Electrode for solid oxide cell, method of manufacturing the same, solid oxide cell, and method of maintaining solid oxide cell

Abstract

To provide an electrode for a solid oxide cell capable of improving cell performance of the solid oxide cell, a method of manufacturing the same, the solid oxide cell using the electrode for the solid oxide cell, and a maintenance method of the solid oxide cell used.SOLUTION: The solid oxide cell electrode 1 includes a fiber structure portion 10 in which a large number of metal fibers 101 form a three dimensional structure, and a large number of oxide particles 12 having ion conductivity. The solid oxide cell electrode 1 includes a region in which the oxide particles 12 are supported on the surface of the metal fiber 101 in a state of having continuity. The solid oxide cell has an electrode 1 for the solid oxide cell. In the manufacturing method of the electrode for the solid oxide cell, the electrode 1 for the solid oxide cell is formed by laminating a metal fiber nonwoven fabric containing an oxide having ion conductivity or its precursor on the surface of a solid electrolyte and heat-treating it.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode for a solid oxide cell, a method for manufacturing the same, a solid oxide cell, and a method for maintaining the solid oxide cell. [Background technology]

[0002] Conventionally, solid oxide cells (SOECs) using solid oxides as electrolytes have been known. Specific examples of solid oxide cells include solid oxide electrochemical cells (SOECs) and solid oxide fuel cells (SOFCs). SOECs are useful for realizing a carbon-recycling society because they can synthesize hydrogen and hydrocarbons. Furthermore, SOECs can also be operated as SOFCs with the same configuration, depending on the materials used.

[0003] In this type of solid oxide cell, metal particles having electronic conductivity and catalytic activity are generally mixed with oxide particles having ionic conductivity such as oxide ion conductivity or proton conductivity, and porous materials in which the particles are continuous are used as electrodes.

[0004] Furthermore, Patent Documents 1 and 2 disclose techniques relating to catalyst materials in which metal particles are supported on a composite oxide carrier. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-106808 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-194340 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to highly activate the electrodes, it is necessary to make the particles finer. However, with the above-mentioned conventionally known porous materials, the finer the particles, the greater the structural changes that occur in the cell operating environment, resulting in a decrease in cell performance.

[0007] Furthermore, the technologies disclosed in the above-mentioned patent documents are unable to improve the amount of metal particles supported, resulting in the metal particles being scattered on the support surface and making it difficult to ensure the continuity of the metal particles. As a result, these technologies often result in interruptions in the electron conduction path, limiting the improvement of cell performance.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide a solid oxide cell electrode capable of improving the cell performance of a solid oxide cell, a method for manufacturing the same, a solid oxide cell using the solid oxide cell electrode, and a method for maintaining the solid oxide cell after use. [Means for solving the problem]

[0009] One aspect of the present invention is a fiber structure (10) in which a large number of metal fibers (101) form a three-dimensional structure; It has a large number of oxide particles (12, 12cp, 12sp) having ion conductivity, The oxide particles are supported on the surface of the metal fiber in a continuous state. Electrode for solid oxide cell (1).

[0010] Another aspect of the present invention is a metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor is laminated on the surface of the solid electrolyte, and the resulting fabric is heat-treated to form an electrode for a solid oxide cell; The present invention relates to a method for manufacturing electrodes for solid oxide cells.

[0011] Yet another aspect of the present invention is a method for producing a semiconductor device comprising: The solid oxide cell has a solid oxide cell electrode (1).

[0012] Yet another aspect of the present invention is a method for producing a semiconductor device comprising: preparing a used solid oxide cell obtained by using the solid oxide cell; The method for maintaining a solid oxide cell comprises applying alternately positive and negative voltages to the solid oxide cell electrodes in the used solid oxide cell for a certain period of time. [Effects of the Invention]

[0013] The solid oxide cell electrode has the above-described configuration. Because the solid oxide cell electrode includes a region in which oxide particles are supported on the surface of metal fibers in a continuous state, contact between the metal fibers is reduced under the cell operating environment, fusion between the metal fibers is suppressed, and structural changes to the electrode can be suppressed. Therefore, the solid oxide cell electrode can exhibit high durability under the cell operating environment and can maintain electronic conductivity due to the metal fibers and ionic conductivity due to the continuous oxide particles. Therefore, the solid oxide cell electrode can improve the cell performance of the solid oxide cell.

[0014] The method for manufacturing a solid oxide cell electrode has the above-described configuration. Therefore, according to the method for manufacturing a solid oxide cell electrode, during heat treatment, particles of the ion-conductive oxide contained in the metal fiber nonwoven fabric or the ion-conductive oxide generated from its precursor are present on the surface of the metal fibers in a continuous state, thereby reducing the chance of contact between the metal fibers and suppressing fusion of the metal fibers. Therefore, according to the method for manufacturing a solid oxide cell electrode, a solid oxide cell electrode that can improve cell performance as described above can be obtained.

[0015] The solid oxide cell has the above-described configuration, and therefore the cell performance of the solid oxide cell is improved due to the effects of the solid oxide cell electrode.

[0016] The solid oxide cell maintenance method has the above-described configuration, and therefore, the solid oxide cell maintenance method can restore cell performance that has declined due to thermal degradation of the solid oxide cell electrodes over long-term use, thereby revitalizing the solid oxide cell.

