Solid oxide electrolyzer cell and use of same

Abstract

The present invention provides technology that makes it possible, during use of a solid oxide electrolyzer cell, to suppress separation at the interface of an air electrode and a solid electrolyte layer and to suppress a decrease in current density. A solid oxide electrolyzer cell according to the present invention comprises an air electrode, a fuel electrode, and a solid electrolyte layer disposed between the air electrode and the fuel electrode, wherein the air electrode contains ZrO2 and a composite oxide that has a perovskite structure represented by general formula ABO3, and the content of ZrO2 is 1×10-3 to 5×10-1 mass% with respect to the entirety of the air electrode.

Description

Solid oxide electrolysis cells and their uses

[0001] The present disclosure relates to solid oxide electrolysis cells 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, resulting in a drop in gas pressure, but in SOECs, oxygen is generated at the air electrode during use, resulting in an increase in gas pressure, which causes stress different from that in SOFCs and may lead to peeling at the interface between the air electrode and the solid electrolyte layer.In addition, generally, technology to suppress the drop in current density is desired for SOECs.

[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, comprising a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode is a solid oxide electrolysis cell having a general formula ABO ３ and a composite oxide having a perovskite structure represented by ZrO ２ and ZrO ２ The content of the cathode is 1×10 －３ Mass% or more 5×10 －１ According to the solid oxide electrolysis cell of this embodiment, during use of the solid oxide electrolysis cell, peeling at the interface between the air electrode and the solid electrolyte layer can be suppressed, while a decrease in current density can be suppressed.

[0008] (2) In the solid oxide electrolysis cell described in (1) above, the air electrode has a Zr content of 7.4 × 10 with respect to the entire air electrode. －４ Mass% or more 3.7 x 10 －１ The solid oxide electrolysis cell of this embodiment can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0009] (3) According to one aspect of the present disclosure, there is provided a solid oxide electrolysis cell, comprising a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode is a solid oxide electrolysis cell having a general formula ABO ３ and Zr, and the content of Zr is 7.4 × 10 with respect to the entire cathode. －４ Mass% or more 3.7 x 10 －１ According to the solid oxide electrolysis cell of this embodiment, during use of the solid oxide electrolysis cell, peeling at the interface between the air electrode and the solid electrolyte layer can be suppressed, while a decrease in current density can be suppressed.

[0010] (4) In the solid oxide electrolysis cell according to any one of (1) to (3) above, the A site of the composite oxide may contain an atom of at least one of La and Sr. The solid oxide electrolysis cell of this configuration can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0011] (5) In the solid oxide electrolysis cell according to any one of (1) to (4) above, the B site of the composite oxide may contain at least one atom of Co and Fe. The solid oxide electrolysis cell of this configuration can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0012] (6) In the solid oxide electrolysis cell according to any one of (1) to (5), the air electrode has an air electrode functional layer on the side of the solid electrolyte layer, and the air electrode functional layer is a metal oxide having a general formula ABO ３ a composite oxide having a perovskite structure represented by the formula: ２ According to the solid oxide electrolysis cell of this embodiment, during use of the solid oxide electrolysis cell, peeling at the interface between the air electrode and the solid electrolyte layer can be further suppressed, while a decrease in current density can be further suppressed.

[0013] (7) In the solid oxide electrolysis cell according to any one of (1) to (6) 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 1.0 MPa. The solid oxide electrolysis cell of this aspect can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0014] (8) In the solid oxide electrolysis cell according to any one of (1) to (7) above, 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 MPa. The solid oxide electrolysis cell of this aspect can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0015] (9) In the solid oxide electrolysis cell according to any one of (1) to (8) above, a fuel gas containing water vapor is supplied to the anode at a rate of 100 to 130 liters / min cm ２ The air electrode is supplied with a gas containing oxygen at a flow rate of 30 to 50 liters / (min cm ２ ) may be supplied at a flow rate of 0.1 to 1.0 MPa. The solid oxide electrolysis cell of this aspect can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0016] (10) In the solid oxide electrolysis cell according to any one of (1) to (9) above, 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, when the solid oxide electrolysis cell is in use, peeling at the interface between the air electrode and the solid electrolyte layer can be suppressed, and a decrease in current density can be suppressed.

