plate. One fuel cell may be used, but generally a plurality of fuel cells are arranged side by side.

[0021] FIG. 4 is a view of the fuel cell seen from the back side of the shielding plate. Holes are formed in the shielding plate for each fuel cell so that the fuel gas is supplied from the fuel chamber to the fuel cell.

[0022] FIG. 5 is a schematic diagram showing a configuration example of the fuel cell 1 according to Embodiment 1. The fuel cell 1 corresponds to the fuel cells shown in FIGS. 2 to 4. A lower electrode layer 20 is formed on the first AAO substrate 4. The first AAO substrate 4 has first pores 51 formed therein, and fuel gas or oxidant gas can be supplied to the lower electrode layer 20 from the back surface through the first pores 51. The lower electrode layer 20 can be formed of, for example, platinum, a cermet material composed of platinum and a metal oxide, nickel, a cermet material composed of nickel and a metal oxide, or the like. Power can be supplied to the lower electrode layer 20 from the back surface of the first AAO substrate 4 through a lower electrode wiring layer 21 formed on the side wall of the first pore 51. The lower electrode wiring layer 21 can be formed of, for example, platinum, nickel, or the like. The lower electrode layer 20 and the lower electrode wiring layer 21 can be formed of a porous material.

[0023] On the upper layer of the lower electrode layer 20, a yttria-doped zirconia thin film serving as the first solid electrolyte layer 101 is formed. The doping amount of yttria can be, for example, 3% or 8%. The first solid electrolyte layer 101 is formed so as to completely cover the lower electrode layer 20 on the first AAO substrate. The film thickness of the first solid electrolyte layer 101 can be equal to or greater than the unevenness (D) of a predetermined region on the surface of the underlying lower electrode layer 20 and equal to or less than twice (2×D) thereof. For example, when D is 100 nm, it can be 100 nm or more and 200 nm or less. The upper surface of the first solid electrolyte layer 101 can be planarized as compared with the surface of the lower electrode layer 20. This can be realized by using a chemical mechanical polishing method (CMP method) after forming the first solid electrolyte layer 101. The unevenness (D) referred to here can be defined, for example, as the sum of the maximum peak height and the maximum valley depth within a predetermined region on the surface.

[0024] On the upper layer of the first solid electrolyte layer 101, a yttria-doped zirconia thin film serving as the second solid electrolyte layer 102 is formed. The doping amount of yttria can be, for example, 3% or 8%. As the material of the second solid electrolyte layer 102, the first solid electrolyte layer 101The same material can be used. The second solid electrolyte layer 102 is formed so as to completely cover the first solid electrolyte layer 101. The film thickness of the second solid electrolyte layer 102 is set to a film thickness such that the current due to electron leakage and hole leakage between the anode layer and the cathode layer can be sufficiently suppressed only by the second solid electrolyte layer 102. Since YSZ has extremely little electron current and hole current that become internal leakage current of the fuel cell 1 even at high temperatures, it is also possible to thin the second solid electrolyte layer 102 to 100 nm or less. By sufficiently reducing the unevenness (D) of the lower electrode layer 20, the total film thickness of the first solid electrolyte layer 101 and the second solid electrolyte layer 102 can be made 1000 nm or less .

[0025] A first interface layer 61 is formed on the upper layer of the second solid electrolyte layer 102. The first interface layer 61 can be formed of, for example, ceria (CeO2) doped with 10% gadolinia (Gd2O3). The first interface layer 61 is formed so as to cover the upper surface of the second solid electrolyte layer 102. The first interface layer 61 is used when it is not preferable to directly contact the second solid electrolyte layer 102 and the upper electrode layer 10 because they are likely to chemically react due to the manufacturing process of the fuel cell 1 or the thermal load during operation. By forming the first interface layer 61 between the upper electrode layer 10 and the second solid electrolyte layer 102, an effect of reducing the polarization resistance in the upper electrode layer 10 during operation may be obtained. Depending on the usage conditions such as the operating temperature of the fuel cell 1, it is also possible not to form the first interface layer 61. Also, as will be described later, it is also possible to separately form an interface layer at the interface between the lower electrode layer 20 and the first solid electrolyte layer 101.

[0026] The upper electrode layer 10 is formed on the upper layer of the first interface layer 61. The upper electrode layer 10 can be formed of, for example, porous platinum or a cermet material composed of platinum and a metal oxide. The upper electrode layer 10 is formed so as to cover a part of the first AAO substrate 4.

[0027] As described above, the thin film process type fuel cell cell 1 includes, from the lower layer, a membrane electrode assembly composed of a first AAO substrate 4, a lower electrode wiring layer 21, a lower electrode layer 20, a first solid electrolyte layer 101, a second solid electrolyte layer 102, a first interface layer 61, and an upper electrode layer 10.

[0028] For example, a fuel gas containing hydrogen is supplied to the lower electrode layer 20 side, and an oxidizing Agent gas such as air is supplied to the upper electrode layer 10 side. The supplied fuel gas reaches the lower electrode layer 20 through the first pores 51 of the first AAO substrate 4. The supplied oxidizing Agent gas is supplied to the surface of the upper electrode layer 10. By ion conduction through the first solid electrolyte layer 101, the second solid electrolyte layer 102, and the first interface layer 61, the oxidizing Agent gas and the fuel gas react, enabling it to operate in the same manner as a normal fuel cell. The lower electrode layer 20 side and the upper electrode layer 10 side are sealed so that the supplied oxidizing Agent gas and the fuel gas do not mix with each other in the gas state.

