Solid oxide electrolyzer cell and use thereof

Abstract

To provide a technology capable of suppressing occurrence of cracking in an air electrode.SOLUTION: A solid oxide electrolyzer cell comprises: an air electrode containing a composite oxide, as a main component, having a perovskite structure represented by the general formula A1xA2yBO3-δ (where 0.9≤x+y<1 and δ denotes an oxygen defective amount); a fuel electrode; and a solid electrolyte layer disposed between the air electrode and the fuel electrode. The air electrode includes: a first sulfur-containing substance and a second substance that is different from the composite oxide, the second substance containing at least one of cobalt and iron. The total of area occupancy ratios of the first substance and the second substance in a cross section of the air electrode is greater in a surface region within 10 μm from the surface opposite to the solid electrolyte layer side than in an interface region within 10 μm from the interface on the solid electrolyte layer side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to solid oxide electrolysis cells and their uses. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known that generate electricity by utilizing an electrochemical reaction between hydrogen and oxygen. For example, a single fuel cell, which is a constituent unit of an SOFC described in Patent Document 1, includes an electrolyte layer containing a solid oxide, an air electrode disposed on one side of the electrolyte layer, and an anode electrode disposed on the other side of the electrolyte layer. Oxygen ions dissociated from oxygen supplied to the air electrode migrate to the anode electrode based on the oxygen conductivity of the solid electrolyte, and react with hydrogen contained in the fuel gas supplied to the anode electrode to generate water vapor and electricity.

[0003] The SOFC can be used as a solid oxide electrolysis cell (hereinafter simply referred to as "SOEC") by passing current in the reverse direction, and is known to be used as an energy storage technology that converts water vapor into hydrogen using surplus electricity, which is an issue in the process of introducing renewable energy. When water vapor is supplied to the anode and an electric current is passed between the cathode and anode, the water vapor is electrolyzed, generating hydrogen from the anode, and oxygen ions generated at the anode migrate to the cathode due to the oxygen conductivity of the solid electrolyte, generating oxygen from the cathode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-080459 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, in SOFCs, oxygen is consumed at the fuel electrode during use, causing a drop in gas pressure on the air chamber side, but in SOECs, oxygen is generated at the air electrode side during use, causing an increase in gas pressure on the air chamber side, and a sudden increase in gas pressure when water vapor, the fuel gas, evaporates, causing stresses different from those in SOFCs, which could lead to cracks in the air electrode.In addition, generally, technology to suppress the decrease in current density is desired for SOECs. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms.

[0007] (1) According to one aspect of the present disclosure, there is provided a solid oxide electrolysis cell. The solid oxide electrolysis cell includes a solid oxide electrolysis cell having a general formula A1 x A2 y BO 3-δ (where 0.9≦x+y<1, δ is the amount of oxygen vacancy), an anode, and a solid electrolyte layer disposed between the anode and the cathode, wherein the cathode comprises a first substance containing sulfur and a second substance different from the complex oxide and containing at least one of cobalt and iron, and the total area occupancy of the first substance and the second substance in the cross section of the cathode is greater in a surface region within 10 μm from the surface opposite the solid electrolyte layer than in an interfacial region within 10 μm from the interface on the solid electrolyte layer side. This type of solid oxide electrolysis cell can suppress the occurrence of cracks in the cathode.

[0008] (2) In the solid oxide electrolysis cell described in (1) above, the total area occupancy of the first material and the second material in the cross section of the air electrode may be 0.1% or more and 10.5% or less in the surface region, and 0.02% or more and 4.6% or less in the interface region. This solid oxide electrolysis cell can suppress the occurrence of cracks in the air electrode.

[0009] (3) In the solid oxide electrolysis cell according to (1) or (2), the fuel electrode is supplied with a fuel gas containing water vapor at a rate of 100 to 130 liters / (min cm 2 ) may be supplied at a flow rate of 0.1 to 1.0 times the flow rate of the solid oxide electrolysis cell of this embodiment. The solid oxide electrolysis cell of this embodiment can suppress the occurrence of cracks in the air electrode.

[0010] (4) In the solid oxide electrolysis cell according to any one of (1) to (3), the air electrode is supplied with an oxygen-containing gas at a rate of 30 to 50 liters / (min cm 2 ) may be supplied at a flow rate of 0.1 to 1.0 times the flow rate of the solid oxide electrolysis cell of this embodiment. The solid oxide electrolysis cell of this embodiment can suppress the occurrence of cracks in the air electrode.

[0011] (5) In the solid oxide electrolysis cell according to any one of (1) to (4), the volume of the air chamber facing the air electrode is 9 cm 3 ~11cm 3 According to the solid oxide electrolysis cell of this configuration, it is possible to suppress the occurrence of cracks in the air electrode.

[0012] (6) According to another aspect of the present disclosure, there is provided a separator-equipped cell including the solid oxide electrolysis cell according to any one of (1) to (5) above and a separator with a central opening disposed on the solid electrolyte layer. The separator-equipped cell of this aspect can suppress the occurrence of cracks in the air electrode.

[0013] (7) According to another aspect of the present disclosure, there is provided an electrolysis stack including a plurality of stacked solid oxide electrolysis cells according to any one of (1) to (5). The electrolysis stack of this aspect can suppress the occurrence of cracks in the air electrode.

[0014] (8) According to another aspect of the present disclosure, there is provided a hot module including the electrolytic stack according to (7), a vaporizer that generates water vapor to be supplied to the electrolytic stack, a heat exchanger that exchanges heat with a gas supplied to the electrolytic stack, a heater that heats the electrolytic stack, and a thermal insulator in which the electrolytic stack, the vaporizer, the heat exchanger, and the heater are disposed. The hot module of this aspect can suppress the occurrence of cracks in the air electrode.

[0015] (9) According to another aspect of the present disclosure, there is provided a hydrogen production device including the hot module described above in (8). The hydrogen production device of this aspect can suppress the occurrence of cracks in the air electrode.

[0016] The present invention can be realized in various forms, for example, in the form of a method for manufacturing a solid oxide electrolysis cell. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view showing an external configuration of an electrolysis stack according to an embodiment of the present disclosure; [Figure 2] FIG. 2 is an exploded schematic diagram of the electrolysis stack taken along line II-II in FIG. 1. [Figure 3] Schematic top view of a cell with a separator. [Figure 4] Block diagram of a hydrogen production device. DETAILED DESCRIPTION OF THE INVENTION

[0018] Fig. 1 is a perspective view showing the external configuration of an electrolysis stack 10 according to one embodiment of the present disclosure. The electrolysis stack 10 in this embodiment is a stack of solid oxide electrolysis cells (SOECs). Fig. 1 shows an example of the configuration of the electrolysis stack 10.

[0019] The electrolysis stack 10 includes a plurality of rectangular reaction units 11 stacked in the thickness direction, and approximately rectangular end plates 12 and 13 sandwiching the reaction units 11 in the thickness direction. Bolts 14 are arranged at the four corners of the periphery of the electrolysis stack 10, penetrating the end plates 12, the reaction units 11, and the end plates 13 in the thickness direction. The reaction units 11 and the end plates 12 and 13 are fastened together by the bolts 14.

