Electrochemical cell

Abstract

Provided is a fuel electrode support-type electrochemical cell (10) in which an air electrode (12), a solid electrolyte layer (11) containing a solid electrolyte, a fuel electrode (13), and a support layer (14) are stacked in this 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 air electrode (12), the fuel electrode (13), the solid electrolyte layer (11), the intermediate layer (17), and the support layer (14) contain the same rare earth element. The rare earth element is preferably lanthanum.

Description

electrochemical cell

[0001] The present invention relates to electrochemical cells.

[0002] Solid electrolyte electrochemical cells are required to have high oxide ion conductivity. For example, Patent Document 1 proposes a solid electrolyte junction having an anode, a cathode, a solid electrolyte, and an intermediate layer, the intermediate layer being made of cerium oxide containing lanthanum and a rare earth element, and the solid electrolyte containing lanthanum oxide. The solid electrolyte junction described in this document is also described as having high ion conductivity.

[0003] US2021 / 0036354A1

[0004] Although various solid electrolyte assemblies with improved oxide ion conductivity have been proposed, as described in Patent Document 1, there is a demand for further improving the oxide ion conductivity of the electrochemical cell as a whole to obtain high electrochemical properties. Therefore, an object of the present invention is to provide an electrochemical cell with improved electrochemical properties.

[0005] The present invention provides an anode-supported electrochemical cell in which an air electrode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer are stacked in this order, the electrochemical cell having an intermediate layer at least either between the air electrode and the solid electrolyte layer or between the anode and the solid electrolyte, and the air electrode, the anode, the solid electrolyte layer, the intermediate layer, and the support layer all contain the same rare earth element.

[0006] Fig. 1 is a schematic diagram of a cross section along the thickness direction showing one embodiment of an electrochemical cell of the present invention. Fig. 2 is a schematic diagram of a cross section along the thickness direction showing another embodiment of an electrochemical cell of the present invention. Fig. 3 is an example of a scanning electron microscope image of a cross section along the thickness direction of the electrochemical cell shown in Fig. 1.

[0007] The present invention will be described below based on preferred embodiments with reference to the drawings. FIG. 1 shows a fuel cell 10, which is one embodiment of an electrochemical cell of the present invention. The fuel cell 10 shown in the figure is an anode-supported fuel cell in which a cathode 12, a layer containing a solid electrolyte (hereinafter also referred to as a "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, namely, the cathode 12 and the anode 13. In other words, the cathode 12 and the anode 13 are located on different sides of the solid electrolyte layer 11.

[0008] 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.

[0009] 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.

[0010] 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. In order to reduce the electrical resistance in the fuel cell 10, it is important to increase the oxide ion conductivity of the solid electrolyte layer 11. However, even if the solid electrolyte layer 11 is formed using a material with high oxide ion conductivity, if the oxide ion conductivity between the solid electrolyte layer 11 and the anode 13 and / or the air electrode 12 is low, there is a limit to how much the oxide ion conductivity of the fuel cell 10 as a whole can be increased. As a result of studies by the present inventors, it has been found that when 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"), the oxide ion conductivity of the fuel cell 10 as a whole is increased, and high power generation characteristics (electrochemical characteristics) can be obtained. The reason for this is not clear, but the inventors speculate that by having the same rare earth element in each layer, the interface resistance between each layer is reduced, improving the conductivity of the entire cell.

[0011] 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.

[0012] Instead of or in addition to containing a common rare earth element, the support layer 14 may contain a metal or an alloy. The term "metal" refers to a substance whose constituent element is only one type of metal element. Because metals and alloys have toughness, if the support layer 14 contains a metal or an alloy, cracking of the solid electrolyte layer 11 can be effectively suppressed even if the support layer 14 does not contain 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.

[0013] 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. In particular, it is preferable to use an oxide of a common rare earth element as the solid electrolyte, as this further increases the oxide ion conductivity. Furthermore, from the viewpoint of further increasing the oxide ion conductivity of the fuel cell 10, it is preferable that the solid electrolyte contains a composite oxide.

