Solid oxide fuel cell and method for manufacturing same

Abstract

Provided is a technology capable of thinning an electrolyte film and coping with enlargement in area of the electrolyte film through highly accurate control of the thickness of the electrolyte film while avoiding mixing of defects. Thus, the power generation efficiency of the solid oxide fuel cell is improved. A solid oxide fuel cell 100 includes: a porous insulating substrate 1; an anode electrode 2 formed on the porous insulating substrate 1; a solid electrolyte film 3 formed on the anode electrode 2; and a cathode electrode 5 formed above the electrolyte film 3. The electrolyte film 3 is a stabilized zirconia film doped with a rare earth element and is an anodic oxidation barrier film.

Description

Solid oxide fuel cell and method of manufacturing the same

[0001] The present invention relates to a solid oxide fuel cell and a method for manufacturing the same, and more particularly to a solid oxide fuel cell using stabilized zirconia to which rare earth elements are added as an electrolyte membrane, and a method for manufacturing the same.

[0002] In recent years, fuel cells have attracted attention as a low-pollution, highly efficient power generation method. Fuel cells can be used as a power source for large-scale power generation systems or electric vehicles. Oxygen that enters the fuel cell from the atmosphere receives electrons at the cathode electrode and becomes oxygen ions. The oxygen ions move through the electrolyte membrane, release electrons at the anode electrode, and react with hydrogen to form water. This series of processes allows current to flow from the anode electrode to an external circuit.

[0003] In particular, solid oxide fuel cells (SOFCs) have a solid oxide electrolyte membrane that allows oxygen ions to pass through (ionic conductivity). Using a solid electrolyte membrane instead of a liquid simplifies the configuration of power generation systems and facilitates maintenance.

[0004] For example, Patent Document 1 discloses the use of yttria stabilized zirconia (YSZ), a solid oxide, as an electrolyte membrane.

[0005] Japanese Patent Application Laid-Open No. 2015-176774

[0006] The power generation efficiency of SOFCs is superior among fuel cells, but it is particularly high when operated at high temperatures, for example, around 1000°C. However, for practical use of SOFCs, operation at lower temperatures is required. However, lowering the temperature also reduces the amount of power that can be obtained. Therefore, it is necessary to reduce resistance loss and improve power generation efficiency by thinning the electrolyte membrane.

[0007] A known method for producing YSZ is thick-film printing using a sintered paste. However, while this method can produce YSZ with a large area of ​​approximately 10 cm square, the thickness of the YSZ is several micrometers, making it difficult to produce a thin film.

[0008] Other methods for producing YSZ include vacuum deposition, such as using an alloy target and reactive sputtering, using a ceramic target and sputtering, using chemical vapor deposition (CVD), or using atomic layer deposition (ALD). While these methods can form YSZ with a thickness of 10 nm to 1 μm, the area of ​​the YSZ is limited to a small area of ​​approximately a few mm square.

[0009] Furthermore, the YSZ obtained by the above-mentioned vacuum deposition method deviates from the stoichiometric composition, and therefore requires crystallization by high-temperature oxidation after deposition. Even if the coating achieved by vacuum deposition is perfect, the inclusion of electrical defects that cause poor insulation is inevitable. The effects of defects become more pronounced as the YSZ is grown in size and thinned. As a result, there are limitations to the thickness and area that can be achieved by vacuum deposition. This makes it difficult to put thin-film SOFCs into practical use.

[0010] The main purpose of this application is to provide a technology that can reduce the thickness of electrolyte membranes while controlling the thickness with high precision and avoiding the inclusion of defects, and that can accommodate larger electrolyte membrane areas, thereby improving the power generation efficiency of solid oxide fuel cells.

[0011] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0012] A solid oxide fuel cell according to one embodiment includes a porous insulating substrate, an anode electrode formed on the porous insulating substrate, a solid electrolyte membrane formed on the anode electrode, and a cathode electrode formed on the electrolyte membrane. The electrolyte membrane is a stabilized zirconia membrane doped with a rare earth element and also serves as an anodization barrier membrane.

