Fuel polar layer and electrochemical cell

Abstract

The present invention provides a fuel electrode layer capable of suppressing degradation due to Ni migration, and a solid oxide type electrochemical cell using this layer. [Solution] The fuel electrode layer 1 is used in a solid oxide type electrochemical cell 2 and has catalyst material particles 11, solid electrolyte particles 12, and at least one metal M selected from metals whose standard electrode potential is more negative than Ni. The catalyst material particles 11 mainly contain Ni and also contain metal M. The solid electrolyte particles 12 mainly contain ceria oxide and also contain metal M. The electrochemical cell 2 has the fuel electrode layer 1, the solid electrolyte layer 22, and the air electrode layer 23 which is an electrode paired with the fuel electrode layer in this order. The solid electrolyte layer 22 has an electrolyte body layer 221 that is in contact with the fuel electrode layer 1. The electrolyte body layer 221 mainly contains ceria oxide and also contains metal M.

Description

[Technical Field]

[0001] This invention relates to fuel polar layers and electrochemical cells. [Background technology]

[0002] Conventionally, solid oxide electrochemical cells using solid oxides as electrolytes are known. Specifically, solid oxide electrochemical cells include solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs). SOECs are useful for realizing a carbon-recycling society because they can synthesize hydrogen and hydrocarbons. SOFCs, on the other hand, can generate electricity from fuels such as hydrogen and are highly efficient among fuel cells, making them effective for energy conservation and decarbonization. Depending on the material, solid oxide electrochemical cells can also be reversibly operated as both SOECs and SOFCs with the same configuration.

[0003] In general, the fuel electrode layer used in this type of electrochemical cell is widely known to consist of a cermet made of a mixture of catalytic material particles, such as Ni particles, and solid electrolyte particles such as yttria-stabilized zirconia (hereinafter sometimes referred to as YSZ).

[0004] Furthermore, Patent Document 1 proposes a hydrogen electrode (corresponding to the fuel electrode layer) for an electrochemical cell, comprising an oxide sintered body having metal nanoparticles on its surface and the surface covered with a mixed conductive film together with the metal nanoparticles, and an ionic conductive sintered body, wherein the oxide sintered body is an Al-based oxide or Mg-based oxide, and the metal nanoparticles are Ni metal, etc.

[0005] The document states that the metal particles have good compatibility with the Al2O3 substrate and possess strong bonds, so they do not easily move even when exposed to a high-temperature reducing atmosphere. It also states that because the metal particles are fine and isolated, volume expansion is locally suppressed even under rapid oxidation, making them less likely to break. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 5244423 [Overview of the project] [Problems that the invention aims to solve]

[0007] The fuel electrode layer of a solid oxide electrochemical cell is exposed to a high-temperature reducing atmosphere during cell operation. Conventional cermet fuel electrode layers, when exposed to a high-temperature reducing atmosphere during cell operation, undergo particle growth, aggregation, and migration of nickel, leading to degradation of the fuel electrode layer.

[0008] Among the degradation modes of the fuel polar layer, Ni migration, in particular, is caused by the wetting and spreading of Ni in a high-temperature reducing atmosphere. This wetting and spreading of Ni occurs because the surface energy difference decreases by the amount of electrostatic energy of the capacitor formed between the catalyst material and the solid electrolyte material, and the contact angle decreases (electrowetting phenomenon).

[0009] However, there are limitations to suppressing the decrease in the surface energy difference and inhibiting the wetting spread of Ni solely through the combination of catalyst and solid electrolyte materials. Furthermore, there are constraints on the materials that can be selected from the viewpoint of ensuring the electrode activity of the fuel electrode layer. Therefore, it is difficult to suppress the deterioration of the fuel electrode layer due to Ni migration with this type of improvement.

[0010] In the technology of Patent Document 1, in order to bond Ni with an Al-based oxide or the like, addition of an Al-based oxide or the like is essential. When an Al-based oxide or the like is not added, deterioration of the fuel electrode layer due to movement of Ni cannot be suppressed.

[0011] The present invention has been made in view of such problems, and aims to provide a fuel electrode layer capable of suppressing deterioration due to movement of Ni, and a solid oxide type electrochemical cell using the same.

Means for Solving the Problems

[0012] One aspect of the present invention is a fuel electrode layer (1) used in a solid oxide type electrochemical cell (2), having catalyst material particles (11), solid electrolyte particles (12), and at least one metal M selected from metals having a standard electrode potential more negative than that of Ni, wherein the catalyst material particles contain Ni as a main component and also contain the metal M, the solid electrolyte particles contain a ceria-based oxide as a main component and also contain the metal M, and is in the fuel electrode layer (1).

[0013] Another aspect of the present invention is a solid oxide type electrochemical cell (2) having a fuel electrode layer (1), a solid electrolyte layer (22), and an air electrode layer (23) which is an electrode paired with the fuel electrode layer, in this order, wherein the solid electrolyte layer has an electrolyte main body layer (221) in contact with the fuel electrode layer, the electrolyte main body layer contains a ceria-based oxide as a main component and also contains the metal M, and is in the electrochemical cell (2).

Effects of the Invention

[0014] The fuel electrode layer has the above configuration. Therefore, in the fuel electrode layer exposed to a high-temperature reducing atmosphere during cell operation when a voltage is applied, at the interface between the catalyst material particles and the solid electrolyte particles, on the side of the catalyst material particles, M and O react with each other prior to Ni, and on the side of the solid electrolyte particles, M and O react with each other, forming an oxide of M. Therefore, according to the fuel electrode layer, the catalyst material particles can be fixed to the solid electrolyte particles by utilizing the binding force through oxygen. Therefore, according to the fuel electrode layer, the wetting spread of Ni in the high-temperature reducing atmosphere during cell operation when a voltage is applied is suppressed, and among the deterioration modes of the fuel electrode layer, deterioration of the fuel electrode layer due to the movement of Ni can be suppressed. react with each other, and on the side of the solid electrolyte particles, M and O 2- react with each other, forming an oxide of M. Therefore, according to the fuel electrode layer, the catalyst material particles can be fixed to the solid electrolyte particles by utilizing the binding force through oxygen. Therefore, according to the fuel electrode layer, the wetting spread of Ni in the high-temperature reducing atmosphere during cell operation when a voltage is applied is suppressed, and among the deterioration modes of the fuel electrode layer, deterioration of the fuel electrode layer due to the movement of Ni can be suppressed.

[0015] The electrochemical cell has the above configuration. Therefore, even when the fuel electrode layer is exposed to a high-temperature reducing atmosphere during cell operation when a voltage is applied, deterioration of the fuel electrode layer due to the movement of Ni can be suppressed. Therefore, according to the electrochemical cell, the durability of the fuel electrode layer as an electrode is excellent.