[0017] (11) 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 (10) 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 peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0018] (12) 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 (10) above. The electrolysis stack of this aspect can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of the solid oxide electrolysis cell.

[0019] (13) According to another aspect of the present disclosure, there is provided a hot module comprising the electrolysis stack according to (12) 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 peeling at the interface between the air electrode and the solid electrolyte layer and suppress a decrease in current density during use of a solid oxide electrolysis cell.

[0020] (14) According to another aspect of the present disclosure, there is provided a hydrogen production device including the hot module described in (13) above. The hydrogen production device of this aspect can suppress peeling at the interface between the air electrode and the solid electrolyte layer while suppressing a decrease in current density during use of a solid oxide electrolysis cell.

[0021] The present invention can be realized in various forms, for example, in the form of a method for manufacturing a solid oxide electrolysis cell.

[0022] The present disclosure relates to an electrolysis stack, an electrolysis device, and a hydrogen production apparatus.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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."

[0043] 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. A specific example of such a composite oxide is LSCF, i.e., (La,Sr)(Co,Fe)O, which is the material for 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 electron 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 Co ０．２ Fe ０．８ O ３ It is a porous, thin-plate-shaped sintered body formed from a material containing

[0044] 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.

[0045] The cathode current collecting layer 27 is made of a material having the general formula ABO ３ The 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 of the solid electrolyte layer 24 (e.g., ceria or zirconia), which will be described later. 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. The cathode functional layer 26 may not be provided, and the cathode functional layer 26 may not contain Ce.

[0046] 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 high-resistance material SrZrO ３ Since there is a problem of the formation of SZO (hereinafter referred to as "SZO"), 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 an electrolyte and a composite oxide are mixed in a mass ratio of about 1:1 can be disposed between the air electrode 29 and the solid electrolyte layer 24, and this intermediate layer is the air electrode functional layer 26. However, the air electrode 29 does not necessarily have to have the air electrode functional layer 26.

[0047] In addition, to prevent Sr (strontium) contained in the air electrode 29 from diffusing toward the solid electrolyte layer 24 and reacting with Zr (zirconium) contained in the solid electrolyte layer 24 to produce 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 prevents Sr diffused from the air electrode 29 from reacting with Zr contained in the solid electrolyte layer 24 to produce SZO. However, the electrolysis cell 20 does not necessarily have to include the reaction prevention layer 25. The reaction prevention layer 25 is preferably, but is not particularly limited to, 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).

[0048] The content of zirconia in the air electrode 29 is 1×10 －３ Mass% or more 5×10 －１ In other words, when the content of zirconia is converted into the content of Zr, the content of Zr is 7.4 × 10 －４ Mass% or more 3.7 x 10 －１The zirconia content is 0.05 mass % or less. The zirconia content can be measured, for example, by analyzing the electrode material using SIMS (Secondary Ion Mass Spectrometry). The zirconia content can also be measured, for example, by analyzing the electrode material using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). The Zr content can be measured, for example, by analyzing the electrode material using SIMS. When adding zirconia, zirconia powder may be mixed with the pulverized composite oxide having a perovskite structure, or the pre-pulverized composite oxide and zirconia pieces may be pulverized together. Furthermore, the zirconia content may be adjusted to within the above range by adding a zirconia-containing compound (e.g., YSZ (yttria-stabilized zirconia)) or by adding both a zirconia-containing compound and zirconia.

[0049] 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)

[0050] 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.

[0051] 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. ２ In 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.

[0052] 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.

[0053] 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 space occupied by current collecting members and the like.

[0054] (Manufacturing Method) Next, an example of a manufacturing method for the electrolysis cell 20 will be described.

[0055] (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.

[0056] (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).

[0057] (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.

[0058] 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.

[0059] (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.

[0060] (Formation of 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 ZrO ２ After the powder is added, polyvinyl alcohol as an organic binder and butyl carbitol as an organic solvent are mixed, and the viscosity is adjusted to prepare a paste for the air electrode functional layer. ２ The amount of ZrO added at the time of product completion ２ The content of the cathode 29 is 1×10 －３ Mass% or more 5×10 －１ The content is adjusted to be % by mass or less. For example, ZrO ２or by adding a compound containing ZrO ２ Compounds containing ZrO ２ By adding both of these, ZrO can be made within the above range. ２ The content of the cathode functional layer paste can be adjusted. Next, the prepared cathode 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. Here, since the cathode functional layer paste contains GDC powder, the produced cathode functional layer 26 contains Ce.

