Electrochemical cell

Abstract

To provide an electrochemical cell capable of reducing the reduction expansion of an electrolyte body layer even when the electrolyte body layer in contact with a fuel electrode layer is exposed to a high-temperature, reducing atmosphere during operation.SOLUTION: An electrochemical cell 1 has a fuel electrode layer 2, a solid electrolyte layer 3, and an air electrode layer 4, in this order. The solid electrolyte layer 3 includes an electrolyte main body layer 31 having a fluorite structure, composed of a composite electrolyte material containing 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 RE element is Gd and / or Sm). In the composite electrolyte material, the average oxygen coordination number NAVE, given by a formula 4×(2-x / 2), oxygen coordination numbers around Ce NCe and around the RE element NRE, as determined by EXAFS spectral analysis, satisfy the condition, 0<NAVE-(NCe+NRE) / 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to electrochemical cells. [Background technology]

[0002] Electrochemical cells using a solid electrolyte layer with oxygen ion conductivity as an electrolyte layer have been known. Examples of this type of electrochemical cell include solid oxide fuel cells (SOFCs) and solid oxide electrochemical cells (SOECs).

[0003] 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. The document also 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-243473 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 not effective enough in suppressing the reduction expansion of the solid electrolyte layer.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide an electrochemical cell that can reduce the reductive expansion of the electrolyte main layer, even when the electrolyte main layer in contact with the fuel electrode layer is exposed to a high temperature and a reducing atmosphere during operation. [Means for solving the problem]

[0007] One aspect of the present invention is An electrochemical cell (1) comprising, 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, the solid electrolyte layer has an electrolyte main body layer (31) in contact with the fuel electrode layer, The electrolyte body layer is It 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, The composite electrolyte material is Ce 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, In an electrochemical cell (1). [Effects of the Invention]

[0008] 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.

[0009] In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory view showing a schematic example of a stacked structure of an electrochemical cell according to an embodiment. [Figure 2] FIG. 2 is an explanatory view schematically showing another example of the stacked structure of the electrochemical cell according to the embodiment. [Figure 3] FIG. 3 shows the Ce K-absorption edge EXAFS spectra of the electrolyte main layer, CeO2, and Ce0.9Gd0.1O1.95 in the electrochemical cells of Samples 4 and 9 prepared in Experimental Example 1. [Figure 4] FIG. 4 shows the Ce K-edge radial structure functions of the electrolyte main layer, CeO 2 , and Ce 0.9 Gd 0.1 O 1.95 in the electrochemical cells of Samples 4 and 9 prepared in Experimental Example 1. [Figure 5] FIG. 5 shows the Gd K-absorption edge EXAFS spectra of the electrolyte main layer, Gd2O3, and Ce0.9Gd0.1O1.95 in the electrochemical cells of Samples 4 and 9 prepared in Experimental Example 1. [Figure 6] FIG. 6 shows the Gd K-absorption edge radial structure functions of the electrolyte main layer, Gd2O3, and Ce0.9Gd0.1O1.95 in the electrochemical cells of Samples 4 and 9 prepared in Experimental Example 1. [Figure 7]FIG. 7 is a graph showing the relationship between NAVE-{(NCe+NRE) / 2} (horizontal axis) in the composite electrolyte material of the electrolyte main layer obtained in Experimental Example 1 and the linear expansion coefficient of the electrolyte main layer (×10-6 / K, 4 vol% H2, temperature 650°C) (vertical axis). [Figure 8] FIG. 8 is a graph showing the relationship between NAVE-{(NCe+NRE) / 2} (horizontal axis) in the composite electrolyte material of the electrolyte main layer obtained in Experimental Example 1 and the linear expansion coefficient of the electrolyte main layer (×10-6 / K, 4 vol% H2, temperature 700°C) (vertical axis). [Figure 9] FIG. 9 is a graph showing the relationship between LCe—O (horizontal axis) in the composite electrolyte material of the electrolyte main layer and the oxygen ion conductivity (×10 S / cm, temperature 650° C.) (vertical axis) of the electrolyte main layer, obtained in Experimental Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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).

[0012] 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 an air 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 air 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 air 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 air 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 air cathode layer 4 is an electrode that forms a pair with the anode layer 2. In other words, the air cathode layer 4 can be considered an electrode layer having electrode activity that allows it to function as an air 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 structure.