[0017] In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is an explanatory view schematically showing the solid oxide cell electrode of the first embodiment. [Figure 2] FIG. 2 is a scanning electron microscope (SEM) photograph of the outer surface of the solid oxide cell electrode of Sample 1 obtained in Experimental Example 1, viewed from a direction perpendicular to the surface of the solid electrolyte plate. [Figure 3] FIG. 3 is an SEM photograph of the outer surface of the solid oxide cell electrode of Sample 1 obtained in Experimental Example 1, taken at a higher magnification than that of FIG. 2, viewed from a direction perpendicular to the surface of the solid electrolyte plate. [Figure 4] FIG. 4 is an SEM photograph of the outer surface of the solid oxide cell electrode of Sample 2 obtained in Experimental Example 1, viewed from a direction perpendicular to the surface of the solid electrolyte plate. [Figure 5] FIG. 5 is an SEM photograph of the outer surface of the solid oxide cell electrode of Sample 2 obtained in Experimental Example 1, taken at a higher magnification than that of FIG. 4, viewed from a direction perpendicular to the surface of the solid electrolyte plate. [Figure 6] FIG. 6 is an SEM photograph of the outer surface of the solid oxide cell electrode of Sample 6 obtained in Experimental Example 1, viewed from a direction perpendicular to the surface of the solid electrolyte plate. [Figure 7] FIG. 7 is an SEM photograph of the solid oxide cell electrode of Sample 6 obtained in Experimental Example 1, taken at a higher magnification than that of FIG. [Figure 8]FIG. 8 is an SEM photograph of the solid oxide cell electrode of Sample 6 obtained in Experimental Example 1, taken at a higher magnification than that of FIG. [Figure 9] FIG. 9 is an explanatory diagram for explaining a method for measuring the aspect ratio of metal fibers and the average particle size of oxide particles in a solid oxide cell electrode in Experimental Example 1. [Figure 10] FIG. 10 is a diagram showing the electrolysis current density (A / cm 2 ) of each solid oxide cell using each solid oxide cell electrode obtained in Experimental Example 1. [Figure 11] FIG. 11 is an SEM photograph of the outer surface of the solid oxide cell electrode of Sample 1R obtained in Experimental Example 2, viewed from a direction perpendicular to the surface of the solid electrolyte plate. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the solid oxide cell electrode and its manufacturing method, the solid oxide cell, and the maintenance method for the solid oxide cell of this embodiment will be described in detail with reference to the drawings. Note that the solid oxide cell electrode and its manufacturing method, the solid oxide cell, and the maintenance method for the solid oxide cell of this embodiment are not limited to the following examples. Furthermore, the lower and upper limits of the numerical ranges shown below can be arbitrarily combined (omitted below).

[0020] (Embodiment 1) The solid oxide cell electrode of embodiment 1 will be described with reference to Fig. 1. As illustrated in Fig. 1, the solid oxide cell electrode 1 of this embodiment is an electrode used in a solid oxide cell. Details of the solid oxide cell will be described in embodiment 3.

[0021] In this embodiment, the solid oxide cell electrode 1 can be formed on the surface of a solid electrolyte 2, as exemplified in FIG. 1. FIG. 1 shows an example in which the solid oxide cell electrode 1 is formed on one surface of a solid electrolyte 2 formed in a layer shape (e.g., a plate shape, a film shape, etc.). Depending on the shape of the solid electrolyte 2, the solid oxide cell electrode 1 may be formed on the entire surface of the solid electrolyte 2, or may be formed on a part of the surface of the solid electrolyte 2. Furthermore, when the solid electrolyte 2 has one surface and an opposite surface, such as a layer-shaped solid electrolyte 2, the solid oxide cell electrode 1 can be formed on either one or the other surface of the solid electrolyte 2, or on both. FIG. 1 shows an example in which the solid oxide cell electrode 1 is formed on one surface of the solid electrolyte 2.

[0022] Examples of the solid electrolyte 2 include zirconium-based oxides such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ), ceria (CeO) doped with one or more elements selected from Gd, Sm, Y, La, Nd, Yb, Ca, and Ho, cerium-based oxides such as ceria, and lanthanum-silicon-based oxides (e.g., La 9.33 SiO 26 and lanthanum silicate apatite-based oxides in which lanthanum silicon-based oxides are doped with one or more elements selected from Sr, Ba, B, Mg, Al, and Ge.

[0023] As shown in FIG. 1, the solid oxide cell electrode 1 has a fibrous structure 10 and a large number of oxide particles 12.

[0024] In the solid oxide cell electrode 1, the fiber structure 10 has a three-dimensional structure formed by a large number of metal fibers 101. Specifically, the fiber structure 10 can be formed by spreading a large number of metal fibers 101 in a three-dimensional mesh shape. The fiber structure 10 has voids between the metal fibers 101. These voids are useful as locations for gas diffusion. In this embodiment, the voids are derived from the metal fiber nonwoven fabric.

[0025] The metal fiber 101 can be suitably formed by connecting a large number of metal particles (not shown) on the order of nanometers (nano-size). The metal particles being on the order of nanometers means that the average particle size of the metal particles is greater than 0 nm and less than 1000 nm. The average particle size of the metal particles is the arithmetic mean value of the particle size measurements of any 100 metal particles that make up the metal fiber 101, as observed with a scanning transmission electron microscope-energy dispersive X-ray analyzer (STEM-EDS).

[0026] The average particle size of the metal particles can be 1 nm or more and 500 nm or less from the viewpoint of the stability of the electrode structure during long-term use. The average particle size of the metal particles can be preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more. From the viewpoint of forming reaction sites at a high density within a limited electrode volume, the average particle size of the metal particles can be preferably 450 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less.

[0027] The aspect ratio of the metal fibers 101 can be set to 100 or more. This configuration makes it possible to realize a larger electrode volume and improve the electrolysis current density of the solid oxide cell. From the viewpoint of ensuring the above-mentioned effects, the aspect ratio of the metal fibers 101 can be set to preferably 5 or more, more preferably 10 or more, and even more preferably 50 or more. Furthermore, from the viewpoint of increasing the entanglement of the metal fibers 101 and improving the density of the bonding interface with the oxide particles 12, the aspect ratio of the metal fibers 101 can be set to, for example, 500 or less. The aspect ratio of the metal fibers 101 can be calculated using the formula (average fiber length of the metal fibers 101) / (average fiber diameter of the metal fibers 101). A method for measuring the aspect ratio of the metal fibers 101 will be described later in the experimental examples.

