Electrochemical cell

Abstract

This electrochemical cell (1) has, in the following order, a fuel electrode layer (2) that is an electrode to which a fuel is supplied, a solid electrolyte layer (3) that has oxygen ion conductivity, and an air electrode layer (4) that is an electrode which is paired with the fuel electrode layer (2). The solid electrolyte layer (3) has an electrolyte main body layer (31) that is in contact with the fuel electrode layer (2). The electrolyte main body layer (31) has a fluorite structure, and has a composite oxide phase that comprises a first crystal phase represented by Ce1-x(RE)xO2-x / 2 (wherein x is 0.05 to 0.2 inclusive, and RE element is at least one of Gd and Sm) and a second crystal phase represented by (ZnO)(CeO2-δ)y (wherein δ > 0 and y is 0.15 to 0.7 inclusive).

Description

electrochemical cell CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-072885, filed on April 26, 2024, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to electrochemical cells.

[0003] Electrochemical cells using a solid electrolyte layer having oxygen ion conductivity as an electrolyte layer have been known in the art, including solid oxide fuel cells (hereinafter sometimes referred to as SOFCs) and solid oxide electrolysis cells (hereinafter sometimes referred to as SOECs).

[0004] For example, Patent Document 1 discloses an SOFC using a ceria-based solid electrolyte in which an oxide layer having a perovskite crystal structure of MCe(1-x)R(x)O(3-α) (M represents an alkaline earth element, R represents a rare earth element or Zn, Mn, or In, and 0.05≦x≦0.20) is formed on the surface of a ceria-based base material. This document describes that the use of the ceria-based solid electrolyte suppresses the reduction of cerium on the fuel electrode side, which is exposed to a reducing gas and is in a particularly harsh environment.

[0005] Japanese Patent Application Laid-Open No. 2005-243473

[0006] The prior art has the following problems. In Patent Document 1, Ce in the oxide layer having a perovskite crystal structure is tetravalent, and this Ce atom changes to trivalent when exposed to high temperature and a reducing atmosphere. Therefore, the technology of Patent Document 1 does not have a sufficient effect of suppressing the reduction expansion of the solid electrolyte layer, making it difficult to suppress the occurrence of cracks during operation. In addition, this material is also known as a proton conductor, and is known to chemically expand due to a hydration reaction. Therefore, H ２ When exposed to a reducing gas containing O, it is more difficult to suppress cracks during operation.

[0007] An object of the present disclosure is to provide an electrochemical cell that can suppress the occurrence of cracks during operation in the main electrolyte layer that contacts the fuel electrode layer.

[0008] One aspect of the present disclosure is an electrochemical cell having, in this order, an anode layer which is an electrode to which fuel is supplied, a solid electrolyte layer having oxygen ion conductivity, and an air cathode layer which is an electrode paired with the anode layer, wherein the solid electrolyte layer has a main electrolyte layer in contact with the anode layer, and the main electrolyte layer has a fluorite structure and contains Ce. １－ｘ (RE) ｘ O ２－ｘ／２ (where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm), and a first crystalline phase represented by (ZnO)(CeO ２－δ ) ｙ (where δ>0, and y is 0.15 or more and 0.7 or less).

[0009] The electrochemical cell has the above-described configuration. Therefore, even if the electrolyte main layer in contact with the anode layer is exposed to a high temperature and a reducing atmosphere during operation, the electrochemical cell can reduce reduction expansion of the electrolyte main layer. Therefore, the electrochemical cell can suppress cracking in the electrolyte main layer during operation.

[0010] 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.

[0011] 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 an explanatory diagram schematically illustrating an example of the layered structure of an electrochemical cell according to an embodiment, Fig. 2 is an explanatory diagram schematically illustrating another example of the layered structure of an electrochemical cell according to an embodiment, Fig. 3 is an SEM image illustrating the layered structure of an electrochemical cell fabricated in an experimental example, Fig. 4 is an enlarged view of a portion of the SEM image shown in Fig. 3, Fig. 5 is a diagram illustrating the results of identifying the crystalline phase of the main electrolyte layer obtained in Experimental Example 1, and Fig. 6 is a graph illustrating the relationship between the Zn molar fraction (ratio to Ce) in the composite oxide phase (horizontal axis) and the linear expansion coefficient (×10) of the main electrolyte layer obtained in Experimental Example 1. －６ / K, 4 vol% H ２ 7 is a graph showing the relationship between the Zn molar ratio (ratio to Ce) in the composite oxide phase (horizontal axis) and the oxygen ion conductivity (×10 －２ 8 is a graph showing the relationship between the temperature (°C) (horizontal axis) and the linear expansion coefficient (×10 －６ / K, 4 vol% H ２ ) (vertical axis).

[0012] The electrochemical cell of this embodiment will be described with reference to Figures 1 and 2. In the present disclosure, the lower limit and upper limit of the numerical ranges can be arbitrarily combined (omitted below).

[0013] As illustrated in FIGS. 1 and 2 , the electrochemical cell 1 of this embodiment includes an anode layer 2, a solid electrolyte layer 3, and a cathode layer 4, in this order. In FIGS. 1 and 2 , the anode layer 2 is disposed on one side of the solid electrolyte layer 3, and the cathode layer 4 is disposed on the other side of the solid electrolyte layer 3. Specifically, FIGS. 1 and 2 show an example in which the anode layer 2, the solid electrolyte layer 3, and the cathode layer 4 are stacked in this order, the anode layer 2 and the solid electrolyte layer 3 are bonded to each other, and the solid electrolyte layer 3 and the cathode layer 4 are bonded via an intermediate layer 6 (described later). The anode layer 2 is an electrode to which fuel is supplied. In other words, the anode layer 2 can be considered an electrode layer having electrode activity that allows it to function as an anode. The cathode layer 4 is an electrode paired with the anode layer 2. In other words, the cathode layer 4 can be considered an electrode layer having electrode activity that allows it to function as an cathode. The electrochemical cell 1 may have a flat cell structure as exemplified in Figures 1 and 2, or may have a cylindrical cell structure (not shown). The electrochemical cell 1 of this embodiment may have any of an electrolyte-supported type, an electrode-supported type (anode-supported type, cathode-supported type), and a metal-supported type.

[0014] In the electrochemical cell 1, the solid electrolyte layer 3 has oxygen ion conductivity. The solid electrolyte layer 3 includes an electrolyte main layer 31 in contact with the fuel electrode layer 2. The solid electrolyte layer 3 may be composed of multiple layers, as illustrated in FIGS. 1 and 2 , or may be composed of a single layer (not shown). FIGS. 1 and 2 show an example in which the solid electrolyte layer 3 includes two layers: an electrolyte main layer 31 and an electron blocking layer 32 formed on the surface of the electrolyte main layer 31 facing the air electrode layer 4. The electrolyte main layer 31 is an electrolyte layer that forms the main body of the solid electrolyte layer 3 and functions as the electrolyte of the electrochemical cell 1. When the solid electrolyte layer 3 is a single layer, the single layer serves as the electrolyte main layer 31. The electron blocking layer 32 is a layer that blocks electron migration. When the electron blocking layer 32 is included, the electron blocking layer 32 can block electron migration, so the electrolyte main layer 31 may exhibit electron conductivity in addition to oxygen ion conductivity, for example, under a reducing atmosphere. As described above, the solid electrolyte layer 3 has the main electrolyte layer 31 in contact with the fuel electrode layer 2, and the layer configuration is not particularly limited as long as it is configured to function as the electrolyte of the electrochemical cell 1.