[0013] In the electrochemical cell 1, the solid electrolyte layer 3 has oxygen ion conductivity. The solid electrolyte layer 3 has 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 has 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 the movement of electrons. When the electron blocking layer 32 is included, the electron blocking layer 32 can block the movement of electrons, so the electrolyte main layer 31 may exhibit electronic conductivity in addition to oxygen ion conductivity, for example, under a reducing atmosphere. As described above, the solid electrolyte layer 3 has an electrolyte main body 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.

[0014] As illustrated in FIG. 2 , the electrochemical cell 1 may 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 may 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 may also be configured to function not only as a fuel diffusion layer, such as diffusing the fuel in the planar direction, but also 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.

[0015] 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. FIGS. 1 and 2 show an example 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.

[0016] 2, the electrochemical cell 1 can also have an air electrode current collecting layer 7 on the side of the air electrode layer 4 opposite to the solid electrolyte layer 3. The air electrode current collecting layer 7 functions as a current collector for the air electrode layer 4.

[0017] 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.

[0018] 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 solid electrolyte material is composed of a composite electrolyte material containing an M-containing oxide containing element M in a solid electrolyte material represented by the formula: 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+ , Mg2+ , Ca 2+ , Sr 2+ , La 3+ , Y 3+ It can be included in the state.

[0019] 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.

[0020] In the composite electrolyte material, specific examples of the M-containing oxide include ZnO, MgO, CaO, SrO, La2O3, Y2O3, etc. More specifically, the M-containing oxide can be selected from the viewpoints of being a stable material in air or a water vapor atmosphere and being inexpensive, and CaO, SrO, La2O3, Y2O3, etc. from the viewpoint of being easily doped into cerium oxides having a fluorite structure, such as ZnO and MgO.

[0021] The composite electrolyte material is specifically Ce 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.

[0022] The composite electrolyte material is <N AVE -(N Ce +N RE ) / 2 relationship. N AVE is the above-mentioned Ce 1-x (RE) x O 2-x / 2 In the composition formula, the average oxygen coordination number is calculated from the formula 4 × (2-x / 2). Ceis the actual oxygen coordination number around Ce in the composite electrolyte material, determined by EXAFS spectrum analysis. N 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.

[0023] 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 difference in the value of the oxygen vacancy means that there is a local difference between the oxygen coordination number around the Ce element that constitutes the fluorite structure and the oxygen range number around the RE element that is doped into the fluorite structure. 4+ →Ce 3+ According to the experimental results described below, in the ceria-based composite electrolyte material, Ce is formed from the beginning. 3+ It is believed that by making the composition contain 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 reducing atmosphere.

[0024] The composite electrolyte material is 0.15 <N AVE -(N Ce +N RE ) / 2. 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.

[0025] 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.

[0026] The composite electrolyte material is N AVE -(N Ce +N RE ) / 2<0.4. 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.

[0027] 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.

[0028] 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. Ce-O is 2.341 Å or more, the oxygen ions O 2- However, the Ce atoms (Ce 3+ , Ce 4+ ) and oxygen ions O 2- This is thought to be because the decrease in mobility can be suppressed.

[0029] L Ce-OFrom 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.

[0030] 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. This configuration makes it possible to more effectively suppress the reduction expansion of the electrolyte main body layer 31 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 effects, 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.

[0031] 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 high oxygen ion conductivity in comparison with a case where the M molar ratio (ratio to Ce) exceeds 4.6 mol%. Therefore, this configuration makes it easier to improve the output of the electrochemical cell 1. From the viewpoint of further ensuring the above-mentioned effects, the M 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.

[0032] 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 X-ray diffraction (XRD) measurement results and ICP (inductively coupled plasma) emission spectroscopy. Details will be described in the experimental examples.

[0033] The above-described electrochemical cell 1 can reduce reductive 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 reductive expansion of the electrolyte main layer 31 is advantageous for suppressing cracks in the electrolyte main layer 31 during operation.

[0034] The electrochemical cell 1 of this embodiment also has the following advantages.

[0035] 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 in the electrochemical cell of Patent Document 1.

[0036] In addition, solid electrolyte materials with a perovskite crystal structure have low oxygen ion conductivity. Therefore, when an oxide layer with 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 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.

[0037] In addition, a solid electrolyte material having a perovskite crystal structure is a material that has hydrogen ion conductivity. Therefore, when the electrochemical cell of Patent Document 1 is used as an SOEC, H generated by electrolysis of HO introduced into the anode is transferred to the cathode. + A part of Ce flows out to the air electrode side through the electrolyte layer, reducing the amount of hydrogen produced. 1-x (RE) xO 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), the H generated by the electrolysis of HO is + This can prevent a decrease in the amount of hydrogen produced due to a part of the hydrogen leaking to the air electrode side.

