Electrochemical cell

Abstract

An electrochemical cell (10) is obtained by laminating an air electrode (12), a solid electrolyte layer (11) containing a solid electrolyte, and a fuel electrode (13) in the stated order. An intermediate layer (17) is provided between the air electrode (12) and the solid electrolyte layer (11) and / or between the fuel electrode (13) and the solid electrolyte layer (11). The solid electrolyte layer (11) has a main phase composed of an oxide ion conductor. At least one of the intermediate layers (17) includes a first component constituted of cerium oxide containing a rare earth element other than cerium, and a second component constituted of an oxide ion conductor different from the first component. The substance amount of zirconium in the intermediate layer (17) is 10 mol% or less based on total substance amount of all metal elements in the intermediate layer (17).

Description

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[0002] Electrochemical cells are required to have high oxide ion conductivity and durability. For example, Patent Document 1 proposes a solid oxide fuel cell in which an intermediate layer containing ceria-based particles containing a rare earth element other than cerium and ceramic particles made of an oxide of a metal element different from the ceria-based particles is disposed between a solid electrolyte layer and an oxygen electrode layer. The solid oxide fuel cell described in the document also describes that peeling of the intermediate layer can be reduced.

[0003] Patent Document 2 proposes providing an intermediate layer made of cerium oxide containing lanthanum and a rare earth element between a solid electrolyte layer and an electrode layer, and the solid electrolyte junction described in the document is also described as having high ionic conductivity.

[0004] Patent Document 3 proposes a fuel cell in which an intermediate layer containing cerium and zirconium is disposed between a solid electrolyte layer made of YSZ (yttria-stabilized zirconia) and a barrier layer made of GDC (gadolinium-doped ceria). The document also describes that the solid oxide fuel cell described in the document can prevent peeling between the solid electrolyte layer and the barrier layer.

[0005] US Patent Application Publication No. 2014 / 0377683 US Patent Application Publication No. 2021 / 0036354 JP 2016-081718 A

[0006] In the solid oxide fuel cell described in Patent Document 1, the ceramic particles contained in the intermediate layer are not oxide ion conductors, resulting in a problem of reduced power generation characteristics of the fuel cell as a whole. Furthermore, the solid electrolyte junction described in Patent Document 2 has a risk of peeling of the intermediate layer over long-term use, resulting in a problem in terms of durability. Furthermore, in the fuel cell described in Patent Document 3, cerium and zirconium form a high-resistance layer, which raises concerns about increased cell resistance during firing in cell production and during long-term operation. Therefore, an object of the present invention is to provide an electrochemical cell that combines durability and electrochemical characteristics.

[0007] The present invention provides an electrochemical cell in which an air electrode, a solid electrolyte layer containing a solid electrolyte, and an anode are stacked in this order, the electrochemical cell having an intermediate layer at least one between the air electrode and the solid electrolyte layer and between the anode and the solid electrolyte, the solid electrolyte layer having a main phase made of an oxide ion conductor, at least one of the intermediate layers comprising: a first component which is cerium oxide containing a rare earth element other than cerium; and a second component which is an oxide ion conductor different from the first component, wherein the amount of substance of zirconium element in the intermediate layer is 10 mol % or less based on the total amount of substance of all metal elements in the intermediate layer.

[0008] Fig. 1 is a schematic diagram of a cross section taken along the thickness direction of one embodiment of an electrochemical cell of the present invention. Fig. 2 is a schematic diagram of a cross section taken along the thickness direction of another embodiment of an electrochemical cell of the present invention. Fig. 3 is a backscattered electron image taken under a scanning electron microscope of a cross section taken along the thickness direction of the electrochemical cell produced in Example 1. Fig. 4 is a backscattered electron image taken under a scanning electron microscope of a cross section taken along the thickness direction of the electrochemical cell produced in Example 2. Fig. 5 is a backscattered electron image taken under a scanning electron microscope of a cross section taken along the thickness direction of the electrochemical cell produced in Comparative Example 1.

[0009] The present invention will now be described based on preferred embodiments with reference to the drawings. FIG. 1 shows a solid oxide fuel cell 10 (hereinafter also referred to as "fuel cell 10"), which is one embodiment of the electrochemical cell of the present invention. The fuel cell 10 is an anode-supported fuel cell in which a cathode 12, a layer containing a solid electrolyte (hereinafter also referred to as "solid electrolyte layer") 11, an anode 13, and a support layer 14 are stacked in this order. The solid electrolyte layer 11 is made of a material that exhibits oxide ion conductivity above a predetermined temperature. The solid electrolyte layer 11 is located between two electrodes, i.e., the cathode 12 and the anode 13. That is, the cathode 12 and the anode 13 are located on different sides of the solid electrolyte layer 11.

[0010] An air electrode-side intermediate layer 15 is disposed between the air electrode 12 and the solid electrolyte layer 11. Meanwhile, an air electrode-side intermediate layer 16 is disposed between the air electrode 13 and the solid electrolyte layer 11. In FIG. 1 , the air electrode 12 and the air electrode-side intermediate layer 15 are shown as having the same size, but the size relationship between them is not limited to this. For example, the air electrode 12 and the air electrode-side intermediate layer 15 may have different sizes. The same applies to the air electrode 13 and the air electrode-side intermediate layer 16; they may have the same size, or, for example, the air electrode-side intermediate layer 16 may be larger than the air electrode 13. Furthermore, in FIG. 1 , the air electrode-side intermediate layer 15 and the solid electrolyte layer 11 are shown as having the same size, but the size relationship between them is not limited to this. For example, the solid electrolyte layer 11 and the air electrode-side intermediate layer 15 may have different sizes. The same applies to the air electrode 13 side.

[0011] 1 , the air electrode-side intermediate layer 15 is in direct contact with the air electrode 12 and the solid electrolyte layer 11. Therefore, no layer is interposed between the air electrode-side intermediate layer 15 and the air electrode 12. The air electrode-side intermediate layer 15 is also in direct contact with the solid electrolyte layer 11, with no layer interposed between them. The same is true on the anode 13 side, where the anode-side intermediate layer 16 is in direct contact with the solid electrolyte layer 11 and the anode 13.

[0012] The air electrode-side intermediate layer 15 and the anode-side intermediate layer 16 (hereinafter, for convenience, they may be collectively referred to simply as "intermediate layer 17") are used for the purpose of improving oxide ion conductivity between the solid electrolyte layer 11 and the air electrode 12 and / or the anode 13 in the fuel cell 10. From the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and obtaining high power generation characteristics, it is preferable that the air electrode 12, the anode 13, the solid electrolyte layer 11, and the intermediate layer 17 contain the same rare earth element (hereinafter, also referred to as a "common rare earth element"). Although the reason for this is unclear, the inventors believe that having the same rare earth element in each layer reduces the interfacial resistance between the layers and improves the conductivity of the entire cell. However, the air electrode 12, the anode 13, the solid electrolyte layer 11, and the intermediate layer 17 do not necessarily have to contain a common rare earth element.

[0013] The support layer 14 serves to increase the mechanical strength of the fuel cell 10. Because the support layer 14 increases the mechanical strength of the fuel cell 10, the thicknesses of the air electrode 12, the anode 13, the solid electrolyte layer 11, and the intermediate layer 17 can be reduced compared to when the support layer 14 is not present. In the fuel cell 10, it is preferable that the support layer 14 also contains a common rare earth element in addition to the air electrode 12, the anode 13, the solid electrolyte layer 11, and the intermediate layer 17. This allows both the solid electrolyte layer 11 and the support layer 14 to contain a common rare earth element, making it easier to control the linear expansion coefficients of the solid electrolyte layer 11 and the support layer 14 to similar values. As a result, cracks in the solid electrolyte layer 11 due to the difference between the linear expansion coefficients are less likely to occur during use of the fuel cell 10. From the viewpoint of further enhancing the effect of the common rare earth element, the common rare earth element is preferably lanthanum. Furthermore, from the viewpoint of improving the oxide ion conductivity of the fuel cell 10, it is preferable that the air electrode 12, the anode 13, the solid electrolyte layer 11, the intermediate layer 17, and the support layer 14 all contain an oxide. In summary, it is preferable that the air electrode 12, the anode 13, the solid electrolyte layer 11, the intermediate layer 17, and the support layer 14 all contain an oxide of a common rare earth element. The solid electrolyte layer 11, the air electrode 12, the anode 13, the support layer 14, and the intermediate layer 17 are described in detail below.

[0014] The solid electrolyte layer 11 is a conductor in which oxide ions serve as carriers. A single crystal or polycrystalline material is used as the solid electrolyte contained in the solid electrolyte layer 11. The solid electrolyte layer 11 preferably has a main phase made of an oxide ion conductor. As the oxide ion conductor, for example, any oxide ion conductor known in the art can be used as appropriate.

[0015] In this specification, the term "main phase" refers to a layer that accounts for the largest proportion of the total amount of all crystalline phases that constitute the solid electrolyte layer 11. From the viewpoint of increasing the oxide ion conductivity of the solid electrolyte layer 11, the area of ​​the main phase of the solid electrolyte layer 11 in the cross section of the fuel cell 10 is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more of the entire area of ​​the solid electrolyte layer 11. The method for observing the cross section of the fuel cell 10 is not particularly limited. For example, the cross section of the fuel cell 10 can be observed using a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy (SEM-EDS). The cross section to be observed may be a cross section along the thickness direction of the fuel cell 10, or a cross section along another direction.

[0016] From the viewpoint of further increasing the oxide ion conductivity, the solid electrolyte preferably contains an oxide of a common rare earth element, and more preferably the main phase of the solid electrolyte layer 11 is made of an oxide of a common rare earth element. Also, from the viewpoint of further increasing the oxide ion conductivity of the fuel cell 10, the solid electrolyte layer 11 preferably contains a composite oxide, and more preferably the main phase of the solid electrolyte layer 11 is made of a composite oxide.

[0017] Examples of the composite oxide include a composite oxide containing lanthanum and a composite oxide containing samarium. Examples of the composite oxide containing lanthanum include a composite oxide containing lanthanum and gallium, a composite oxide obtained by adding strontium, magnesium, or cobalt to the composite oxide, and a composite oxide containing lanthanum and molybdenum. Among these, an oxide-ion conductive material made of a composite oxide of lanthanum and silicon is preferably used because of its high oxide ion conductivity. Examples of the composite oxide containing samarium include a composite oxide containing samarium and cerium, a composite oxide containing samarium, barium, and cobalt, and a composite oxide containing samarium and silicon. Among these, a composite oxide containing samarium and cerium is preferably used because of its high oxide ion conductivity.

[0018] The above-mentioned composite oxide of lanthanum and silicon includes, for example, an apatite-type composite oxide containing lanthanum and silicon and having an apatite-type crystal structure. Among them, an apatite-type composite oxide containing lanthanum, which is a trivalent element, silicon, which is a tetravalent element, and O, and having a composition of La ｘ Si ６ O １．５ｘ＋１２ (X is a number of 8 or more and 10 or less) is preferred from the viewpoint of high oxide ion conductivity. The most preferred composition of this apatite-type composite oxide is La ９．３３ Si ６ O ２６ When this apatite-type composite oxide is used as a solid electrolyte, it is preferable that the c-axis coincides with the thickness direction of the solid electrolyte layer 11. This composite oxide can be produced, for example, according to the method described in JP 2013-51101 A.

[0019] Another example of the composite oxide is a compound represented by the general formula: A ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚExamples of the composite oxide include those represented by the formula: This composite oxide also has an apatite-type crystal structure. In the formula, A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. In the formula, T is an element containing Si or Ge, or both. In the formula, M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W, and Mo. From the viewpoint of improving c-axis orientation, M is preferably one or more elements selected from the group consisting of B, Ge, and Zn.

[0020] In the formula, x is preferably -1.33 or more and 3.00 or less, more preferably 0.00 or more and 2.50 or less, and even more preferably 0.45 or more and 1.50 or less, from the viewpoint of increasing the degree of orientation and oxide ion conductivity. In the formula, y is preferably 0.00 or more and 3.00 or less, more preferably 0.40 or more and 2.00 or less, and even more preferably 0.40 or more and 1.00 or less, from the viewpoint of filling the T element position in the apatite-type crystal lattice. In the formula, z is preferably -5.00 or more and 5.20 or less, more preferably -2.00 or more and 1.50 or less, and even more preferably -1.00 or more and 1.00 or less, from the viewpoint of maintaining electrical neutrality in the apatite-type crystal lattice.

