JPH05121084A - Fuel cell with solid electrolyte - Google Patents

Abstract

PURPOSE:To prevent laminate layers of an internal modification type SOFC in the form of a flat plate from exfoliating at the interfaces when it is in high temp. service. CONSTITUTION:A sheet of an air electrode (oxidating agent electrode) 1 made from a specific material is used also as a cell supporting plate, and on one side of this air electrode 1 a zirconia sole layer 21 is provided as an electrolyte layer, and thereover a Ni-containing zirconia layer 22 and a fuel modification layer 5 are formed as a fuel electrode. In this Ni-containing zirconia layer 22, the content of nickel working as a fuel electrode is varied continuously from the boundary zone of the Zirconia sole layer 21 to eliminate existence of interface where the nickel distribution differs distinctly. Also in the fuel modification layer 5, the content of nickel committing to modification is varied continuously from the boundary region of the Ni-containing zirconia layer 22 to nullify existence of interface where nickel distribution differs expressly. Thus exfoliation of layers in high temp. service is prevented by eliminating existence of distinct interface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte fuel cell, which uses an oxidizer electrode (air electrode) as a support, on which an electrolyte, a fuel electrode, and a fuel reforming layer are integrated in a dense structure. The present invention relates to a solid electrolyte fuel cell in which a thin film having excellent adhesion to an oxidizer electrode can be provided.

[0002]

2. Description of the Related Art A solid oxide fuel cell (hereinafter abbreviated as SOFC) is constructed by using a substance having oxygen ion permeability as an electrolyte and arranging an air electrode which is an oxidizer electrode and a fuel electrode through the electrolyte. To be done. Generally, yttria-stabilized zirconia, which has excellent oxygen ion permeability, is used as a substance used as an electrolyte. But this substance
Since the electrical conductivity (oxygen ion permeability) is low at room temperature, S
It is used under the condition that the operating temperature of the OFC is raised to about 1000 ° C. and the conductivity is high. However, increasing the operating temperature is not sufficient, so further thinning (50-20
0 μm) to suppress the voltage drop during power generation. On the other hand, the air electrode and the fuel electrode have higher conductivity than the electrolyte (at 1000 ° C, the electrolyte is 6 × 10 ^-2 S / c).
m, air electrode; 8 × 10 ^-1 S / cm, fuel electrode; 1 × 10 ³
S / cm), it is not always necessary to make the film extremely thin like an electrolyte, but it is generally formed in a film shape having a thickness similar to that of the electrolyte. In general, the material currently used is LaSrMnO ₃ perovskite structure oxide for the air electrode and nickel or nickel oxide and yttria-stabilized zirconia for the fuel electrode. The physical properties of these three membranes are clear when considering the power generation mechanism of SOFC, but the electrolyte is required to be a dense membrane that prevents gas permeation and allows only oxygen ions to pass. It is required to be porous so that the gas can easily enter the inside. SOFC is constructed by combining three kinds of films having such characteristics.

FIG. 3 shows an example of a conventional configuration of such a SOFC unit power generation cell. This figure is called a flat plate type SOFC, in which 1 is an oxidizer electrode, 3 is an electrolyte, and 4 is a fuel electrode. In this conventional example, the electrolyte 3 is sandwiched between a flat plate-shaped oxidizer electrode 1 and a fuel electrode 4, and is formed in a flat plate shape as a whole. As a manufacturing method, for example, there is a method in which thin green sheets manufactured by respective materials are laminated by a doctor blade method, and then the laminated film is sintered to obtain a cell. Further, as another manufacturing method, a method of applying a slurry of an electrode to a thin film of the electrolyte 3 which is manufactured by the doctor blade method and then sintered and used as a base, and sintering is adopted.

In this flat plate type SOFC cell, three layers are closely adhered to each other, but in any case, three types of layers having completely different compositions are laminated.
Therefore, it is necessary to determine the composition and materials so that the difference in the coefficient of thermal expansion of these three layers can be suppressed in the configuration of this flat plate type SOFC. Has been taken. Therefore, the difference in the coefficient of thermal expansion of the three layers is suppressed to a considerably small value.

On the other hand, SOFC uses hydrogen as a fuel, but it is not generally sent directly to hydrogen, and city gas containing methane as a main component is reformed into hydrogen by catalytic reaction to obtain hydrogen. .. Therefore, it is necessary to arrange a catalyst for converting city gas into hydrogen on the upstream side of the reaction section. However, in SOFC, the reaction temperature is as high as 1000 ° C., and the metal effective for the decomposition reaction of methane is the same as that used for the fuel electrode.
There is a concept of so-called "internal reforming SOFC" in which such a reforming layer is installed in the OFC electrode plate group. In such an “internal reforming SOFC”, a fuel reforming layer that preferentially acts on reforming is installed in the fuel electrode, and the fuel electrode itself is used as an electrode and also used as a fuel reforming layer. There is a way to do it.