[0038] 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 number of oxygen vacancies near the grain boundaries and decreasing the number of oxygen vacancies within the grains. As a result, oxygen vacancy aggregation and Schottky barriers occur near the grain boundaries, reducing oxygen ion conductivity and cell output. 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, increasing manufacturing costs. In contrast, the electrochemical cell 1 can reduce reduction expansion of the electrolyte main layer 31 without locally concentrating rare earth elements on the surfaces of 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. 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.

[0039] 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.

[0040] The fuel electrode layer 2 may contain the specific composite electrolyte material described above in the main electrolyte layer 31. In this case, the fuel electrode layer 2 may specifically contain an internal fuel electrode catalyst material, a composite electrolyte material, and voids. This configuration also makes it possible to suppress reduction expansion in the fuel electrode layer 2.

[0041] When the fuel electrode layer 2 contains a composite electrolyte material, the M molar ratio (relative to Ce) of the composite electrolyte material contained in the fuel electrode layer 2 can be configured to be smaller than the M molar ratio (relative to 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 to that extent 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.

[0042] 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 without the above-described composite electrolyte material. In this case, the anode layer 2 may specifically be configured without the above-described composite electrolyte material, but instead include an anode catalyst material, an anode electrolyte material, and voids. The anode catalyst material may be composed of a catalyst material having electron conductivity. The anode electrolyte material may be composed of a solid electrolyte material having oxygen ion conductivity.

[0043] 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 (metal and alloy oxides, 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. Among these, Ni, Ni alloys, and Ni oxides (NiO, etc.) are preferred from the viewpoint of catalytic activity (electrode activity), and Ni and NiO are more preferred. 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 (hereinafter referred to as 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. The fuel electrode layer 2, which includes a catalyst material in the fuel electrode made of a metal, alloy, or oxide thereof, and the above-mentioned composite electrolyte material, can be called a cermet electrode layer.

[0044] 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 made 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 preferable because it is stable in a reducing atmosphere and does not exhibit electronic conductivity. The solid electrolyte layer 3 is usually formed as a dense material to prevent gas permeation.

[0045] Specifically, the air electrode layer 4 can include a catalyst material in the air electrode, an electrolyte material in the air electrode, and voids. The catalyst material in the air electrode can be composed of a catalyst material having electron conductivity and oxygen ion conductivity, etc. The electrolyte material in the air electrode can be composed of a solid electrolyte material having oxygen ion conductivity, etc.

[0046] Examples of the catalyst material in the air electrode include perovskite-type oxides containing La, Sr, and Co, perovskite-type oxides containing Pr, Ba, and Co, perovskite-type oxides containing Gd, Ba, and Co, perovskite-type oxides containing Nd, Ba, and Co, etc. These can be used alone or in combination of two or more. From the viewpoints such as excellent mixed conductivity in which both electron conductivity and oxygen ion conductivity coexist and high air electrode catalyst activity, perovskite-type oxides containing La, Sr, and Co, etc. can be preferably used as the catalyst material in the air electrode. Specific examples of the above-mentioned perovskite-type oxides containing La, Sr, and Co include La 0.6 Sr 0.4 CoO3, etc., and metal oxides represented by La 1-x Sr x CoO 3-δ (0 < x ≤ 1, preferably 0.1 ≤ x ≤ 0.5), etc. Specific examples of the perovskite-type oxides containing Pr, Ba, and Co include metal oxides represented by Pr 2-x Ba x Co2O 5+δ (0.7 ≤ x ≤ 1.3, preferably 0.8 ≤ x ≤ 1), etc. Specific examples of the perovskite-type oxides containing Gd, Ba, and Co include metal oxides represented by Gd 2-x Ba x Co2O 5+δ (0.7 ≤ x ≤ 1.3, preferably 0.8 ≤ x ≤ 1), etc. Specific examples of the perovskite-type oxides containing Nd, Ba, and Co include metal oxides represented by Nd 2-x Ba x Co2O 5+δ(0.7≦x≦1.3, preferably 0.8≦x≦1). The oxides described above may or may not have oxygen non-stoichiometry.

[0047] 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 Gd, can be suitably used, from the viewpoint of excellent oxygen ion conductivity at a relatively low temperature of about 700°C.

[0048] 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. This configuration can also suppress reduction expansion in the fuel diffusion layer 5.

