JP4849774B2 - Solid electrolyte fuel cell and solid electrolyte fuel cell - Google Patents

Description

The present invention relates to a solid electrolyte fuel cell, and more particularly, to a fuel cell and a fuel cell of a solid electrolyte having a oxygen electrode through the reaction-preventing layer on the solid electrolyte layer.

  In recent years, various fuel cells in which a cell stack formed by connecting a plurality of fuel cells is accommodated in a storage container have been proposed as next-generation energy. Various types of fuel cells are known, such as solid polymer type, phosphoric acid type, molten carbonate type, and solid electrolyte type. Among them, solid electrolyte type fuel cells have an operating temperature. Although it is as high as 800 to 1000 ° C., it has advantages such as high power generation efficiency and the ability to use exhaust heat, and its research and development is being promoted.

  A solid electrolyte fuel cell has a basic structure in which a fuel electrode is provided on one surface of a solid electrolyte layer and an oxygen electrode (air electrode) is provided on the other surface. In such a solid electrolyte fuel cell, since the oxygen ion conductivity of the solid electrolyte generally increases from about 600 ° C., a gas containing oxygen on the oxygen electrode side in the temperature range of 600 ° C. or higher is used as the fuel electrode. By supplying each gas containing hydrogen to the side, a potential difference is generated between both electrodes based on the oxygen concentration difference between the oxygen electrode and the fuel electrode.

  Oxygen ions that have moved from the oxygen electrode to the fuel electrode through the solid electrolyte are combined with hydrogen ions at the fuel electrode to become water. At this time, electrons move simultaneously. Therefore, in the fuel cell, by supplying a gas containing oxygen and a gas containing hydrogen, the above reaction is continuously caused to generate electric power. That is, power is generated by causing an electrode reaction represented by the following formula at the oxygen electrode and the fuel electrode, respectively.

Oxygen electrode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte)
Fuel electrode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻

Usually, in the solid oxide fuel cell used, for example, the cell structure as described above is formed on a porous conductive support having a gas passage therein, and the gas passage inside the conductive support is formed. By supplying a fuel gas (hydrogen gas) to the surface of the fuel electrode, hydrogen is supplied to the surface of the fuel electrode via the conductive support, and at the same time, an oxygen-containing gas such as air is flowed to the outer surface of the oxygen electrode to As a result, an electrode reaction as described above is caused at each electrode, and the generated current is taken out by an interconnector provided on the conductive support. Fuel cell having such a structure, the cell stack by connecting the plurality in series with each other by the current collecting member, to accommodate such a cell stack multiple, in a suitable retract and container, conductive each cell stack By connecting with a member, it is used as a fuel cell.

  In the solid electrolyte fuel cell as described above, especially as an oxygen electrode forming material, a La—Sr—Co based perovskite complex oxide has a surface diffusion function and a volume diffusion with respect to oxygen ions, and has a low temperature. It is widely used in that it has excellent operability in (see, for example, Patent Document 1).

In addition, it is known that elemental diffusion from the oxygen electrode to the solid electrolyte layer occurs due to heating during power generation or manufacturing, and an insulating layer is formed at the interface between the oxygen electrode and the solid electrolyte layer due to such element diffusion. In order to prevent such element diffusion, it is proposed to provide a reaction prevention layer made of, for example, an ion conductive material or an electron conductive material (for example, Ce oxide) between the solid electrolyte layer and the oxygen electrode. (See, for example, Patent Document 2)
Japanese Patent Laid-Open No. 08-130018 JP 2002-15754 A

However, when the reaction preventing layer is provided at the interface between the oxygen electrode and the solid electrolyte layer as described above, there is a problem that the original characteristics of the oxygen electrode are deteriorated. In particular, even when an oxygen electrode is formed with an electrode material having a surface diffusion function and a volume diffusion function with respect to the oxygen ions described above, there is a problem that the performance is not sufficiently exhibited and high output cannot be obtained. there were.

  Accordingly, an object of the present invention is to provide a solid electrolyte fuel capable of ensuring a sufficient output without damaging the original characteristics of the oxygen electrode even when a reaction preventing layer is formed between the oxygen electrode and the solid electrolyte layer. It aims at providing a battery cell and a fuel cell.

According to the present invention, the solid electrolyte layer has an oxygen electrode layer on one surface and a fuel electrode layer on the other surface, and the oxygen electrode layer is interposed between the solid electrolyte layer and the reaction preventing layer. In the solid oxide fuel cell provided above,
The oxygen electrode layer is made of sintered particles of perovskite complex oxide, has a single layer structure, and has the following formula (1):
W = n ₁ · L (1)
In the formula, n ₁ is a unit length (10 μm) measured at the interface between the oxygen electrode layer and the reaction preventing layer at each of the cut surfaces by cutting the solid electrolyte fuel cell at three different points. The average value of the number of contacts per contact, L represents the thickness (μm) of the oxygen electrode layer,
In being defined electrode function index W is Ri Do and 300 to 500, a solid electrolyte fuel cell, characterized by being formed and 5 ≦ n ₁ ≦ 20 der so that is provided.
Moreover, according to the present invention,
The solid electrolyte layer has an oxygen electrode layer on one surface and a fuel electrode layer on the other surface, and the oxygen electrode layer is provided on the solid electrolyte layer via a reaction preventing layer. in the solid electrolyte fuel cell, the oxygen electrode layer is an inner layer positioned on the reaction preventing layer side, has a two-layer structure of a surface layer located on the surface side, wherein the inner layer, the CeO ₂ It is formed from a mixed sintered particle of composite oxide particles in which Sm ₂ O ₃ is dissolved and perovskite composite oxide particles, and the surface layer is formed from sintered particles of perovskite composite oxide. As well as
It said inner layer and said surface layer in the oxygen electrode layer is represented by the following formula (2) to (6):
W ₁ = n ₁ · L ₁ (2)
W ₂ = n ₂ · L ₂ (3)
W = W ₁ + W ₂ (4)
n ₁ > n ₂ (5)
L ₁ <L ₂ (6)
In the formula, n ₁ is a unit per unit length (10 μm) measured at the interface between the inner layer and the reaction preventing layer at each of the cut surfaces by cutting the solid oxide fuel cell at three different points. Shows the average number of contacts,
L ₁ represents the thickness (μm) of the inner layer,
n ₂ is an average value of the number of contacts per unit length (10 μm) measured at the interface between the inner layer and the surface layer in each cut surface by cutting the solid electrolyte fuel cell at three different points. Indicate
L ₂ represents the thickness (μm) of the surface layer,
In being defined electrode function index W is Ri Do and 300 to 500, a solid electrolyte fuel cell, characterized by being formed and 30 ≦ L ₂ ≦ 70 der so that is provided.
According to the present invention, there is also provided a solid oxide fuel cell characterized in that the solid electrolyte fuel cell is accommodated in a storage container.

