Electrochemical cell

Abstract

An electrochemical cell (1) has a fuel electrode layer (2), a solid electrolyte layer (3), and an air electrode layer (4) in this order. An electrolyte body layer (31) of the solid electrolyte layer (3) has a fluorite structure and is constituted of a composite electrolyte material that contains an M-containing oxide containing at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y, in a solid electrolyte material represented by Ce1-x(RE)xO2-x / 2 (where 0.05 ≤ x ≤ 0.2 and the element RE is Gd and / or Sm). The average oxygen coordination number NAVE according to the formula 4 × (2-x / 2) and the oxygen coordination number NCe around Ce and the oxygen coordination number NRE around the element RE, as determined by EXAFS spectral analysis, satisfy 0 < NAVE-(NCe + NRE) / 2 in the composite electrolyte material.

Description

electrochemical cell CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2024-072886 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 conventional technology has the following problem: 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 a high temperature and a reducing atmosphere. Therefore, the technology of Patent Document 1 is insufficient in its effect of suppressing the reduction expansion of the solid electrolyte layer.

[0007] The present disclosure aims to provide an electrochemical cell that can reduce reductive expansion of an electrolyte main layer, even when the electrolyte main layer in contact with a fuel electrode layer is exposed to a high temperature and a reducing atmosphere during operation.

[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 the composite electrolyte material contains an M-containing oxide containing at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y, and the composite electrolyte material is １－ｘ (RE) ｘ O ２－ｘ／２ In the composition formula, the average oxygen coordination number calculated from the formula 4×(2−x / 2) is N ＡＶＥ The oxygen coordination number around Ce was determined by EXAFS spectrum analysis. Ｃｅ , the oxygen coordination number around the RE element is N ＲＥ When 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 is satisfied in the electrochemical cell (1).

[0009] The electrochemical cell has the above-described configuration, and therefore, even when the main electrolyte layer in contact with the fuel electrode layer is exposed to a high-temperature reducing atmosphere during operation, the electrochemical cell can reduce reduction-induced expansion of the main electrolyte layer.

[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 a layered structure of an electrochemical cell according to an embodiment, Fig. 2 is an explanatory diagram schematically illustrating another example of a layered structure of an electrochemical cell according to an embodiment, and Fig. 3 is an explanatory diagram illustrating the main electrolyte layer, CeO ２ , and Ce ０．９ Gd ０．１ O １．９５ 4 shows the Ce-K absorption edge EXAFS spectrum of the electrolyte main layer, CeO ２ , and Ce ０．９ Gd ０．１ O １．９５ 5 shows the Ce-K absorption edge radial structure function of the electrolyte body layer, Gd ２ O ３ , and Ce ０．９ Gd ０．１ O １．９５ 6 shows the Gd-K absorption edge EXAFS spectrum of the electrolyte main layer, Gd ２ O ３ , and Ce ０．９ Gd ０．１ O １．９５ 7 is a diagram showing the Gd-K absorption edge radial structure function of the composite electrolyte material of the electrolyte body layer obtained in Experimental Example 1. ＡＶＥ -{(N Ｃｅ +N ＲＥ ) / 2} (horizontal axis) and the linear expansion coefficient of the electrolyte main layer (×10 －６ / K, 4 vol% H ２ 8 is a graph showing the relationship between the temperature (650°C) and the N content of the composite electrolyte material of the main electrolyte layer obtained in Experimental Example 1. ＡＶＥ -{(N Ｃｅ +N ＲＥ ) / 2} (horizontal axis) and the linear expansion coefficient of the electrolyte main layer (×10 －６ / K, 4 vol% H２ 9 is a graph showing the relationship between the temperature (700°C) and the L Ｃｅ－Ｏ (horizontal axis) and the oxygen ion conductivity of the electrolyte main layer (×10 －２ 1 is a graph showing the relationship between the tensile strength (S / cm) and the temperature (650° C.) (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 and upper limits 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 fluorite structure and contains Ce. １－ｘ (RE) ｘ O ２－ｘ／２ The composite electrolyte material is composed of a solid electrolyte material represented by the formula: and an M-containing oxide containing element M. In the above chemical composition, x is 0.05 or more and 0.2 or less, and the RE element is at least one of Gd and Sm. In the M-containing oxide, the element M is at least one selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y. Specifically, in the M-containing oxide, the element M is Zn, ２＋ , Mg ２＋ , Ca ２＋ , Sr２＋ , La ３＋ , Y ３＋ It can be included in the state.

