Air electrode of solid oxide electrolytic cell and use thereof

Abstract

Provided is a technology capable of suppressing the occurrence of cracks in an air electrode and the detaching at an interface between the air electrode and a solid electrolyte layer when using a solid oxide electrolytic cell. This air electrode of a solid oxide electrolytic cell contains a composite oxide having a perovskite structure. In a cross section of the air electrode, the standard deviation value of the atomic concentration of each element of the composite oxide measured by an energy dispersive X-ray spectroscopy at 10 spots in one field of view is 13.5 or less.

Description

Solid oxide electrolysis cell cathode and its applications.

[0001] The present disclosure relates to solid oxide electrolysis cell cathodes and their uses.

[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 above-mentioned 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 in the form of converting 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 the anode, the water vapor is electrolyzed to generate 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.

[0004] JP 2023-080459 A

[0005] Generally, in SOFCs, oxygen is consumed at the fuel electrode during use, causing the gas pressure to decrease. However, in SOECs, oxygen is generated at the air electrode during use, causing the gas pressure to increase, resulting in stresses different from those experienced with SOFCs, which may cause cracks to occur in the air electrode or peeling at the interface between the air electrode and the solid electrolyte layer.

[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 cathode for a solid oxide electrolysis cell. The cathode for the solid oxide electrolysis cell contains a composite oxide having a perovskite structure, and the standard deviation of the atomic concentrations of each element of the composite oxide measured by energy dispersive X-ray spectroscopy at 10 spots within a single field of view on a cross section of the cathode is 13.5 or less. The cathode for the solid oxide electrolysis cell of this aspect can suppress the occurrence of cracks in the cathode and peeling at the interface between the cathode and the solid electrolyte layer during use of the solid oxide electrolysis cell.

[0008] (2) According to one embodiment of the present disclosure, there is provided an air electrode for a solid oxide electrolysis cell. The air electrode for this solid oxide electrolysis cell contains a complex oxide having a perovskite structure, and the standard deviation of the atomic concentrations of each element of the complex oxide measured by energy dispersive X-ray spectroscopy at 10 spots within a single field of view on a cross section of the air electrode is 7.5 or less. The air electrode for a solid oxide electrolysis cell of this embodiment can suppress the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer during use of the solid oxide electrolysis cell.

[0009] (3) According to another aspect of the present disclosure, there is provided a solid oxide electrolysis cell comprising the air electrode according to (1) or (2), an anode, and a solid electrolyte layer disposed between the air electrode and the anode. The solid oxide electrolysis cell of this aspect can suppress the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer during use of the solid oxide electrolysis cell.

[0010] (4) In the solid oxide electrolysis cell described in (3) above, a fuel gas containing water vapor is supplied to the fuel electrode at a rate of 100 to 130 liters / min cm ２ ) may be supplied at a flow rate of 0.1 to 1.5 times the flow rate of the air electrode. According to the solid oxide electrolysis cell of this embodiment, stress is applied to the solid electrolyte layer due to the generation of hydrogen and oxygen during use of the solid oxide electrolysis cell, but the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer can be effectively suppressed during use of the solid oxide electrolysis cell.

[0011] (5) In the solid oxide electrolysis cell according to (3) or (4), the air electrode is supplied with an oxygen-containing gas at a flow rate of 30 to 50 liters / min cm ２ ) may be supplied at a flow rate of 0.1 to 1.5 times the flow rate of the air electrode. According to the solid oxide electrolysis cell of this embodiment, stress is applied to the solid electrolyte layer due to the generation of hydrogen and oxygen during use of the solid oxide electrolysis cell, but the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer can be effectively suppressed during use of the solid oxide electrolysis cell.

[0012] (6) In the solid oxide electrolysis cell according to any one of (3) to (5), 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 embodiment, stress is applied to the solid electrolyte layer due to the generation of hydrogen and oxygen during use of the solid oxide electrolysis cell, but the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer can be effectively suppressed during use of the solid oxide electrolysis cell.

[0013] (7) 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 (3) to (6) above and a separator with a central opening that is disposed on the solid electrolyte layer. The separator-equipped cell of this aspect can suppress the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer during use of the solid oxide electrolysis cell.

[0014] (8) 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 (3) to (6) above. The electrolysis stack of this aspect can suppress the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer during use of the solid oxide electrolysis cells.

[0015] (9) According to another aspect of the present disclosure, there is provided a hot module comprising the electrolysis stack according to (8) above, a vaporizer that generates water vapor to be supplied to the electrolysis stack, a heat exchanger that performs heat exchange with a gas supplied to the electrolysis stack, a heater that heats the electrolysis stack, and a thermal insulator in which the electrolysis 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 and peeling at the interface between the air electrode and the solid electrolyte layer during use of a solid oxide electrolysis cell.

[0016] (10) According to another aspect of the present disclosure, there is provided a hydrogen production device including the hot module according to the above aspect (9). The hydrogen production device of this aspect can suppress the occurrence of cracks in the air electrode and peeling at the interface between the air electrode and the solid electrolyte layer during use of the solid oxide electrolysis cell.

