Solid oxide electrolysis cell

Abstract

A solid oxide electrolysis cell (1) has: a metal support (2) having a through-pore formation region (22) in which a large number of through-pores (21) penetrating in the thickness direction are formed; and a cell portion (3) layered on one surface of the through-pore formation region (22). The cell portion (3) has, in order from the metal support (2) side, a fuel diffusion layer (31) that diffuses fuel gas, a fuel electrode layer (32) to which the fuel gas is supplied from the fuel diffusion layer (31), a solid electrolyte layer (33), and an air electrode layer (34) that pairs with the fuel electrode layer (32). The solid oxide electrolysis cell (1) satisfies the relationship: metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity, where the metal support porosity is the area ratio of voids in a cross section along the surface direction of the metal support (2), the fuel diffusion layer porosity is the area ratio of voids in a cross section along the surface direction of the fuel diffusion layer (31), and the fuel electrode layer porosity is the area ratio of voids in a cross section along the surface direction of the fuel electrode layer (32).

Description

Solid oxide electrolysis cell CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-106017, filed on July 1, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to solid oxide electrolysis cells.

[0003] Conventionally, solid oxide electrolysis cells (hereinafter sometimes referred to as SOECs) that use a solid oxide as an electrolyte for electrolyzing fuel gases such as water vapor and carbon dioxide have been known. Some SOECs of this type have a cell section supported by a metal support.

[0004] For example, Patent Document 1 discloses an electrochemical cell that can be used in an SOEC, which includes a metal support having a plurality of through holes penetrating between one surface and the other surface, and a cell portion joined to one surface of the metal support, wherein the cell portion includes a first electrode layer formed on one surface of the metal support, a solid electrolyte layer formed on the first electrode layer, and a second electrode layer formed on the solid electrolyte layer, and the first electrode layer has through-hole regions corresponding to positions on the one surface where the through-hole openings are located, and non-through-hole regions corresponding to positions on the one surface where the through-hole openings are not located, and the gas diffusion resistance in the through-hole regions is greater than the gas diffusion resistance in the non-through-hole regions.

[0005] International Publication No. 2023 / 013205

[0006] When the above-described conventional electrochemical cell is used as an SOEC, there is room for improvement in the following respect: In this conventional technology, the fuel gas that flows into the through-hole region of the first electrode layer from the through-holes in the metal support diffuses into the non-through-hole region around the through-hole region, which has a low gas diffusion resistance, due to the high gas diffusion resistance of the through-hole region.

[0007] The technique of partially increasing the gas diffusion resistance in the region where the through-holes are located in the fuel electrode layer, which is the electrode to which the fuel gas is supplied, is unlikely to cause problems if it is limited to low-power electrolysis of the fuel gas (operation at low current density). However, to obtain more hydrogen or carbon monoxide, it is necessary to supply more fuel gas, such as water vapor or carbon dioxide, which has a larger molecular weight than hydrogen. This technique makes it difficult to uniformly supply the fuel gas across the surface of the fuel electrode layer. Therefore, it is difficult to achieve high-power electrolysis (operation at high current density) with conventional technology. It is possible to increase the porosity of the metal support by increasing the through-holes to uniformly supply the fuel gas across the surface of the fuel electrode layer, but this technique reduces the strength of the metal support and the structural reliability of the metal-supported SOEC.

[0008] An object of the present disclosure is to provide a solid oxide electrolysis cell that can achieve high-power electrolysis while ensuring the strength of the metal support.

[0009] One aspect of the present disclosure is a solid oxide electrolysis cell comprising: a metal support having a through pore-formed region in which a large number of through pores are formed penetrating in the thickness direction; and a cell portion laminated on one surface of the through pore-formed region, wherein the cell portion comprises, in this order from the metal support side, a fuel diffusion layer that diffuses a fuel gas, an anode layer that is an electrode to which the fuel gas is supplied from the fuel diffusion layer, a solid electrolyte layer, and an air cathode layer that is an electrode that forms a pair with the anode layer, wherein the relationship of metal support porosity < fuel diffusion layer porosity < anode layer porosity is satisfied, where the area ratio of voids in a cross section along the surface direction of the metal support is defined as metal support porosity, the area ratio of voids in a cross section along the surface direction of the fuel diffusion layer is defined as fuel diffusion layer porosity, and the area ratio of voids in a cross section along the surface direction of the anode layer is defined as anode layer porosity.

[0010] The solid oxide electrolysis cell has the above configuration. Therefore, with the solid oxide electrolysis cell, the amount of fuel gas flowing in the plane direction of the fuel diffusion layer is greater than the amount of fuel gas flowing in the thickness direction of the fuel diffusion layer, and the fuel gas supplied through the through-pores of the metal support can be uniformly diffused within the plane of the fuel diffusion layer before being supplied to the anode layer. Therefore, the solid oxide electrolysis cell is less likely to develop a fuel gas depletion region in the anode layer, and can cause a uniform electrolysis reaction within the plane of the anode layer. As a result, the solid oxide electrolysis cell can supply a larger amount of fuel gas, such as water vapor or carbon dioxide, which has a larger molecular weight than hydrogen, and operate under high current density. Furthermore, the solid oxide electrolysis cell can ensure the strength of the metal support by keeping the porosity of the through-pores of the metal support low, and therefore does not result in a decrease in the structural reliability of the SOEC.

[0011] Therefore, the solid oxide electrolysis cell can achieve high-power electrolysis while ensuring the strength of the metal support.

[0012] Note that the symbols in parentheses in the claims indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present disclosure.

[0013] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a diagram schematically illustrating an example of a cross section along the thickness direction of a solid oxide electrolysis cell of Embodiment 1, Fig. 2 is a diagram schematically illustrating an example of a cross section along the thickness direction of a fuel diffusion layer of the solid oxide electrolysis cell of Embodiment 1, and Fig. 3 is a diagram illustrating a pore size distribution of a solid oxide electrolysis cell that satisfies the relationship of metal support porosity < fuel diffusion layer porosity < anode layer porosity and that satisfies the relationship of thickness direction pore size average value = plane direction pore size average value and / or thickness direction pore size standard deviation = plane direction pore size standard deviation. ＡＶＥ and P ＡＶＥFIG. 4 is an explanatory diagram for explaining the relationship between t and t for a solid oxide electrolysis cell that satisfies the relationship of metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity, and also satisfies the relationship of thickness direction pore diameter average value < plane direction pore diameter average value and / or the relationship of thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation. ＡＶＥ and P ＡＶＥ 5 is an SEM image of a cross section along the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1 obtained in an experimental example; FIG. 6A is a frequency distribution of pore diameters in the plane direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1 obtained in an experimental example; FIG. 6B is a frequency distribution of pore diameters in the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1 obtained in an experimental example; and FIG. 7 is an SEM image of a cross section along the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1C obtained in an experimental example. 8A is a frequency distribution of the pore diameter in the plane direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1C obtained in an Experimental Example, FIG. 8B is a frequency distribution of the pore diameter in the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cell of Sample 1C obtained in an Experimental Example, and FIG. 9 is a diagram collectively showing the ratio of the median pore diameter in the plane direction to the median pore diameter in the thickness direction, the ratio of the average pore diameter in the plane direction to the average pore diameter in the thickness direction, and the ratio of the standard deviation of pore diameter in the plane direction to the standard deviation of pore diameter in the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cells of Sample 1 and Sample 1C obtained in an Experimental Example.

[0014] The solid oxide electrolysis cell of this embodiment will be described in detail below with reference to the drawings. Note that the solid oxide electrolysis cell of this embodiment is not limited to the following examples. Furthermore, the lower and upper limits of the following numerical ranges can be arbitrarily combined (omitted below).