[0013] A method for manufacturing a solid oxide fuel cell according to one embodiment includes the steps of: (a) preparing a porous insulating substrate; (b) forming an anode electrode on the porous insulating substrate; (c) forming a rare earth element-doped zirconium alloy film on the anode electrode; (d) anodizing the zirconium alloy film to form a solid electrolyte membrane; and (e) forming a cathode electrode on the electrolyte membrane. The electrolyte membrane is a rare earth element-doped stabilized zirconia membrane and also serves as an anodization barrier film.

[0014] According to one embodiment, the power generation efficiency of a solid oxide fuel cell can be improved.

[0015] FIG. 1 is a cross-sectional view showing a solid oxide fuel cell in embodiment 1. FIG. 2 is an enlarged cross-sectional view showing a part of a porous insulating substrate in embodiment 1. FIG. 3 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 1. FIG. 4 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 1. FIG. 5 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 1. FIG. 6 is a plan view showing a jig used in the method for manufacturing a solid oxide fuel cell in embodiment 1. FIG. 7 is a graph showing current and voltage during anodization treatment in embodiment 1. FIG. 8 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 2. FIG. 9 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 9. FIG. 10 is a cross-sectional view showing a method for manufacturing a solid oxide fuel cell in embodiment 1.

[0016] Hereinafter, embodiments will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. In the following embodiments, explanations of the same or similar parts will not be repeated unless particularly necessary.

[0017] Furthermore, the X, Y, and Z directions described herein intersect and are perpendicular to one another. In this application, the Z direction is described as the up-down direction, height direction, or thickness direction of a structure. Furthermore, expressions such as "plan view" or "plan view" used in this application mean that a surface formed by the X and Y directions is a "plane," and that this "plane" is viewed from the Z direction.

[0018] (Embodiment 1) <Structure of Solid Oxide Fuel Cell> A solid oxide fuel cell (SOFC) 100 in embodiment 1 will be described below with reference to Figures 1 and 2. As shown in Figure 1, the solid oxide fuel cell 100 includes a porous insulating substrate 1, an anode electrode 2, a solid electrolyte membrane 3, a conductive oxide membrane 4, and a cathode electrode 5.

[0019] Oxygen contained in the air (O ２ ) enters the solid oxide fuel cell 100, receives electrons at the cathode electrode 5, and becomes oxygen ions (O － The oxygen ions move through the conductive oxide film 4 and the electrolyte film 3, release electrons at the anode electrode 2, and become hydrogen (H ２ ) reacts with water (H ２ O) As oxygen ions pass through the solid oxide fuel cell 100, a current can be passed from the anode electrode 2 to an external circuit.

[0020] The porous insulating substrate 1 is a substrate containing, for example, anodized aluminum, formed by anodizing aluminum to form a porous coating. As shown in FIG. 2 , the porous insulating substrate 1 has a plurality of holes 1a formed therein. A conductive film 1b is formed on the surfaces of the plurality of holes 1a. The conductive film 1b contains, for example, Pt or Ni. The thickness of the porous insulating substrate 1 is, for example, 80 μm or more and 120 μm or less. The diameter of the holes 1a is, for example, 100 nm or more and 150 nm or less.

[0021] By covering the porous insulating substrate 1 with the conductive film 1b, the porous insulating substrate 1 can also be used as part of the anode electrode 2. Furthermore, the conductive film 1b is formed thin so as not to fill the inside of each pore 1a, allowing hydrogen to pass through the porous insulating substrate 1. The thickness of the conductive film 1b is, for example, 10 nm or more and 20 nm or less.

[0022] The anode electrode 2 is formed on the porous insulating substrate 1. The anode electrode 2 is made of a porous metal film and contains a transition metal. The transition metal is, for example, Ni. As will be described later, when the solid oxide fuel cell 100 generates electricity, it is exposed to high-temperature water vapor, for example, at 500°C. Therefore, the anode electrode 2 is required to have high heat resistance and oxidation resistance. The thickness of the anode electrode 2 is, for example, 50 nm or more and 500 nm or less. Note that, as shown in a modified example described later, the anode electrode 2 may also contain a precious metal such as Pt.