[0014] For example, when the common rare earth element is lanthanum, examples of the oxide of the common rare earth element include a composite oxide containing lanthanum and gallium, a composite oxide obtained by adding strontium, magnesium, or cobalt to the composite oxide, a composite oxide containing lanthanum and silicon, 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 preferred due to its high oxide-ion conductivity. Furthermore, when the common rare earth element is samarium, examples of the oxide of the common rare earth element 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 preferred due to its high oxide-ion conductivity.

[0015] 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. The apatite-type composite oxide contains lanthanum, which is a trivalent element, silicon, which is a tetravalent element, and O, and has 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 ２６When 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.

[0016] Another example of the solid electrolyte is a solid electrolyte having the general formula: ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚ Examples 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.

[0017] 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.

[0018] 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.

[0019] Among the composite oxides represented by the above formula, it is preferable to use a composite oxide in which A contains lanthanum, in view of further increasing the oxide ion conductivity. Specific examples of composite oxides in which A contains lanthanum 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.

[0020] 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.

[0021] 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.

[0022] 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)

[0023] 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.

[0024] 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.

[0025] If the solid electrolyte layer 11 contains an excessive amount of cerium element, the oxide ion conductivity of the solid electrolyte layer 11 may decrease. From the viewpoint of suppressing this decrease in oxide ion conductivity and improving the power generation characteristics (electrochemical characteristics) of the fuel cell 10 as a whole, the content of cerium element in the solid electrolyte layer 11 is preferably 8 mol % or less, more preferably 6 mol % or less, and even more preferably 4 mol % or less, relative to the total content of all rare earth elements in the solid electrolyte layer 11. Ideally, the solid electrolyte layer 11 does not contain cerium element.

[0026] Similarly, if the solid electrolyte layer 11 contains an excessive amount of samarium, the oxide ion conductivity of the solid electrolyte layer 11 may decrease. From the viewpoint of suppressing this decrease in oxide ion conductivity and improving the electrochemical characteristics of the electrochemical cell 10 as a whole, the content of samarium in the solid electrolyte layer 11 is preferably 8 mol % or less, more preferably 4 mol % or less, and even more preferably 2 mol % or less, with respect to the total content of all rare earth elements in the solid electrolyte layer 11. Ideally, the solid electrolyte layer 11 does not contain samarium.

[0027] The intermediate layer 17 is made of cerium oxide (hereinafter referred to as "La-Ln") containing lanthanum and rare earth elements (excluding lanthanum and cerium). １ In this case, the rare earth elements other than lanthanum or lanthanum and cerium are common rare earth elements. 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.

[0028] La-Ln constituting the intermediate layer 17 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 intermediate layer 17 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 intermediate layer 17 is preferably composed of 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 the La-Ln cerium oxide constituting both intermediate layers 15 and 16 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.

[0029] La-Ln １In 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 １ The 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.

[0030] 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.

[0031] La-Ln constituting the fuel electrode side intermediate layer 16 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.

[0032] 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.

[0033] The air electrode 12 and the anode 13, which are disposed in direct contact with the intermediate layer 17, preferably contain a common rare earth element and an oxide having oxide ion conductivity. The air electrode 12 and the anode 13 may each independently further contain a metal material. The metal material preferably contains nickel or a platinum group element, more preferably nickel, due to advantages such as high catalytic activity. Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements can be used alone or in combination. 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.

[0034] The oxide contained in the air electrode 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, and a part of it contains a common rare earth element. 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 is３－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.

[0035] The content of the common rare earth element in oxide a, 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 the common rare earth element in part of the A site forms a path in oxide a that facilitates the movement of oxide ions.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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 １Since 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.

[0044] La-Ln １ When 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.

[0045] 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.

[0046] 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 (electrochemical characteristics) of the fuel cell 10. Note that, when the anode 13 contains a cermet of a 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.