[0015] As illustrated in Figures 1 to 4, the solid oxide electrolysis cell 1 of this embodiment is a metal-supported solid oxide electrolysis cell in which a cell section 3 is supported by a metal support 2. The solid oxide electrolysis cell 1 includes the metal support 2 and the cell section 3. The solid oxide electrolysis cell 1 may be flat or cylindrical. Figure 1 illustrates a solid oxide electrolysis cell 1 in which a flat cell section 3 is supported by a plate-shaped metal support 2.

[0016] The metal support 2 has a through hole formed region 22 in which a large number of through holes 21 are formed. Fig. 1 shows an example in which, in addition to the through hole formed region 22, a through hole non-formed region 23 in which no through holes 21 are formed is provided on the outer periphery of the through hole formed region 22. The through hole non-formed region 23 is formed solidly from the metal material that constitutes the metal support 2. The metal support 2 can be formed, for example, in a plate shape, as exemplified in Fig. 1.

[0017] The through holes 21 penetrate the metal support 2 in the thickness direction. That is, the through holes 21 penetrate between one surface and the other surface of the through hole formation region 22 of the metal support 2 along the thickness direction of the metal support 2. Therefore, when viewed in a cross section along the thickness direction of the metal support, the through holes 21 are formed linearly so as to be perpendicular to the one surface and the other surface of the through hole formation region 22. The through holes 21 serve as flow paths for supplying fuel gas introduced from the side opposite to the cell portion 3 side of the metal support 2 to a fuel diffusion layer 31 (described later) of the cell portion 3. From the viewpoint of workability of the through holes 21, the through holes 21 can be formed in a columnar shape such as a cylindrical shape (straight pipe shape), for example.

[0018] The average value φ of the hole diameter (diameter) φ of the through-holes 21 ＡＶＥ (Hereinafter, this will be referred to as the average pore diameter φ of the through-holes 21. ＡＶＥ The average diameter φ of the through-holes 21 can be, for example, 0.01 mm or more and 2 mm or less. ＡＶＥ When the average diameter φ of the through-holes 21 is 0.01 mm or more, the supply of fuel gas to the fuel diffusion layer 31 of the cell portion 3 and the formation of the through-holes 21 in the metal support 2 are easily improved. ＡＶＥThe average pore diameter φ of the through-holes 21 can be set to preferably 0.02 mm or more, more preferably 0.03 mm or more, and even more preferably 0.05 mm or more. ＡＶＥ When the average diameter φ of the through-holes 21 is 2 mm or less, it is easy to ensure the strength of the metal support 2. In addition, since a large portion of the metal support 2 with high thermal conductivity can be left, the temperature distribution within the surface of the fuel electrode layer 32 can be kept uniform. Furthermore, since the distance for supporting the fuel electrode layer 32 and the solid electrolyte layer 33 formed on the upper part of the metal support 2 can be set short, there is also the advantage that deformation during their formation can be prevented. ＡＶＥ The average pore diameter φ of the through-holes 21 can be set to preferably 1.0 mm or less, more preferably 0.5 mm or less, and even more preferably 0.1 mm or less. ＡＶＥ is the arithmetic mean value of the pore diameters φ measured for 25 or more through-pores 21.

[0019] The average value P of the distance P between adjacent through holes 21 (hereinafter, this may be referred to as the pitch P of the through holes 21) ＡＶＥ (Hereinafter, this will be referred to as the average pitch P of the through holes 21. ＡＶＥ The average pitch P of the through holes 21 can be set to, for example, 0.01 mm or more and 2 mm or less. ＡＶＥ When the average pitch P of the through-holes 21 is 0.01 mm or more, the strength of the metal support 2 can be easily ensured, and the reliability of the solid oxide electrolysis cell 1 can be improved. ＡＶＥ The average pitch P of the through holes 21 can be set to preferably 0.02 mm or more, more preferably 0.03 mm or more, and even more preferably 0.05 mm or more. ＡＶＥ When the average pitch P of the through-holes 21 is 2 mm or less, the supply of fuel gas to the fuel diffusion layer 31 can be improved. ＡＶＥ The average pitch P of the through holes 21 can be set to preferably 1.5 mm or less, more preferably 1.0 mm or less, and further preferably 0.5 mm or less. ＡＶＥis the arithmetic mean value of the lengths of ten line segments A-B, where a line connecting the central axes of adjacent through holes 21 in a direction perpendicular to the central axes intersects with the edge of one through hole 21 at point A and the line connecting with the edge of the other through hole 21 at point B in a cross section obtained by cutting the metal support 2 along the thickness direction so as to include the hole diameter (diameter) φ of the through hole 21.

[0020] Examples of metal materials constituting the metal support 2 include Fe—Cr alloys containing Fe and Cr, Fe—Cr—Al alloys containing Fe, Cr, and Al, ferritic stainless steel (such as SUS430), austenitic stainless steel (such as SU304), Ni alloys, Ni—Cr alloys containing Ni and Cr, Ni—Cr—Al alloys containing Ni, Cr, and Al, Ni—Cr—Fe alloys containing Ni, Cr, and Fe, Ni—Cr—Si alloys containing Ni, Cr, and Si, and Ni—Fe alloys containing Ni and Fe. These types of metal materials make it easy to achieve a balance between electronic conductivity, corrosion resistance, structural strength, cost, and the like.

[0021] The cell section 3 is laminated on one surface of the through-hole formation region 22. Specifically, the cell section 3 has, in this order from the metal support 2 side, a fuel diffusion layer 31, a fuel electrode layer 32, a solid electrolyte layer 33, and an air electrode layer 34. Therefore, the fuel diffusion layer 31 closest to the metal support 2 contacts one surface of the through-hole formation region 22 of the metal support 2.

[0022] In the solid oxide electrolysis cell 1, the through-holes 21 of the metal support 2 penetrate the metal support 2 in the thickness direction, and therefore the fuel gas is introduced in the thickness direction (arrow T in FIG. 2 ) of the fuel diffusion layer 31 that contacts the metal support 2. The fuel diffusion layer 31 has the function of diffusing the fuel gas introduced through the through-holes 21 of the metal support 2 in the planar direction (arrow S in FIG. 2 ).

[0023] The fuel electrode layer 32 is an electrode to which fuel gas is supplied from the fuel diffusion layer 31. In other words, the fuel electrode layer 32 can be said to be an electrode layer having electrode activity that allows it to function as a fuel electrode.

[0024] The solid electrolyte layer 33 functions as an electrolyte in the solid oxide electrolysis cell 1 and has oxygen ion conductivity. The solid electrolyte layer 33 may be composed of a single layer or multiple layers. FIG. 1 shows an example in which the solid electrolyte layer 33 has two layers: an electrolyte main layer 331 in contact with the anode layer 32, and an electron blocking layer 332 formed on the surface of the electrolyte main layer 331 facing the cathode layer 34. The electrolyte main layer 331 is an electrolyte layer that forms the main body of the solid electrolyte layer 33 and functions as the electrolyte of the solid oxide electrolysis cell 1. When the solid electrolyte layer 33 is a single layer, the single layer functions as the electrolyte main layer 331. The electron blocking layer 332 is a layer that blocks electron movement. When the electron blocking layer 332 is included, the electron blocking layer 332 can block electron movement, and therefore the electrolyte main layer 331 may exhibit electron conductivity in addition to oxygen ion conductivity, for example, under a reducing atmosphere. 1 , the solid electrolyte layer 33 laminated on the surface of the fuel electrode layer 32 may be formed so as to cover the outer peripheral end surfaces of the fuel diffusion layer 31 and the fuel electrode layer 32. In this case, fuel gas leakage can be suppressed with a relatively simple configuration. In this case, at least one of the electrolyte main body layer 331 and the electron blocking layer 332 can be configured to cover the outer peripheral end surfaces of the fuel diffusion layer 31 and the fuel electrode layer 32.