[0023] The electrolyte membrane 3 is formed on the anode electrode 2. The electrolyte membrane 3 is a stabilized zirconia membrane having the property of passing oxygen ions (ionic conductivity) and having rare earth elements added thereto. The rare earth elements are, for example, Y, Sc, Yb, Er, Dy, or Gd. The rare earth element is most preferably Y. In particular, the yttria-stabilized zirconia (YSZ) of the electrolyte membrane 3 has a chemical composition (Y ２ O ３ ) Ｘ (ZrO ２ ) １－Ｘ The electrolyte membrane 3 is most preferably 8YSZ, where X=8% in the above formula. The electrolyte membrane 3 is an anodized barrier film formed by anodizing the zirconium alloy film to which the rare earth element is added.

[0024] The conductive oxide film 4 is formed on the electrolyte membrane 3. The conductive oxide film 4 is, for example, a GDC film (Gd ２ O ３ CeO doped with ２ film), LSC film ((La, Sr)CoO ３ membrane), LSFC membrane ((La, Sr) (Co, Fe) O ３ membrane), or BSCF membrane ((Ba,Sr)(Co,Fe)O３ When the solid oxide fuel cell 100 operates at a low temperature of 300° C. or less, the conductive oxide film 4 is an ITO film (In ２ O ３ and SnO ２ Inorganic mixtures of these may also be used.

[0025] In the solid oxide fuel cell 100 of the first embodiment, the conductive oxide film 4 is not essential. However, the conductive oxide film 4 has the property of transmitting oxygen ions and electrons, and is provided for the purpose of promoting the ionization of oxygen. By providing the conductive oxide film 4, the efficiency of generating oxygen ions can be improved, and the power generation efficiency can be improved.

[0026] The cathode electrode 5 is formed on the electrolyte membrane 3 via the conductive oxide film 4. The cathode electrode 5 contains, for example, Ni or Pt. The thickness of the cathode electrode 5 is, for example, not less than 50 nm and not more than 150 nm.

[0027] As described above, the electrolyte membrane 3 is an anodized barrier film formed by anodizing. The anodizing process, which provides a barrier coating, produces a highly uniform oxide film thickness, automatically repairing local defects. Therefore, the final anodized barrier film has a uniform thickness and is defect-free. The thickness of the electrolyte membrane 3 thus obtained is, for example, 10 nm or more and 500 nm or less. The area of ​​the electrolyte membrane 3 is approximately 10 cm square.

[0028] Thus, according to the first embodiment, the electrolyte membrane 3 can be made thinner, and can accommodate a larger area of ​​the electrolyte membrane 3. Therefore, the power generation efficiency of the solid oxide fuel cell 100 can be improved.

[0029] The relationship between the operating temperature of the solid oxide fuel cell 100 and the power obtained is described below. Note that the power values ​​below are calculated values ​​assuming that the rare earth element added to the electrolyte membrane 3 is Y, the electrolyte membrane 3 is made of the above-mentioned 8YSZ single crystal, and the thickness of the electrolyte membrane 3 is 10 nm.

[0030] When the operating temperature is 450°C, the obtained power is 6.7 x 10 １ W / cm ２When the operating temperature is 400°C, the power obtained is about 2.0 x 10 １ W / cm ２ When the operating temperature is 350°C, the obtained power is 5.8 W / cm ２ When the operating temperature is 300°C, the obtained power is 1.3 W / cm ２ You can expect a degree of.

[0031] <Method of Manufacturing Solid Oxide Fuel Cell> Each manufacturing step included in the method of manufacturing the solid oxide fuel cell 100 will be described below with reference to FIGS. 3 to 7. FIG.

[0032] As shown in Fig. 3, first, a porous insulating substrate 1 is prepared. Next, a conductive film 1b is formed on the surfaces of the plurality of holes 1a formed in the porous insulating substrate 1 by a film formation process using, for example, an ALD method (see Fig. 2). The conductive film 1b is formed so as not to fill the interiors of the holes 1a.

[0033] Next, the anode electrode 2 is formed by sputtering on the porous insulating substrate 1. This sputtering is performed, for example, under a film formation pressure of 10 Pa or more and 15 Pa or less. The anode electrode 2 formed in this manner is made of a porous metal film.

