JPH0950812A - Electrode substrate for solid electrolytic fuel cell and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode substrate which has excellent gas permeative property and at the same time high mechanical strength and conductivity and moreover a large number of three-phase interfaces where battery reactions occur and is useful for a solid electrolytic fuel cell. SOLUTION: An electrode substrate is one to be used for a solid electrolytic fuel cell and the electrode substrate having different diameter of pores and porosity in the thickness direction is installed in a solid electrolytic fuel cell. A ceramic sheet of a powder of electrode raw materials for a solid electrolytic fuel cell, a ceramic sheet produced by adding a foaming agent with 20μm average particle size to the powder of electrode raw materials, and a ceramic sheet produced by adding a foaming agent with 5μm average particle size to the powder of electrode raw materials are layered, press-bonded, and fired. An electrode substrate having a three-layer structure and an electrode substrate having a fourth layer formed, if necessary, between the first layer and the second layer are practical examples of the electrode substrate of the solid electrolytic fuel cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow flat plate electrode substrate made of an electrode material used in a solid oxide fuel cell and having a gas flow passage therein, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Since fuel cell power generation is highly efficient and has a small effect on the environment, various studies have been made for practical use as a next-generation power generation method. Among them, the solid oxide fuel cell has an operating temperature as high as 1000 ° C, so that the power generation efficiency is particularly high, and the cells are all solid and have a large degree of freedom in shape, so cells of various structures are proposed. Has been done. The basic configuration of a fuel cell is one in which an ion conductive solid electrolyte is sandwiched between two electrodes, and air (oxygen) and fuel (hydrogen) gas are supplied to both electrodes to generate electricity. In actual use, several single cells are stacked and used in a stack to obtain a sufficient output, but at this time, if gas leaks, both gases react directly and the power generation efficiency decreases, so Airtightness is required. Further, if the unit cell is fragile, it will be damaged by the stress applied from the outside during stacking, so that the cell itself needs a certain strength. Therefore, as a structure satisfying such requirements, there has been proposed a method of forming cells on a hollow flat electrode substrate having a plurality of gas flow passages therein as shown in FIG. 36417). In FIG. 3, 1 is an electrolyte, 2 is a fuel electrode, 3 is an air electrode, 4 is an interconnector, 5 is a gas flow path, and 6 is a dense membrane.
In this method, either one of the gases passes through the gas flow path inside the substrate, so that the airtightness can be maintained by the gas seals only at both ends of the cell. Further, since the strength of the single cell is ensured by the hollow flat electrode substrate, it is possible to reduce the thickness of the electrolyte formed on the substrate, and it is expected that the power generation characteristic is improved by reducing the internal resistance. The hollow substrate used in this method is composed of a fuel electrode or an air electrode. Currently, both electrode materials are Ni-zirconia because of their compatibility with yttria-stabilized zirconia, which is an electrolyte material, and thermal expansion coefficient. cermet and _{La (1-x) Sr x} MnO 3 system material (x = 0.05 to 0.5) are most commonly used. As described above, the power generation of the battery is performed by supplying the respective reaction gases to these electrodes. Therefore, both electrodes must have sufficient porosity to allow these reaction gases to permeate to the electrode / electrolyte interface, which is the field of the cell reaction. In order to improve the gas permeability, it is considered that the porosity of the electrode substrate and its pore diameter are increased. However, when the porosity of the substrate is increased, the strength of the substrate is reduced and the cross-sectional area of the electrode is reduced, which may increase the internal resistance. Further, if the pore diameter is increased, the three-phase interface between the electrode, the electrolyte and the reaction gas is reduced, and the effective electrode area involved in the battery reaction is reduced, so that the output of the battery is reduced.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode substrate which is excellent in gas permeability, mechanical strength and conductivity, and which has many three-phase interfaces involved in battery reaction.