[0025] The air electrode layer 34 is an electrode that forms a pair with the fuel electrode layer 32. In other words, the air electrode layer 34 can be said to be an electrode layer that has electrode activity and can function as an air electrode.

[0026] 1 , the cell unit 3 can have an intermediate layer 35 between the solid electrolyte layer 33 and the air cathode layer 34. The intermediate layer 35 is a layer (reaction suppression layer) that mainly suppresses reaction between the material of the solid electrolyte layer 33 and the material of the air cathode layer 34. Although not shown, the cell unit 3 can also have a cathode current collecting layer on the side of the air cathode layer 34 opposite to the solid electrolyte layer 33 side. The cathode current collecting layer functions as a current collector for the air cathode layer 34.

[0027] As described above, the cell unit 3 has, from the metal support 2 side, the fuel diffusion layer 31, the anode layer 32, the solid electrolyte layer 33, and the cathode layer 34 in this order, and there are no particular limitations on the layer configuration as long as it is configured to function as an electrolysis cell. Specifically, Figure 1 illustrates the cell unit 3 in which, from the metal support side, the fuel diffusion layer 31, the anode layer 32, the electrolyte main body layer 331 (solid electrolyte layer 33), the electron blocking layer 332 (solid electrolyte layer 33), the intermediate layer 35, and the cathode layer 34 are stacked in this order, with the layers joined together.

[0028] In the solid oxide electrolysis cell 1, the average thickness t of the fuel diffusion layer 31 ＡＶＥ (Hereinafter, the average thickness t of the fuel diffusion layer 31 ＡＶＥ The average thickness t of the fuel diffusion layer 31 can be set to, for example, 30 μm or more and 400 μm or less. ＡＶＥ When the average thickness t of the fuel diffusion layer 31 is 30 μm or more, the fuel gas can be easily diffused throughout the fuel electrode layer 32, and a uniform supply of the fuel gas can be achieved. ＡＶＥ is preferably 40 μm or more, more preferably 45 μm or more, and even more preferably 50 μm or more. ＡＶＥ When the average thickness t of the fuel diffusion layer 31 is 400 μm or less, the supply of fuel gas to the fuel electrode layer 32 is easily improved. ＡＶＥ The average thickness t of the fuel diffusion layer 31 is preferably 300 μm or less, more preferably 200 μm or less, and further preferably 100 μm or less. ＡＶＥ is the arithmetic mean value of thickness measurements at nine points on the cross section of the fuel diffusion layer 31 cut along the thickness direction.

[0029] Similarly, the average thickness of the solid electrolyte layer 33 can be, for example, 2 μm or more and 20 μm or less. The average thickness of the electrolyte main body layer 331 can be, for example, 1 μm or more and 15 μm or less. The average thickness of the electron blocking layer 332 can be, for example, 1 μm or more and 15 μm or less. The average thickness of the air electrode layer 34 can be, for example, 10 μm or more and 100 μm or less. The average thickness of the intermediate layer 35 can be, for example, 1 μm or more and 20 μm or less. The average thickness of the air electrode current collecting layer can be, for example, 1 μm or more and 100 μm or less. The average thickness of each layer is calculated based on the average thickness t of the fuel diffusion layer 31. ＡＶＥ can be found in the same way.

[0030] The solid oxide electrolysis cell 1 that can have the above-described stacked structure satisfies the relationship metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity, where the area ratio of voids in a cross section along the surface direction of the metal support 2 is defined as metal support porosity, the area ratio of voids in a cross section along the surface direction of the fuel diffusion layer 31 is defined as fuel diffusion layer porosity, and the area ratio of voids in a cross section along the surface direction of the fuel electrode layer 32 is defined as fuel electrode layer porosity.

[0031] The voids appearing in a cross section taken along the surface direction of the metal support 2 are due to the through holes 21 formed in the through hole-forming region 22. Specifically, the porosity of the metal support can be calculated by cutting out any cross section taken along the surface direction of the metal support 2, mirror-polishing the surface, and then imaging it with an optical microscope. From the image obtained, the total area of ​​the through holes 21 in the cross section taken along the surface direction of the metal support 2 and the total area of ​​the through hole-forming region 22 in the cross section taken along the surface direction of the metal support 2 are determined, and then the porosity of the metal support can be calculated by the formula: 100 × (total area of ​​the through holes 21 in the cross section taken along the surface direction of the metal support 2) / (total area of ​​the through hole-forming region 22 in the cross section taken along the surface direction of the metal support 2).

[0032] The voids that appear in a cross section of the fuel diffusion layer 31 taken along the surface direction are due to voids (sometimes referred to as pores) contained within the fuel diffusion layer 31. Specifically, after embedding the cell portions 3 in a resin, an arbitrary cross section of the fuel diffusion layer 31 taken along the surface direction is cut out, the surface is subjected to ion milling, and then an image is taken with a scanning electron microscope (SEM). The voids are identified from the contrast of the image obtained, and the total area of ​​the voids in the cross section taken along the surface direction of the fuel diffusion layer 31 and the total area of ​​the fuel diffusion layer 31 taken along the surface direction of the fuel diffusion layer 31 are calculated, and the void ratio can be calculated using the formula: 100 × (total area of ​​the voids in the cross section taken along the surface direction of the fuel diffusion layer 31) / (total area of ​​the fuel diffusion layer 31 taken along the cross section taken along the surface direction of the fuel diffusion layer 31).

[0033] The voids that appear in a cross section taken along the surface direction of the fuel electrode layer 32 are due to voids (sometimes referred to as pores) contained within the fuel electrode layer 32. Specifically, after embedding the cell unit 3 in resin, an arbitrary cross section taken along the surface direction of the fuel electrode layer 32 is cut out, the surface is subjected to ion milling, and then an image is taken with an SEM. The voids are identified from the contrast of the obtained image, and the total area of ​​the voids in the cross section taken along the surface direction of the fuel electrode layer 32 and the total area of ​​the fuel electrode layer 32 in the cross section taken along the surface direction of the fuel electrode layer 32 are determined, and the porosity of the fuel electrode layer can be calculated using the formula: 100 × (total area of ​​the voids in the cross section taken along the surface direction of the fuel electrode layer 32) / (total area of ​​the fuel electrode layer 32 in the cross section taken along the surface direction of the fuel electrode layer 32).

[0034] Ideally, the higher the metal support porosity, the more uniformly the fuel gas can be supplied across the fuel diffusion layer 31, and as a result, the more uniformly the fuel gas can be supplied across the anode layer 32. Furthermore, because the fuel diffusion layer 31 primarily functions to diffuse the fuel gas, the fuel diffusion layer porosity is typically set higher than the anode layer porosity. Therefore, it would seem ideal to adopt a configuration that satisfies the relationship: anode layer porosity < fuel diffusion layer porosity < metal support porosity. However, increasing the metal support porosity would cause the metal support 2 to become porous, reducing its strength. This would undermine the advantage of metal-supported SOECs, namely, that highly reliable SOECs can be constructed using strong, relatively inexpensive metal materials. Therefore, in practice, a configuration that satisfies the relationship: metal support porosity < anode layer porosity < fuel diffusion layer porosity.