[0034] Next, a zirconium alloy film 3a doped with a rare earth element is formed on the anode electrode 2 by sputtering. The rare earth element is, for example, Y, Sc, Yb, Er, Dy, or Gd. The rare earth element is most preferably Y. This sputtering is performed at a lower deposition pressure than the sputtering of the anode electrode 2, for example, under a deposition pressure of 0.5 Pa or more and 1.0 Pa or less. The zirconium alloy film 3a thus formed is not a porous film but a dense continuous film with a substantially uniform thickness.

[0035] For example, if the sputtering method for the zirconium alloy film 3a is performed at high pressure, as in the sputtering method for the anode electrode 2, the zirconium alloy film 3a grows as columnar crystals and becomes porous. In this case, in the subsequent anodization treatment, oxidation progresses along the grain boundaries of the columnar crystals, resulting in an uneven thickness of the electrolyte film. Therefore, it becomes difficult to obtain a high-quality electrolyte film.

[0036] The electrolyte membrane 3 is formed from the zirconium alloy film 3a by the subsequent anodization treatment, but taking into consideration the thickness consumed by the anodization, thickness variations, and oxidation margins, the thickness of the zirconium alloy film 3a is set to be thicker than the desired thickness of the electrolyte membrane 3. For example, when the desired thickness of the electrolyte membrane 3 is 10 nm to 500 nm, the thickness of the zirconium alloy film 3a is set to be approximately 10% thicker than the desired thickness of the electrolyte membrane 3.

[0037] 4, the zirconium alloy film 3a is anodized to form a solid electrolyte film 3. The electrolyte film 3 is a stabilized zirconia film to which a rare earth element, similar to the zirconium alloy film 3a, is added, and also serves as an anodization barrier film.

[0038] Fig. 6 is a plan view showing a jig 40 used in the anodization treatment. The chamber region 30, the oxidation region 31, and the alloy region 32 shown in Fig. 6 are each part of the zirconium alloy film 3a. The oxidation region 31 is the region where the zirconium alloy film 3a is anodized, and the chamber region 30 is part of the oxidation region 31 and is the region that essentially functions as a solid oxide fuel cell 100. In other words, the cross-sectional view of the chamber region 30 corresponds to Figs. 1, 3, 4, and 5.

[0039] In the anodizing treatment, an electric field is applied to the zirconium alloy film 3a while it is immersed in a chemical conversion solution, thereby forming the electrolyte membrane 3 from the zirconium alloy film 3a. This chemical conversion solution is, for example, an aqueous solution containing water, ammonium tartrate as an electrolyte, and ethylene glycol as a solvent. In this case, it is undesirable for the back surface of the porous insulating substrate 1 to come into contact with the chemical conversion solution. This is because the chemical conversion solution would permeate the back surface of the porous insulating substrate 1, causing anodic oxidation to occur also at the interface between the porous insulating substrate 1 and the anode electrode 2.

[0040] Furthermore, since the periphery of the alloy region 32 is used as an electrode for power supply, it is necessary to create an interface between the gas and the chemical conversion solution inside the alloy region 32. Therefore, a jig 40 is used to isolate the alloy region 32 from the oxidized region 31. That is, after a portion of the surface of the zirconium alloy film 3a is surrounded by the jig 40 as the oxidized region 31, only the oxidized region 31 is selectively immersed in the chemical conversion solution. In this state, an electric field is applied to the oxidized region 31 to form the electrolyte membrane 3 from the zirconium alloy film 3a in the oxidized region 31. The jig 40 is then removed.

[0041] The jig 40 is composed of an O-ring 41 and a protective film 42 that covers the periphery of the O-ring 41. The protective film 42 is provided at least between the zirconium alloy film 3a and the O-ring 41. If the jig 40 were composed only of the O-ring 41, the chemical solution would locally penetrate through the O-ring 41 during anodization at the interface between the gas and the chemical solution, causing rapid oxidation and frequent corrosion of the alloy film, commonly known as "burning." Therefore, it is effective to protect the gas / liquid interface with the protective film 42. The protective film 42 is, for example, a resist film or an insulating film such as a silicon oxide film.

[0042] However, even with such treatment, localized corrosion cannot be avoided. Furthermore, holes are formed in the alloy region 32 at the point of contact with the jig 40. If such a location exists, oxygen and hydrogen will directly combust without passing through the electrolyte membrane. To avoid this, only the chamber region 30 of the oxidation region 31, which is far from the location where the jig 40 is installed, is used as the solid oxide fuel cell 100.