[0017] The present invention can be realized in various forms, for example, in the form of a method for manufacturing a solid oxide electrolysis cell.

[0018] Fig. 1 is a perspective view showing the external configuration of an electrolysis stack according to an embodiment of the present disclosure. Fig. 2 is an exploded schematic view of the electrolysis stack taken along line II-II in Fig. 1. Fig. 3 is a schematic top view of a cell with a separator. Fig. 4 is a block diagram of a hydrogen production device. Fig. 5 is a flow diagram illustrating a method for manufacturing an air electrode material using a solid-phase method. Fig. 6 is a flow diagram illustrating a method for manufacturing an air electrode material using a liquid-phase method.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 from outside the electrolysis stack 10 to a fuel chamber 33 (described later) of the reaction unit 11, a passage 15b through which gas exits from the fuel chamber 33 to the outside of the electrolysis stack 10, a passage 15c through which gas enters from outside the electrolysis stack 10 to an air chamber 35 (described later) of the reaction unit 11, and a passage 15d through which gas exits from the air chamber 35 to the outside of the electrolysis stack 10, respectively.

[0023] 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 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.

[0024] 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 through the interconnector 16, the anode frame 17, the separator 30, and the cathode frame 19. The electrolytic cell 20 will be described later.

[0025] The separator 30 is a substantially rectangular frame-shaped member provided with an opening 37 that is larger than the air electrode 29 (described later). 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 later) with a brazing material 31, avoiding the air electrode 29.

[0026] 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 an example of a material for the interconnectors 16.

[0027] The anode 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 anode frame 17. The anode frame 17 surrounds the electrolysis cell 20 and a current collector 32 provided in the center of the interconnector 16.

[0028] The current collector 32 electrically connects the anode 21 and the interconnector 16. An example of a material for the current collector 32 is a gas-permeable porous body made of a metal such as Ni. A fuel chamber 33 surrounded by the interconnector 16, the anode frame 17, and the separator 30 is formed inside the anode frame 17.

[0029] 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 limitative. It is of course possible for the current collector 34 to be a member separate from the interconnector 16.

[0030] 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.

[0031] A hydrogen production device 60 including the 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.

[0032] 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 disposed inside a thermal insulator 65 to reduce heat radiation.

[0033] 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 that 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 the heater 64, and is supplied to the air chamber 35 of the electrolysis stack 10.

[0034] 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.

[0035] 2 , the electrolysis cell 20 includes a cathode 29, an anode 21, and a solid electrolyte layer 24 disposed between the cathode 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 cathode 29, although the reaction prevention layer 25 may be omitted. In this embodiment, the cathode 29 includes, in order from closest to the solid electrolyte layer 24, a cathode functional layer 26 and an cathode current collecting layer 27. The shape of the electrolysis cell 20 as viewed from above is not particularly limited, and 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.

[0036] 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 sintered body made of nickel and YSZ (yttria stabilized zirconia). Examples of ceramic materials having oxygen ion conductivity include YSZ (yttria stabilized zirconia), ScSZ (scandia stabilized zirconia), and (Gd, Ce)O. ２ That is, GDC (Gadolinium doped ceria), (Sm, Ce)O ２ SDC (Samarium doped ceria) and LaGaO ３ (lanthanum gallate), etc. The ceramic material contained in the anode may be one type or two or more types. The thickness of the anode 21 is not particularly limited, but is, for example, 0.3 to 3 mm. In this embodiment, the thickness of the anode 21 is the greatest among the thicknesses of the components of the electrolytic cell 20, and the anode 21 functions as a support (support substrate, the member with the highest rigidity) for the electrolytic cell 20.

[0037] The solid electrolyte layer 24 is a dense, thin-plate 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. An example of a perovskite-type oxide is a lanthanum gallate-based oxide 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.

[0038] The air electrode 29 contains a complex oxide having a perovskite structure. The composition of the complex oxide is represented by the general formula ABO ３However, the ratio of A, B, and O does not necessarily have to be 1:1:3. ３ The ideal unit lattice of a complex oxide having a perovskite structure represented by the formula (1) is a cube, with element A located at a corner of the unit lattice, element B located at a body-center position of the unit lattice, and element oxygen located at a face-center position of the unit lattice. In the present disclosure, the corner position of the unit lattice where element A is located is referred to as the "A site," and the body-center position of the unit lattice where element B is located is referred to as the "B site."

[0039] The A site may contain at least one of La and Sr. A specific example of such a composite oxide is, for example, LSCF, i.e., (La,Sr)(Co,Fe)O, which is the material of the air electrode 29. ３ , LSF, i.e. (La,Sr)FeO ３ , LSC i.e. (La,Sr)CoO ３ , LNF, that is, La(Ni,Fe)O ３ , SSC, i.e. (Sm,Sr)CoO ３ These composite oxides are substances that have both oxygen ion conductivity and electronic conductivity, and are also called mixed conductive materials.