[0028] The metal constituting the metal fibers 101 is preferably at least one selected from the group consisting of Pt, Ir, Ni, Ru, Cu, Rh, Fe, and alloys thereof. This configuration can achieve greater catalytic activity and improve the electrolysis current density of the solid oxide cell. The metal constituting the metal fibers 101 is more preferably Pt, Ir, Ni, Fe, or alloys thereof. These can be used alone or in combination of two or more.

[0029] In the solid oxide cell electrode 1, the oxide particles 12 have ion conductivity. The ion conductive species of the oxide particles 12 can be selected so as to correspond to the ion conductive species of the solid electrolyte of the solid oxide cell to which the solid oxide cell electrode 1 is applied. Specifically, the oxide particles 12 can have oxide ion conductivity (oxygen ion conductivity) or proton conductivity.

[0030] The oxide constituting the oxide particles 12 can be any of a variety of composite oxides, and preferably at least one selected from the group consisting of zirconium-based oxides, lanthanum-strontium-manganese-based oxides, lanthanum-strontium-cobalt-iron-based oxides, and cerium-based oxides. This configuration can achieve higher ionic conductivity and improve the electrolysis current density of the solid oxide cell. The oxide constituting the oxide particles 12 is more preferably zirconium-based oxides, lanthanum-strontium-manganese-based oxides, lanthanum-strontium-cobalt-iron-based oxides, or the like. These oxides can be used alone or in combination.

[0031] Examples of zirconium-based oxides include yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ). Examples of lanthanum-strontium-manganese-based oxides include La 0.8 Sr 0.2 Mn 1.0 O 3-δ (δ is 0 to 0.5). Examples of lanthanum-strontium-cobalt-iron oxides include La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (δ is 0 to 0.5) and the like can be exemplified. Examples of cerium-based oxides include ceria (CeO2) and ceria doped with one or more elements selected from Gd, Sm, Y, La, Nd, Yb, Ca, and Ho.

[0032] The solid oxide cell electrode 1 includes a region (hereinafter sometimes referred to as a "particle continuous region") in which oxide particles 12 are supported in a continuous state on the surface of the metal fibers 101. In other words, it can be said that the surface of the metal fibers 101 is covered with a large number of oxide particles 12 in a continuous state.

[0033] Specific examples of the state in which the oxide particles 12 have continuity include a state in which the oxide particles 12 are in continuous contact with each other (connected to each other), a state in which the oxide particles 12 are stacked, a combination of these, etc. The solid oxide cell electrode 1 may contain oxide particles 12 that exist independently on the surface of the metal fibers 101, as long as a particle continuous region is formed on the surface of the metal fibers 101.

[0034] Because the solid oxide cell electrode 1 includes a region where the oxide particles 12 are supported in a continuous state on the surface of the metal fibers 101, the metal fibers 101 are less likely to come into contact with each other under the cell operating environment, preventing fusion between the metal fibers 101 and suppressing structural changes in the electrode. As a result, the solid oxide cell electrode 1 can exhibit high durability under the cell operating environment and can maintain the electronic conductivity provided by the metal fibers 101 and the ionic conductivity provided by the continuous oxide particles 12. Therefore, the solid oxide cell electrode 1 can improve the cell performance of the solid oxide cell.

[0035] (Embodiment 2) A description will be given of a method for manufacturing an electrode for a solid oxide cell according to embodiment 2. Note that, among the symbols used in embodiment 2 and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0036] The method for producing the solid oxide cell electrode of this embodiment (hereinafter sometimes referred to as the present method) is a method capable of producing the solid oxide cell electrode 1 of embodiment 1. This method will be described in detail below.

[0037] In this manufacturing method, a metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor is laminated on the surface of a solid electrolyte, and the resulting laminate is heat-treated to form an electrode for a solid oxide cell.

[0038] A metal fiber nonwoven fabric containing an ionically conductive oxide or its precursor can be prepared, for example, by contacting a metal fiber nonwoven fabric with a solution containing an oxide having a predetermined ion conductivity or a solution capable of forming a precursor of an oxide having a predetermined ion conductivity, and then drying, hardening, heating, and / or fusing the fabric as necessary to adhere the ionically conductive oxide or its precursor to the metal fibers. The contact of the metal fiber nonwoven fabric with the solution can be carried out, for example, by immersing the metal fiber nonwoven fabric in the solution, or by spraying or applying the solution to the metal fiber nonwoven fabric.

[0039] In addition, in this manufacturing method, for the production of a metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor, which is used as one of the starting materials, reference can be made to International Publication No. WO2019 / 049996A1, Japanese Patent Application Laid-Open No. 2021-143442, etc., and the techniques of each of these publications can be incorporated into the present disclosure as necessary.

[0040] Specifically, a metal fiber nonwoven fabric containing a precursor of an ion-conductive oxide can be prepared, for example, as follows: A solution is prepared by dissolving in water one or more water-soluble metal sources (e.g., acetates, nitrates, etc. of the metals) containing the metals that constitute the ion-conductive oxide to be formed, and the metal fiber nonwoven fabric is brought into contact with the solution, and then dried as necessary to adhere the precursor of the ion-conductive oxide to the surface of the metal fibers.

[0041] Specifically, a metal fiber nonwoven fabric containing an ion-conductive oxide can be prepared, for example, as follows: A solution in which the ion-conductive oxide to be formed is dispersed in water is brought into contact with the metal fiber nonwoven fabric, and then the fabric is dried as necessary to adhere the ion-conductive oxide to the surface of the metal fibers.

[0042] At least one metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor can be laminated on the surface of the solid electrolyte. Furthermore, the heat treatment after lamination can be performed once or multiple times. The heat treatment atmosphere can be air or hydrogen. The heat treatment temperature can be, for example, 600°C or higher and 1200°C or lower. The heat treatment time can be, for example, 1 hour or higher and 10 hours or lower. This allows the production of a solid oxide cell electrode.