[0029] Conversely, for the supply of the fuel gas and the oxidant gas, an oxidizing Agent gas such as air can be supplied to the lower electrode layer 20 side, and a fuel gas containing hydrogen, for example, can be supplied to the upper electrode layer 10 side. Also in this case, the lower electrode layer 20 side and the upper electrode layer 10 side are sealed so that the supplied oxidizing Agent gas and the fuel gas do not mix with each other in the gas state.

[0030] <Embodiment 1: Manufacturing Method> Figs. 6 to 12 are diagrams for explaining an example of a method for forming the fuel cell cell 1 shown in Fig. 5. First, a first AAO substrate 4 is formed on a silicon substrate 2 (Fig. 6). The first AAO substrate 4 has a plurality of first pores 51 penetrating between the front and back surfaces. The diameter of the first pores 51 can be, for example, 50 to 100 nm.

[0031] Next, a lower electrode layer 20 is formed on the first AAO substrate 4 (FIG. 7). For example, the lower electrode layer 20 can be formed by sputtering using a cermet composed of nickel and YSZ, and the film thickness can be set to 100 to 200 nm. Since the upper surface of the first AAO substrate 4 has an uneven shape and the lower electrode layer 20 is formed in a porous state, the upper surface of the lower electrode layer 20 has an uneven shape. In addition, when forming the porous lower electrode layer 20, foreign matter is likely to be generated and adhere to the surface of the lower electrode layer 20. The foreign matter generated in the film formation process of the lower electrode layer 20 has conductivity, and as will be described later, in a fuel cell of the prior art, it causes electron leakage and hole leakage between the anode layer and the cathode layer, reducing the output voltage of the fuel cell, so countermeasures are essential. As shown in FIG. 7, the lower electrode layer 20 is formed not only on the upper surface of the first AAO substrate 4 but also on the side surface of the first AAO substrate 4 and the upper surface of the silicon substrate 2. The silicon substrate 2 can be replaced with a substrate made of other materials as long as it has sufficient strength, surface flatness, and ease of processing.

[0032] Next, a first solid electrolyte layer 101 is formed on the upper surface of the lower electrode layer 20 (FIG. 8). The material of the first solid electrolyte layer 101 can have, for example, a yttria doping amount of 3% or 8%. Since the solid electrolyte layer serves to prevent the mixing of gases on the anode side and the cathode side, it is formed densely. For example, a dense first solid electrolyte layer 101 can be formed by sputtering using an oxide target or reactive sputtering using a metal target. Since the upper surface of the lower electrode layer 20 has an uneven shape, the upper surface of the first solid electrolyte layer 101 has an uneven shape. Further, when foreign matter is formed on the lower electrode layer 20 described above, the first solid electrolyte layer 101 does not reach the desired film thickness at the foreign matter portion. The shape of the foreign matter portion will be described later (FIG. 13). As shown in FIG. 8, the first solid electrolyte layer 101 is formed not only on the upper surface of the first AAO substrate 4 but also on the side surface of the first AAO substrate 4 and the upper surface of the silicon substrate 2.

[0033] Next, a part of the surface of the first solid electrolyte layer 101 is removed by chemical mechanical polishing (CMP method) (FIG. 9). At this time, the first solid electrolyte layer 101So that it is completely removed and the lower electrode layer 20 is exposed, or so that the remaining film thickness of the first solid electrolyte layer 101 is not too thick and the output voltage of the fuel cell 1 does not extremely decrease, the remaining film thickness of the first solid electrolyte layer 101 is set to be not less than the unevenness (D) of a predetermined region on the surface of the underlying lower electrode layer 20 and not more than twice (2×D) thereof. For example, when D is 100 nm, it is set to be not less than 100 nm and not more than 200 nm. When the CMP method is used, a part of the first solid electrolyte layer 101 on the upper surface of the first AAO substrate 4 is removed, but the first solid electrolyte layer 101 formed on the silicon substrate 2 with a low elevation remains with the film thickness formed without being removed. When there is the above-described foreign matter on the lower electrode layer 20 on the first AAO substrate 4, the foreign matter is polished simultaneously with the first solid electrolyte layer 101 in the polishing process by the CMP method, so that the surface is flattened even at the foreign matter part. The shape of the foreign matter part will be described later (FIG. 13). As shown in FIG. 9, a part of the first solid electrolyte layer 101 is removed on the upper surface of the first AAO substrate 4, but it is not removed on the side surface of the first AAO substrate 4 and the upper surface of the silicon substrate 2.

[0034] Next, a second solid electrolyte layer 102 is formed on the upper surface of the first solid electrolyte layer 101 (FIG. 10). The material of the second solid electrolyte layer 102 can have a yttria doping amount of, for example, 3% or 8%. As the second solid electrolyte layer 102, the same composition as that of the first solid electrolyte layer 101 can also be used. Since the solid electrolyte layer serves to prevent the mixing of gases on the anode side and the cathode side, it is formed densely. For example, a dense second solid electrolyte layer 102 can be formed by a sputtering method using an oxide target or a reactive sputtering method using a metal target. In the upper surface region of the first AAO substrate 4, since the surface of the first solid electrolyte layer 101 is planarized, the second solid electrolyte layer 102 can be formed with a uniform film thickness. Strictly speaking, although some irregularities remain on the surface of the first solid electrolyte layer 101 even after polishing by the CMP method, the irregularities due to the irregular shape of the lower electrode layer 20 have disappeared. Therefore, the in-plane distribution of the second solid electrolyte layer 102 is not affected by the local irregularities of the lower electrode layer 20. Similarly, the second solid electrolyte layer 102 can be formed with a uniform film thickness even in the foreign matter portion described above. The film thickness of the second solid electrolyte layer 102 can be, for example, 100 nm. The shape of the foreign matter portion will be described later (FIG. 13). The second solid electrolyte layer 102 is formed not only on the upper surface of the first AAO substrate 4 but also on the side surface of the first AAO substrate 4 and the upper surface of the silicon substrate 2 as shown in FIG. 10.