[0015] As illustrated in FIG. 2 , the electrochemical cell 1 can also have a fuel diffusion layer 5 in contact with the fuel electrode layer 2 on the side of the fuel electrode layer 2 opposite the solid electrolyte layer 3. The fuel diffusion layer 5 has the function of diffusing the fuel supplied to the fuel electrode layer 2. The fuel diffusion layer 5 can also have the function of diffusing electrons. When the fuel diffusion layer 5 is provided, the diffused fuel can be supplied to the fuel electrode layer 2. The fuel diffusion layer 5 not only has the fuel diffusion function of diffusing the fuel in the planar direction, but may also function as a support layer that supports each layer on the fuel electrode layer 2 side. The fuel diffusion layer 5 may also function as a current collector for the fuel electrode layer 2.

[0016] 1 and 2, the electrochemical cell 1 can also have an intermediate layer 6 between the solid electrolyte layer 3 and the air cathode layer 4. The intermediate layer 6 is a layer (reaction suppression layer) that mainly suppresses reaction between the material of the solid electrolyte layer 3 and the material of the air cathode layer 4. In FIGS. 1 and 2, an example is shown in which the intermediate layer 6 is in contact with the solid electrolyte layer 3 and the air cathode layer 4 and is bonded to these layers.

[0017] 2 , the electrochemical cell 1 can also have a cathode current collecting layer 7 on the side of the cathode layer 4 opposite to the solid electrolyte layer 3. The cathode current collecting layer 7 is a layer that functions as a current collector for the cathode layer 4.

[0018] In the electrochemical cell 1, the thickness of the fuel electrode layer 2 can be, for example, 10 μm or more and 100 μm or less. The thickness of the solid electrolyte layer 3 can be, for example, 2 μm or more and 20 μm or less. The thickness of the electrolyte main body layer 31 can be, for example, 1 μm or more and 15 μm or less. The thickness of the electron blocking layer 32 can be, for example, 1 μm or more and 15 μm or less. The thickness of the air electrode layer 4 can be, for example, 10 μm or more and 100 μm or less. The thickness of the fuel diffusion layer 5 can be, for example, 100 μm or more and 800 μm or less. The thickness of the intermediate layer 6 can be, for example, 1 μm or more and 20 μm or less. The thickness of the air electrode current collecting layer 7 can be, for example, 1 μm or more and 100 μm or less.

[0019] In the electrochemical cell 1 that can have the above-described laminated structure, the electrolyte main layer 31 has a composite oxide phase including a first crystalline phase and a second crystalline phase. In the composite oxide phase, the first crystalline phase has a fluorite structure, and Ce １－ｘ (RE) ｘ O ２－ｘ／２ The first crystal phase has a chemical composition represented by the following formula: where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm.

[0020] In the first crystal phase, x is preferably 0.06 or more and 0.18 or less, more preferably 0.08 or more and 0.15 or less, from the viewpoint of obtaining high oxygen ion conductivity, etc. Furthermore, the RE element is preferably Gd, from the viewpoint of obtaining high oxygen ion conductivity at relatively low cost, etc.

[0021] In the composite oxide phase, the second crystalline phase is (ZnO)(CeO ２－δ ) ｙ The second crystal phase has a chemical composition represented by the formula: where δ>0 and y is 0.15 or more and 0.7 or less.

[0022] In the second crystal phase, y is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, and even more preferably 0.55 or more from the viewpoint of suppressing reductive expansion, etc. δ is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.7 or more from the viewpoint of suppressing reductive expansion, etc.

[0023] The state of the first crystalline phase and the second crystalline phase in the composite oxide phase is not particularly limited, and examples thereof include a state in which the second crystalline phase is contained in the first crystalline phase (a state in which the second crystalline phase is mixed in the first crystalline phase, a state in which a part of the second crystalline phase is solid-dissolved in the first crystalline phase, a state in which the second crystalline phase is dispersed in the first crystalline phase, etc.), and a state having a core-shell structure in which the first crystalline phase serves as a core and the surface of the core is covered with the second crystalline phase.

[0024] The electrolyte main layer 31 may contain a phase other than the complex oxide phase. Examples of the other phase include a phase containing elements constituting the electron blocking layer 32 for improving the bonding strength with the electron blocking layer 32, and a partially stabilized ZrO ２ Phase, CeO ２ -ZrO ２ Examples of the phase include a solid solution phase, etc. These may be contained in one phase or in two or more phases.

[0025] In the composite oxide phase, the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystal phase (sometimes referred to as the "Zn molar ratio (ratio to Ce)" in the present disclosure) is preferably 1.1 mol% or more. With this configuration, reduction expansion of the electrolyte main body layer 31 can be more effectively suppressed than when the Zn molar ratio (ratio to Ce) is less than 1.1 mol%, and cracks in the electrolyte main body layer 31 during operation can be avoided with a high probability. From the viewpoint of further ensuring the above-mentioned effects, the Zn molar ratio (ratio to Ce) can be more preferably 1.3 mol% or more, even more preferably 1.5 mol% or more, and even more preferably 1.8 mol% or more.

[0026] The composite oxide phase preferably has a Zn molar ratio (ratio to Ce) of 4.6 mol% or less. This configuration makes it possible to prevent cracks during operation in the electrolyte main layer 31 and maintain high oxygen ion conductivity in the electrolyte main layer 31, compared to when the Zn molar ratio (ratio to Ce) is greater than 4.6 mol%. This configuration therefore facilitates improving the output of the electrochemical cell 1. From the viewpoint of further ensuring the above-mentioned effects, the Zn molar ratio (ratio to Ce) can be more preferably 4.4 mol% or less, even more preferably 4.2 mol% or less, and even more preferably 4.0 mol% or less.

[0027] The detailed structure of the composite oxide phase and the Zn molar ratio (ratio to Ce) can be determined by Lieveld analysis of the results of X-ray diffraction (XRD), as will be described in detail in the Experimental Examples.

[0028] The above-described electrochemical cell 1 can reduce reduction expansion of the electrolyte main layer 31, even when the electrolyte main layer 31 in contact with the fuel electrode layer 2 is exposed to a high temperature and a reducing atmosphere during operation. Therefore, even when the electrochemical cell 1 uses a ceria-based solid electrolyte material, it can suppress the occurrence of cracks in the electrolyte main layer 31 during operation.