In the present invention, in any of the solid oxide fuel cells,
(A) The reaction preventing layer is made of a composite oxide sintered body in which Sm ₂ O ₃ is solid-solved in CeO ₂ ;
(B) The composite oxide forming the reaction preventing layer has the following general formula:
(CeO ₂ ) _1-x (SmO _3/2 ) _x
Where x is a number 0 <x ≦ 0.3.
Having a molar composition represented by:
(C) the perovskite complex oxide is a (La, Sr) (Co, Fe) O ₃ oxide;
Is preferred.

In the present invention, the oxygen electrode layer formed on the solid electrolyte layer via the reaction preventing layer is formed so that the polar function index W defined by the above formula (1) is 300 to 500, whereby oxygen The original characteristics of the electrode layer are sufficiently exhibited, and the oxygen electrode is formed of a material having a surface diffusion function and a volume diffusion function with respect to oxygen ions, such as a La-Sr-Co perovskite oxide. Even in this case, the surface diffusion function and the volume diffusion function are sufficiently developed, and a high output can be obtained.

That is, the functions of the oxygen electrode with respect to oxygen ions include a surface diffusion function and a volume diffusion function. In the surface diffusion function, gas phase oxygen becomes atomic oxygen active on the surface of the oxygen electrode, and this serves as a reaction field. It moves to the interface with the reaction preventing layer (or solid electrolyte layer) through the electrode surface and receives electrons from the interface to generate oxygen ions. On the other hand, the volume diffusion function is that the gas phase oxygen is the oxygen electrode. The generated oxygen ions are transferred to the interface with the reaction preventing layer (or the solid electrolyte layer). In the present invention, by forming the oxygen electrode so that the polar function index W is in a certain range, both the surface diffusion function and the volume diffusion function are expressed in a balanced manner.

  For example, please refer to FIG. 4 for explaining the function of the present invention. In FIG. 4, A shows a reaction preventing layer and B shows an oxygen electrode layer.

That is, many contact number n ₁ of the reaction-preventing layer A and the oxygen electrode layer B, and the thickness L of the oxygen electrode layer B is thicker (see FIG. 4 (a)), volume diffusion is mainly, reaction-preventing layer B Because the air (oxygen) is difficult to reach the interface, the surface diffusion function is hardly expressed. Also, fewer number of contacts n _1, and the thickness L of the oxygen electrode layer B is thick (see FIG. 4 (b)), it hardly occurs volume diffusion, the surface diffusion is the main, less reaction field, surface The diffusion function is also low. Further, many contact number n _1, and the thickness L of the oxygen electrode layer B is thin (see FIG. 4 (c)), the reaction field is large, although the surface diffusion function is sufficiently expressed, the number of particles by volume diffusion The volume diffusion function is unsatisfactory. However, according to the present invention, the electrode function index W to form an oxygen electrode layer B to be constant in the range described above (see FIG. 4 (d)), the thickness L of the contact number n ₁ and the oxygen electrode layer B Both are in an appropriate range. As a result, both volume diffusion and surface diffusion function sufficiently, the utilization rate of air (oxygen) is increased, and high output can be secured.

Hereinafter, the present invention will be described in detail based on specific examples shown in the accompanying drawings.
Figure 1 is a longitudinal sectional view of a solid electrolyte fuel cell of the present invention,
FIG. 2 is a cross-sectional view of an essential part showing another example of the solid oxide fuel cell of the present invention,
FIG. 3 is a schematic cross-sectional view showing a cell stack formed using the solid oxide fuel cell of the present invention.

In FIG. 1, the solid electrolyte fuel cell of the present invention indicated by 1 as a whole (hereinafter sometimes abbreviated as “fuel cell”) has an elongated rod shape, a flat cross section, and an elliptical shape as a whole ( A flat-plate support substrate 2 is provided. Inside the support substrate 2, a plurality of fuel gas passages 2 a are formed penetrating in the axial direction at appropriate intervals, and a cell structure described below is formed on the support substrate 1. As shown in FIG. 3, a plurality of fuel cells 1 are connected to each other in series by a current collecting member 20 to form a cell stack constituting the fuel cell.

  As shown in FIG. 1, the support substrate 2 includes a flat portion A and a curved portion B formed at both ends of the flat portion A. Both surfaces of the flat part A are formed substantially parallel to each other, and the fuel electrode layer 5 is provided on one surface of the flat part A, and the dense solid electrolyte layer covers the fuel electrode layer 5. 7 are stacked. Further, on the solid electrolyte layer 7, the reaction preventing layer 9 and the oxygen electrode layer 11 are laminated in this order from one surface of the flat portion A to the arc-shaped portions B on both sides so as to face the fuel electrode layer 5. ing. Further, an interconnector 13 is formed on the other surface of the flat portion A of the support substrate 2. As is clear from FIG. 1, the solid electrolyte layer 7 extends to both sides of the interconnector 13 and is configured so that the surface of the support substrate 2 is not exposed to the outside.

  In the fuel cell having the above structure, the portion where the fuel electrode layer 5 and the oxygen electrode layer 11 face each other with the solid electrolyte layer 7 interposed therebetween is the power generation unit. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode layer 11, and a fuel gas (hydrogen) is supplied to the gas passage 2 a in the support substrate 2, and the oxygen electrode layer 11 is heated to a predetermined operating temperature. Then, power is generated by causing the electrode reaction described above in the fuel electrode layer 5.

  The current generated by such power generation is collected via the interconnector 13 attached to the support substrate 2.

(Support substrate 2)
In the fuel cell 1 of the present invention having the above-described structure, the support substrate 2 is gas permeable so as to allow the fuel gas to permeate to the fuel electrode layer 5, and collects current via the interconnector 13. However, in order to satisfy such a demand and to avoid the disadvantages caused by simultaneous firing, the support substrate 2 is made of an iron group metal component and a specific rare earth oxide. It is good to constitute.

The iron group metal component is for imparting conductivity to the support substrate 2 and may be an iron group metal alone, or an iron group metal oxide, an iron group metal alloy or an alloy oxide. May be. The iron group metals include iron, nickel, and cobalt. In the present invention, any of them can be used, but Ni and / or NiO is changed to iron group because it is inexpensive and stable in fuel gas. It is preferable to contain as a metal component.