[0040] The air electrode 29 can contain a composite oxide as a "main component." The phrase "composition X contains substance Y as a "main component"" means that substance Y preferably accounts for 60 mass % or more, more preferably 70 mass % or more, and even more preferably 90 mass % or more of the entire composition X. The air electrode 29 may contain components other than the composite oxide. The material of the air electrode 29 may be a powder (e.g., average particle size of about 0.1 μm to 5 μm) or a crushed material (e.g., average particle size of about 5 μm to 500 μm), or may be a lump larger than the crushed material.

[0041] The cathode current collecting layer 27 is made of a material having the general formula ABO ３The cathode functional layer 26 includes a complex oxide having a perovskite structure represented by the formula (I). Examples of such complex oxides include, but are not limited to, LSCF, LSF, LSC, LNF, and SSC. The cathode functional layer 26 may contain a component other than the complex oxide contained in the cathode current collecting layer 27. For example, the cathode functional layer 26 may be composited with a material (e.g., ceria or zirconia) of the solid electrolyte layer 24 described below. The thickness of the cathode current collecting layer 27 is not particularly limited, but may be, for example, 5 to 100 μm. The thickness of the cathode functional layer 26 is not particularly limited, but may be, for example, 5 to 20 μm.

[0042] Here, it is preferable that the composition distribution of the complex oxide contained in the air electrode 29 has high uniformity. Specifically, the standard deviation value of the atomic concentration of each element of the complex oxide measured by EDS (Energy Dispersive X-ray Spectroscopy) at 10 spots within one field of view on the cross section of the air electrode 29 is 13.5 or less, more preferably 7.5 or less. Specifically, when the atomic concentrations of each element contained in the A site are obtained and then the standard deviation value of the atomic concentrations is obtained, the standard deviation value obtained at the A site is 13.5 or less, more preferably 7.5 or less. Furthermore, when the atomic concentrations of each element contained in the B site are obtained and then the standard deviation value of the atomic concentrations is obtained, the standard deviation value obtained at the B site is 13.5 or less, more preferably 7.5 or less.

[0043] For example, suppose that n elements, A1, A2, A3, ... An, are contained in the A site. When the standard deviation of the atomic concentration of each element is obtained based on the atomic concentrations obtained from 10 spots, if the standard deviation of the atomic concentration of element A1 is larger than the standard deviations of A2 to An, the standard deviation of element A1 is 13.5 or less, more preferably 7.5 or less. The same applies to the elements contained in the B site.

[0044] As with the air electrode current collecting layer 27, even if the air electrode functional layer 26 contains components other than the complex oxide, it is sufficient that the standard deviation of the atomic concentrations of elements contained in the A site and B site of the complex oxide is 13.5 or less, more preferably 7.5 or less. Therefore, when the air electrode functional layer 26 is composed of a composite of the complex oxide and the material of the solid electrolyte layer 24, it is sufficient to select and observe only the complex oxide that is exposed in the cross section of the air electrode functional layer 26.

[0045] Note that one field of view refers to any one field of view, and can be observed in a range observed at a magnification of 100x to 5000x using an electron microscope such as an SEM (Scanning Electron Microscope) or an EPMA (Electron Probe Microanalyzer). Note that, when the atomic concentration distribution described below is evaluated based on observation at a magnification of less than 100x, it tends to be difficult to determine the uniformity of the distribution of each element in the microscopic range targeted by the present disclosure. On the other hand, when the atomic concentration distribution is evaluated based on observation at an excessively large magnification of more than 5000x, the observation range becomes too narrow, increasing the likelihood of observing only non-uniform regions or only uniform regions.

[0046] The analysis spot size of each of the 10 spots can be 1 μm or less. The positions of the 10 spots can be selected according to 10 concentration levels set based on the atomic concentration distribution measured by, for example, EPMA. The 10 concentration levels are preferably set across substantially the entire range of the atomic concentration distribution. The 10 concentration levels can be set, for example, by dividing the range between the maximum and minimum values ​​of the characteristic X-ray intensity within the field of view into 10 parts.

[0047] Furthermore, the air electrode 29 preferably contains additives (P, Cr, B, and Si) at a predetermined mass ratio relative to the entire complex oxide. Specifically, the air electrode 29 preferably contains 1 ppm to 500 ppm of P, more preferably 1 ppm to 50 ppm of P, and even more preferably 1 ppm to 30 ppm, relative to the mass ratio of the entire complex oxide. The air electrode 29 preferably contains 1 ppm to 500 ppm of Cr, and even more preferably 1 ppm to 100 ppm, relative to the mass ratio of the entire complex oxide. The air electrode 29 preferably contains 1 ppm to 500 ppm of B, more preferably 1 ppm to 50 ppm of B, and even more preferably 1 ppm to 10 ppm. The air electrode 29 preferably contains 1 ppm or more and 500 ppm or less of Si, more preferably 1 ppm or more and 100 ppm or less, by mass ratio of the entire composite oxide. The air electrode 29 may contain additives other than P, Cr, B, and Si. Examples of additives other than P, Cr, B, and Si include small amounts of Na, Mg, Al, Ca, Sc, Ti, Ni, Zn, Y, Zr, Ba, Ce, Gd, etc. The content of these additives can be measured, for example, by analyzing the electrode material using GDMS (glow discharge mass spectrometry).