[0043] 7 is a graph showing the current and voltage during anodization treatment, and is a graph showing the results when anodization treatment is performed on a zirconium alloy film 3a formed by a low-pressure sputtering method with a deposition pressure of 0.5 Pa or more and 1.0 Pa or less. Y is used as the rare earth element added to this zirconium alloy film 3a.

[0044] The anodization process is performed in two stages: constant current mode and constant voltage mode. In the constant current mode, an oxidation current Ia is passed to grow an anodic oxide barrier film. As the anodic oxide barrier film grows, resistance increases, so the oxidation voltage Va increases linearly. After the oxidation voltage Va reaches a predetermined value, the process switches to the constant voltage mode.

[0045] In the constant voltage mode, the oxidation current Ia gradually decreases. This eliminates variations in the thickness of the anodic oxide barrier film and automatically repairs local defects. Ultimately, an anodic oxide barrier film with a substantially uniform thickness and no defects is obtained. Note that, in order to perform this constant voltage mode, it is necessary to leave an unoxidized Zr alloy on the base. If there is no base and oxidizing species (mainly O －２ ) reaches the anode electrode 2, oxidation of the anode electrode 2 or generation of oxygen gas occurs. In this case, the oxidation current Ia does not decrease, and repair of the barrier film cannot be expected.

[0046] Thus, the chemical composition of the electrolyte membrane 3 obtained from the zirconium alloy film 3a formed by the low-pressure sputtering method is (Y ２ O ３ ) Ｘ (ZrO ２ ) １－Ｘ In this case, X=8%, and yttria-stabilized zirconia having a composition nearly close to 8YSZ was obtained. Also, the thickness of the electrolyte membrane 3 can be made 10 nm or more and 500 nm or less.

[0047] Note that the zirconium alloy film 3a that has not been anodized, such as the alloy region 32, is oxidized to an oxide during assembly of the solid oxide fuel cell 100 after manufacture or during operation of the solid oxide fuel cell 100 due to heat treatment. In other words, in a plan view, an oxide of the zirconium alloy film 3a formed by a method other than anodization is formed on the outer periphery of the electrolyte membrane 3. The chemical composition of this oxide of the zirconium alloy film 3a is different from that of the electrolyte membrane 3. In other words, the electrolyte membrane 3 contains a boundary that defines the anodization barrier film, i.e., a boundary between the gas phase region and the liquid phase region in the anodization process. This liquid phase region is an anodization barrier film and also contains an electrochemical reaction region (chamber region 30) involved in power generation.

[0048] In the oxidation region 31 (chamber region 30), it is ideal that the entire zirconium alloy film 3a is anodized. However, as described above, taking into consideration variations in thickness and the oxidation margin, the thickness of the zirconium alloy film 3a is set to be thicker than the desired thickness of the electrolyte membrane 3. Therefore, in the oxidation region 31 (chamber region 30), a portion of the zirconium alloy film 3a may remain between the electrolyte membrane 3 and the anode electrode 2. In this case, as in the alloy region 32, the remaining zirconium alloy film 3a will later become an oxide.

[0049] Although the oxide of the zirconium alloy film 3a differs from ideal yttria-stabilized zirconia in terms of chemical composition and crystalline state, it still has oxygen ion conductivity. However, electronic insulation cannot be expected from the oxide of the zirconium alloy film 3a. Therefore, the oxide of the zirconium alloy film 3a can also function as part of the electrolyte membrane 3, allowing oxygen ions to reach the anode electrode 2. For example, if the thickness of the oxide of the zirconium alloy film 3a is about 10% of the thickness of the electrolyte membrane 3, it will have almost no effect on the overall electrolyte characteristics.

[0050] After the anodization treatment, a conductive oxide film 4 and a cathode electrode 5 are successively formed by sputtering on the electrolyte membrane 3, as shown in Fig. 5. In this manner, the solid oxide fuel cell 100 according to the first embodiment is manufactured.

[0051] 8 to 10, a solid oxide fuel cell 100 according to a second embodiment will be described below. The following description will mainly focus on differences from the first embodiment, and will omit a description of points that overlap with the first embodiment.