[0029] The electrochemical cell 1 of this embodiment also has the following advantages.

[0030] As described above, in the electrochemical cell of Patent Document 1, in which an oxide layer having a perovskite crystal structure is formed on the surface of a ceria-based base material, the effect of suppressing the reduction expansion of the electrolyte layer is insufficient, and the occurrence of cracks during operation cannot be suppressed, making it practically difficult to reduce the thickness of the electrolyte layer. In contrast, the electrochemical cell 1 can suppress the occurrence of cracks due to reduction expansion, making it easier to achieve a thinner electrolyte main layer 31 than the electrochemical cell of Patent Document 1.

[0031] Furthermore, solid electrolyte materials having a perovskite crystal structure have low oxygen ion conductivity. Therefore, if an oxide layer having a perovskite crystal structure is formed on the surface of a ceria-based base material, as in the electrochemical cell of Patent Document 1, this oxide layer becomes a resistive phase, resulting in a decrease in cell output. In contrast, in electrochemical cell 1, a composite oxide phase containing a specific ceria-based first crystal phase having a fluorite structure and a specific second crystal phase containing Ce and Zn is used in the electrolyte main layer 31 in contact with the fuel electrode layer 2. Therefore, the electrochemical cell 1 is easier to improve cell output than the electrochemical cell of Patent Document 1.

[0032] In addition, the solid electrolyte material having a perovskite crystal structure is a material having hydrogen ion conductivity. Therefore, when the electrochemical cell of Patent Document 1 is used as an SOEC, the H introduced into the fuel electrode ２ H generated by electrolysis of O ＋ In contrast, in the electrochemical cell 1, a composite oxide phase containing a specific second crystalline phase containing Ce and Zn in addition to a specific ceria-based first crystalline phase having a fluorite structure is used in the electrolyte main layer 31 that contacts the fuel electrode layer 2. Therefore, even when the electrochemical cell 1 is used as an SOEC (described later), the H ２ H generated by electrolysis of O ＋ This can prevent a decrease in the amount of hydrogen produced due to a part of the hydrogen leaking to the air electrode side.

[0033] Furthermore, if a technique for locally concentrating rare earth elements on the surfaces of ceria-based crystal particles is adopted instead of the technique described in Patent Document 1, the rare earth elements will segregate near the grain boundaries when a sintered body is formed, increasing the amount of oxygen vacancies near the grain boundaries and decreasing the amount of oxygen vacancies within the grains. Therefore, in this case, oxygen vacancies may aggregate or Schottky barriers may form near the grain boundaries, resulting in a decrease in oxygen ion conductivity and a decrease in cell output. Furthermore, this requires manufacturing at an oxygen partial pressure higher than atmospheric pressure, which increases manufacturing costs. In contrast, the electrochemical cell 1 can reduce the reduction expansion of the electrolyte main layer 31 without locally concentrating rare earth elements on the surfaces of the ceria-based crystal particles. Therefore, the electrochemical cell 1 is more likely to suppress a decrease in cell output than the above-mentioned technique. Furthermore, because the electrolyte main layer 31 can be manufactured under atmospheric pressure, the electrochemical cell 1 is more likely to be manufactured at lower cost than the above-mentioned technique.

[0034] As long as the above-described electrochemical cell 1 is configured as a solid oxide cell using a material having oxygen ion conductivity as the electrolyte, there are no particular limitations on the materials or configurations of the above-described fuel electrode layer 2, solid electrolyte layer 3 (electron blocking layer 32, etc.), air electrode layer 4, fuel diffusion layer 5, intermediate layer 6, air electrode current collecting layer 7, etc. other than the electrolyte main layer 31. Specifically, each of these layers can be configured as follows.

[0035] The fuel electrode layer 2 may contain the above-described complex oxide phase. In this case, the fuel electrode layer 2 may specifically contain an intra-fuel electrode catalyst phase, the above-described complex oxide phase, and voids. This configuration can also suppress reduction expansion in the fuel electrode layer 2, thereby suppressing cracking in the fuel electrode layer 2.

[0036] When the fuel electrode layer 2 includes a complex oxide phase, the molar ratio of Zn (relative to Ce) in the complex oxide phase included in the fuel electrode layer 2 can be configured to be smaller than the molar ratio of Zn (relative to Ce) in the complex oxide phase included in the electrolyte main body layer 31. Because the fuel electrode layer 2 includes voids, reduction expansion is mitigated accordingly compared to the dense electrolyte main body layer 31, but reduction expansion usually occurs. In contrast, with the above configuration, it is possible to suppress the occurrence of cracks due to reduction expansion of the fuel electrode layer 2 while achieving higher output by improving electrode performance.

[0037] The anode layer 2 may contain, in addition to the above-described complex oxide phase, an anode internal electrolyte phase that is different from the complex oxide phase. The anode layer 2 may also be configured to not contain the above-described complex oxide phase. In this case, the anode layer 2 may specifically be configured to not contain the above-described complex oxide phase, but to contain an anode internal catalyst phase, an anode internal electrolyte phase, and voids. The anode internal catalyst phase may be composed of an anode catalyst material having electronic conductivity, or the like. The anode internal electrolyte phase may be composed of an oxygen ion conductive solid electrolyte material, or the like.

[0038] Examples of the anode catalyst material constituting the catalyst phase in the anode 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 can be used alone or in combination of two or more. Of these, from the viewpoint of catalytic activity (electrode activity), etc., preferred are Ni, Ni alloys, Ni oxides (NiO, etc.), and more preferred are Ni and NiO. Furthermore, examples of the solid electrolyte material constituting the electrolyte phase in the anode include ceria (CeO) doped with one or more elements selected from Gd, Sm, Y, Sc, La, Nd, Yb, Ca, and Ho. ２Examples of suitable oxides include ceria, yttria-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ). These may be used alone or in combination. The fuel electrode layer 2, which includes an anode catalyst phase made of an anode catalyst material such as a metal, alloy, or oxide thereof, and the composite oxide phase, can be referred to as a cermet electrode layer.

[0039] For example, when the solid electrolyte layer 3 includes an electron blocking layer 32 in addition to the main electrolyte layer 31, as illustrated in FIG. 1 , the electron blocking layer 32 can be composed of a solid electrolyte material that does not have electronic conductivity but has oxygen ion conductivity under the oxygen partial pressure during operation. Examples of solid electrolyte materials that do not have electronic conductivity but have oxygen ion conductivity include yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ). These materials can be used alone or in combination. Of these, yttria-stabilized zirconia (YSZ) is preferred because it is stable in a reducing atmosphere and does not exhibit electronic conductivity. The solid electrolyte layer 3 is typically formed to be dense so as to be gas impermeable.

[0040] Specifically, the air electrode layer 4 can include an air electrode catalyst phase, an air electrode electrolyte phase, and voids. The air electrode catalyst phase can be composed of an air electrode catalyst material that has electronic conductivity and oxygen ion conductivity. The air electrode electrolyte phase can be composed of a solid electrolyte material that has oxygen ion conductivity.