[0035] The film thickness of the second solid electrolyte layer 102 is uniform, but it is not necessarily strictly the same for all parts. At least, the difference between the maximum film thickness and the minimum film thickness of the second solid electrolyte layer 102 is smaller than the irregularity (D) of the lower electrode layer 20. Thus, it can be said that the second solid electrolyte layer 102 is formed flatter than the lower electrode layer 20. The same applies when the second solid electrolyte layer 102 is formed flat in the following embodiments.

[0036] Next, a first interface layer 61 is formed on the upper surface of the second solid electrolyte layer 102 (FIG. 11). The first interface layer 61 can be formed of, for example, ceria (CeO2) doped with 10% gadolinia (Gd2O3). The first interface layer 61 is formed so as to cover the upper surface of the second solid electrolyte layer 102. In the upper surface region of the first AAO substrate 4, since the surface of the second solid electrolyte layer 102 is flat, the first interface layer 61 can be formed with a uniform film thickness. The first interface layer 61 is formed not only on the upper surface of the first AAO substrate 4 but also on the side surface of the first AAO substrate 4 and the upper surface of the silicon substrate 2. Next, an upper electrode layer 10 is formed on the upper surface of the first interface layer 61 (FIG. 11). The upper electrode layer 10 is formed on a part of the upper surface of the first AAO substrate 4. The upper electrode layer 10 can be formed of, for example, porous platinum or a cermet material composed of platinum and a metal oxide.

[0037] Next, after removing a part of the silicon substrate 2 in the region where the first AAO substrate 4 is formed from the back side, a lower electrode wiring layer 21 is formed on the inner wall of the first hole 51 by ALD method to complete the fuel cell 1 (FIG. 12). The lower electrode wiring layer 21 can be formed of, for example, platinum or nickel. The lower electrode layer 20 and the lower electrode wiring layer 21 can be formed of a porous material. The back side of the first AAO substrate 4 and the lower electrode layer 20 can be electrically connected via the lower electrode wiring layer 21. The lower electrode wiring layer 21 is formed on the side wall of the first hole 51 and does not completely fill the first hole 51. Therefore, the fuel gas or the oxidant gas supplied from the back side of the first AAO substrate 4 can reach the lower electrode layer 20 through the first hole 51. As shown in FIG. 12, the formed lower electrode layer 20, the first solid electrolyte layer 101, the second solid electrolyte layer 102, the first interface layer 61, and the upper electrode layer 10 are formed on the first fuel cell end portion 301. The first solid electrolyte layer 101 in the first fuel cell end portion 301 is formed thicker than the first solid electrolyte layer 101 in the region of the upper surface of the first AAO substrate 4 because it is not removed in the CMP process of FIG. 9.

[0038] <Embodiment 1: Effect> FIG. 13 shows the difference in the shape between a fuel cell of the prior art and the fuel cell 1 according to Embodiment 1 at the site where the foreign matter 200 exists on the lower electrode layer 20 described above. As shown in the upper part of FIG. 13, in a fuel cell according to the prior art without performing the CMP process, in the vicinity of the foreign matter 200, regions where the first solid electrolyte layer 101 and the first interface layer 61 become extremely thin are formed. As described above, the foreign matter generated in the film formation process of the lower electrode layer 20 is conductive. As a result, during the operation of the fuel cell 1, leakage current due to electron current and hole current occurs between the anode layer and the cathode layer through the conductive foreign matter 200, reducing the output voltage of the fuel cell 1. On the other hand, in the fuel cell 1 according to Embodiment 1, even at the site where the foreign matter 200 exists, the upper part of the foreign matter is removed and flattened simultaneously with a part of the upper part of the first solid electrolyte layer 101 in the CMP process of FIG. 9, so that the second solid electrolyte layer 102 is formed with a uniform film thickness. If the film thickness of the second solid electrolyte layer 102 is sufficient to suppress the leakage current due to electron current and hole current, there will be no decrease in the output power.

[0039] In other words, it can be said that the second solid electrolyte layer 102 is configured as follows. When the fuel cell 1 generates electricity, the potential difference between the lower electrode layer 20 and the upper electrode layer 10 becomes the output voltage of the fuel cell 1. Even when this potential difference occurs, a film thickness is ensured at any location of the second solid electrolyte layer 102 (i.e., at the location where the film thickness of the second solid electrolyte layer 102 is the thinnest) such that the leakage current between the first solid electrolyte layer 101 and the second solid electrolyte layer 102 is less than the allowable value (the second solid electrolyte layer 102 blocks the leakage current). The specific film thickness may be appropriately determined in view of the balance between the performance of blocking the leakage current and the performance of the fuel cell 1.