[0043] According to this manufacturing method, particles of ion-conductive oxides generated from the ion-conductive oxides or their precursors contained in the metal fiber nonwoven fabric are present on the surface of the metal fibers in a continuous state during heat treatment, thereby reducing the chance of contact between the metal fibers and suppressing fusion between the metal fibers. Therefore, according to this manufacturing method, it is possible to obtain a solid oxide cell electrode that can improve the cell performance as described above.

[0044] In the present production method, the heat-treated solid oxide cell electrode can be subjected to an electrical treatment, which results in a solid oxide cell electrode that can improve the electrolysis current density of the solid oxide cell compared to a case where the heat-treated solid oxide cell electrode is not subjected to an electrical treatment.

[0045] The electrical treatment can be carried out by applying alternately positive and negative voltages to the solid oxide cell electrode after the heat treatment for a certain period of time.

[0046] The voltage application time can be, for example, 10 minutes to 10 hours. The voltage can be changed, for example, between -3.0 V and +3.0 V. The voltage can be applied once or multiple times. The voltage application can be carried out, for example, in an air atmosphere. The temperature during voltage application can be, for example, 500°C to 1100°C.

[0047] For other configurations, the description of embodiment 1 can be appropriately referred to. In addition, the descriptions of other embodiments can also be appropriately referred to as necessary.

[0048] (Embodiment 3) A description will be given of a solid oxide cell of embodiment 3. The solid oxide cell of this embodiment has the solid oxide cell electrode of embodiment 1.

[0049] Specifically, a solid oxide cell has a solid electrolyte layer, a first electrode, and a second electrode paired with the first electrode. The first electrode is disposed on one side of the solid electrolyte layer. The second electrode is disposed on the other side opposite the one side of the solid electrolyte layer. The solid electrolyte layer, the first electrode, and the second electrode can all be formed in layers. Specifically, in the case of an SOEC, the first electrode can function as a cathode electrode, and the second electrode can function as an anode electrode. In the case of an SOFC, the first electrode can function as an anode electrode, and the second electrode can function as a cathode electrode. Furthermore, the first electrode can function as a fuel electrode to which fuel gas is supplied, and the second electrode can function as an air electrode (oxygen electrode) paired with the fuel electrode. In a solid oxide cell, the first electrode, the solid electrolyte layer, and the second electrode are stacked in this order and joined together. In addition, in a solid oxide cell, the outer shape of the solid electrolyte layer can be formed to be larger than the outer shapes of the first electrode and second electrode that face each other with the solid electrolyte layer therebetween.

[0050] The solid oxide cell may further include an intermediate layer between the solid electrolyte layer and the first electrode or between the solid electrolyte layer and the second electrode. The solid oxide cell may have a flat cell structure or a cylindrical cell structure. The solid oxide cell may be configured so that the first electrode also functions as a support, the solid electrolyte layer also functions as a support, the second electrode also functions as a support, or the first electrode or the second electrode is supported by another support such as a metal member.

[0051] The solid electrolyte layer has ion conductivity. Specifically, the solid electrolyte layer may have oxide ion conductivity or proton conductivity. Specifically, the solid electrolyte layer can be formed in a layered form from a solid electrolyte having ion conductivity. The solid electrolyte layer is usually formed as a dense material to ensure gas tightness. The thickness of the solid electrolyte layer can be several μm or more and several hundred μm or less, for example, 1 μm or more and 500 μm or less.

[0052] Suitable solid electrolyte materials having oxide ion conductivity for forming the solid electrolyte layer include zirconium oxides such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ), and cerium oxides such as ceria (CeO) doped with one or more elements selected from Gd, Sm, Y, La, Nd, Yb, Ca, and Ho. In this case, yttria-stabilized zirconia is suitable as the solid electrolyte material for forming the solid electrolyte layer from the viewpoints of oxide ion conductivity, mechanical stability, compatibility with other materials, and chemical stability in both oxidizing and reducing atmospheres.

[0053] The first electrode is made of the solid oxide cell electrode described above in embodiment 1. The thickness of the first electrode can be, for example, 0.1 μm or more and 10 μm or less.

[0054] The second electrode may have the same structure as the first electrode, or may be made of a different electrode material. When the first electrode is made of a different electrode material from the first electrode, examples of the electrode material include transition metal perovskite oxides such as lanthanum-strontium-cobalt oxide, lanthanum-strontium-cobalt-iron oxide, lanthanum-strontium-manganese-iron oxide, and lanthanum-strontium-manganese composite oxide. These may be used alone or in combination of two or more.

[0055] In a solid oxide cell, for example, HO is supplied as an input gas to a first electrode, and electric power is supplied to the solid oxide cell to generate an electrochemical reaction, electrolyzing HO at the first electrode and obtaining H as an output gas. In this case, the cell operating temperature of the solid oxide cell can be set to, for example, 400°C or higher, preferably 500°C or higher, and more preferably 600°C or higher, from the viewpoint of sufficiently increasing the reaction rate. Furthermore, the cell operating temperature of the solid oxide cell can be set to, for example, 1000°C or lower, preferably 950°C or lower, and more preferably 900°C or lower, from the viewpoint of suppressing the rate of characteristic degradation. The solid oxide cell can be heated to an optimal temperature by a cell heating source such as an electric furnace or heater. Furthermore, the solid oxide cell can perform not only water (steam) electrolysis, but also co-electrolysis, in which HO is supplied together with CO as an input gas and hydrogen and CO are obtained as output gases.

[0056] For other configurations, the description of embodiment 1 can be appropriately referred to. In addition, the descriptions of other embodiments can also be appropriately referred to as necessary.

[0057] The solid oxide cell of this embodiment has the solid oxide cell electrode of embodiment 1. Therefore, the solid oxide cell of this embodiment can improve cell performance, such as an increase in electrolysis current density, due to the effects of the solid oxide cell electrode of embodiment 1.