[0047] Furthermore, from the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and improving the power generation characteristics (electrochemical 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.

[0048] 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.

[0049] From the viewpoint of increasing the oxide ion conductivity of the fuel cell 10 as a whole and improving the power generation characteristics (electrochemical 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.

[0050] 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.

[0051] 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.

[0052] The support layer 14 preferably contains an oxide containing a common rare earth element. Examples of such oxides that can be used include the various oxides listed above as examples of solid electrolytes. 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 solid electrolytes. From the viewpoint of suppressing an increase in electrical resistance of current collection, the support layer 14 is preferably electrically conductive.

[0053] As described above, the support layer 14 may contain a metal or an alloy instead of or in addition to containing the common rare earth element. In an embodiment in which the support layer 14 contains a metal or an alloy, it is preferable that the support layer 14 be mainly composed of a metal or an alloy, from the viewpoint of effectively suppressing cracking of the solid electrolyte layer 11. More specifically, the total content of the metal and alloy in the support layer 14 is preferably 70 vol% or more, more preferably 80 vol% or more, even more preferably 90 vol% or more, and ideally 100 vol%, based on the volume of the support layer 14. The total content of the metal and alloy can be measured by energy dispersive X-ray spectroscopy (EDS).

[0054] Examples of metals that can be contained in the support layer 14 include iron and nickel. Examples of alloys that can be contained in the support layer 14 include stainless steels such as ferritic stainless steel and austenitic stainless steel, carbon steels that are alloys of iron and carbon, and nickel-based alloys such as Ni—Fe alloys and Ni—Cr alloys.

[0055] 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.

[0056] 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.

[0057] 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, 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).

[0058] 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 1.0 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.

[0059] 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.

[0060] Next, a preferred method for manufacturing an electrochemical cell of the present invention will be described using the method for manufacturing 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, the majority of the fuel cell can be manufactured by heating the first stack, which is composed of several layers, in the first firing step. This makes it easier to manufacture the fuel cell 10 shown in FIG. 1 or 2, which is the embodiment described above, compared to conventional manufacturing methods that require heating each layer separately.

[0061] 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.

[0062] The raw material composition used to manufacture the solid electrolyte layer 11 contains lanthanum and silicon. Examples of such raw material compositions include those having the composition formula La ２ Si ２ O ７ It is possible to prepare an oxide represented by the following formula:

[0063] The raw material composition used to manufacture the fuel electrode-side intermediate layer 16 contains the common rare earth elements described above, and preferably also contains cerium and oxygen. 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:

[0064] The raw material composition used to manufacture the anode 13 contains a common rare earth element and oxygen. This raw material composition may further 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 cerium oxide having the composition formula La ０．５ Ce ０．５ O １．７５ Examples of the compound include compounds represented by the following formula:

[0065] If the raw material composition used to manufacture the anode 13 contains samarium, the samarium may diffuse into the solid electrolyte layer 11 (the first sheet described below) during the first firing step, which may result in a decrease in the oxide ion conductivity of the solid electrolyte layer 11. Therefore, it is preferable that the raw material composition used to manufacture the anode 13 does not contain samarium.

[0066] 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 (electrochemical 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Once the first laminate is obtained, it can be cut into a desired shape, if necessary.

[0073] 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, 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 is 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 first sheet 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. It is considered that the diffusion of La from the first sheet to the second sheet due to the heating is negligible. When the first laminate includes a fourth sheet, elements also diffuse between the first sheet and the fourth sheet by heating the first laminate, 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 into 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 Si ２ O ７If it contains La ２ Si ２ O ７ From SiO ２ is liberated, and the liberated SiO ２ The Si derived from the first sheet may diffuse from the second sheet. Through this diffusion of elements, a solid electrolyte consisting of a composite oxide of lanthanum and silicon is produced. Note that the diffusion of La from the first sheet to the fourth sheet due to the heating is considered to be negligible.