[0020] In the composite electrolyte material, x is preferably 0.06 to 0.18, more preferably 0.08 to 0.15, 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 electrolyte material, specific examples of the M-containing oxide include ZnO, MgO, CaO, SrO, and La. ２ O ３ , Y ２ O ３ More specifically, the M-containing oxides include CaO, SrO, La, etc., from the viewpoints that they are stable materials in air or a water vapor atmosphere and are inexpensive, and that they can be easily doped into cerium oxides having a fluorite structure, such as ZnO and MgO. ２ O ３ , Y ２ O ３ You can select, etc.

[0022] Specifically, the composite electrolyte material is １－ｘ (RE) ｘ O ２－ｘ／２ The solid electrolyte material may be a material in which an M-containing oxide containing a specific element M is mixed in a solid electrolyte material having a fluorite structure, and a part of the M-containing oxide may be Ce. １－ｘ (RE) ｘ O ２－ｘ／２ The fluorite structure may be solid-solved in a solid electrolyte material having the above-mentioned fluorite structure.

[0023] The composite electrolyte material is ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 relationship is satisfied. ＡＶＥ is the above-mentioned Ce １－ｘ (RE) ｘ O ２－ｘ／２ is the average oxygen coordination number calculated from the formula 4×(2−x / 2) in the composition formula. Ｃｅis the actual oxygen coordination number around Ce in the composite electrolyte material, determined by EXAFS spectrum analysis. ＲＥ is the oxygen coordination number around the actual RE element in the composite electrolyte material, determined by EXAFS spectrum analysis. The EXAFS spectrum analysis of the composite electrolyte material will be described in detail in the Experimental Examples.

[0024] The composite electrolyte material is 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 relationship means that Ce １－ｘ (RE) ｘ O ２－ｘ／２ This means that the amount of oxygen vacancies is greater than the amount of oxygen vacancies generated by doping RE elements into a solid electrolyte material having a fluorite structure of N. Ｃｅ and N ＲＥ The deviation of the value of γ means that there is a local deviation between the oxygen coordination number around the Ce element constituting the fluorite structure and the oxygen range number around the RE element doped in the fluorite structure. ４＋ →Ce ３＋ According to the experimental results described later, in the ceria-based composite electrolyte material, Ce is formed from the beginning. ３＋ It is believed that by making the composition into a form containing the above, it is possible to exert the effect of making it difficult for the composition to undergo reduction and expansion even when exposed to a high temperature and a reducing atmosphere.

[0025] The composite electrolyte material has a resistance of 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ In this case, it is preferable that the composite electrolyte material satisfies 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2≦0.15 is satisfied, the linear expansion coefficient of the electrolyte main body layer 31 is reduced more effectively, and the reduction expansion of the electrolyte main body layer 31 can be more effectively suppressed.

[0026] The composite electrolyte material is made of N ＡＶＥ -(N Ｃｅ +N ＲＥ) / 2 can be preferably 0.16 or more, more preferably 0.17 or more, even more preferably 0.18 or more, even more preferably 0.19 or more, and even more preferably 0.20 or more.

[0027] The composite electrolyte material is N ＡＶＥ -(N Ｃｅ +N ＲＥ In this case, it is preferable that the composite electrolyte material satisfies 0.4≦N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2, reduction expansion of the electrolyte main body layer 31 in the high temperature range can be more easily suppressed.

[0028] The composite electrolyte material is made of N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 can be preferably 0.39 or less, more preferably 0.38 or less, even more preferably 0.37 or less, even more preferably 0.36 or less, and even more preferably 0.35 or less.

[0029] The composite electrolyte material has a bond distance L between Ce and O determined by EXAFS spectrum analysis. Ｃｅ－Ｏ In this case, the reduction expansion of the electrolyte main body layer 31 can be suppressed and the oxygen ion conductivity of the electrolyte main body layer 31 can be kept high, which makes it easier to improve the output of the electrochemical cell 1. This is because L Ｃｅ－Ｏ is 2.341 Å or more, the oxygen ions O ２－ is the Ce atom (Ce ３＋ , Ce ４＋ ) and are less likely to be captured by oxygen ions O ２－ This is thought to be because the decrease in mobility can be suppressed.

[0030] L Ｃｅ－Ｏ From the viewpoint of ensuring the above-mentioned effects, the thickness can be set to preferably 2.342 Å or more, more preferably 2.343 Å or more, and even more preferably 2.344 Å or more.