[0016] Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments below, and do not limit the technical scope of the present invention.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a diagram schematically showing a cross section along the thickness direction of a fuel electrode layer according to Embodiment 1. [Figure 2] FIG. 2 is a diagram schematically showing an enlarged view of the portion surrounded by a square in FIG. 1. [Figure 3] FIG. 3 is a diagram schematically showing a mechanism for suppressing deterioration due to the movement of Ni in a fuel electrode layer according to Embodiment 1. [Figure 4] FIG. 4 is a diagram of a fuel electrode layer of Comparative Form 1 corresponding to FIG. 2. [Figure 5]Figure 5 is a schematic diagram showing an example of the stacked structure of an electrochemical cell according to Embodiment 2. [Figure 6] Figure 6 is a schematic diagram showing another example of the stacked structure of the electrochemical cell according to Embodiment 2. [Figure 7] Figure 7 shows the XRD measurement results of the raw materials used to create the fuel polar layer, which were synthesized in Experimental Example 1. [Figure 8] Figure 8 shows the SEM-EDX analysis results of the fuel polar layer in the electrochemical cell of sample 1 obtained in Experimental Example 1. [Figure 9] Figure 9 shows the SEM-EDX analysis results of the fuel polar layer in the electrochemical cell of sample 1C obtained in Experimental Example 1. [Figure 10] Figure 10 shows the relationship between endurance time (h) (horizontal axis) and voltage (V) (vertical axis) in the electrochemical cells of Sample 1 and Sample 1C obtained in Experimental Example 1. [Figure 11] Figure 11 shows the relationship between Cr content (mol%) (horizontal axis), initial voltage (V), and voltage change (V) (vertical axis) in the electrochemical cells of samples 2 to 7 and sample 2C obtained in Experimental Example 2. [Figure 12] Figure 12 shows the SEM-EDX analysis results of the fuel polar layer in the electrochemical cell of sample 1 obtained in Experimental Example 3 (however, the measurement location is different from that in Figure 8). [Figure 13] Figure 13 shows the mass ratios of Ni, Cr, and O elements at points P1 and P2, which are concentrated Cr points, and at point P3, which is predominantly Ni, as obtained in Experimental Example 3. [Modes for carrying out the invention]

[0018] The fuel electrode layer and electrochemical cell of this embodiment will be described in detail below with reference to the drawings. Note that the fuel electrode layer and electrochemical 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 combined arbitrarily (details omitted below).

[0019] (Embodiment 1) The fuel electrode layer of Embodiment 1 will be described with reference to Figures 1 to 4. As illustrated in Figures 1 to 3, the fuel electrode layer 1 of this embodiment is used in a solid oxide type electrochemical cell 2. Preferably, the fuel electrode layer 1 of this embodiment can be suitably used in an electrochemical cell 2 having a solid electrolyte layer 22 in contact with the fuel electrode layer 1, wherein the solid electrolyte layer 22 uses a ceria oxide as the electrolyte. The detailed configuration of the electrochemical cell 2 will be described in detail in Embodiment 2.

[0020] The fuel electrode layer 1 of this embodiment comprises catalyst material particles 11, solid electrolyte particles 12, and metal M. Since metal M is a metallic element, and it is difficult to indicate metal M with a reference numeral in the figure, the reference numeral is omitted.

[0021] Figure 1 shows an example in which the fuel electrode layer 1 further has voids 13. Also in Figure 1, an example is shown in which the particle size of the catalyst material particles 11 is smaller than the particle size of the solid electrolyte particles 12, and the catalyst material particles 11 are present on the surface of the solid electrolyte particles 12. The relative particle sizes of the catalyst material particles 11 and the solid electrolyte particles 12 can be determined by obtaining a scanning electron microscope (SEM) image of the cross-section of the fuel electrode layer 1 and comparing the average particle sizes calculated for 10 particles of each.

[0022] In the fuel electrode layer 1, metal M is selected from at least one metal whose standard electrode potential is more negative than that of Ni. Note that Ni has a standard electrode potential of -0.257°C and a melting point (in metallic state, omitted below) of 1455°C. Examples of metal M include Co (standard electrode potential: -0.277, melting point: 1495°C), Cd (standard electrode potential: -0.403, melting point: 321°C), Fe (standard electrode potential: -0.447, melting point: 1538°C), Cr (standard electrode potential: -0.744, melting point: 1907°C), V (standard electrode potential: -1.130, melting point: 1910°C), Mn (standard electrode potential: -1.185, melting point: 1246°C), Mg (standard electrode potential: -1.55, melting point: 650°C), and Al (standard electrode potential: -1.6, melting point: 660.3°C). These can be used individually or in combination of two or more.

[0023] The catalyst material particles 11 contain Ni as the main component and also contain metal M. In the catalyst material particles 11, "containing Ni as the main component" means that the Ni content in the catalyst material particles 11 is 70% by mass or more. If the Ni content is less than 70% by mass, a decrease in hydrogen production output is a concern. From the viewpoint of catalytic activity and electron conductivity, the Ni content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. Specific examples of catalyst material particles 11 include Ni particles containing metal M (including alloy particles of Ni and metal M) (hereinafter sometimes referred to as Ni-M particles).

[0024] In catalyst material particles 11, the metal M can be dispersed within the catalyst material particles 11 when viewed in cross-section. This configuration has advantages such as minimizing the decrease in catalytic activity. Examples of such catalyst material particles 11 include particles in which metal M is dispersed within Ni particles, and particles in which metal M is diffused from the surface into the interior of Ni particles. However, since the diffusion of metal M within metallic Ni is very fast because it is between metals, it is usually difficult to imagine a situation where metal M exists in a distributed manner.

[0025] The solid electrolyte particles 12 mainly contain ceria oxide and also contain metal M. In the context of solid electrolyte particles 12, "mainly containing ceria oxide" means that the ceria oxide content in the solid electrolyte particles 12 is 60% by mass or more. If the ceria oxide content falls below 60% by mass, a decrease in hydrogen production output is a concern. From the viewpoint of oxygen ion conductivity and particle strength, the ceria oxide content is preferably 65% ​​by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and even more preferably 80% by mass or more. Specific examples of solid electrolyte particles 12 include ceria oxide particles containing metal M.

[0026] Examples of ceria-based oxides that can be used in the solid electrolyte particles 12 include ceria (CeO2) doped with one or more elements selected from Gd, Sm, Y, Sc, La, Nd, Yb, Ca, and Ho, and ceria. These can be used individually or in combination of two or more. Preferably, the above ceria-based oxide is ceria doped with at least one of Gd and Sm, and more preferably ceria doped with Gd, from the viewpoint of excellent oxygen ion conductivity at relatively low temperatures.

[0027] In solid electrolyte particles 12, the metal M can exist with a concentration distribution from the surface to the interior of the solid electrolyte particle 12 when viewed in cross-section. In other words, the concentration of the metal M can be such that, when viewed in cross-section, it decreases from the surface to the interior of the solid electrolyte particle 12. This configuration has advantages such as minimizing the decrease in oxygen ion conductivity. Examples of such solid electrolyte particles 12 include particles in which the metal M exists with a concentration distribution from the surface to the interior of ceria oxide particles, and particles in which the metal M is diffused from the surface to the interior of ceria oxide particles. Since the diffusion of metal M in ceria oxide is slow, the metal M can exist with a concentration distribution from the oxide surface to the interior (higher concentration at the surface, decreasing in concentration towards the interior).