[0006] For example, as the former example, Japanese Patent Application No. 3-36005 previously filed by the present applicant can be cited. Figure 4
(A), (b) is a figure showing the section structure, 1 is an oxidizer electrode, 3 is an electrolyte, 4 is a fuel electrode, 5 is a fuel reforming layer, and 6
Is a fuel gas flow path, and 7 is an oxidant gas flow path.
(A) shows the fuel reforming layer 5 formed on the entire one side of the fuel electrode 4, and (b) shows the island-shaped fuel reforming layer 5 formed on a part of the one side of the fuel electrode 4. In these examples, the structure in which the electrolyte 3 is sandwiched between the fuel electrode 4 and the oxidant electrode 1 is used.
To the fuel gas flow path 6 side, and the oxidant electrode 1 to the oxidant gas flow path 7
The cells are arranged on the side. A fuel reforming layer 5 is provided on the surface of the fuel electrode 4 on the side of the fuel gas flow path 6 in a single layer as shown in (a) or in a partially island shape as shown in (b). The reforming layer 5 reforms the fuel so that the fuel electrode 1 mainly causes a cell reaction to suppress the deterioration of the fuel electrode.

[0007]

However, in the plate type SOFC according to the above-mentioned conventional technique, it can be said that the difference in the coefficient of thermal expansion between the layers of the oxidizer electrode 1, the electrolyte 3 and the fuel electrode 4 is suppressed to a considerably small level. As mentioned above, the operating temperature is 1
Since the temperature is as high as 000 ° C., dimensional changes inevitably occur in each layer due to thermal expansion. If an SOFC is used in which a dimensional change due to such a difference in coefficient of thermal expansion occurs during power generation, there is a problem that peeling of the joint portion of each layer occurs.

On the other hand, in the internal reforming type SOFC according to Japanese Patent Application No. 3-36005, the fuel reforming layer is simply arranged as a single layer superposed on the fuel electrode, or partially over the fuel electrode. It is only arranged in a shape. If only reforming is performed in the fuel reforming layer, it is advantageous that the ratio of metals involved in reforming is large. However, if the ratio of the metal is increased, the difference in the coefficient of thermal expansion becomes large, and if the conventional structure proposed in Japanese Patent Application No. 3-36005 remains as it is, the adhesive force at the joint portion with the fuel electrode becomes weak and the There was a serious drawback that peeling occurred in a short time after the start.

An object of the present invention is to provide an internal reforming type SOFC which solves the problem that the conventional flat plate type SOFC is inherently present and the interface between the laminated layers is apt to peel off at high temperature. Especially.

[0010]

To achieve the above object, in a solid electrolyte fuel cell of the present invention, a fuel electrode and an oxidizer electrode are arranged via a solid electrolyte, and natural gas is used as a fuel on the fuel electrode side. Reactants such as, oxidizer such as air to the oxidizer electrode side, in a solid electrolyte fuel cell to generate power by respectively supplying, a thin plate made of the oxidizer electrode material as a substrate, the electrolyte layer on one side, A fuel electrode is stacked on the electrolyte layer, and a fuel reforming layer is further stacked on the fuel electrode, and a metal acting as a fuel electrode is continuously extended outward from a portion corresponding to the surface of the electrolyte layer. Increased to a predetermined ratio in the layer corresponding to the fuel electrode,
Further, it is characterized in that the metal that acts on the fuel reforming increases continuously from the surface portion of the fuel electrode toward the outside, and has a predetermined ratio in the portion corresponding to the fuel reforming layer.

[0011]

In the solid electrolyte fuel cell of the present invention, a thin plate made of an oxidizer electrode material is used as an electrode and also as a supporting plate of a cell, and an electrolyte layer is arranged on one side of the thin plate, A fuel electrode and a fuel reforming layer are formed on top of the electrolyte layer, and the distribution of the metal is clarified by continuously changing the ratio of the metal acting as the fuel electrode in this fuel electrode from the boundary area with the electrolyte layer. In the fuel reforming layer, the ratio of the metal that participates in reforming is continuously changed from the boundary area with the fuel electrode to clarify the metal distribution. It is formed as a thin film having no different interfaces. In this way, by eliminating the existence of interfaces having distinctly different compositions, peeling of each layer is prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a unitary power generation cell showing the configuration of an embodiment of the present invention. In the figure, 1 is an air electrode (oxidizer electrode) that also serves as a support plate of a unit power generation cell, 2 is a thin film layer containing zirconia as a main component, 5 is a fuel reforming layer, 21 is a zirconia layer of 100% zirconia, and 22 Is a nickel-containing zirconia layer containing nickel. This cell is produced by forming a thin film by a plasma spraying method on the basis of a thin plate of the air electrode 1 which has been sintered in advance.