The rare earth oxide component is used for approximating the thermal expansion coefficient of the support substrate 2 to the thermal expansion coefficient of the solid electrolyte layer 7, maintains high conductivity, and is applied to the solid electrolyte layer 7 and the like. In order to prevent element diffusion, a rare earth oxide containing at least one rare earth element selected from the group consisting of Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm, and Pr is an iron group. It is preferred to use in combination with ingredients. Such rare earth oxides include Y ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , Tm ₂ O ₃ , Er ₂ O ₃ , Ho ₂ O ₃ , Dy ₂ O ₃ , Gd ₂ O ₃ , Sm. ₂ O ₃ and Pr ₂ O ₃ can be exemplified, and Y ₂ O ₃ and Yb ₂ O ₃ are preferable in that they are particularly inexpensive.

  These rare earth oxides hardly cause solid solution or reaction with the iron group metal or its oxide during firing or during power generation, and the iron group metal or its oxide in the support substrate 2, and Any of the rare earth oxides is difficult to diffuse. Therefore, even when the support substrate 2 and the solid electrolyte layer 7 are simultaneously fired, the diffusion of rare earth elements into the solid electrolyte layer 7 is effectively suppressed, and adverse effects on the ionic conductivity and the like of the solid electrolyte layer 7 are avoided. can do.

In the present invention, in particular, the iron group metal component is contained in the support substrate 2 in an amount of 65 to 35% by volume in that the thermal expansion coefficient of the support substrate 2 is approximated to the thermal expansion coefficient of the solid electrolyte layer 7. It is preferable that the rare earth oxide is contained in the support substrate 2 in an amount of 35 to 65% by volume. The support substrate 2 may contain other metal components and oxide components as long as required characteristics are not impaired.

  Since the support substrate 2 composed of the iron group metal component and the rare earth oxide as described above needs to have fuel gas permeability, the open porosity is usually 30% or more, particularly 35. It is preferable to be in the range of up to 50%. Further, the conductivity of the support substrate 2 is preferably 300 S / cm or more, and particularly preferably 440 S / cm or more.

  Further, the length of the flat portion A of the support substrate 31 is normally 15 to 35 mm, the length of the curvature portion B (the length of the arc) is about 3 to 8 mm, and the thickness of the support substrate 2 is (flat portion). The distance between both surfaces of A) is preferably about 2.5 to 5 mm.

(Fuel electrode layer 5)
In the present invention, the fuel electrode layer 5 causes an electrode reaction, and is formed of a known porous cermet. For example, it is formed from ZrO ₂ or CeO ₂ in which a rare earth element is dissolved, and Ni and / or NiO.

The ZrO ₂ or CeO ₂ content in the fuel electrode layer 5 is preferably in the range of 35 to 65% by volume, and the Ni or NiO content is preferably 65 to 35% by volume. Further, the open porosity of the fuel electrode layer 5 should be 15% or more, particularly in the range of 20 to 40%, and its thickness is 1 to 1 in order to prevent performance degradation and peeling due to a difference in thermal expansion. 30 μm is desirable.

In addition, as the rare earth element dissolved in ZrO ₂ or CeO ₂ , the same elements as those shown for the rare earth oxide used in the support substrate 2 can be exemplified, but the cell polarization value is lowered. Therefore, it is preferable that Y is about 3 to 10 mol% with respect to ZrO _{2 and} Sm is about 5 to 20 mol% with respect to CeO ₂ .

  Further, it is sufficient that the fuel electrode layer 5 exists at least at a position facing the oxygen electrode layer 11. That is, in the example of FIG. 1, the support substrate 2 extends from the flat part A on one side to the other flat part A and extends to both ends of the interconnector 13, but is formed only on the flat part A on one side. Further, the fuel electrode layer 5 can be formed over the entire circumference of the support substrate 2.

Although not shown, if necessary, a diffusion suppression layer (different from the reaction preventing layer 9) is provided on the fuel electrode layer 5, and such a diffusion suppression layer is formed between the fuel electrode layer 5 and the solid electrolyte layer 7. It can also be interposed between the two. This diffusion suppression layer is for suppressing element diffusion from the fuel electrode layer or the support substrate 2 to the solid electrolyte layer 7 and for avoiding performance degradation due to the formation of the insulating layer. CeO ₂ in which La is dissolved, Alternatively, it is formed from La ₂ O ₃ in which Ce is dissolved, or a mixture thereof. Furthermore, in order to enhance the effect of blocking or suppressing element diffusion, oxides of other rare earth elements may be contained in this reaction preventing layer. Examples of the rare earth element include Sc, Y, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  Moreover, it is preferable that such a diffusion suppression layer extends to both ends of the interconnector 13 together with the solid electrolyte layer 7. This is because element diffusion from the support substrate 2 and the fuel electrode layer 5 to the solid electrolyte layer 7 can be reliably prevented.

(Solid electrolyte layer 7)
The solid electrolyte layer 7 has a function as an electrolyte that bridges electrons between the electrodes, and at the same time has a gas barrier property in order to prevent leakage of fuel gas and oxygen-containing gas such as air. is necessary. Thus, the solid body electrolyte layer 7, dense ceramics which has such properties, for example, it is preferable that 3 to 15 mole% of the rare earth element is formed using the stabilized ZrO ₂ solid solution . Examples of rare earth elements in the stabilized ZrO ₂ include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Td, Dy, Ho, Er, Tm, Yb, and Lu. However, Y and Yb are preferable because they are inexpensive.

Furthermore, a perovskite-type lanthanum gallate complex oxide containing La and Ga can also be used as the solid electrolyte. This composite oxide has high oxygen ion conductivity, and high power generation efficiency can be obtained by using it as a solid electrolyte. This lanthanum gallate complex oxide has La and Sr at the A site, and Ga and Mg at the B site. For example, the following general formula (i):
_{(La 1-x Sr x)} (Ga 1-y Mg y) O 3 ... (i)
Where x is a number 0 <x <0.3;
y is a number 0 <y <0.3,
It is desirable to have the composition represented by these. High power generation performance can also be exhibited by using a composite oxide having such a composition as a solid electrolyte.

  The solid electrolyte layer 7 preferably has a thickness of 10 to 100 μm from the viewpoint of preventing gas permeation, and further has a relative density (according to Archimedes method) of 93% or more, particularly 95% or more.