[0020] The electrolysis stack 10 includes a terminal plate 52 disposed between the end plate 12 and the reaction unit 11, and a terminal plate 53 disposed between the end plate 13 and the reaction unit 11. The reaction units 11 are connected in series between the terminal plates 52 and 53. The protruding portions of the terminal plates 52 and 53 function as terminals. It is of course possible to omit the terminal plates 52 and 53 and electrically connect the reaction units 11 to the end plates 12 and 13, thereby using the end plates 12 and 13 as terminals of the electrolysis stack 10.

[0021] Four spaces penetrating the electrolysis stack 10 in the thickness direction are formed at the periphery of the electrolysis stack 10. These four spaces function as a passage 15a through which gas enters the electrolysis stack 10 from the outside to a fuel chamber 33 (described later) of the reaction unit 11, a passage 15b through which gas exits the electrolysis stack 10 from the fuel chamber 33, a passage 15c through which gas enters the electrolysis stack 10 from the outside to an air chamber 35 (described later) of the reaction unit 11, and a passage 15d through which gas exits the electrolysis stack 10 from the air chamber 35.

[0022] Figure 2 is an exploded schematic view of the electrolysis stack 10 taken along line II-II in Figure 1, which passes through the passages 15a and 15b. Figure 2 shows a schematic cross-sectional view taken along line II-II, in which components constituting one reaction unit 11 are separated in the thickness direction. The reaction unit 11 includes, in that order in the thickness direction, an interconnector 16, an anode frame 17, a separator-equipped cell 47, and an cathode frame 19. Note that the thickness of each part is exaggerated in Figure 2.

[0023] 3 is a schematic top view of a separator-equipped cell 47. The separator-equipped cell 47 includes an electrolytic cell 20 and a separator 30 disposed in the electrolytic cell 20. Holes (passages 15a, 15b, 15c, 15d) penetrate the interconnector 16, the fuel electrode frame 17, the separator 30, and the air electrode frame 19. The electrolytic cell 20 will be described later.

[0024] The separator 30 is a substantially rectangular frame-shaped member provided with an opening 37 that is larger than the air electrode 29 described below. The separator 30 can be made of stainless steel, for example. The separator 30 is airtightly joined to the surface 24a of the solid electrolyte layer 24 described below with a brazing material 31, avoiding the air electrode 29.

[0025] The interconnectors 16 are disposed at both ends of the electrolysis cell 20 in the thickness direction. The interconnectors 16 are formed of conductive, substantially rectangular plate-like members. The interconnectors 16 electrically connect the reaction units 11 adjacent to each other in the thickness direction. Stainless steel is exemplified as a material for the interconnectors 16.

[0026] The fuel electrode frame 17 is a substantially rectangular frame-shaped member disposed between the interconnector 16 and the separator 30. Stainless steel is an example of the material for the fuel electrode frame 17. The fuel electrode frame 17 surrounds the electrolysis cell 20 and a current collector 32 provided in the center of the interconnector 16.

[0027] The current collector 32 electrically connects the fuel electrode 21 and the interconnector 16. An example of a material for the current collector 32 is a porous body made of a gas-permeable metal such as Ni. Inside the fuel electrode frame 17, a fuel chamber 33 is formed which is surrounded by the interconnector 16, the fuel electrode frame 17, and the separator 30.

[0028] The air electrode frame 19 is a substantially rectangular frame-shaped member disposed between the interconnector 16 and the separator 30. An example of the material of the air electrode frame 19 is an insulator such as mica. The air electrode frame 19 surrounds a current collector 34 provided in the center of the interconnector 16. The current collector 34 electrically connects the air electrode 29 and the interconnector 16. In this embodiment, the current collector 34 is formed integrally with the interconnector 16, but this is not limiting. It is of course possible for the current collector 34 to be a member separate from the interconnector 16.

[0029] An air chamber 35 is formed inside the air electrode frame 19 and is surrounded by the interconnector 16, the air electrode frame 19, and the separator 30. The separator 30 separates the fuel chamber 33 from the air chamber 35, preventing the fuel gas in the fuel chamber 33 and the oxidant gas (oxygen, air, etc.) in the air chamber 35 from mixing.

[0030] A hydrogen production device 60 including an electrolysis stack 10 and a hot module 61 will be described with reference to Fig. 4. Fig. 4 is a block diagram of the hydrogen production device 60. The hydrogen production device 60 is a device that produces hydrogen from water, and includes a hot module 61.

[0031] The hot module 61 includes the electrolysis stack 10, a vaporizer 62 that generates steam to be supplied to the electrolysis stack 10, a heat exchanger 63 that exchanges heat between the gas supplied to the electrolysis stack 10 and the gas generated by the electrolysis stack 10, and a heater 64 that heats the electrolysis stack 10. In the hot module 61, the electrolysis stack 10, the vaporizer 62, the heat exchanger 63, and the heater 64 are arranged inside a thermal insulator 65 to reduce heat radiation.

[0032] The vaporizer 62 includes a heat exchanger that exchanges heat with high-temperature gas containing oxygen produced by the electrolysis stack 10, and heats water to produce water vapor. The water vapor produced by the vaporizer 62 contains hydrogen, which reduces oxidation of the catalyst contained in the anode 21. The hydrogen-containing water vapor exchanges heat with hydrogen and oxygen produced by the electrolysis stack 10 in a heat exchanger 63, is heated to the operating temperature of the electrolysis stack 10 by a heater 64, and is supplied to the fuel chamber 33 of the electrolysis stack 10. The air exchanges heat with hydrogen and oxygen produced by the electrolysis stack 10 in the heat exchanger 63, is heated to the operating temperature of the electrolysis stack 10 by a heater 64, and is supplied to the air chamber 35 of the electrolysis stack 10.

[0033] Examples of the heat insulating material 65 include heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), and biosoluble fiber (AES), and a heat-resistant container made of heat-resistant fibers. The heat-resistant fibers fill gaps between the electrolysis stack 10, the vaporizer 62, the heat exchanger 63, and the heater 64. The condenser 66 is a device that cools the hydrogen gas, and liquefied water is supplied to the vaporizer 62 as raw water.

[0034] (Electrolytic cell) As shown in FIG. 2 , the electrolysis cell 20 includes an air electrode 29, an anode 21, and a solid electrolyte layer 24 disposed between the air electrode 29 and the anode 21. The electrolysis cell 20 of this embodiment includes a reaction prevention layer 25 between the solid electrolyte layer 24 and the air electrode 29. Furthermore, in this embodiment, the air electrode 29 includes, in order from the side closest to the solid electrolyte layer 24, an air electrode functional layer 26 and an air electrode current collecting layer 27. The thickness of the electrolysis cell 20 is not particularly limited, but may be, for example, 300 μm to 3 mm. The shape of the electrolysis cell 20 viewed from above is not particularly limited, but examples include a square with sides measuring 1 to 10 cm, a rectangle with long sides measuring 5 to 30 cm and short sides measuring 3 to 15 cm, or a circle with a diameter of 10 cm. A plurality of electrolysis cells 20 are connected in series by interconnectors 16 to form an electrolysis stack 10.