[0052] When attempting to obtain a thin electrolyte membrane 3, the thickness of the base zirconium alloy film 3a is thin, so there is a risk that the anode electrode 2 will also be anodized during the anodization process. In the second embodiment, a stopper film 6 is provided between the anode electrode 2 and the electrolyte membrane 3 (zirconium alloy film 3a) to protect the anode electrode 2. For example, providing the stopper film 6 is effective when the thickness of the electrolyte membrane 3 (the thickness of the zirconium alloy film 3a) is 10 nm or more and 100 nm or less.

[0053] As shown in Figure 8, a porous insulating substrate 1 is prepared in the same manner as in embodiment 1, a conductive film 1b is formed on the surfaces of the multiple holes 1a, and an anode electrode 2 is formed on the porous insulating substrate 1.

[0054] Next, a stopper film 6 is formed on the anode electrode 2 by sputtering. This sputtering is performed under a film formation pressure of, for example, 10 Pa or more and 15 Pa or less. The stopper film 6 thus formed is made of a porous metal film. The thickness of the stopper film 6 is, for example, 5 nm or more and 50 nm or less.

[0055] The stopper film 6 is preferably made of a valve metal. This valve metal is selected from metals that can be anodized and whose oxide film exhibits oxygen ion conductivity and electronic insulation. Examples of such valve metals include Ti, Mg, Al, Hf, Ta, and Zr. Because the stopper film 6 has such properties, the stopper film 6 can function as part of the anode electrode 2.

[0056] As materials other than valve metals, materials that constitute the conductive oxide film 4 are also effective. In these materials, oxygen vacancies in the crystal are responsible for electronic conductivity, so it is expected that the supply of oxygen ions during anodization will cause the material to lose electronic conductivity and become highly resistive (electronically insulating).

[0057] Next, a zirconium alloy film 3a doped with a rare earth element is formed on the stopper film 6 by the same method as in the first embodiment. In the second embodiment, the thickness of the zirconium alloy film 3a is 10 nm or more and 100 nm or less.

[0058] 9, a solid electrolyte film 3 is formed by anodizing the zirconium alloy film 3a in the same manner as in the first embodiment. Since the stopper film 6 is formed under the zirconium alloy film 3a, the stopper film 6 may be anodized, but the anode electrode 2 is protected from the anodization.

[0059] 10, a conductive oxide film 4 and a cathode electrode 5 are sequentially formed on an electrolyte membrane 3 in the same manner as in the first embodiment. In this manner, a solid oxide fuel cell 100 according to the second embodiment is manufactured.

[0060] (Modification) A modification of the second embodiment will be described below.

[0061] In the first and second embodiments, the anode electrode 2 contains a transition metal such as Ni, but the anode electrode 2 of the modified example contains a noble metal, such as Pt. The anode electrode 2 of the modified example is formed by a sputtering method under a deposition pressure of 10 Pa or more and 15 Pa or less, and is made of a porous metal film.

[0062] If a noble metal is used for the anode electrode 2 without the stopper film 6 formed as in the first embodiment, the noble metal is likely to be ionized and diffused during anodization, regardless of the thickness of the zirconium alloy film 3a. In other words, there is a risk of the anode electrode 2 being destroyed. If the stopper film 6 is formed as in the second embodiment, such a problem can be prevented, and a noble metal can be used for the anode electrode 2.

[0063] The present invention has been specifically described above based on the above embodiment, but the present invention is not limited to the above embodiment and can be modified in various ways without departing from the spirit of the present invention.

[0064] REFERENCE SIGNS LIST 100 Solid oxide fuel cell 1 Porous insulating substrate 1a Hole 1b Conductive film 2 Anode electrode 3 Electrolyte film 3a Zirconium alloy film 4 Conductive oxide film 5 Cathode electrode 6 Stopper film 30 Chamber region 31 Oxidized region 32 Alloy region 40 Jig 41 O-ring 42 Protective film

Claims

1. A solid oxide fuel cell comprising: a porous insulating substrate; an anode electrode formed on the porous insulating substrate; a solid electrolyte membrane formed on the anode electrode; and a cathode electrode formed on the electrolyte membrane, wherein the electrolyte membrane is a stabilized zirconia membrane doped with a rare earth element and also serves as an anodization barrier membrane.