(Reaction prevention layer 9)
The reaction preventing layer 9 formed on the solid electrolyte layer 7 and interposed between the oxygen electrode layer 11 and the solid electrolyte layer 7 is for blocking element diffusion from the oxygen electrode layer 11 to the solid electrolyte layer 7. In general, it is preferably formed from a sintered body of a Ce-containing composite oxide. As this Ce-containing composite oxide, a composite oxide in which Sm ₂ O ₃ is dissolved in CeO ₂ , particularly the following general formula (ii):
(CeO ₂ ) _1-x (SmO _3/2 ) _x (ii)
Where x is a number 0 <x ≦ 0.3, in particular 0.1 ≦ x ≦ 0.2.
In addition to high element diffusion barrier properties, the composite oxide having the composition represented by the above is used very suitably in that it is excellent in oxygen ion conductivity and electronic conductivity. That is, by forming the reaction preventing layer 9 using a Ce-based composite oxide having the above molar composition (hereinafter sometimes referred to as SDC composite oxide), a three-phase structure is formed at the interface with the solid electrolyte layer 7. It is possible to effectively block element diffusion from the oxygen electrode layer 11 to the solid electrolyte layer 7 without forming an interface and hindering electrode reaction or increasing interelectrode resistance. In addition, as long as the outstanding characteristic of said Ce type complex oxide is not impaired, the reaction prevention layer 9 can also be formed together with another rare earth element oxide if necessary.

  In addition, since the reaction preventing layer 9 exhibits a predetermined element diffusion blocking function and does not inhibit the electrode reaction, the reaction preventing layer 9 is generally formed of a relatively dense sintered body having a relative density of 80% or more, and the thickness thereof is It is good that it is about 3 to 10 μm.

(Oxygen electrode layer 11)
The oxygen electrode layer 11 formed on the reaction preventing layer 9 causes the above-described electrode reaction. As shown in FIG. 1, the oxygen electrode layer 11 is sandwiched between the solid electrolyte layers 7 and described above. The fuel electrode layer 5 is disposed at a position facing the fuel electrode layer 5. That is, it is arranged at least in a portion located on one flat portion A of the support 2.

The oxygen electrode layer 11 is composed of sintered particles of a so-called ABO ₃ type perovskite oxide. As such a perovskite type oxide, at least one of transition metal type perovskite oxide, particularly LaMnO ₃ oxide, LaFeO ₃ oxide, LaCoO ₃ oxide having La at the A site is preferable. (La, Sr) (Co, Fe) O ₃ system because of its high electrical conductivity at a relatively low temperature of about ˜1000 ° C. and excellent surface diffusion function and volume diffusion function for oxygen ions. Oxides (hereinafter sometimes referred to as La-Sr-Co based composite oxides), for example, the following general formula (iii):
_{La y Sr 1-y Co Z} Fe 1-Z O 3 ... (iii)
In the formula, y is a number satisfying 0.5 ≦ y ≦ 0.7,
z is a number of 0.2 ≦ z ≦ 0.8,
A composite oxide having a composition represented by:

In the present invention, in order to fully exhibit the surface diffusion function and volume diffusion function of the oxygen electrode layer 11 and increase the output, the oxygen electrode layer is composed of sintered particles of perovskite complex oxide, and has a single layer structure. And the above formula (1), that is,
W = n ₁ · L (1)
In the formula, n ₁ is a unit length (10 μm) measured at the interface between the oxygen electrode layer and the reaction preventing layer at each of the cut surfaces by cutting the solid electrolyte fuel cell at three different points. Indicates the number of contacts per contact,
L represents the thickness (μm) of the oxygen electrode layer 11;
The oxygen electrode layer 11 is formed so that the polar function index W defined by is 300 to 500, preferably 350 to 450. That is, as already described, the number of contacts n ₁ at the interface between the oxygen electrode layer 11 and the reaction preventing layer 9 and the thickness L of the oxygen electrode layer 11 are adjusted so that the polar function index W is in the above range. As a result, the surface diffusion function and the volume diffusion function of the oxygen electrode layer 11 are sufficiently exhibited in a well-balanced manner, the utilization rate of the oxygen-containing gas (air) is improved, and high output can be secured. In particular, when the oxygen electrode layer 11 is formed using the above-described (La, Sr) (Co, Fe) O ₃ -based oxide, the excellent surface diffusion function and volume diffusion function of the oxide are sufficiently exhibited. Therefore, the present invention is most effective.

The number of contacts n ₁ between the oxygen electrode layer 11 and the reaction preventing layer 9 is determined by cutting the fuel cell and observing the interface between the oxygen electrode layer 11 and the reaction preventing layer 9 with an electron microscope at the cut surface. For example, as shown in the examples to be described later, three cut surfaces are formed at arbitrary positions, and the number of contacts per unit length (10 μm) at the interface at each cut surface Is obtained as an average value. In general, the number of contacts n _1, in order to avoid extreme thinning by strength reduction and extreme圧肉of the oxygen electrode layer 11 is preferably set in a range of 5 to about 15.

The number of contacts n ₁ can be adjusted by adjusting the firing conditions or the coating conditions when forming the oxygen electrode layer 11 as will be described later.

In the present invention, the oxygen electrode layer 11 may be divided into two layers. That is, as shown in FIG. 2, the oxygen electrode layer 11 is composed of an inner layer 11a located on the reaction preventing layer 9 side and a surface layer 11b formed on the inner layer 11a. The bonding strength with the layer 9 can be increased. For example, in the case where the oxygen electrode layer 11 has a single-layer structure, if power is generated for a long time, peeling occurs partially at the interface between the reaction preventing layer 9 and the oxygen electrode layer 11, and the performance of the fuel cell is reduced. However, when the oxygen electrode layer 11 has the two-layer structure as described above, the bonding strength between both layers can be increased, and such inconvenience can be effectively prevented.

In the two-layer structure of the oxygen electrode layer 11 as shown in FIG. 2, the inner layer 11 a contains Ce-containing ceramic particles used for forming the reaction preventing layer 9 in addition to the ceramic particles made of the La—Sr—Co based composite oxide. The surface layer 11b is formed from ceramic particles composed of the aforementioned La—Sr—Co based composite oxide. The surface layer 11b is formed from mixed particles with the composite oxide, particularly ceramic particles composed of the SDC composite oxide of the general formula (ii). The That is, the SDC composite oxide is a mixed conductor having excellent ionic conductivity and electronic conductivity, and forms a so-called three-phase interface by being mixed with the perovskite oxide, and the reaction preventing layer 9 Used for formation. Therefore, in addition to the oxygen electrode layer forming material (La—Sr—Co based composite oxide), the layer (inner layer) 11 a containing the SDC composite oxide as the reaction preventing layer forming material is used to prevent reaction in the oxygen electrode layer 11. By forming it on the interface side with the layer 9, it is possible to increase the bonding strength with the reaction preventing layer 9 without causing the performance degradation of the oxygen electrode layer 11.

In the inner layer 11a, the content of the La—Sr—Co-based composite oxide that is the oxygen electrode layer forming material is preferably in the range of 70 to 90 mass%, and the content of the SDC composite oxide is 10 A range of ˜30% by mass is desirable. That is, the content of La-Sr-Co-based composite oxide, when it is more than the above range, the bypass function for moving oxygen ions is insufficient and less than the above range, the oxygen electrode performance is degraded There is a tendency.