[0028] Furthermore, the state of the metal M in the catalyst material particles 11 and solid electrolyte particles 12 described above can be determined by SEM-energy dispersive X-ray fluorescence analysis (EDX analysis).

[0029] The fuel electrode layer 1 of this embodiment has the above configuration. That is, in the fuel electrode layer 1 of this embodiment, metal M, which is a metal whose standard electrode potential is more negative than Ni, is placed on both the catalyst material particles 11 and the solid electrolyte particles 12. Therefore, in the fuel electrode layer 1 exposed to a high-temperature reducing atmosphere when a voltage is applied during cell operation, as shown in Figure 3, at the interface between the catalyst material particles 11 and the solid electrolyte particles 12, metal M and O are present before Ni on the catalyst material particle 11 side. 2- The two react, and on the solid electrolyte particle 12 side, metal M and O 2- The metals react with the oxygen to form an oxide of metal M. Therefore, according to the fuel electrode layer 1 of this embodiment, the catalyst material particles 11 can be fixed to the solid electrolyte particles 12 by utilizing the bonding force via oxygen. In other words, according to the fuel electrode layer 1 of this embodiment, the bonding force between the catalyst material particles 11 and the solid electrolyte particles 12 is increased. In the fuel electrode layer 1 of this embodiment, the oxide used for the solid electrolyte particles 12 is not a zirconia-based oxide, but a ceria-based oxide that has oxygen storage capacity, and metal M and O2- This is considered to be advantageous in ensuring compatibility with the other elements. Therefore, according to the fuel electrode layer 1 of this embodiment, the wetting and spreading of Ni in a high-temperature reducing atmosphere during cell operation when a voltage is applied is suppressed, and among the degradation modes of the fuel electrode layer 1, the degradation of the fuel electrode layer 1 due to Ni migration can be suppressed.

[0030] In contrast, as shown in Figure 4, in the case of the fuel electrode layer 1C of comparative form 1, which includes, for example, Ni particles 11C that do not contain metal M and ceria oxide particles 12C that do not contain metal M, when exposed to a high-temperature reducing atmosphere during cell operation with applied voltage, the surface energy difference decreases by the amount of electrostatic energy of the capacitor formed between the Ni particles 11C and the ceria oxide particles 12C, and the contact angle decreases, causing wetting and spreading of the Ni particles 11C, which do not have guaranteed bonding to the ceria oxide particles 12C. This is due to a phenomenon called electrowetting, which can be understood from the fact that the contact angle between the Ni particles 11C and the ceria oxide particles 12C depends on the voltage, as shown in the following equation. Therefore, the configuration of the fuel electrode layer 1C of comparative form 1 cannot suppress degradation due to Ni migration. cosθ(V) = cosθ0 - (C / 2)V 2 (θ(V): Wetting angle of catalyst material particles 11 relative to solid electrolyte particles 12 when voltage is applied to the electrode, θ0: Wetting angle of catalyst material particles 11 relative to solid electrolyte particles 12 under no load, C: Capacitance component between catalyst material particles 11 and solid electrolyte particles 12, V: Applied voltage)

[0031] Furthermore, although not shown in the diagram, in the case of comparative form 2 of the fuel electrode layer, where zirconia oxide particles containing metal M are used instead of ceria oxide particles containing metal M, the zirconia oxide is too stable, so even though it contains metal M, metal M and O 2- It is difficult to ensure bonding with the zirconia oxide particles, and as a result, it is difficult to increase the bonding strength between the Ni particles and the zirconia oxide particles. Therefore, even with the fuel polar layer of comparative form 2, degradation due to Ni migration cannot be suppressed.

[0032] In the fuel electrode layer 1 of this embodiment, the metal M is preferably at least one selected from the group consisting of Cr, V, and Mn. In this case, the melting point of the metal M is higher than the operating temperature of the solid oxide type electrochemical cell (for example, 550°C to 750°C), making it materially stable. Furthermore, its standard electrode potential is sufficiently negative compared to Ni, effectively suppressing the migration of Ni and reducing environmental burdens such as toxicity. Preferably, the metal M contains at least Cr from the viewpoint of electrical resistance and suppression of poisoning of the electrolyte material.

[0033] In the fuel electrode layer 1 of this embodiment, it is preferable that the concentration of metal M present in the solid electrolyte particles 12 is higher than the concentration of metal M present in the catalyst material particles 11. With this configuration, the migration of Ni can be suppressed more effectively, and the electrode performance of the fuel electrode layer 1 can be maintained. This is thought to be because the presence of a large amount of metal M on the solid electrolyte particles 12 side, which is stable at high temperatures, suppresses the electrowetting phenomenon described above, and an anchoring effect is obtained, which effectively suppresses changes. The concentration of metal M present in the solid electrolyte particles 12 and catalyst material particles 11 can be determined by SEM-EDX analysis.

[0034] In the fuel electrode layer 1 of this embodiment, the content of metal M contained in the fuel electrode layer 1 relative to the Ni contained in the fuel electrode layer 1 is preferably 1 mol% or more and 30 mol% or less in terms of oxide. By having a metal M content of 1 mol% or more, the effect of suppressing degradation due to Ni migration can be reliably achieved. The metal M content is more preferably 2 mol% or more, and even more preferably 3 mol% or more. On the other hand, by having a metal M content of 30 mol% or less, the electrode reaction in the fuel electrode layer 1 is less likely to be inhibited, and it becomes possible to effectively obtain the effect of suppressing degradation due to Ni migration while maintaining the hydrogen production output of the electrochemical cell 2. The metal M content is more preferably 25 mol% or less, even more preferably 20 mol% or less, even more preferably 15 mol% or less, and even more preferably 10 mol% or less.

[0035] The content of metal M can be measured as follows: A sample cut from the fuel electrode 1 is quantitatively analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the mass percentage of metal M. The obtained mass percentage of metal M is then converted to a molar percentage using the molecular weight of the metal M oxide. For example, a Hitachi High-Tech Corporation "SPS-3500" can be used as an ICP-AES instrument.

[0036] In the fuel electrode layer 1 of this embodiment, it is preferable that the proportion of metal M contained in the fuel electrode layer 1 is larger than that of Ni contained in the fuel electrode layer 1, as it exists as an oxide. This configuration makes it easier to induce a mechanism to suppress degradation due to the movement of the target Ni, and ensures improved durability of the fuel electrode layer 1.

[0037] The proportions of metal M and Ni present as oxides in the fuel electrode layer 1 can be determined as follows: A plane is obtained from the cross-section of the catalyst material particles 11 in the fuel electrode layer 1 by ion milling, and mapping images of Ni, O, and metal M are obtained from the same location by SEM-EDX analysis. These mapping images are then compared, and locations where metal M is concentrated (two locations, sometimes referred to as P1 and P2) and locations where Ni is mainly present and metal M is scarce (not concentrated) (one location, sometimes referred to as P3) are arbitrarily selected. Next, the mass ratio of O at each of these points P1 to P3 is measured. Then, the mass ratio of O at point P3, where Ni is mainly present, is compared with the mass ratio of O at points P1 and P2, which are metal M concentration points. If the relationship (mass ratio of O at point P3) < (mass ratio of O at point P1, mass ratio of O at point P2) is satisfied, then it is determined that the proportion of metal M contained in fuel electrode 1 is larger than that of Ni contained in fuel electrode 1, in the form of oxide.