[0021] In the above formula, the ratio of the number of moles of A to the number of moles of T, in other words, (9.33+x) / (6.00-y) in the above formula, is preferably 1.33 or more and 3.61 or less, more preferably 1.40 or more and 3.00 or less, and even more preferably 1.50 or more and 2.00 or less, from the viewpoint of maintaining the spatial occupancy rate in the apatite-type crystal lattice. ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚ In the formula (9.33+x) / (6.00-y), when both T and M contain Ge, y=0.

[0022] Among them, the composite oxide is preferably an apatite-type composite oxide containing a rare earth element and an element T (wherein T is at least one selected from the group consisting of Si (silicon) and Ge (germanium)). Examples of such composite oxides include those represented by the general formula: ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚ In the composite oxide represented by the formula (1), A is selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. In the formula, the details of T, M, x, and y are as described above.

[0023] From the viewpoint of further increasing the oxide ion conductivity, it is preferable to use a composite oxide containing lanthanum among the composite oxides represented by the above formula, and it is more preferable to use a composite oxide containing lanthanum and silicon. Specific examples of such composite oxides include (La ａ Sm ｂ Ce ｃ ) ９．３３＋ｘ [Si ６．００ ]O ２６．００ (0.95<a+b+c<1.05.), (La ａ Ce ｂ ) ９．３３＋ｚ [Si ６．００ ]O ２６．００ (0.95<a+b<1.05.), (La ａ Sm ｂ ) ９．３３＋ｘ [Si ６．００ ]O ２６．００ (0.95<a+b<1.05.), (La ａ Nd ｂ Sm ｃ ) ９．３３＋ｘ [Si ６．００ ]O ２６．００＋ｚ (0.95<a+b+c<1.05), and (La ａ Nd ｂ ) ９．３３＋ｘ [Si ６．００ ]O ２６．００＋ｚ (0.95<a+b<1.05) The composite oxide represented by the above formula can be produced, for example, according to the method described in International Publication WO2016 / 111110.

[0024] The content ratio of the metal elements in the solid electrolyte layer 11 can be measured by, for example, energy dispersive X-ray spectroscopy (EDS). The same applies to the content ratio of the metal elements contained in layers other than the solid electrolyte layer 11 that constitute the fuel cell 10.

[0025] When the fuel cell 10 is manufactured by the preferred manufacturing method described below, the solid electrolyte contained in the solid electrolyte layer 11 has particularly excellent c-axis orientation, and therefore the oxide ion conductivity of the solid electrolyte layer 11 is improved.

[0026] The degree of c-axis orientation f of the solid electrolyte can be calculated by the Rotterdam method. Specifically, the ratio ρ of the sum of the peak intensities (ΣI(001)) attributable to the (002) and (004) planes of the solid electrolyte to the sum of all peak intensities (ΣI(hkl)) obtained by X-ray diffraction (hereinafter also referred to as "XRD") of the solid electrolyte can be used to calculate the degree of c-axis orientation f based on the following formula (1). The reason for adopting the (002) and (004) planes is that the peaks attributable to the (002) and (004) planes are peaks specific to c-axis orientation and are independent peaks that do not overlap with the diffraction angle values ​​attributable to other planes. Degree of c-axis orientation f = (ρ - ρ0) / (1 - ρ0) ... (1) Here, in formula (1), ρ0 and ρ have the following values. ρ0: Theoretical value ρ0 = ΣI0(001) / ΣI0(hkl) ρ: Measured value ρ = ΣI(001) / ΣI(hkl)

[0027] Alternatively, the c-axis orientation of the solid electrolyte can be confirmed by determining that the proportion of crystals with a deviation angle of 20 degrees or less from the c-axis orientation of the solid electrolyte, as measured by EBSD crystal orientation analysis, is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. The higher the proportion, the better, but in reality, it is, for example, 90% or less.

[0028] As will be described later, the solid electrolyte layer 11 and the intermediate layer 17 are preferably formed by firing. However, during this firing, the components contained in the solid electrolyte layer 11 and the components contained in the intermediate layer 17 may react with each other to form a high resistance layer. In particular, if the solid electrolyte layer 11 contains Zr (zirconium) and the intermediate layer 17 contains Ce (cerium), a ceria-zirconia solid solution (Ce １－ｘ Zr ｘ O ２－δ ), which may impair the power generation characteristics (electrochemical characteristics) of the fuel cell 10 as a whole. From the viewpoint of suppressing such a deterioration in power generation characteristics, the amount of Zr element contained in the solid electrolyte layer 11 is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less, based on the amount of all metal elements contained in the solid electrolyte layer 11. Ideally, the solid electrolyte layer 11 does not contain Zr element.

[0029] In this specification, the term "metal element" refers to an element of Groups 1 to 14, excluding hydrogen and carbon.

[0030] The content of Zr element and other metal elements in the solid electrolyte layer 11 can be measured using, for example, SEM-EDS. Specifically, a cross section of the fuel cell approximately parallel to the thickness direction is processed with a cross section polisher (CP) to obtain a cross section with minimal irregularities, and then SEM-EDS analysis is performed.

[0031] From the viewpoint of effectively reducing the electrical resistance of the fuel cell 10, the thickness of the solid electrolyte layer 11 is preferably 10 nm to 30 μm, more preferably 100 nm to 20 μm, even more preferably 1000 nm to 15 μm, and particularly preferably 5 μm to 15 μm. The thickness of the solid electrolyte layer 11 can be measured using, for example, a stylus step gauge or an electron microscope. This also applies to measuring the thickness of each layer other than the solid electrolyte layer 11. For example, when measuring the thickness of each layer using a scanning electron microscope (SEM), a cross section of the fuel cell 10 along the thickness direction is observed using the SEM. FIG. 3 shows an example of an SEM image of the cross section. In FIG. 3, the boundaries between each layer constituting the fuel cell 10 are clearly observed. Therefore, the thickness of each layer constituting the fuel cell 10 can be measured using this image.

[0032] At least one of the intermediate layers 17 (air electrode-side intermediate layer 15 and fuel electrode-side intermediate layer 16) preferably contains a first component which is cerium oxide containing a rare earth element other than cerium, and a second component which is an oxide ion conductor different from the first component. The first component may contain only one rare earth element other than cerium, or may contain two or more rare earth elements other than cerium. An example of the first component containing two or more rare earth elements other than cerium is cerium oxide (hereinafter referred to as "La-Ln"). １ In such cerium oxide, lanthanum or a rare earth element other than lanthanum and cerium may be a common rare earth element. １ In DC, the base material, cerium oxide (CeO ２) in the form of a solid solution (doped) with a rare earth element other than lanthanum and cerium. Here, the doped rare earth element usually exists at a site where cerium is located in the crystal lattice of cerium oxide by substituting the site. Lanthanum exists in the form of a solid solution of cerium oxide. That is, lanthanum can exist at a site where cerium is located in the crystal lattice of cerium oxide by substituting the site, or it can exist at the grain boundary of cerium oxide doped with a rare earth element.

[0033] La-Ln １ In DC, examples of rare earth elements doped into cerium oxide include samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium. These rare earth elements may be used singly or in combination of two or more. In other words, the first component preferably contains cerium oxide containing lanthanum and one or more elements selected from the group consisting of samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium. In particular, the first component preferably contains cerium oxide containing lanthanum and samarium or gadolinium, in order to further enhance the oxide ion conductivity of the entire fuel cell 10. Note that when both intermediate layers 15 and 16 are made of La-Ln １ When DC is included, the La-Ln １ The DC may be the same or different. In addition, one of the air electrode side intermediate layer 15 and the fuel electrode side intermediate layer 16 is La-Ln １ One may be composed of DC and the other may be composed of another substance.

[0034] La-Ln １ In DC, the ratio of rare earth elements doped into cerium oxide is the ratio of rare earth elements to cerium (Ln １ ) is the atomic ratio of Ln １The doping ratio of the rare earth element to the solid electrolyte layer 11 is preferably 0.05 or more and 0.5 or less, more preferably 0.1 or more and 0.4 or less, and even more preferably 0.2 or more and 0.3 or less, expressed as / Ce. By setting the doping level of the rare earth element within this range, the oxide ion conductivity between the solid electrolyte layer 11 and the air electrode 12 and / or the fuel electrode 13 is improved.

[0035] The above Ln １ The value of / Ce is measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), etc. Furthermore, the presence of a rare earth element in cerium oxide as a solid solution can be confirmed by X-ray diffraction.

[0036] La-Ln １ In DC, lanthanum is contained for the purpose of improving the oxide ion conductivity of the entire fuel cell 10. For this purpose, La-Ln １ In DC, the La / Ce atomic ratio, which is the atomic ratio of lanthanum to cerium, is preferably 0.10 or more. Furthermore, since excessive lanthanum content reduces ionic conductivity, the La / Ce value is preferably 1.2 or less. From the same perspective, the La / Ce value is more preferably 0.20 or more and 1.0 or less, and even more preferably 0.25 or more and 0.80 or less. The La / Ce value is measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), or the like.

[0037] The second component is used to improve adhesion between the intermediate layer 17 and the solid electrolyte layer 11. The reason why including the second component in the intermediate layer 17 improves adhesion to the solid electrolyte layer 11 is as follows. When the intermediate layer 17 contains only the first component, stress concentration occurs in the intermediate layer 17 formed on the solid electrolyte layer 11 due to differences in the firing shrinkage behavior between the first component and the material of the solid electrolyte layer 11, which may cause the intermediate layer 17 to easily peel off from the solid electrolyte layer 11. On the other hand, when the intermediate layer 17 contains the second component, the firing shrinkage behavior of the intermediate layer 17 and the solid electrolyte layer 11 becomes similar, improving adhesion between the intermediate layer 17 and the solid electrolyte layer 11. Therefore, the fuel cell 10 has high durability. Furthermore, by using an oxide ion conductor as the second component, the oxide ion conductivity of the intermediate layer 17 can be improved compared to when a component that is not an oxide ion conductor is used as the second component, and the power generation characteristics (electrochemical characteristics) of the fuel cell 10 as a whole can be improved. In this way, in the fuel cell 10, by including the second component in the intermediate layer 17, it is possible to achieve both durability and power generation characteristics (electrochemical characteristics).

[0038] From the viewpoint of more reliably increasing the adhesion between the intermediate layer 17 and the solid electrolyte layer 11 and the oxide ion conductivity of the intermediate layer 17, it is preferable to use, as the second component, any of the composite oxides exemplified above as being contained in the solid electrolyte layer 11.

[0039] The intermediate layer 17 preferably contains the first component and the second component in an appropriate ratio. Specifically, from the viewpoint of more reliably obtaining the durability-improving effect resulting from the second component, in the intermediate layer containing the first component and the second component, the mass ratio M2 / M1 of the content M2 of the second component to the content M1 of the first component is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.20 or more. Furthermore, from the viewpoint of further improving electrochemical properties, in the intermediate layer containing the first component and the second component, the mass ratio M2 / M1 is preferably 4.00 or less, more preferably 2.00 or less, and even more preferably 1.00 or less. M2 / M1 can be measured by analyzing a cross section of the fuel cell 10 using SEM-EDS. Details of the measurement conditions will be described in the Examples below. The method for observing the cross section of the fuel cell 10 is as described above. The cross section to be observed may be a cross section along the thickness direction of the fuel cell 10, or may be a cross section along another direction.

[0040] The intermediate layer 17 may be crystalline or amorphous. When the intermediate layer 17 is crystalline, the intermediate layer 17 includes a crystalline phase consisting of the first component and a crystalline phase consisting of the second component.

[0041] If the intermediate layer 17 contains zirconium element, the zirconium element may react with the first component to form a highly resistive compound when the fuel cell 10 is operated at high temperatures or during firing in the manufacture of the fuel cell 10. Such a compound may cause a deterioration in the overall characteristics of the fuel cell 10. Therefore, from the perspective of suppressing the formation of such a highly resistive compound, the amount of zirconium element in the intermediate layer 17 is preferably 10 mol % or less, more preferably 5 mol % or less, and even more preferably 3 mol % or less, based on the total amount of substance of all metal elements in the intermediate layer 17, and is ideally 0 mol % (i.e., the intermediate layer 17 does not contain zirconium element).