[0049] When the fuel-diffusion layer 5 contains a composite electrolyte material, the M molar ratio (ratio to Ce) of the composite electrolyte material contained 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 contained in the electrolyte main body layer 31. This configuration can suppress the reduction expansion of the fuel-diffusion layer 5. Furthermore, the important thing about 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Examples of metal materials constituting the fuel diffusion layer 5 and the metal support include Fe-based alloys. Fe-based alloys contain alloying elements added to Fe as a base. 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. An Fe-based alloy containing Cr as the most added metal element may be referred to as an Fe-Cr-based alloy. Similarly, an Fe-based alloy containing Mn as the most added metal element may be referred to as an Fe-Mn-based alloy, and an Fe-based alloy containing Ti as the most added metal element may be referred to as an Fe-Ti-based alloy.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Examples of the air electrode current collecting material include metal materials such as Pt, Pt alloys, Ag, Ag alloys, and Au, and electronically conductive oxides 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 these, metal materials such as Pt and Pt alloys and electronically conductive oxides such as perovskite oxides containing La, Sr, and Co are preferred, from the viewpoints of being resistant to oxidation in high-temperature oxidizing atmospheres and having high electronic conductivity.

[0059] 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 may be operated 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.

[0060] Specifically, when the electrochemical cell 1 is operated as an SOFC, a hydrogen-containing gas such as hydrogen gas can be supplied to the anode layer 2 as the fuel gas. In this case, an oxygen-containing gas such as air or oxygen gas can be supplied to the cathode layer 4. On the other hand, when the electrochemical cell 1 is operated as an SOEC, the anode layer 2 can function as a hydrogen electrode. A water (H2O)-containing gas such as water vapor gas can be supplied to the anode layer 2 as the fuel gas. In this case, the cathode layer 4 can function as an oxygen electrode. A gas such as air may or may not be supplied to the cathode layer 4. Note that the hydrogen-containing gas may contain water vapor for humidification, and the water-containing gas may contain a reducing gas such as hydrogen gas. Furthermore, when operating as a co-electrolysis cell, the fuel gas may contain carbon dioxide (CO2) in addition to water.

[0061] The operating temperature of the electrochemical cell 1 can be set to 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 set to 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.

[0062] 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 layer 31 can be easily suppressed, which has the advantage of making it easier to achieve high output from the electrochemical cell 1.

[0063] (Experimental example) The electrochemical cell of the present disclosure will be described in detail below using experimental examples. In these experimental examples, an electrochemical cell was fabricated having a stacked 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.

[0064] (Experimental Example 1) <Material preparation> -GDC powder- Gd-doped ceria powder, Ce 0.9 Gd 0.1 O 1.95 Specifically, the GDC powder was prepared by weighing CeO2 as a Ce source and Gd2O3 as a Gd source to achieve the specified chemical composition, firing them at 800°C, and then pulverizing them.

[0065] -M source- The M sources used to form the composite electrolyte material were 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), and YO3 powder (average particle size: 1 μm). The average particle sizes are the particle size (diameter) d50 at which the volume-based cumulative frequency distribution measured by laser diffraction and scattering shows 50% (the same applies below).

[0066] In this experimental example, oxides and hydroxides of the M element were used as the M source of the starting material, but acetates, nitrates, etc. of the M element can also be used as appropriate.

[0067] -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 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 1 to 8 and Sample 1C.

[0068] -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 NiO powder to 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.

[0069] -Electrolyte body 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. The GDC powder and M source powder were weighed and added to achieve a predetermined molar ratio. Subsequently, 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.

[0070] Note that this experimental example attempts to form a composite electrolyte material through a process of mixing GDC powder with an M source, and differs from a process in which CeO2, Gd2O3, and an M source are weighed out to prepare a composite oxide containing Ce, Gd, and the element M, which is then used as a raw material. Furthermore, this experimental example does not prepare the main electrolyte layer as a glass material to which SiO2, B2O3, etc. are added in addition to the M source.

[0071] -Electron Blocking Layer- Yttria-stabilized zirconia (hereinafter referred to as 8YSZ) containing 8 mol% of Y2O3 (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 electron blocking 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.

[0072] -Middle class- A slurry was prepared by mixing GDC powder (average particle size: 0.5 μm), polyvinyl butyral, isoamyl acetate, 2-butanol, and ethanol in a ball mill. After that, the intermediate 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 sheets.

[0073] -Air electrode layer- La 0.6 Sr 0.4 CoO powder (hereinafter referred to as LSC) (average particle diameter: 0.8 μm) and 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 this and mixed in a ball mill to prepare pastes for forming the air electrode layer used in Samples 1 to 8 and Sample 1C.

[0074] -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 the air electrode current collecting layer used in Samples 1 to 8 and Sample 1C.