[0061] (Formation of Air Electrode Current Collecting Layer 27) Next, the air electrode current collecting layer 27 is formed. First, LSCF powder and ZrO ２ The powder, 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 a paste for the current collecting layer for the air electrode. ２ The amount of ZrO added at the time of product completion ２ The content of the cathode 29 is 1×10 －３ Mass% or more 5×10 －１ The content is adjusted to be % by mass or less. For example, ZrO ２ or by adding a compound containing ZrO ２ Compounds containing ZrO ２ By adding both of these, ZrO can be made within the above range. ２ The content of the cathode current collecting layer paste can be adjusted. Next, the prepared cathode current collecting layer paste is applied to the surface of the intermediate laminate on the cathode functional layer 26 side by, for example, screen printing, and dried. The intermediate laminate with the current collecting layer paste applied is fired at a predetermined firing temperature (for example, 1100°C). This firing step forms the cathode current collecting layer 27, and produces a laminate of the anode 21, the solid electrolyte layer 24, the reaction prevention layer 25, the cathode functional layer 26, and the cathode current collecting layer 27, i.e., the single electrolytic cell 20.

[0062] 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.

[0063] (Explanation of Effects) As explained above, the air electrode 29 of the above-mentioned embodiment is a cathode material represented by the general formula ABO ３ and a composite oxide having a perovskite structure represented by ZrO ２ and ZrO ２ The content of the cathode is 1×10 －３ Mass% or more 5×10 －１ The present inventors have found that use of such an air electrode 29 can suppress peeling at the interface between the air electrode 29 and the solid electrolyte layer 24 while suppressing a decrease in current density during use of the solid oxide electrolysis cell (electrolysis cell 20). As a result, the durability of the electrolysis cell 20 can be improved.

[0064] 1×10 to the air electrode 29 －３ Mass% or more, 5×10 －１ ZrO to a content of % by mass or less ２ It is believed that by adding ZrO to the air electrode 29, the Sr that diffuses from the air electrode 29 toward the solid electrolyte layer 24 can be trapped by the Zr present in the air electrode 29. This makes it possible to prevent Sr from diffusing to the region near the boundary between the air electrode 29 and the solid electrolyte layer 24, and to prevent a layer of high-resistance SZO from being generated in this region, thereby preventing a decrease in the performance of the electrochemical reaction cell. ２ The content is 5 x 10 －１% by mass or less, it is believed that excessive diffusion of elements other than Sr from the air electrode 29 can be prevented, and that a decrease in reliability due to a change in the composition of the air electrode 29 can be prevented. As a result, it is believed that the electrolytic cell 20 can operate for a long period of time without deterioration.

[0065] Furthermore, in order to prevent peeling of the air electrode 29 and reduce the difference in thermal expansion coefficient between the air electrode 29 and the solid electrolyte layer 24, there is a technique in which a composite material obtained by mixing an electrolyte material with the air electrode 29 is provided 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, SZO is generated, which may result in an increase in the electrical resistance of the electrolytic cell 20, a decrease in reaction active sites, a decrease in the output density due to non-uniformity in the composition of the air electrode, etc.

[0066] Therefore, for example, gadolinium-doped ceria (GDC) or samarium-doped ceria (SDC) is used as the electrolyte material to be mixed. Preferably, an intermediate layer in which the electrolyte and the composite oxide are mixed in a mass ratio of about 1:1 can be disposed between the air electrode 29 and the solid electrolyte layer 24, and this intermediate layer is used as the air electrode functional layer 26.

[0067] In order to suppress the generation of SZO, a zirconia (ZrO ２ There is a technique for providing an electrolyte layer that does not contain zirconia. Such a reaction prevention layer 25 may be formed.

[0068] Trace amounts of ZrO in the air electrode material ２ By incorporating the cathode material, the diffusion of Sr into the solid electrolyte layer 24 is suppressed, thereby suppressing the formation of highly resistive SZO. The provision of an air electrode functional layer, which is a composite layer of the air electrode material and the electrolyte material, is preferable because it suppresses peeling due to the reduction in the difference in thermal expansion coefficients. Furthermore, the provision of the reaction prevention layer 25 is preferable because it ensures long-term stability.