[0035] The fuel electrode 21 is formed using nickel oxide and oxygen-ion conductive ceramic particles as materials. Nickel oxide (NiO) used as the material of the fuel electrode 21 is converted into nickel through a reduction process described below. The fuel electrode 21 of this embodiment is a porous, thin-plate-shaped sintered body composed of nickel and YSZ (yttria-stabilized zirconia). Examples of ceramic materials having oxygen ion conductivity include YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), (Gd,Ce)O2, i.e., GDC (gadolinium-doped ceria), (Sm,Ce)O2, i.e., SDC (samarium-doped ceria), and LaGaO3 (lanthanum gallate). The ceramic material contained in the fuel electrode 21 may be one type or two or more types. The thickness of the fuel electrode 21 is not particularly limited, but is, for example, 0.3 to 3 mm. In this embodiment, the fuel electrode 21 has the greatest thickness among the thicknesses of the components of the electrolysis cell 20, and functions as a support (support substrate, the member with the highest rigidity) for the electrolysis cell 20.

[0036] The anode 21 functions as the cathode of the electrolysis cell 20. The anode 21 includes, in order from the solid electrolyte layer 24 side, an anode functional layer 23 and an anode substrate layer 22. In this embodiment, the anode 21 includes, in order from the solid electrolyte layer 24 side, the anode functional layer 23 and the anode substrate layer 22, which has a porosity greater than that of the anode functional layer 23. This ensures the strength of the anode functional layer 23. The thickness of the anode substrate layer 22 is preferably greater than that of the anode functional layer 23. The porosity of the anode functional layer 23 is not particularly limited, but is, for example, preferably 30% or less, more preferably 25% or less, and preferably 5% or more, and more preferably 10% or more. The porosity of the anode substrate layer 22 is not particularly limited, but is, for example, preferably 50% or less, more preferably 40% or less, and preferably 10% or more, and more preferably 20% or more. The anode 21 may be formed of a single layer instead of the anode functional layer 23 and the anode substrate layer 22.

[0037] The anode substrate layer 22 is a porous, plate-shaped sintered body containing a transition metal and an oxygen ion conductive material. The anode substrate layer 22 may contain nickel (Ni) as the transition metal. The anode substrate layer 22 may contain, as the oxygen ion conductive material, a zirconia-based material such as yttria-stabilized zirconia (8YSZ, 10YSZ, etc.) or scandia-stabilized zirconia (ScSZ), a ceria-based material such as gadolinium-doped ceria (GDC:(Ce,Gd)O) or samarium-doped ceria (SDC:(Ce,Sm)O), or yttria (YO).

[0038] The thickness of the anode substrate layer 22 can be, for example, 0.2 mm to 5.0 mm. When the anode substrate layer 22 functions as a substrate, the thickness of the anode substrate layer 22 may be the largest among the components of the electrolysis cell 20. In the anode substrate layer 22, the volume ratio of Ni can be, for example, 20 to 50 volume %, and the volume ratio of the oxygen ion conductive material can be, for example, 30 to 60 volume %.

[0039] The anode functional layer 23 is disposed between the anode substrate layer 22 and the solid electrolyte layer 24. The anode functional layer 23 is a porous, sintered plate containing a transition metal and an oxygen ion conductive material. The anode functional layer 23 contains at least Ni as a transition metal. The anode functional layer 23 may further contain Fe or Cu as a transition metal. The anode functional layer 23 contains, as an oxygen ion conductive material, a zirconia-based material such as yttria-stabilized zirconia (8YSZ, 10YSZ, etc.) or scandia-stabilized zirconia (ScSZ), or a ceria-based material such as gadolinium-doped ceria (GDC:(Ce,Gd)O2) or samarium-doped ceria (SDC:(Ce,Sm)O2).

[0040] The thickness of the anode functional layer 23 can be, for example, 1.0 μm to 30 μm. In the anode functional layer 23, the volume ratio of Ni can be, for example, 30 to 60 volume %, and the volume ratio of the oxygen ion conductive material can be, for example, 40 to 70 volume %.

[0041] The solid electrolyte layer 24 is a dense, thin-plate-like sintered body. The solid electrolyte layer 24 is formed of a solid oxide such as YSZ (yttria-stabilized zirconia), ScSZ (scandia-stabilized zirconia), SDC (samarium-doped ceria), GDC (gadolinium-doped ceria), or a perovskite-type oxide. Examples of perovskite-type oxides include lanthanum gallate-based oxides having a perovskite-type structure. The thickness of the solid electrolyte layer 24 is not particularly limited, but is, for example, 3 to 30 μm.

[0042] In this embodiment, the solid electrolyte layer 24 is disposed between the anode 21 and the reaction prevention layer 25. The solid electrolyte layer 24 has a function of allowing oxygen ions generated in the cathode 29 to pass therethrough. The solid electrolyte layer 24 may contain zirconium (Zr), or the solid electrolyte layer 24 may contain Zr as zirconia (ZrO2). The solid electrolyte layer 24 may contain ZrO2 as a main component. The solid electrolyte layer 24 may also contain additives such as Y2O3 and / or Sc2O3 in addition to ZrO2. These additives function as stabilizers. In the solid electrolyte layer 24, the molar composition ratio of the stabilizer to ZrO2 (stabilizer:ZrO2) is preferably approximately 3:97 to 20:80. That is, examples of materials for the solid electrolyte layer 24 include yttria-stabilized zirconia such as 3YSZ, 8YSZ, and 10YSZ, and zirconia-based materials such as ScSZ.

[0043] The air electrode 29 is disposed on the reaction prevention layer 25. The air electrode 29 functions as the anode of the electrolysis cell 20. The air electrode 29 contains a complex oxide having a perovskite structure. The composition of the complex oxide is represented by the general formula A1 x A2 y BO 3-δ(where 0.9≦x+y<1, δ is the amount of oxygen vacancy). The ideal unit cell of a complex oxide having a perovskite structure is a cube. When simply represented as ABO3, element A is located at the corner of the unit cell, element B is located at the body-center of the unit cell, and element oxygen is located at the face-center of the unit cell. In the present disclosure, the corner of the unit cell where element A is located is referred to as the "A site," and the body-center of the unit cell where element B is located is referred to as the "B site." Two different elements, A1 and A2, are located at the A site. In this embodiment, the composition of the complex oxide has an A-site deficiency perovskite structure rather than a 1:1:3 ratio of A, B, and O. Specifically, an A-site deficiency perovskite structure satisfies the condition 0.9≦x+y<1 in the above general formula. In other words, x+y is less than 1. Since x+y is smaller than 1, the vacancies in the structure can increase the current density (high ionic conductivity). On the other hand, if x+y is less than 0.9, the number of vacancies in the structure increases, resulting in insufficient strength. 3-δ " represents the amount of oxygen vacancies, and voids can also be formed in the structure by this amount of oxygen vacancies. The amount of oxygen vacancies does not have to exceed 0.1, and may be 0. In other words, the amount of oxygen vacancies is 0≦δ≦0.1. Similarly, if δ exceeds 0.1, the number of voids in the structure increases, resulting in insufficient strength.