[0042] Only one of the air electrode-side intermediate layer 15 and the fuel electrode-side intermediate layer 16 may contain the first component and the second component, or both intermediate layers 15, 16 may contain the first component and the second component. In particular, if the fuel electrode-side intermediate layer 16 contains the first component and the second component, the firing shrinkage behavior of the fuel electrode-side intermediate layer, which is exposed to a reducing atmosphere during operation of the electrochemical cell, can be matched with that of the solid electrolyte layer, thereby further improving the durability of the entire cell. When either the air electrode-side intermediate layer 15 or the fuel electrode-side intermediate layer 16 does not contain both the first component and the second component, it is preferable that the intermediate layer contain at least the first component from the viewpoint of improving the oxide ion conductivity of the entire fuel cell 10.

[0043] The inventors have found through their investigations that the intermediate layer 17 having a certain thickness or greater can effectively improve the oxide ion conductivity between the solid electrolyte layer 11 and the air electrode 12 and / or the anode 13. In particular, the thickness of the intermediate layer 17 on the air electrode 12 side and the anode 13 side is preferably 10 nm or more and 30 μm or less, more preferably 50 nm or more and 20 μm or less, and even more preferably 100 nm or more and 10 μm or less. The thickness of the air electrode-side intermediate layer 15 and the thickness of the anode-side intermediate layer 16 may be the same as or different from each other.

[0044] The air electrode 12 and the anode 13, which are disposed in direct contact with the intermediate layer 17, preferably contain a rare earth element and an oxide having oxide ion conductivity. It is also preferable that such an oxide contain a common rare earth element. Furthermore, the air electrode 12 and the anode 13 may each independently further contain a metal material. Because of advantages such as high catalytic activity, the metal material preferably contains nickel or a platinum group element, and more preferably nickel. Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements can be used alone or in combination of two or more. Furthermore, the anode 13 and the air electrode 12 can each independently be a cermet containing an oxide containing a common rare earth element and the above-mentioned metal material.

[0045] The oxide contained in the cathode 12 is ABO ３－δ Preferably, oxides having a perovskite structure represented by the formula (hereinafter also referred to as "oxide a") are used. In the formula, A represents an alkaline earth metal element, which may contain a common rare earth element in part. B represents a transition metal element, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Ta, and W. δ is a fraction resulting from the valence and amount of A, B, and O. ABO ３－δ Various oxides having a perovskite structure represented by the formula (I) are known, and it is known that such oxides have various crystal systems, such as cubic, tetragonal, rhombohedral, and orthorhombic. Among these crystal systems, ABO having a cubic perovskite structure is ３－δ It is preferable to use an oxide of this type as the air electrode 12. By directly bonding the air electrode 12 made of such an oxide to the intermediate layer 17 made of the above-mentioned material, the oxide ion conductivity can be further increased.

[0046] When oxide a contains a common rare earth element, the content of the common rare earth element, expressed as the atomic ratio of the common rare earth element to all elements located at the A site, is preferably 0.010 to 0.80, more preferably 0.050 to 0.80, even more preferably 0.10 to 0.70, still more preferably 0.15 to 0.70, and most preferably 0.15 to 0.60. When the content of the common rare earth element in oxide a is within the above range, the oxide ion conductivity of oxide a can be improved. Although the reason for this is not clear, the present inventors believe that the inclusion of a common rare earth element in part of the A site forms a path in oxide a that facilitates the movement of oxide ions.

[0047] Whether or not a common rare earth element is located in part of the A site in oxide a can be confirmed by X-ray diffraction. The proportion of lanthanum in all elements located in the A site can be measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), or ICP optical emission spectroscopy.

[0048] When oxide a is used as the material constituting the air electrode 12, it is preferable that the alkaline earth metal element occupying the A site be one or more elements selected from the group consisting of barium and strontium, from the viewpoint of enhancing the oxide ion conductivity of the entire fuel cell 10. In other words, it is preferable that at least lanthanum and one or more elements selected from the group consisting of barium and strontium are located at the A site of oxide a.

[0049] It is preferable that a portion of the transition metal elements occupying the B site of oxide a includes at least one of elements belonging to the fourth and fifth periods of the periodic table. In particular, the transition metal elements located at the B site preferably include at least one element selected from the group consisting of iron, cobalt, nickel, copper, titanium, zirconium, and niobium, and it is even more preferable that at least a portion of the transition metal elements be iron, from the viewpoint of improving the oxide ion conductivity of the entire fuel cell 10. From the same viewpoint, it is particularly preferable that both iron and copper are located at least a portion of the B site.

[0050] When iron is located at the B site of oxide a, from the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and not affecting the crystal system of oxide a, the atomic ratio of iron to all elements located at the B site is preferably 0.05 to 0.95, more preferably 0.10 to 0.90, and even more preferably 0.20 to 0.80. Furthermore, when iron and copper are located at the B site of oxide a, the total atomic ratio of iron and copper to all elements located at the B site is preferably 0.80 to 1.00, more preferably 0.85 to 1.00, and even more preferably 0.90 to 1.00. In this case, the atomic ratio of iron to copper, Fe / Cu, is preferably 1.00 to 10.0, more preferably 2.00 to 9.50, and even more preferably 5.00 to 9.00. The atomic ratio and Fe / Cu value can be measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), or ICP optical emission spectroscopy. Whether iron is located at the B site in oxide a can be confirmed by X-ray diffraction.

[0051] The oxide a preferably has the general formula: La １－ｘ A ｘ BO ３－δ (wherein A is an element containing Ba or Sr, or both; B is one or more elements selected from Fe, Ni, Co, Ti, Zr, and Nb; it is particularly preferable that B is one or more elements selected from Fe, Cu, and Zr; and x is a number of 0.010 or more and 0.80 or less).

[0052] Particularly preferred oxides as oxide a are those shown in (i) to (iv) below. (i) Oxides in which lanthanum and strontium occupy the A site and iron and cobalt occupy the B site. (ii) Oxides in which lanthanum and strontium occupy the A site and iron, cobalt, and nickel occupy the B site. (iii) Oxides in which lanthanum and barium occupy the A site and iron occupy the B site. (iv) Oxides in which lanthanum and barium occupy the A site and iron and copper occupy the B site.

[0053] Oxide a can be obtained by a breakdown method, which uses mechanical energy to reduce particle size, or a build-up method, which controls the growth of atomic or molecular aggregates through chemical reactions. The build-up method is preferable from the perspective of reducing electrical resistance. The build-up method is believed to produce the above-mentioned effects because it is easy to obtain fine particles and can increase the contact area between particles. Specifically, it can be obtained, for example, by the following method. Specifically, acetates or nitrates of metals mixed in a stoichiometric ratio according to the composition of the oxide having the desired perovskite structure and DL-malic acid are dissolved in ion-exchange water, and ammonia water is added while stirring to adjust the pH to 5-6. The solution is then evaporated at 350°C, and the resulting powder is pulverized in a mortar. The powder thus obtained is pre-calcined in air at 700°C to 1000°C for 5 hours and then pulverized again. However, the method for producing oxide a is not limited to this method.

[0054] Suitable oxides contained in the air electrode 12 and the fuel electrode 13 include the above-mentioned La-Ln oxide in addition to the oxide a. １ DC can also be exemplified. １ Regarding DC, La-Ln contained in the intermediate layer 17 １ Since the above description of DC applies, the following description will be made of La-Ln contained in the intermediate layer 17. １ Only the differences from DC will be explained.

[0055] La-Ln １When DC is contained in the fuel electrode 13, the atomic ratio La / Ce of La to Ce is preferably 0.10 or more and 1.2 or less, more preferably 0.20 or more and 1.0 or less, and even more preferably 0.25 or more and 0.80 or less.

[0056] In particular, from the viewpoint of increasing the oxide ion conductivity of the entire fuel cell 10, the anode 13 preferably contains cerium oxide containing lanthanum and one or more elements selected from the group consisting of samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium. Also, from the viewpoint of increasing the oxide ion conductivity of the entire fuel cell 10 while increasing the catalytic activity of the anode, the anode 13 preferably contains La-Ln １ More preferably, it comprises a cermet of DC and nickel.

[0057] When the anode 13 contains an oxide containing a common rare earth element (hereinafter also referred to as the "first oxide") and the solid electrolyte in the solid electrolyte layer 11 contains an oxide containing a common rare earth element (hereinafter also referred to as the "second oxide"), it is preferable that the content of the common rare earth element in the first oxide and the content of the common rare earth element in the second oxide have a predetermined relationship. Specifically, the ratio of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the first oxide is defined as n1, and the ratio of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the second oxide is defined as n2. In this case, the ratio n1 / n2 is preferably 0.30 or more, more preferably 0.35 or more, and even more preferably 0.40 or more. Furthermore, n1 / n2 is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less. Setting n1 / n2 within the above range increases the oxide ion conductivity of the fuel cell 10 as a whole, thereby improving the power generation characteristics of the fuel cell 10. Note that, when the anode 13 contains a cermet of the first oxide and a metallic material, the number of moles of the metallic elements contained in the metallic material is not included in the "total number of moles of elements other than oxygen" used in calculating n1. The same applies to the calculation of n2 and n3 to n6 described below.

[0058] Furthermore, from the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and improving the power generation characteristics of the fuel cell 10, n1 is preferably 8.0 mol% or more and 50 mol% or less, more preferably 9.0 mol% or more and 45 mol% or less, and even more preferably 10 mol% or more and 40 mol% or less. From the same viewpoint, n2 is preferably 45 mol% or more and 80 mol% or less, more preferably 50 mol% or more and 75 mol% or less, and even more preferably 55 mol% or more and 70 mol% or less.

[0059] From a similar viewpoint, when the air electrode 12 contains an oxide containing a common rare earth element (hereinafter also referred to as the "third oxide"), the ratio n3 of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the third oxide is preferably 20 mol% to 40 mol%, more preferably 25 mol% to 38 mol%, and even more preferably 30 mol% to 35 mol%. Furthermore, when the air electrode-side intermediate layer 15 contains an oxide containing a common rare earth element (hereinafter also referred to as the "quaternary oxide"), the ratio n4 of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the quaternary oxide is preferably 3 mol% to 27 mol%, more preferably 5 mol% to 25 mol%, and even more preferably 6 mol% to 20 mol%. Furthermore, when the fuel electrode-side intermediate layer 16 contains an oxide containing a common rare earth element (hereinafter also referred to as a "fifth oxide"), the ratio n5 of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the fifth oxide is preferably 3 mol% or more and 50 mol% or less, more preferably 10 mol% or more and 40 mol% or less, and even more preferably 15 mol% or more and 35 mol% or less. Furthermore, when the support layer 14 contains an oxide containing a common rare earth element (hereinafter also referred to as the "sixth oxide"), the ratio n6 of the number of moles of the common rare earth element to the total number of moles of elements other than oxygen in the sixth oxide is preferably 9 mol% to 80 mol%, more preferably 10 mol% to 75 mol%, even more preferably 12 mol% to 70 mol%, still more preferably 30 mol% to 70 mol%, still more preferably 40 mol% to 70 mol%, and particularly preferably 45 mol% to 65 mol%. In the fuel cell 10, only one of n1 to n6 may be within the above-mentioned preferred numerical range, or any combination of two or more may be within the above-mentioned preferred numerical range.

[0060] From the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and improving the power generation characteristics of the fuel cell 10, the ratio of n4 to n2, n4 / n2, is preferably 0.0010 or more, more preferably 0.0050 or more, even more preferably 0.010 or more, particularly preferably 0.080 or more, and preferably 0.60 or less, more preferably 0.45 or less, even more preferably 0.30 or less, and particularly preferably 0.20 or less. From the same viewpoint, the ratio of n5 to n2, n5 / n2, is preferably 0.070 or more, more preferably 0.20 or more, even more preferably 0.27 or more, and preferably 0.70 or less, more preferably 0.65 or less, and even more preferably 0.60 or less.

[0061] From the viewpoint of reducing electrical resistance, the average particle diameter of the oxide contained in the air electrode 12 and the anode 13 is preferably 1000 nm or less, more preferably 600 nm or less, even more preferably 300 nm or less, and even more preferably 200 nm or less. Furthermore, the average particle diameter of the oxide contained in the air electrode 12 and the anode 13 is preferably 1 nm or more, even more preferably 2 nm or more, and even more preferably 3 nm or more. The average particle diameter can be calculated using images of particles obtained by observation with a scanning electron microscope and known image analysis software. For example, the outlines of 10 randomly selected particles are observed at 1000 to 100,000 magnifications to determine the particle contours. If necessary, processing such as contrast enhancement or drawing lines along the contours can be performed, and the average particle diameter can be calculated by performing image analysis.