[0058] (Embodiment 4) A description will now be given of a method for maintaining a solid oxide cell according to embodiment 4. The method for maintaining a solid oxide cell according to this embodiment involves preparing a used solid oxide cell obtained by using the solid oxide cell according to embodiment 3 described above, and applying alternately positive and negative voltages to the solid oxide cell electrodes of the used solid oxide cell for a certain period of time.

[0059] The solid oxide cell electrodes described above in embodiment 1 can suppress structural changes in the electrodes under the cell operating environment and exhibit high durability, but from a long-term perspective, it is difficult to completely prevent thermal degradation. In contrast, the solid oxide cell maintenance method of this embodiment can restore cell performance that has deteriorated due to thermal degradation of the solid oxide cell electrodes over long-term use, and can regenerate the solid oxide cell.

[0060] Although the details are unclear, it is thought that when alternating positive and negative voltages are applied to the electrodes of solid oxide cells for a certain period of time, the interruptions in the electronic and ionic conduction paths caused by the aggregation of metal fibers and oxide particles resulting from thermal degradation during long-term use are re-fine-grained by the applied electrical energy, thereby restoring the paths to a certain extent.

[0061] The voltage application time can be, for example, 10 minutes to 10 hours. The voltage can be changed, for example, between -3.0 V and +3.0 V. The voltage can be applied once or multiple times, but is preferably applied multiple times from the viewpoint of effective recovery of cell performance. The voltage application can be carried out, for example, in an air atmosphere. The temperature during voltage application can be, for example, 500°C to 1100°C.

[0062] The recovery of cell performance is considered to be achieved when, when comparing before and after application of a voltage to the solid oxide cell electrode, the current density of the solid oxide cell after the voltage application is higher than the current density of the solid oxide cell before the voltage application.

[0063] For other configurations, the description of embodiment 3 can be appropriately referred to. In addition, the descriptions of other embodiments can also be appropriately referred to as necessary.

[0064] (Experimental Example 1) <Sample preparation> -Sample 1- First, a metal fiber nonwoven fabric and a solid electrolyte plate were prepared. Specifically, an 8% by mass solution of polyvinylpyrrolidone (PVP) in methanol was electrospun at 1 kV / cm to produce a nonwoven fabric consisting of PVP polymer nanowires with an average diameter of approximately 271 nm (hereinafter referred to as PVP nanowire nonwoven fabric).

[0065] A Pt film was formed on the surface of this PVP nanowire nonwoven fabric by sputtering. The resulting PVP nanowire nonwoven fabric was placed in the vacuum chamber of a sputtering device. -2 After evacuating the chamber to a vacuum of 10.0 Pa or less, Ar was introduced at a flow rate of 30 sccm. The pressure inside the chamber was then adjusted to 10.0 Pa, and the Pt target was discharged at an output power of 42 W for 1575 seconds to sputter Pt, forming a Pt film. The amount of Pt can be controlled by the sputtering time. In this case, the amount of Pt was 300 μg / cm. 2 A Pt film was formed.

[0066] The PVP nanowire nonwoven fabric with a Pt film formed on its surface was cut into a 12 mm diameter piece and stirred in water to remove the PVP. This produced a Pt nonwoven fabric composed of Pt fibers. The Pt fibers had a structure in which numerous Pt particles on the nanometer order were accumulated with tiny gaps between them.

[0067] Furthermore, 8 mol% Y2O3 stabilized ZrO2 (YSZ: yttria stabilized zirconia) powder was compacted to a diameter of 25 mm and a thickness of 200 μm, and this was fired at 1500°C in an air atmosphere to prepare a solid electrolyte plate.

[0068] Next, a La electrode with a diameter of 8 mm was placed on one side of the solid electrolyte plate as an anode electrode. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ The porous body (δ is 0 to 0.5) was formed by printing and baking. The baking atmosphere was air and the baking temperature was 1100°C.

[0069] Next, the Pt nonwoven fabric was immersed in an aqueous solution prepared by dissolving yttrium acetate tetrahydrate and zirconium nitrate dihydrate in pure water to form 0.2 mol / L of 8 mol% Y2O3-stabilized ZrO2 (YSZ) and thoroughly stirred. The Pt nonwoven fabric was then removed from the aqueous solution and attached to one side of a solid electrolyte plate opposite the anode electrode, followed by vacuum drying. Next, one drop (0.03 mg) of an aqueous solution prepared by dissolving yttrium acetate tetrahydrate and zirconium nitrate dihydrate in pure water to form 0.2 mol / L of 8 mol% Y2O3-stabilized ZrO2 (YSZ) was added and vacuum dried three times to adjust the Pt to YSZ charge ratio to 1:1. The cathode electrode (the solid oxide cell electrode in this experiment) was then integrated into the solid electrolyte plate by baking at 1000°C for 1 hour in an air atmosphere. As a result, a solid oxide cell electrode and a solid oxide cell of Sample 1 were obtained.

[0070] -Sample 2- The cathode electrode of a solid oxide cell prepared in the same manner as Sample 1 was subjected to an electrical treatment in which a voltage of +2.0 V and -2.0 V was applied alternately for 2 minutes at 900°C in an air atmosphere, 100 times each. This produced Sample 2, an electrode for a solid oxide cell, and a solid oxide cell.

[0071] -Sample 3- In the preparation of sample 1, the Pt nonwoven fabric was 0.8 Sr 0.2 Mn 1.0 O 3-δ A solid oxide cell electrode and a solid oxide cell of Sample 3 were obtained in the same manner, except that the electrode was immersed in an aqueous solution prepared by dissolving lanthanum nitrate hexahydrate, strontium nitrate, and manganese acetate tetrahydrate in pure water in amounts corresponding to the amount of lanthanum nitrate hexahydrate, strontium nitrate, and manganese acetate tetrahydrate.