[0044] The A site preferably contains at least one of La and Sr atoms. The B site preferably contains at least one of Co and Fe atoms. Specific examples of such complex oxides, for example, in the case of the material of the air electrode 29, include materials such as LSCF (i.e., (La,Sr)(Co,Fe)O3), LSF (i.e., (La,Sr)FeO3), LSC (i.e., (La,Sr)CoO3), LNF (i.e., La(Ni,Fe)O3), and SSC (i.e., (Sm,Sr)CoO3). These complex oxides are substances that have both oxygen ion conductivity and electronic conductivity, and are also called mixed conductive materials. In this embodiment, the air electrode 29 is made of lanthanum strontium cobalt ferrite LSCF (La 0.6 Sr 0.4 Co0.2 Fe 0.8 O3) is a porous, thin, fired body formed from a material containing

[0045] The air electrode 29 contains a composite oxide having a perovskite structure as a "main component." Here, "contains as a main component" means that the composite oxide having a perovskite structure accounts for 60 mass% or more, preferably 70 mass% or more, and more preferably 90 mass% or more of the entire air electrode 29. The air electrode 29 may contain components other than the composite oxide. The material of the air electrode 29 may be a powder (for example, an average particle size of about 0.1 μm to 5 μm) or a crushed material (for example, an average particle size of about 5 μm to 500 μm), or may be a lump larger than the crushed material. The thickness of the air electrode 29 may be, for example, 5 μm to 150 μm.

[0046] The cathode current collecting layer 27 is a compound represented by the general formula A1 x A2 y BO 3-δ (where 0.9≦x+y<1, δ is the amount of oxygen deficiency). Examples of such complex oxides include, but are not limited to, LSCF, LSF, LSC, LNF, and SSC. The air electrode functional layer 26 may contain a component other than the complex oxide contained in the air electrode current collecting layer 27. For example, the air electrode functional layer 26 may be composited with a material of the solid electrolyte layer 24 (e.g., ceria or zirconia), which will be described later. The thickness of the air electrode current collecting layer 27 is not particularly limited, but may be, for example, 10 to 200 μm. The thickness of the air electrode functional layer 26 is not particularly limited, but may be, for example, 5 to 20 μm. The air electrode functional layer 26 may not be provided, or the air electrode functional layer 26 may not contain Ce. The air electrode current collecting layer 27 may not be provided depending on the actual usage environment.

[0047] In this embodiment, the air electrode 29 includes a first material containing sulfur and a second material containing at least one of cobalt and iron, which is different from a composite oxide having a perovskite structure as its primary component. In the following description, the first material containing sulfur will also be referred to as the "sulfur-containing material," and the second material containing at least one of cobalt and iron, which is different from a composite oxide having a perovskite structure as its primary component, will also be referred to as the "material containing at least one of cobalt and iron." Examples of sulfur-containing materials include, but are not limited to, strontium sulfate (SrSO4). Examples of materials containing at least one of cobalt and iron include, but are not limited to, (Co,Fe)3O4, Co3O4, and Fe3O4. The total area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron in the cross section of the air electrode 29 is greater in the surface region R2 within 10 μm from the surface opposite the solid electrolyte layer 24 than in the interface region R1 within 10 μm from the interface Q on the solid electrolyte layer 24 side. The inventors discovered that this configuration can suppress the occurrence of cracks in the air electrode 29. The total area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron in the cross section of the air electrode 29 is preferably 0.02% or more and 10.5% or less. This total area occupancy is preferably 0.1% or more and 10.5% or less in the surface region R2, and is preferably 0.02% or more and 4.6% or less in the interface region R1. When the reaction prevention layer 25 is present, the interface region "R1" within 10 μm from the interface Q on the solid electrolyte layer 24 side can be the interface region "R1" within 10 μm from the interface on the reaction prevention layer 25 side. The present inventors have discovered that this effectively prevents cracks from occurring in the air electrode 29. One method for adjusting the area occupancy of the sulfur-containing material and the material containing at least one of cobalt and iron in the cross section of the air electrode 29 is to adjust the amounts of the sulfur-containing material and the material containing at least one of cobalt and iron blended when manufacturing the air electrode 29.The area occupancy of the sulfur-containing material and the material containing at least one of cobalt and iron in the cross section of the air electrode 29 depends on the amounts of the sulfur-containing material and the material containing at least one of cobalt and iron mixed in the air electrode 29, and therefore the value in the air electrode functional layer 26 is substantially the same regardless of location, and the value in the air electrode current collecting layer 27 is also substantially the same regardless of location. Therefore, the area occupancy of the sulfur-containing material and the material containing at least one of cobalt and iron in the cross section of the air electrode 29 is expected to be a value between the value in the interface region R1 and the value in the surface region R2.

[0048] Although there are no particular limitations on how the composite oxide having a perovskite structure, which is the main component, the sulfur-containing substance, and the substance containing at least one of cobalt and iron are distributed in the cross section of the air electrode 29, it is preferable that the composite oxide having a perovskite structure, the sulfur-containing substance, and the substance containing at least one of cobalt and iron are distributed generally uniformly.More preferably, the sulfur-containing substance and the substance containing at least one of cobalt and iron are distributed among particles of the composite oxide having a perovskite structure.

[0049] The method for calculating the area occupancy of the sulfur-containing material and the material containing at least one of cobalt and iron in the cross section of the cathode 29 is described below. First, the cross section of the cathode 29 is precision-machined and then subjected to ion milling using an IM4000PLUS manufactured by Hitachi High-Tech Corporation. Next, a scanning electron microscope (SEM) is used to obtain an SEM image of the cross section of the cathode 29 at a magnification of 10,000 times. Then, energy dispersive X-ray spectroscopy (EDS) is used to obtain a map of each elemental component. The positions of the main component, sulfur, cobalt, and iron are then identified based on the elemental distribution. Particles in which sulfur or at least one of cobalt and iron is detected in the elemental mapping are identified as sulfur-containing materials or materials containing at least one of cobalt and iron. Next, the SEM image is analyzed using image analysis software to obtain the areas of the sulfur-containing substance and the substance containing at least one of cobalt and iron, and the area occupancy (%) of the sulfur-containing substance and the substance containing at least one of cobalt and iron is calculated by dividing the total area of ​​the sulfur-containing substance and the substance containing at least one of cobalt and iron by the total area of ​​all components in the analyzed image. This analysis is performed at five locations on the same cross section of the air electrode 29, and the arithmetic mean of the area percentages of the sulfur-containing substance and the substance containing at least one of cobalt and iron calculated at each of the five locations is the area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron in the air electrode 29. While the method for calculating the area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron has been described above, the area occupancy of the composite oxide having a perovskite structure, which is the main component, can also be calculated in a similar manner. When identifying a complex oxide having a perovskite structure, the atomic concentrations of the elements contained in the A1 site, the A2 site, the B site, and the oxygen element are obtained, and the compound represented by the general formula A1 x A2 y BO 3-δ(where 0.9≦x+y<1, δ is the amount of oxygen vacancy) the composition ratio of A1, A2, B, and O can be obtained.