2. The solid oxide fuel cell according to claim 1, wherein the electrolyte membrane has a thickness of 10 nm or more and 500 nm or less.

3. A solid oxide fuel cell according to claim 1, wherein the anode electrode is made of a porous metal membrane.

4. A solid oxide fuel cell as claimed in claim 3, further comprising a stopper film containing a valve metal or a conductive oxide film between the anode electrode and the electrolyte membrane, the electrolyte membrane having a thickness of 10 nm or more and 100 nm or less, and the anode electrode containing a transition metal.

5. A solid oxide fuel cell according to claim 3, further comprising a stopper film containing a valve metal or a conductive oxide film between the anode electrode and the electrolyte membrane, the anode electrode containing a precious metal.

6. A solid oxide fuel cell according to claim 3, wherein a conductive film is formed on the surfaces of the plurality of holes formed in the porous insulating substrate.

7. A solid oxide fuel cell according to claim 6, wherein the electrolyte membrane is a yttria-stabilized zirconia membrane, the anode electrode contains Ni or Pt, the porous insulating substrate contains anodized aluminum, and the conductive membrane contains Pt or Ni.

8. A solid oxide fuel cell as described in claim 1, wherein, in a plan view, the electrolyte membrane contains a boundary that defines the anodization barrier film, i.e., the boundary between the gas phase region and the liquid phase region in the anodization process, and the liquid phase region is the anodization barrier film and contains an electrochemical reaction region involved in power generation.

9. A method for manufacturing a solid oxide fuel cell, comprising: (a) preparing a porous insulating substrate; (b) forming an anode electrode on the porous insulating substrate; (c) forming a zirconium alloy film having a rare earth element added thereto on the anode electrode; (d) forming a solid electrolyte membrane by performing anodizing treatment on the zirconium alloy membrane; and (e) forming a cathode electrode on the electrolyte membrane, wherein the electrolyte membrane is a stabilized zirconia membrane having a rare earth element added thereto and is also an anodization barrier membrane.

10. A method for producing a solid oxide fuel cell as described in claim 9, wherein the step (d) comprises: (d1) a step of surrounding a portion of the surface of the zirconium alloy film as an oxidized region with a jig; (d2) a step of selectively immersing only the oxidized region of the zirconium alloy film in a chemical conversion solution and applying an electric field to the oxidized region to form the electrolyte membrane from the zirconium alloy film in the oxidized region; and (d3) a step of removing the jig after the step (d2).

11. A method for producing a solid oxide fuel cell as described in claim 9, wherein the zirconium alloy film and the anode electrode are each formed by a sputtering method, the sputtering method for the zirconium alloy film is performed at a lower deposition pressure than the sputtering method for the anode electrode, and the anode electrode is made of a porous metal membrane.

12. A method for producing a solid oxide fuel cell according to claim 11, wherein the sputtering method for the zirconium alloy film is carried out under a film formation pressure of 0.5 Pa or more and 1.0 Pa or less.

13. A method for producing a solid oxide fuel cell as described in claim 11, further comprising: (f) a step between the step (b) and the step (c) of forming a stopper film containing a valve metal or a conductive oxide film on the anode electrode, wherein in the step (c), the zirconium alloy film is formed on the stopper film, the thickness of the zirconium alloy film is 10 nm or more and 100 nm or less, and the anode electrode contains a transition metal.

14. A method for producing a solid oxide fuel cell as described in claim 11, further comprising: (f) a step between the step (b) and the step (c) of forming a stopper film containing a valve metal or a conductive oxide film on the anode electrode, wherein in the step (c), the zirconium alloy film is formed on the stopper film, and the anode electrode contains a precious metal.

15. A method for producing a solid oxide fuel cell as described in claim 11, further comprising: (g) a step of forming a conductive film on the surfaces of a plurality of holes formed in the porous insulating substrate between steps (a) and (b), wherein the electrolyte film is an yttria-stabilized zirconia film, the anode electrode contains Ni or Pt, the porous insulating substrate contains anodized aluminum oxide, and the conductive film contains Pt or Ni.

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