[0048] Due to the difference in thermal expansion coefficient, there is a risk that the air electrode 29 may peel off from the solid electrolyte layer 24. To prevent this, there is a technique of 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, the composite material may peel off from the solid electrolyte layer 24. ３ In this case, for example, gadolinium-doped ceria (GDC) or samarium-doped ceria (SDC) is used as the mixed electrolyte material. Preferably, an intermediate layer in which the electrolyte and the composite oxide are mixed in a ratio of about 1:1 can be disposed between the air electrode 29 and the solid electrolyte layer 24. This intermediate layer is the air electrode functional layer 26.

[0049] In order to prevent the occurrence of a phenomenon in which the YSZ in the solid electrolyte layer 24 reacts with the strontium in the cathode functional layer 26 in the electrolytic cell 20 during cell fabrication or operation of the SOEC, resulting in an increase in electrical resistance, a reaction prevention layer 25 may be formed between the solid electrolyte layer 24 and the cathode functional layer 26. The reaction prevention layer 25 is not particularly limited, but is preferably, for example, a dense, thin-plate sintered body made of ceria. Examples of ceria include, but are not limited to, gadolinium-doped ceria (GDC) and samarium-doped ceria (SDC).

[0050] 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, and the chemical reactions shown in the following formulas (1) and (2) occur. As a result, hydrogen is generated from the fuel electrode 21, and oxygen is generated from the air electrode 29. H ２ O + 2e － →H ２ +O ２－ (Location: Fuel electrode 21) …(1) O ２－ → (1 / 2)・O ２ +2e － (At: air electrode 29) ... (2)

[0051] 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 a current to flow. Then, hydrogen gas generated from the fuel electrode 21 is collected.

[0052] 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 In the case of co-electrolysis, water vapor and CO may be used as fuel gases. ２In a stack in which cells are stacked in multiple stages, the amount of fuel gas to be introduced by a blower, pump, etc. naturally increases in proportion to the number of cells stacked.

[0053] The air electrode 29 is supplied with a gas containing oxygen at a flow rate of, for example, 20 to 60 liters / min.cm. ２ ) and may be used at a flow rate of 30 to 50 liters / (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 to the air electrode side by a blower, pump, etc. naturally increases in proportion to the number of cells stacked.

[0054] 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, 9 cm ３ ~11cm ３ Here, the volume of the air chamber 35 facing the air electrode 29 refers to the volume per cell, excluding the volume occupied by the current collecting members and the like.

[0055] (Manufacturing Method) Next, an example of a manufacturing method for the electrolysis cell 20 will be described.

[0056] (Preparation of Anode Green Sheet) 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 to a mixed powder of NiO powder and YSZ powder, 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. During the firing process described below, the organic beads are burned, and the locations where the organic beads were present become pores. The resulting slurry is thinned by a doctor blade method to prepare an anode green sheet of 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.

[0057] (Preparation of Green Sheet for Solid Electrolyte Layer) To the YSZ powder, 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 obtained slurry is thinned by a doctor blade method to prepare a green sheet for the solid electrolyte layer of a predetermined thickness (for example, 10 μm).

[0058] (Fabrication of a laminate of the solid electrolyte layer 24 and the anode 21) The anode green sheet and the solid electrolyte layer green sheet are attached together and degreased at a predetermined temperature (e.g., about 280°C). The degreased green sheet laminate is then fired at a predetermined temperature (e.g., about 1350°C). This produces a laminate of the solid electrolyte layer 24 and the anode 21.

[0059] 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, forming a green body for the solid electrolyte layer 24. This green body stack is then co-sintered in air in an electric furnace (in an oxygen-containing atmosphere) at, for example, 1350°C to form a green body for 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.

[0060] (Formation of Reaction Preventive Layer 25) Next, the reaction preventive 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 preventive layer. The obtained paste for the reaction preventive layer is applied by, for example, screen printing to the surface of the above-mentioned laminate of the solid electrolyte layer 24 and the anode 21 on the side of the solid electrolyte layer 24, and then fired at, for example, 1180°C. This forms the reaction preventive layer 25, and a laminate of the anode 21, the solid electrolyte layer 24, and the reaction preventive layer 25 (hereinafter referred to as the "intermediate laminate") is produced.

[0061] (Formation of Air Electrode Functional Layer 26) Next, the air electrode functional layer 26 is formed. First, LSCF powder, GDC powder, and trace amounts of additives are mixed with polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent, and the viscosity is adjusted to prepare an air electrode functional layer paste. The trace amounts of additives preferably contain 1 ppm to 500 ppm of P, 1 ppm to 500 ppm of Cr, 1 ppm to 500 ppm of B, and 1 ppm to 500 ppm of Si. Next, the prepared air electrode functional layer paste 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.