[0035] However, with this conventional configuration, although the strength of the metal support 2 can be ensured, the fuel gas supplied through the through holes 21 of the metal support 2 cannot be diffused uniformly within the surface of the fuel diffusion layer 31, resulting in a fuel gas depletion region in the fuel electrode layer 32 and preventing a uniform electrolytic reaction within the surface of the fuel electrode layer 32. This is because the through holes 21 of the metal support 2 penetrate in the thickness direction, and the fuel gas introduced into the fuel diffusion layer 31 from the through holes 21 diffuses directly along the thickness direction of the fuel diffusion layer 31 and is supplied to the fuel electrode layer 32.

[0036] In contrast, in the solid oxide electrolysis cell 1, the metal support porosity, fuel diffusion layer porosity, and anode layer porosity as viewed in the plane direction defined above satisfy the relationship metal support porosity < fuel diffusion layer porosity < anode layer porosity. Therefore, in the solid oxide electrolysis cell 1, the amount of fuel gas flowing in the plane direction of the fuel diffusion layer 31 (passing in the plane direction) is greater than the amount of fuel gas flowing in the thickness direction of the fuel diffusion layer 31 (passing in the thickness direction), and the fuel gas supplied through the through-holes 21 of the metal support 2 can be uniformly diffused within the plane of the fuel diffusion layer 31 before being supplied to the anode layer 32. Therefore, in the solid oxide electrolysis cell 1, a fuel gas depletion region is unlikely to occur in the anode layer 32, and the electrolytic reaction can occur uniformly within the plane of the anode layer 32. As a result, the solid oxide electrolysis cell 1 can supply a larger amount of fuel gas, such as water vapor or carbon dioxide, which has a larger molecular weight than hydrogen, and can operate at a high current density. Furthermore, the solid oxide electrolysis cell 1 can ensure the strength of the metal support 2 by keeping the porosity of the through-holes 21 in the metal support 2 low, and therefore does not lead to a decrease in the structural reliability of the SOEC. Thus, the solid oxide electrolysis cell 1 can achieve high-power electrolysis while ensuring the strength of the metal support 2.

[0037] In the solid oxide electrolysis cell 1, the fuel diffusion layer 31 can be configured so that, in a cross section along the thickness direction of the fuel diffusion layer 31, the relationship of thickness direction pore diameter average value < thickness direction pore diameter average value is satisfied, where the average value of the pore diameters in the plane direction of the fuel diffusion layer 31 is the plane direction pore diameter average value and the average value of the pore diameters in the thickness direction of the fuel diffusion layer 31 is the thickness direction pore diameter average value.

[0038] According to this configuration, the fuel gas can be efficiently and uniformly diffused within the surface of the fuel diffusion layer 31 before being supplied to the fuel electrode layer 32, making it possible to obtain a larger output.

[0039] The ratio of the average void diameter in the plane direction to the average void diameter in the thickness direction can be preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more, from the viewpoint of making the above-mentioned effect more clear.

[0040] In the solid oxide electrolysis cell 1, the fuel diffusion layer 31 can be configured to satisfy the relationship of thickness direction pore diameter standard deviation < thickness direction pore diameter standard deviation, where the standard deviation of pore diameters in the plane direction of the fuel diffusion layer 31 is the plane direction pore diameter standard deviation and the standard deviation of pore diameters in the thickness direction of the fuel diffusion layer 31 is the thickness direction pore diameter standard deviation.

[0041] According to this configuration, the fuel gas can be efficiently and uniformly diffused within the surface of the fuel diffusion layer 31 before being supplied to the fuel electrode layer 32, making it possible to obtain a larger output.

[0042] The ratio of the standard deviation of void diameter in the plane direction to the standard deviation of void diameter in the thickness direction can be preferably 1.2 or more, more preferably 1.3 or more, even more preferably 1.4 or more, and even more preferably 1.5 or more, from the viewpoint of making the above-mentioned effect more clear.

[0043] Specifically, the above-mentioned average pore diameter in the in-plane direction and the average pore diameter in the thickness direction can be determined as follows. After embedding the cell portion 3 in resin, an arbitrary cross section along the thickness direction of the fuel diffusion layer 31 is cut out, the surface is subjected to ion milling, and then an image is taken using a scanning electron microscope (SEM). In the obtained image, multiple straight lines are drawn along the in-plane direction of the fuel diffusion layer 31 at intervals equal to or smaller than the observed particle diameter. The lengths of the line segments cut by voids formed between particles on each line are counted as the void diameters of the voids in the in-plane direction of the voids, and a frequency distribution of the void diameters in the in-plane direction of the fuel diffusion layer 31 is created. The average value of the void diameters in the in-plane direction of the fuel diffusion layer 31 in this frequency distribution is defined as the average pore diameter in the in-plane direction, and the standard deviation of the pore diameters in the in-plane direction of the fuel diffusion layer 31 is defined as the standard deviation of the pore diameters in the in-plane direction of the fuel diffusion layer 31. Similarly, in the obtained image, multiple straight lines are drawn along the thickness direction of the fuel diffusion layer 31 at intervals equal to or smaller than the observed particle diameter. The length of each line segment cut by a gap formed between particles on each straight line is counted as the void diameter of the gap in the thickness direction, and a frequency distribution is created for the void diameters in the thickness direction of the fuel diffusion layer 31. The average value of the void diameters in the thickness direction of the fuel diffusion layer 31 in this frequency distribution is defined as the thickness direction void diameter average value, and the standard deviation of the void diameters in the thickness direction of the fuel diffusion layer 31 is defined as the thickness direction void diameter standard deviation.

[0044] In the solid oxide electrolysis cell 1, the fuel diffusion layer 31 may be in contact with, but not bonded to, one surface of the through-pore-forming region 22 of the metal support 2, or may be bonded to one surface of the through-pore-forming region 22 of the metal support 2. The latter is preferable. In the former case, there is a risk that the contact interface between the one surface of the through-pore-forming region 22 and the fuel diffusion layer 31 will serve as a gas flow path for the fuel gas introduced through the through-pores 21. In contrast, in the latter case, because the one surface of the through-pore-forming region 22 and the fuel diffusion layer 31 are bonded, the fuel gas introduced through the through-pores 21 is reliably introduced into the fuel diffusion layer 31. This makes it possible to more effectively achieve the above-mentioned effects, making it easier to obtain a large output.

[0045] When one side of the through hole formation region 22 in the metal support 2 is joined to the fuel diffusion layer 31, a joining reaction layer formed by a joining reaction such as diffusion joining, or a joining layer may be interposed between the one side of the through hole formation region 22 in the metal support 2 and the fuel diffusion layer 31.

[0046] When the solid oxide electrolysis cell 1 satisfies the relationship of thickness direction pore diameter average value < plane direction pore diameter average value and / or thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation, the average pitch P of the through holes 21 in the metal support 2 described above is ＡＶＥ , the average thickness t of the fuel diffusion layer 31 ＡＶＥ But, t ＡＶＥ <P ＡＶＥ It is preferable that the following relationship is satisfied.

[0047] In this case, not only is it possible for the fuel diffusion layer 31 to provide a uniform in-plane gas supply to the anode layer 32, but the thickness of the fuel diffusion layer 31 can be reduced, thereby reducing the material costs of the fuel diffusion layer 31, and the pitch of the through holes 21 can be increased, thereby reducing the processing costs of the through holes 21. Therefore, in this case, a low-cost, high-output solid oxide electrolysis cell 1 can be obtained. This will be explained in more detail using Figures 3 and 4.