[0041] Examples of the air electrode catalyst material constituting the catalytic phase 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. As the air electrode catalyst material, perovskite oxides containing La, Sr, and Co are preferably used from the viewpoints of excellent mixed conductivity in which both electronic conductivity and oxygen ion conductivity coexist, and high air electrode catalytic activity. Specific examples of the above-mentioned perovskite oxides containing La, Sr, and Co include La, Sr, and Co. 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) and the like. The oxides described above may or may not have oxygen non-stoichiometry.

[0042] Examples of the solid electrolyte material constituting the electrolyte phase in the air electrode include the above-mentioned ceria-based oxides and ceria. These can be used alone or in combination of two or more. As the solid electrolyte material constituting the electrolyte phase in the air electrode, ceria doped with at least one of Gd and Sm, and more preferably ceria doped with Gd, can be suitably used from the viewpoint of excellent oxygen ion conductivity at a relatively low temperature of about 700°C.

[0043] The fuel diffusion layer 5 can be configured to be porous, for example, having voids and / or through-holes so as not to impede the supply of fuel to the fuel electrode layer 2. The fuel diffusion layer 5 can contain the above-mentioned complex oxide phase. In this case, the fuel diffusion layer 5 can specifically contain an electronic conductive phase, the above-mentioned complex oxide phase, and voids. These configurations can also suppress reduction expansion in the fuel diffusion layer 5, thereby suppressing the occurrence of cracks in the fuel diffusion layer 5.

[0044] When the fuel diffusion layer 5 includes a complex oxide phase, the Zn molar ratio (ratio to Ce) in the complex oxide phase included in the fuel diffusion layer 5 can be configured to be smaller than the Zn molar ratio (ratio to Ce) in the complex oxide phase included in the electrolyte main body layer 31. This configuration can suppress the occurrence of cracks due to reduction and expansion of the fuel diffusion layer 5. Furthermore, the important factor for the fuel diffusion layer 5 is electronic conductivity rather than oxygen ion conductivity. Therefore, by configuring the fuel diffusion layer 5 with a small Zn molar ratio (ratio to Ce) as described above, the proportion of Ce that changes from +4 to +3 valence can be increased, which has the advantage of being expected to result in a reduction in electronic resistance due to hole conduction.

[0045] The fuel diffusion layer 5 may contain, in addition to the above-described complex oxide phase, an oxide phase in the diffusion layer that is different from the complex oxide phase. The fuel diffusion layer 5 may also be configured without the above-described complex oxide phase. In this case, the fuel diffusion layer 5 may specifically be configured without the above-described complex oxide phase, but instead include an electronically conductive phase, an oxide phase in the diffusion layer, and voids. The electronically conductive phase may be composed of an electronically conductive material, etc. The oxide phase in the diffusion layer may be composed of various oxide materials, etc.

[0046] Examples of the electronically conductive material constituting the electronically conductive phase include electronic conductors 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 oxides (e.g., NiO), Cu oxides, and Co oxides. These materials can be used alone or in combination. The electronically conductive material constituting the electronically conductive phase may or may not have catalytic activity. Among these, Ni, Ni alloys, and Ni oxides (e.g., NiO) are preferred from the viewpoint of catalytic activity (electrode activity), and Ni and NiO are more preferred. Examples of oxide materials constituting the oxide phase in the diffusion layer include solid electrolyte materials such as ceria-based oxides, 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 materials can be used alone or in combination. The fuel diffusion layer 5, which includes an electron conductive phase made of a metal, alloy, or oxide thereof, and the above-mentioned composite oxide phase or oxide phase within the diffusion layer, can be called a cermet layer.

[0047] In addition to the above, the fuel diffusion layer 5 can also be made of a metal (including an alloy, omitted below) material, etc. The electrochemical cell 1 can be supported by, for example, a metal support (not shown) arranged on the fuel diffusion layer 5 on the side opposite to the fuel electrode layer 2 side.

[0048] Examples of metal materials constituting the fuel diffusion layer 5 and the metal support include Fe-based alloys. Fe-based alloys are composed of Fe as a base material and alloying elements added thereto. The alloying elements include at least one metal element and may also include at least one non-metal element. The alloying elements do not include Fe. The metal elements may include metalloid elements. Examples of metal elements included in the alloying elements include Cr, Mn, Ti, Ni, Al, Cu, Mo, Nb, V, La, Ta, Hf, Zr, Si, and B. These elements may be used alone or in combination. Specifically, the metal elements included in the alloying elements may include at least Cr, and more specifically, may include at least Cr and at least one element selected from the group consisting of Mn, Ti, Ni, Al, Cu, Mo, Nb, V, La, Ta, Hf, Zr, Si, and B. The metal element with the highest content among the metal elements contained in the alloying elements of an Fe-based alloy may be, for example, one selected from the group consisting of Cr, Mn, and Ti. Note that an Fe-based alloy containing Cr as the metal element with the highest content may be referred to as an Fe-Cr alloy. Similarly, an Fe-based alloy containing Mn as the metal element with the highest content may be referred to as an Fe-Mn alloy, and an Fe-based alloy containing Ti as the metal element with the highest content may be referred to as an Fe-Ti alloy.

[0049] The intermediate layer 6 can contain the above-described complex oxide phase. In this case, the intermediate layer 6 may specifically be composed of the above-described complex oxide phase, or may contain the above-described complex oxide phase and a cathode material phase composed of some or all of the cathode material forming the cathode layer 4 (such as the above-described cathode catalyst material forming the cathode catalyst phase or the solid electrolyte material forming the cathode electrolyte phase). In the electrochemical cell 1, the intermediate layer 6 is separated from the anode layer 2 by the solid electrolyte layer 3 and is therefore not normally exposed to a reducing atmosphere and does not undergo reduction-induced expansion. However, if the intermediate layer 6 contains the above-described complex oxide phase, it becomes easier to match the thermal expansion coefficients in the electrochemical cell 1, thereby suppressing the occurrence of cracks due to differences in thermal expansion between the layers.

[0050] The intermediate layer 6 may contain, in addition to the above-described complex oxide phase, an electrolyte phase in the intermediate layer that is different from the complex oxide phase. The intermediate layer 6 may also be configured without containing the above-described complex oxide phase. In this case, specifically, the intermediate layer 6 may be configured with the electrolyte phase in the intermediate layer without containing the above-described complex oxide phase, or may contain the electrolyte phase in the intermediate layer and a cathode material phase.

[0051] The electrolyte phase in the intermediate layer can be composed of a solid electrolyte material having oxygen ion conductivity. Examples of the solid electrolyte material constituting the electrolyte phase in the intermediate layer include the above-mentioned ceria-based oxides, ceria, yttria-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ). These can be used alone or in combination of two or more.

[0052] The air electrode current collecting layer 7 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.