[0050] Due to the difference in thermal expansion coefficients, there is a risk that the air electrode 29 will peel off from the solid electrolyte layer 24. To address this issue, one technique involves providing a composite material, in which an electrolyte is mixed into the air electrode 29, between the air electrode 29 and the solid electrolyte layer 24. However, when a Zr-based material is used as the electrolyte material, if the air electrode 29 contains Sr, there is a problem that SrZrO3 (SZO) is produced. In this case, for example, GDC (gadolinium-doped ceria) or SDC (samarium-doped ceria) is used as the mixed electrolyte material. Preferably, an intermediate layer, in which an electrolyte and a composite oxide are mixed, can be disposed between the air electrode 29 and the solid electrolyte layer 24; this intermediate layer is the air electrode functional layer 26.

[0051] When Sr (strontium) contained in the air electrode 29 diffuses toward the solid electrolyte layer 24 and reacts with Zr (zirconium) contained in the solid electrolyte layer 24, a highly resistive substance called SrZrO3 (hereinafter also referred to as "SZO") is generated. If SZO is generated in a layer in the region between the air electrode 29 and the solid electrolyte layer 24, electrolysis performance deteriorates. To suppress the generation of SZO, it is preferable to dispose a reaction prevention layer 25 containing, for example, gadolinium-doped ceria (GDC) between the air electrode 29 and the solid electrolyte layer 24. This effectively suppresses the reaction of Sr diffused from the air electrode 29 with Zr contained in the solid electrolyte layer 24 to generate SZO. However, the electrolysis cell 20 does not necessarily have to include the reaction prevention layer 25. Examples of materials for the reaction prevention layer 25 include ceria-based materials containing cerium (Ce) and rare earth metal oxides dissolved in Ce. The reaction prevention layer 25 is preferably, but not limited to, a dense, thin-plate-shaped sintered body made of ceria. Examples of ceria include, but are not limited to, GDC (gadolinium-doped ceria) and SDC (samarium-doped ceria).

[0052] In this embodiment, the reaction prevention layer 25 is disposed between the solid electrolyte layer 24 and the air electrode 29. The reaction prevention layer 25 has the function of preventing a high-resistance layer from being formed between the solid electrolyte layer 24 and the air electrode 29. The thickness of the reaction prevention layer 25 can be set to, for example, 3 μm to 20 μm.

[0053] In this SOEC electrolysis cell 20, water vapor is supplied to the fuel electrode 21, and a gas containing oxygen is supplied to the air electrode 29. At the same time, a current is passed between the fuel electrode 21 and the air electrode 29, causing the chemical reactions shown in the following formulas (1) and (2). As a result, hydrogen is generated from the fuel electrode 21, and oxygen is generated from the air electrode 29. H2O+2e - →H2+O 2- (At: Fuel electrode 21) …(1) O 2- →(1 / 2)·O2+2e - (At: Air electrode 29) ... (2)

[0054] In this SOEC electrolysis cell 20, conductive connecting members (interconnectors 16) for collecting current are usually joined and fixed to each of the fuel electrode 21 and the air electrode 29 with a bonding agent, and a potential difference is applied via each interconnector 16 to allow current to flow. Then, hydrogen gas generated from the fuel electrode 21 is collected.

[0055] The fuel electrode 21 is supplied with a fuel gas containing water vapor at a rate of, for example, 90 to 140 liters / (min cm 2 ) and may be used at a flow rate of 100 to 130 liters / (min cm 2 ) may be supplied at a flow rate of 1000 kJ / s. In the case of co-electrolysis, a gas containing water vapor and CO2 may be supplied as the fuel gas. In a stack in which cells are stacked in multiple stages, the amount of fuel gas input by blowers, pumps, etc. naturally increases in proportion to the number of cells stacked.

[0056] The air electrode 29 is supplied with an oxygen-containing gas at a rate of, for example, 20 to 60 liters / (min cm 2 ) and may be used at a flow rate of 30 to 50 L / (min cm 2) may be supplied and used. As the oxygen-containing gas, oxygen gas or air may be used. In a stack in which cells are stacked in multiple stages, the amount of gas introduced into the air electrode side by a blower, pump, etc. naturally increases in proportion to the number of cells stacked.

[0057] The volume of the air chamber 35 facing the air electrode 29 is not particularly limited, but is preferably 8 cm 3 ~13cm 3 Preferably, 9cm 3 ~11cm 3 Here, the volume of the air chamber 35 facing the air electrode 29 refers to the volume per cell, excluding the space occupied by current collecting members and the like.

[0058] (Manufacturing method) Next, an example of a method for manufacturing the electrolytic cell 20 will be described. The various conditions described below, such as the material, particle size, temperature, and application method, can be changed as appropriate depending on the manufacturing environment, etc. In the following description, the term "molded body" refers to the state before firing.

[0059] (Preparation of green sheet for fuel electrode substrate layer) To a mixed powder of NiO powder and YSZ powder, organic beads as a pore former, butyral resin, DOP as a plasticizer, Florene G-700 as a dispersant, and a mixed solvent of toluene and ethanol are added, and the mixture is mixed in a ball mill to prepare a slurry. The organic beads are spherical particles formed from a polymer such as polymethyl methacrylate or polystyrene. The obtained slurry is thinned by a doctor blade method to prepare a green sheet for an anode substrate layer having a predetermined thickness (e.g., 200 μm to 300 μm). The mixing ratio of NiO powder and YSZ powder when preparing the anode green sheet can be appropriately set as long as the performance is satisfied. The mixing ratio of NiO powder and YSZ powder may be, for example, 20 to 50 volume % NiO and 30 to 60 volume % YSZ.

[0060] (Preparation of green sheet for fuel electrode functional layer) A mixed powder of NiO powder and YSZ powder is added with butyral resin, DOP (a plasticizer), Florene G-700 (a dispersant), and a mixed solvent of toluene and ethanol, and mixed in a ball mill to prepare a slurry. The resulting slurry is thinned by a doctor blade method to prepare a green sheet for an anode functional layer having a predetermined thickness (e.g., 5 μm to 50 μm). The mixing ratio of NiO powder and YSZ powder when preparing the green sheet for an anode functional layer can be appropriately set as long as the performance is satisfied. The mixing ratio of NiO powder and YSZ powder may be, for example, 30 to 60 volume % NiO and 40 to 70 volume % YSZ.

[0061] (Preparation of green sheets for solid electrolyte layers) Butyral resin, DOP (a plasticizer), Florene G-700 (a dispersant), and a mixed solvent of toluene and ethanol are added to the YSZ powder and mixed in a ball mill to prepare a slurry. The resulting slurry is thinned by a doctor blade method to produce a green sheet for the solid electrolyte layer with a predetermined thickness (e.g., 10 μm).

[0062] (Fabrication of a Laminate of Solid Electrolyte Layer 24, Anode Functional Layer 23, and Anode Substrate Layer 22) The green sheet for the anode substrate layer, the green sheet for the anode functional layer, and the green sheet for the solid electrolyte layer are attached and degreased at a predetermined temperature (e.g., about 280°C). The degreased green sheet stack is then fired at a predetermined temperature (e.g., about 1350°C). This results in a stack of the solid electrolyte layer 24, the anode functional layer 23, and the anode substrate layer 22.

