JPH06196180A - Manufacture of solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To provide a solid electrolyte fuel cell excellent in gas permeability, mechanical strength and thermal consistency. CONSTITUTION:A matrix 11 being an anode is a porous body having the same main component with a solid electrolyte body 12, and inside pares change in a thickness direction in the diameter within a prescribed range, and it contains an electron conductive body, and acts as the anode. In the matrix 11 being the anode, cells are laminated on the one main surface, and the pores become small on the cell side, and are increased in a main surface direction opposed to the cells.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell and a manufacturing method thereof, and more particularly to a matrix supporting a single cell and a manufacturing method thereof.

[0002]

2. Description of the Related Art A solid oxide fuel cell is a fuel cell which uses solid zirconia as an electrolyte and is operated at a high temperature of 800 to 1000 ° C., and there is no problem of electrolyte support or corrosion and the activation overvoltage during operation is lowered. It has excellent characteristics such as no catalyst and is being actively researched.

FIG. 4 is a perspective view showing a unit cell of a conventional solid oxide fuel cell. In this battery, the porous support tube 17 is provided with mechanical strength and a single cell is formed on the outer side of the porous support tube 17. The output density cannot be increased as in the flat plate type or the integrated type, but the axial direction or the direction perpendicular to the axis This is an optimal mechanical structure that can cope with the stress relief caused by the temperature gradient of.

More specifically, a nickel-zirconia Ni-ZrO ₂ cermet is formed as an anode 18 on a porous support tube 17, a layer made of yttria-stabilized zirconia YSZ is formed as a solid electrolyte body 12, and a cathode 13 is formed.
As a result, a layer of strontium-doped lanthanum strontium manganite La (Sr) MnO ₃ is formed. An anode 18, which is an internal electrode, is electronically connected between the unit cells by an interconnection 14 made of lanthanum chromite LaCrO ₃ . A fuel gas such as oxygen or carbon monoxide flows axially inside the support tube as shown by an arrow 15, and an oxidant gas such as air flows outside the unit cell as shown by an arrow 16. According to this method, the porous support tube 17 having air permeability gives the unit cell structural rigidity.

The main specifications required for the support tube of the solid oxide fuel cell are as follows. 1) It has a through hole large enough so that the diffusion of the gas is not rate-determining, and the diffusibility of the gas is good. 2) It must have mechanical strength to withstand thermal shock during manufacturing or power generation. 3) It is chemically stable in an oxidizing or reducing atmosphere. 4) Not chemically react with other fuel cell components. 5) The coefficient of thermal expansion is compatible with the fuel cell constituent members.

Among the above, there is a correlation between the diffusivity of gas and the mechanical strength, and if the porosity is increased, the gas diffusivity is improved but the mechanical strength is reduced. On the other hand, if the porosity is lowered, the gas diffusivity is lowered, but the mechanical strength is improved.
Therefore, in order to optimize the performance of the support tube, it is necessary to control the pores, and the optimum point is required from the gas diffusivity and mechanical strength. Conventionally, calcia-stabilized zirconia, nickel and yttria-stabilized zirconia cermet, α-alumina, etc. have been used for the support tube.

When the fuel is hydrogen, the current i₀And Anor
Required H to do₂Theoretical feed rate Q _H2The relation with
expressed. Q_H2= I₀/ 2F (1) where F is a Faraday constant. With this, 1A / c
m²At the current density, assuming that the fuel utilization rate is 40%,
H to node₂Theoretical feed rate of 17.4 ml / min
・ Cm²Becomes This is the minimum required amount
When considering the operating temperature, utilization factor, etc.
Flow rate is required.

The gas supply rate Q of the porous support tube which is the anode and the gas permeation coefficient φ have the following relationship. Q / S = φ · ΔP / t (2) where ΔP is the differential pressure applied to the support tube, t is the thickness of the support tube,
S is a cross-sectional area. Using the above equation, the gas diffusivity of the porous support tube can be evaluated by the value of the gas permeability coefficient φ. Considering the volume expansion of the gas at 1000 ° C., the gas permeability coefficient required for the support tube is expected to be about 10 ⁻² .