[0069] ZrO ２ The content of 1 x 10 －３The mechanism by which peeling of the air electrode 29 is suppressed when the content of ZrO is 100% by mass or more is not clear, but it is thought that ZrO ２ This is thought to be because the addition of 7.4×10 zirconia to 7.4×10 ceria forms a solid solution of zirconia and ceria at the interface between the air electrode 29 and the solid electrolyte layer 24 in contact therewith, and this solid solution contributes to improving the adhesive strength between the air electrode 29 and the solid electrolyte layer 24. －４ % by mass or more. In this example, the layer in contact with the air electrode 29 is the solid electrolyte layer 24, but it is believed that the same effect can be obtained with other layers such as the reaction prevention layer 25 made of a dense, thin-plate sintered body made of ceria, specifically, GDC (gadolinium-doped ceria), SDC (samarium-doped ceria), or the like. ２ The content of 1 x 10 －３ % by mass or more, it is considered that the effect of stabilizing the microstructure of the air electrode 29 is exhibited. －４ It is believed that by making the content of the cathode 29 equal to or greater than 100 mass %, the effect of stabilizing the microstructure of the cathode 29 can be achieved.

[0070] On the other hand, ZrO ２ The content of is 5 x 10 －１ When the Zr content was greater than 3.7 × 10 mass %, the power density decreased, as shown in the test results described later. －１ When the content was greater than 100% by mass, the power density decreased, as shown in the test results described below. Although the mechanism is unclear, it is thought that lanthanum zirconate or strontium zirconate or the like is produced by a reaction between lanthanum (La) or strontium (Sr), which are components of the air electrode 29, and zirconia. As a result, it is thought that at least one of the following occurs: (i) the resistance value of the electrolytic cell 20 increases because the conductivity of these reaction products is low; (ii) the number of reaction active sites decreases; or (iii) the composition in the air electrode 29 becomes non-uniform. Hereinafter, ZrO ２ The test for checking the content of the compound, the current density at the thermal neutral point after the thermal cycle test, and the presence or absence of peeling at the interface between the air electrode 29 and the solid electrolyte layer 24 will be described below.

[0071] (Test 1) A. Method In this test, the electrolysis cell 20 without the cathode functional layer 26 was subjected to a ZrO ２ A plurality of types of test samples (fired bodies) were used, each containing different amounts of . Specifically, as shown in Table 1, eight levels were prepared, and one test sample was produced for each level.

[0072] In these samples, the thickness of the fuel electrode 21 (NiO-YSZ) was 400 μm, the thickness of the solid electrolyte layer 24 (8YSZ) was 10 μm, and the thickness of the air electrode 29 (LSCF) was 100 μm. Furthermore, when viewed from above, these samples had a square shape with sides of 10 cm.

[0073] 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 as the gas on the air electrode side during the reduction process. Note that the reducing gas may also have a reducing agent concentration of less than 100% by volume, in which case it may be composed of hydrogen and nitrogen.

[0074] B. Evaluation B-1. Current Density Using the electrolytic cell 20 thus fabricated, the current density at 1.3 V was measured at 700°C.

[0075] B-2. Thermal Cycle Test A thermal cycle test was performed on the electrolytic cell 20 using an infrared lamp. The thermal cycle test was performed 50 times under the condition of heating to 700°C over 10 minutes and then cooling to room temperature over 30 minutes. After the test, the electrolytic cell 20 was observed using a microscope for the presence or absence of peeling at the interface between the air electrode 29 and the solid electrolyte layer 24.

[0076] The current density is set at the reference value of 0.8 A / cm ２ If a cell exhibited a current density above this level, it was rated as "good," and if not, it was rated as "poor." However, cells that showed peeling during the thermal cycle test were rated as "poor" even if their output density met the standard value.

[0077] C. Results The evaluation results of the current density and thermal cycle tests are shown in Table 1.

[0078]

[0079] As shown in Table 1, ZrO ２ The content of 1 x 10 －３ When the content was less than 1% by mass, peeling was observed. ２ The content of 1 x 10 －３ When the zirconia content was converted to Zr content, the Zr content was 7.4 × 10 －４ On the other hand, when the Zr content was less than 7.4 × 10 －４ When the content was 100% by mass or more, no peeling was observed.