[0048] In the solid oxide electrolysis cell 1, for example, even if the thickness direction pore diameter average value and the plane direction pore diameter average value are the same, or even if the thickness direction pore diameter standard deviation and the plane direction pore diameter standard deviation are the same, it is possible to satisfy the relationship of metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity. In this case, as illustrated in FIG. 3, the fuel gas ejected from the through holes 21 penetrating the metal support 2 in the thickness direction to the fuel diffusion layer 31 can only spread up to a 45° direction. In other words, the diffusion area DA of the fuel gas is as shown in FIG. 3. Therefore, in this case, in order to deliver the fuel gas uniformly to the fuel electrode layer 32, P ＡＶＥ <t ＡＶＥHowever, in such a configuration, the thickness of the fuel diffusion layer 31 is increased, which increases the material cost of the fuel diffusion layer 31, and the pitch of the through holes 21 is reduced, which increases the number of the through holes 21, which increases the processing cost of the through holes 21.

[0049] In contrast, in the solid oxide electrolysis cell 1, when the relationship of thickness direction pore size average value < plane direction pore size average value and / or the relationship of thickness direction pore size standard deviation < plane direction pore size standard deviation is satisfied, the pores extend more in the plane direction of the fuel diffusion layer 31 than in the thickness direction of the fuel diffusion layer 31. Therefore, the fuel gas injected from the through-holes 21 penetrating the metal support 2 in the thickness direction onto the fuel diffusion layer 31 can be preferentially diffused in the plane direction of the fuel diffusion layer 31. In other words, the diffusion coefficient of the fuel gas in the plane direction of the fuel diffusion layer 31 can be made larger than the diffusion coefficient of the fuel gas in the thickness direction of the fuel diffusion layer 31. Therefore, in this case, as illustrated in FIG. 4 , the fuel gas injected from the through-holes 21 penetrating the metal support 2 in the thickness direction onto the fuel diffusion layer 31 can spread in a direction of 45° or more. In other words, the diffusion area DA of the fuel gas is as shown in FIG. 4 . Therefore, t ＡＶＥ <P ＡＶＥ Even if the relationship between the thickness of the fuel diffusion layer 31 and the thickness of the fuel electrode layer 32 is not satisfied, the fuel gas can be uniformly delivered to the fuel electrode layer 32. Therefore, by reducing the thickness of the fuel diffusion layer 31, it is possible to reduce the material costs of the fuel diffusion layer 31, and by increasing the pitch of the through holes 21 and reducing the number of the through holes 21, it is possible to reduce the processing costs of the through holes 21. Note that, in the above-mentioned Figures 3 and 4, only the main parts of the solid oxide electrolysis cell 1 are shown for the sake of simplicity.

[0050] As long as the above-described solid oxide electrolysis cell 1 is configured as a solid oxide electrolysis cell using a material with oxygen ion conductivity as the electrolyte, there are no particular limitations on the materials or configurations of the fuel diffusion layer 31, anode layer 32, solid electrolyte layer 33 (such as the electrolyte main body layer 331 and electron blocking layer 332), intermediate layer 35, cathode layer 34, cathode current collecting layer, bonding reaction layer, bonding layer, etc. Specifically, each of these layers can be configured as follows.

[0051] Specifically, the fuel diffusion layer 31 can include an electron conductive material 311, an oxide material 312 in the diffusion layer, and voids 313, as illustrated in Fig. 2. Both the electron conductive material 311 and the oxide material 312 in the diffusion layer can exist as particles. Fig. 2 shows an example in which the fuel diffusion layer 31 includes a large number of voids 313 that are connected in the surface direction of the fuel diffusion layer 31 (extending in the surface direction of the fuel diffusion layer 31).

[0052] Examples of the electron conductive material 311 that can be used in the fuel diffusion layer 31 include electron conductors (metals and alloys, hereinafter omitted) such as Ni, Ni alloys, Cu, Cu alloys, Co, and Co alloys, and oxides of electron conductors (oxides of metals and alloys, hereinafter omitted) that become electron conductors upon reduction, such as Ni oxides (NiO, etc.), Cu oxides, and Co oxides. These materials can be used alone or in combination of two or more. The electron conductive material 311 used in the fuel diffusion layer 31 may or may not have catalytic activity. Among these, Ni, Ni alloys, Ni oxides (NiO, etc.), etc. are preferred from the viewpoint of catalytic activity, and Ni, NiO, etc. are more preferred. The oxide material 312 in the diffusion layer can be, for example, ceria (CeO) doped with one or more elements selected from Gd, Sm, Y, Sc, La, Nd, Yb, Ca, and Ho. ２Examples of the ceria-based oxide include solid electrolyte materials such as 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 oxides can be used alone or in combination. 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 a relatively low temperature of about 700°C. The fuel diffusion layer 31, which includes the electron conductive material 311 made of a metal, alloy, or oxide thereof, and the diffusion layer oxide material 312, can be referred to as a cermet layer.

[0053] Specifically, the anode layer 32 can include an anode catalytic material, an anode electrolyte material, and voids. Both the anode catalytic material and the anode electrolyte material can exist as particles.

[0054] Examples of the catalyst material in the anode include electron conductors such as Ni, Ni alloys, Cu, Cu alloys, Co, and Co alloys, and oxides of electron conductors that become electron conductors upon reduction, such as Ni oxides (e.g., NiO), Cu oxides, and Co oxides. These can be used alone or in combination. Among these, Ni, Ni alloys, and Ni oxides (e.g., NiO) are preferred from the standpoint of catalytic activity (electrode activity), and Ni and NiO are more preferred. Examples of the electrolyte material in the anode include the above-mentioned ceria-based oxides, ceria, yttria-stabilized zirconia, and scandia-stabilized zirconia. These can be used alone or in combination. The anode layer 32, which includes the catalyst material in the anode made of a metal, alloy, or oxide thereof, and the electrolyte material in the anode, can be referred to as a cermet electrode layer.

[0055] 1 , when the solid electrolyte layer 33 is composed of an electrolyte main layer 331 and an electron blocking layer 332, the electrolyte main layer 331 can be composed of a solid electrolyte material having electronic conductivity and oxygen ion conductivity, and the electron blocking layer 332 can be composed of a solid electrolyte material having no electronic conductivity but oxygen ion conductivity. Furthermore, when the solid electrolyte layer 33 is composed of a single layer of the electrolyte main layer 331, the solid electrolyte layer 33 (electrolyte main layer 331) can be composed of a solid electrolyte material having no electronic conductivity but oxygen ion conductivity. The solid electrolyte layer 33 is usually formed to be dense so as to be gas impermeable.

[0056] In the solid electrolyte layer 33, examples of solid electrolyte materials having electronic conductivity and oxygen ion conductivity include the above-mentioned ceria-based oxides, ceria, and other solid electrolyte materials. These may be used alone or in combination of two or more. Examples of solid electrolyte materials having oxygen ion conductivity but no electronic conductivity include yttria-stabilized zirconia and scandia-stabilized zirconia. These may be used alone or in combination of two or more.

[0057] The intermediate layer 35 can be made of a mixed material containing a solid electrolyte material having oxygen ion conductivity and the air electrode material constituting the air electrode layer 34, a solid electrolyte material having oxygen ion conductivity, etc. The solid electrolyte material having oxygen ion conductivity used in the intermediate layer 35 may or may not have electronic conductivity.

[0058] Examples of the solid electrolyte material having oxygen ion conductivity used in the intermediate layer 35 include the above-mentioned ceria-based oxides, solid electrolyte materials such as ceria, yttria-stabilized zirconia, scandia-stabilized zirconia, etc. These may be used alone or in combination of two or more.

[0059] The cathode layer 34 may include, specifically, an cathode catalytic material, an cathode electrolyte material, and voids. Both the cathode catalytic material and the cathode electrolyte material may exist as particles. The cathode catalytic material may be composed of an cathode catalytic material having electronic conductivity and oxygen ion conductivity. The cathode electrolyte material may be composed of a solid electrolyte material having oxygen ion conductivity.