[0031] In the composite electrolyte material, the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material (sometimes referred to as the "M molar ratio (ratio to Ce)" in the present disclosure) is preferably 0.5 mol% or more. With this configuration, reduction expansion of the electrolyte main body layer 31 can be more effectively suppressed compared to when the M molar ratio (ratio to Ce) is less than 0.5 mol%. From the viewpoint of further ensuring the above-mentioned effect, the M molar ratio (ratio to Ce) can be preferably 1.1 mol% or more, more preferably 1.3 mol% or more, even more preferably 1.5 mol% or more, and even more preferably 1.8 mol% or more.

[0032] The composite electrolyte material preferably has an M molar ratio (ratio to Ce) of 4.6 mol% or less. This configuration suppresses the reduction expansion of the electrolyte main body layer 31 and maintains a high oxygen ion conductivity in the electrolyte main body layer 31, compared to when the M 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 M molar ratio (ratio to Ce) is more preferably 4.4 mol% or less, even more preferably 4.2 mol% or less, and even more preferably 4.0 mol% or less.

[0033] The detailed composition of the composite electrolyte material and the molar ratio of Mn (ratio to Ce) can be determined by Lieveld analysis of the results of X-ray diffraction (XRD) measurement and by ICP (inductively coupled plasma) emission spectroscopy. Details will be described in the experimental examples.

[0034] The above-described electrochemical cell 1 can reduce the 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. Note that suppressing the reduction expansion of the electrolyte main layer 31 is advantageous for suppressing cracks in the electrolyte main layer 31 during operation.

[0035] The electrochemical cell 1 of this embodiment also has the following advantages.

[0036] 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, making it practically difficult to thin the electrolyte layer. In contrast, the electrochemical cell 1 can reduce the reduction expansion of the electrolyte main layer 31, making it easier to thin the electrolyte main layer 31 than the electrochemical cell of Patent Document 1.

[0037] In addition, solid electrolyte materials having a perovskite crystal structure have low oxygen ion conductivity. Therefore, when 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 the cell output. In contrast, in electrochemical cell 1, Ce １－ｘ (RE) ｘ O ２－ｘ／２ A composite electrolyte material containing an M-containing oxide containing a specific element M in a solid electrolyte material having a fluorite structure as described above is used for the electrolyte main body layer 31 in contact with the fuel electrode layer 2. Therefore, the electrochemical cell 1 is easier to improve the cell output compared to the electrochemical cell of Patent Document 1.

[0038] 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 ＋ A part of Ce flows out to the air electrode side through the electrolyte layer, reducing the amount of hydrogen produced. １－ｘ (RE) ｘ O ２－ｘ／２ A composite electrolyte material containing an M-containing oxide containing a specific element M in a solid electrolyte material having a fluorite structure is used for the electrolyte main body layer 31 in contact with the fuel electrode layer 2. Therefore, even when the electrochemical cell 1 is used as an SOEC (described later), it is possible to use 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.

[0039] 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 the 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, while this technique may be effective in suppressing reduction expansion at operating temperatures of around 850°C, its effectiveness at operating temperatures below 700°C is unclear. Furthermore, this technique 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, compared to the above case, the electrochemical cell 1 can achieve the effect of suppressing reduction expansion of the electrolyte main layer 31 even when the operating temperature is set to a low temperature of 700° C. or less. Furthermore, because the electrolyte main layer 31 can be manufactured under atmospheric pressure, the electrochemical cell 1 can be manufactured at lower costs than the above case.

[0040] 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.

[0041] The anode layer 2 may contain the specific composite electrolyte material described above in the main electrolyte layer 31. In this case, the anode layer 2 may specifically contain an anode catalyst material, a composite electrolyte material, and voids. This configuration also makes it possible to suppress reduction expansion in the anode layer 2.

[0042] When the fuel electrode layer 2 contains a composite electrolyte material, the M molar ratio (ratio of Ce) of the composite electrolyte material contained in the fuel electrode layer 2 can be configured to be smaller than the M molar ratio (ratio of Ce) of the composite electrolyte material contained in the electrolyte main body layer 31. Because the fuel electrode layer 2 contains voids, reduction expansion is mitigated accordingly compared to the electrolyte main body layer 31, which is formed as a dense material; however, reduction expansion usually occurs. In contrast, with the above configuration, reduction expansion of the fuel electrode layer 2 can be suppressed while achieving higher output by improving electrode performance.