[0063] The cell manufacturing method is not limited to this method, and the following method may also be used. A slurry is prepared by adding polyvinyl alcohol (PVA) as a binder to a mixture of NiO powder and YSZ powder. This slurry is then dried and granulated using a spray dryer, and a green body for the anode 21 is formed by die press molding. Next, water and a binder are added to the YSZ powder, and the mixture is mixed in a ball mill for 24 hours to prepare a slurry. This slurry is then applied and molded onto the green body for the anode 21, thereby forming a green body for the solid electrolyte layer 24. This stack of green bodies is then co-sintered in air in an electric furnace (in an oxygen-containing atmosphere) at, for example, 1350°C, to form a stack of the anode 21 and the solid electrolyte layer 24. A tape lamination method, printing method, or the like may also be used to form a film that will later become the solid electrolyte layer 24 on the anode 21.

[0064] (Formation of reaction prevention layer 25) Next, the reaction prevention layer 25 is formed. Specifically, polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent are added to and mixed with GDC powder, and the viscosity is adjusted to prepare a paste for the reaction prevention layer. The obtained paste for the reaction prevention layer is applied by, for example, screen printing to the surface of the solid electrolyte layer 24 side of the laminate of the solid electrolyte layer 24 and the anode 21, and then fired at, for example, 1180°C. This forms the reaction prevention layer 25, and a laminate of the anode 21, solid electrolyte layer 24, and reaction prevention layer 25 (hereinafter referred to as the "intermediate laminate") is produced.

[0065] (Method for manufacturing the material of the air electrode 29) An example of a method for manufacturing the material of the air electrode 29 is described below. Methods for obtaining a composite oxide include, for example, a solid-phase method and a liquid-phase method. Here, a case where the material of the air electrode 29 is manufactured using a solid-phase method is sequentially described.

[0066] (Method for manufacturing the material of the air electrode 29 using the solid phase method) First, raw materials are prepared according to the type of composite oxide. When manufacturing LSCF as the composite oxide, for example, La2O3, SrCO3, Co3O4, and Fe2O3 are prepared. It is preferable to control the average particle size and particle size distribution of each raw material. Next, each raw material is classified. Specifically, the specific surface area of ​​each raw material is adjusted by classifying it using, for example, an air classifier.

[0067] Next, the raw materials are mixed at a predetermined mixing ratio. In this embodiment, this mixing process includes the steps of weighing the raw materials at a predetermined mixing ratio and charging them into a pot mill together with balls (e.g., alumina or zirconia balls are applicable); rotating the pot mill in a dry state for a predetermined time (10 to 120 hours); then charging a predetermined amount (50% to 200% by mass of the raw materials) of solvent (e.g., ion-exchanged water for aqueous systems, or acetone for solvent systems) into the pot mill; and rotating the pot mill in a wet state for a predetermined time (10 to 300 hours). To uniformly mix the raw material powders in the wet mixing, it is preferable to thoroughly crush the raw material powders under appropriate mixing conditions in the dry mixing. After the wet mixing, a drying process is performed to remove the solvent. This drying process can be performed using, for example, a box (tray) dryer, a band dryer, or a spray dryer.

[0068] Next, the dried mixed powder raw material is fired in a firing furnace to synthesize the material for the air electrode 29. The firing process preferably basically consists of three steps: crude firing, pre-firing, and main firing. However, it may consist of two steps: crude firing and main firing, or two steps: crude firing and main firing, or a process consisting of only main firing. The crude firing, pre-firing, and main firing all have different firing temperatures. Alumina may be used as the material for the firing container, and examples of such materials include mullite and cordierite.

[0069] (rough firing) In the crude firing step, the temperature of the firing furnace is preferably raised to the target firing temperature (300 to 500°C) at a heating rate of 20 to 800°C / hour. Setting the temperature at 300°C or higher can prevent carbon components from remaining. Setting the temperature at 500°C or lower can prevent segregation of constituent elements. The firing time for crude firing is not particularly limited, but is preferably 4 to 24 hours, for example. Setting the firing time at 4 hours or longer can prevent carbon components from remaining. The atmosphere in the firing furnace during crude firing is preferably an oxygen-containing atmosphere, more preferably an atmosphere with an oxygen concentration equal to or lower than that of air (atmospheric air), i.e., an oxygen concentration of 20% by volume or less. The oxygen-containing atmosphere burns excess carbon components in the raw material mixed powder, and setting the oxygen concentration at 20% by volume or less partially promotes oxidation, making the mixture more susceptible to oxygen deficiency.

[0070] Next, the oxide obtained in the crude firing step is crushed. Crushing is preferably performed using a mill such as a pot mill, jet mill, or atomizer, and is generally carried out in a dry manner. The volume average particle size after crushing is preferably 5 to 10 μm. Furthermore, it is preferable to control the particle size distribution of the raw material. Specifically, it is desirable to remove coarse particles of 50 μm or more in advance using an air classifier or the like.

[0071] (Pre-firing) Subsequently, the crushed coarsely fired powder is pre-fired at a pre-fire temperature (500 to 800°C). In the pre-fire step, the temperature of the firing furnace is preferably raised to the target firing temperature at a temperature increase rate of 100 to 400°C / hour. By setting the temperature to 500°C or higher, it is possible to prevent carbon components from remaining. Furthermore, by setting the temperature to 800°C or lower, it is possible to prevent the fired powder from being excessively sintered. The firing time is not particularly limited, but is preferably 4 to 20 hours, for example. By setting the firing time to 4 hours or more, it is possible to prevent carbon components from remaining. The atmosphere in the firing furnace during pre-fire is preferably a low-oxygen atmosphere similar to that used during coarse firing.

[0072] Next, the oxide obtained by the calcination is crushed in the same manner as after the coarse calcination. Crushing is preferably carried out using a mill such as a pot mill, jet mill, or atomizer, and is generally carried out in a dry manner. The volume average particle size after crushing is preferably 5 to 10 μm. Furthermore, it is preferable to control the particle size distribution of the raw material. Specifically, it is desirable to remove coarse particles of 30 μm or more in advance using an air classifier or the like.

[0073] (Final firing) The calcined powder is then fired at a firing temperature (800 to 1400°C). In the firing step, the temperature of the firing furnace is preferably increased to the target firing temperature at a rate of 100 to 400°C / hour. By setting the heating rate to 400°C / hour or less, the chemical changes of the reactants at each temperature do not proceed sufficiently, and the reactants reach the target firing temperature in a non-uniform state, which can prevent the generation of by-products in the fired product. The firing temperature is not particularly limited, but is preferably 1000 to 1400°C, for example. By setting the temperature within this preferred range, it is possible to prevent the target crystalline phase from not being formed. The firing time is not particularly limited, but is preferably 4 to 20 hours, for example. By setting the firing time to 4 hours or more, it is possible to prevent unreacted substances from being mixed into the target oxide, and it is also possible to prevent the target crystalline phase from not being obtained, even if a single crystalline phase is obtained.