[0060] Examples of the catalytic material in the air electrode include perovskite oxides containing La, Sr, and Co, perovskite oxides containing Pr, Ba, and Co, perovskite oxides containing Gd, Ba, and Co, and perovskite oxides containing Nd, Ba, and Co. These can be used alone or in combination of two or more. Specific examples of the perovskite oxides containing La, Sr, and Co described above include La, ０．６ Sr ０．４ CoO ３ etc., La １－ｘ Sr ｘ CoO ３－δ (0<x≦1, preferably 0.1≦x≦0.5). Specific examples of perovskite oxides containing Pr, Ba, and Co include Pr, ２－ｘ Ba ｘ Co ２ O ５＋δ (0.7≦x≦1.3, preferably 0.8≦x≦1). Specific examples of perovskite oxides containing Gd, Ba, and Co include Gd ２－ｘ Ba ｘ Co ２ O ５＋δ (0.7≦x≦1.3, preferably 0.8≦x≦1). Specific examples of perovskite oxides containing Nd, Ba, and Co include Nd ２－ｘ Ba ｘ Co ２ O ５＋δ(0.7≦x≦1.3, preferably 0.8≦x≦1). The oxides described above may or may not have oxygen non-stoichiometry. Examples of the electrolyte material in the air electrode include the ceria-based oxides and ceria described above. These may be used alone or in combination of two or more.

[0061] The air electrode current collecting layer can be made of an air electrode current collecting material having electronic conductivity suitable for current collection on the air electrode side exposed to a high-temperature oxidizing atmosphere.

[0062] Examples of the air electrode current collecting material include metal materials such as Pt, Pt alloys, Ag, Ag alloys, and Au, and oxides having electronic conductivity such as perovskite-type oxides containing La, Sr, and Co, and perovskite-type oxides containing La, Ni, and Fe. These may be used alone or in combination of two or more.

[0063] Specifically, the solid oxide electrolysis cell 1 is ２ - Co-electrolysis of water vapor and CO ２ The present invention can be used for at least one electrolysis selected from the group consisting of electrolysis.

[0064] In steam electrolysis, a gas containing at least water vapor is used as a fuel gas. ２ - In the case of co-electrolysis of water vapor, at least CO ２ Gas containing CO and water vapor is used as the fuel gas. ２ In electrolysis, CO ２ In the above case, a gas containing hydrogen is used as the fuel gas. Compared to hydrogen gas, these fuel gases have a larger molecular weight and higher viscosity at the cell operating temperature. Therefore, in the above case, the effect of the solid oxide electrolysis cell 1 is clearly obtained, that is, the fuel gas can be supplied in larger amounts, the cell can be operated under high current density, and high-power electrolysis can be achieved. Therefore, in the above case, it becomes easier to realize a high-power electrolysis system using the solid oxide electrolysis cell 1 or a solid oxide electrolysis cell stack in which a plurality of solid oxide electrolysis cells 1 are stacked.

[0065] It is generally known that an SOEC can be used as a solid oxide fuel cell (SOFC) by changing the gases introduced into the fuel electrode layer and the air electrode layer while maintaining the same configuration, and therefore the solid oxide electrolysis cell 1 can also be used as an SOFC.

[0066] The operating temperature of the solid oxide electrolysis cell 1 can be preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 650°C or higher, from the viewpoint of, for example, reducing cell resistance and facilitating high-power electrolysis. Furthermore, the operating temperature of the solid oxide electrolysis cell 1 can be preferably 825°C or lower, more preferably 800°C or lower, and even more preferably 775°C or lower, from the viewpoint of, for example, facilitating suppression of reduction expansion.

[0067] (Experimental Example) <Solid oxide electrolysis cell of sample 1> - Metal support - A flat metal support (thickness: 0.4 mm) made of an Fe-Cr alloy was prepared. The metal support was annealed at 800°C to stabilize the surface condition.

[0068] A slurry was prepared by mixing Ni powder (average particle size: 0.4 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. The slurry was applied in layers to a resin sheet using a doctor blade method, dried, and then the resin sheet was peeled off to prepare a rectangular cell bonding sheet (thickness 1 μm). The average particle size is the particle size (diameter) d50 at which the volume-based cumulative frequency distribution measured by laser diffraction / scattering method shows 50% (the same applies below).

[0069] A cell portion joining sheet was attached to one surface of a plate-shaped metal support, and multiple through holes were formed by laser processing in the area where the cells were to be placed on the metal support, penetrating between the one and other surface in the thickness direction. The through holes had a diameter of 0.03 mm and a pitch of 0.15 mm. By forming the through holes simultaneously in the metal support and the cell portion joining sheet in this way, the positions of the through holes could be formed without misalignment.

[0070] - Sheet for forming fuel diffusion layer - NiO powder (average particle size: 0.5 μm) and Gd-doped CeO ２ A slurry was prepared by mixing NiO powder (hereinafter referred to as GDC) powder (average particle size: 0.3 μm), a pore former (acrylic beads, average particle size: 0.8 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol in a ball mill. The doping amount of Gd was 10 mol%. The mass ratio of NiO powder to GDC powder was 50:50. The slurry was applied in a layer on a resin sheet using a doctor blade method, dried, and then the resin sheet was peeled off to prepare a fuel diffusion layer forming sheet.

[0071] In the preparation of the fuel diffusion layer forming sheet, low-solvent-resistant acrylic beads were specifically used as the pore-forming acrylic beads. The surfaces of the low-solvent-resistant acrylic beads are dissolved by the solvent used (here, isoamyl acetate). Therefore, in the slurry, the low-solvent-resistant acrylic beads form a weak agglomeration state. The agglomerated low-solvent-resistant acrylic beads are aligned in the plane direction by shear during sheet formation using the doctor blade method. By firing the fuel diffusion layer forming sheet prepared in this manner to form a fuel diffusion layer, it is possible to form pores that are connected in the plane direction. The porosity can be changed by adjusting the amount of pore-forming material burned off during firing.

[0072] In contrast, when highly solvent-resistant acrylic beads, whose bead surfaces are not dissolved by the solvent used, or commonly used carbon particles, are used as the pore-forming material, these pore-forming materials are uniformly dispersed in the slurry using the solvent as a dispersion medium. Therefore, even when subjected to shear during sheet formation, these pore-forming materials remain uniformly contained in the sheet. Therefore, when a fuel diffusion layer is formed by firing a fuel diffusion layer-forming sheet prepared in this manner, it is difficult to form pores that are connected in the plane direction, and pores that are isotropic in the plane direction and thickness direction are formed.

[0073] - Sheet for forming fuel electrode layer - NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.3 μm), acrylic beads (pore former, average particle size: 0.8 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol were mixed in a ball mill to prepare a slurry. The Gd doping amount in the GDC powder was 10 mol%. Highly solvent-resistant acrylic beads were used as the pore former acrylic beads. The mass ratio of NiO powder to GDC powder was 45:55. The fuel electrode layer forming sheet was then prepared in the same manner as in the production of the fuel diffusion layer forming sheet.

[0074] - Sheet for forming electrolyte main layer - GDC powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. The Gd doping amount in the GDC powder was 10 mol %. The subsequent steps were the same as in the preparation of the sheet for forming the fuel diffusion layer, and the sheet for forming the electrolyte main layer was prepared.