[0043] The anode layer 2 may contain, in addition to the above-described composite electrolyte material, an anode electrolyte material different from the composite electrolyte material. The anode layer 2 may also be configured not to contain the above-described composite electrolyte material. In this case, the anode layer 2 may specifically be configured not to contain the above-described composite electrolyte material, but to contain an anode catalyst material, an anode electrolyte material, and voids. The anode catalyst material may be composed of a catalyst material having electron conductivity, or the like. The anode electrolyte material may be composed of a solid electrolyte material having oxygen ion conductivity, or the like.

[0044] Examples of the catalyst material 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 material 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 materials include ceria, yttria-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScSZ). These materials can be used alone or in combination. The fuel electrode layer 2, which includes a fuel electrode catalyst material made of a metal, alloy, or oxide thereof, and the composite electrolyte material described above, can be referred to as a cermet electrode layer.

[0045] 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.

[0046] Specifically, the air electrode layer 4 can include an air electrode catalytic material, an air electrode electrolyte material, and voids. The air electrode catalytic material can be composed of a catalytic material having electronic conductivity and oxygen ion conductivity. The air electrode electrolyte material can be composed of a solid electrolyte material having oxygen ion conductivity.

[0047] 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. As the catalytic material in the air electrode, perovskite oxides containing La, Sr, and Co can be preferably used from the viewpoint 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.

[0048] Examples of the solid electrolyte material constituting the electrolyte material 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 material 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.

[0049] 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-described composite electrolyte material. In this case, the fuel diffusion layer 5 can specifically contain an electron conductive material, the above-described composite electrolyte material, and voids. These configurations can also suppress reduction expansion in the fuel diffusion layer 5.

[0050] When the fuel-diffusion layer 5 includes a composite electrolyte material, the M molar ratio (ratio to Ce) of the composite electrolyte material included in the fuel-diffusion layer 5 can be configured to be smaller than the M molar ratio (ratio to Ce) of the composite electrolyte material included in the electrolyte main body layer 31. This configuration can suppress the reduction expansion of the fuel-diffusion layer 5. Furthermore, the important factor for the fuel-diffusion layer 5 is not oxygen ion conductivity but electronic conductivity. Therefore, by configuring the fuel-diffusion layer 5 with a small M 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 reduce electronic resistance due to hole conduction.

[0051] The fuel-diffusion layer 5 may contain, in addition to the above-described composite electrolyte material, an oxide material in the diffusion layer that is different from the composite electrolyte material. Alternatively, the fuel-diffusion layer 5 may be configured without the above-described composite electrolyte material. In this case, the fuel-diffusion layer 5 may specifically be configured without the above-described composite electrolyte material, but instead include an electron-conductive material, an oxide material in the diffusion layer, and voids.

[0052] Examples of electron-conductive materials that can be used in the fuel diffusion layer 5 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 materials can be used alone or in combination. The electron-conductive materials used in the fuel diffusion layer 5 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 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 material made of a metal, alloy, or oxide thereof, and the above-mentioned composite electrolyte material and oxide material in the diffusion layer, can be called a cermet layer.

[0053] 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.

[0054] 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.

[0055] The intermediate layer 6 can contain the composite electrolyte material described above. In this case, the intermediate layer 6 may specifically be composed of the composite electrolyte material described above, or may contain the composite electrolyte material described above and some or all of the air electrode material (such as the above-described air electrode catalyst material or air electrode electrolyte material) that forms the air electrode layer 4. In the electrochemical cell 1, the intermediate layer 6 is separated from the fuel electrode layer 2 by the solid electrolyte layer 3, and therefore is not normally exposed to a reducing atmosphere and does not undergo reduction-induced expansion. However, if the intermediate layer 6 contains the composite electrolyte material described above, 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.

[0056] The intermediate layer 6 may contain, in addition to the above-described composite electrolyte material, an intermediate layer electrolyte material different from the composite electrolyte material. The intermediate layer 6 may also be configured without containing the above-described composite electrolyte material. In this case, the intermediate layer 6 may specifically be configured from the intermediate layer electrolyte material without containing the above-described composite electrolyte material, or may contain the intermediate layer electrolyte material and a cathode material.

[0057] The electrolyte material 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 material 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] (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 was fabricated having a layered structure in which a fuel diffusion layer, an anode layer, a solid electrolyte layer, an intermediate layer, an air cathode layer, and an air cathode current collecting layer were stacked in this order. In this electrochemical cell, the solid electrolyte layer was composed of an electrolyte body layer and an electron blocking layer.