[0074] The atmosphere in the firing furnace during the main firing is preferably a low-oxygen atmosphere, similar to that used during the crude firing or pre-firing. Furthermore, it is more preferable to use a weakly reducing atmosphere at high temperatures above 500°C after the carbon component has been burned off, as this facilitates oxygen deficiency. After the main firing is performed for a predetermined time, the temperature is lowered to room temperature. The temperature lowering rate is preferably 50 to 800°C / hour. A temperature lowering rate of 50°C / hour or higher improves productivity. Furthermore, a temperature lowering rate of 800°C / hour or lower can prevent the target substance from being produced. Next, the oxide obtained by the main firing is crushed in the same manner as after the crude firing. Crushing is preferably performed using a grinder such as a pot mill, jet mill, or atomizer, and is generally performed dry. The volume average particle size of the crushed powder is preferably 5 to 10 μm. Furthermore, it is preferable to control the particle size distribution of the raw materials. Specifically, it is desirable to remove coarse particles of 20 μm or larger in advance using an air classifier or the like.

[0075] Next, the synthesized aggregated material for the air electrode 29 is pulverized. As with the disintegration, pulverization is preferably performed using a pulverizer such as a pot mill, jet mill, or atomizer, and is generally performed dry. When using a pot mill, the material for the air electrode 29 is preferably placed in the pot mill together with balls (for example, balls made of alumina or zirconia) and rotated for a predetermined time (5 hours to 20 hours) to adjust the average particle size of the material for the air electrode 29 to 0.3 μm to 1.2 μm. If necessary, wet pulverization may be performed to adjust the particle size.

[0076] By carrying out rough firing, pre-firing and main firing in this order, a material with a more uniform composition and good crystallinity is produced.

[0077] Finally, the pulverized material for the air electrode 29 is classified. Specifically, for example, the specific surface area of ​​the material for the air electrode 29 can be adjusted by classifying it using an air flow classifier. When LSCF is produced as the composite oxide, the specific surface area is adjusted to 3 m 2 / g~12m 2 It is preferable to adjust the saturation temperature to 1000°C / g.

[0078] (Formation of the air electrode functional layer 26) Next, the air electrode functional layer 26 is formed. First, LSCF powder and GDC powder are mixed in a mass ratio of 1:1, and then strontium sulfate (SrSO4) as a sulfur-containing substance, Co2FeO4 as a substance containing at least one of cobalt and iron, polyvinyl alcohol as an organic binder, and butyl carbitol as an organic solvent are mixed. The viscosity is then adjusted to prepare a paste for the air electrode functional layer. Next, the prepared paste for the air electrode functional layer is applied to the surface of the intermediate laminate on the side of the reaction prevention layer 25 by, for example, screen printing, and then dried.

[0079] (Formation of Air Electrode Current Collecting Layer 27) Next, the cathode current collecting layer 27 is formed. First, LSCF powder, strontium sulfate (SrSO4) as a sulfur-containing substance, Co2FeO4 as a substance containing at least one of cobalt and iron, polyvinyl alcohol as an organic binder, butyl carbitol as an organic solvent, and organic beads as a pore-forming material are mixed, and the viscosity is adjusted to prepare an cathode current collecting layer paste. Next, the prepared cathode current collecting layer paste is applied to the surface of the intermediate laminate facing the cathode functional layer 26 by, for example, screen printing and dried. The intermediate laminate with the applied current collecting layer paste is then fired at a predetermined firing temperature (for example, 1100°C). This firing process forms the cathode current collecting layer 27, and a laminate of the anode 21, solid electrolyte layer 24, reaction prevention layer 25, cathode functional layer 26, and cathode current collecting layer 27, i.e., a single electrolysis cell 20, is produced.

[0080] Thereafter, a reduction step is performed to reduce the fuel electrode 21 (i.e., reduce NiO contained in the fuel electrode 21 to Ni) to enable the electrolysis cell 20 to operate for hydrogen production. The reduction step is achieved, for example, by exposing the fuel electrode 21 to a hydrogen atmosphere at a predetermined temperature for a predetermined time. The reducing gas used in the reduction step is not limited to hydrogen, but may be other gases such as methane gas, and the concentration of the reducing gas is also not limited. A reducing gas with a reducing agent concentration of less than 100% by volume may contain, for example, nitrogen gas in addition to hydrogen gas.

[0081] (Explanation of effect) As described above, the air electrode 29 of the above embodiment includes a composite oxide having a perovskite structure as a primary component, a first substance containing sulfur, and a second substance different from the composite oxide as a primary component, the second substance containing at least one of cobalt and iron. The total area occupancy of the first substance containing sulfur and the second substance containing at least one of cobalt and iron in the cross section of the air electrode 29 is greater in a surface region R2 within 10 μm from the surface opposite the solid electrolyte layer 24 than in an interface region R1 within 10 μm from the interface Q on the solid electrolyte layer 24 side. The inventors have found that use of such an air electrode 29 can suppress the occurrence of cracks in the air electrode 29. As a result, a decrease in current density at the thermal neutral point (1.3 V) can be suppressed. Furthermore, as a result, an electrolysis cell 20 capable of operating for a long period of time can be provided. The mechanism by which the air electrode 29 of the above embodiment suppresses the occurrence of cracks in the air electrode 29 is unclear, but the following mechanism is considered. In other words, by adjusting the area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron to the above-mentioned area occupancy, the gaps between the particles of the composite oxide having a perovskite structure are filled, improving sinterability and strengthening the bonding strength between particles in the air electrode 29. The sulfur-containing substance and the substance containing at least one of cobalt and iron do not contribute to the reaction in the air electrode 29. If the total area occupancy of the sulfur-containing substance and the substance containing at least one of cobalt and iron is smaller in the surface region R2 than in the interface region R1, the inactive areas that do not contribute to the reaction in the air electrode 29 are likely to be more prevalent in the interface region R1. This is considered undesirable because it results in a decrease in current density. In particular, because the air electrode functional layer 26 near the interface Q is closely related to current density, it is considered preferable to have fewer inactive areas that do not contribute to the reaction. Furthermore, in the interface region R1, the area containing a large amount of the sulfur-containing substance and the substance containing at least one of cobalt and iron is considered to have fewer cracks as a result of improved sinterability.However, if the interface region R1 contains a large amount of sulfur-containing substances and substances containing at least one of cobalt and iron, the strain between the interface region R1 and the surface region R2, which has a large thermal expansion coefficient, will increase, resulting in an increase in cracks in the surface region R2, which will result in a decrease in current density, which is considered to be undesirable.

[0082] The following describes a test that confirmed that the occurrence of cracks in the air electrode 29 of the above configuration was suppressed.