[0038] In the fuel electrode layer 1 of this embodiment, the volume ratio of catalyst material particles to solid electrolyte particles can be, for example, catalyst material particles:solid electrolyte particles = 20:80 to 80:20. Preferably, the volume ratio of catalyst material particles to solid electrolyte particles can be 30:70 to 70:30, more preferably 35:65 to 65:35, and even more preferably 40:60 to 60:40.

[0039] In the fuel electrode layer 1 of this embodiment, the thickness of the fuel electrode layer 1 can be, for example, 10 μm or more and 100 μm or less. The thickness of the fuel electrode layer 1 is the arithmetic mean of the thickness measurements taken at nine locations on the cross-section of the fuel electrode layer 1 when it is cut along the thickness direction.

[0040] Furthermore, the description of Embodiment 2, which will be described later, can be applied to Embodiment 1, either alone or in any combination as needed.

[0041] (Embodiment 2) The electrochemical cell of Embodiment 2 will be described with reference to Figures 5 and 6. Note that, among the reference numerals used in Embodiment 2 and later, those that are the same as those used in the previously described embodiments represent the same components as those in the previously described embodiments, unless otherwise specified.

[0042] As illustrated in Figures 5 and 6, the electrochemical cell 2 of this embodiment is a solid oxide type electrochemical cell. The electrochemical cell 2 has a fuel electrode layer 1, a solid electrolyte layer 22, and an air electrode layer 23 in that order. Specifically, Figures 5 and 6 show an example in which the fuel electrode layer 1, the solid electrolyte layer 22, and the air electrode layer 23 are stacked in that order, the fuel electrode layer 1 and the solid electrolyte layer 22 are joined to each other, and the solid electrolyte layer 22 and the air electrode layer 23 are joined via an intermediate layer 24 (described later).

[0043] The electrochemical cell 2 may have a flat cell structure, as illustrated in Figures 5 and 6, or it may have a cylindrical cell structure, although this is not shown. Furthermore, the electrochemical cell 2 may have any of the following structures: electrolyte-supported, electrode-supported (fuel polar layer-supported, air polar layer-supported), or metal-supported.

[0044] The fuel electrode layer 1 is the electrode to which fuel is supplied. In other words, the fuel electrode layer 1 can be described as an electrode layer having electrode activity that allows it to function as a fuel electrode. Here, the fuel electrode layer 1 of Embodiment 1 is applied as the fuel electrode layer 1.

[0045] The solid electrolyte layer 22 is a layer that functions as an electrolyte in the electrochemical cell 2 and has oxygen ion conductivity. The solid electrolyte layer 22 has an electrolyte body layer 221 that is in contact with the fuel electrode layer 1. The solid electrolyte layer 22 may consist of a single layer or multiple layers. Figures 5 and 6 show an example in which the solid electrolyte layer 22 has two layers: an electrolyte body layer 221 that is in contact with the fuel electrode layer 1 and an electron blocking layer 222 formed on the air electrode layer 23 side of the electrolyte body layer 221. The electrolyte body layer 221 is the main electrolyte layer of the solid electrolyte layer 22 and is the layer that functions as the electrolyte of the electrochemical cell 2. If the solid electrolyte layer 22 is a single layer, that single layer functions as the electrolyte body layer 221. The electron blocking layer 222 is a layer that blocks the movement of electrons. If an electron blocking layer 222 is present, the electron blocking layer 222 can block the movement of electrons, so the electrolyte body layer 221 may exhibit electron conductivity in addition to oxygen ion conductivity, for example, under a reducing atmosphere. As described above, the solid electrolyte layer 22 has an electrolyte body layer 221 in contact with the fuel electrode layer 1 and is configured to function as an electrolyte for the electrochemical cell 2, but its layer configuration is not particularly limited.

[0046] Furthermore, although not shown in the figures, the solid electrolyte layer 22 laminated on the surface of the fuel electrode layer 1 may be formed to cover the outer peripheral end surfaces of the fuel electrode layer 1 and the fuel diffusion layer 25 (described later). In this case, fuel gas leakage can be suppressed with a relatively simple configuration. In this case, at least one of the electrolyte body layer 22 and the electron block layer 222 may be configured to cover the outer peripheral end surfaces of the fuel electrode layer 1 and the fuel diffusion layer 25.

[0047] The air electrode layer 23 is an electrode paired with the fuel electrode layer 1. In other words, the air electrode layer 23 can be described as an electrode layer that has electrode activity capable of functioning as an air electrode.

[0048] The electrochemical cell 2 may have an intermediate layer 24 between the solid electrolyte layer 22 and the air electrode layer 23, as illustrated in Figures 5 and 6. The intermediate layer 24 is primarily a reaction-inhibiting layer for suppressing the reaction between the material of the solid electrolyte layer 22 and the material of the air electrode layer 23. Figures 5 and 6 show an example in which the intermediate layer 24 is in contact with and bonded to the solid electrolyte layer 22 and the air electrode layer 23.

[0049] As illustrated in Figure 6, the electrochemical cell 2 may have a fuel diffusion layer 25 in contact with the fuel electrode layer 1 on the side opposite to the solid electrolyte layer 22 in the fuel electrode layer 1. The fuel diffusion layer 25 is a layer that has the function of diffusing the fuel supplied to the fuel electrode layer 1. The fuel diffusion layer 25 may also have the function of diffusing electrons. When a fuel diffusion layer 25 is present, the diffused fuel can be supplied to the fuel electrode layer 1. In addition, the fuel diffusion layer 25 may be configured to function not only as a fuel diffusion layer that diffuses fuel in the planar direction, but also as a support layer that supports each layer on the fuel electrode layer 1 side. Furthermore, the fuel diffusion layer 25 may also function as a current collector for the fuel electrode layer 1.

[0050] As illustrated in Figure 6, the electrochemical cell 2 may also have an air electrode current collector layer 26 on the side of the air electrode layer 23 opposite to the solid electrolyte layer 22. The air electrode current collector layer 26 is a layer that functions as a current collector for the air electrode layer 23.

[0051] In the electrochemical cell 2, the thickness of the fuel electrode layer 1 can be, for example, 10 μm to 100 μm. The thickness of the solid electrolyte layer 22 can be, for example, 2 μm to 20 μm. The thickness of the electrolyte body layer 221 can be, for example, 1 μm to 15 μm. The thickness of the electron block layer 222 can be, for example, 1 μm to 15 μm. The thickness of the air electrode layer 23 can be, for example, 10 μm to 100 μm. The thickness of the intermediate layer 24 can be, for example, 1 μm to 20 μm. The thickness of the fuel diffusion layer 25 can be, for example, 100 μm to 800 μm. The thickness of the air electrode current collector layer 26 can be, for example, 1 μm to 100 μm. The average value of the thickness of each layer can be determined in the same manner as the thickness of the fuel electrode layer 1 described above in Embodiment 1.