[0062] The inventors have found through their investigations that if the air electrode 12 and the anode 13 have a predetermined thickness, the oxide ion conductivity of the entire fuel cell 10 can be more effectively increased. Specifically, the thickness of the air electrode 12 and the anode 13 bonded to the intermediate layer 17 is preferably independently 100 nm or more, more preferably 200 nm or more, even more preferably 500 nm or more, and particularly preferably 1000 nm or more. Furthermore, the thickness of the air electrode 12 and the anode 13 is preferably independently 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 10 μm or less.

[0063] The support layer 14 preferably contains an oxide containing a rare earth element, and more preferably contains an oxide containing a common rare earth element. Examples of such oxides include the various oxides listed above as examples of oxides that can be contained in the solid electrolyte layer 11. The support layer 14 may also contain a metal material. From the viewpoint of enhancing catalytic performance and electronic conductivity, the metal material preferably contains nickel or a platinum group element, and more preferably contains nickel. The support layer 14 may also be a cermet of a metal material and one of the oxides listed above as examples of oxides that can be contained in the solid electrolyte layer 11. From the viewpoint of suppressing an increase in electrical resistance of current collection, the support layer 14 is preferably conductive.

[0064] The thickness of the support layer 14 is preferably 200 μm or more, more preferably 300 μm or more, even more preferably 500 μm or more, and particularly preferably 1000 μm or more, from the viewpoint of sufficiently increasing the mechanical strength of the fuel cell 10. Furthermore, from the viewpoint of making the thermal shrinkage the same as that of the other layers and from the viewpoint of maintaining electrical conductivity, the thickness of the support layer 14 is preferably 3000 μm or less, more preferably 2500 μm or less, and even more preferably 2000 μm or less.

[0065] Figure 2 shows another embodiment of a fuel cell of the present invention. The following mainly describes configurations that differ from the fuel cell 10 shown in Figure 1, and configurations that are similar to those of the fuel cell 10 shown in Figure 1 are given the same reference numerals and descriptions thereof will be omitted. For configurations that are not specifically described in the embodiment of the fuel cell 10 shown in Figure 2, the description of the fuel cell 10 shown in Figure 1 applies as appropriate.

[0066] The fuel cell 10 shown in Fig. 2 does not have the support layer 14 of the fuel cell 10 shown in Fig. 1, and the anode 13 functions as the support layer. As a constituent material of the anode 13, any of the oxides described above as being contained in the anode 13 of the fuel cell 10 shown in Fig. 1 can be used. In this embodiment, it is preferable that the air electrode 12, the anode 13, the solid electrolyte layer 11, and the intermediate layer 17 contain the same rare earth element (common rare earth element).

[0067] In the fuel cell 10 of this embodiment, as described above, the anode 13 functions as a support layer. Therefore, it is preferable to make the thickness of the anode 13 larger than that of the fuel cell 10 shown in FIG. 1 . Specifically, the thickness of the anode 13 in this embodiment is preferably 1 μm or more, more preferably 10 μm or more, even more preferably 100 μm or more, and particularly preferably 500 μm or more. Furthermore, from the viewpoint of making the thermal shrinkage comparable to that of the other layers and maintaining electrical conductivity, the thickness of the anode 13 is preferably 3000 μm or less, more preferably 2500 μm or less, even more preferably 2000 μm or less, and particularly preferably 1500 μm or less.

[0068] 1 and 2 can be operated, for example, by the following method. First, hydrogen, methane, propane, biogas, or the like is supplied to the fuel electrode 13, and air is supplied to the air electrode. Under this condition, the fuel cell 10 is heated to, for example, 600°C to 1000°C, and the fuel cell 10 is operated.

[0069] Next, the electrochemical half-cell of the present invention will be described. The electrochemical half-cell of the present invention has a structure in which a solid electrolyte layer, an intermediate layer (corresponding to the "fuel electrode-side intermediate layer 16" in the above embodiment), and an anode are stacked in this order. The details of the solid electrolyte layer, the intermediate layer, and the anode are the same as those of the above embodiment, and the above description applies as appropriate. The electrochemical half-cell of the present invention has excellent durability and electrochemical properties due to the intermediate layer containing the first component and the second component.

[0070] <First Manufacturing Method> Next, a preferred manufacturing method for an electrochemical cell of the present invention (hereinafter also referred to as the "first manufacturing method") will be described using the manufacturing method for the fuel cell 10 shown in FIGS. 1 and 2 as an example. This manufacturing method includes the following steps: (1) preparing a first stack in which raw material compositions for the solid electrolyte layer 11, the anode 13, and the intermediate layer 17 are stacked in layers (first stack-forming step); (2) heating the first stack at a predetermined temperature to obtain a sintered body (first firing step); (3) preparing a second stack by disposing a raw material composition for the cathode 12 on the surface of the sintered body opposite the anode 13 (second stack-forming step); and (4) heating the second stack at a predetermined temperature to obtain the fuel cell 10 (second firing step). According to the present invention, by heating the first stack consisting of several layers in the first firing step, most of the fuel cell can be manufactured. Therefore, the fuel cell shown in FIG. 1 or 2, which is the embodiment described above, can be manufactured more easily than conventional manufacturing methods that require heating each layer separately.

[0071] 1. First Stack Formation Step First, a method for manufacturing the fuel cell 10 shown in Fig. 2 will be described. A green sheet can be suitably used for the first stack. The green sheet is obtained by preparing slurries containing raw material compositions for the solid electrolyte layer 11, the anode 13, and the intermediate layer 17, respectively, and forming them into a sheet shape.

[0072] The raw material composition used to manufacture the solid electrolyte layer 11 may contain lanthanum and silicon. Such a raw material composition may be, for example, a composition having the formula La ２ Si ２ O ７It is possible to prepare an oxide represented by the following formula:

[0073] The raw material composition used in the production of the fuel electrode-side intermediate layer 16 preferably contains the common rare earth elements described above, and more preferably contains cerium and oxygen in addition to these. Such oxides may be doped with an Ln element (Ln represents a rare earth element other than Ce), or may be undoped. When the second raw material composition is doped with an Ln element, the Ln element is preferably at least one element selected from the group consisting of La, Nd, and Sm. The second raw material composition preferably contains cerium oxide doped or undoped with an Ln element (Ln represents a rare earth element other than Ce), and has the composition formula La ０．５ Ce ０．５ O １．７５ It is more preferable that the compound contains a compound represented by the following formula:

[0074] The raw material composition used to manufacture the anode 13 preferably contains a common rare earth element and oxygen. Furthermore, this raw material composition may contain a metal element such as nickel. Nickel functions as a catalyst for the reaction. As such a raw material composition, for example, nickel (II) oxide and cerium oxide doped or undoped with Ln elements (Ln represents a rare earth element other than Ce) can be prepared. As cerium oxide doped with Ln elements, for example, a compound having the composition formula La ０．５ Ce ０．５ O １．７５ Examples of the compound include compounds represented by the following formula:

[0075] If necessary, a raw material composition to be used in manufacturing the air electrode-side intermediate layer 15 may be prepared. As the raw material composition, the materials described above as the raw material composition to be used in manufacturing the fuel electrode-side intermediate layer 16 can be used. The raw material composition to be used in manufacturing the air electrode-side intermediate layer 15 may be the same as or different from the raw material composition to be used in manufacturing the fuel electrode-side intermediate layer 16. From the viewpoint of further improving the oxide ion conductivity of the fuel cell 10 as a whole and enhancing the power generation characteristics of the fuel cell 10, it is preferable to prepare the same raw material composition to be used in manufacturing the air electrode-side intermediate layer 15 as the raw material composition to be used in manufacturing the fuel electrode-side intermediate layer 16.

[0076] Once the above raw material compositions are prepared, one of the raw material compositions is mixed with a liquid such as water or an organic solvent to prepare a slurry of the raw material composition. Slurries are prepared for each of the raw material compositions for the solid electrolyte layer 11, the anode-side intermediate layer 16, and the anode 13. If necessary, a raw material composition for the air electrode-side intermediate layer 15 is also prepared. Examples of organic solvents that can be used include ethanol, isopropyl alcohol, and toluene. These organic solvents can be used alone or in combination. Mixing can be performed using, for example, an ultrasonic homogenizer, a shaker, a thin film rotary mixer, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, an attritor, a ball mill, a vibrator mill, and a high-speed impeller mill. During mixing, additives such as dispersants, antifoaming agents, binders, and plasticizers can be used as needed. The mixing time and temperature are not particularly limited and can be adjusted appropriately depending on the type of raw material composition and liquid.

[0077] Once the slurry is prepared, it is formed into a sheet to obtain a green sheet. Forming is performed for each of the slurries for the solid electrolyte layer 11, the anode-side intermediate layer 16, and the anode 13. If necessary, the same is performed for the slurry for the air electrode-side intermediate layer 15. As a result, a first sheet is obtained from the slurry for the solid electrolyte layer 11. A second sheet is obtained from the slurry for the anode-side intermediate layer 16. A third sheet is obtained from the slurry for the anode. Furthermore, a fourth sheet is obtained from the slurry for the air electrode-side intermediate layer 15. Forming can be performed using various forming machines such as a film applicator, doctor blade, spray, and spin coater.

[0078] It is preferable that the first to fourth sheets are each molded to have a predetermined thickness, from the viewpoint of successfully obtaining the desired fuel cell 10 by heating the first laminate, as described below. Specifically, the thickness of the first sheet is preferably 5 μm or more and 40 μm or less. The thickness of the second sheet is preferably 10 μm or more and 100 μm or less. The thickness of the third sheet is preferably 10 μm or more and 100 μm or less. Furthermore, the thickness of the fourth sheet is preferably 0.1 μm or more and 50 μm or less. The thickness of each sheet can be adjusted appropriately by changing the type of applicator used during molding.

[0079] Next, the sheets are stacked and thermocompression bonded. This results in a first laminate. The first, second, third, and fourth sheets are stacked in a manner corresponding to the stacking order of the layers of the intended fuel cell 10. For example, the first, second, and third sheets are stacked in this order. Alternatively, the fourth sheet, the first, second, and third sheets may be stacked in this order. The first to fourth sheets may be in partial contact with each other in their opposing regions, or may be in contact with each other over the entire opposing region. From the viewpoint of effectively producing a solid electrolyte having an apatite structure and c-axis orientation, it is preferable that the first to fourth sheets be in contact with each other over the entire opposing region.

[0080] The heating temperature in thermocompression bonding is preferably 50° C. or higher, more preferably 55° C. or higher, and even more preferably 60° C. or higher, from the viewpoint of softening the sheets with heat and increasing adhesion. From the same viewpoint, the heating temperature is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower. The pressure during thermocompression bonding is preferably 0.1 MPa or higher, more preferably 0.2 MPa or higher, and even more preferably 0.3 MPa or higher, from the viewpoint of increasing adhesion between the sheets to be laminated.

[0081] Once the first laminate is obtained, it can be cut into a desired shape, if necessary.

[0082] 2. First Firing Step Next, the first laminate is heated to obtain a sintered body. This heating causes elements to diffuse between the first sheet and the second sheet, and a solid electrolyte having an apatite structure and c-axis orientation is produced from the raw material composition in the first sheet. To explain the element diffusion in more detail, the La element contained in the second sheet diffuses into the first sheet. In addition, elements may diffuse from the first sheet to the second sheet. For example, if the first sheet contains La, ２ Si ２ O ７ If it contains La ２ Si ２ O ７ From SiO ２ is liberated, and the liberated SiO ２ Si derived from the second component may diffuse from the first sheet to the second sheet. Through this diffusion of elements, a solid electrolyte consisting of a composite oxide of lanthanum and silicon is produced, and the fuel electrode side intermediate layer 16 containing the second component is formed. Note that the diffusion of La from the first sheet to the second sheet due to this heating is considered to be negligible. When the first stack includes a fourth sheet, elements also diffuse between the first and fourth sheets by heating the first stack, and a solid electrolyte having an apatite structure and c-axis orientation is produced from the raw material composition in the first sheet. To explain the diffusion of elements in more detail, the La element contained in the fourth sheet diffuses to the first sheet. In addition, elements may also diffuse from the first sheet to the fourth sheet. For example, when the first sheet contains La, ２ Si２ O ７ If it contains La ２ Si ２ O ７ From SiO ２ is liberated, and the liberated SiO ２ Si derived from the second component may diffuse from the first sheet to the second sheet. Through this diffusion of elements, a solid electrolyte made of a composite oxide of lanthanum and silicon is produced, and the air electrode-side intermediate layer 15 containing the second component is also formed. Note that the diffusion of La from the first sheet to the fourth sheet due to this heating is considered to be negligible.