[0083] (test) In this test, for the SOEC (electrolysis cell 20) according to the above embodiment, several types of test samples (fired bodies) were used, each having different thicknesses of the air electrode functional layer 26 and the air electrode current collecting layer 27. Specifically, as shown in Table 1, 21 levels of samples No. 1 to 21 were prepared, and one test sample was produced for each level. Table 1 shows the results of evaluation of each of samples No. 1 to No. 21 regarding the main component of the air electrode 29, the type of sulfur-containing substance, the type of substance containing at least one of cobalt and iron, the total area occupied by the sulfur-containing substance and the substance containing at least one of cobalt and iron in the surface region R2 of the air electrode 29, the area occupied by the sulfur-containing substance in the surface region R2 of the air electrode 29, the area occupied by the substance containing at least one of cobalt and iron in the surface region R2 of the air electrode 29, the total area occupied by the sulfur-containing substance and the substance containing at least one of cobalt and iron in the interface region R1 of the air electrode 29, the area occupied by the sulfur-containing substance in the interface region R1 of the air electrode 29, the area occupied by the substance containing at least one of cobalt and iron in the interface region R1 of the air electrode 29, the current density at the thermal neutral point, and whether or not cracks occurred.

[0084] In these test specimens, the thickness of the air electrode 29 was constant at 100 μm, the thickness of the fuel electrode 21 was constant at 500 μm, and the thickness of the solid electrolyte layer 24 (8YSZ) was constant at 10 μm. Furthermore, the shape of these test specimens viewed from above was a 10 cm square. The type and amount of sulfur-containing material in the air electrode 29 was adjusted during the manufacture of the air electrode 29. Hydrogen was used as the reducing agent in the reducing gas. The reducing gas with a reducing agent concentration of 100% by volume consisted of only hydrogen. Air was used for the air electrode 29 during the reduction process.

[0085] Using the test specimens prepared in this way, the current density was measured at 1.3 V at 700°C, and all initial performances were 0.75 A / cm 2 More than 1A / cm 2 It was confirmed that the thickness was below 100 μm and that there were no cracks in 10 fields of view in the interface region R1 and surface region R2 of each test piece.

[0086] These test specimens were then subjected to the following thermal cycle electrolysis test using an infrared lamp. Specifically, the test specimens were heated from room temperature (25°C) to 700°C in 10 minutes, then cooled from 700°C to room temperature in 30 minutes. This cycle was repeated 50 times, and the current density at 1.3 V was measured again at 700°C. The results are shown in Table 1. The test specimens that had undergone this thermal cycle electrolysis test were then examined for the presence or absence of cracks in the interface region R1 and the surface region R2 using an electron microscope, with 10 fields of view for each. In the evaluation results, the denominator indicates the total number of test specimens, and the numerator indicates the number of test specimens with cracks. A comprehensive evaluation was then conducted using the current density and the presence or absence of cracks as criteria for judgment.

[0087] (result) The evaluation results are shown in Table 1.

[0088] [Table 1]

[0089] As shown in Table 1, the general formula A1 x A2y BO 3-δ (where 0.9≦x+y<1, δ is the amount of oxygen vacancy), and when the total area occupied by the sulfur-containing substance and the substance containing at least one of cobalt and iron in the cross section of the air electrode 29 was larger in the surface region R2 than in the interface region R1, no cracks were observed in the air electrode 29. Furthermore, it was found that when the total area occupied by the sulfur-containing substance and the substance containing at least one of cobalt and iron in the cross section of the air electrode 29 was 0.1% or more and 10.5% or less in the surface region R2 and 0.02% or more and 4.6% or less in the interface region R1, the current density was higher than in other cases.

[0090] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0091] The electrolysis cell 20 only needs to have the fuel electrode 21, the solid electrolyte layer 24, and the air electrode 29, and the presence or absence of other components, as well as the shape, material, dimensions, etc. of each component can be modified. For example, the configuration of the electrolysis cell 20 may be modified as follows. (1) The shape of the electrolysis cell 20 may be, for example, an anode-supported type, a flat type, a cylindrical type, a flat type, a vertically striped type, a horizontally striped type, a type for a single-end-supported stack, a type for a double-end-supported stack, etc. The cross section of the cell may also be elliptical. (2) The configurations listed as different forms can be combined with each other. [Explanation of symbols]

[0092] 10...electrolysis stack, 11...reaction unit, 12, 13...end plates, 14...bolt, 15a, 15b, 15c, 15d...passage, 16...interconnector, 17...anode frame, 19...cathode frame, 20...electrolysis cell, 21...anode, 22...anode substrate layer, 23...anode functional layer, 24...solid electrolyte layer, 24a...surface, 25...reaction prevention layer, 26...cathode functional layer, 27...air Electrode current collecting layer, 29...air electrode, 30...separator, 31...brazing material, 32...current collector, 33...fuel chamber, 34...current collector, 35...air chamber, 37...opening, 47...cell with separator, 52, 53...terminal plate, 60...hydrogen production device, 61...hot module, 62...vaporizer, 63...heat exchanger, 64...heater, 65...insulation material, 66...condenser, Q...interface, R1...interface region, R2...surface region

Claims

1. General formula A1 ｘ A2 ｙ BO ３－δ (where 0.9≦x+y<1, and δ is the amount of oxygen deficiency), and a fuel electrode; a solid electrolyte layer disposed between the air electrode and the fuel electrode; Equipped with The air electrode is a first substance containing sulfur; a second substance that is different from the composite oxide and contains at least one of cobalt and iron; Including, a total area occupancy of the first material and the second material in a cross section of the air electrode is larger in a surface region within 10 μm from the surface opposite to the solid electrolyte layer side than in an interfacial region within 10 μm from the interface on the solid electrolyte layer side; Solid oxide electrolysis cell.

2. 2. The solid oxide electrolysis cell according to claim 1, The total area occupancy of the first material and the second material in the cross section of the air electrode is in the surface region, greater than or equal to 0.1% and less than or equal to 10.5%; In the interface region, 0.02% or more and 4.6% or less; Solid oxide electrolysis cell.

3. The solid oxide electrolysis cell according to claim 1 or 2, The fuel electrode is supplied with a fuel gas containing water vapor at a rate of 100 to 130 liters / min.cm. ２ ) is supplied and used at a flow rate of Solid oxide electrolysis cell.

4. The solid oxide electrolysis cell according to claim 1 or 2, The air electrode is supplied with a gas containing oxygen at a rate of 30 to 50 liters / min.cm. ２ ) is supplied and used at a flow rate of Solid oxide electrolysis cell.

5. The solid oxide electrolysis cell according to claim 1 or 2, The volume of the air chamber facing the air electrode is 9 cm ３ ~11cm ３ That is, Solid oxide electrolysis cell.

6. The solid oxide electrolysis cell according to claim 1 or 2; and a separator having an opening in the center and disposed on the solid electrolyte layer; Cell with separator.

7. An electrolysis stack comprising a plurality of solid oxide electrolysis cells according to claim 1 or 2 stacked one on top of the other.

8. 8. The electrolytic stack of claim 7 ; a vaporizer that generates water vapor that is supplied to the electrolysis stack; a heat exchanger that exchanges heat with the gas supplied to the electrolysis stack; a heater for heating the electrolysis stack; a thermal insulator in which the electrolysis stack, the vaporizer, the heat exchanger, and the heater are disposed, Hot module.

9. A hydrogen production device comprising the hot module according to claim 8.

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