[0052] In the electrochemical cell 2 having the layered structure described above, the electrolyte body layer 221 contains ceria oxide as the main component and also contains metal M. In the electrolyte body layer 221, "containing ceria oxide as the main component" means that the ceria oxide content in the electrolyte body layer 221 is 60% by mass or more. If the ceria oxide content is less than 60% by mass, a decrease in hydrogen production output is a concern. From the viewpoint of oxygen ion conductivity and electrolyte strength, the ceria oxide content is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Specifically, the electrolyte body layer 221 can be composed of ceria oxide containing metal M.

[0053] Examples of ceria-based oxides that can be used in the electrolyte body layer 221 include ceria (CeO2) doped with one or more elements selected from Gd, Sm, Y, Sc, La, Nd, Yb, Ca, and Ho, and ceria. These can be used individually or in combination of two or more. Preferably, the above ceria-based oxide is ceria doped with at least one of Gd and Sm, and more preferably ceria doped with Gd, from the viewpoint of excellent oxygen ion conductivity at relatively low temperatures.

[0054] In the electrolyte body layer 221, the metal M can exist with a concentration distribution from the surface on the fuel electrode layer 1 side to the interior when viewed in cross-section of the electrolyte body layer 221. In other words, the concentration of metal M can be such that, when viewed in cross-section of the electrolyte body layer 221, it decreases as you move from the surface on the fuel electrode layer 1 side to the interior. This configuration has advantages such as preventing poisoning of the electron block layer 222 and maintaining oxygen ion conductivity. Examples of such configurations for the electrolyte body layer 221 include a configuration in which the metal M exists with a concentration distribution from the surface on the fuel electrode layer 1 side to the interior of the ceria oxide layer, and a configuration in which the metal M is diffused from the surface to the interior of the ceria oxide layer. Since the diffusion of metal M in the ceria oxide layer is slow, the metal M can exist with a concentration distribution from the surface to the interior of the ceria oxide layer (higher concentration at the surface on the fuel electrode layer 1 side, and lower concentration as you move in).

[0055] Furthermore, the state of metal M in the electrolyte body layer 221 can be determined by SEM-EDX analysis.

[0056] The electrochemical cell 2 described above has the above configuration. Therefore, even when the fuel electrode layer 1 is exposed to a high-temperature reducing atmosphere during cell operation when a voltage is applied, the electrochemical cell 2 can suppress the deterioration of the fuel electrode layer 1 due to Ni migration. Thus, the electrochemical cell 2 provides excellent durability for the fuel electrode layer 1, which is the electrode.

[0057] Furthermore, the electrochemical cell 2 also has the following advantages. Specifically, in the electrochemical cell 2, the electrolyte body layer 221 in contact with the fuel electrode layer 1 is made of the same material as the solid electrolyte particles 12 contained in the fuel electrode layer 1. Therefore, differences in Ni wettability are less likely to occur between the fuel electrode layer 1 and the electrolyte body layer 221, making it possible to more reliably suppress the deterioration of the fuel electrode layer 1 due to Ni migration.

[0058] As long as the electrochemical cell 2 described above is configured as a solid oxide cell, and the fuel electrode layer 1 has the configuration described above in Embodiment 1, and the electrolyte body layer 222 has the configuration described above, the materials and configurations of the fuel diffusion layer 25, the electron blocking layer 222 of the solid electrolyte layer 22, the intermediate layer 24, the air electrode layer 23, the air electrode current collector layer 27, etc., are not particularly limited. Specifically, each of these layers can be configured as follows.

[0059] The fuel diffusion layer 25 may specifically include an electronically conductive material, an oxide material within the diffusion layer, and voids. Both the electronically conductive material and the oxide material within the diffusion layer can exist as particles.

[0060] Examples of electronically conductive materials that can be used in the fuel diffusion layer 25 include electronic conductors (metals and alloys, hereafter omitted) such as Ni, Ni alloys, Cu, Cu alloys, Co, and Co alloys, and oxides of electronic conductors that become electronic conductors upon reduction, such as Ni oxide (NiO, etc.), Cu oxide, and Co oxide (oxides of metals and alloys, hereafter omitted). These can be used individually or in combination of two or more. The electronically conductive material used in the fuel diffusion layer 25 may or may not have catalytic activity. Of these, Ni, Ni alloys, Ni oxide (NiO, etc.) are preferred from the viewpoint of catalytic activity, and Ni, NiO, etc. are preferred. Furthermore, examples of the oxide material 312 in the diffusion layer include solid electrolyte materials such as ceria (CeO2) doped with one or more elements selected from Gd, Sm, Y, Sc, La, Nd, Yb, Ca, and Ho, ceria, yttria-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ), as well as various oxides that are not solid electrolyte materials such as CaO and MgO. These can be used individually or in combination of two or more. The ceria-based oxide is preferably ceria doped with at least one of Gd and Sm, more preferably ceria doped with Gd, from the viewpoint of excellent oxygen ion conductivity at relatively low temperatures of about 700°C.

[0061] If the solid electrolyte layer 22 has an electron blocking layer 222 in addition to the electrolyte body layer 221, as illustrated in Figures 5 and 6, the electron blocking layer 222 can be made of a solid electrolyte material that does not conduct electrons but conducts oxygen ions. Examples of solid electrolyte materials that do not conduct electrons but conduct oxygen ions include yttria-stabilized zirconia and scandia-stabilized zirconia. These can be used individually or in combination of two or more. The solid electrolyte layer 22 is usually formed to be dense so as not to allow gas to pass through.

[0062] The intermediate layer 24 can be composed of a mixed material containing a solid electrolyte material having oxygen ion conductivity and an air electrode material constituting the air electrode layer 23, a solid electrolyte material having oxygen ion conductivity, and the like. Note that the solid electrolyte material having oxygen ion conductivity used for the intermediate layer 24 may have electronic conductivity or may not have electronic conductivity.

[0063] Examples of the solid electrolyte material having oxygen ion conductivity used for the intermediate layer 24 include, for example, the above-described ceria-based oxides, solid electrolyte materials such as ceria, yttria-stabilized zirconia, scandia-stabilized zirconia, and the like. These can be used alone or in combination of two or more.

[0064] Specifically, the air electrode layer 23 can include an air electrode inner catalyst material, an air electrode inner electrolyte material, and voids. Both the air electrode inner catalyst material and the air electrode inner electrolyte material can exist as particles. The air electrode inner catalyst material can be composed of an air electrode catalyst material having electronic conductivity and oxygen ion conductivity, and the like. The air electrode inner electrolyte material can be composed of a solid electrolyte material having oxygen ion conductivity, and the like.