[0062] (Formation of Air Electrode Current Collecting Layer 27) Next, the air electrode current collecting layer 27 is formed. First, LSCF powder and trace amounts of additives are mixed with polyvinyl alcohol as an organic binder, butyl carbitol as an organic solvent, and organic beads as a pore-forming material, and the viscosity is adjusted to prepare an air electrode current collecting layer paste. The trace amounts of additives preferably contain 1 ppm to 500 ppm of P, 1 ppm to 500 ppm of Cr, 1 ppm to 500 ppm of B, and 1 ppm to 500 ppm of Si. Next, the prepared air electrode current collecting layer paste is applied to the surface of the intermediate laminate facing the air electrode functional layer 26 by, for example, screen printing and dried, and the intermediate laminate with the applied current collecting layer paste is fired at a predetermined firing temperature (for example, 1100°C). Thereafter, the air electrode current collecting layer 27 is formed by this firing step, and a laminate of the fuel electrode 21, the solid electrolyte layer 24, the reaction prevention layer 25, the air electrode functional layer 26, and the air electrode current collecting layer 27, i.e., the single electrolytic cell 20, is produced.

[0063] 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 having a reducing agent concentration of less than 100% by volume may contain, for example, nitrogen gas in addition to hydrogen gas.

[0064] (Method for Manufacturing the Material of the Air Electrode 29) An example of a method for manufacturing the material of the air electrode 29 will be described below. Methods for obtaining a composite oxide include, for example, a solid phase method and a liquid phase method. Examples of liquid phase methods include the citric acid method, the Pechini method, and a coprecipitation method.

[0065] The "solid phase method" is a technique in which raw materials (powders) containing constituent elements are mixed in a predetermined ratio, the resulting mixture is fired, and then pulverized to obtain the target material.

[0066] The "liquid phase method" is a technique for obtaining a target material through the following steps: (i) dissolving raw materials containing constituent elements in a solution; (ii) obtaining a precursor of the target material from the solution by precipitation or the like; and (iii) drying, firing, and pulverizing the resulting material.

[0067] Hereinafter, the case where the material for the air electrode 29 is produced by the solid phase method and the case where the material for the air electrode 29 is produced by the liquid phase method will be described in order with reference to the drawings.

[0068] (Method for Producing the Material of the Air Electrode 29 Using a Solid-Phase Method) FIG. 5 is a flow diagram for explaining a method for producing the material of the air electrode 29 using a solid-phase method.

[0069] First, in step P101, raw materials are prepared according to the type of composite oxide. When LSCF is to be produced as the composite oxide, for example, La ２ O ３ , SrCO ３ , Co ３ O ４ and Fe ２ O ３ Prepare the following. ２ O ３ The volume average particle size of SrCO is preferably 0.1 μm to 0.7 μm. ３ The volume average particle size of Co is 0.1 μm to 0.5 μm. ３ O ４ The volume average particle size of is 0.1 μm to 1.0 μm, Fe ２ O ３ The volume average particle size of the raw material is preferably 0.1 μm to 0.8 μm. Furthermore, it is preferable to control the particle size distribution of the raw material. Specifically, it is desirable to remove coarse particles of 20 μm or more in advance using an air classifier or the like. Removing coarse particles is effective for homogenization during mixing and synthesis in the subsequent steps. As a result, it is possible to adjust the standard deviation of the atomic concentration of each element in the composite oxide.

[0070] Next, in process P102, the raw materials are classified. Specifically, the specific surface area of ​​each raw material is adjusted by classifying the raw materials using, for example, an air classifier. When LSCF is produced as the composite oxide, La ２ O３ The specific surface area of ​​1m ２ / g to 5m ２ / g, and SrCO ３ The specific surface area of ​​1m ２ / g~7m ２ / g, Co ３ O ４ The specific surface area of ​​1m ２ / g~7m ２ / g, Fe ２ O ３ The specific surface area of ​​1m ２ / g to 10m ２ It is preferable to adjust the value to / g.

[0071] Next, in process P103, 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 adding them to a pot mill together with balls (e.g., alumina or zirconia balls), rotating the pot mill in a dry state for a predetermined time (10 to 120 hours), and then adding 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) to 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. The balls preferably have a diameter of 0.5 to 5 mm, and are preferably adjusted to approximately 0.5 to 3 times the mass of the raw material powders.

[0072] After the wet mixing, a drying treatment is required to remove the solvent, which can be carried out using, for example, a tray dryer, a band dryer, or a spray dryer.

[0073] Next, in process P104, 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 also consist of two steps: crude firing and main firing, or two steps: crude firing and main firing, or a process consisting of main firing only. 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.