[0040] FIG. 14 is a diagram for explaining the leakage current of the fuel cell 1 according to Embodiment 1. The upper part of FIG. 14 shows the leakage currents of Samples #1 to #5 of the fuel cell 1 according to Embodiment 1. Since the probability of containing foreign matter increases as the fuel cell area increases, defects due to leakage current are likely to occur. The cell areas of Samples #1 to #5 are larger than the minimum cell area acceptable from the perspective of cost. As shown in the upper part of FIG. 14, it is possible to suppress the leakage current below the allowable value. It is considered that the leakage at the site where the foreign matter 200 shown in the lower part of FIG. 13 exists can be suppressed. The lower part of FIG. 14 is a diagram showing the relationship between the cell area and the yield. In the fuel cell of the prior art, the yield decreases rapidly as the area increases. For a cell area larger than the minimum cell area acceptable from the perspective of cost, the acceptable yield cannot be maintained. This is considered to be because the defect rate due to the leakage current at the site of the foreign matter 200 shown in the upper part of FIG. 13 increases rapidly as the cell area increases. On the other hand, in the fuel cell 1 according to Embodiment 1, a high yield can be ensured even for a cell area larger than the minimum cell area acceptable from the perspective of cost.

[0041] <Embodiment 1: Modification Example> FIGS. 15 to 19 show a manufacturing method of a modification example in which the first porous metal substrate 71 is used for the substrate of the fuel cell 1. In FIGS. 6 to 12, the structure and manufacturing method of the fuel cell 1 using the first AAO substrate 4 were described, but the first porous metal substrate 71 can also be used for the substrate of the fuel cell 1. Using FIGS. 15 to 19, a manufacturing method of a modification example of Embodiment 1 in which the first porous metal substrate 71 is used for the substrate of the fuel cell 1 will be described.

[0042] First, prepare the first porous metal substrate 71 (FIG. 15). Since it is porous, its surface has an uneven shape. For the material of the first porous metal substrate 71, a ferritic stainless steel such as SUS can be used, for example. Next, form the lower electrode layer 20 on the upper surface of the first porous metal substrate 71 (FIG. 16). For example, the lower electrode layer 20 can be formed by sputtering using a cermet composed of nickel and YSZ, and the film thickness can be set to 100 to 200 nm. Due to the uneven shape of the upper surface of the first porous metal substrate 71 and the formation of the porous lower electrode layer 20, the upper surface of the lower electrode layer 20 becomes uneven. Also, when forming the porous lower electrode layer 20, foreign matter is likely to occur and adhere to the surface of the lower electrode layer 20. The foreign matter generated in the film formation process of the lower electrode layer 20 is conductive. As will be described later, in a fuel cell of the prior art, it causes electron leakage and hole leakage between the anode layer and the cathode layer, reducing the output voltage of the fuel cell. Therefore, countermeasures are essential.

[0043] Next, form the first solid electrolyte layer 101 on the upper surface of the lower electrode layer 20 (FIG. 17). For the material of the first solid electrolyte layer 101, the doping amount of yttria can be set to, for example, 3% or 8%. Since the solid electrolyte layer serves to prevent the mixing of gases on the anode side and the cathode side, it is formed densely. For example, a dense first solid electrolyte layer 101 can be formed by sputtering using an oxide target or reactive sputtering using a metal target. Due to the uneven shape of the upper surface of the lower electrode layer 20, the upper surface of the first solid electrolyte layer 101 becomes uneven. If foreign matter is formed on the lower electrode layer 20, the first solid electrolyte layer 101 will not have the desired film thickness at the foreign matter part.

[0044] Next, remove a part of the surface of the first solid electrolyte layer 101 by an appropriate method such as chemical mechanical polishing (CMP method) (FIG. 18). At this time, the first solid electrolyte layer 101 may be completely removed and the lower electrode layer 20 may be exposed, or the first solid electrolyte layer 101So that the remaining film thickness is not too thick and the output voltage of the fuel cell 1 does not extremely decrease, the remaining film thickness of the first solid electrolyte layer 101 is set to be not less than the unevenness (D) of a predetermined region on the surface of the underlying lower electrode layer 20 and not more than twice (2×D) thereof. For example, when D is 100 nm, it is set to be not less than 100 nm and not more than 200 nm. When there is the above-described foreign matter on the lower electrode layer 20 on the upper surface of the first porous metal substrate 71, since the foreign matter is polished simultaneously with the first solid electrolyte layer 101 in the polishing process by the CMP method, the surface is flattened even at the foreign matter portion.

[0045] Next, a second solid electrolyte layer 102 is formed on the upper surface of the first solid electrolyte layer 101 (FIG. 19). The amount of yttria doping of the material of the second solid electrolyte layer 102 can be, for example, 3% or 8%. As the second solid electrolyte layer 102, the same composition as that of the first solid electrolyte layer 101 can also be used. Since the solid electrolyte layer serves to prevent the mixing of the gases on the anode side and the cathode side, it is formed densely. For example, a dense second solid electrolyte layer 102 can be formed by a sputtering method using an oxide target or a reactive sputtering method using a metal target. The film thickness of the second solid electrolyte layer 102 can be, for example, 100 nm. In the upper surface region of the first porous metal substrate 71, since the surface of the first solid electrolyte layer 101 is flattened, the second solid electrolyte layer 102 can be formed with a uniform film thickness. Strictly speaking, although some unevenness remains on the surface of the first solid electrolyte layer 101 even after polishing by the CMP method, the unevenness due to the uneven shape of the lower electrode layer 20 has disappeared. For this reason, the in-plane distribution of the second solid electrolyte layer 102 is not affected by the local unevenness of the lower electrode layer 20. Similarly, the second solid electrolyte layer 102 can be formed with a uniform film thickness even at the above-described foreign matter portion.