[0053] 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 oxides containing La, Sr, and Co, and perovskite oxides containing La, Ni, and Fe. These can be used alone or in combination of two or more. Of these, from the viewpoints of being resistant to oxidation in a high-temperature oxidizing atmosphere and having high electronic conductivity, metal materials such as Pt and Pt alloys and oxides having electronic conductivity such as perovskite oxides containing La, Sr, and Co are preferred.

[0054] The electrochemical cell 1 can be used as at least one of a solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC). That is, the electrochemical cell 1 may be operated as an SOFC or as an SOEC, or may be configured to be switchable between an SOFC mode in which it operates as an SOFC and an SOEC mode in which it operates as an SOEC, and may be operated as both an SOFC and an SOEC.

[0055] Specifically, when the electrochemical cell 1 is operated as an SOFC, a hydrogen-containing gas such as hydrogen gas can be supplied to the fuel electrode layer 2 as a fuel gas. In this case, an oxygen-containing gas such as air or oxygen gas can be supplied to the air electrode layer 4. On the other hand, when the electrochemical cell 1 is operated as an SOEC, the fuel electrode layer 2 can function as a hydrogen electrode. The fuel electrode layer 2 can be supplied with water (H ) such as water vapor gas as a fuel gas. ２ A gas containing carbon dioxide (CO O ) can be supplied to the air electrode layer 4. In this case, the air electrode layer 4 can function as an oxygen electrode. A gas such as air may be supplied to the air electrode layer 4, or no gas may be supplied. The hydrogen-containing gas may contain water vapor for humidification or the like, and the water-containing gas may contain a reducing gas such as hydrogen gas. When operating as a co-electrolytic cell, carbon dioxide (CO O ) can be added to the fuel gas in addition to water. ２ ) may also be contained.

[0056] The operating temperature of the electrochemical 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 obtaining high output. The operating temperature of the electrochemical 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, easily suppressing reduction expansion.

[0057] In particular, when the operating temperature of the electrochemical cell 1 is 755°C or lower, the electrochemical cell 1 can be operated within a range in which rapid reduction expansion in the electrolyte main body layer 31 can be easily suppressed, which has the advantage of making it easier to achieve high output from the electrochemical cell 1.

[0058] (Experimental Example) The electrochemical cell of the present disclosure will be described in detail below using an experimental example. In this experimental example shown below, an electrochemical cell 1 was fabricated having a layered structure in which a fuel diffusion layer 5, an anode layer 2, a solid electrolyte layer 3, an intermediate layer 6, an air cathode layer 4, and an air cathode current collecting layer 7 were laminated in this order, as illustrated in Figures 3 and 4. In this electrochemical cell 1, the solid electrolyte layer 3 is composed of an electrolyte main layer 31 and an electron blocking layer 32. Note that Figures 3 and 4 show the electrochemical cell of Sample 13 fabricated in Experimental Example 3, which will be described later.

[0059] (Experimental Example 1) <Material Preparation> - GDC Powder - Gd-doped ceria powder was prepared using Ce. ０．９ Gd ０．１ O １．９５ Specifically, the GDC powder was prepared by mixing CeO as a Ce source so as to have the above-mentioned predetermined chemical composition. ２ , Gd as a Gd source ２ O ３ These were weighed, fired at 800° C., and then crushed to prepare the powder.

[0060] ZnO powder (average particle size: 0.1 μm) was prepared as a Zn source for forming the composite oxide phase. The average particle size was the particle size (diameter) d50 at which the cumulative frequency distribution on a volume basis measured by a laser diffraction / scattering method showed 50% (the same applies hereinafter).

[0061] In this experimental example, ZnO was used as the Zn source for the starting material. However, other materials such as zinc acetate, zinc acetate dihydrate, zinc nitrate, zinc nitrate hexahydrate, and zinc oxide nanoparticle suspensions can also be used. When using materials other than zinc oxide nanoparticle suspensions, voids may form due to the evaporation of acetic acid and nitric acid components during firing. Therefore, when using zinc nitrate as a starting material for forming layers requiring denseness, such as the electrolyte main layer or intermediate layer, it is recommended to weigh out the desired amount of zinc nitrate, dissolve it in water, add GDC powder, mix it in a ball mill, spread the recovered slurry on a tray, and dry it at approximately 100°C before using the powder. When using zinc acetate as a starting material, it is recommended to further heat it to approximately 250°C to 300°C. By performing such a treatment before preparing the slurry for forming the desired layer, the acetic acid and nitric acid components can be decomposed and evaporated. When using these materials as Zn sources for the fuel electrode layer or fuel diffusion layer, they can also be used as pore-forming components, so such treatment may not be necessary.

[0062] - Fuel Diffusion Layer - NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.5 μm), acrylic resin (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. The mass ratio of NiO powder to GDC powder was 65:35. The slurry was applied in the form of a layer onto a resin sheet using a doctor blade method, dried, and then the resin sheet was peeled off to prepare fuel diffusion layer-forming sheets for Samples 1 to 6 and Sample 1C.

[0063] -Fuel electrode layer- NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.5 μm), acrylic resin (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol were mixed in a ball mill to prepare a slurry. The mass ratio of the NiO powder to the GDC powder was 50:50. The amount of pore-forming agent in the fuel electrode layer-forming sheet was smaller than the amount of pore-forming agent in the fuel diffusion layer-forming sheet. Subsequently, the fuel electrode layer-forming sheets used for Samples 1 to 6 and Sample 1C were prepared in the same manner as in the preparation of the fuel diffusion layer-forming sheet.

[0064] - Electrolyte Main Layer - GDC powder (average particle size: 0.5 μm), ZnO powder (average particle size: 0.1 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol were mixed in a ball mill to prepare a slurry. The GDC powder and ZnO powder were weighed and added to obtain a predetermined molar ratio. Subsequently, the electrolyte main layer forming sheets used for Samples 1 to 6 were prepared in the same manner as in the preparation of the fuel diffusion layer forming sheets. Furthermore, the electrolyte main layer forming sheet used for Sample 1C was prepared in the same manner, except that ZnO powder was not added.

[0065] In this experimental example, a composite oxide phase is formed through a process of mixing GDC powder with a Zn source, and CeO ２ , Gd ２ O ３ , ZnO were weighed to prepare a composite oxide containing Ce, Gd, and Zn, and this was used as a raw material. ２ Or B ２ O ３ The electrolyte main layer is not made of a glass material to which the above-mentioned additives are added.

[0066] -Electron blocking layer- 8 mol % Y ２ O ３A slurry was prepared by mixing yttria-stabilized zirconia (hereinafter referred to as 8YSZ) (average particle size: 0.5 μm) containing 8YSZ, polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol in a ball mill. The electron blocking layer sheets used for Samples 1 to 6 and Sample 1C were prepared in the same manner as in the preparation of the fuel diffusion layer sheets.

[0067] - Intermediate layer - GDC powder (average particle size: 0.5 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol were mixed in a ball mill to prepare a slurry. After that, the intermediate layer sheets used for Samples 1 to 6 and Sample 1C were prepared in the same manner as in the preparation of the fuel diffusion layer sheets.