[0074] (Crude Firing) In the crude firing step, it is preferable to raise the temperature of the firing furnace to the target firing temperature (300 to 500°C) at a temperature increase rate of 20 to 800°C / hour. The firing temperature during crude firing is not particularly limited, but is preferably 300 to 500°C, and more preferably 350 to 450°C, for example. By setting the temperature at 300°C or higher, it is possible to suppress the residue of carbon components. Furthermore, by setting the temperature at 500°C or lower, it is possible to suppress the segregation of constituent elements. The firing time for crude firing is not particularly limited, but is preferably 4 to 24 hours, and more preferably 8 to 20 hours, for example. By setting the firing time at 4 hours or longer, it is possible to suppress the residue of carbon components. The atmosphere in the firing furnace during crude firing is preferably an oxygen-containing atmosphere, and more preferably air (atmospheric air) or an atmosphere with an oxygen concentration of 20% by volume or less. By setting the oxygen concentration to 20% by volume or less, the carbon component in the raw material mixed powder is burned and the oxidation reaction proceeds partially, which makes it possible to suppress localization of the constituent elements of the product.

[0075] Next, the oxide obtained in the crude firing step is crushed. Crushing is generally carried out in a dry manner using a crusher such as a pot mill, jet mill, or atomizer. The volume average particle size after crushing is preferably 5 to 50 μm, more 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. By doing so, it is possible to adjust the standard deviation of the atomic concentration of each element in the composite oxide.

[0076] (Pre-firing) Subsequently, the crushed coarsely fired powder is pre-fired at a pre-firing temperature (500 to 800°C). In the pre-firing step, it is preferable to raise the temperature of the firing furnace to the target firing temperature at a heating rate of 100 to 400°C / hour. The pre-firing temperature is not particularly limited, but is preferably 500 to 800°C, and more preferably 600 to 800°C. A temperature of 500°C or higher can prevent carbon components from remaining. Furthermore, by setting the temperature to 800°C or lower, excessive sintering of the fired powder can be prevented. The firing time is not particularly limited, but is preferably 4 to 24 hours, and more preferably 8 to 20 hours. A firing time of 4 hours or more can prevent carbon components from remaining. The atmosphere in the firing furnace during pre-firing is preferably the same oxygen-containing atmosphere as that used during coarse firing.

[0077] Next, the oxide obtained by the calcination is crushed in the same manner as after the coarse calcination. Crushing is preferably performed using a grinder such as a pot mill, jet mill, or atomizer, and is generally performed in a dry manner. The volume average particle size after crushing is preferably 5 to 30 μm, more 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. By doing so, it is possible to adjust the standard deviation of the atomic concentration of each element in the composite oxide.

[0078] (Firing) The calcined powder is then fired at a firing temperature (800-1400°C). In this firing step, the temperature of the firing furnace is preferably increased to the target firing temperature at a rate of 50-800°C / hour, more preferably 100-400°C / hour. Furthermore, by setting the heating rate to 800°C / hour or less, the chemical changes of the reactants at each temperature do not proceed sufficiently, resulting in the target firing temperature being reached in a non-uniform state, thereby preventing the generation of by-products in the fired product. The firing temperature is not particularly limited, but is preferably 800-1400°C, and more preferably 1000-1400°C. By setting the temperature within the 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 4-24 hours, and more preferably 5-20 hours. By setting the reaction 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 crystal phase from not being obtained even if a single crystal phase is obtained. In this way, it is possible to adjust the standard deviation value of the atomic concentration of each element in the composite oxide. Furthermore, by setting the reaction time to 24 hours or less, it is possible to prevent a decrease in productivity.

[0079] The atmosphere in the firing furnace during the main firing is preferably an oxygen-containing atmosphere similar to that used during the crude firing or pre-firing. 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 not being produced. Next, the oxide obtained by the main firing is crushed in the same manner as after the crude firing. Crushing is generally performed dry using a grinder such as a pot mill, jet mill, or atomizer. The volume average particle size of the crushed powder is preferably 5 to 20 μm, more 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. This allows the standard deviation of the atomic concentration of each element in the composite oxide to be adjusted.

[0080] Next, in process P105, the synthesized aggregated material for the air electrode 29 is pulverized. Like the disintegration, pulverization is generally performed dry using a pulverizer such as a pot mill, jet mill, or atomizer. When a pot mill is used, 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 used to adjust the particle size.

[0081] 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.

[0082] Next, in process P106, 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 value to / g.

[0083] (Method for Producing the Material of the Air Electrode 29 Using a Liquid-Phase Method) FIG. 6 is a flow diagram for explaining a method for producing the material of the air electrode 29 using a liquid-phase method.

[0084] First, in step P201, raw materials according to the type of composite oxide are prepared. When LSCF as a composite oxide is produced by the coprecipitation method or the citric acid method, La(NO ３ ) ３ ・6H ２ O, Sr(NO ３ ) ２ , Co(NO ３ ) ３ ・9H ２ O and Fe(NO ３ ) ３ ・9H ２ Prepare La(NO ３ ) ３ ・6H ２ The volume average particle size of O is preferably 0.3 μm to 0.6 μm, and Sr(NO ３ ) ２The average particle size of Co(NO ３ ) ３ ・9H ２ The average particle size of O is 0.2 μm to 0.5 μm, and Fe(NO ３ ) ３ ・9H ２ The average particle size of LaO is preferably 0.3 μm to 0.8 μm. When LSCF is produced by the Pechini method, LaO having the above average particle size is preferably used. ２ O ３ , SrO ３ , Co ３ O ４ and Fe(NO ３ ) ３ ・9H ２ O is prepared. Furthermore, it is preferable to control the particle size distribution of the raw materials. Specifically, it is desirable to remove coarse particles of 15 μm or more in advance using an air classifier or the like. Removal of coarse particles is effective for homogenization during mixing and synthesis in the subsequent steps.