[0046] Next, a first interface layer 61 is formed on the upper surface of the second solid electrolyte layer 102. The first interface layer 61 can be formed of, for example, ceria (CeO2) doped with 10% gadolinia (Gd2O3). The first interface layer 61 is formed so as to cover the upper surface of the second solid electrolyte layer 102.

[0047] Next, an upper electrode layer 10 is formed on the upper surface of the first interface layer 61 to complete the fuel cell 1 (FIG. 19). The upper electrode layer 10 is formed on a part of the upper surface of the first porous metal substrate 71. The upper electrode layer 10 can be formed of, for example, porous platinum or a cermet material composed of platinum and a metal oxide.

[0048] In the structure of FIG. 12, since the first AAO substrate 4 is an insulator, it was necessary to form the lower electrode wiring layer 21. However, in the structure of FIG. 19 of the modified example, since the first porous metal substrate 71 is formed of a conductive metal, power supply to the lower electrode layer 20 is easy. Further, since the first porous metal substrate 71 is porous, fuel gas or oxidant gas can be supplied to the lower electrode layer 20 from the back surface of the first porous metal substrate 71.

[0049] Also in this modified example, leakage current generated at the foreign matter portion on the upper surface of the lower electrode layer 20 was suppressed, and a high yield rate was ensured even for a cell area larger than the minimum cell area allowable from the viewpoint of cost.

[0050] <Embodiment 2> In Embodiment 1, the second solid electrolyte layer 102 was formed after planarizing the upper surface of the first solid electrolyte layer 101 by the CMP method. However, the first solid electrolyte layer 101 on the lower electrode layer 20 and the second solid electrolyte layer 102 on the upper electrode layer 10 can also be separately fabricated and then joined.

[0051] Using FIGS. 20 to 26, an example of the manufacturing method of the fuel cell 1 in Embodiment 2 is shown. FIG. 20 is a view in which a part of the back surface of the silicon substrate 2 is removed and the lower electrode wiring layer 21 is formed in the process of FIG. 9 of Embodiment 1. This is different from FIG. 9 in that a first interface layer 61 is formed at the boundary between the lower electrode layer 20 and the first solid electrolyte layer 101. Depending on the usage conditions such as the operating temperature of the fuel cell 1, it is also possible not to form the first interface layer 61. In Embodiment 1, the remaining film thickness of the first solid electrolyte layer 101 was set to be not less than the unevenness (D) of a predetermined region on the surface of the underlying lower electrode layer 20 and not more than twice (2×D) thereof. The remaining film thickness of the first solid electrolyte layer 101 in FIG. 20 needs to be not less than the unevenness (D) of a predetermined region on the surface of the lower electrode layer 20 and to be a film thickness capable of stopping the leakage current with only the thickness of the first solid electrolyte layer 101. It is sufficient that the film thickness in the thinnest region is 100 nm or more.

[0052] Separately from FIG. 20, a second AAO substrate 5 is formed on the silicon substrate 3 as shown in FIG. 21. The second AAO substrate 5 is formed with a plurality of second pores 52 penetrating between the front and back surfaces. The diameter of the second pores 52 can be, for example, 50 to 100 nm. Next, an upper electrode layer 10 is formed on the second AAO substrate 5 (FIG. 22). The upper electrode layer 10 is the first 2 AAO substrate 5It is formed on a part of the upper surface. The upper electrode layer 10 can be formed of, for example, porous platinum or a cermet material composed of platinum and a metal oxide. It can be formed by sputtering, and the film thickness can be 100 to 200 nm. Due to the uneven shape of the upper surface of the second AAO substrate 5 and the formation of the porous upper electrode layer 10, the upper surface of the upper electrode layer 10 becomes uneven. Also, when forming the porous upper electrode layer 10, foreign substances are likely to occur and adhere to the surface of the upper electrode layer 10 with a very high frequency. The foreign substances generated in the film formation process of the upper electrode layer 10 are conductive. As will be described later, in the fuel cell of the prior art, electron leakage and hole leakage between the anode layer and the cathode layer are caused, and the output voltage of the fuel cell is reduced, so countermeasures are essential. The upper electrode layer 10 is formed not only on the upper surface of the second AAO substrate 5 but also on the side surface of the second AAO substrate 5 and the upper surface of the silicon substrate 3 as shown in FIG. 22. The silicon substrate 3 can be replaced with a substrate made of other materials as long as it has sufficient strength, surface flatness, and processability.

[0053] Next, a second interface layer 62 and a second solid electrolyte layer 102 are formed on the upper surface of the upper electrode layer 10 (FIG. 23). The second interface layer 62 can be formed of, for example, ceria (CeO2) doped with 10% gadolinia (Gd2O3). The second interface layer 62 is formed so as to cover the upper electrode layer 10. The material of the second solid electrolyte layer 102 can have a yttria doping amount of, for example, 3% or 8%. Since the solid electrolyte layer serves to prevent the mixing of gases on the anode side and the cathode side, it is formed densely. For example, a dense second solid electrolyte layer 102 can be formed by sputtering using an oxide target or reactive sputtering using a metal target. Due to the uneven shape of the upper surface of the upper electrode layer 10, the upper surface of the second solid electrolyte layer 102 becomes uneven. Also, when foreign substances are formed on the upper electrode layer 10 as described above, the second solid electrolyte layer 102 does not reach the desired film thickness at the foreign substance part. The second interface layer 62 and the second solid electrolyte layer 102 are formed not only on the upper surface of the second AAO substrate 5 but also on the side surface of the second AAO substrate 5 and the upper surface of the silicon substrate 3 as shown in FIG. 23.