[0068] -Air electrode layer- La ０．６ Sr ０．４ CoO ３ A powder (hereinafter referred to as LSC) (average particle diameter: 0.8 μm) and a GDC powder (average particle diameter: 0.3 μm) were weighed out to a volume ratio of 8:2, and carbon (pore-forming agent), ethyl cellulose, and terpineol were added thereto and mixed in a ball mill to prepare pastes for forming the air cathode layer used in Samples 1 to 6 and Sample 1C.

[0069] -Air electrode current collecting layer- LSC powder (average particle size: 0.8 μm), carbon (pore-forming agent), ethyl cellulose, and terpineol were added and mixed in a ball mill to prepare pastes for forming air electrode current collecting layers used in Samples 1 to 6 and Sample 1C.

[0070] <Fabrication of Electrochemical Cell> A laminate was obtained by stacking a predetermined fuel diffusion layer sheet, a fuel electrode layer sheet, an electrolyte main layer sheet, an electron blocking layer sheet, and an intermediate layer sheet in this order. The resulting laminate was pressed using a hot isostatic press (WIP) method and then degreased. The WIP conditions were a temperature of 80°C, a pressure of 50 MPa, and a pressing time of 10 minutes. The resulting pressed body was then cut to a predetermined size. The pressed body was then fired in air at a predetermined temperature (selected from a range of 1000°C to 1370°C) for 2 hours. This resulted in a predetermined ceramic substrate (sintered body) in which a fuel diffusion layer (200 μm thick), a fuel electrode layer (40 μm thick), an electrolyte main layer (5 μm thick), an electron blocking layer (5 μm thick), and an intermediate layer (5 μm thick) were stacked in this order.

[0071] Next, a predetermined paste for forming an air cathode layer was applied to the surface of the intermediate layer of the obtained ceramic substrate by screen printing, and the paste was baked in the air at 1125°C for 10 minutes to form an air cathode layer (thickness 50 µm). At this time, the outer shape of the air cathode layer was formed smaller than the outer shape of the fuel electrode layer.

[0072] Next, a predetermined paste for forming an air electrode current collecting layer was applied to the surface of the air electrode layer by screen printing, and fired (baked) at 900°C for 1 hour in an air atmosphere to form an air electrode current collecting layer (thickness 50 μm).

[0073] As described above, flat electrochemical cells (single cells) of Samples 1 to 6 and Sample 1C shown in Table 1 were fabricated.

[0074] <Identification of Crystalline Phases in the Electrolyte Main Layer, and Zn Molar Ratio (Ratio to Ce)> Unnecessary layers other than the electrolyte main layer were scraped off in advance from the electrochemical cell of each sample, and the material for analysis was collected from only the electrolyte main layer. This was then pulverized in a mortar to obtain powder for analysis for XRD. Next, XRD measurement was performed on the analysis powder of each sample using a large synchrotron radiation facility (SPring-8, beamline: BL19B2) under the following measurement conditions. In addition, Lieveld analysis was performed using the obtained XRD measurement results. From the above, the crystalline phases in the electrolyte main layer were identified, and the mass ratio of each crystalline phase contained therein was calculated. In addition, the Zn molar ratio (ratio to Ce) was calculated based on the information from the Lieveld analysis. X-ray diffractometer: High-throughput powder X-ray diffractometer X-ray wavelength: 0.7 Å Measurement range: 2.1° to 84.8° Step interval: 0.005° Crystal phase analysis software: PDXL (manufactured by Rigaku Corporation) Structural analysis software: RIETAN-FP (profile function: extended pseudo-fork function)

[0075] In this experimental example, XRD measurements were performed using synchrotron radiation equipment, but XRD measurements may also be performed using laboratory equipment. In this case, the powder X-ray diffractometer may be a RINT 2000 or SmartLab manufactured by Rigaku Corporation. The measurement conditions may be a Cu tube X-ray source, a tube voltage of 40 kV, a tube current of 30 mA, a measurement range of 10° to 90°, and a step interval of 0.01°.

[0076] The results of identifying the crystalline phase of the electrolyte main layer are shown in Figure 5. Note that Figure 5 shows the results for Samples 2, 4, 6, and 1C as representatives. As shown in Figure 5 (see also Table 1 below), Ce ０．９ Gd ０．１ O １．９５ The electrolyte main layer of the electrochemical cells of Samples 2, 4, and 6, which are made of a material containing ZnO added to Ce, has a fluorite structure. ０．９ Gd ０．１ O １．９５ and a first crystalline phase represented by (ZnO)(CeO １．６９５ ) ０．５６２５It was confirmed that the composite oxide phase contained a second crystalline phase represented by the formula: Zn molar ratio (ratio to Ce) of the composite oxide phase in the main electrolyte layer. ０．９ Gd ０．１ O １．９５ The electrolyte main layer of the electrochemical cell of sample 1C, which uses raw materials without adding ZnO, is (ZnO)(CeO １．６９５ ) ０．５６２５ The second crystal phase represented by ０．９ Gd ０．１ O １．９５ It was confirmed that the material was a single phase and did not contain a complex oxide phase.

[0077] In addition, while FIG. 5 shows the results for Samples 2, 4, 6, and 1C as representatives, similar results were obtained for Samples 1, 3, and 5. In addition, in this experimental example, Ce was used to form the main electrolyte layer. ０．９ Gd ０．１ O １．９５ According to the above results, the powder was used. １－ｘ (RE) ｘ O ２－ｘ／２ (where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm) powder is used, which has a fluorite structure and Ce １－ｘ (RE) ｘ O ２－ｘ／２ (where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm) is generated. In this experimental example, the second crystal phase in the complex oxide phase is (ZnO)(CeO １．６９５ ) ０．５６２５ However, by changing the amount of Zn source such as ZnO added, the firing temperature, and the starting state of the Zn source such as ZnO, other (ZnO)(CeO ２－δ ) ｙ (where δ>0, y is 0.15 or more and 0.7 or less) can be generated.

[0078] <Linear Expansion Coefficient of Electrolyte Main Layer> The slurry prepared during the preparation of the electrolyte main layer sheet was dried, and the resulting powder was compacted to form a green body. The resulting green body was then fired at the same predetermined firing temperature and firing time as during the preparation of the electrochemical cell to prepare an electrolyte main layer sample. Next, a strip-shaped sample measuring 4 mm wide, 2 mm high, and 10 mm long was obtained from the electrolyte main layer sample by polishing. Next, using a daylight meter DIL402 Expedis Select & Supreme (manufactured by Netsch), the strip-shaped sample was heated from room temperature to 800°C while flowing 4% by volume of hydrogen gas-Ar gas. The relationship between temperature and the linear expansion coefficient of the electrolyte main layer was measured, and the linear expansion coefficient of the electrolyte main layer at 650°C was determined.