[0085] Next, in process P202, each raw material is classified. Specifically, for example, the specific surface area of ​​each raw material is adjusted by classification using an air classifier. When LSCF as a composite oxide is produced by the coprecipitation method or the citric acid method, La(NO ３ ) ３ ・6H ２ The specific surface area of ​​O is 2m ２ / g~8m ２ / g, and Sr(NO ３ ) ２ The specific surface area of ​​1m ２ / g to 5m ２ / g, Co(NO ３ ) ３ ・9H ２ The specific surface area of ​​O is 2m ２ / g to 5m ２ / g, Fe(NO ３ ) ３ ・9H ２ The specific surface area of ​​O is 3m ２ / g to 10m ２ It is preferable to adjust the value to / g.

[0086] Next, in process P203, the raw materials are mixed at a predetermined mixing ratio. Specifically, when LSCF is produced by the coprecipitation method, the raw materials are dissolved in pure water to prepare a 0.2 M aqueous solution, and then a nitrate aqueous solution is added while stirring the precipitant. When LSCF is produced by the citric acid method, the raw materials are dissolved in pure water, and citric acid is added until all the metals are precipitated, and the mixture is heated in a water bath at approximately 60°C and then dehydrated to adjust the viscosity. When LSCF is produced by the Pechini method, nitrate aqueous solutions of the raw materials are prepared and mixed together, and then citric acid and ethylene glycol are added.

[0087] Next, in step P204, the aqueous solution prepared in step P203 is dried. In the coprecipitation method, the aqueous solution can be dried under vacuum at about 110°C, in the citric acid method, the aqueous solution can be dried at about 70°C, and in the Pechini method, the aqueous solution can be dried at about 200°C.

[0088] Next, in process P205, the dried raw material is fired to synthesize the material for the air electrode 29. Details of this process are the same as those of process P104 above.

[0089] Next, in process P206, the synthesized aggregate material for the air electrode 29 is pulverized, and in process P207, the pulverized material for the air electrode 29 is classified. Details of process P206 are the same as those of P105 above, and details of process P207 are the same as those of P106 above.

[0090] The present inventors have found that an air electrode 29 containing a composite oxide having a perovskite structure, in which the standard deviation of the atomic concentration of each element in the composite oxide measured by energy dispersive X-ray spectroscopy at 10 spots within one field of view on a cross section of the air electrode is 7.5 or less, can suppress the occurrence of cracks in the air electrode 29 and peeling at the interface between the air electrode 29 and the solid electrolyte layer 24 during use of a solid oxide electrolysis cell. As a result, the durability of the electrolysis cell 20 can be improved. Although the mechanism behind this is unclear, it is thought that the closer the composite oxide contained in the air electrode 29 is to the theoretical composition ratio, the better the crystallinity and structural stability, and therefore the more likely it is that the effects of composition changes and thermal cycles can be suppressed. Examples of methods for making the standard deviation of the atomic concentration of each element in the composite oxide 7.5 or less include (i) using a highly pure raw material, (ii) using a material with a small volume average particle size and a narrow particle size distribution, (iii) controlling the volume average particle size during firing as described above, and (iv) slowly increasing the temperature during firing and sintering for a long period of time. Below, we will explain a test that confirmed the relationship between the standard deviation of the atomic concentration of each element and the presence or absence of cracks.

[0091] (Test) In this test, multiple types of test samples (sintered bodies) were prepared for the electrolytic cell according to the above embodiment. Specifically, 14 test samples were prepared, as shown in Table 2. Of samples No. 1 to No. 14, the measurement results of the concentration at the cross section of the air electrode for sample No. 1 as an example, and the calculation results of the average value and standard deviation are shown in Table 1.

[0092]

[0093] The evaluation results are shown in Table 2. Specifically, for each of Samples No. 1 to No. 14, Table 2 lists the standard deviation of the atomic concentration of each element, the content of the additive in the composite oxide, the current density at the thermal neutral point after the thermal cycle test, and the presence or absence of peeling or cracking.

[0094]

[0095] In these test specimens, the thickness of the fuel electrode 21 (NiO-YSZ) was constant at 400 μm, the thickness of the solid electrolyte layer 24 (8YSZ) was constant at 10 μm, and the thickness of the air electrode 29 (LSCF) was constant at 100 μm. Furthermore, when viewed from above, these test specimens had a shape of a 10 cm square.