[0083] The heating temperature of the first laminate may be sufficient to allow diffusion of elements between the first sheet and the second and / or fourth sheet. Specifically, it is preferably 1200°C or higher, more preferably 1300°C or higher, and even more preferably 1500°C or higher. A heating temperature of at least the above value effectively diffuses the T element (Si or Ge) from the first sheet to the second and / or fourth sheet, thereby facilitating the production of the second component in the intermediate layer 17. For this reason, a higher heating temperature is preferable, but the desired effect can be sufficiently achieved even at 1700°C or lower. The heating time of the first laminate may also be sufficient to allow diffusion of elements between the first sheet and the second and / or fourth sheet. Specifically, it is preferably 0.5 hours or higher, more preferably 1.0 hours or higher, and even more preferably 2.0 hours or higher. For the same reason, it is preferably 10 hours or lower, more preferably 8.0 hours or lower, and even more preferably 6.0 hours or lower. Heating can be performed, for example, using an electric furnace, a tubular furnace, or the like. The atmosphere may be an oxygen-containing atmosphere such as air, or an inert gas atmosphere such as nitrogen gas or argon gas. Other layers described later can also be heated in the same manner.

[0084] By the above heating, the first sheet, the second sheet, the third sheet, and the fourth sheet respectively produce the solid electrolyte layer 11, the fuel electrode-side intermediate layer 16, the fuel electrode 13, and the air electrode-side intermediate layer 15. When producing the above-mentioned electrochemical half-cell instead of the fuel cell 10, the stack of the first to third sheets can be heated under the above-mentioned conditions.

[0085] 3. Second Stack Formation Step Next, a raw material composition to be used in manufacturing the air electrode 12 is prepared. This raw material composition contains a common rare earth element. For example, a raw material composition having the composition formula La ０．６ Sr ０．４ Co ０．２ Fe ０．８ O ３ A compound represented by the formula (I) can be prepared. Once the raw material composition is prepared, the raw material composition for the air electrode 12 is placed on the surface of the sintered body obtained in the first firing step opposite the anode 13, thereby obtaining a second laminate. The raw material composition for the air electrode 12 can be applied as a coating by, for example, applying a slurry containing the raw material composition. The slurry can be obtained, for example, by adding the raw material composition to a binder prepared by dissolving ethyl cellulose in α-terpineol and adjusting the concentration. When the sintered body comprises a solid electrolyte layer 11, an anode-side intermediate layer 16, and an anode 13, a coating is formed on the surface of the solid electrolyte layer 11. When the sintered body comprises a solid electrolyte layer 11, an anode-side intermediate layer 16, an anode 13, and an anode-side intermediate layer 15, a coating can be formed on the surface of the anode-side intermediate layer 15. When forming the coating, the slurry and the solid electrolyte layer 11 or the air electrode-side intermediate layer 15 may be in partial contact with each other in the opposing regions, or may be in contact with each other over the entire opposing regions. From the viewpoint of further improving the oxide ion conductivity of the fuel cell 10 as a whole and enhancing the power generation characteristics of the fuel cell 10, it is preferable that the slurry and the solid electrolyte layer 11 or the air electrode-side intermediate layer 15 are in contact with each other in all opposing regions of the respective layers. From the viewpoint of successfully obtaining a desired fuel cell 10, it is preferable that the coating film be formed so that the thickness of the fifth sheet is 1.0 μm or more and 30.0 μm or less.

[0086] 4. Second Firing Step: Next, the second stack is heated to form the air electrode 12. The heating temperature of the second stack is preferably lower than the heating temperature of the first stack in the first firing step. This prevents element diffusion between the solid electrolyte layer 11 and the anode-side intermediate layer 16 and / or the cathode-side intermediate layer 15 during firing of the second stack, thereby producing a stable fuel cell 10. For this reason, the heating temperature of the second stack is preferably 1600°C or lower, more preferably 1500°C or lower, and even more preferably 1400°C or lower. Furthermore, from the viewpoint of sufficiently heating the fifth sheet to form the air electrode, the heating temperature of the second stack is preferably 600°C or higher, more preferably 700°C or higher, and even more preferably 800°C or higher. The heating time of the second stack may be long enough to form the air electrode, and specifically, is preferably 0.1 hours or higher, more preferably 0.3 hours or higher, and even more preferably 0.5 hours or higher. Furthermore, from the viewpoint of suppressing diffusion of elements between the solid electrolyte layer 11 and the anode-side intermediate layer 16 and / or the cathode-side intermediate layer 15, the heating time for the second stack is preferably 10 hours or less, more preferably 9.0 hours or less, even more preferably 8.0 hours or less, even more preferably 5.0 hours or less, and particularly preferably 2.0 hours or less. The heating time for the second stack and the heating time for the first stack may be the same or different. Regardless of the heating temperature and pressure used, it is preferable to perform heating so that the thickness of the cathode 12 becomes 1.0 μm or more and 30 μm or less, from the viewpoint of successfully obtaining the desired fuel cell 10.

[0087] Thereafter, if necessary, the fuel cell 10 may be reduced to reduce metal oxides such as nickel oxide contained in the fuel electrode 13 of the fuel cell 10. This allows, for example, nickel oxide to be reduced to metallic nickel. The reduction can be performed, for example, by hydrogen reduction. The hydrogen reduction can be performed under conditions commonly used in this technical field.

[0088] Instead of heating the first laminate formed by stacking the first through fourth sheets to obtain a sintered body, the first laminate formed by stacking the first through third sheets may be heated to obtain a sintered body. In this case, the raw material composition used to manufacture the air electrode-side intermediate layer 15 is placed on the surface of the sintered body opposite the anode to form a third laminate, and the third laminate is then heated to obtain a sintered body formed by stacking the air electrode-side intermediate layer 15, solid electrolyte layer 11, anode-side intermediate layer 16, and anode 13 in this order. The raw material composition used to manufacture the air electrode-side intermediate layer 15 can be applied as a coating film by, for example, applying a slurry containing the raw material composition. The slurry can be obtained, for example, by adding the raw material composition to a binder prepared by dissolving ethyl cellulose in α-terpineol and adjusting the concentration. The heating temperature for the third laminate is preferably 1000°C or higher, more preferably 1150°C or higher, and even more preferably 1300°C or higher. The heating temperature of the third stack is preferably 2000°C or less, more preferably 1900°C or less, and even more preferably 1800°C or less. The heating time of the third stack is sufficient to bake the air electrode-side intermediate layer 15 onto the first stack, and specifically is preferably 0.1 hour or more, more preferably 0.3 hour or more, and even more preferably 0.5 hour or more. The heating time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 2 hours or less.

[0089] Next, a method for manufacturing the fuel cell 10 shown in FIG. 1 will be described. The fuel cell 10 shown in FIG. 1 has a support layer 14 in addition to the anode 13. In the following description, differences from the method for manufacturing the fuel cell 10 shown in FIG. 2 will be mainly described. In this manufacturing method, a raw material composition used for manufacturing the support layer 14 is prepared in addition to raw material compositions for the solid electrolyte layer 11, the air electrode side intermediate layer 15 and / or the anode side intermediate layer 16, and the anode 13. The raw material composition used for manufacturing the support layer preferably contains a common rare earth element. Examples of such raw material compositions include nickel (II) oxide and La. ９．３３ Si ６ O ２６A composition containing a compound represented by the formula (I) can be prepared. Once the raw material composition is prepared, a slurry of the raw material composition is prepared. The slurry preparation method can be the same as the slurry preparation method described above. If necessary, a pore-forming agent can be used when preparing the slurry. The pore-forming agent thermally decomposes or sublimes at a predetermined temperature, so the support layer obtained by heating the green sheet containing the pore-forming agent has numerous pores. This facilitates gas diffusion. As the pore-forming agent, for example, crosslinked polymethyl methacrylate particles can be used. Once the slurry is prepared, it is molded into a sheet to obtain a green sheet. A support layer sheet is thus obtained from the support layer slurry. The molding method is as described above. It is preferable to mold the support layer sheet to a predetermined thickness, from the viewpoint of successfully obtaining the desired fuel cell 10 by heating the laminate described below. Specifically, the support layer sheet preferably has a thickness of 10 μm or more and 300 μm or less.

[0090] Next, the prepared sheets are stacked and thermocompression bonded. This results in a laminate. The first to fourth sheets and the support layer sheet are stacked in a manner that corresponds to the order of the layers of the intended fuel cell 10. For example, the first sheet, second sheet, third sheet, and support layer sheet are stacked in this order. Alternatively, the fourth sheet, first sheet, second sheet, third sheet, and support layer sheet are stacked in this order. The first to fourth sheets and the support layer sheet may be in partial contact with each other in opposing regions, or may be in contact with each other over the entire opposing region of each layer. From the viewpoint of effectively producing a solid electrolyte having an apatite structure and c-axis orientation, it is preferable that the first to fourth sheets and the support layer sheet be in contact with each other over the entire opposing region of each layer.

[0091] The procedure for obtaining the fuel cell 10 from the stack can be the same as the method for manufacturing the fuel cell 10 shown in FIG.

[0092] <Second Manufacturing Method> Next, another manufacturing method for an electrochemical cell of the present invention (hereinafter also referred to as the "second manufacturing method") will be described using as an example a manufacturing method for the fuel cell 10 shown in Fig. 1. This manufacturing method is broadly divided into the following steps 1 and 2. Step 1: A step of producing a laminate including an intermediate layer precursor layer and a solid electrolyte layer precursor layer. Step 2: A step of firing the laminate. Each step will be described below.

[0093] <Step 1> In this step, an intermediate layer precursor layer and a solid electrolyte layer precursor layer are prepared. The intermediate layer precursor layer is a layer serving as a precursor for forming the air electrode-side intermediate layer 15 and / or the fuel electrode-side intermediate layer 16 shown in Figure 1. The solid electrolyte layer precursor layer is a layer serving as a precursor for forming the solid electrolyte layer 11 shown in Figure 1.

[0094] <Intermediate Layer Precursor Layer> The intermediate layer precursor layer is a layer containing a rare earth element. The intermediate layer precursor layer may be, for example, a layer containing an oxide of a rare earth element. Specifically, the intermediate layer precursor layer may be a layer containing cerium oxide particles containing a rare earth element other than cerium and a solvent. Examples of rare earth elements other than cerium include lanthanum, samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium.

[0095] The intermediate layer precursor layer preferably contains lanthanum-doped cerium oxide (hereinafter also referred to as "LDC"). LDC is a cerium oxide (CeO ２ ) in the form of a solid solution (doped) of lanthanum. Lanthanum may exist at sites in the crystal lattice of cerium oxide by substituting for cerium sites, or it may exist at the grain boundaries of cerium oxide doped with a rare earth element. When both the air electrode-side intermediate layer 15 and the anode-side intermediate layer 16 are formed as the intermediate layer 17, the intermediate layer precursor layer for forming the air electrode-side intermediate layer 15 and the intermediate layer precursor layer for forming the anode-side intermediate layer 16 may be of the same type or different types.

[0096] Lanthanum is contained in the LDC for the purposes of improving the oxide ion conductivity of the entire fuel cell 10 and for the purposes of diffusing into the solid electrolyte layer precursor layer to form the solid electrolyte layer 11. For this purpose, the value of La / Ce, which is the atomic ratio of lanthanum to cerium in the LDC, is preferably 0.10 or more. Furthermore, since excessive lanthanum content actually reduces ion conductivity, the value of La / Ce is preferably 1.5 or less. From the same perspective, the value of La / Ce is more preferably 0.20 or more and 1.2 or less, and even more preferably 0.25 or more and 1.0 or less. The value of La / Ce is measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), or the like.

[0097] LDC is, for example, lanthanum oxide (La ２ O ３ ) and cerium oxide (La ２ O ３ ) in a predetermined ratio to obtain a mixed powder, which is then fired in an oxygen-containing atmosphere. LDC having a desired La / Ce value can be obtained by adjusting the mixing ratio of lanthanum oxide and cerium oxide. The La / Ce value may be increased to use a mixture of LDC and a compound containing La.