[0075] <Preparation of electrochemical cell> A laminate was obtained by stacking a predetermined fuel diffusion layer-forming sheet, a fuel electrode layer-forming sheet, an electrolyte main layer-forming sheet, an electron blocking layer-forming sheet, and an intermediate layer-forming 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 sintered in air at 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.

[0076] Next, a predetermined paste for forming an air electrode 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 electrode layer (thickness 50µm). At this time, the outer shape of the air electrode layer was formed smaller than the outer shape of the fuel electrode layer.

[0077] 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).

[0078] As described above, flat plate electrochemical cells (single cells) of Samples 1 to 8 and Sample 1C shown in Table 1 were fabricated.

[0079] <Chemical composition of the electrolyte body layer, Mn molar ratio (relative to Ce)> Unnecessary layers other than the main electrolyte layer were removed from the electrochemical cell of each sample. The material for analysis was extracted from the main electrolyte layer alone and pulverized in a mortar to obtain powder for XRD analysis. Next, XRD measurements were performed on the analysis powder of each sample at a large synchrotron radiation facility (SPring-8, beamline: BL19B2) under the following measurement conditions. Furthermore, Lieveld analysis was performed using the XRD measurement results to calculate the amount of M element doping in the solid electrolyte material from the lattice constant change. 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 check for weighing errors, ICP atomic emission spectroscopy was performed to determine the element ratios of the elements actually contained in the main electrolyte layer. From these results, the chemical composition of the main electrolyte layer was determined, and the Mn molar ratio (relative to Ce) was calculated based on the information from the Lieveld analysis. X-ray Diffractometer: High-Throughput Powder X-ray Diffractometer X-ray wavelength: 0.7Å Measurement range: 2.1°~84.8° Step interval: 0.005° Crystal phase analysis software: PDXL (Rigaku) Structural analysis software: RIETAN-FP (profile function: extended pseudo-fork function) ICP emission spectrometer: Agilent 8800 (Agilent Technologies)

[0080] 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 used may be a Rigaku "RINT 2000" or "SmartLab." 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°.

[0081] 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 O1.95 It was confirmed that the solid electrolyte material shown in Fig. 1 was composed of a composite electrolyte material containing an M-containing oxide containing the specified 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 was composed of the materials shown in Table 1. 1-x (RE) x O 2-x / 2 The RE elements, x, M molar ratio (ratio to Ce), etc. are shown together.

[0082] <EXAFS spectrum analysis of the electrolyte body 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 spectrum analysis. Next, EXAFS measurements were performed on each analysis sample under the following measurement conditions at a large synchrotron radiation facility (SPring-8, beamline: BL14B2), and the Ce-K absorption edge EXAFS spectrum and the Gd-K absorption edge EXAFS spectrum were obtained. Figure 3 shows the main electrolyte layer, CeO2, and CeO2 in the electrochemical cells of representative samples 4 and 9. 0.9 Gd 0.1 O 1.95 Figure 5 shows the Ce K-edge EXAFS spectra of the electrolyte body layer, Gd2O3, and Ce in the electrochemical cells of sample 4 and sample 9 as representative samples. 0.9 Gd 0.1 O 1.95 The Gd K-edge EXAFS spectrum of the above is shown. 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: 1.4-3.8Å (Ce-K), 1.2-2.3Å (Gd-K)

[0083] 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 (S0 2 ), and the energy correction term (ΔE0) was determined from the CeO2 reference sample. Specifically, for the Ce-O bond, S0 2 = 1.24, ΔE0 = -2.32 eV, and for the Ce-Ce bond, S0 2 = 1.07, ΔE0 = -5.08 eV were used. All data were fitted with a fixed ΔE0. For the Gd-K edge EXAFS spectrum, fitting was performed with the first-neighbor Gd-O. The attenuation factor (S0 2 ), energy correction term (ΔE0), 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, ΔE0 and σ 2 The Ce-K absorption edge radial structure function and the Gd-K absorption edge radial structure function were calculated by fixing S0 2 is less than 1, but the sample, detector, and background processing are 2 Therefore, it is common to use the values ​​obtained from the standard sample as they are. Figure 4 shows the main electrolyte layer, CeO2, and Ce in the electrochemical cells of sample 4 and sample 9 as representatives of each sample. 0.9 Gd 0.1 O 1.95 Figure 6 shows the radial structure function of the Ce K-edge absorption of the electrolyte body layer, Gd2O3, and Ce in the electrochemical cells of sample 4 and sample 9 as representatives of each sample. 0.9 Gd 0.1 O 1.95 The radial structure function of the Gd-K absorption edge of the fluorine-containing ... Ce , NRE , L Ce-O Search for N AVE -(N Ce +N RE ) / 2 was calculated. Ce-O This will be explained in Experimental Example 2, but N Ce , N RE This is explained in Experimental Example 1 together with how to obtain

[0084] As shown in Table 1, the composite electrolyte materials constituting the electrolyte main layers of the electrochemical cells of Samples 1 to 8 were all 0 <N AVE -(N Ce +N RE ) / 2 was satisfied. In contrast, the electrolyte body 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.