[0080] Also, ZrO ２ The content of is 5 x 10 －１ When the content of ZrO was higher than 1% by mass, the current density was low. ２ The content of is 5 x 10 －１ When the zirconia content was converted to a Zr content, a high current density was obtained when the Zr content was 3.7 × 10 －１ When the Zr content was greater than 3.7 × 10 by mass, the current density was low. －１ When the content was 0.05 wt % or less, a high current density was obtained.

[0081] (Test 2) In Test 2, the electrolysis cell 20 having the air electrode functional layer 26 was subjected to a test in which ZrO ２ Several types of test samples (fired bodies) were used, with different contents of . Specifically, as shown in Table 2, eight levels were prepared, and one test sample was produced for each level. The test sample production method, evaluation conditions, and evaluation criteria were the same as in Test 1. The evaluation results of the current density and thermal cycle test are shown in Table 2.

[0082]

[0083] As shown in Table 2, ZrO ２ The content of 1 x 10 －３ When the content was less than 1% by mass, peeling was observed. ２ The content of 1 x 10 －３ When the zirconia content was converted to Zr content, the Zr content was 7.4 × 10－４ On the other hand, when the Zr content was less than 7.4 × 10 －４ When the content was 100% by mass or more, no peeling was observed.

[0084] Also, ZrO ２ The content of is 5 x 10 －１ When the content of ZrO was higher than 1% by mass, the current density was low. ２ The content of is 5 x 10 －１ When the zirconia content was converted to a Zr content, a high current density was obtained when the Zr content was 3.7 × 10 －１ When the Zr content was greater than 3.7 × 10 by mass, the current density was low. －１ When the content was 0.05 wt % or less, a high current density was obtained.

[0085] 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.

[0086] 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.

[0087] 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...opening, 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. A method for manufacturing a solid electrolyte battery comprising: an air electrode; an anode; and a solid electrolyte layer disposed between the air electrode and the anode; ３ A composite oxide having a perovskite structure represented by ZrO ２ and ZrO ２ The content of the cathode is 1×10 －３ Mass% or more 5×10 －１ % by weight or less.

2. In the solid oxide electrolysis cell according to claim 1, the air electrode has a Zr content of 7.4×10 －４ Mass% or more 3.7 x 10 －１ % by weight or less.

3. A cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode, the cathode being represented by the general formula ABO ３ and Zr, the content of Zr being 7.4×10 relative to the entire air electrode. －４ Mass% or more 3.7 x 10 －１ % by weight or less.

4. A solid oxide electrolysis cell according to any one of claims 1 to 3, wherein the A site of the composite oxide contains at least one of La and Sr atoms.

5. A solid oxide electrolysis cell according to any one of claims 1 to 3, wherein the B site of the composite oxide contains at least one atom of Co and Fe.

6. In the solid oxide electrolysis cell according to any one of claims 1 to 3, the air electrode has an air electrode functional layer on the side of the solid electrolyte layer, and the air electrode functional layer is a material represented by the general formula ABO ３ A composite oxide having a perovskite structure represented by the formula: ２ and a solid oxide electrolysis cell comprising:

7. In the solid oxide electrolysis cell according to any one of claims 1 to 3, a fuel gas containing water vapor is supplied to the fuel electrode 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.

8. In the solid oxide electrolysis cell according to any one of claims 1 to 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.

9. In the solid oxide electrolysis cell according to any one of claims 1 to 3, a fuel gas containing water vapor is supplied to the fuel electrode at a flow rate of 100 to 130 liters / min.cm ２ The air electrode is supplied with a gas containing oxygen 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.

10. In the solid oxide electrolysis cell according to any one of claims 1 to 3, the volume of the air chamber facing the air electrode is 9 cm ３ ~11cm ３ A solid oxide electrolysis cell.

11. A cell with a separator, comprising: a solid oxide electrolysis cell according to any one of claims 1 to 3; and a separator with a central opening disposed on the solid electrolyte layer.

12. An electrolysis stack comprising a plurality of solid oxide electrolysis cells according to any one of claims 1 to 3 stacked together.

13. A hot module comprising: an electrolytic stack according to claim 12; 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.

14. A hydrogen production device comprising the hot module according to claim 13.

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