[0096] Hydrogen was used as the reducing agent in the reducing gas. The reducing gas with a reducing agent concentration of 100% by volume was composed of only hydrogen. Air was used on the air electrode side during the reduction treatment.

[0097] Using the electrolytic cell thus prepared, the current density at 1.3 V was measured at 700°C.

[0098] A thermal cycle test was conducted on this cell using an infrared lamp. The cell was heated to 700°C in 10 minutes and then cooled to room temperature in 30 minutes. This thermal cycle test was repeated 50 times, and the current density at 1.3 V was measured again at 700°C. The current density at the time of the re-measurement was 0.85 A / cm, which is the reference value. ２ If the above is indicated, it is marked as "◎", and if it is 0.75 A / cm ２ If the result was above 10%, it was evaluated as "Good", and if it was below 10%, it was evaluated as "Poor". After the test, the electrolytic cell was observed using a microscope for cracks on the surface of the air electrode and for peeling at the interface between the air electrode and the electrolyte layer.

[0099] The results in Table 2 show that when the standard deviation of the element concentrations at the A site and the B site in the composite oxide is 13.5 or less, no peeling or cracking is observed. However, although samples Nos. 3, 7, 13, and 14 were evaluated as "Good" due to the low current density, it is more preferable that the standard deviation be 7.5 or less because there is a risk of small peeling or cracking. It was also found that the liquid-phase method tends to have a much smaller standard deviation than the solid-phase method. This is thought to be because the liquid-phase method uses a solution containing each component, which makes mixing easier than the solid-phase method, which involves mixing powders.

[0100] 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.

[0101] The electrolysis cell only needs to have the anode 21, the solid electrolyte layer 24, and the cathode 29, and the presence or absence of other components, as well as the shape, material, and dimensions of each component, can be modified. For example, the configuration of the electrolysis cell can be modified as follows: (1) The shape of the electrolysis cell can be, for example, anode-supported, flat, cylindrical, oblate, vertically striped, horizontally striped, for a single-end-supported stack, or for a double-end-supported stack. The cross section of the cell can also be elliptical. (2) The configurations listed as different forms can be combined with each other.

[0102] 10...electrolysis stack, 11...reaction unit, 12, 13...end plates, 14...bolt, 15a, 15b, 15c, 15d...passage, 16...interconnector, 17...fuel electrode frame, 19...cathode frame, 20...electrolysis cell, 21...fuel electrode, 24...solid electrolyte layer, 24a...surface, 25...reaction prevention layer, 26...cathode functional layer, 27...cathode current collecting layer, 29...cathode, 30...separator, 31...brazing material, 32...current collector, 33...fuel chamber, 34...current collector, 35...air chamber, 37...openings 37, 47...cell with separator, 52, 53...terminal plates, 60...hydrogen production device, 61...hot module, 62...vaporizer, 63...heat exchanger, 64...heater, 65...insulation material, 66...condenser

Claims

1. An air electrode for a solid oxide electrolysis cell, comprising a complex oxide having a perovskite structure, wherein the standard deviation of the atomic concentration of each element of the complex oxide measured by energy dispersive X-ray spectroscopy at 10 spots within one field of view in a cross section of the air electrode is 13.5 or less.

2. An air electrode for a solid oxide electrolysis cell, comprising a complex oxide having a perovskite structure, wherein the standard deviation of the atomic concentration of each element of the complex oxide measured by energy dispersive X-ray spectroscopy at 10 spots within one field of view on a cross section of the air electrode is 7.5 or less.

3. A solid oxide electrolysis cell comprising: an air electrode according to claim 1 or 2; an anode; and a solid electrolyte layer disposed between the air electrode and the anode.

4. In the solid oxide electrolysis cell according to claim 3, the fuel electrode is supplied with a fuel gas containing water vapor at a flow rate of 100 to 130 liters / min.cm ２ 3. A solid oxide electrolysis cell in which the electrolysis gas is supplied with a flow rate of 1000 .mu.m.

5. In the solid oxide electrolysis cell according to claim 3, the air electrode is supplied with an oxygen-containing gas at a flow rate of 30 to 50 liters / min.cm ２ 3. A solid oxide electrolysis cell in which the electrolysis gas is supplied with a flow rate of 1000 .mu.m.

6. In the solid oxide electrolysis cell according to claim 3, the volume of the air chamber facing the air electrode is 9 cm ３ ~11cm ３ A solid oxide electrolysis cell.

7. A cell with a separator, comprising: the solid oxide electrolysis cell according to claim 3; and a separator with a central opening disposed on the solid electrolyte layer.

8. An electrolysis stack comprising a plurality of solid oxide electrolysis cells according to claim 3 stacked together.

9. A hot module comprising: an electrolytic stack according to claim 8; a vaporizer that generates water vapor to be supplied to the electrolytic stack; a heat exchanger that exchanges heat with a gas to be supplied to the electrolytic stack; a heater for heating the electrolytic stack; and a thermal insulation material in which the electrolytic stack, the vaporizer, the heat exchanger and the heater are disposed.

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