The method of constructing the unit cell of this embodiment is as follows. First, in the air electrode 1, L is set such that X satisfies 0 ≦ X ≦ 0.8.
a _1-X Sr _X MnO ₃ powder (particle size; 0.5 to 5 μm) to which polyvinyl alcohol was added as a binder was 1 to
After press molding at 3 ton / cm ² , 1300 to 1400 ℃
It can be produced by sintering at the temperature of. If a large air electrode plate cannot be produced by the above pressing method,
A slurry may be prepared by using polyvinyl butyral as a binder, and a green body may be produced by a doctor blade method or a casting method and then sintered.

Next, the thin film layer 2 can also be produced by the plasma spraying method. In this case, yttria-stabilized zirconia (YSZ) and nickel powder or nickel oxide powder are supplied into the plasma jet from the powder supply unit of the plasma spraying apparatus. Layer 2 of this thin film
Among these, the YSZ 100% layer 21 formed directly on the air electrode 1 substrate is a layer that acts as an electrolyte and is required to be a dense and thin film. The layer 21 was formed by supplying only the YSZ powder to the thermal spraying device, and in order to improve the adhesion between the thermal sprayed powder and the sample, the output of the thermal spraying device was increased to sufficiently dissolve the YSZ. Apply under conditions and apply. This dense YSZ layer 21 is 50 to 200 μm thick.
After forming the layer 22 having a thickness of m, the layer 22 which acts as a fuel electrode containing nickel is formed. However, the fuel electrode is not required to be dense, and rather, it is porous to prevent diffusion of hydrogen gas. Sex is required. Therefore, when forming the layer 22, the output of the thermal spraying apparatus is lowered while gradually adding the nickel powder or the nickel oxide powder together with the YSZ powder to form a film having a predetermined thickness.

The distribution of nickel in the layer 21 in the thickness direction is as follows. In the cermet in which nickel and zirconia are mixed, the relationship between the nickel ratio and the electrical conductivity is the lower limit at which the nickel content of 20 wt% is the electrical conductivity of 1000 S / cm ² order. The rate improves,
On the contrary, since the expansion coefficient becomes large, a composition around this is generally used at present. By the way, in this composition, the coefficient of thermal expansion is 10.1 × 10 ⁻⁶ / ° C., which is close to that of YSZ of 9.9 × 10 ⁻⁶ / ° C. In this embodiment as well, a film is formed by considering this composition as a standard, but in this case, 20 wt% of nickel is formed from the YSZ 100% layer 21.
% Of the nickel distribution between the layers. At this time, the coefficient of thermal expansion is 9.9 × 10 ^{−6 of the} YSZ 100% layer 21.
/ ° C., 10.1 × 10 ⁻⁶ / of 20 wt% nickel layer
Since it changes continuously up to ℃, and the two absolute values are small, the difference in the coefficient of thermal expansion at the interface is relaxed as compared with the conventional one in which a layer of YSZ and nickel of 20 wt% is directly bonded. ..

Next, in this embodiment, after forming a nickel 20 wt% layer in the layer 22, a fuel reforming layer 5 having a nickel content higher than this layer is formed. That is, on the layer 22 having a nickel content of 20 wt%, nickel 4
A layer of 0 wt% is formed as the fuel reforming layer 5. 40
The coefficient of thermal expansion of the wt% layer is 10.6 × 10 ⁻⁶ / ° C., so if such a material is directly bonded to the nickel 20 wt% layer, the thermal expansion difference during continuous operation at 1000 ° C. is large,
It becomes difficult to form the fuel reforming layer 5. Therefore, in the present embodiment, nickel 40 is formed in the same manner as the method for forming the layer 21 described above.
Place a layer of 20 wt% under the layer of wt%, 40 wt%
In the layer of, the nickel concentration gradually increased to 40 in the thickness direction.
%, The difference in the coefficient of thermal expansion at such an interface is reduced.

The operation of the embodiment configured as described above will be described. In this embodiment, the thin film structure is as shown in FIG. That is, FIG. 2A is a diagram showing the distribution of the nickel content in the AA ′ cross section of FIG. 1, and shows the structure of the nickel 22 wt% layer 22 on the YSZ layer 21. The distribution of nickel between increases monotonically along the thickness of the film.
2B is a diagram showing the distribution of the nickel content in the BB ′ cross section of FIG. 1, in which the nickel 20 wt% layer 2 is formed.
In the case where the fuel reforming layer 5 of 40 wt% nickel was further formed on the No. 2 layer, the formation of the 40 wt% nickel layer was also monotonically increased along the thickness as in the previous example.