[0079] <Oxygen Ion Conductivity of the Electrolyte Main Layer> The slurry prepared during the preparation of the electrolyte main layer sheet was dried, and the resulting powder was compacted to form a green body. The resulting green body was then fired at the same predetermined firing temperature and firing time as during the preparation of the electrochemical cell to produce an electrolyte main layer sample. The surface of the electrolyte main layer sample was then polished, and Au sputtering was performed on both sides to form a pair of electrodes. Impedance measurements were then performed on this electrolyte main layer sample using an impedance analyzer E4990A (manufactured by Keysight Corporation), a high-temperature / high-frequency compatible sample rod HT-Z2-HF-ROD (manufactured by Toyo Corporation), and an HT-Z2-HF high-frequency compatible heating furnace system (manufactured by Toyo Corporation). Impedance measurements were performed at 50°C intervals from 450°C to 700°C. The obtained data was analyzed using Z-View, and the oxygen ion conductivity at 650°C was calculated based on the electrode area and electrolyte main layer sample thickness.

[0080] <Cracks during operation> A gas seal structure was formed by placing glass rings on both sides of the electrochemical cell and fusing them at high temperature. Then, the fuel electrode layer and the fuel diffusion layer were subjected to reduction treatment. Next, using an SOFC fuel cell evaluation device (manufactured by Nishiyama Manufacturing Co., Ltd.), humidified N 2 gas at 80°C was applied to the fuel electrode layer. ２ (50 ml) and H ２An electrolysis test (operating temperature: 650°C) was conducted with 50 ml of electrolyte introduced into the cathode layer and 100 ml of air introduced into the cathode layer, and the IV characteristics were measured. If the electrolyte main layer cracked, the open circuit voltage (OCV) would deviate significantly from the theoretical value. ２ and O ２ A thermocouple attached near the cell detects a temperature rise as the electrolyte reacts and burns. These factors were used to determine whether or not cracks occurred in the electrolyte main layer during operation. The above evaluation was performed three times for each level, and the results are shown in Table 1 below as X / 3 (X = 0, no cracks occurred during operation in the three tests; X = 1, cracks occurred once during operation in the three tests; X = 2, cracks occurred twice during operation in the three tests; and X = 3, cracks occurred three times during operation in the three tests). To be sure, the electrolyte main layer was also observed using an SEM to confirm whether or not cracks occurred during operation in the electrolyte main layer. Where necessary, the current value that could be swept until the voltage reached 1.3 V was calculated as the current density.

[0081] The details and evaluation results of Experimental Example 1 described above are summarized in Table 1. Fig. 6 shows the relationship between the Zn molar ratio (ratio to Ce) in the composite oxide phase and the linear expansion coefficient of the electrolyte main layer. Fig. 7 shows the relationship between the Zn molar ratio (ratio to Ce) in the composite oxide phase and the oxygen ion conductivity of the electrolyte main layer.

[0082]

[0083] Table 1, Figures 6 and 7 reveal the following: In Sample 1C, the electrolyte main layer in contact with the fuel electrode layer is an oxide containing Zn and Ce (ZnO) (CeO ２－δ ) ｙ Therefore, when the electrolyte main layer is exposed to a high temperature and a reducing atmosphere during operation, sample 1C is unable to reduce the reduction expansion of the electrolyte main layer, and is unable to suppress the occurrence of cracks in the electrolyte main layer during operation.

[0084] In contrast, in Samples 1 to 6, the electrolyte main layer in contact with the fuel electrode layer has a fluorite structure, and Ce １－ｘ (RE) ｘ O ２－ｘ／２(where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm), and an oxide containing Zn and Ce, (ZnO) (CeO ２－δ ) ｙ (where δ>0, and y is 0.15 to 0.7) and a second crystalline phase represented by the formula: Therefore, it was confirmed that Samples 1 to 6 can reduce the reduction expansion of the electrolyte main layer even when the electrolyte main layer is exposed to a high temperature and a reducing atmosphere during operation, and can suppress the occurrence of cracks in the electrolyte main layer during operation.

[0085] The reason why the reduction expansion of the electrolyte main body layer could be reduced is presumed to be as follows: The ceria-based electrolyte material has a low oxygen partial pressure (low P Ｏ２ ), when exposed to a high temperature environment, oxygen atoms are released. ４＋ →Ce ３＋ A valence change of Ce occurs. ４＋ The ionic radius of Ce is 0.97 Å. ３＋ The ionic radius of is 1.14 Å, and the ionic radius increases due to the above-mentioned change in valence, causing lattice expansion. Ｏ２ Before being exposed to a high temperature environment, some Ce ４＋ Ce ３＋ By forming a solid solution with ZnO in this state, Ｏ２ , Ce that changes when exposed to a high-temperature environment ４＋ It is believed that this makes it possible to reduce the amount of , and as a result, it becomes possible to reduce the reduction expansion of the electrolyte main body layer.

[0086] Furthermore, according to FIG. 6 and Table 1, when the Zn molar ratio (ratio to Ce) is 1.1 mol % or more, reduction expansion of the electrolyte main body layer can be more effectively suppressed than when the Zn molar ratio (ratio to Ce) is less than 1.1 mol %, and it can be seen that cracks in the electrolyte main body layer during operation can be avoided with a high probability.

[0087] Furthermore, according to FIG. 7 and Table 1, when the Zn molar ratio (ratio to Ce) is 4.6 mol % or less, cracking in the electrolyte main layer during operation can be avoided and the oxygen ion conductivity of the electrolyte main layer can be maintained high, making it easier to improve the output of the electrochemical cell, compared to when the Zn molar ratio (ratio to Ce) is more than 4.6 mol %.

[0088] Experimental Example 2 Six electrochemical cells were fabricated in the same manner as the electrochemical cell of Sample 3 in Experimental Example 1. In this experiment, the electrochemical cells were operated at an operating temperature of 600°C (Sample 7), 650°C (Sample 8), 700°C (Sample 9), 750°C (Sample 10), 755°C (Sample 11), and 760°C (Sample 12), as in Experimental Example 1. Cracks during operation were confirmed for each electrochemical cell. The main electrolyte layer of each of Samples 7 to 12 contained the specific composite oxide phase described above. The results are summarized in Table 2. Furthermore, the linear expansion coefficient of the main electrolyte layer of Samples 3 and 1C was measured over a temperature range of 400°C to 800°C, as in Experimental Example 1. The results are shown in Figure 8.

[0089]

[0090] 8, it can be seen that when the operating temperature of the electrochemical cell is 755° C. or less, the electrochemical cell can be operated within a range in which rapid reduction expansion of the main electrolyte layer can be easily suppressed. Therefore, it can be seen that when the operating temperature of the electrochemical cell is 755° C. or less, it is easy to achieve high output from the electrochemical cell.

[0091] (Experimental Example 3) An electrochemical cell was fabricated in the same manner as the electrochemical cell of Sample 3 in Experimental Example 1. In this Experimental Example, the electrochemical cell fabricated above was designated as the electrochemical cell of Sample 13. Note that in all of the electrochemical cells of Sample 13, the main electrolyte layer contained the specific complex oxide phase described above, but neither the fuel electrode layer nor the fuel diffusion layer contained the specific complex oxide phase described above.