[0004]

The present invention will be described in brief. The electrode substrate of the solid oxide fuel cell according to the present invention is characterized in that the pore diameter and the porosity are different in the thickness direction of the substrate. Further, the electrode substrate of the solid oxide fuel cell according to the present invention is a hollow flat plate having a large number of gas passages inside, and has a structure having different porosities in the thickness direction, and the first layer has a porosity. 10% or less dense layer, the second layer has a porosity of 35
A porous layer having a porosity of 10 to 20 μm at ˜45%, and a third layer having a porosity of 2 to 5 μm with a porosity of 25 to 35%, and the second layer is superposed on the first layer. , And a third layer stacked on the second layer, if necessary, a porosity of 20 to 3
Characterized by placing 0% of the fourth layer between the first and second layers. Furthermore, the method for producing an electrode substrate of a solid oxide fuel cell according to the present invention is directed to a ceramic sheet of electrode material powder, a ceramic sheet obtained by adding a porosifying agent having an average particle size of 20 μm to the electrode material powder, and the electrode material powder. It is characterized in that ceramic sheets to which a porosifying agent having an average particle diameter of 5 μm is added are laminated, pressed and sintered.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. FIG. 1 is a perspective view showing an example of the structure of a hollow flat plate-shaped air electrode electrode substrate manufactured according to the present invention. FIG.
3-1 is a dense air electrode layer, 3-2 is a porous air electrode layer with a large pore diameter, 3-3 is a porous air electrode layer with a small pore diameter, and 5 is a gas flow path. 2 shows a schematic diagram of the porous electrode portions (3-2 and 3-3) of the substrate of FIG. 1, the porous electrode portion in the present invention has a large pore diameter as shown in FIG. By forming a thin layer electrode having a small pore size on the electrode layer, the gas diffusibility in the electrode is improved and the three-phase interface is secured. In FIG. 2, reference numeral 7 is a pore. That is, the electrode substrate of the solid oxide fuel cell according to the present invention comprises a stack of ceramic sheets made of electrode materials and having different porosities,
The ceramic sheet was made porous by adding a porosifying agent that completely burned during the sintering of the sheet and later formed pores. Further, the porosity and the pore diameter of such a ceramic sheet can be controlled by the addition amount of the porosifying agent and the particle diameter. Although the electrode substrate made of the air electrode material is shown here, the present invention can be similarly applied to the fuel electrode.

As shown in Examples below, in one example of the present invention, a hollow flat plate-like electrode substrate composed of an air electrode is produced by laminating and sintering three types of ceramic sheets having different porosities. As a result, the strength and conductivity of the substrate itself are secured,
At the same time, the porosity that allows sufficient gas diffusion to the electrode / electrolyte interface and the increase in the three-phase interface length, which is the field of the electrode reaction, are achieved, and high strength and high activity suitable for the formation of SOFC cells. It is possible to obtain a different electrode substrate.

Since the present invention is a method of forming a substrate by laminating electrode sheets having different porosities, the ratio of each layer and the thickness of the substrate can be freely changed by changing the number of laminated sheets. it can. For example, in FIG.
FIG. 3 is a cross-sectional view of a hollow flat plate-shaped substrate obtained by sandwiching a strip-shaped laminated body in which each layer is 1: 1 with a plate-shaped laminated body of 3-1 and 3-2 electrodes. Since half of the side surface of the electrode is the porous electrode layer, the gas can be smoothly supplied to the reaction surface during power generation. Further, FIG. 5 is a cross-sectional view of a substrate in which the thickness of the plate-shaped laminated body of 3-2 is thinned and the layer of 3-1 is thickened correspondingly, and as a result of the reduction of the thickness of 3-2,
Gas diffusion resistance decreases because the gas flow path approaches the reaction surface,
Moreover, since the dense electrode layer 3-1 having high strength is thickened, the strength of the electrode substrate itself is improved.