[0074] 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, 1000°C or higher is preferred, 1300°C or higher is more preferred, and 1500°C or higher is even more preferred. A heating temperature of at least the above value effectively diffuses Si from the first sheet to the second and / or fourth sheet, thereby facilitating stabilization of the apatite structure. For this reason, a higher heating temperature is preferred, but the desired effect can be fully 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, 0.5 hours or higher is preferred, 1.0 hours or higher is more preferred, and 2.0 hours or higher is even more preferred. For the same reason, 10 hours or less is preferred, 8.0 hours or less is more preferred, and 6.0 hours or less is even more preferred. Heating can be performed, for example, using an electric furnace, tubular furnace, etc. 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.

[0075] By the above heating, the solid electrolyte layer 11, the fuel electrode side intermediate layer 16, the fuel electrode 13, and the air electrode side intermediate layer 15 are produced from the first sheet, the second sheet, the third sheet, and the fourth sheet, respectively.

[0076] 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 ０．２Fe 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 the coating is formed, 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 (electrochemical 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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 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.

[0081] 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.

[0082] 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.

[0083] 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 also be used as an electrolysis cell in addition to a fuel cell. The electrolysis cell can be used, for example, as an electrolysis device including the same.

[0084] 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.

[0085] The above-described embodiments of the present invention encompass the following technical concepts: [1] An anode-supported electrochemical cell having a cathode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer stacked in this order, wherein an intermediate layer is provided at least one between the cathode and the solid electrolyte layer and between the anode and the solid electrolyte layer, and wherein the cathode, anode, solid electrolyte layer, intermediate layer, and support layer contain the same rare earth element. [2] An electrochemical cell having a cathode, a solid electrolyte layer containing a solid electrolyte, and an anode stacked in this order, wherein an intermediate layer is provided at least one between the cathode and the solid electrolyte layer and between the anode and the solid electrolyte layer, and wherein the cathode, anode, solid electrolyte layer, and intermediate layer contain the same rare earth element, and wherein the thickness of the anode is 1.0 μm to 3000 μm. [3] The electrochemical cell according to [1] or [2], wherein the rare earth element is lanthanum. [4] The electrochemical cell according to any one of [1] to [3], wherein the solid electrolyte contains a composite oxide. [5] The electrochemical cell according to [4], wherein the composite oxide has an apatite-type crystal structure. [6] The solid electrolyte is A ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚ(In the formula, A is one or more elements selected from the group consisting of La, Ce, Y, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. T in the formula is an element containing Si or Ge, or both. M in the formula is Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, S and n is one or more elements selected from the group consisting of W and Mo.) wherein x in the formula is a number of -1.33 or more and 3.00 or less, y in the formula is a number of 0.00 or more and 3.00 or less, z in the formula is a number of -5.00 or more and 5.20 or less, and the ratio of the number of moles of A to the number of moles of T (A / T) is 1.33 or more and 3.61 or less. [7] The electrochemical cell according to any one of [1] to [6], wherein the thickness of the solid electrolyte layer is 10 nm or more and 30 μm or less, and the thickness of the intermediate layer is 10 nm or more and 30 μm or less. [8] The electrochemical cell according to any one of [1] to [7], further comprising: an intermediate layer between the anode and the solid electrolyte layer, the intermediate layer being located between the anode and the solid electrolyte layer and containing a quinone oxide containing the rare earth element, the solid electrolyte being located between the anode and the solid electrolyte layer and containing a quinone oxide containing the rare earth element, the solid electrolyte being located between the cathode ...

[10] The electrochemical cell according to [1], wherein the air electrode, the anode, the solid electrolyte layer, the intermediate layer, and the support layer all contain an oxide.

[11] The electrochemical cell according to [2], wherein the air electrode, the anode, the solid electrolyte layer, and the intermediate layer all contain an oxide.