[0054] Next, a part of the surface of the second solid electrolyte layer 102 is removed by an appropriate method such as, for example, a chemical mechanical polishing method (CMP method) (FIG. 24). At this time, the remaining film thickness of the second solid electrolyte layer is set to be equal to or greater than the unevenness (D) of a predetermined region on the surface of the upper electrode layer 10 serving as a base so that the second solid electrolyte layer is not completely removed and the second interface layer 62 and the upper electrode layer 10 are not exposed. Further, it is necessary that the film thickness be such that the leakage current can be stopped only by the thickness of the second solid electrolyte layer 102. It is sufficient that the film thickness in the thinnest region is 100 nm or more. When the CMP method is used, a part of the second solid electrolyte layer 102 on the upper surface of the second AAO substrate 5 is removed, but the second solid electrolyte layer 102 formed on the silicon substrate 3 having a low elevation remains with the film thickness formed without being removed. When there are foreign substances on the upper electrode layer 10 on the second AAO substrate 5, the surface is flattened even at the foreign substance portion because the foreign substances are polished simultaneously with the second solid electrolyte layer 102 in the polishing process by the CMP method. As shown in FIG. 24, a part of the second solid electrolyte layer 102 is removed on the upper surface of the second AAO substrate 5, but is not removed on the side surface of the second AAO substrate 5 and the upper surface of the silicon substrate 3.

[0055] Next, after removing a part of the silicon substrate 3 in the region where the second AAO substrate 5 is formed from the back side, an upper electrode wiring layer 11 is formed on the inner wall of the second pore 52 by ALD method (FIG. 25). The upper electrode wiring layer 11 can be formed of, for example, nickel or platinum. The back side of the second AAO substrate 5 and the upper electrode layer 10 can be electrically connected via the upper electrode wiring layer 11. The upper electrode wiring layer 11 is formed on the side wall of the second pore 52 and does not completely fill the second pore 52. Therefore, the fuel gas or the oxidant gas supplied from the back side of the second AAO substrate 5 can reach the upper electrode layer 10 through the second pore 52. As shown in FIG. 25, the formed upper electrode layer 10, the second interface layer 62, and the second solid electrolyte layer 102 are formed in the second fuel cell cell end portion 302. The second solid electrolyte layer 102 in the second fuel cell cell end portion 302 is not removed in the CMP process of FIG. 24, and thus is formed thicker than the second solid electrolyte layer 102 in the region on the upper surface of the second AAO substrate 5.

[0056] Next, the surface of the first solid electrolyte layer 101 in FIG. 20 and the surface of the second solid electrolyte layer 102 in FIG. 25 are brought into contact with each other as shown in FIG. 26 and fired to be joined, thereby completing the fuel cell 1. Since the second solid electrolyte layer 102 is formed on the upper surface of the upper electrode layer 10 and then planarized by CMP, its film thickness is independent of the unevenness of the surface of the upper electrode layer 10. Similarly, since the first solid electrolyte layer 101 is formed on the upper surface of the lower electrode layer 20 and then planarized by CMP, its film thickness is independent of the unevenness of the surface of the lower electrode layer 20.

[0057] The thermal load due to the firing temperature will be applied to each part of the fuel cell 1. Regarding the thermal load on the lower electrode wiring layer 21 and the upper electrode wiring layer 11, it can be avoided by changing the process order and forming them after joining the first solid electrolyte layer 101 and the second solid electrolyte layer 102.

[0058] FIG. 27 shows the shape of the fuel cell 1 according to Embodiment 2 at the site where the foreign matter 200 exists on the lower electrode layer 20 and the upper electrode layer 10 described above. Even at the site where the foreign matter 200 exists, the upper part of the foreign matter is removed and planarized by the CMP process of the first solid electrolyte layer 101 and the CMP process of the second solid electrolyte layer. The film thicknesses of the first solid electrolyte layer 101 and the second solid electrolyte layer 102 are each a thickness capable of suppressing leakage current independently. Since the probability that the positions of the foreign matters in the first solid electrolyte layer 101 and the positions of the foreign matters in the second solid electrolyte layer 102 overlap at the time of joining in FIG. 25 is sufficiently low, in the fuel cell 1 according to Embodiment 2, the defective rate due to the leakage current between the anode and the cathode through the foreign matter can be sufficiently reduced. Also in the fuel cell according to Embodiment 2, the leakage current generated at the foreign matter part is suppressed, and a high yield rate can be ensured even for a cell area larger than the minimum cell area allowable from the cost perspective.

[0059] In other words, it can be said that the second embodiment is configured as follows. The film thickness of the second solid electrolyte layer 102 in the second embodiment is ensured to be such that, even when an output voltage of the fuel cell 1 is generated between the lower electrode layer 20 and the upper electrode layer 10 as in the first embodiment, leakage current between the first solid electrolyte layer 101 and the second solid electrolyte layer 102 can be blocked at any location. Further, in the second embodiment, the film thickness of the first solid electrolyte layer 101 is also ensured to be such that leakage current between the first solid electrolyte layer 101 and the second solid electrolyte layer 102 can be blocked at any location (i.e., at the location where the film thickness is the thinnest).

[0060] <Second Embodiment: Modification Example> FIG. 28 shows a modification example of the second embodiment. In FIGS. 20 to 26, the first AAO substrate 4 and the second AAO substrate 5 are used, but as in the modification example of the second embodiment shown in FIG. 28, the first porous metal substrate 71 and the second porous metal substrate 72 can also be used.