In the examples, a substrate having a three-layer structure of electrodes having different porosities was shown, but the present invention is not limited to the three-layer structure. In the example of FIG. 1, in order to make the gas diffusion smoother, it is conceivable to add a large amount of a porosifying agent to the 3-2 layer to increase the porosity. However, as the amount of the porosifying agent added to the 3-2 layer increases, the difference in shrinkage rate between the 3-1 layer and the layer during sintering increases, and the stress at the interface between both layers increases. Since such stress causes distortion and cracking of the substrate, it is desirable to suppress it as much as possible. FIG. 6 is a strip-shaped stack of a fourth layer: 3-4 having a porosity (20 to 30%) intermediate between the plate-shaped stacks of the dense electrode layer 3-1 and the porous electrode layer 3-2. It is an example in which a body is sandwiched to produce a hollow substrate. By thus providing the intermediate layer between the 3-1 layer and the 3-2 layer,
The difference in shrinkage rate between the two during sintering is relaxed, and the warp or crack of the substrate can be prevented. FIG. 7 is a cross-sectional view of a substrate produced by sandwiching a strip-shaped laminated body in which the 3-1 and 3-4 layers have a thickness of 1: 1 between the 3-1 and 3-2 layered plate-shaped laminated bodies. However, as a result, it is possible to reduce the internal resistance and improve the substrate strength by increasing the thickness of the dense electrode layer 3-1.

[0009]

EXAMPLES Specific examples of the present invention will be described in detail below, but the present invention is not limited to the following specific examples.

Example 1 In this example, La _0.7 Sr _0.3 MnO was used as the air electrode material.
_{Using 3} powders, polyvinyl butyral as a binder and a mixed solvent of isopropyl alcohol: toluene = 77: 23 as a dispersion medium were added thereto, and mixed by a ball mill to obtain a slurry. After defoaming the slurry to adjust the viscosity, it was formed into a sheet having a thickness of 100 μm by the doctor blade method. This sheet is referred to as sheet 1. Further, in the production of the porous air electrode, a sheet-shaped compact was similarly prepared by adding spherical polyethylene as a porosifying agent in the above-mentioned slurry preparation. The particle size of the porosifying agent used here was 20 μm for the porous air electrode having a large pore size and 5 μm for the porous air electrode having a small pore size, and the sheet thickness was 100 μm and 15 μm, respectively.
These porous air electrode sheets are hereinafter referred to as sheet 2 and sheet 3. Prior to manufacturing an electrode substrate using these sheets, the sheets 1 to 3 are laminated and
The porosity was measured by degreasing the stick-shaped pieces that were thermocompression-bonded and cut at 360 ° C. and then sintered at 1450 ° C. for 2 hours. As a result, the porosities of the sintered bodies formed of the sheets 1 to 3 were 7%, 38% and 30%, respectively. Although spherical polyethylene is used as the porosifying agent here, the present invention is not limited to this, and any material can be used as long as it burns during the sintering of the ceramic sheet to form pores in the sintered body. It can be used as a porosifying agent. In the example of FIG. 1, the air electrode sheets 1 to 3 were used to manufacture a hollow flat plate electrode substrate having a three-layer structure having different porosities in the thickness direction.
Specifically, the sheet 1 is laminated to have a thickness of 2 mm.
One plate-like laminate 1 thermocompressed and cut into 10 × 5 cm, and a strip-like laminate 1 cut into 10 × 0.2 cm
0 sheets were produced. This strip-shaped laminated body was arranged on the plate-shaped laminated body at equal intervals, and then the plate-shaped laminated body of Sheet 2 and a sheet-shaped laminated body of Sheet 2 which were made in the same size as the plate-shaped laminated body of Sheet 1 were manufactured.
A single sheet of sheet 3 of 5 cm was sequentially superposed thereon, and these were bonded by hot pressing to give a hollow flat plate-shaped body. The molded body obtained in this way is processed at 360 ° C.
After degreasing in 1., it was sintered at 1450 ° C. for 2 hours to obtain a hollow flat plate-shaped electrode substrate having a three-layer structure having different porosities in the thickness direction. The size of this substrate is 8 × 4 cm, and the thickness is 0.
It is 5 cm.

Next, the resistance, bending strength, and three-phase interface length in the thickness direction of the electrode substrate prepared above were measured. Here, for comparison, an electrode substrate having the same structure as that of the embodiment of the present invention shown in FIG. 1 was produced using only the sheet 2,
This was a comparative example. The specific resistance in the thickness direction of the electrode substrate is
I-V measured at 1000 ° C with terminals on the top and bottom of the board
Obtained from the characteristics. The bending strength is JIS R 16
It was determined by a three-point bending strength test according to No. 01. The three-phase interface length was obtained from the sum of the outer peripheries of the pores by performing SEM observation of the surface forming the electrolyte on the electrode substrates of the comparative example and the example. The results of these measurements are shown in Table 1. As a result,
The resistance of the substrate was reduced by 42% and the strength was improved by 53%. On the other hand, since the electrode reaction proceeds at the three-phase interface between the electrode, the electrolyte, and the reaction gas, the number and length of the three-phase interfaces are important. However, in the present invention, as shown in FIG. By providing a thin layer having pores, the interface length could be 2.6 times that of the comparative example.