[12] An anode-supported electrochemical cell having a cathode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer stacked in this order, wherein an intermediate layer is provided at least one between the cathode and the solid electrolyte layer and between the anode and the solid electrolyte layer, wherein the cathode, the anode, the solid electrolyte layer, and the intermediate layer contain the same rare earth element, and the support layer contains a metal or an alloy.

[13] The electrochemical cell according to any one of [1] to

[12] , which is a fuel cell cell.

[14] The electrochemical cell according to any one of [1] to

[12] , which is an electrolysis cell.

[15] An anode-supported electrochemical cell having a cathode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer stacked in this order, wherein an intermediate layer is provided at least one between the cathode and the solid electrolyte layer and between the anode and the solid electrolyte layer, and the cathode, the anode, the solid electrolyte layer, the intermediate layer, and the support layer contain the same rare earth element.

[16] An electrochemical cell having a cathode, a solid electrolyte layer containing a solid electrolyte, and an anode stacked in this order, wherein an intermediate layer is provided at least one between the cathode and the solid electrolyte layer and between the anode and the solid electrolyte layer, and the cathode, the anode, the solid electrolyte layer, and the intermediate layer contain the same rare earth element, and the anode has a thickness of 1.0 μm to 3000 μm.

[0086] 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."

[0087] [Example 1] (1) Production of First Laminate A first laminate in which a first sheet (corresponding to a solid electrolyte layer), a second sheet (corresponding to a fuel electrode-side intermediate layer), a third sheet (corresponding to a fuel electrode), and a support layer sheet (corresponding to a support layer) were laminated in this order was produced by the following procedure. ２ Si ２ O ７9.005 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 ７ Instead 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.

[0088] (2) Heating of 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.

[0089] (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.

[0090] (4) 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 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.

[0091] [Example 2] The thickness of the applicator was changed to 60 μm gap so that the thickness of the electrolyte was increased. ０．２ Ce ０．８ O １．９ The amount of powder was 1.5 g, and a slurry prepared using 2.2 g of an α-terpineol solution of ethyl cellulose was used. Except for the above, an electrochemical cell was obtained in the same manner as in Example 1.

[0092] [Example 3] In the production of the third sheet, La ０．５ Ce ０．５ O １．７５ Instead of powder, Sm ０．２ Ce ０．８ O １．９The firing temperature of the third laminate was changed to 900° C. Except for the above points, an electrochemical cell was obtained in the same manner as in Example 1.

[0093] [Evaluation] For the electrochemical cells obtained in the Examples and Comparative Examples, the composition of the oxide contained in each layer was determined, and the lanthanum contents n1 to n6 in each layer were calculated. The thickness of each layer was also measured. Furthermore, the maximum power density of the electrochemical cells obtained in the Examples and Comparative Examples was measured using the following method. The results are shown in Table 1.

[0094] [Content of Metal Elements in Each Layer] The contents of Sr, Co, Fe, and La in the air electrode were measured by point analysis using SEM (scanning electron microscope)-EDS analysis on a cross section of the electrochemical cell approximately parallel to the thickness direction. Table 1 shows the measured content of each element as a percentage (mol %) relative to the total amount of Sr, Co, Fe, and La. Similarly, the contents of Sm, Ce, and La contained in the air electrode-side intermediate layer, the fuel electrode-side intermediate layer, and the fuel electrode were measured, and the results are shown in Table 1 as a percentage (mol %) relative to the total amount of Sm, Ce, and La. Furthermore, the contents of Si, Sm, Ce, and La contained in the solid electrolyte layer and the support layer were also measured, and the results are shown in Table 1 as a percentage (mol %) relative to the total amount of Si, Sm, Ce, and La.

[0095] [Thickness of Each Layer] The thickness of each layer was measured by SEM-EDS.

[0096] [Maximum power density] At 700°C, 100 ccm of hydrogen was flowed as fuel gas to the anode, and 80 ccm of nitrogen and 20 ccm of oxygen were flowed to the cathode. The voltage was swept at 10 mV / mV 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.