[0065] (Experimental Example 1) <Material Preparation> - GDC Powder - As ceria powder doped with Gd, Ce ０．９ Gd ０．１ O １．９５ (hereinafter referred to as GDC) powder was prepared. Specifically, GDC powder was prepared by weighing CeO ２ as a Ce source and Gd ２ O ３ as a Gd source so as to have the above-mentioned predetermined chemical composition, firing them at 800 °C, and then pulverizing them.

[0066] - M Source - As an M source for forming a composite electrolyte material, ZnO powder (average particle size: 0.1 μm), MgO powder (average particle size: 0.1 μm), Ca(OH) ２ powder (average particle size: 5 μm), Sr(OH) ２ powder (average particle size: 5 μm), La(OH) ３ powder (average particle size: 1 μm), Y ２ O ３ powder (average particle size: 1 μm) were prepared. The above average particle size is the particle size (diameter) d50 when the volume-based cumulative frequency distribution measured by the laser diffraction / scattering method shows 50% (hereinafter the same).

[0067] In this experimental example, oxides and hydroxides of M elements were used as the M source of the starting materials, but other M element acetates, nitrates, etc. can also be used as appropriate.

[0068] - Fuel Diffusion Layer - A slurry was prepared by mixing NiO powder (average particle size: 0.5 μm), GDC powder (average particle size: 0.5 μm), an acrylic resin (pore-forming agent), polyvinyl butyral, isoamyl acetate, and 1-butanol in a ball mill. The mass ratio of NiO powder to GDC powder was 65:35. Using the doctor blade method, the above slurry was coated layer by layer on a resin sheet, dried, and then the resin sheet was peeled off to prepare sheets for forming fuel diffusion layers for Samples 1 to 8 and Sample 1C, respectively.

[0069] -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 8 and Sample 1C were prepared in the same manner as in the preparation of the fuel diffusion layer-forming sheet.

[0070] - Electrolyte Main Layer - A slurry was prepared by mixing GDC powder (average particle size: 0.5 μm), a predetermined M source powder, polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol in a ball mill. At this time, the GDC powder and the M source powder were weighed and added so as to achieve a predetermined molar ratio. Thereafter, the electrolyte main layer forming sheets used for Samples 1 to 8 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 the M source powder was not added.

[0071] In this experimental example, a composite electrolyte material is formed through a process of mixing GDC powder and an M source, and CeO ２ , Gd ２ O ３ , and the M source were weighed to prepare a composite oxide containing Ce, Gd, and element M, which was then 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.

[0072] -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 8 and 1C were prepared in the same manner as in the preparation of the fuel diffusion layer sheets.

[0073] - 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 8 and Sample 1C were prepared in the same manner as in the preparation of the fuel diffusion layer sheets.

[0074] -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 to the mixture and mixed in a ball mill to prepare pastes for forming the air cathode layer used in Samples 1 to 8 and Sample 1C.

[0075] -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 8 and Sample 1C.

[0076] <Preparation of Electrochemical Cell> 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 were laminated in this order to obtain a laminate. The obtained laminate was pressed using a hot isostatic press (WIP) method and then degreased. The WIP molding conditions were a temperature of 80°C, a pressure of 50 MPa, and a pressing time of 10 minutes. The obtained pressed body was then cut to a predetermined size. The pressed body was then sintered in air at 1370°C for 2 hours. This resulted in a predetermined ceramic substrate (sintered body) in which a fuel diffusion layer (thickness 200 μm), a fuel electrode layer (thickness 40 μm), an electrolyte main layer (thickness 5 μm), an electron blocking layer (thickness 5 μm), and an intermediate layer (thickness 5 μm) were laminated in this order.

[0077] 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.

[0078] 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).

[0079] As described above, flat electrochemical cells (single cells) of Samples 1 to 8 and Sample 1C shown in Table 1 were fabricated.

[0080] <Chemical Composition and Mn Molar Ratio (Ratio to Ce) of the Electrolyte Main Layer> Unnecessary layers other than the electrolyte main layer were scraped off in advance from the electrochemical cell of each sample, and the analysis material was collected from only the electrolyte main layer. This was then pulverized in a mortar to prepare an analysis powder 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. Furthermore, Lieveld analysis was performed using the obtained XRD measurement results to calculate the doping amount of the M element in the solid electrolyte material from the lattice constant change. In this case, the actual doping amount was determined using a calibration curve of the lattice constant change versus the doping amount of each M element, which had been prepared in advance. Furthermore, to confirm the presence or absence of weighing errors, ICP emission spectroscopy was performed to determine the elemental ratio of the elements actually contained in the electrolyte main layer. From the above, the chemical composition of the electrolyte main layer was determined, and the Mn 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) ICP optical emission spectrometer: Agilent 8800 (manufactured by Agilent Technologies)

[0081] 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°.