[0012]

[Table 1] *: Relative value when the comparative example is 1.

[0013]

As described above, according to the present invention, when the electrode substrate used for the solid oxide fuel cell is manufactured, the ceramic sheets having different porosities are laminated and sintered.
It is intended to produce an electrode substrate having high strength and conductivity, and having sufficient gas permeability to the reaction interface and many three-phase interfaces. Conventionally, in improving the performance of an electrode substrate, the improvement of conductivity and strength, the porosity, and the increase of three-phase interface are contradictory, and an electrode substrate satisfying all of these cannot be manufactured. In the present invention, preferably, a dense layer having a porosity of 10% or less, a gas diffusion layer having a porosity of 35 to 45% and a pore diameter of 10 to 20 μm, and a porosity of 25 to 3 are used.
By laminating and sintering thin layers with a pore diameter of 2-5 μm at 3%, it has excellent conductivity and strength, and also has a porosity that allows sufficient gas to be supplied to the reaction interface and many three-phase interfaces. An electrode substrate is provided. This makes it possible to increase the strength of the electrode substrate and suppress the voltage drop inside the substrate and the electrode reaction interface portion during power generation, and as a result, the cell output is improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a hollow flat plate-shaped electrode substrate including a plurality of electrode layers having different porosities according to the present invention.

FIG. 2 is a schematic diagram of a porous electrode portion of the electrode substrate of FIG.

FIG. 3 is a perspective view of a fuel cell using an electrode substrate having a gas channel inside.

FIG. 4 is a cross-sectional view of an electrode substrate having a three-layer structure in which 3-1 and 3-2 layers have the same thickness.

FIG. 5 is a cross-sectional view of an electrode substrate having a three-layer structure in which the thickness ratios of 3-1 and 3-2 layers are changed.

6 is a cross-sectional view of a four-layer structure electrode substrate in which an intermediate layer 3-4 is provided between the layers 3-1 and 3-2 of FIG.

7 is a cross-sectional view of a four-layer structure electrode substrate in which the thickness ratio of 3-1 and 3-4 layers in FIG. 6 is changed.

[Explanation of symbols]

1: Electrolyte, 2: Fuel electrode, 3: Air electrode, 4: Interconnector, 5: Gas channel, 6: Dense membrane, 7: Pore, 3-
1: dense air electrode layer, 3-2: porous air electrode layer with large pore diameter, 3-3: porous air electrode layer with small pore diameter, 3-
Air electrode layer having an intermediate porosity of 4: 3-1 and 3-2

Claims (3)

[Claims] 1. An electrode substrate used in a solid oxide fuel cell, wherein the pore size and the porosity are different in the thickness direction of the substrate. 2. An electrode substrate for a solid oxide fuel cell is a hollow flat plate having a large number of gas flow passages inside, and has a structure having different porosities in the thickness direction, and the first layer has a porosity. 1
0% or less dense layer, the second layer is a porous layer having a porosity of 35 to 45% and a pore diameter of 10 to 20 μm, and the third layer is a porous layer having a porosity of 25 to 35% and a pore diameter of 2 to 5 μm. Is a quality layer,
The second layer is stacked on the first layer, and the third layer is stacked on the second layer. If necessary, a fourth layer having a porosity of 20 to 30% may be added to the first layer and the second layer. An electrode substrate for a solid oxide fuel cell, which is arranged between layers. 3. A ceramic sheet of electrode material powder for a solid oxide fuel cell, and an average particle size of 2 in the electrode material powder.
A solid electrolyte fuel, comprising: a ceramic sheet to which a 0 μm porosifying agent is added, and a ceramic sheet to which the porosifying agent having an average particle diameter of 5 μm is added to the electrode material powder are laminated, pressed and sintered. Method for manufacturing battery electrode substrate.