[0065] Examples of the air electrode inner catalyst material include perovskite-type oxides containing La, Sr, and Co, perovskite-type oxides containing Pr, Ba, and Co, perovskite-type oxides containing Gd, Ba, and Co, perovskite-type oxides containing Nd, Ba, and Co, and the like. These can be used alone or in combination of two or more. Specific examples of the perovskite-type oxide containing La, Sr, and Co described above include La 0.6 Sr 0.4 CoO3 and the like, La 1-x Sr x CoO 3-δ metal oxides represented by (0 < x ≦ 1, preferably 0.1 ≦ x ≦ 0.5), and the like. Specific examples of the perovskite-type oxide containing Pr, Ba, and Co include Pr 2-x Ba xHo2O 5+δ Examples include metal oxides represented by (0.7≦x≦1.3, preferably 0.8≦x≦1). Specifically, perovskite-type oxides containing Gd, Ba, and Co include Gd 2-x Ba x Ho2O 5+δ Examples include metal oxides represented by (0.7≦x≦1.3, preferably 0.8≦x≦1). Specifically, perovskite-type oxides containing Nd, Ba, and Co include Nd 2-x Ba x Ho2O 5+δ Examples include metal oxides represented by (0.7 ≤ x ≤ 1.3, preferably 0.8 ≤ x ≤ 1). The oxides mentioned above may or may not have oxygen nonstoichiometric properties. Examples of the electrolyte material inside the air electrode include the ceria-based oxides and ceria mentioned above. These can be used individually or in combination of two or more.

[0066] The air electrode current collector layer 26 can be made of an air electrode current collector material having electronic conductivity suitable for current collection on the air electrode side, which is exposed to a high-temperature oxidizing atmosphere.

[0067] Examples of air electrode current collector materials include metallic materials such as Pt, Pt alloys, Ag, Ag alloys, and Au; perovskite-type oxides containing La, Sr, and Co; and electron-conductive oxides such as perovskite-type oxides containing La, Ni, and Fe. These can be used individually or in combination of two or more.

[0068] The electrochemical cell 2 can be used as at least one of a solid oxide electrolytic cell (SOEC) and a solid oxide fuel cell (SOFC). In other words, the electrochemical cell 1 may operate as an SOEC, or as an SOFC, or it may be configured to be switchable between an SOEC mode and an SOFC mode, and operated as either an SOEC or an SOFC.

[0069] Specifically, when the electrochemical cell 2 is operated as an SOEC, the fuel electrode 1 can function as a hydrogen electrode. The fuel electrode 1 can be supplied with a water (H2O)-containing gas, such as a gas containing water vapor, as fuel. In this case, the air electrode 23 can function as an oxygen electrode. The air electrode 23 may or may not be supplied with a gas such as air. Furthermore, when the electrochemical cell 2 is operated as an SOEC, it can be applied not only to water vapor electrolysis but also to CO2-water vapor co-electrolysis, CO2 electrolysis, etc. In CO2-water vapor co-electrolysis, at least CO2 gas and a gas containing water vapor can be used as fuel, and in CO2 electrolysis, a gas containing CO2 gas can be used as fuel. On the other hand, when the electrochemical cell 2 is operated as an SOFC, the fuel electrode 1 can be supplied with a hydrogen-containing gas, such as hydrogen gas, as fuel. In this case, the air electrode 23 can be supplied with an oxygen-containing gas, such as air or oxygen gas. Furthermore, the water-containing gas mentioned above may contain reducing gases such as hydrogen gas, and the hydrogen-containing gas may contain water vapor for humidification purposes.

[0070] The operating temperature of the electrochemical cell 2 can preferably be 500°C or higher, more preferably 600°C or higher, and even more preferably 650°C or higher, from viewpoints such as reducing cell resistance and obtaining high output. Alternatively, the operating temperature of the electrochemical cell 2 can preferably be 825°C or lower, more preferably 800°C or lower, and even more preferably 775°C or lower, from viewpoints such as easily suppressing reductive expansion.

[0071] Furthermore, the description of Embodiment 1 above can be applied to Embodiment 2, either individually or in any combination as needed.

[0072] (Experimental Example 1) <Electrochemical cell for sample 1> -Fuel electrode layer- NiO powder and Cr(NO3)3 were mixed at room temperature in a solvent prepared by mixing water and ethanol in a 1:1 mass ratio. The solvent was then evaporated and dried while the mixture was being heated and dispersed, thereby concentrating Cr(NO3)3 on the surface of the NiO particles. Next, this was heat-treated at 350°C for 1 hour to remove the Cr(NO3)3 on the surface of the NiO particles, converting it to Cr oxide. This was then heat-treated at 800°C for 2 hours to separate NiO and CrO x The compound was determined to be NiO and CrO. This compound was subjected to XRD analysis using an X-ray diffractometer (MiniFlex, Rigaku). The XRD measurement results are shown in Figure 7. According to these results, the above compound is NiO and CrO. x It can be seen that the reaction between the two has resulted in a mixed crystal of NiCr2O4 and NiO. In this experiment, a nitrate was used, but it is not limited to this, and other salts such as acetates, oxalates, and carbonates can also be used.

[0073] Next, the obtained mixed crystalline particles were mixed with terpineol (solvent), a dispersant, a leveling agent, and a settling inhibitor, and the particle size was adjusted using a ball mill. Here, the particles were crushed so that the average particle size was 0.1 to 1.0 μm. This yielded a catalyst material slurry. The above average particle size is the particle size (diameter) d50 when the volume-based cumulative frequency distribution measured by laser diffraction and scattering method shows 50% (the same applies hereafter).

[0074] Next, the obtained catalyst material slurry was mixed with Gd-doped CeO2 (hereinafter referred to as GDC) powder, a solid electrolyte material of ceria oxide, and carbon (pore-forming material), and then dispersed using a ball mill. The amount of Gd doping was 10 mol%. Next, an acrylic resin (binder) was added and stirred, and then kneaded using a three-roll mill. A paste for fuel polar layer formation was obtained. In this experimental example, Cr was selected as the metal M, but if a metal M other than Cr is selected, a catalyst material slurry containing mixed crystalline particles of Ni and a composite oxide containing metal M, formed by the reaction of NiO and the oxide of metal M, and NiO can be prepared in accordance with the above, and the paste for fuel polar layer formation can be prepared by mixing this catalyst material slurry with a ceria oxide.

[0075] -Fuel diffusion layer formation sheet- A slurry was prepared by mixing NiO powder (average particle size: 0.4 μm), GDC powder (average particle size: 0.3 μm), carbon (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. This slurry was coated in layers onto a resin sheet using the doctor blade method, dried, and then peeled off to prepare a sheet for forming the fuel diffusion layer. The amount of carbon in the sheet for forming the fuel diffusion layer is said to be larger than the amount of carbon in the paste for forming the fuel electrode layer.

[0076] -Sheet for forming the electrolyte main layer- A slurry was prepared by mixing GDC powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. Subsequently, the sheet for forming the electrolyte main layer was prepared in the same manner as the sheet for forming the fuel diffusion layer.

[0077] -Sheet for forming an electron blocking layer- A slurry was prepared by mixing 8 mol% yttria-doped ZrO2 (hereinafter referred to as 8YSZ) powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. Subsequently, a sheet for forming the electron block layer was prepared in the same manner as the sheet for forming the fuel diffusion layer.

[0078] - Sheet for forming the intermediate layer - A slurry was prepared by mixing GDC powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. Subsequently, a sheet for forming the intermediate layer was prepared in the same manner as the sheet for forming the fuel diffusion layer.