[0082] As a result of the above, the electrolyte main layer of the electrochemical cells of Samples 1 to 8 has a fluorite structure, and Ce ０．９ Gd ０．１ O １．９５It was confirmed that the solid electrolyte material shown in Fig. 1 was composed of a composite electrolyte material containing an M-containing oxide containing a predetermined element M contained in the M source of the starting material. In contrast, the electrolyte main layer of the electrochemical cell of Sample 1C had a fluorite structure and contained Ce. ０．９ Gd ０．１ O １．９５ It was confirmed that the solid electrolyte layers were made of the solid electrolyte materials shown in Table 1. １－ｘ (RE) ｘ O ２－ｘ／２ The RE element, x, M molar ratio (ratio to Ce), etc. are shown together.

[0083] <EXAFS Spectral Analysis of the Electrolyte Main Layer> Unnecessary layers other than the main electrolyte layer were scraped off in advance from the electrochemical cell of each sample, and the analysis material collected from only the main electrolyte layer was crushed and mixed in a mortar with boron nitride as a diluent, and then compacted to prepare an analysis sample for EXAFS spectral analysis. Next, EXAFS measurements were performed on each analysis sample using a large synchrotron radiation facility (SPring-8, beamline: BL14B2) under the following measurement conditions to obtain the Ce-K absorption edge EXAFS spectrum and the Gd-K absorption edge EXAFS spectrum. Figure 3 shows the main electrolyte layer, CeO in the electrochemical cell of sample 4 and sample 9 as representative samples. ２ , and Ce ０．９ Gd ０．１ O １．９５ The Ce-K absorption edge EXAFS spectrum of the sample 4 and the sample 9 is shown in FIG. ２ O ３ , and Ce ０．９ Gd ０．１ O １．９５ The Gd-K absorption edge EXAFS spectrum is shown below. Measurement method: Transmission method Analysis software: Demeter 0.9.26 k range: 3 to 17 Å －１ (Ce-K), 3-9 Å －１ (Gd-K) R range: 1.4-3.8 Å (Ce-K), 1.2-2.3 Å (Gd-K)

[0084] Next, the Ce K-edge EXAFS spectrum was fitted with two paths: the first nearest neighbor Ce—O and the second nearest neighbor Ce—Ce. The attenuation factor (S ０ ２ ), energy correction term (ΔE ０ ) is CeO ２ Specifically, the Ce—O bond was determined from the S ０ ２ = 1.24, ΔE ０ = -2.32 eV, and for the Ce-Ce bond, S ０ ２ = 1.07, ΔE ０ = -5.08 eV was used. For all data, ΔE ０ The fitting was performed with the fixed value. For the Gd-K absorption edge EXAFS spectrum, fitting was performed with the first-neighbor Gd-O. The attenuation factor (S ０ ２ ), energy correction term (ΔE ０ ), σ ２ (Debye-Waller factor) is Ce ０．９ Gd ０．１ O １．９５ The Gd-O coordination number was fixed at 8. For all data, ΔE ０ and σ ２ was fixed to 1.08 and -1.93 eV and fitted. From this, the Ce-K absorption edge radial structure function and the Gd-K absorption edge radial structure function were obtained. ０ ２ is less than 1, but the sample, detector, and background processing are ０ ２ Therefore, it is common to use the values ​​obtained from the standard sample as they are. Figure 4 shows the main electrolyte layer, CeO ２ , and Ce ０．９ Gd ０．１ O １．９５ The Ce-K absorption edge radial structure function of the sample 4 and the sample 9 is shown in FIG. ２ O ３ , and Ce０．９ Gd ０．１ O １．９５ The radial structure function of the Gd-K absorption edge of the fluorine-containing ... Ｃｅ , N ＲＥ , L Ｃｅ－Ｏ Find N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 was calculated. Ｃｅ－Ｏ will be explained in Experimental Example 2, but N Ｃｅ , N ＲＥ This has been explained in Experimental Example 1 together with the method for determining

[0085] As shown in Table 1, the composite electrolyte materials constituting the electrolyte main layers of the electrochemical cells of Samples 1 to 8 all had a value of 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 was satisfied. In contrast, the main electrolyte layer of the electrochemical cell of sample 1C was not made of a composite solid electrolyte material, and ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2=0.