Further, the total thickness of the oxygen electrode layer 11 is within the above-described range of the polar function index W defined by the number of contacts n ₁ between the reaction preventing layer 9 and the oxygen electrode layer 11 (inner layer 11a) and the thickness L of the oxygen electrode layer ( 300-500, but is set to become particularly 350 to 450), the thickness _{L 1} of the inner layer 11a in the oxygen electrode layer does not reduce the oxygen electrode performance, of increasing the bonding strength between the reaction-preventing layer 9 From the viewpoint, it is usually good to be in the range of 3 to 20 μm, particularly 5 to 10 μm, and the thickness of the surface layer 11b in the oxygen electrode layer 11 is high in the range of 35 to 85 μm, particularly 40 to 60 μm. This is suitable in terms of ensuring power generation performance.

Further, in the two-layer structure of the oxygen electrode layer 11 as described above, in order to sufficiently exhibit the surface diffusion function and the volume diffusion function as the oxygen electrode layer 11, the following formulas (2) to (6):
W ₁ = n ₁ · L ₁ (2)
W ₂ = n ₂ · L ₂ (3)
W = W ₁ + W ₂ (4)
n ₁ > n ₂ (5)
L ₁ <L ₂ (6)
In the formula, n ₁ is a unit per unit length (10 μm) measured at the interface between the inner layer 11a and the reaction preventing layer 9 at each cut surface by cutting the solid oxide fuel cell 1 at three different points. Shows the average number of contacts,
L ₁ indicates the thickness (μm) of the inner layer 11a,
n ₂ is an average of the number of contacts per unit length (10 μm) measured at the interface between the inner layer 11a and the surface layer 11b on each cut surface by cutting the solid oxide fuel cell 1 at three different points. Value,
L ₂ indicates the thickness (μm) of the surface layer,
It is preferable that it is formed so as to satisfy the condition represented by

  That is, the above conditional expression (5) means that the inner layer 11a for improving the bonding strength has a dense three-dimensional particle structure as compared with the surface layer 11b.

  The reason why the surface diffusion function and the volume diffusion function of the oxygen electrode layer 11 can be expressed more effectively by satisfying the conditional expression (5) as described above has not been elucidated. In the oxygen electrode layer structure, the inner layer 11a containing another material (SDC composite oxide) different from the electrode forming material that can exhibit the surface diffusion function and the volume diffusion function is considered to be formed. It is.

(Interconnector 13)
The interconnector 13 provided on the support substrate 2 at the position facing the oxygen electrode layer 11 is made of conductive ceramics, but is in contact with the fuel gas (hydrogen) and the oxygen-containing gas. It is necessary to have oxidation resistance. For this reason, lanthanum chromite perovskite oxides (LaCrO ₃ oxides) are generally used as the conductive ceramics. Further, in order to prevent leakage of the fuel gas passing through the inside of the support substrate 2 and the oxygen-containing gas passing through the outside of the support substrate 2, such conductive ceramics must be dense, for example, 93% or more, particularly 95%. It is preferable to have the above relative density.

  The thickness of the interconnector 13 is preferably 10 to 200 μm from the viewpoint of preventing gas leakage and electric resistance. That is, if the thickness is smaller than this range, gas leakage is likely to occur, and if the thickness is larger than this range, the electric resistance is large, and the current collecting function may be reduced due to a potential drop. .

Further, the interconnector 13 can be directly provided on the other flat portion A of the support substrate 2, but can also be formed on the support substrate 2 through a bonding layer made of Y ₂ O ₃ or the like, for example. . As described above, when the fuel electrode layer 5 is provided over the entire circumference of the support substrate 2, the interconnector 13 is formed on the support substrate 2 with the fuel electrode layer 5 interposed therebetween. It will be.

  Furthermore, it is preferable to provide a P-type semiconductor layer 15 on the outer surface (upper surface) of the interconnector 13. That is, in the cell stack assembled from the fuel cells (see FIG. 3), the conductive current collecting member 20 is connected to the interconnector 13, but when the current collecting member 20 is directly connected to the interconnector 13. By non-ohmic contact, the potential drop becomes large, and the current collecting performance deteriorates. However, by connecting the current collecting member 20 to the interconnector 13 via the P-type semiconductor layer 15, the contact between the two becomes an ohmic contact, the potential drop is reduced, and the deterioration of the current collecting performance is effectively avoided. For example, the current from the oxygen electrode layer 11 of one fuel cell 1 can be efficiently transmitted to the support substrate 2 of the other fuel cell 1.

Examples of the P-type semiconductor as described above include transition metal perovskite oxides.
Specifically, those having higher electron conductivity than LaCrO ₃ oxides constituting the interconnector 13, such as LaMnO ₃ oxides and LaFeO ₃ oxides in which Mn, Fe, Co, etc. are present at the B site P-type semiconductor ceramics made of at least one of LaCoO ₃ -based oxides can be used. In general, the thickness of the P-type semiconductor layer 15 is preferably in the range of 30 to 100 μm.

(Manufacture of fuel cells)
The fuel cell having the above-described structure itself, except that the contact number n ₁ and the thickness L of the oxygen electrode layer 11 are adjusted so that the polar function index W is within the predetermined range described above. It is produced by a known method.

In order to adjust the number of contacts n ₁ and the thickness adjustment L of the oxygen electrode layer 11, the oxygen electrode layer 11 uses a coating solution containing a predetermined oxygen electrode layer forming material, and this coating solution is preliminarily applied to the solid electrolyte. It may be formed by coating and baking on the reaction preventing layer 9 formed on the layer 7.

The above coating solution is prepared by a predetermined oxide is an oxygen electrode layer forming material particles (such as La-Sr-Co-based composite oxide as described above) are dispersed in an organic solvent such as isopropyl alcohol or toluene The

In such a coating solution, the oxide particles having a cumulative average particle diameter (D ₅₀ ) in the range of 0.4 to 1 μm, particularly 0.6 to 0.8 μm, can be obtained when the number of contacts is n ₁ . This is preferable for adjustment. That is, when the cumulative average particle size to use those outside the above range, by baking as described below, or increasingly more than necessary number of contacts n _1, or becomes small, the desired range of polar functional index W This is because the thickness must be significantly reduced or increased. The oxide particles preferably have as sharp a particle size distribution as possible. For example, particles having a large diameter of 1.2 μm or more are 5% by mass or less, and fine particles having a particle size of 0.3 μm or less are 3%. It is preferable that it is below mass%. That is, even if the cumulative average particle diameter (D ₅₀ ) is within the above range, if the particle size distribution is broad, the number of contacts n ₁ may vary greatly.