[0079] -Paste for forming an air polar layer- LSC(La 0.6 Sr 0.4 A paste for forming an air pole layer was prepared by kneading CoO3 powder (average particle size: 2.0 μm), ethylcellulose, and terpineol using a three-roll mixing machine.

[0080] <Preparation of single cells> A fuel electrode layer-forming paste was applied to one surface of a fuel diffusion layer-forming sheet using a screen printing method and dried to form a fuel electrode layer-forming sheet. Next, an electrolyte body layer-forming sheet, an electron block layer-forming sheet, and an intermediate layer-forming sheet were laminated on this fuel electrode layer-forming sheet in that order, and a laminate was obtained by pressing them together using a water-impeded pressing (WIP) method. The pressing conditions were a temperature of 85°C, a pressure of 50 MPa, and a pressing time of 10 minutes. After pressing, the laminate was degreased. In order to improve the dimensional accuracy of the resulting cell, the outer circumference of the laminate was cut after pressing to adjust its dimensions. Next, the laminate was fired in an atmospheric environment at 1350°C for 2 hours. This resulted in a sintered body in which the fuel diffusion layer, fuel electrode layer, electrolyte body layer, electron block layer, and intermediate layer were laminated in that order.

[0081] Next, an air electrode layer formation paste was applied to the surface of the intermediate layer of the obtained sintered body by screen printing, and the air electrode layer was formed by firing (baking) in an atmospheric environment at 950°C for 2 hours. At this time, the outer shape of the air electrode layer was formed to be smaller than the outer shape of the solid electrolyte layer (in this case, the electrolyte body layer + electron block layer).

[0082] Next, the fuel electrode and the air electrode were attached to an evaluation jig to separate them spatially, and then sealed with glass to form a gas seal structure. Subsequently, the fuel electrode side was subjected to a hydrogen atmosphere, and an activation treatment (reduction treatment) of the fuel electrode was carried out at a temperature of 650°C.

[0083] Based on the above, an electrochemical cell (single cell) of Sample 1 was obtained, in which the fuel diffusion layer (thickness 300 μm), fuel electrode layer (thickness 25 μm), electrolyte main layer (thickness 3 μm), electron blocking layer (thickness 3 μm), intermediate layer (thickness 3 μm), and air electrode layer (thickness 25 μm) were stacked in this order. The Cr content in the fuel electrode layer of Sample 1 is 1 mol% in terms of oxide.

[0084] <Electrochemical cell for sample 1C> In the preparation of the electrochemical cell for Sample 1, the electrochemical cell for Sample 1C was prepared in the same manner as for Sample 1, except that Cr(NO3)3 was not mixed when preparing the paste for forming the fuel electrode layer, and a Cr-free NiO slurry was used as the catalyst material slurry; 8YSZ powder, which is a zirconia oxide, was mixed into the catalyst material slurry instead of a ceria oxide as the solid electrolyte material; 8YSZ powder was used instead of GDC powder when preparing the sheet for forming the electrolyte body layer; and the solid electrolyte layer was composed of a single layer of the electrolyte body layer.

[0085] <Various measurements and evaluations> -SEM-EDX analysis- SEM-EDX analysis was performed on the fuel electrode layers of the electrochemical cells of the prepared samples 1 and 1C. Specifically, a planar cross-section of the catalyst material particles in the fuel electrode layer was obtained by ion milling, and SEM-EDX analysis was performed on the same area to obtain mapping images of Ni, Ce, Zr, and Cr. In this experiment, the electrolyte body layer and the solid electrolyte particles were mainly composed of the same ceria oxide, and catalyst material particles that were in clear contact with the electrolyte body layer were selected for reasons such as the ease of observing the diffusion of Cr. A HORIBA EMAXENERGY was used for the SEM-EDX analysis. The results are shown in Figures 8 and 9.

[0086] As shown in Figure 8, in sample 1, which uses a ceria-based oxide as the solid electrolyte material, it can be seen that Cr diffuses from the surface to the interior of the Ni particles and is dispersed within the Ni particles. Furthermore, in the electrolyte body layer in contact with the fuel electrode layer of the solid electrolyte layer, even though a raw material that does not contain Cr is used, it can be seen that Cr is present from the surface on the fuel electrode side of the electrolyte body layer to the interior. This is because the Cr contained in the mixed crystalline particles used in the catalyst material slurry diffused from the surface on the fuel electrode side of the ceria-based oxide layer that constitutes the electrolyte body layer to the interior. The concentration of Cr was higher at the surface on the fuel electrode side of the ceria-based oxide layer and decreased in concentration towards the interior. In addition, from the brightness of the Cr element mapping, it can be seen that the concentration of Cr present in the ceria-based oxide is higher than the concentration of Cr present in the Ni particles.

[0087] From the above results, it can be said that in sample 1, the fuel electrode has catalyst material particles mainly composed of Ni and containing Cr, and solid electrolyte particles mainly composed of ceria oxide and containing Cr. Furthermore, it can be said that the concentration of Cr present in the solid electrolyte particles is higher than the concentration of Cr present in the catalyst material particles.

[0088] In contrast, as shown in Figure 9, in sample 1C, which uses a zirconia-based oxide as the solid electrolyte material, Cr diffused from the surface into the interior of the Ni particles, and Cr was dispersed within the Ni particles, similar to sample 1. However, Cr did not diffuse from the surface of the electrolyte body layer on the fuel electrode side into the interior, indicating that Cr was not present inside the electrolyte body layer. In other words, the desired effect could not be obtained in sample 1C.

[0089] From the above results, it can be said that in sample 1C, the fuel electrode has catalyst material particles that mainly contain Ni and also contain Cr, and solid electrolyte particles that mainly contain zirconia oxide and do not contain Cr.

[0090] -Durability Test- The electrochemical cells of Sample 1 and Sample 1C were used as SOECs, and the temperature was raised to 650°C while introducing N2 (500 ml) into both the fuel and air electrodes. Next, water vapor and H2 were introduced into the fuel electrode (by volume, H2 / H2O = 1), and air was introduced into the air electrode for an electrolytic test (operating temperature: 650°C). In this experiment, Us (water vapor utilization rate) was set to 50%. The results are shown in Figure 10.

[0091] As shown in Figure 10, even though the catalyst material particles contained Ni and Cr, sample 1C, in which the solid electrolyte particles contained zirconia-based oxide but not Cr, showed a gradual increase in cell resistance and voltage as the durability time increased. This is because the fuel electrode layer of sample 1C could not suppress the wetting and spreading of Ni in a high-temperature reducing atmosphere during cell operation when voltage was applied, and therefore could not suppress the deterioration of the fuel electrode layer due to Ni migration, which is one of the deterioration modes of the fuel electrode layer.

[0092] In contrast, sample 1C, in which catalyst material particles contain Ni and Cr, and solid electrolyte particles contain ceria oxide and Cr, satisfies the requirements of this disclosure, and it was confirmed that the cell resistance remained stable even after extended durability time and no increase in voltage was observed. This is because the fuel electrode layer of sample 1 was able to suppress the wetting and spreading of Ni in a high-temperature reducing atmosphere during cell operation when voltage was applied, and thus suppressed the deterioration of the fuel electrode layer due to Ni migration, which is one of the deterioration modes of the fuel electrode layer.