[0086] <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 for 2 hours at 1,370°C, the same temperature as used during the preparation of the electrochemical cell, to prepare an electrolyte main layer sample. Next, a strip 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 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 coefficients of the electrolyte main layer at 650°C and 700°C were determined.

[0087] The details of the above-mentioned Experimental Example 1 and the results of various measurements are summarized in Table 1. In addition, FIG. ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 and the linear expansion coefficient of the electrolyte main body layer (at 650°C). ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 and the linear expansion coefficient of the electrolyte main body layer (at 700° C.).

[0088]

[0089] Table 1, Figures 7 and 8 reveal the following: In Sample 1C, the main electrolyte layer in contact with the fuel electrode layer does not contain an M-containing oxide, and ０．９ Gd ０．１ O １．９５ The solid electrolyte material has a fluorite structure of 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 relationship was not satisfied. Therefore, Sample 1C had the highest linear expansion coefficient of the electrolyte main layer at 650°C and 700°C. Therefore, it can be said that it is difficult to reduce the reduction expansion of the electrolyte main layer when the electrolyte main layer is exposed to a high temperature and a reducing atmosphere.

[0090] In contrast, in Samples 1 to 8, the main electrolyte layer in contact with the fuel electrode layer is made of Ce. ０．９ Gd ０．１ O １．９５ The composite electrolyte material is composed of a solid electrolyte material having a fluorite structure and a predetermined M-containing oxide, and the composite electrolyte material has a fluorite structure of 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2. Therefore, it can be seen that Samples 1 to 8 are able to reduce the linear expansion coefficient of the electrolyte main layer at 650°C and 700°C compared to Sample 1C. Therefore, it can be said that Samples 1 to 8 are able to 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.

[0091] The reason why the reduction expansion of the electrolyte main layer could be reduced is presumed to be as follows. That is, as described above, the composite electrolyte material constituting the electrolyte main layer has a 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 relationship means that Ce １－ｘ (RE) ｘ O ２－ｘ／２ This means that the amount of oxygen vacancies is greater than the amount of oxygen vacancies generated by doping RE elements into a solid electrolyte material having a fluorite structure of Ce. ４＋ →Ce ３＋ It is thought that this was formed due to a change in the valence of Ce. ３＋ It is believed that by making the shape of the material containing the compound, it is possible to exert the effect of making the material less susceptible to reduction expansion even when exposed to a high temperature and reducing atmosphere.

[0092] Furthermore, when comparing Samples 1 to 8, the composite electrolyte material had a resistance of 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2, the composite electrolyte material satisfies 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2≦0.15, the reduction effect of the linear expansion coefficient of the electrolyte main body layer is greater, and the reduction expansion of the electrolyte main body layer can be more effectively suppressed. ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2<0.4, the composite electrolyte material satisfies 0.4≦N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2 is satisfied, the reduction expansion of the electrolyte main body layer in the high temperature range is more easily suppressed.

[0093] N ＡＶＥ -(N Ｃｅ +N ＲＥ When the ratio of Ce to Ce / 2 is 0.4 or more, the effect of suppressing the reduction expansion of the electrolyte main layer in the high temperature range tends to be small. ４＋ →Ce３＋ This is thought to be because the lattice strain energy caused by expansion to the axial direction can be absorbed by the oxygen vacancy portions.

[0094] Furthermore, the results of Experimental Example 1 show that the specific composite electrolyte material can reduce the linear expansion coefficient when exposed to a high temperature and a reducing atmosphere. From these results, it can be said that by using this specific composite electrolyte material in the fuel electrode layer and the fuel diffusion layer, which are exposed to a high temperature and a reducing atmosphere like the main electrolyte layer in contact with the fuel electrode layer, it is also possible to suppress reduction expansion in the fuel electrode layer and the fuel diffusion layer.

[0095] (Experimental Example 2) Electrochemical cells of Samples 9 to 12 and Sample 3 shown in Table 2 were fabricated in the same manner as Samples 1 to 8 in Experimental Example 1. Furthermore, in the same manner as Experimental Example 1, the chemical composition of the electrolyte main layer, the Mn molar ratio (ratio to Ce), EXAFS spectrum analysis of the electrolyte main layer, and the linear expansion coefficient of the electrolyte main layer were investigated.

[0096] Furthermore, in Experimental Example 2, the oxygen ion conductivity of the electrolyte main layer was measured as follows. In addition, the bond distance L between Ce and O was measured for the composite electrolyte material of the electrolyte main layer by EXAFS spectrum analysis as described above. Ｃｅ－Ｏ asked for.