[0061] After forming the lower electrode layer 20, the first interface layer 61, and the first solid electrolyte layer 101 on the first porous metal substrate 71, a part of the upper portion of the first solid electrolyte layer 101 is removed by CMP method and flattened. After forming the upper electrode layer 10, the second interface layer 62, and the second solid electrolyte layer 102 on the second porous metal substrate 72, a part of the upper portion of the second solid electrolyte layer 102 is removed by CMP method and flattened. The two parts are brought into contact with each other at the surface of the first solid electrolyte layer 101 and the surface of the second solid electrolyte layer 102 and fired to be joined, thereby completing the fuel cell 1. The remaining film thickness of the first solid electrolyte layer 101 in the CMP process needs to be equal to or greater than the unevenness (D) of a predetermined region on the surface of the underlying lower electrode layer 20 and to be a film thickness capable of stopping leakage current only with the thickness of the first solid electrolyte layer 101. It is sufficient that the film thickness in the thinnest region is 100 nm or more. The remaining film thickness of the second solid electrolyte layer 102 in the CMP process needs to be equal to or greater than the unevenness (D) of a predetermined region on the surface of the underlying upper electrode layer 10 and to be a film thickness capable of stopping leakage current only with the thickness of the second solid electrolyte layer 102. It is sufficient that the film thickness in the thinnest region is 100 nm or more.

[0062] Since the second solid electrolyte layer 102 is formed on the upper surface of the upper electrode layer 10 and then planarized by CMP, its film thickness is independent of the unevenness of the surface of the upper electrode layer 10. Conversely, since the first solid electrolyte layer 101 is formed on the upper surface of the lower electrode layer 20 and then planarized by CMP, its film thickness is independent of the unevenness of the surface of the lower electrode layer 20.

[0063] In the structure of FIG. 26, since the first AAO substrate 4 and the second AAO substrate 5 are insulators, it was necessary to form the lower electrode wiring layer 21 and the upper electrode wiring layer 11. However, in the structure of FIG. 28 of the modified example, since the first porous metal substrate 71 and the second porous metal substrate 72 are formed of a conductive metal, it is easy to supply power to the lower electrode layer 20 and the upper electrode layer 10. Since the first porous metal substrate 71 and the second porous metal substrate 72 are porous, fuel gas or oxidant gas can be supplied to the lower electrode layer 20 and the upper electrode layer 10 via the first porous metal substrate 71 and the second porous metal substrate 72, respectively.

[0064] The film thicknesses of the first solid electrolyte layer 101 and the second solid electrolyte layer 102 are each a thickness capable of suppressing leakage current alone, and the probability that the positions of foreign substances in the first solid electrolyte layer 101 and the positions of foreign substances in the second solid electrolyte layer 102 overlap at the time of joining in FIG. 28 is sufficiently low. Therefore, in the fuel cell 1 according to the modified example of Embodiment 2, the defect rate due to leakage current between the anode and the cathode via foreign substances can be sufficiently reduced. Also in the fuel cell according to the modified example of Embodiment 2 of the present invention, the leakage current generated at the foreign substance portion was suppressed, and a high yield could be ensured even for a cell area larger than the minimum cell area allowable from the viewpoint of cost.

[0065] <Regarding the modified example of the present invention> The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

[0066] In the above embodiments, there are cases where the lower electrode layer 20 functions as an anode layer and the upper electrode layer 10 functions as a cathode layer, and cases where the upper electrode layer 10 functions as an anode layer and the lower electrode layer 20 functions as a cathode layer. In any case, the effects of the present invention can be exhibited.

Explanation of Reference Numerals

[0067] 1 Fuel cell 2 Silicon substrate 3 Silicon substrate 4 First anodic aluminum oxide substrate (AAO substrate) 5 Second anodic aluminum oxide substrate (AAO substrate) 10 Upper electrode layer 11 Upper electrode wiring layer 20 Lower electrode layer 21 Lower electrode wiring layer 51 First pore 52 Second pore 61 First interface layer 62 Second interface layer 71 First porous metal substrate 72 Second porous metal substrate 101 First solid electrolyte layer 102 Second solid electrolyte layer 200 Foreign matter 301 First fuel cell end 302 Second fuel cell end

Claims

1. A fuel cell, comprising: a first porous substrate; a first porous electrode layer formed on the first porous substrate; a first solid electrolyte layer formed on the first porous electrode layer; a second solid electrolyte layer formed in direct contact with the first solid electrolyte layer; a second porous electrode layer formed on a side of the second solid electrolyte layer not in contact with the first solid electrolyte layer; wherein an interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than an interface between the first solid electrolyte layer and the first porous electrode layer; and a portion where the film thickness of the second solid electrolyte layer is thinnest due to foreign matter adhering to the base of the first solid electrolyte layer has a thickness that blocks leakage current between the first solid electrolyte layer and the second solid electrolyte layer even when an output voltage of the fuel cell is generated between the first porous electrode layer and the second porous electrode layer. A fuel cell characterized by the above.

2. The difference between the maximum film thickness and the minimum film thickness of the second solid electrolyte layer is smaller than the sum of the maximum peak height and the maximum valley depth on the surface of the first porous electrode layer. The fuel cell according to Claim 1, characterized by the above.

3. The film thickness of the first solid electrolyte layer is equal to or greater than the sum of the maximum peak height and the maximum valley depth on the surface of the first porous electrode layer, and is equal to or less than twice the sum; and the sum of the film thickness of the first solid electrolyte layer and the film thickness of the second solid electrolyte layer is 1 micrometer or less. The fuel cell according to Claim 1, characterized by the above.