[0098] The intermediate layer precursor layer can be obtained, for example, by mixing the above-described LDC particles with a solvent to form a slurry, applying this slurry to a pre-formed air electrode 12 or anode 13 to form a coating film, and then removing at least a portion of the solvent from the coating film. Methods for manufacturing the air electrode 12 and anode 13 are well known in the art and require no further explanation. Wet coating methods such as screen printing, spin coating, and spray coating can be used as the coating method. Water and organic solvents can be used as the solvent. Examples of organic solvents that can be used include ethanol, isopropyl alcohol, terpineol, and toluene. The organic solvents can be used alone or in combination. Mixing can be performed using, for example, a rotation-revolution mixer, an ultrasonic homogenizer, a shaker, a thin film rotary mixer, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, an attritor, a ball mill, a vibrator mill, and a high-speed impeller mill. During mixing, additives such as dispersants, antifoaming agents, binders, and plasticizers may be used as needed. Alternatively, a green sheet may be produced using the slurry, and this green sheet may be used as the intermediate layer precursor layer.

[0099] <Solid Electrolyte Layer Precursor Layer> The solid electrolyte layer precursor layer prepared by this manufacturing method is a layer containing a first element and a second element (the first element and the second element will be described in detail later). The solid electrolyte layer precursor layer may be, for example, (i) a layer of a mixture containing a simple substance or compound of the first element and a simple substance or compound of the second element. Alternatively, the solid electrolyte layer precursor layer may be, for example, (ii) a layer containing a single compound containing the first element and the second element. By firing the solid electrolyte layer precursor layer having the aspect (i) or (ii), a solid electrolyte layer that is dense and has high oxide ion conductivity can be obtained, despite being fired at a low temperature.

[0100] In either embodiment (i) or (ii) of the solid electrolyte layer precursor layer, the first element is at least one element selected from the group consisting of Si and Ge. From the viewpoint of high oxide ion conductivity, the first element is preferably Si.

[0101] Whether the solid electrolyte layer precursor layer is in the form (i) or (ii), the second element is preferably at least one selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba. It is believed that the inclusion of the second element in the solid electrolyte layer precursor layer can lower the softening point and melting point of the solid electrolyte layer precursor layer, thereby facilitating densification of the solid electrolyte at low temperatures. Among these elements, from the viewpoint of high oxide ion conductivity, the second element is more preferably at least one selected from the group consisting of Al, Mg, In, Ti, Cr, Mn, Fe, Nb, B, Zn, P, W, and Mo, and even more preferably at least one selected from the group consisting of Al, Mg, and B.

[0102] Whether the solid electrolyte layer precursor layer is in the form (i) or (ii), it is preferable that the molar ratio of the second element to the first element in the solid electrolyte layer precursor layer be 0.50 or less, from the viewpoint of obtaining a solid electrolyte layer with high oxide ion conductivity by low-temperature firing. From this viewpoint, the molar ratio of the second element to the first element is more preferably 0.40 or less, and even more preferably 0.30 or less. From the same viewpoint as above, the molar ratio of the second element to the first element is preferably 0.010 or more, more preferably 0.050 or more, and even more preferably 0.10 or more. Below, matters specific to the form (i) and the form (ii) are respectively explained.

[0103] <Aspect (i)> When the first element is contained in the solid electrolyte layer precursor layer in the form of its compound, examples of the compound include oxides, hydroxides, nitrates, sulfates, halides, etc. Among these compounds, it is preferable to use oxides, from the viewpoint that a solid electrolyte layer having high oxide ion conductivity can be obtained by low-temperature firing.

[0104] In particular, when the first element is Si, Si is in the form of an oxide, for example, silicon oxide (SiO ２) is preferably contained in the solid electrolyte layer precursor layer from the viewpoint of obtaining a solid electrolyte layer having high oxide ion conductivity by low-temperature firing.

[0105] The same applies to the second element as to the first element, and when the second element is contained in the solid electrolyte layer precursor layer in the form of a compound thereof, examples of the compound include oxides, hydroxides, nitrates, sulfates, halides, etc. Among these compounds, it is preferable to use oxides, from the viewpoint that a solid electrolyte layer having high oxide ion conductivity can be obtained by low-temperature firing.

[0106] In particular, when the second element is Al, and Al is in the form of an oxide, for example, aluminum oxide (Al ２ O ３ ) is preferably contained in the solid electrolyte layer precursor layer from the viewpoint of obtaining a solid electrolyte layer having high oxide ion conductivity by low-temperature firing.

[0107] In addition to the first and second elements described above, the solid electrolyte layer precursor layer may contain one or more elements selected from the group consisting of La, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu (hereinafter, these elements may also be referred to as "third elements"). A solid electrolyte layer having high oxide ion conductivity can be obtained by including the third element or a compound containing the third element in the solid electrolyte layer precursor layer. From this viewpoint, it is more preferable that the third element include La or a compound containing La.

[0108] When the solid electrolyte layer precursor layer contains the first element, the second element, and the third element, the following aspects can be mentioned: (a) An aspect in which the solid electrolyte layer precursor layer contains the first element alone or a compound containing the first element, the second element alone or a compound containing the second element, and the third element alone or a compound containing the third element. (b) An aspect in which the solid electrolyte layer precursor layer contains the first element alone or a compound containing the first element, and compounds containing the second element and the third element. (c) An aspect in which the solid electrolyte layer precursor layer contains the second element alone or a compound containing the second element, and compounds containing the first element and the third element.

[0109] In the case of (a), examples of the compound containing a third element include oxides, hydroxides, nitrates, sulfates, halides, etc. Among these compounds, it is preferable to use oxides or hydroxides, from the viewpoint that a solid electrolyte layer having high oxide ion conductivity can be obtained by low-temperature firing.

[0110] In particular, when the third element is La, La is in the form of its oxide or hydroxide, for example, La ２ O ３ or La(OH) ３ It is preferable that the solid electrolyte layer precursor layer contains the metal oxide in this state.

[0111] In any of the cases (a) to (c), when the solid electrolyte layer precursor layer contains a third element, it is preferable to set the molar ratio of the third element to the first element to less than 1, from the viewpoint of obtaining a highly dense solid electrolyte layer by low-temperature firing. By setting the molar ratio of the third element to the first element to less than 1, a highly dense solid electrolyte layer can be obtained by low-temperature firing. Furthermore, since the volume expansion of the solid electrolyte layer precursor layer due to the diffusion of the rare earth element into the solid electrolyte layer precursor layer can be utilized, it is thought that a highly dense solid electrolyte layer is more likely to be obtained. From this viewpoint, the molar ratio of the third element to the first element is more preferably 0.8 or less, even more preferably 0.7 or less, and even more preferably 0.5 or less. Furthermore, from the viewpoint of obtaining a solid electrolyte layer with high oxide ion conductivity, the molar ratio of the third element to the first element is preferably 0.1 or more, even more preferably 0.15 or more, and even more preferably 0.3 or more.

[0112] The solid electrolyte layer precursor layer can be obtained, for example, by mixing the above-mentioned first element alone or a compound containing the first element, the second element alone or a compound containing the second element, and the third element alone or a compound containing the third element with a solvent to form a slurry, applying this slurry to the intermediate layer precursor layer to form a coating film, and removing at least a part of the solvent from this coating film. Alternatively, the slurry may be used to produce a green sheet, and this green sheet may be used as the solid electrolyte layer precursor layer.

[0113] <Aspect (ii)> In aspect (ii), the solid electrolyte layer precursor layer is a layer containing a single compound containing a first element and a second element. Examples of this compound include a composite oxide containing the first element and the second element. In particular, it is preferable that the first element is Si and the second element is Al, and the solid electrolyte layer precursor layer contains an oxide containing Si and Al, from the viewpoint of obtaining a solid electrolyte layer with high oxide ion conductivity by low-temperature firing.

[0114] As in embodiment (i), in embodiment (ii), the solid electrolyte layer precursor layer may also contain a third element. Details of the third element are the same as those described in embodiment (i). The third element preferably constitutes a single compound together with the first and second elements. For example, the solid electrolyte layer precursor layer preferably contains a single compound containing the first, second, and third elements. Examples of this compound include a composite oxide containing the first, second, and third elements. Alternatively, the third element may be contained in the solid electrolyte layer precursor layer in the form of a simple substance of the third element or a compound containing the third element. In this case, the solid electrolyte layer precursor layer contains a compound containing the first and second elements, and a simple substance of the third element or a compound containing the third element.

[0115] In the embodiment (ii), when the solid electrolyte layer precursor layer contains the first element, the second element, and the third element, the molar ratio of the third element to the first element is preferably less than 1, more preferably 0.9 or less, and even more preferably 0.8 or less. From the same viewpoint as above, the molar ratio of the third element to the first element is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more.

[0116] In the embodiment (ii), the solid electrolyte layer precursor layer can be obtained, for example, by mixing a single compound containing the first, second, and third elements described above with a solvent to form a slurry, applying the slurry to the intermediate layer precursor layer to form a coating film, and removing at least a portion of the solvent from the coating film. The mixing method and the slurry application method can be the same as those used to form the intermediate layer precursor layer. Alternatively, a green sheet can be produced using the slurry, and the green sheet can be used as the solid electrolyte layer precursor layer.

[0117] <Step 2> In this step, the laminate obtained in Step 1 is fired to form a solid electrolyte layer from the solid electrolyte layer precursor layer. In this manufacturing method, by using the above-described solid electrolyte layer precursor layer, the firing of the laminate can be performed at a lower temperature than conventional methods. As a result, a solid electrolyte layer can be formed by a simple process without firing at a high temperature above 1400°C or using a vacuum deposition apparatus such as ALD. The firing of the laminate can be performed at 1400°C or lower, preferably 1350°C or lower, and more preferably 1320°C or lower. Furthermore, from the viewpoint of imparting high oxide ion conductivity to the solid electrolyte layer and reliably forming an intermediate layer containing the second component, the firing of the laminate is preferably performed at a temperature above 1000°C, more preferably 1100°C or higher. The firing atmosphere can be an oxygen-containing atmosphere such as air, or an inert atmosphere such as nitrogen and argon. From the viewpoint of imparting high oxide ion conductivity to the solid electrolyte layer and reliably forming an intermediate layer containing the second component, using an oxygen-containing atmosphere is advantageous. The firing time is adjusted so that the solid electrolyte layer exhibits sufficient oxide ion conductivity. Generally, a firing time of 1 hour or more and 30 hours or less is used to exhibit satisfactory oxide ion conductivity in the solid electrolyte layer.

[0118] By firing the laminate, the rare earth element, e.g., lanthanum, contained in the intermediate layer precursor layer diffuses into the solid electrolyte layer precursor layer. The rare earth element diffused into the solid electrolyte layer precursor layer reacts with the first and second elements contained in the solid electrolyte layer precursor layer to produce an oxide-ion conductive oxide containing at least the rare earth element and the first and second elements. This reaction forms a solid electrolyte layer containing this oxide. The produced oxide-ion conductive oxide preferably has an apatite-type crystal structure, since this can enhance the oxide-ion conductivity of the solid electrolyte layer. Meanwhile, with regard to the intermediate layer precursor layer, while a portion of the rare earth element contained in the intermediate layer precursor layer diffuses into the solid electrolyte layer precursor layer, the remaining rare earth element remains in the intermediate layer precursor layer. Therefore, the intermediate layer formed from the intermediate layer precursor layer contains cerium oxide (first component) doped with a rare earth element (except cerium). In addition, the first element diffused from the solid electrolyte layer precursor layer to the intermediate layer precursor layer reacts with the rare earth element contained in the intermediate layer precursor layer to generate the second component. That is, by firing the laminate, an intermediate layer containing the first component and the second component is formed.

[0119] In addition, by incorporating the second component or a precursor thereof into the intermediate layer precursor layer in advance, it is possible to form an intermediate layer containing the first component and the second component without relying on the diffusion of the first element from the solid electrolyte layer precursor layer. ９．３３ Si ６ O ２６ The "precursor of the second component" refers to a material that is converted into the second component by the firing in step 2, for example, La ２ SiO ５Examples include the second component or its precursor contained in the intermediate layer precursor layer. The amount of the second component or its precursor contained in the intermediate layer precursor layer is preferably 10 parts by mass or more and 80 parts by mass or less, more preferably 20 parts by mass or more and 70 parts by mass or less, and even more preferably 30 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the intermediate layer precursor layer. When this intermediate layer precursor layer is used, the firing temperature of the laminate in step 2 is preferably 900°C or more and 1400°C or less, more preferably 1000°C or more and 1350°C or less, and even more preferably 1100°C or more and 1320°C or less. The firing atmosphere in step 2 can be an oxygen-containing atmosphere such as air, an inert atmosphere such as nitrogen or argon, or a reducing atmosphere containing hydrogen.