[0097] <Oxygen Ion Conductivity 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 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.

[0098] The above results are summarized in Table 2. In addition, FIG. 9 shows the L Ｃｅ－Ｏ and the oxygen ion conductivity of the electrolyte main layer (×10 －２ S / cm, temperature 650°C (vertical axis).

[0099]

[0100] According to Table 2 and FIG. 9, the bond distance between Ce and O, L Ｃｅ－Ｏ As the length of the electrode decreases, the oxygen ion conductivity decreases. Ｃｅ－Ｏ It can be seen that the oxygen ion conductivity drops significantly when the thickness is 2.34 Å or less. This is because the oxygen ions O ２－ is the Ce atom (Ce ３＋ , Ce ４＋ ) and oxygen ions O ２－ This is thought to be due to a decrease in the mobility of L Ｃｅ－Ｏ By making the thickness 2.341 Å or more, it is possible to suppress the reduction expansion of the main electrolyte layer and also to maintain high oxygen ion conductivity of the main electrolyte layer 31, which can facilitate improving the output of the electrochemical cell.

[0101] 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.

[0102] 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 the composite electrolyte material contains an M-containing oxide containing at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y, and the composite electrolyte material is １－ｘ (RE) ｘ O ２－ｘ／２ In the composition formula, the average oxygen coordination number calculated from the formula 4×(2−x / 2) is N ＡＶＥ The oxygen coordination number around Ce was determined by EXAFS spectrum analysis. Ｃｅ , the oxygen coordination number around the RE element is N ＲＥ When 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2. [2] The composite electrolyte material satisfies 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ) / 2。 [3] The electrochemical cell according to [1], wherein the composite electrolyte material satisfies 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2<0.4. [4] The composite electrolyte material has a bond distance L between Ce and O determined by the EXAFS spectrum analysis. Ｃｅ－Ｏ

[0013] The electrochemical cell according to any one of [1] to [3], wherein the thickness of the anode layer is 2.341 Å or more. [5] The electrochemical cell according to any one of [1] to [4], wherein the anode layer contains the composite electrolyte material. [6] The electrochemical cell according to any one of [1] to [5], wherein the anode layer has a fuel diffusion layer (5) in contact with the anode layer on the side opposite to the solid electrolyte layer, the fuel diffusion layer containing the composite electrolyte material. [7] The electrochemical cell according to [5], wherein the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the anode layer is smaller than the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte main layer. [8] The electrochemical cell according to [6], wherein the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel diffusion layer is less than the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte main body 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 electrolyte material.

[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 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 the composite electrolyte material contains an M-containing oxide containing at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y, and the composite electrolyte material is １－ｘ (RE) ｘ O ２－ｘ／２ In the composition formula, the average oxygen coordination number calculated from the formula 4×(2−x / 2) is N ＡＶＥ The oxygen coordination number around Ce was determined by EXAFS spectrum analysis. Ｃｅ , the oxygen coordination number around the RE element is N ＲＥ When 0<N ＡＶＥ -(N Ｃｅ +N ＲＥ ) / 2.

2. The composite electrolyte material has a resistance of 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ 2. The electrochemical cell of claim 1 , wherein:

3. The composite electrolyte material has a resistance of 0.15<N ＡＶＥ -(N Ｃｅ +N ＲＥ 2. The electrochemical cell of claim 1 , wherein ρ / 2<0.4 is satisfied.

4. The composite electrolyte material has a bond distance L between Ce and O determined by the EXAFS spectrum analysis. Ｃｅ－Ｏ 2. The electrochemical cell of claim 1 , wherein:

5. The electrochemical cell according to any one of claims 1 to 4, wherein the anode layer comprises the composite electrolyte material.

6. The electrochemical cell according to any one of claims 1 to 4, 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 composite electrolyte material.

7. The electrochemical cell according to claim 5, wherein the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel electrode layer is smaller than the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte main layer.

8. The electrochemical cell according to claim 6, wherein the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel diffusion layer is less than the ratio of the number of moles of element M to the number of moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte main layer.

9. The electrochemical cell according to any one of claims 1 to 4, further comprising an intermediate layer (6) between the solid electrolyte layer and the air electrode layer, the intermediate layer containing the composite electrolyte material.

10. An electrochemical cell according to any one of claims 1 to 4, which is used as at least one of a solid oxide fuel cell and a solid oxide electrolysis cell.

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