Coating the coating liquid, it is possible to perform in any manner, in that adjusting the number of contact points n _1, is preferably performed by spraying. That is, using a solvent amount that the spray becomes possible to prepare a coating liquid, depending on the amount of solvent, by adjusting the spray distance and spray pressure, it is possible to control the number of contacts n _1. For example, if the spray distance or spray pressure is increased, the amount of solvent dried in the spray increases, so the solvent content of the coating layer on the reaction preventing layer 9 decreases, and the number of contacts n ₁ can be increased. Conversely, when the spray distance or spray pressure is reduced, the amount of solvent dried in the spray is reduced, and the solvent content of the coating layer on the reaction preventing layer 9 is increased. As a result, the number of contacts n ₁ can be reduced. it can.

Thus, while the adjustment of the contact number n _1, as in accordance with the number of contacts n ₁ of interest, the thickness as obtained the desired electrode function index W L is formed, preventing the reaction a coating solution Spray on layer 9.

Baking after application is preferably performed at a relatively low temperature of about 1000 to 1200 ° C. If the baking is performed at a very low temperature, the particles are not sintered and layer formation becomes difficult. If the baking is performed at a too high temperature, the particles are integrated with each other, and the number of contacts n ₁ is significantly reduced. This is because the gas permeability of the oxygen electrode layer 11 that is generated or formed is impaired and the electrode characteristics are deteriorated.

  In the case where the oxygen electrode layer 11 has a two-layer structure of the inner layer 11a and the surface layer 11b, the inner layer 11a and the surface layer 11b are sequentially formed according to the above-described method, thereby obtaining a desired polar function index W, The oxygen electrode layer 11 having a two-layer structure that satisfies the conditional expressions (2) and (3) can be obtained.

  In the present invention, the portion excluding the oxygen electrode layer 11 as described above can be produced by the following simultaneous firing.

  First, the powder of the support substrate forming material is mixed with an organic binder and a solvent to prepare a slurry, and a support substrate molding sheet (support substrate molded body) is produced by extrusion molding using this slurry. This is dried. The support substrate molded body is calcined at 900 to 1000 ° C. to prepare a support substrate calcined body. The support substrate molded body may not be calcined as long as it has a predetermined strength.

Further, the powder of a given fuel electrode layer forming material, is mixed with an organic binder and a solvent slurry was prepared, to prepare a fuel electrode layer molding sheet (fuel electrode layer formed body) the slurry by a doctor blade method or the like Then, it is laminated on the support substrate calcined body. Incidentally, instead of producing a fuel electrode layer formed body, the raw material for the fuel electrode layer dispersed in a solvent paste was applied and dried at a predetermined position of the supporting substrate calcined body formed by the fuel electrode A coating layer for the layer can also be formed.

Furthermore, a powder obtained by adding a solid electrolyte layer forming material powder (usually, the particle diameter should be in the range of 0.5 to 3 μm) to a slurry by adding toluene, a binder, and a commercially available dispersant is a doctor blade method. For example, a sheet-like solid electrolyte layer molded body is formed by molding to a thickness of 10 to 50 μm, for example. This solid electrolyte layer molded body is laminated on the fuel electrode layer molded body on the support substrate calcined body and dried. In this case, the above fuel electrode layer formed body on, using a slurry containing a diffusion barrier layer forming material, previously formed diffusion suppressing layer molded article, for a solid electrolyte layer formed on the diffusion suppressing molded body layer The body can also be placed.

Incidentally, after providing the fuel electrode layer formed body as described above and the solid electrolyte layer formed body and the support base ItaNaru on feature, it may be performed calcination.

Next, a reaction preventing layer molded body is provided on the solid electrolyte layer molded body. This reaction-prevention layer molded body is prepared by mixing a ceramic powder of a reaction-prevention layer-forming material with a binder such as an acrylic resin and a solvent such as toluene, and applying this slurry to the solid electrolyte layer molded body. It is formed by doing.

The ceramic powder preferably has a cohesion degree adjusted to 5 to 35, whereby the firing shrinkage can be controlled, and the solid electrolyte layer 7 can be prevented from peeling and cracking. In particular, it is desirable to adjust the aggregation degree to 5 to 15 in that the power generation performance can be prevented from being lowered. In addition, the degree of aggregation is obtained by the following formula.
Aggregation degree = (particle diameter determined by laser light scattering method) / (pseudo sphere diameter determined from BET specific surface area)

When the degree of aggregation is large, since the primary particles in the aggregated particles are very small and the sintering activity is high, the sintering between the primary particles proceeds faster than the sintering between the aggregated particles. As a result, the shrinkage of the aggregated particles proceeds, the overall shrinkage is delayed, and cracks such as gaps are formed between the aggregated particles such as stone walls. On the other hand, since the raw material for the solid electrolyte layer has a particle size of 0.5 to 3 μm in consideration of co-sintering with the support substrate , the solid electrolyte layer 7 that is in contact with the reaction preventing layer 9 is the reaction preventing layer 9. It is pulled by the firing shrinkage of the steel and cracks and peeling like a stone wall occur. When the degree of aggregation is small, the sintering of the primary particles, the sintering between the agglomerated particles, and the sintering of the solid electrolyte layer 7 start almost simultaneously, so that a uniform sintered body is obtained. For example, after the raw material powder is pulverized using a vibration mill to adjust the particle size, calcined at a temperature of about 800 to 1000 ° C. for several hours, and then pulverized again using a ball mill or the like. This can be done.

  After providing the reaction preventing layer molded body as described above, the interconnector material is mixed with an organic binder and a solvent to prepare a slurry, and an interconnector sheet is prepared. This interconnector sheet is further laminated at a predetermined position of the laminated molded body obtained above to produce a fired laminated molded body.

Next, the above laminated molded body for firing is subjected to binder removal treatment, and simultaneously fired in the atmosphere at 1350 to 1600 ° C., and the oxygen electrode layer 11 is formed at a predetermined position of the obtained sintered body according to the method described above. By forming, the target fuel cell can be manufactured. In addition to the formation of the oxygen electrode layer 11, if necessary, a paste containing a P-type semiconductor layer material (for example, LaFeO ₃ oxide powder) and a solvent is applied by dipping or the like, and baked at 1000 to 1300 ° C. A P-type semiconductor layer 15 can be formed on the interconnector 13.