4. A first interface layer disposed at an interface between the first solid electrolyte layer and the first porous electrode layer and formed of a metal oxide different from the material of the first solid electrolyte layer; or a second interface layer disposed at an interface between the second solid electrolyte layer and the second porous electrode layer and formed of a metal oxide different from the material of the second solid electrolyte layer. The fuel cell according to Claim 1, characterized by including at least one of the above.

5. The first porous substrate has a first hole at a depth in contact with the first porous electrode layer, and a first wiring layer for supplying power to the first porous electrode layer is formed on an inner wall of the first hole. The fuel cell according to Claim 1, characterized by the above.

6. The fuel cell further includes a second porous substrate formed on the second porous electrode layer, and the second porous substrate has a second hole at a depth in contact with the second porous electrode layer. ​ ​ ​ ​ On the inner wall of the second hole, a second wiring layer for supplying power to the second porous electrode layer is formed. The interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than the interface between the second solid electrolyte layer and the second porous electrode layer. The fuel cell cell according to claim 1, characterized in that the thinnest part of the first solid electrolyte layer has a thickness that blocks the leakage current between the first solid electrolyte layer and the second solid electrolyte layer even when the output voltage of the fuel cell cell is applied between the first porous electrode layer and the second porous electrode layer.

7. The first porous substrate is an anodized alumina substrate or a porous metal substrate. The fuel cell cell according to claim 1, characterized in that.

8. A method for manufacturing a fuel cell cell, comprising: forming a first porous electrode layer on a first porous substrate; forming a first solid electrolyte layer on the first porous electrode layer; flattening the surface of the first solid electrolyte layer; forming a second solid electrolyte layer in direct contact with the flattened surface of the first solid electrolyte layer; forming a second porous electrode layer on the side of the second solid electrolyte layer not in contact with the first solid electrolyte layer; having The interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than the interface between the first solid electrolyte layer and the first porous electrode layer. The portion where the film thickness of the second solid electrolyte layer is thinnest due to foreign matter adhering to the base of the first solid electrolyte layer has a thickness that blocks the leakage current between the first solid electrolyte layer and the second solid electrolyte layer even when the output voltage of the fuel cell cell is generated between the first porous electrode layer and the second porous electrode layer. A method for manufacturing a fuel cell cell, characterized in that.

9. The difference between the maximum film thickness and the minimum film thickness of the second solid electrolyte layer is smaller than the sum of the maximum peak height and the maximum valley depth on the surface of the first porous electrode layer. The method for manufacturing a fuel cell cell according to claim 8, characterized in that.

10. The film thickness of the first solid electrolyte layer is equal to or greater than the sum of the maximum peak height and the maximum valley depth on the surface of the first porous electrode layer and equal to or less than twice the sum. The sum of the film thickness of the first solid electrolyte layer and the film thickness of the second solid electrolyte layer is 1 micrometer or less. The method for manufacturing a fuel cell cell according to claim 8, characterized in that.

11. a step of forming the first solid electrolyte layer, and between the step of forming the first porous electrode layer, a step of forming a first interface layer disposed at an interface between the first solid electrolyte layer and the first porous electrode layer and formed of a metal oxide different from the first solid electrolyte layer, or a step of forming the second solid electrolyte layer, and between the step of forming the second porous electrode layer, a step of forming a second interface layer disposed at an interface between the second solid electrolyte layer and the second porous electrode layer and formed of a metal oxide different from the second solid electrolyte layer, having at least any one of The method for manufacturing a fuel cell according to claim 8, characterized in that.

12. The first porous substrate has a first hole at a depth in contact with the first porous electrode layer, The method further includes Before the step of forming the first porous electrode layer, a step of disposing the first porous substrate on a first flat substrate, By removing a part of the surface of the first flat substrate on the side not in contact with the first porous substrate, a step of forming a void at a depth in contact with the first porous substrate, A step of forming a first wiring layer for supplying power to the first porous electrode layer on the inner wall of the first hole, having The method for manufacturing a fuel cell according to claim 8, characterized in that.

13. The step of forming the second solid electrolyte layer and the step of forming the second porous electrode layer are A step of forming the second porous electrode layer on a second porous substrate, A step of forming the second solid electrolyte layer on the second porous electrode layer, A step of flattening the surface of the second solid electrolyte layer, A step of joining the flattened surface of the second solid electrolyte layer and the flattened surface of the first solid electrolyte layer, having The method for manufacturing a fuel cell according to claim 8, characterized in that.

14. The second porous substrate has a second hole at a depth in contact with the second porous electrode layer, The method further includes Before the step of forming the second porous electrode layer, a step of disposing the second porous substrate on a second flat substrate, By removing a part of the surface of the second flat substrate on the side not in contact with the second porous substrate, a step of forming a void at a depth in contact with the second porous substrate, A step of forming a second wiring layer for supplying power to the second porous electrode layer on the inner wall of the second hole, having The interface between the first solid electrolyte layer and the second solid electrolyte layer is flatter than the interface between the second solid electrolyte layer and the second porous electrode layer. The thinnest part of the first solid electrolyte layer has a thickness that blocks the leakage current between the first solid electrolyte layer and the second solid electrolyte layer even when the output voltage of the fuel cell is applied between the first porous electrode layer and the second porous electrode layer. The method for manufacturing a fuel cell according to claim 13, characterized in that.

15. The first porous substrate is an anodized alumina substrate or a porous metal substrate. The method for manufacturing a fuel cell according to claim 8, characterized in that.

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