As described above, in the SOFC of this example, the electrolyte layer (zirconia single layer 21), the fuel electrode layer (nickel-containing zirconia layer 22), and the fuel reforming were performed on the surface of the SOFC by using the air electrode as a support. By continuously forming the layer 5, an internal reforming type SOFC single cell having an internal reforming layer is produced. Moreover, in forming the electrolyte layer and the fuel electrode layer, after forming the electrolyte layer first, The process proceeds to the formation of the fuel electrode, but at this time, at the position corresponding to the interface of each layer, the amount of nickel, which is a metal that acts as an electrode, is continuously increased and controlled so that the fuel electrode layer has a predetermined concentration. ing. Further, in the fuel reforming layer above the fuel electrode, similarly to the formation of the fuel electrode, the amount of the metal acting as the reforming catalyst is continuously increased at the position corresponding to the interface of the layer, so that the fuel reforming layer is formed in the fuel reforming layer. Is controlled so that the concentration becomes a predetermined value, and the existence of a clear interface between these three layers is eliminated. Therefore, there is no conventional interface where the composition between layers is clearly different, and it is possible to prevent cell destruction due to peeling or the like at the interface due to the difference in thermal expansion coefficient.

The unit power generation cell of the present invention can be constructed by the EVD method. Also in this case, first, a thin plate of the air electrode is prepared, and a YSZ layer and a zirconia layer containing nickel similar to those produced by the plasma spraying method are formed on this plate. In the case of the EVD method, a chloride is generally used as a raw material, but a film similar to the above can be formed by controlling the supply rate of each raw material. Regarding the adhesion and denseness of the electrolyte to the air electrode used as the support, the thermal spraying method, E
According to the VD method, it is possible to obtain a product without any problem. As the oxidizer electrode material, in addition to the La _1-X Sr _X MnO ₃ perovskite structure oxide in which _X is a value of 0 ≦ X ≦ 0.8, a part of Mn is used as a matrix and a part of Mn is shown in the fourth period table. ，
An oxide substituted with a transition metal of the 5th period can be used. As the electrolyte material, stabilized zirconia can be used, and as the fuel electrode / fuel reforming layer material, metal of Group 8 of the periodic table or its oxide and stabilized zirconia or zirconia can be used. As described above, the present invention can be applied in various ways in accordance with the gist thereof and can take various embodiments.

[0021]

As is apparent from the above description, according to the solid electrolyte fuel cell of the present invention, the oxidizer electrode, the electrolyte, the fuel electrode and the fuel reforming layer forming the internal reforming type fuel cell are continuously formed. Since each layer is formed by eliminating the existence of a clear interface, it is possible to prevent the destruction of the cell due to the peeling at the interface due to the difference in the coefficient of thermal expansion due to the operation at high temperature.

[Brief description of drawings]

FIG. 1 is a sectional view of a unitary power generation cell showing an embodiment of the present invention.

2 (a) and 2 (b) are views showing distributions of nickel content in cross-sections of respective portions of the above-mentioned embodiment.

FIG. 3 is a sectional view showing the basic structure of a conventional SOFC unit power generation cell.

4A and 4B are cross-sectional views showing a structural example of a conventional internal reforming SOFC.

[Explanation of Codes] 1 ... Air electrode (oxidizer electrode), 2 ... Layer containing zirconia as a main component, 5 ... Fuel reforming layer, 21 ... Zirconia single layer, 22
... Nickel-containing zirconia layer.

Claims (2)

[Claims] 1. A fuel electrode and an oxidizer electrode are arranged via a solid electrolyte, and a reactant such as natural gas as a fuel is supplied to the fuel electrode side and an oxidizer such as air is supplied to the oxidizer electrode side to generate electricity. In the solid electrolyte fuel cell, a thin plate made of an oxidizer electrode material is used as a substrate, and an electrolyte layer is formed on one surface of the substrate, a fuel electrode is formed on the electrolyte layer, and a fuel reforming layer is formed on the fuel electrode. At the same time, the metal acting as a fuel electrode continuously increases from the portion corresponding to the surface of the electrolyte layer toward the outside, and has a predetermined ratio in the layer corresponding to the fuel electrode, and acts on the fuel reforming. The solid electrolyte fuel cell, wherein the metal continuously increases from the surface portion of the fuel electrode toward the outside and has a predetermined ratio in the portion corresponding to the fuel reforming layer. 2. The solid electrolyte fuel cell according to claim 1, wherein the oxidizer electrode material is L having an X value of 0 ≦ X ≦ 0.8.
a _1-X Sr _X MnO ₃ perovskite structure oxide and an oxide obtained by substituting a part of Mn with a transition metal of 4th period and 5th period of the periodic table using this as a matrix, stabilized zirconia electrolyte material, fuel electrode A solid electrolyte fuel cell in which the fuel reforming layer material is a metal of Group 8 of the periodic table or an oxide thereof and stabilized zirconia or zirconia.