[0085] <Linear expansion coefficient of the electrolyte body layer> The slurry prepared for the electrolyte main layer sheet fabrication 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 for the electrochemical cell fabrication, to produce an electrolyte main layer sample. A strip sample measuring 4 mm wide, 2 mm high, and 10 mm long was then polished from the electrolyte main layer sample. The strip sample was then heated from room temperature to 800°C using a daylight meter DIL402 Expedis Select & Supreme (manufactured by Netsch) while flowing 4% by volume of hydrogen gas and 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.

[0086] 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 body layer (at 650°C). AVE -(N Ce +N RE ) / 2 and the linear expansion coefficient of the electrolyte main layer (at 700°C).

[0087] [Table 1]

[0088] Table 1, Figures 7 and 8 reveal the following: In Sample 1C, the electrolyte main layer in contact with the fuel electrode layer does not contain M-containing oxide, and Ce 0.9 Gd 0.1 O 1.95 It is made of a solid electrolyte material with a fluorite structure, <N AVE -(N Ce +N RE ) / 2 relationship. 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 Sample 1C is exposed to a high-temperature reducing atmosphere.

[0089] In contrast, in Samples 1 to 8, the electrolyte main 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 is <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 reducing atmosphere.

[0090] 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 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. 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.

[0091] In addition, when comparing Samples 1 to 8, the composite electrolyte material was 0.15 <N AVE -(N Ce +N RE ) / 2, the composite electrolyte material is 0 <N AVE -(N Ce +N RE ) / 2≦0.15, the reduction effect of the linear expansion coefficient of the electrolyte main layer is greater, and the reduction expansion of the electrolyte main layer can be more effectively suppressed. <N AVE -(N Ce +N RE ) / 2<0.4, the composite electrolyte material satisfies 0.4≦N AVE -(N Ce +N RE ) / 2 is satisfied, it is clear that the reduction expansion of the main electrolyte layer in the high temperature range is more easily suppressed.

[0092] N AVE -(N Ce +N RE When ) / 2 is 0.4 or more, the suppression effect of the reduction expansion amount of the electrolyte main layer in the high temperature range tends to be small.4+ →Ce 3+ 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.

[0093] 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 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 fuel diffusion layer.

[0094] (Experimental Example 2) Electrochemical cells for 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 (relative to Ce), EXAFS spectrum analysis of the electrolyte main layer, and the linear expansion coefficient of the electrolyte main layer were investigated.

[0095] Furthermore, in Experimental Example 2, the oxygen ion conductivity of the electrolyte main layer was measured as follows. In addition, for the composite electrolyte material of the electrolyte main layer, the bond distance L between Ce and O was determined by EXAFS spectrum analysis as described above. Ce-O asked for.

[0096] <Oxygen ion conductivity of the main electrolyte layer> The slurry prepared for the electrolyte main layer sheet fabrication 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 used for the electrochemical cell fabrication to produce an electrolyte main layer sample. The surface of the electrolyte main layer sample was then polished, and Au was sputtered onto both sides to form a pair of electrodes. Impedance measurements were then performed on this electrolyte main layer sample using an impedance analyzer E4990A (Keysight Corporation), a high-temperature, high-frequency compatible sample rod HT-Z2-HF-ROD (Toyo Corporation), and an HT-Z2-HF high-frequency compatible heating furnace system (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.

[0097] 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 body layer (×10 -2 The relationship between the tensile strength and the temperature (650°C) is shown on the vertical axis.

[0098] [Table 2]

[0099] According to Table 2 and Figure 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 distance is 2.34 Å or less. This is because the oxygen ions O 2- However, the Ce atoms (Ce 3+ , Ce 4+ ) and oxygen ions O 2- This is thought to be due to a decrease in the mobility of L Ce-OBy making the thickness 2.341 Å or more, it is possible to suppress the reductive 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.

[0100] The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible without departing from the spirit and scope of the present invention. Furthermore, the configurations shown in the above-described embodiments and experimental examples can be combined in any manner.