(Cell stack)
As shown in FIG. 3, the cell stack includes a plurality of the fuel cells 1 described above, and a metal felt and / or between one fuel cell 1 a and the other fuel cell 1 b that are vertically adjacent to each other. A current collecting member 20 made of a metal plate is interposed, and both are connected in series. That is, the support substrate 2 of one fuel cell 1a is electrically connected to the oxygen electrode layer 11 of the other fuel cell 1b through the interconnector 13, the P-type semiconductor layer 15, and the current collecting member 20. Yes. Further, such cell stacks are arranged adjacent to each other as shown in FIG. 3, and the adjacent cell stacks are connected in series by a conductive member 22.

The fuel cell of the present invention is configured by accommodating the cell stack of FIG. 3 in a storage container. The storage container is provided with an introduction pipe for introducing a fuel gas such as hydrogen into the fuel battery cell 1 from the outside, and an introduction pipe for introducing an oxygen-containing gas such as air into the external space of the fuel battery cell 1. The fuel cell 1 is heated to a predetermined temperature (for example, 600 to 900 ° C.) to generate electric power, and surplus fuel gas and oxygen-containing gas are burned and discharged out of the storage container.

  In addition, this invention is not limited to the said form, As long as the oxygen electrode layer 11 is formed so that predetermined conditions may be satisfied, various changes are possible. For example, the support substrate 2 can have a cylindrical shape.

The invention is illustrated by the following experimental example.
In the following experimental examples, the number of contacts n _{1 at} the interface between the reaction preventing layer and the oxygen electrode layer and the number of contacts n ₂ in the oxygen electrode layer having a two-layer structure were determined by the following methods.

Measuring the number of contacts;
The fuel cell of the sample was cut at three different locations in the vertical direction, and at each cut surface (10 μm), the number of contacts n ₁ at the interface with the reaction preventing layer and the interface between the inner layer and the surface layer were measured by an electron microscope. the contact number n ₂ in was determined as the mean value.
The thickness was determined by electron microscope observation within the measurement range of the number of contacts on the cut surface, and the maximum thickness was defined as the thickness of the inner layer and the surface layer.

  In the following experimental examples, the following powders were used as a single layer oxygen electrode layer forming material, a two-layer structure inner layer forming material, and a surface layer forming material.

Oxygen electrode layer forming material in a single layer La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ powder Average particle diameter (D ₅₀ ): 0.8 μm
Coarse grain (particle size 1.2 μm or more) content: 5% by weight or less Fine particle (particle size 0.3 μm or less) content: 3% by weight or less

Inner layer forming material Mixed powder of La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ powder and (CeO ₂ ) ₈₅ (SmO _3/2 ) ₁₅ powder (referred to as SDC15) SDC15 content: 10 mass % (In mixed powder)
Particle size distribution of mixed powder Average particle size (D ₅₀ ): 0.6 μm
Coarse grain (particle size 1.2 μm or more) content: 5% by weight or less Fine particle (particle size 0.3 μm or less) content: 3% by weight or less

Surface layer La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O ₃ powder Average particle diameter (D ₅₀ ): 0.8 μm
Coarse grain (particle size 1.2 μm or more) content: 5% by weight or less Fine particle (particle size 0.3 μm or less) content: 3% by weight or less

(Experimental example 1)
First, NiO powder having an average particle size of 0.5 μm and Y ₂ O ₃ powder having an average particle size of 0.9 μm have a volume ratio of Ni: 48 vol% and Y ₂ O ₃ : 52 vol after firing and reduction. The slurry prepared with an organic binder and a solvent was molded by an extrusion molding method, dried and degreased to prepare a support substrate molded body.

Further, a slurry in which Ni powder having an average particle size of 0.5 μm, ZrO ₂ powder in which a rare earth element is dissolved, an organic binder, and a solvent is mixed is prepared, and the support substrate molded body is subjected to screen printing. Coating and drying were performed to form a coating layer for the fuel electrode layer.

Next, a slurry obtained by mixing ZrO ₂ powder in which 10 mol% of scandium is dissolved, an organic binder, and a solvent is prepared by a doctor blade method to produce a sheet for a solid electrolyte layer having a thickness of 40 μm, and then supported. It stuck on the coating layer for fuel electrode layers on a board | substrate molded object, and dried. This laminated molded body was calcined at 1000 ° C.

Furthermore, after pulverizing the composite oxide (SDC15) containing 85 mol% CeO ₂ and 15 mol% Sm ₂ O ₃ with a vibration mill for 24 hours, a calcination treatment is performed at 900 ° C. for 4 hours, The powder was agglomerated to adjust the powder agglomeration degree (particle diameter by laser diffraction / pseudo-spherical particle diameter calculated from BET specific surface area) to 13-16. Was added acrylic binder and toluene into the powder, the slurry prepared by mixing, on the surface of the solid electrolyte layer formed body of the calcined body obtained in the above, reaction-preventing layer was coated by screen printing the adult form was produced.

Further, a slurry in which a LaCrO ₃ oxide, an organic binder, and a solvent are mixed is prepared, and this is laminated on the support substrate molded body exposed portion of the above-mentioned laminated molded body, and in an oxygen-containing atmosphere, 1485 Simultaneous firing was performed at the firing temperature.

  The thickness of the support substrate in the obtained sintered body was 3 mm, the open porosity was 35%, the thickness of the fuel electrode layer was 10 μm, the open porosity was 24%, the thickness of the solid electrolyte layer was 30 μm, and the relative density was 97%. The thickness of the reaction preventing layer was 5 μm.

Next, a single-layer oxygen electrode layer forming material powder, a coating solution obtained by mixing the isopropyl alcohol, and spray coating to form an oxygen electrode layer coating layer, baked at 1150 ° C., the oxygen electrode layer The fuel cell was formed. The produced fuel cell has a size of 25 mm × 140 mm.

  As described above, the conditions for forming the coating layer for the oxygen electrode layer (solvent concentration of the coating solution, spray pressure and spray interval) and thickness were variously changed. 1 to 15 fuel cells were prepared. The number of contacts n1, the polar function index W, and the thickness of the formed oxygen electrode layer are shown in Table 1.

Also, hydrogen gas is allowed to flow inside each fuel cell produced as described above, and after the reduction treatment of the support substrate and the fuel electrode layer is performed at 850 ° C., the fuel gas flows into the fuel gas flow path of each fuel cell. was circulated, was circulated oxygen-containing gas outside the fuel cell to heat the fuel cell up to 750 ° C. using an electric furnace, a power generation test was performed. The power generation characteristics (power density) at this time are shown in Table 1.

From the results shown in Table 1, sample No. No. 1 (the number of contacts n ₁ is small and the oxygen electrode layer thickness L is thick), and the sample No. 4 (thin contact number n ₁ is less oxygen electrode layer thickness), poor power generation performance.
Sample No. No. 1 is because there are few reaction fields, and even if oxygen ions are carried by surface diffusion, the thickness is large and there is a distance to the reaction field. 4 is because there are few reaction fields and there are few oxygen electrode layers themselves for producing adsorbed oxygen.