[0120] The above procedure results in a fired laminate. This laminate (electrochemical half cell) includes the cathode 12 or anode 13, the intermediate layer 17 thereon, and the solid electrolyte layer 11 thereon. Another intermediate layer 17 is formed on the solid electrolyte layer 11 of this laminate using the procedure described above, and the anode 13 or cathode 12 is then formed thereon by a conventional method, thereby obtaining the desired fuel cell 10. To form the other intermediate layer 17 on the solid electrolyte layer 11, wet coating methods such as screen printing, spin coating, and spray coating, PVD methods (such as sputtering and pulse laser deposition), and CVD methods can also be used.

[0121] 1 , the fuel cell 10 having the support layer 14 may be manufactured by forming the anode 13 on the support layer 14 by a conventional method, then forming the intermediate layer precursor layer and the solid electrolyte layer precursor layer by the above-described method, and then performing the above-described firing. Even when the support layer 14 is made of a metal, for example, the temperature range for firing the intermediate layer precursor layer and the solid electrolyte layer precursor layer can be made lower than in the past, which has the advantage that the metal support layer 14 is less susceptible to thermal damage.

[0122] The fuel cell thus obtained can be used, for example, as a fuel cell including the same. The electrochemical cell of the present invention can be used not only as a solid oxide fuel cell but also as a solid oxide electrolysis cell. The solid oxide electrolysis cell can be used, for example, as an electrolysis device including the same.

[0123] Although the present invention has been described above based on preferred embodiments thereof, the present invention is not limited to these embodiments. For example, in the above embodiment, the intermediate layer 17 is disposed both between the air electrode 12 and the solid electrolyte layer 11 and between the anode 13 and the solid electrolyte layer 11. However, instead, the intermediate layer 17 may be disposed only between the air electrode 12 and the solid electrolyte layer 11, or only between the anode 13 and the solid electrolyte layer 11. When the intermediate layer 17 is disposed only on one of the air electrode 12 and the anode 13, it is preferable to dispose the intermediate layer 17 only between the air electrode 12 and the solid electrolyte layer 11 from the viewpoint of effectively improving the oxide ion conductivity of the entire fuel cell 10.

[0124] The above-described embodiments of the present invention encompass the following technical concepts: [1] An electrochemical cell comprising an air electrode, a solid electrolyte layer containing a solid electrolyte, and an anode stacked in this order, the electrochemical cell having an intermediate layer between the air electrode and the solid electrolyte layer and / or between the anode and the solid electrolyte, the solid electrolyte layer having a main phase made of an oxide ion conductor, at least one of the intermediate layers comprising: a first component which is cerium oxide containing a rare earth element other than cerium; and a second component which is an oxide ion conductor different from the first component, the amount of substance of zirconium element in the intermediate layer being 10 mol % or less based on the total amount of substance of all metal elements in the intermediate layer. [2] The electrochemical cell according to [1], further comprising: an intermediate layer containing the first component and the second component between the anode and the solid electrolyte. [3] The electrochemical cell according to [1] or [2], wherein the solid electrolyte layer has a main phase made of an apatite-type composite oxide containing a rare earth element and a T element (T is one or more selected from the group consisting of silicon and germanium). [4] The electrochemical cell according to [3], wherein the solid electrolyte layer has a main phase made of an apatite-type composite oxide containing lanthanum and silicon. [5] The electrochemical cell according to any one of [1] to [4], wherein the second component is an apatite-type composite oxide containing a rare earth element and a T element (T is one or more selected from the group consisting of silicon and germanium). [6] The electrochemical cell according to [5], wherein the second component is an apatite-type composite oxide containing lanthanum and silicon. [7] The electrochemical cell according to any one of [1] to [6], wherein in the intermediate layer containing a first component and a second component, a mass ratio M2 / M1 of a content M2 of the second component to a content M1 of the first component is 0.05 or more and 4.00 or less. [8] The electrochemical cell according to any one of [1] to [7], further comprising a support layer, in which the air electrode, the solid electrolyte layer, the fuel electrode, and the support layer are stacked in this order. [9] The electrochemical cell according to any one of [1] to [8], which is a solid oxide fuel cell.

[10] The electrochemical cell according to any one of [1] to [8], which is a solid oxide electrolysis cell.

[11] An electrochemical half-cell having a solid electrolyte layer, an intermediate layer, and an anode laminated in this order, wherein the solid electrolyte layer has a main phase made of an oxide ion conductor, the intermediate layer contains: a first component which is cerium oxide containing a rare earth element other than cerium; and a second component which is an oxide ion conductor different from the first component, and wherein the amount of substance of zirconium element in the intermediate layer is 10 mol % or less based on the total amount of substance of all metal elements in the intermediate layer.

[0125] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0126] Example 1 (1) Production of First Laminate A first laminate was produced by the following procedure, in which a first sheet (corresponding to the solid electrolyte layer), a second sheet (corresponding to the fuel electrode-side intermediate layer), a third sheet (corresponding to the fuel electrode), and a support layer sheet (corresponding to the support layer) were laminated in this order. ２ Si ２ O ７ 9.005 g of powder was mixed with 4.934 g of ethanol solution to form a slurry, which was then mixed with 0.831 g of PVB resin powder as a binder and 0.955 g of dibutyl phthalate as a plasticizer to obtain a slurry, which was then formed into a green sheet using an applicator. The thickness gap of the applicator was 40 μm. The second sheet was made of La ２ Si ２ O ７ La instead of powder ０．５ Ce ０．５ O １．７５ The third sheet was produced in the same manner as the first sheet, except that 10.104 g of La powder, 9.242 g of ethanol, 1.136 g of PVB resin powder, and 1.164 g of dibutyl phthalate were used. ２ Si ２ O ７Instead of powder, 7.291 g of nickel oxide powder and La ０．５ Ce ０．５ O １．７５ The support layer sheet was produced in the same manner as the first sheet except that 9.008 g of NiO powder, 15.75 g of ethanol, 1.445 g of PVB resin powder, and 1.514 g of dibutyl phthalate were used. ９．３３ Si ６ O ２６ 19.657 g of powder, 30.340 g of ethanol, and 10.115 g of spherical microparticles (average particle size 30 μm) composed of cross-linked polymethyl methacrylate as a pore-forming agent were mixed to form a slurry, and then 4.953 g of PVB resin powder as a binder and 6.219 g of dibutyl phthalate as a plasticizer were further mixed to obtain a slurry. This slurry was then formed into a green sheet using an applicator. The applicator thickness gap was 40 μm. The resulting first sheet was 20 μm thick. The second sheet was 19 μm thick. The third sheet was 33 μm thick. The support layer sheet was 220 μm thick. Next, the first sheet, second sheet, third sheet, and support layer sheet were stacked in this order and thermocompression-bonded in one direction to obtain a first laminate. Thermocompression bonding was performed at 60°C and 0.3 MPa.

[0127] (2) Heating of the first laminate The obtained first laminate was heated in an air atmosphere at 1600° C. for 5 hours, thereby obtaining a sintered body of the first laminate.

[0128] (3) Formation of the air electrode side intermediate layer Sm ０．２ Ce ０．８ O １．９ 4.5 g of the powder was weighed out. This powder was mixed with 3.0 g of a solution in which 5 wt % of ethyl cellulose was dissolved in α-terpineol to prepare a slurry. This slurry was applied to a thickness of 5 μm on the surface of the solid electrolyte layer in the sintered body opposite the surface facing the fuel electrode-side intermediate layer, to obtain a third laminate. This third laminate was heated at 1400°C for 1 hour in an air atmosphere.

[0129] (4) Formation of the air electrode La ０．６ Sr ０．４ Co０．２ Fe ０．８ O ３－δ 3.0 g of the powder was weighed out. This powder was mixed with 4.5 g of a solution in which 5 wt % of ethyl cellulose was dissolved in α-terpineol to prepare a slurry. This slurry was applied to a thickness of 10 μm on the surface of the air electrode-side intermediate layer opposite the surface facing the solid electrolyte layer, to obtain a second laminate. This second laminate was heated at 900°C for 1 hour in an air atmosphere to form an air electrode. In this way, the desired electrochemical cell was obtained.

[0130] [Example 2] (1) Preparation of Support A laminate having a structure in which a porous support layer sheet (corresponding to a support layer) is sandwiched between dense support layer sheets was produced by the following procedure. The dense support layer is a layer for improving the applicability of the slurry in the subsequent process. The dense support layer sheet was prepared by mixing 7.293 g of nickel oxide powder and La ９．３３ Si ６ O ２６ The porous support layer was prepared by mixing 7.92 g of powder with 16.0368 g of ethanol to form a slurry, which was then mixed with 1.1592 g of PVB resin powder as a binder and 6.215 g of dibutyl phthalate as a plasticizer. The slurry was then formed into a green sheet using an applicator. The thickness gap of the applicator was 150 μm. The porous support layer sheet was prepared by mixing 20.755 g of NiO powder, 20.755 g of La powder, and 16.0368 g of ethanol. ９．３３ Si ６ O ２６ A slurry was prepared by mixing 19.675 g of powder, 31.3378 g of ethanol, and 7.995 g of spherical microparticles (average particle size 30 μm) composed of cross-linked polymethyl methacrylate (a pore-forming agent). Then, 3.9672 g of PVB resin powder (a binder) and 6.215 g of dibutyl phthalate (a plasticizer) were added to obtain a slurry. This slurry was then formed into a green sheet using an applicator. The applicator thickness gap was 900 μm. The porous support layer sheet was sandwiched between dense support layer sheets and thermocompressed from one direction to obtain a laminate.

[0131] The laminate obtained by the above method was heated at 1600°C for 3 hours in an air atmosphere. One side of the laminate was polished, and a support body, which was a sintered body of the laminate, was obtained. The support body ensures the strength of the electrochemical cell and allows gas to pass through.

[0132] (2) Preparation of slurry for fuel electrode layer 4.000 g of NiO powder and 6.000 g of La synthesized by the method described below ０．５ Ce ０．５ O ２－δ Ethanol was added to the powder to form a slurry. This slurry was mixed and milled for 1 hour using a planetary ball mill at 300 rpm. Zirconia balls were used as the milling media. The ethanol was removed by evaporation from the slurry, and the resulting powder was recovered. This powder was dispersed in α-terpineol containing 5% ethyl cellulose to form a slurry. The amount of powder was 7.000 g, and the amount of α-terpineol containing ethyl cellulose was 3.00 g. This slurry was mixed to prepare a slurry for the fuel electrode layer. (3) Preparation of Slurry for Intermediate Layer Precursor Layer 29.176 g of La ２ O ３ powder and 30.978 g of CeO ２ Ethanol was added to the powder to form a slurry. This slurry was mixed and ground in a uniaxial ball mill for 15 hours. Zirconia balls were used as the grinding media. The ethanol was removed by volatilization from the slurry, and the resulting powder was collected. This powder was fired at 1300°C for 10 hours in an air atmosphere to obtain a fired powder. Ethanol was added to the resulting fired powder to form a slurry. This slurry was ground in a uniaxial ball mill for 50 hours. Zirconia balls were used as the grinding media. The ethanol was removed by volatilization from the slurry, and the fired powder (La ０．５ Ce ０．５ O ２－δ The calcined powder was dispersed in α-terpineol containing 5% ethyl cellulose to form a slurry. The amount of powder was 2.34 g, and the amount of α-terpineol containing ethyl cellulose was 1.00 g. The resulting slurries were mixed to prepare a slurry for the intermediate layer precursor layer.

[0133] (4) Preparation of slurry for solid electrolyte precursor layer: 2.0540 g of SiO ２ powder, 0.3486 g Al ２ O ３ powder and 2.5974 g of La(OH) ３ Ethanol was added to the powder to form a slurry. This slurry was mixed and milled for 1 hour using a planetary ball mill at a rotation speed of 250 rpm. Zirconia balls were used as the milling media. The ethanol was evaporated and removed from the slurry, and the resulting powder was recovered. This powder was dispersed in α-terpineol containing 5% ethyl cellulose to form a slurry. The amount of powder was 5.0000 g, and the amount of α-terpineol containing ethyl cellulose was 6.9185 g. This slurry was mixed and degassed to prepare a slurry for the solid electrolyte layer precursor layer.