[0072] -Sample 4- In the preparation of sample 1, the Pt nonwoven fabric was 0.8 Sr 0.2 Co 0.8 Fe 0.2 O 3-δ A solid oxide cell electrode and a solid oxide cell of Sample 4 were obtained in the same manner, except that the electrode was immersed in an aqueous solution prepared by dissolving lanthanum nitrate hexahydrate, cobalt nitrate hexahydrate, and manganese acetate tetrahydrate in pure water in amounts corresponding to the amounts indicated.

[0073] -Sample 5- An electrode for a solid oxide cell and a solid oxide cell of Sample 5 were obtained in the same manner as in the preparation of Sample 1, except that an Ir nonwoven fabric obtained by forming an Ir film was used instead of the Pt nonwoven fabric, and the temperature was changed to air up to 500°C, and from 500°C onwards, the hydrogen reducing atmosphere was changed to an N-based hydrogen atmosphere containing 4 volume % H, and the Ir nonwoven fabric was baked at 1000°C for 1 hour.

[0074] -Sample 6- An electrode for a solid oxide cell and a solid oxide cell of Sample 6 were obtained in the same manner as in Sample 1, except that a Ni nonwoven fabric obtained by forming a Ni film was used instead of the Pt nonwoven fabric, and the Ni nonwoven fabric was baked in air up to 500°C, and then in a hydrogen reducing atmosphere containing an N-based H2 containing 4% by volume from 500°C onwards, at 1000°C for 1 hour.

[0075] -Sample 7- An electrode for a solid oxide cell and a solid oxide cell of Sample 7 were obtained in the same manner as in the preparation of Sample 1, except that a Ru nonwoven fabric obtained by forming a Ru film was used instead of the Pt nonwoven fabric, and the temperature was changed to air up to 500°C, and from 500°C onwards, the hydrogen reducing atmosphere was changed to an N-based hydrogen atmosphere containing 4 volume % H, and the Ru nonwoven fabric was baked at 1000°C for 1 hour.

[0076] -Sample 8- In the preparation of Sample 1, a Cu nonwoven fabric obtained by forming a Cu film was used instead of the Pt nonwoven fabric, and the Cu nonwoven fabric was baked in air up to 500°C, and then in a hydrogen reducing atmosphere containing an N2-based H2 containing 4% by volume from 500°C onwards, at 1000°C for 1 hour. In this manner, a solid oxide cell electrode and a solid oxide cell were obtained as Sample 8.

[0077] -Sample 9- An electrode for a solid oxide cell and a solid oxide cell of Sample 9 were obtained in the same manner as in the preparation of Sample 1, except that an Rh nonwoven fabric obtained by forming an Rh film was used instead of the Pt nonwoven fabric, and the Rh nonwoven fabric was baked in air up to 500°C, and then in a hydrogen reducing atmosphere containing an N-based H containing 4% by volume from 500°C onwards, at 1000°C for 1 hour.

[0078] -Sample 10- An electrode for a solid oxide cell and a solid oxide cell of Sample 10 were obtained in the same manner as in Sample 1, except that an Fe nonwoven fabric obtained by forming an Fe film was used instead of the Pt nonwoven fabric, and the Fe nonwoven fabric was baked in air up to 500°C, and then in a hydrogen reducing atmosphere containing an N-based H2 containing 4% by volume from 500°C onwards, at 1000°C for 1 hour.

[0079] -Sample 1C- In the same manner as in the preparation of Sample 1, a solid electrolyte plate having an anode electrode formed on one side thereof was prepared.

[0080] Next, on one side of the solid electrolyte plate on the side opposite to the formation side of the anode electrode, a mixed paste of spherical Pt particles and YSZ particles diluted with terpineol (mass ratio, Pt:YSZ = 7:2) was spin-coated so that the diameter was 12 mm and the Pt amount was 600 μg / cm 2 and baked under the conditions of 1000 °C for 1 hour in an air atmosphere. As a result, as a comparative sample, an electrode for a solid oxide fuel cell and a solid oxide fuel cell of Sample 1C were obtained. The electrode for the solid oxide fuel cell of Sample 1C is a general electrode composed of a porous material in which Pt particles having electron conductivity and catalytic activity and YSZ particles having oxide ion conductivity are mixed and each particle is continuous.

[0081] In addition, the solid oxide fuel cell of each sample in this experimental example is specifically a solid oxide electrolysis cell (SOEC) (hereinafter, the description is omitted for the same reason).

[0082] <SEM Observation> Regarding the electrode for the solid oxide fuel cell formed on the solid oxide fuel cell of each sample, scanning electron microscope (SEM) observation was performed from a direction perpendicular to the surface of the solid electrolyte plate. As representatives of the electrodes for the solid oxide fuel cells of each sample, SEM photographs of the electrodes for the solid oxide fuel cells of Sample 1, Sample 2, and Sample 6 are shown in FIGS. 2 to 8. For the SEM, S-4800 manufactured by Hitachi, Ltd. was used.

[0083] According to FIGS. 2 to 8, in the electrodes for the solid oxide fuel cells of Sample 1, Sample 2, and Sample 6, a large number of metal fibers form a three-dimensional structure, and oxide particles having ion conductivity (specifically, composite oxide particles) are supported on the surface of the metal fibers constituting the fiber structure portion, and it was confirmed that a large number of oxide particles exist in a continuous state. Although not shown, regarding the electrodes for the solid oxide fuel cells of the remaining Samples 3 to 5 and Samples 7 to 10, the same structure as that of the electrodes for the solid oxide fuel cells of Sample 1, Sample 2, and Sample 6 was confirmed.