[0092] A slurry was prepared by mixing NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.5 μm), ZnO powder (average particle size: 0.1 μm), acrylic resin (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. The GDC powder and ZnO powder were weighed and added to achieve a predetermined molar ratio. The mass ratio of the NiO powder to the GDC powder was 65:35. The slurry was applied in layers onto a resin sheet using a doctor blade method, dried, and then the resin sheet was peeled off to prepare fuel diffusion layer-forming sheets for Samples 14 and 15.

[0093] A slurry was prepared by mixing NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.5 μm), ZnO powder (average particle size: 0.1 μm), acrylic resin (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. The GDC powder and ZnO powder were weighed and added to achieve a predetermined molar ratio. The mass ratio of the NiO powder to the GDC powder was 50:50. The amount of pore-forming agent in the fuel electrode layer-forming sheet was smaller than the amount of pore-forming agent in the fuel diffusion layer-forming sheet. Subsequently, fuel electrode layer-forming sheets for Samples 14 and 15 were prepared in the same manner as in the preparation of the fuel diffusion layer-forming sheet.

[0094] An electrochemical cell of Sample 14 was fabricated in the same manner as in the fabrication of the electrochemical cell of Sample 3 in Experimental Example 1, except that the above-prepared fuel diffusion layer-forming sheet and fuel electrode layer-forming sheet for Sample 14 were used. Note that the electrochemical cell of Sample 14 has an electrolyte main layer, a fuel electrode layer, and a fuel diffusion layer that all contain the specific complex oxide phase described above.

[0095] An electrochemical cell of Sample 15 was fabricated in the same manner as in the fabrication of the electrochemical cell of Sample 3 in Experimental Example 1, except that the above-prepared fuel diffusion layer-forming sheet and fuel electrode layer-forming sheet for Sample 15 were used. Note that the electrochemical cell of Sample 15 has an electrolyte main layer, a fuel electrode layer, and a fuel diffusion layer that all contain the above-described specific complex oxide phase.

[0096] The electrochemical cells of Samples 13 to 15 were subjected to an electrolysis test (operating temperature: 650°C) and the current density was measured in the same manner as in Experimental Example 1. No cracks were observed during operation in any of the electrochemical cells of Samples 13 to 15. The results are summarized in Table 3.

[0097]

[0098] Table 3 shows the following: The fuel electrode layer and the fuel diffusion layer must be electronically conductive. The ceria-based solid electrolyte material has Ce during operation. ４＋ →Ce ３＋ Since electron conductivity is exhibited by being reduced to Ce, a small Zn molar amount is used. ４＋ It can be seen that a higher current density can be obtained by reducing a portion of the

[0099] 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.

[0100] The present disclosure has the following features: [1] An electrochemical cell (1) having, in this order, a fuel electrode layer (2) that is an electrode to which fuel is supplied, a solid electrolyte layer (3) that has oxygen ion conductivity, and an air electrode layer (4) that is an electrode that forms a pair with the fuel electrode layer, wherein the solid electrolyte layer has an electrolyte main layer (31) that is in contact with the fuel electrode layer, and the electrolyte main layer has a fluorite structure and contains Ce １－ｘ (RE) ｘ O ２－ｘ／２ (where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm), and a first crystalline phase represented by (ZnO)(CeO ２－δ) ｙ (where δ > 0, y is 0.15 or more and 0.7 or less). [2] The electrochemical cell according to [1], wherein the composite oxide phase has a ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystal phase of 1.1 mol % or more. [3] The electrochemical cell according to [1] or [2], wherein the composite oxide phase has a ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystal phase of 4.6 mol % or less. [4] The electrochemical cell according to any one of [1] to [3], wherein the operating temperature is 755°C or less. [5] The electrochemical cell according to any one of [1] to [4], wherein the fuel electrode layer contains the composite oxide phase. [6] The electrochemical cell according to any one of [1] to [5], further comprising a fuel diffusion layer (5) in contact with the fuel electrode layer on a side of the fuel electrode layer opposite to the solid electrolyte layer side, the fuel diffusion layer including the complex oxide phase. [7] The electrochemical cell according to [5], wherein the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase included in the fuel electrode layer is less than the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase included in the main electrolyte layer. [8] The electrochemical cell according to [6], wherein the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase included in the fuel diffusion layer is less than the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase included in the main electrolyte layer. [9] The electrochemical cell according to any one of [1] to [8], which has an intermediate layer (6) between the solid electrolyte layer and the air cathode layer, and the intermediate layer contains the composite oxide phase.

[10] The electrochemical cell according to any one of [1] to [9], which is used as at least one of a solid oxide fuel cell and a solid oxide electrolysis cell.

Claims

1. An electrochemical cell (1) having, in this order, a fuel electrode layer (2) which is an electrode to which fuel is supplied, a solid electrolyte layer (3) having oxygen ion conductivity, and an air electrode layer (4) which is an electrode paired with the fuel electrode layer, wherein the solid electrolyte layer has an electrolyte main layer (31) in contact with the fuel electrode layer, and the electrolyte main layer has a fluorite structure and contains Ce １－ｘ (RE) ｘ O ２－ｘ／２ (where x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm), and a first crystalline phase represented by (ZnO)(CeO ２－δ ) ｙ (where δ>0, and y is 0.15 or more and 0.7 or less).

2. The electrochemical cell according to claim 1, wherein the composite oxide phase has a ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystal phase of 1.1 mol % or more.

3. An electrochemical cell according to claim 1 or 2, wherein the composite oxide phase has a ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystal phase of 4.6 mol % or less.

4. An electrochemical cell according to claim 1 or claim 2, wherein the operating temperature is 755°C or less.

5. The electrochemical cell according to claim 1 or 2, wherein the fuel electrode layer contains the composite oxide phase.

6. The electrochemical cell according to claim 1 or 2, further comprising a fuel diffusion layer (5) in contact with the fuel electrode layer on the side of the fuel electrode layer opposite to the solid electrolyte layer side, the fuel diffusion layer including the complex oxide phase.

7. The electrochemical cell according to claim 5, wherein the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase contained in the fuel electrode layer is less than the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase contained in the main electrolyte layer.

8. The electrochemical cell according to claim 6, wherein the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase contained in the fuel diffusion layer is less than the ratio of the number of moles of Zn to the number of moles of Ce contained in the first crystalline phase in the complex oxide phase contained in the main electrolyte layer.

9. The electrochemical cell according to claim 1 or 2, further comprising an intermediate layer (6) between the solid electrolyte layer and the air cathode layer, the intermediate layer containing the composite oxide phase.

10. The electrochemical cell according to claim 1 or 2, which is used as at least one of a solid oxide fuel cell and a solid oxide electrolysis cell.

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