[0134] (5) Preparation of Fuel Electrode Layer The slurry for the fuel electrode layer prepared in (2) was applied to one surface of the support prepared in (1) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical permeability of 50 μm was used for the screen printing. The resulting coating film was dried at 120°C to prepare the fuel electrode layer. (6) Preparation of Intermediate Layer Precursor Layer The slurry for the intermediate layer precursor layer prepared in (3) was applied to one surface of the fuel electrode layer prepared in (5) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical permeability of 50 μm was used for the screen printing. The resulting coating film was dried at 120°C to prepare the intermediate layer precursor layer.

[0135] (7) Preparation of Solid Electrolyte Layer Precursor Layer and Laminate The slurry for the solid electrolyte layer precursor layer prepared in (4) was applied onto the intermediate layer precursor layer prepared in (6) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical permeation volume of 50 μm was used for the screen printing. The resulting coating film was dried at 120°C. In this manner, a solid electrolyte layer precursor layer was prepared. As a result, a laminate was obtained in which the fuel electrode layer, intermediate layer precursor layer, and solid electrolyte layer precursor layer were laminated in this order on the support.

[0136] (8) Firing of Laminate The laminate obtained in (7) was fired in an air atmosphere at a temperature of 1,300°C for 20 hours. This resulted in the formation of an intermediate layer from the intermediate layer precursor layer and a solid electrolyte layer from the solid electrolyte layer precursor layer. In this way, an electrochemical half-cell including a support, an anode, an anode-side intermediate layer, and a solid electrolyte was obtained.

[0137] (9) Formation of the air electrode side intermediate layer Sm ０．２ Ce ０．８ O １．９ The powder was mixed with a solvent to prepare a slurry, which was then applied to the surface of the solid electrolyte layer in the sintered body opposite to the surface facing the fuel electrode-side intermediate layer, and heated at 1250°C for 1 hour in an air atmosphere.

[0138] (10) Formation of the air electrode La ０．６ Sr ０．４ Co ０．２ Fe ０．８ O ３－δ 3.0 g of the powder was weighed out. This powder was mixed with 4.5 g of a solution in which 5% by mass of ethyl cellulose was dissolved in α-terpineol to prepare a slurry. This slurry was applied to the surface of the air electrode-side intermediate layer opposite the surface facing the solid electrolyte layer, to obtain a second laminate. This second laminate was heated at 900°C for 1 hour in an air atmosphere to form an air electrode. In this way, the desired electrochemical cell was obtained.

[0139] Comparative Example 1 (1) Production of First Laminate A first laminate was produced by the following procedure, in which a first sheet (corresponding to the solid electrolyte layer), a second sheet (corresponding to the fuel electrode-side intermediate layer), a third sheet (corresponding to the fuel electrode), and a support layer sheet (corresponding to the support layer) were laminated in this order. ２ 1.600 g of powder and Al ２ O ３The powder (0.271 g) was mixed with 5.7208 g of ethanol solution to form a slurry, which was then mixed with 0.5332 g of PVB resin powder (a binder) and 0.774 g of dibutyl phthalate (a plasticizer) to obtain a slurry. This slurry was then formed into a green sheet using an applicator. The gap in the applicator thickness was 80 μm. The second sheet was made by replacing the powder used in the first sheet with La. ０．５ Ce ０．５ O １．７５ The third sheet was produced in the same manner as the first sheet, except that 10.109 g of the powder was used, and 9.467 g of ethanol, 0.904 g of PVB resin powder, and 1.15 g of dibutyl phthalate were used instead of the powder used in the first sheet. ９．３３ Si ６ O ２６ The first sheet was prepared in the same manner as the first sheet, except that 7.92 g of SUS430 powder, 16.0368 g of ethanol, 1.1592 g of PVB resin powder, and 1.512 g of dibutyl phthalate were used. The support layer sheet was prepared by mixing 78.839 g of SUS430 powder, 11.168 g of ethanol, and 2.599 g of spherical microparticles (average particle size 30 μm) composed of cross-linked polymethyl methacrylate as a pore-forming agent to form a slurry, followed by further mixing 1.892 g of PVB resin powder as a binder and 1.600 g of dibutyl phthalate as a plasticizer to obtain a slurry. This slurry was then formed into a green sheet using an applicator. The applicator thickness gap was 980 μm. The first sheet, second sheet, third sheet, and support layer sheet were stacked in this order and thermocompressed from one direction to obtain a first laminate.

[0140] (2) Heating of the first laminate The obtained first laminate was heated to 3.5% by volume H ２ N containing ２ The first laminate was heated at 1200° C. for 10 hours in an atmosphere to obtain a sintered body (electrochemical half cell).

[0141] [Evaluation] The electrochemical cells and electrochemical half-cells obtained in the examples and comparative examples were evaluated as follows.

[0142] [Determination of Crystal Structure of Main Phase of Solid Electrolyte Layer] The crystal structure of the main phase of the solid electrolyte layer was determined by XRD analysis of the solid electrolyte side of the electrochemical half-cell or by EBSD analysis of a cross section approximately parallel to the thickness direction of the electrochemical cell that had been processed by CP. As a result, it was confirmed that the main phase of the solid electrolyte layer was an apatite-type lanthanum silicate phase in all electrochemical cells and electrochemical half-cells.

[0143] [Measurement of Composition of Fuel Electrode-Side Intermediate Layer and Solid Electrolyte Layer] The composition of the fuel electrode-side intermediate layer (the composition of the entire fuel electrode-side intermediate layer, the composition of the crystalline phase consisting of the first component, and the composition of the crystalline phase consisting of the second component) and the composition of the main phase of the solid electrolyte layer were measured by analysis using SEM (scanning electron microscope)-EDS. Specifically, a cross section of the electrochemical cell or electrochemical half-cell approximately parallel to the thickness direction was first processed with a cross-section polisher (CP) to obtain a cross section with minimal irregularities. Next, a backscattered electron image of the cell cross section was obtained, and this backscattered electron image was subjected to SEM-EDS analysis. The proportion (mol %) of each metal element detected in this analysis relative to the total metal elements is shown in Table 1. Furthermore, backscattered electron images of cross sections along the thickness direction of the electrochemical cells and electrochemical half-cells of each Example and Comparative Example are shown in Figures 3 to 5.

[0144] [Phase Identification of Fuel Electrode-Side Intermediate Layer] Phase identification of the fuel electrode-side intermediate layer was performed using the following procedure. First, a backscattered electron image of the cell cross section that had been subjected to CP processing was obtained. When it was determined that the composition of the intermediate layer was uniform based on this backscattered electron image (Comparative Example 1), the phase was identified from the results of the SEM-EDS analysis. When it was determined that the composition of the fuel electrode-side intermediate layer was not uniform (Examples 1 and 2), the phase was identified using EBSD (electron backscattered diffraction) analysis. EBSD analysis was performed on a cross section approximately parallel to the thickness direction of the electrochemical cell that had been subjected to CP processing, and it was found that the fuel electrode-side intermediate layer contained an apatite-type lanthanum silicate phase (a crystalline phase consisting of the second component) and CeO ２ It was confirmed that the intermediate layer on the fuel electrode side contained a crystalline phase (a crystalline phase consisting of the first component). The constituent phases of the intermediate layer on the fuel electrode side confirmed by the above method are shown in Table 1.

[0145] [Measurement of M2 / M1] Based on the composition of the entire fuel electrode-side intermediate layer, the composition of the crystalline phase consisting of the first component, and the composition of the crystalline phase consisting of the second component measured by the above-mentioned method, the molar ratio of the crystalline phase consisting of the first component to the crystalline phase consisting of the second component was determined so that these three compositions were consistent with each other. This molar ratio was converted to a mass ratio (M2 / M1) using the molecular weights of the crystalline phase consisting of the first component and the crystalline phase consisting of the second component. The results are shown in Table 1.

[0146] [Measurement of Maximum Power Density] For Example 1, 100 ccm of hydrogen was flowed as fuel gas to the anode at 1700°C, and 80 ccm of nitrogen and 20 ccm of oxygen were flowed to the cathode. The voltage was swept at 10 mV / min from OCV to OCV-0.9 V, and the voltage and current values ​​were measured. The maximum value obtained by multiplying the measured voltage and current density values ​​was taken as the maximum power density. For Example 2, the hydrogen flowing through the anode was humidified by bubbling it through water at room temperature. The maximum power density was calculated in the same manner as in Example 1 except for the above. For Comparative Example 1, as shown in Figure 5, delamination occurred between the solid electrolyte layer and the anode-side intermediate layer, and it was determined that evaluation of the maximum power density was not possible. These results are shown in Table 1.

[0147]

[0148] XRD analysis of the solid electrolyte surface of the electrochemical half-cells and EBSD analysis of the cross-sections of the electrochemical cells confirmed that the main phase of the solid electrolyte layer in each example and comparative example was an apatite-type lanthanum silicate phase. Furthermore, EBSD analysis of the cross-sections of the electrochemical cells revealed that the first and second components of the fuel electrode-side intermediate layer in each example were ceria and apatite-type lanthanum silicate phases. As is clear from Figures 3 to 5 , the electrochemical cells of the examples in which the intermediate layer contained both the first and second components had fewer voids between the solid electrolyte layer and the intermediate layer and stronger adhesion between the two layers compared to the electrochemical half-cell of the comparative example in which the intermediate layer did not contain the second component. Therefore, the electrochemical cells of each example had high durability. Furthermore, the intermediate layers of each example exhibited high maximum power densities due to the first and second components both being oxide-ion conductors.

[0149] According to the present invention, an electrochemical cell that combines durability and electrochemical properties is provided.

Claims

1. An electrochemical cell comprising an air electrode, a solid electrolyte layer containing a solid electrolyte, and an anode laminated in this order, the electrochemical cell having an intermediate layer at least one between the air electrode and the solid electrolyte layer and between the anode and the solid electrolyte, the solid electrolyte layer having a main phase made of an oxide ion conductor, at least one of the intermediate layers comprising: a first component which is cerium oxide containing a rare earth element other than cerium; and a second component which is an oxide ion conductor different from the first component, the amount of substance of zirconium element in the intermediate layer being 10 mol % or less based on the total amount of substance of all metal elements in the intermediate layer.

2. The electrochemical cell according to claim 1, further comprising an intermediate layer between said anode and said solid electrolyte, said intermediate layer comprising a first component and a second component.

3. The electrochemical cell according to claim 1, wherein the solid electrolyte layer has a main phase made of an apatite-type composite oxide containing a rare earth element and an element T (wherein T is at least one element selected from the group consisting of silicon and germanium).

4. The electrochemical cell according to claim 3, wherein the solid electrolyte layer has a main phase made of an apatite-type composite oxide containing lanthanum and silicon.

5. The electrochemical cell according to claim 1, wherein the second component is an apatite-type composite oxide containing a rare earth element and an element T (wherein T is at least one element selected from the group consisting of silicon and germanium).

6. The electrochemical cell according to claim 5, wherein the second component is an apatite-type composite oxide containing lanthanum and silicon.

7. The electrochemical cell according to claim 1, wherein in the intermediate layer containing the first component and the second component, the mass ratio M2 / M1 of the content M2 of the second component to the content M1 of the first component is 0.05 or more and 4.00 or less.

8. The electrochemical cell according to claim 1, further comprising a support layer, wherein the air electrode, the solid electrolyte layer, the fuel electrode, and the support layer are stacked in this order.

9. The electrochemical cell according to any one of claims 1 to 8, which is a solid oxide fuel cell.

10. The electrochemical cell of any one of claims 1 to 8, which is a solid oxide electrolysis cell.

11. An electrochemical half-cell comprising a solid electrolyte layer, an intermediate layer, and a fuel electrode stacked in this order, wherein the solid electrolyte layer has a main phase made of an oxide ion conductor, and the intermediate layer comprises: a first component which is cerium oxide containing a rare earth element other than cerium; and a second component which is an oxide ion conductor different from the first component; and wherein the amount of zirconium in the intermediate layer is 10 mol % or less based on the total amount of substance of all metal elements in the intermediate layer.

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