[0101] The features of the present invention are as follows. [1] An electrochemical cell (1) comprising, 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, the solid electrolyte layer has an electrolyte main body layer (31) in contact with the fuel electrode layer, The electrolyte body layer is It 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, The composite electrolyte material is Ce 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, Electrochemical cell (1). [2] The composite electrolyte material is 0.15 <N AVE -(N Ce +N RE ) / 2, [1] The electrochemical cell according to [1]. [3] The composite electrolyte material is 0.15 <N AVE -(N Ce +N RE ) / 2<0.4, [1] The electrochemical cell according to [1]. [4] The composite electrolyte material is The bond distance L between Ce and O obtained by the EXAFS spectrum analysis Ce-O is 2.341 Å or more, [1] An electrochemical cell according to any one of [1] to [3]. [5] the anode layer contains the composite electrolyte material; [1] to [4]. An electrochemical cell according to any one of [1] to [4]. [6] a fuel diffusion layer (5) in contact with the fuel electrode layer on the side opposite to the solid electrolyte layer side of the fuel electrode layer, the fuel diffusion layer includes the composite electrolyte material; [1] to [5]. An electrochemical cell according to any one of [1] to [5]. [7] a 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 a 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; [5] The electrochemical cell according to [5]. [8] a 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 smaller than a 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; [6] An electrochemical cell according to [6]. [9] an intermediate layer (6) between the solid electrolyte layer and the air cathode layer; the intermediate layer includes the composite electrolyte material; [1] to [8], an electrochemical cell according to any one of [1] to [8].

[10] Used as at least one of a solid oxide fuel cell and a solid oxide electrolysis cell, [1] An electrochemical cell according to any one of [1] to [9]. [Explanation of symbols]

[0102] 1. Electrochemical cell 2 Fuel electrode layer 3 Solid electrolyte layer 31 Electrolyte body layer 4. Air electrode layer

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) which has oxygen ion conductivity, and an air electrode layer (4) which is an electrode paired with the fuel electrode layer, The solid electrolyte layer has an electrolyte body layer (31) in contact with the fuel electrode layer, The electrolyte body layer is It has a fluorite structure, Ce １－ｘ (RE) ｘ O ２－ｘ／２ The solid electrolyte material is represented by (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 is composed of a composite electrolyte material containing an M-containing oxide that contains at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y. The aforementioned composite electrolyte material is The above Ce １－ｘ (RE) ｘ O ２－ｘ／２ In the compositional formula of, when the average oxygen coordination number calculated from the formula 4×(2−x / 2) is N ＡＶＥ , the oxygen coordination number around Ce, determined by EXAFS spectrum analysis, is N Ｃｅ , the oxygen coordination number around the RE element is N ＲＥ when it is defined as such, 0 < N ＡＶＥ - (N Ｃｅ +N ＲＥ ) / 2 is satisfied, The fuel electrode layer comprises the composite electrolyte material, The ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel electrode layer is less than the ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. Electrochemical cell (1).

2. The aforementioned composite electrolyte material is 0.15 < N ＡＶＥ - (N Ｃｅ +N ＲＥ ) / 2 satisfies, The electrochemical cell according to claim 1.

3. The aforementioned composite electrolyte material is 0.15 < N ＡＶＥ - (N Ｃｅ +N ＲＥ ) / 2 < 0.4 The electrochemical cell according to claim 1.

4. The aforementioned composite electrolyte material is The bond distance L between Ce and O was determined by the aforementioned EXAFS spectral analysis. Ｃｅ－Ｏ The value is 2.341 Å or greater. The electrochemical cell according to claim 1.

5. The fuel electrode layer has a fuel diffusion layer (5) in contact with the fuel electrode layer on the side opposite to the solid electrolyte layer, The fuel diffusion layer includes the composite electrolyte material, The electrochemical cell according to any one of claims 1 to 4.

6. The ratio of moles of element M to 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 moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. The electrochemical cell according to claim 5.

7. An intermediate layer (6) is provided between the solid electrolyte layer and the air electrode layer. The intermediate layer includes the composite electrolyte material, The electrochemical cell according to any one of claims 1 to 4.

8. Used as at least one of a solid oxide fuel cell and a solid oxide electrolytic cell, An electrochemical cell according to any one of claims 1 to 4.