[0093] (Experimental Example 2) Similar to the electrochemical cell of Sample 1 in Experimental Example 1, several electrochemical cells with different Cr content (oxide equivalent, mol%) in the fuel electrode layer were prepared. Here, the Cr content was adjusted by changing the amount of Cr(NO3)3 mixed with NiO powder to obtain electrochemical cells for Samples 2 to 7. The Cr content in the fuel electrode layer of Samples 2 to 7, in terms of oxide equivalent, was 1 mol% (Sample 2), 10 mol% (Sample 3), 20 mol% (Sample 4), 30 mol% (Sample 5), 40 mol% (Sample 6), and 50 mol% (Sample 7), respectively.

[0094] For comparison, the electrochemical cell for sample 2C was prepared in the same manner as the electrochemical cell for sample 1, except that Cr(NO3)3 was not mixed when preparing the paste for forming the fuel polar layer, and a Cr-free NiO slurry was used as the catalyst material slurry.

[0095] Electrolytic tests were conducted using each electrochemical cell under the same conditions as the durability test in Experimental Example 1. The initial voltage (V) and the voltage after 100 hours of durability (V) were measured. The voltage change (V) was calculated using the formula (voltage after durability - initial voltage). The results are shown in Figure 11.

[0096] As shown in Figure 11, the voltage after durability can be maintained in the range of Cr content from 1 mol% to 30 mol%, but when the Cr content exceeds 30 mol%, the voltage after durability tends to increase and durability deteriorates. Furthermore, from the perspective of initial voltage, it can be seen that by keeping the Cr content below 30 mol%, it is possible to reliably prevent output reduction due to voltage increase. From these results, it can be said that by keeping the Cr content between 1 mol% and 30 mol%, the degradation suppression effect due to Ni migration can be reliably achieved, and the degradation suppression effect due to Ni migration can be effectively obtained while maintaining the hydrogen production output of electrochemical cell 2.

[0097] (Experimental Example 3) For the fuel electrode layer of the electrochemical cell of sample 1, the cross-section of the catalyst material particles was prepared as a plane using ion milling, and mapping images of Ni, O, and Cr elements were obtained from the same area by SEM-EDX analysis. The results are shown in Figure 12.

[0098] As shown in Figure 12, comparing the elemental mapping images reveals the presence of oxygen (O) in both the Ni and Cr regions. This indicates that Cr, the metal M used in this experiment, is present as an oxide rather than Ni, confirming that the desired structure has been achieved.

[0099] Next, we arbitrarily selected areas in the Cr element mapping image where Cr was concentrated (points P1 and P2 in Figure 12) and areas where Ni was mainly present and Cr was scarce (not concentrated) (point P3 in Figure 12). Then, we measured the mass percentage of O element at each of these points P1 to P3. In addition, we also measured the mass percentages of Ni and Cr elements at each of these points P1 to P3. The results are shown in Figure 13.

[0100] As shown in Figure 13, comparing the mass ratio of element O at point P3, which is mainly Ni, with points P1 and P2, which are Cr-concentrated points, we can see that the relationship (mass ratio of O at point P3) < (mass ratio of O at point P1, mass ratio of O at point P2) is satisfied. Therefore, from this result, it can be said that the proportion of Cr contained in the fuel electrode layer is larger in the form of oxide compared to the Ni contained in fuel electrode layer 1. Furthermore, from the results of Experimental Example 1 described above, it can be said that when such a configuration is present, the mechanism for suppressing degradation due to the movement of the target Ni is more likely to be expressed, and the durability of the fuel electrode layer can be reliably improved.

[0101] The present invention is not limited to the embodiments and experimental examples described above, and various modifications are possible without departing from the spirit of the invention. Furthermore, each of the configurations shown in the embodiments and experimental examples can be combined in any way.

[0102] The features of this invention are as follows. Section 1. A fuel polar layer (1) used in a solid oxide type electrochemical cell (2), The device comprises catalyst material particles (11), solid electrolyte particles (12), and at least one metal M selected from metals whose standard electrode potential is more negative than that of Ni. The catalyst material particles mainly contain Ni and also contain the metal M. The solid electrolyte particles mainly consist of ceria oxides and also contain the metal M. Fuel electrode layer (1). Section 2. The aforementioned metal M is at least one selected from the group consisting of Cr, V, and Mn. The fuel polar layer described in item 1. Section 3. The concentration of metal M present in the solid electrolyte particles is higher than the concentration of metal M present in the catalyst material particles. The fuel polar layer described in item 1 or item 2. Section 4. The content of the metal M contained in the fuel electrode layer relative to the Ni contained in the fuel electrode layer is 1 mol% or more and 30 mol% or less in terms of oxide. The fuel polar layer described in any one of items 1 to 3. Section 5. The metal M contained in the fuel electrode layer exists in a larger proportion as an oxide compared to the Ni contained in the fuel electrode layer. The fuel polar layer described in any one of items 1 through 4. Section 6. A solid oxide type electrochemical cell (2) having, in this order, a fuel electrode layer (1) as described in any one of items 1 to 5, a solid electrolyte layer (22), and an air electrode layer (23) which is an electrode paired with the fuel electrode layer, The solid electrolyte layer has an electrolyte body layer (221) in contact with the fuel electrode layer, The electrolyte body layer mainly contains ceria oxides and also contains the metal M. Electrochemical cell (2). [Explanation of Symbols]

[0103] 1 Fuel electrode layer 11 Catalyst material particles 12 Solid electrolyte particles 2 Electrochemical Cell 22 Solid electrolyte layer 23. Polar air layer

Claims

1. A fuel polar layer (1) used in a solid oxide type electrochemical cell (2), The device comprises catalyst material particles (11), solid electrolyte particles (12), and at least one metal M selected from metals whose standard electrode potential is more negative than that of Ni. The catalyst material particles mainly contain Ni and also contain the metal M. The solid electrolyte particles mainly consist of ceria oxides and also contain the metal M. Fuel electrode layer (1).

2. The aforementioned metal M is at least one selected from the group consisting of Cr, V, and Mn. The fuel polar layer according to claim 1.

3. The concentration of the metal M present in the solid electrolyte particles is higher than the concentration of the metal M present in the catalyst material particles. The fuel polar layer according to claim 1.

4. The content of the metal M contained in the fuel electrode layer relative to the Ni contained in the fuel electrode layer is 1 mol% or more and 30 mol% or less in terms of oxide. The fuel polar layer according to claim 1.

5. The metal M contained in the fuel electrode layer exists in a larger proportion as an oxide compared to the Ni contained in the fuel electrode layer. The fuel polar layer according to claim 1.

6. A solid oxide type electrochemical cell (2) having, in this order, a fuel electrode layer (1) according to any one of claims 1 to 5, a solid electrolyte layer (22), and an air electrode layer (23) which is an electrode paired with the fuel electrode layer, The solid electrolyte layer has an electrolyte body layer (221) in contact with the fuel electrode layer, The electrolyte body layer mainly contains ceria oxides and also contains the metal M. Electrochemical cell (2).

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