[0075] -Electron blocking layer forming sheet- ZrO doped with 8 mol% yttria ２ (hereinafter referred to as 8YSZ) powder (average particle size: 0.2 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. Thereafter, a sheet for forming an electron blocking layer was prepared in the same manner as in the preparation of a sheet for forming a fuel diffusion layer.

[0076] - Intermediate layer forming sheet - GDC powder (average particle size: 0.3 μm), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. The Gd doping amount in the GDC powder was 10 mol %. The subsequent steps were the same as in the preparation of the fuel diffusion layer forming sheet, and the intermediate layer forming sheet was prepared.

[0077] -Paste for forming air cathode layer- LSC (La ０．６ Sr ０．４ CoO ３ A paste for forming an air cathode layer was prepared by kneading a powder (average particle size: 2.0 μm), ethyl cellulose, and terpineol using a triple roll.

[0078] -Cell section- A sheet for forming a fuel electrode layer, a sheet for forming an electrolyte main layer, a sheet for forming an electron blocking layer, and a sheet for forming an intermediate layer were laminated in this order on a sheet for forming a fuel diffusion layer, and the laminated sheets were pressed together using a hydrostatic press (WIP) method to obtain a pressed body. The pressed body was degreased after pressing. The WIP molding conditions were a temperature of 80°C, a pressure of 50 MPa, and a pressing time of 10 minutes.

[0079] The resulting pressed body was then sintered in an air atmosphere at 1400° C. for 2 hours, thereby obtaining a sintered body having a rectangular outer shape.

[0080] Next, the paste for forming an air electrode layer was applied to the surface of the intermediate layer of the obtained sintered body by screen printing, and the paste was fired (baked) in an air atmosphere at 950°C for 2 hours to form an air electrode layer. The outer shape of the air electrode layer was formed to be smaller than the outer shape of the fuel electrode layer.

[0081] - Metal-supported solid oxide electrolysis cell The cell part was laminated on one surface of the metal support, with the fuel diffusion layer facing the metal support. Then, 10 g / cm ２ A load of 1000 kJ / cm was applied to the metal support, and the metal support was fired at 850°C for 3 hours in an air atmosphere while the load was applied. After firing, the load was removed. This resulted in the fuel diffusion layer being bonded to one side of the through-hole formation region of the metal support.

[0082] Next, the cell portion was appropriately sealed with glass to form a gas seal structure, after which the fuel diffusion layer and the fuel electrode layer of this cell portion were subjected to reduction treatment in a hydrogen atmosphere at 700° C. for 3 hours.

[0083] As a result, a solid oxide electrolysis cell for Sample 1 was obtained in which a cell section (thickness 185 μm) consisting of a fuel diffusion layer (thickness 100 μm), a fuel electrode layer (thickness 30 μm), a main electrolyte layer (thickness 5 μm), an electron blocking layer (thickness 5 μm), an intermediate layer (thickness 5 μm), and an air electrode layer (thickness 40 μm) laminated in that order was joined to one surface of the metal support via a joining layer (thickness 1 μm). Note that the thickness of each layer is the average value of the thickness of each layer.

[0084] <Solid oxide electrolysis cell of sample 2> A solid oxide electrolysis cell of sample 2 was prepared in the same manner as in the preparation of the solid oxide electrolysis cell of sample 1, except that highly solvent-resistant acrylic beads were used as the acrylic beads serving as the pore-forming material when the fuel diffusion layer-forming sheet was prepared.

[0085] <Solid oxide electrolysis cell of sample 3> The solid oxide electrolysis cell of sample 3 was prepared in the same manner as in the preparation of the solid oxide electrolysis cell of sample 3, except that highly solvent-resistant acrylic beads were used as the acrylic beads serving as the pore-forming material when preparing the fuel diffusion layer-forming sheet, and that the cell portion joining sheet was not attached to one of the plate surfaces of the plate-shaped metal support, so that the metal support and the fuel diffusion layer were only in contact with each other without being joined to each other.

[0086] <Solid oxide electrolytic cell of sample 1C> A solid oxide electrolytic cell of sample 1C was prepared in the same manner as in the solid oxide electrolytic cell of sample 3, except that the amount of highly solvent-resistant acrylic beads was increased.

[0087] <Various Measurements> For each of the prepared solid oxide electrolysis cells, the metal support porosity, fuel diffusion layer porosity, anode layer porosity, pore diameter in the surface direction of the fuel diffusion layer (median, mean, and standard deviation of the frequency distribution of pore diameter in the surface direction), pore diameter in the thickness direction of the fuel diffusion layer (median, mean, and standard deviation of the frequency distribution of pore diameter in the thickness direction), and average thickness t ＡＶＥ , the average pitch P of the through holes in the metal support ＡＶＥetc. were measured.

[0088] In addition, using an SOFC fuel cell evaluation device (manufactured by Chino Corporation), a single cell that had been subjected to reduction treatment was fixed to a dedicated holder, and both the fuel electrode layer and the air electrode layer were filled with N. ２ The temperature was raised to 650° C. while introducing water vapor (300 ml) and H ２ An electrolysis test (operating temperature: 650°C) was conducted with air (500 ml) introduced into the cathode layer and IV measurement was performed to determine the cell resistance from the slope of the IV characteristics.

[0089] Table 1 summarizes the detailed configuration of each solid oxide electrolysis cell and various measurement results. Figs. 5 and 7 show SEM images of cross sections along the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cells of Sample 1 and Sample 1C. In Figs. 5 and 7, the black areas represent voids, and the gray areas represent particle skeletons. Figs. 6A, 6B, 8A, and 8B show the frequency distribution of pore diameters in the fuel diffusion layer in the solid oxide electrolysis cells of Sample 1 and Sample 1C. Fig. 9 also summarizes the ratios of the median pore diameter in the plane direction to the median pore diameter in the thickness direction, the ratios of the average pore diameter in the plane direction to the average pore diameter in the thickness direction, and the ratios of the standard deviation of pore diameter in the plane direction to the standard deviation of pore diameter in the thickness direction of the fuel diffusion layer in the solid oxide electrolysis cells of Sample 1 and Sample 1C.

[0090]

[0091] Table 1 and FIGS. 5 to 9 reveal the following: The solid oxide electrolysis cell of sample 1C does not satisfy the relationship of metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity. Therefore, although the solid oxide electrolysis cell of sample 1C can ensure the strength of the metal support due to the small metal support porosity, the cell resistance is high, making it difficult to achieve high-power electrolysis.

[0092] In contrast, the solid oxide electrolysis cells of Samples 1 to 3 satisfy the relationship: metal support porosity < fuel diffusion layer porosity < fuel electrode layer porosity. Therefore, the solid oxide electrolysis cell of Sample 1 can reduce cell resistance and achieve high-output electrolysis by supplying a larger amount of fuel gas, such as water vapor or carbon dioxide, which has a larger molecular weight than hydrogen. Furthermore, the small metal support porosity ensures the strength of the metal support.

[0093] Furthermore, a comparison of the solid oxide electrolysis cells of Samples 1 to 3 reveals the following: The solid oxide electrolysis cell of Sample 1 satisfies the relationship of average thickness direction pore diameter < average plane direction pore diameter, and therefore was able to lower the cell resistance compared to the solid oxide electrolysis cell of Sample 2, which does not satisfy the relationship of average thickness direction pore diameter < average plane direction pore diameter. Therefore, the solid oxide electrolysis cell of Sample 1, which satisfies the relationship of average thickness direction pore diameter < average plane direction pore diameter, can efficiently and uniformly diffuse the fuel gas within the plane of the fuel diffusion layer before supplying it to the anode layer, and therefore can obtain greater output.