Sample No. ₁ with 12 contacts and 12 polar function index W was used. 9 also has a low power density. This is also because the oxygen electrode layer for forming an adsorbed oxygen with respect to the contact field is insufficient. Furthermore, the sample No. ₁ with the contact number n ₁ of 20 and the polar function index W of 600 was used. 14, since there are many number of contacts, and densely packed oxygen electrode layer itself, as a result, although transport of oxygen ions to a volume diffusion, many oxygen ions are transported by volume diffusion due to the large thickness It is thought that the resistance deteriorates because of passing through the grain boundaries of the steel, and the performance deteriorates. Other sample No. 2, 3, 5-8 and 10-13 (examples of the present invention) are considered to have a high output due to the balance between surface diffusion and volume diffusion due to the balance between the number of contacts n ₁ and the thickness L.

(Experimental example 2)
Instead of forming a single oxygen electrode layer, the thickness of the coating solution obtained by mixing the inner layer forming material powder and isopropyl alcohol while changing the forming conditions (solvent concentration of the coating solution, spray pressure, spray interval) The coating solution obtained by mixing the surface layer forming material powder and isopropyl alcohol after forming the coating layer for the inner layer oxygen electrode layer, drying at 120 ° C. (Solvent concentration of coating solution, spray pressure, spray interval) while changing the thickness, spray coating with various changes in thickness, forming a coating layer for the surface layer oxygen electrode layer, drying at 120 ° C, and baking at 1050 ° C, A two-layer oxygen electrode layer was formed to produce a fuel cell. The produced fuel cell has a size of 25 mm × 140 mm.

  Thereafter, a power generation test similar to that of Experimental Example 1 was performed, and the power generation characteristics (power density) at this time are shown in Table 2.

As shown in Table 2, electrode function index W is greater than 500 Sample No. 18 and 20 (less number of contacts of the oxygen electrode layer of the surface layer, a thick thickness) is poor power generation performance. This is because both the number of contacts with the inner layer is large and the thickness is large, so even if oxygen ions are carried by surface diffusion, the thickness is large and there is a distance to the inner layer. In addition, the inner layer has a thicker sample No. No. 23 shows that the adsorbed oxygen transported by the surface layer is too thick in the dense oxygen electrode layer of the inner layer, and the movement of the adsorbed oxygen becomes rate limiting, resulting in poor power generation characteristics (power density). Further, (denser towards the front surface layer from the inner layer) the number of contacts are reversed Sample No. 27 has little reaction field generated at the interface with the electrolyte with respect to the adsorbed oxygen sent from the surface, so that it cannot be used effectively and power generation performance is reduced.
Other sample No. 15-17, 19, 21, 22, 24-26, 28, 29 (examples of the present invention) have high output due to the balance between surface diffusion and volume diffusion due to the balance between the number of contacts and the thickness.

The longitudinal cross-sectional view of the solid electrolyte form fuel cell of this invention. The principal part sectional drawing which shows the other example of the solid electrolyte form fuel cell of this invention. The schematic sectional drawing which shows the cell stack formed using the solid electrolyte form fuel cell of this invention. Explanatory drawing for demonstrating the function of this invention.

Explanation of symbols

1: solid electrolyte fuel cell 2: support 2a: fuel gas flow path 5: fuel electrode layer 7: solid electrolyte layer 9: reaction preventing layer 11: oxygen electrode layer 13: interconnector

Claims (6)

The solid electrolyte layer has an oxygen electrode layer on one surface and a fuel electrode layer on the other surface, and the oxygen electrode layer is provided on the solid electrolyte layer via a reaction preventing layer. In a solid oxide fuel cell,
The oxygen electrode layer is made of sintered particles of perovskite complex oxide, has a single layer structure, and has the following formula (1):
W = n ₁ · L (1)
In the formula, n ₁ is a unit length (10 μm) measured at the interface between the oxygen electrode layer and the reaction preventing layer at each of the cut surfaces by cutting the solid electrolyte fuel cell at three different points. The average value of the number of contacts per contact, L represents the thickness (μm) of the oxygen electrode layer,
In being defined electrode function index W is Ri Do and 300-500, and 5 ≦ n ₁ ≦ 20 solid electrolyte fuel cell, characterized by being formed in der so that. The solid electrolyte layer has an oxygen electrode layer on one surface and a fuel electrode layer on the other surface, and the oxygen electrode layer is provided on the solid electrolyte layer via a reaction preventing layer. in the solid electrolyte fuel cell, the oxygen electrode layer is an inner layer positioned on the reaction preventing layer side, has a two-layer structure of a surface layer located on the surface side, wherein the inner layer, the CeO ₂ It is formed from a mixed sintered particle of composite oxide particles in which Sm ₂ O ₃ is dissolved and perovskite composite oxide particles, and the surface layer is formed from sintered particles of perovskite composite oxide. As well as
It said inner layer and said surface layer in the oxygen electrode layer is represented by the following formula (2) to (6):
W ₁ = n ₁ · L ₁ (2)
W ₂ = n ₂ · L ₂ (3)
W = W ₁ + W ₂ (4)
n ₁ > n ₂ (5)
L ₁ <L ₂ (6)
In the formula, n ₁ is a unit per unit length (10 μm) measured at the interface between the inner layer and the reaction preventing layer at each of the cut surfaces by cutting the solid oxide fuel cell at three different points. Shows the average number of contacts,
L ₁ represents the thickness (μm) of the inner layer,
n ₂ is an average value of the number of contacts per unit length (10 μm) measured at the interface between the inner layer and the surface layer in each cut surface by cutting the solid electrolyte fuel cell at three different points. Indicate
L ₂ represents the thickness (μm) of the surface layer,
In being defined electrode function index W Ri is Do and 300-500, and 30 solid electrolyte fuel cell, characterized by being formed into ≦ L ₂ ≦ 70 der so that. _{3. The} solid oxide fuel cell according to claim 1, wherein the reaction prevention layer is made of a composite oxide sintered body in which Sm ₂ O ₃ is solid-solved in CeO ₂ . The composite oxide forming the reaction preventing layer has the following general formula:
(CeO ₂ ) _1-x (SmO _3/2 ) _x
Where x is a number 0 <x ≦ 0.3.
The solid oxide fuel cell according to claim 3, having a molar composition represented by: 5. The solid oxide fuel cell according to claim 1, wherein the perovskite complex oxide is a (La, Sr) (Co, Fe) O ₃ -based oxide.   6. A solid oxide fuel cell comprising the solid electrolyte fuel cell according to claim 1 housed in a housing container.

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