[0084] Despite the heat treatment, the three-dimensional structure of the numerous metal fibers derived from the metal fiber nonwoven fabric was maintained. This is thought to be because the ion-conductive oxide particles generated from the ion-conductive oxide precursor contained in the metal fiber nonwoven fabric were generated on the surface of the metal fibers in a continuous state, reducing the opportunity for contact between the metal fibers and suppressing fusion between the metal fibers. In this experimental example, an ion-conductive oxide precursor was used, but similar results can be obtained even if the ion-conductive oxide itself is used as the starting material.

[0085] In contrast, the solid oxide cell electrode of sample 1C does not use a metal fiber nonwoven fabric containing an ionically conductive oxide precursor as a starting material, but uses a mixed paste containing metal particles and ionically conductive oxide particles, and therefore it was not possible to form a structure similar to that of the solid oxide cell electrodes of samples 1 to 10.

[0086] <Aspect ratio of metal fibers> Using the SEM described above, the solid oxide cell electrode was observed in the electrode thickness direction (i.e., the direction perpendicular to the surface of the solid electrolyte plate) and an SEM image was obtained. An example of the obtained SEM image is shown in Figure 9. In Figure 9, the dark gray area is the solid electrolyte 2 formed on the plate, the medium gray area is the metal fiber 101, and the light gray area covering the surface of the metal fiber 101 is the oxide particles 12, 12sp, and 12cp.

[0087] The aspect ratio of metal fibers can be calculated using the formula: average fiber length / average fiber diameter. The average fiber length is an arithmetic mean value calculated by measuring the fiber lengths of 40 randomly selected metal fibers in an SEM image and using the obtained fiber lengths. The fiber length of the metal fibers is measured at the center in the fiber diameter direction. The average fiber diameter is an arithmetic mean value calculated by measuring the fiber diameters of 40 randomly selected metal fibers in an SEM image and using the obtained fiber diameters. The SEM image in FIG. 6 described above is an example, and the magnification of the SEM image can be selected appropriately to ensure the required number of measurements.

[0088] <Average particle size of oxide particles> SEM images were obtained in the same manner as in the measurement of the aspect ratio of the metal fibers. The average particle diameter of the oxide particles was measured as follows. As shown in FIG. 9, 40 individually identifiable oxide particles (reference numeral 12sp in FIG. 9) among the oxide particles supported on the surface of the metal fiber 101 were surrounded by an ellipse along the outer shape of the oxide particle, and the major axis and minor axis were measured. Using the obtained major axis and minor axis, the arithmetic mean value was calculated using the formula (total of major axes of 40 particles + total of minor axes of 40 particles) / 80, and was defined as the average particle diameter of the oxide particles. Note that, as can be seen in FIG. 9, the portion of the oxide particles (reference numeral 12cp in FIG. 9) that was supported in large numbers on the surface of the metal fiber was not used for measurement because it was difficult to clearly distinguish the boundaries between the oxide particles.

[0089] <Cell performance evaluation> The performance of each solid oxide cell was evaluated by measuring the electrolysis current density. The cell operating temperature was set at 800°C.

[0090] Electrolytic current density is 1.4A / cm 2 When the electrolysis current density was 1.1 A / cm or higher, the cell performance was evaluated as being sufficiently improved and given an "A+" rating. 2 More than 1.4A / cm 2 When the electrolysis current density was less than 0.8 A / cm, the cell performance was evaluated as improved and given a rating of "A." 2 More than 1.1A / cm 2 When the electrolysis current density was less than 0.8 A / cm, the cell performance was evaluated as "B" because it was not as good as the evaluation "A" but the cell performance was improved. 2 If the value was less than this, it was evaluated as "C" as it indicated that the cell performance had not been improved.

[0091] Table 1 shows the manufacturing conditions, configuration, and evaluation results of each sample. Figure 10 shows the electrolysis current density (A / cm) of each solid oxide cell using each solid oxide cell electrode. 2 ) are shown below.

[0092] [Table 1]

[0093] According to Table 1 and FIGS. 2 to 10, the following can be seen.

[0094] The solid oxide cell of Sample 1C does not have the configuration of the solid oxide cell electrode defined in this disclosure, but rather uses oxide particles as a carrier and metal particles are supported on the carrier. Therefore, the solid oxide cell of Sample 1C could not improve its cell performance. This is thought to be because the metal particles and oxide particles in the solid oxide cell electrode of Sample 1C are large, which reduces the density of the bonding interface between the metal particles and the oxide particles.

[0095] In contrast, the solid oxide cells of Samples 1 to 10 use the solid oxide cell electrodes of Samples 1 to 10 defined in the present disclosure. These solid oxide cell electrodes include regions in which oxide particles are supported on the surface of metal fibers in a continuous state. This reduces the chance of contact between metal fibers under the cell operating environment, suppresses fusion between the metal fibers, and suppresses structural changes in the electrode. As a result, these solid oxide cell electrodes exhibit high durability under the cell operating environment and can maintain the electronic conductivity of the metal fibers, the catalytic activity of the metal constituting the metal fibers, and the ionic conductivity of the continuous oxide particles. Therefore, the solid oxide cells of Samples 1 to 10 were able to improve cell performance.

[0096] Furthermore, since the solid oxide cell electrodes of Samples 1 to 10 have metal fibers with an aspect ratio of 100 or more, it is possible to realize a larger electrode volume, which has been confirmed to be advantageous for improving the electrolysis current density of solid oxide cells.

[0097] Furthermore, the solid oxide cell electrodes of Samples 1 to 10 use Pt, Ir, Ni, Ru, Cu, Rh, or Fe as the metal that constitutes the metal fibers, and therefore it has been confirmed that they can achieve greater catalytic activity and are advantageous in improving the electrolysis current density of solid oxide cells.