[0097]

[0098] As is clear from Table 1, the electrochemical cells of each example in which the air electrode, air electrode-side intermediate layer, solid electrolyte layer, fuel electrode-side intermediate layer, fuel electrode, and support layer contain the same rare earth element (lanthanum) have a high maximum power density and excellent electrochemical properties.

[0099] According to the present invention, an electrochemical cell having high electrochemical properties is provided.

Claims

1. An anode-supported electrochemical cell having an air electrode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer stacked in this order, wherein an intermediate layer is provided at least either between the air electrode and the solid electrolyte layer or between the anode and the solid electrolyte layer, and the air electrode, the anode, the solid electrolyte layer, the intermediate layer, and the support layer all contain the same rare earth element.

2. An electrochemical cell in which an air electrode, a solid electrolyte layer containing a solid electrolyte, and an anode are stacked in this order, and an intermediate layer is provided at least either between the air electrode and the solid electrolyte layer or between the anode and the solid electrolyte layer, the air electrode, the anode, the solid electrolyte layer, and the intermediate layer contain the same rare earth element, and the thickness of the anode is 1.0 μm or more and 3000 μm or less.

3. The electrochemical cell of claim 1 or 2, wherein the rare earth element is lanthanum.

4. The electrochemical cell according to claim 1 or 2, wherein the solid electrolyte comprises a composite oxide.

5. The electrochemical cell according to claim 4, wherein the composite oxide has an apatite-type crystal structure.

6. The solid electrolyte is A ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．００＋ｚ (In the formula, A is one or more elements selected from the group consisting of La, Ce, Y, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba. T in the formula is an element containing Si or Ge, or both. M in the formula is Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, G and one or more elements selected from the group consisting of Zn, Sn, W, and Mo. In the formula, x is a number equal to or greater than −1.33 and equal to or less than 3.00, y is a number equal to or greater than 0.00 and equal to or less than 3.00, and z is a number equal to or greater than −5.00 and equal to or less than 5.20, and the ratio of the number of moles of A to the number of moles of T (A / T) is 1.33 or greater and equal to or less than 3.

61.

7. The electrochemical cell according to claim 1 or 2, wherein the thickness of the solid electrolyte layer is 10 nm or more and 30 μm or less, and the thickness of the intermediate layer is 10 nm or more and 30 μm or less.

8. The electrochemical cell according to claim 1 or 2, further comprising: an intermediate layer between the fuel electrode and the solid electrolyte layer; the intermediate layer located between the fuel electrode and the solid electrolyte layer contains a fifth oxide containing the rare earth element; the solid electrolyte contains a second oxide containing the rare earth element; and wherein, when n5 is a ratio of the number of moles of the rare earth element to the total number of moles of elements other than oxygen in the fifth oxide, and n2 is a ratio of the number of moles of the rare earth element to the total number of moles of elements other than oxygen in the second oxide, the ratio n5 / n2 is 0.070 or more and 0.70 or less.

9. The electrochemical cell according to claim 1 or 2, wherein the intermediate layer and the anode contain cerium oxide containing lanthanum and one or more elements selected from the group consisting of samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium.

10. The electrochemical cell of claim 1, wherein the cathode, the anode, the solid electrolyte layer, the intermediate layer, and the support layer all comprise an oxide.

11. The electrochemical cell of claim 2, wherein the cathode, the anode, the solid electrolyte layer, and the intermediate layer all comprise an oxide.

12. An anode-supported electrochemical cell having an air electrode, a solid electrolyte layer containing a solid electrolyte, an anode, and a support layer stacked in this order, wherein an intermediate layer is provided at least either between the air electrode and the solid electrolyte layer or between the anode and the solid electrolyte layer, wherein the air electrode, the anode, the solid electrolyte layer, and the intermediate layer contain the same rare earth element, and the support layer contains a metal or an alloy.

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