9. An electrochemical cell (1) having, in this order, a fuel electrode (2) which is an electrode to which fuel is supplied, a solid electrolyte layer (3) which has oxygen ion conductivity, and an air electrode layer (4) which is an electrode paired with the fuel electrode layer, The solid electrolyte layer has an electrolyte body layer (31) in contact with the fuel electrode layer, The electrolyte body layer is The composite electrolyte material comprises a solid electrolyte material having a fluorite structure and represented as Ce 1-x (RE) x O 2-x / 2 (where x is between 0.05 and 0.2, and the RE element is at least one of Gd and Sm), and containing an M-containing oxide that contains at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y. The aforementioned composite electrolyte material is In the empirical formula Ce 1-x (RE) x O 2-x / 2, when the average oxygen coordination number calculated from the equation 4 × (2-x / 2) is N AVE, the oxygen coordination number around Ce determined by EXAFS spectral analysis is N Ce, and the oxygen coordination number around the RE element is N RE, 0 < N AVE - (N Ce + N RE) / 2 is satisfied, The fuel electrode layer has a fuel diffusion layer (5) in contact with the fuel electrode layer on the side opposite to the solid electrolyte layer, The fuel diffusion layer comprises the composite electrolyte material, The ratio of moles of element M to 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 moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. Electrochemical cell (1).

10. The composite electrolyte material is 0.15 < N AVE - (N Ce + N RE) / 2 The electrochemical cell according to claim 9.

11. The composite electrolyte material is 0.15 < N AVE - (N Ce + N RE) / 2 < 0.4 The electrochemical cell according to claim 9.

12. The composite electrolyte material is The bond distance L Ce-O between Ce, determined by the aforementioned EXAFS spectral analysis, is 2.341 Å or greater. The electrochemical cell according to claim 9.

13. The fuel electrode layer comprises the composite electrolyte material, The electrochemical cell according to any one of claims 9 to 12.

14. The ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel electrode layer is less than the ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. The electrochemical cell according to claim 13.

15. The solid electrolyte layer and the air electrode layer have an intermediate layer (6), The intermediate layer includes the composite electrolyte material, The electrochemical cell according to any one of claims 9 to 12.

16. Used as at least one of a solid oxide fuel cell and a solid oxide electrolytic cell, An electrochemical cell according to any one of claims 9 to 12.

17. An electrochemical cell (1) having, in this order, a fuel electrode (2) which is an electrode to which fuel is supplied, a solid electrolyte layer (3) which has oxygen ion conductivity, and an air electrode layer (4) which is an electrode paired with the fuel electrode layer, The solid electrolyte layer has an electrolyte body layer (31) in contact with the fuel electrode layer, The electrolyte body layer is The composite electrolyte material comprises a solid electrolyte material having a fluorite structure and represented as Ce 1-x (RE) x O 2-x / 2 (where x is between 0.05 and 0.2, and the RE element is at least one of Gd and Sm), and containing an M-containing oxide that contains at least one element M selected from the group consisting of Zn, Mg, Ca, Sr, La, and Y. The aforementioned composite electrolyte material is In the empirical formula Ce 1-x (RE) x O 2-x / 2, when the average oxygen coordination number calculated from the equation 4 × (2-x / 2) is N AVE, the oxygen coordination number around Ce determined by EXAFS spectral analysis is N Ce, and the oxygen coordination number around the RE element is N RE, 0 < N AVE - (N Ce + N RE) / 2 is satisfied, An intermediate layer (6) is provided between the solid electrolyte layer and the air electrode layer. The intermediate layer includes the composite electrolyte material, Electrochemical cell (1).

18. The composite electrolyte material is 0.15 < N AVE - (N Ce + N RE) / 2 The electrochemical cell according to claim 17.

19. The composite electrolyte material is 0.15 < N AVE - (N Ce + N RE) / 2 < 0.4 The electrochemical cell according to claim 17.

20. The composite electrolyte material is The bond distance L Ce-O between Ce, determined by the aforementioned EXAFS spectral analysis, is 2.341 Å or greater. The electrochemical cell according to claim 17.

21. The fuel electrode layer comprises the composite electrolyte material, The electrochemical cell according to any one of claims 17 to 20.

22. The fuel electrode layer has a fuel diffusion layer (5) in contact with the fuel electrode layer on the side opposite to the solid electrolyte layer, The fuel diffusion layer includes the composite electrolyte material, The electrochemical cell according to any one of claims 17 to 20.

23. The ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the fuel electrode layer is less than the ratio of moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. The electrochemical cell according to claim 21.

24. The ratio of moles of element M to 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 moles of element M to moles of Ce contained in the solid electrolyte material in the composite electrolyte material contained in the electrolyte body layer. The electrochemical cell according to claim 22.

25. Used as at least one of a solid oxide fuel cell and a solid oxide electrolytic cell, An electrochemical cell according to any one of claims 17 to 20.

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