[0098] Furthermore, the solid oxide cell electrodes of Samples 1 to 10 use zirconium-based oxide, lanthanum-strontium-manganese-based oxide, or lanthanum-strontium-cobalt-iron-based oxide as the oxide constituting the oxide particles, and therefore were able to achieve higher ionic conductivity, which was confirmed to be advantageous for improving the electrolysis current density of solid oxide cells. Although cerium-based oxide was not used in this experimental example, cerium-based oxide has good ionic conductivity similar to zirconium-based oxide, lanthanum-strontium-manganese-based oxide, or lanthanum-strontium-cobalt-iron-based oxide. Therefore, even when cerium-based oxide is used as the oxide constituting the oxide particles, higher ionic conductivity can be achieved, which can be said to be advantageous for improving the electrolysis current density of solid oxide cells.

[0099] 10, it was confirmed that further electrical treatment of the heat-treated solid oxide cell electrodes can improve the electrolysis current density of the solid oxide cell compared to the case where no electrical treatment is performed. Furthermore, from this result, it can be said that after a solid oxide cell using a heat-treated solid oxide cell electrode that has not been electrically treated is used to become a used solid oxide cell, the cell performance can be restored and the solid oxide cell can be regenerated by applying alternating positive and negative voltages to the solid oxide cell electrodes of the used solid oxide cell for a certain period of time.

[0100] (Experimental Example 2) In the preparation of Sample 1 in Experimental Example 1, a Pt nonwoven fabric was immersed in pure water and thoroughly stirred, and the solid oxide cell electrode and solid oxide cell of Sample 1R were obtained as a reference sample.

[0101] Next, the solid oxide cell electrode formed in the solid oxide cell of Sample 1R was observed with an SEM from a direction perpendicular to the surface of the solid electrolyte plate in the same manner as in Experimental Example 1. The results are shown in FIG.

[0102] As shown in Figure 11, the solid oxide cell electrode of sample 1R had a network structure in which metal interconnects, each consisting of a large number of metal particles, developed two-dimensionally in the in-plane direction on the surface of the solid electrolyte in a mesh-like pattern. This is thought to be because the metal fiber nonwoven fabric attached to the surface of the solid electrolyte did not contain an ion-conductive oxide or its precursor, and therefore the heat treatment caused the metal fibers to fuse together, making it impossible to maintain the three-dimensional structure of the large number of metal fibers derived from the metal fiber nonwoven fabric.

[0103] Thus, the manufacturing method of Experimental Example 2 was unable to obtain the solid oxide cell electrode defined in the present disclosure.

[0104] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible without departing from the spirit of the present invention. Furthermore, the configurations shown in the embodiments and experimental examples can be combined in any manner.

[0105] The features of the present invention are as follows. Section 1. a fiber structure (10) in which a large number of metal fibers (101) form a three-dimensional structure; It has a large number of oxide particles (12, 12cp, 12sp) having ion conductivity, The oxide particles are supported on the surface of the metal fiber in a continuous state. Electrodes for solid oxide cells (1). Section 2. The aspect ratio of the metal fiber is 100 or more. Item 1. The solid oxide cell electrode according to item 1. Section 3. The metal constituting the metal fiber is at least one selected from the group consisting of Pt, Ir, Ni, Ru, Cu, Rh, Fe, and alloys thereof. Item 1 or 2. The solid oxide cell electrode according to item 1 or 2. Section 4. The oxide constituting the oxide particles is at least one selected from the group consisting of zirconium-based oxides, lanthanum-strontium-manganese-based oxides, lanthanum-strontium-cobalt-iron-based oxides, and cerium-based oxides. Item 4. The solid oxide cell electrode according to any one of items 1 to 3. Section 5. a metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor is laminated on the surface of the solid electrolyte, and the resulting fabric is heat-treated to form an electrode for a solid oxide cell; A method for manufacturing electrodes for solid oxide cells. Section 6. subjecting the solid oxide cell electrode after the heat treatment to an electrical treatment; Item 6. A method for producing an electrode for a solid oxide cell according to item 5. Section 7. Item 5. A solid oxide cell having the solid oxide cell electrode according to any one of items 1 to 4. Section 8. Item 7. A used solid oxide cell is prepared by using the solid oxide cell described in Item 7. A maintenance method for a solid oxide cell, comprising applying alternately positive and negative voltages to the solid oxide cell electrodes in the used solid oxide cell for a fixed period of time. [Explanation of symbols]

[0106] 1. Electrodes for solid oxide cells 10 Fiber structure part 101 Metal Fibers 12, 12cp, 12sp oxide particles

Claims

1. a fiber structure (10) in which a large number of metal fibers (101) form a three-dimensional structure; and a large number of oxide particles (12, 12cp, 12sp) having ion conductivity; The oxide particles are supported on the surface of the metal fiber in a continuous state. Electrode for solid oxide cell (1).

2. The aspect ratio of the metal fiber is 100 or more. The solid oxide cell electrode according to claim 1 .

3. The metal constituting the metal fiber is at least one selected from the group consisting of Pt, Ir, Ni, Ru, Cu, Rh, Fe, and alloys thereof. The electrode for a solid oxide cell according to claim 1 or 2.

4. The oxide constituting the oxide particles is at least one selected from the group consisting of zirconium-based oxides, lanthanum-strontium-manganese-based oxides, lanthanum-strontium-cobalt-iron-based oxides, and cerium-based oxides. The electrode for a solid oxide cell according to claim 1 or 2.

5. a metal fiber nonwoven fabric containing an ion-conductive oxide or its precursor is laminated on the surface of the solid electrolyte, and the resulting fabric is heat-treated to form an electrode for a solid oxide cell; A method for manufacturing electrodes for solid oxide cells.

6. subjecting the solid oxide cell electrode after the heat treatment to an electrical treatment; The method for producing the electrode for a solid oxide cell according to claim 5 .

7. A solid oxide cell comprising the solid oxide cell electrode according to claim 1 or 2.

8. A used solid oxide cell according to claim 7 is prepared, A maintenance method for a solid oxide cell, comprising applying alternately positive and negative voltages to the solid oxide cell electrodes in the used solid oxide cell for a fixed period of time.

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