[0094] Similarly, the solid oxide electrolysis cell of Sample 1 satisfied the relationship of thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation, and therefore was able to lower the cell resistance compared to the solid oxide electrolysis cell of Sample 2, which did not satisfy the relationship of thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation. Therefore, the solid oxide electrolysis cell of Sample 1, which satisfied the relationship of thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation, can efficiently and uniformly diffuse the fuel gas within the plane of the fuel diffusion layer before supplying it to the anode layer, and therefore can obtain more power.

[0095] As shown in FIG. 9, it is understood that the thickness-wise median pore diameter and the surface-wise median pore diameter of the fuel diffusion layer cannot clearly distinguish between pores that are connected in the surface direction in the fuel diffusion layer and pores that are isotropic in the surface direction and thickness direction.

[0096] Furthermore, the solid oxide electrolysis cell of sample 1, in which the fuel diffusion layer is bonded to the through-pore formation region of the metal support, exhibits the above-mentioned effects more effectively and is more likely to produce a large output than the solid oxide electrolysis cell of sample 3, in which the fuel diffusion layer is only in contact with the through-pore formation region of the metal support without being bonded thereto. This is because, due to the bonding between the through-pore formation region and the fuel diffusion layer, the contact interface between the through-pore formation region and the fuel diffusion layer does not serve as a gas flow path, and the fuel gas introduced through the through-pores is reliably introduced into the fuel diffusion layer.

[0097] In addition, the solid oxide electrolytic cell of sample 1 has a temperature of t ＡＶＥ <P ＡＶＥ Since the relationship is satisfied, t ＡＶＥ <P ＡＶＥ Compared to the solid oxide electrolysis cell of sample 2, which does not satisfy the relationship (a), the thickness of the fuel diffusion layer can be made thinner, which makes it possible to reduce the material cost of the fuel diffusion layer, and the pitch of the through-holes can be made larger, which makes it possible to reduce the processing cost of the through-holes.

[0098] The present disclosure is not limited to the above-described embodiments and experimental examples, and various modifications are possible within the scope of the present disclosure. Furthermore, the configurations shown in the above-described embodiments and experimental examples can be arbitrarily combined with each other. That is, although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments, structures, etc. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

[0099] The features of the present disclosure are as follows: Item 1. A solid oxide electrolysis cell (1) comprising: a metal support (2) having a through-hole formed region (22) in which a large number of through-holes (21) penetrating in the thickness direction are formed; and a cell section (3) laminated on one side of the through-hole formed region, wherein the cell section comprises, in this order from the metal support side, a fuel diffusion layer (31) that diffuses a fuel gas, an anode layer (32) that is an electrode to which the fuel gas is supplied from the fuel diffusion layer, a solid electrolyte layer (33), and an air cathode layer (34) that is an electrode that forms a pair with the anode layer, wherein the relationship of metal support porosity < fuel diffusion layer porosity < anode layer porosity is satisfied, where the area ratio of voids in a cross section along the surface direction of the metal support is defined as metal support porosity, the area ratio of voids in a cross section along the surface direction of the fuel diffusion layer is defined as fuel diffusion layer porosity, and the area ratio of voids in a cross section along the surface direction of the anode layer is defined as anode layer porosity. Item 2. The solid oxide electrolysis cell according to Item 1, wherein, in a cross section along the thickness direction of the fuel diffusion layer, when the average value of pore diameters in the plane direction of the fuel diffusion layer is defined as the plane direction pore diameter average value and the average value of pore diameters in the thickness direction of the fuel diffusion layer is defined as the thickness direction pore diameter average value, the fuel diffusion layer satisfies the relationship: thickness direction pore diameter average value < plane direction pore diameter average value. Item 3. The solid oxide electrolysis cell according to Item 1 or 2, wherein, in a cross section along the thickness direction of the fuel diffusion layer, when the standard deviation of pore diameters in the plane direction of the fuel diffusion layer is defined as the plane direction pore diameter standard deviation and the standard deviation of pore diameters in the thickness direction of the fuel diffusion layer is defined as the thickness direction pore diameter standard deviation, the fuel diffusion layer satisfies the relationship: thickness direction pore diameter standard deviation < plane direction pore diameter standard deviation. Item 4. The solid oxide electrolysis cell according to any one of Items 1 to 3, wherein the fuel diffusion layer is bonded to one surface of the through-hole formation region of the metal support. Item 5. In a cross section of the metal support and the fuel diffusion layer along the thickness direction, including the pore diameter of the through-hole, the average value of the distance between the adjacent through-holes is defined as P ＡＶＥ , the average thickness of the fuel diffusion layer is t ＡＶＥ When this is the case, t ＡＶＥ <P ＡＶＥItem 6. The solid oxide electrolysis cell according to any one of Items 1 to 4, wherein the following relationship is satisfied: ２ - Co-electrolysis of water vapor and CO ２ Item 6. The solid oxide electrolysis cell according to any one of items 1 to 5, wherein the solid oxide electrolysis cell is used for at least one electrolysis selected from the group consisting of electrolysis.

Claims

1. A solid oxide electrolysis cell (1) comprising: a metal support (2) having a through pore-forming region (22) in which a large number of through pores (21) penetrating in the thickness direction are formed; and a cell section (3) laminated on one side of the through pore-forming region, wherein the cell section comprises, in this order from the metal support side, a fuel diffusion layer (31) that diffuses fuel gas, an anode layer (32) that is an electrode to which the fuel gas is supplied from the fuel diffusion layer, a solid electrolyte layer (33), and an air cathode layer (34) that is an electrode that forms a pair with the anode layer, wherein the relationship of metal support porosity < fuel diffusion layer porosity < anode layer porosity is satisfied, where the area ratio of voids in a cross section along the surface direction of the metal support is defined as metal support porosity, the area ratio of voids in a cross section along the surface direction of the fuel diffusion layer is defined as fuel diffusion layer porosity, and the area ratio of voids in a cross section along the surface direction of the anode layer is defined as anode layer porosity.

2. The solid oxide electrolysis cell according to claim 1, wherein the fuel diffusion layer, in a cross section along the thickness direction of the fuel diffusion layer, satisfies the relationship thickness direction pore diameter average value < thickness direction pore diameter average value, where the average value of the pore diameters in the surface direction of the fuel diffusion layer is the surface direction pore diameter average value and the average value of the pore diameters in the thickness direction of the fuel diffusion layer is the thickness direction pore diameter average value.

3. The solid oxide electrolysis cell according to claim 1, wherein the fuel diffusion layer, in a cross section along the thickness direction of the fuel diffusion layer, satisfies the relationship of thickness direction pore diameter standard deviation < surface direction pore diameter standard deviation, where the standard deviation of pore diameters in the surface direction of the fuel diffusion layer is the surface direction pore diameter standard deviation and the standard deviation of pore diameters in the thickness direction of the fuel diffusion layer is the thickness direction pore diameter standard deviation.

4. A solid oxide electrolysis cell according to any one of claims 1 to 3, wherein the fuel diffusion layer is bonded to one surface of the through-hole forming region of the metal support.

5. In a cross section of the metal support and the fuel diffusion layer along the thickness direction, including the pore diameter of the through-hole, the average value of the distance between the adjacent through-holes is P ＡＶＥ , the average thickness of the fuel diffusion layer is t ＡＶＥ When this is the case, t ＡＶＥ <P ＡＶＥ The solid oxide electrolysis cell according to claim 2 or claim 3, wherein the following relationship is satisfied:

6. Steam electrolysis, CO ２ - Co-electrolysis of water vapor and CO ２ The solid oxide electrolysis cell according to claim 1 , wherein the solid oxide electrolysis cell is used for at least one electrolysis selected from the group consisting of electrolysis

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