In the production of a solid oxide fuel cell, a support tube is molded, then anode and cathode electrodes are laminated and then fired at a temperature of 1200 to 1500.degree. The electrode material should not react with the support tube at such high temperatures.

[0010]

When the coefficient of thermal expansion of the support tube is different from that of the solid electrolyte body, the electrolyte body formed on the surface layer peels off. This problem is particularly likely to occur when alumina is used for the support tube. In order to prevent this problem, it has been attempted to use a zirconia-based support tube, such as calcia-stabilized zirconia, which has a matched coefficient of thermal expansion. When a zirconia-based support tube is used, the compatibility with the solid electrolyte body is improved, but the coefficient of thermal expansion does not match with the metals such as nickel and cobalt used for the anode, and repeated peeling and cracking of the anode occur after repeated heat cycles. Occurs.

Further, when the support tube is prepared from nickel-zirconia Ni-ZrO ₂ cermet, the support tube can be used as an anode, the gas diffusion property can be improved, and the weight reduction of the solid oxide fuel cell can be expected. Such support tubes are nickel oxide NiO yttria stabilized zirconia YSZ.
It is prepared by forming a support tube by using the above and firing it, then assembling a battery and flowing a fuel gas. Nickel oxide is reduced by the fuel gas. However, in the Ni-YSZ support tube thus obtained, volume contraction occurs on the order of% of the support tube surface layer even when the nickel content is reduced to 30% by volume where electron conductivity can be secured. The solid electrolyte body was bent, cracked, and the support tube itself was cracked.

The present invention has been made in view of the above points, and an object thereof is to develop a matrix having thermal compatibility with solid electrolyte bodies and electrodes, and having excellent gas diffusivity and mechanical strength. It is to provide a solid oxide fuel cell having excellent reliability and a method for manufacturing the same.

[0013]

According to the first aspect of the present invention, there is provided a support membrane type solid oxide fuel cell, comprising: (1) a matrix; (2) a single cell; and (3). The matrix has an electron conductor, and the matrix supports the single cell through the solid electrolyte body on its one main surface and carries the electron conductor in its pores. The single cell is formed on the solid electrolyte body and its one main surface. The electrodes are electrodes of a predetermined polarity, and the matrix is a porous substrate whose main component is the same as that of the solid electrolyte body, and the diameter of the pores increases from the main surface supporting the single cell toward the opposite main surface. The electron conductor is supported on the matrix and functions as an electrode having a polarity opposite to that of the electrode, and according to the second invention, a method for manufacturing a solid oxide fuel cell of a supporting membrane system, (1) Matrix preparation step, and (2) The matrix preparation step is a step of preparing a matrix by impregnating a porous plastic sheet with a slurry of powder having the same main component as the solid electrolyte body and then heat-treating the matrix. The step of impregnating the body is achieved by impregnating the matrix with the slurry of the electron conductor and heat-treating the matrix to support the electron conductor.

[0014]

Since the matrix has the same main component as the solid electrolyte body, the thermal compatibility with the solid electrolyte body is enhanced. Since the electron conductor functioning as an electrode is supported on the matrix, the electrode does not peel off from the solid electrolyte body. Since the pore diameter of the matrix changes in the thickness direction of the matrix within a predetermined range, both gas diffusivity and mechanical strength are improved.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. Example 1 FIG. 1 is a perspective view showing a unit cell of a solid oxide fuel cell according to an example of the present invention. This battery comprises a matrix 11 as an anode, a solid electrolyte body 12 and interconnections 14 laminated on the outer peripheral surface of the matrix 11, and a cathode 13 laminated on the outer peripheral surface of the solid electrolyte body 12. A fuel gas is flown inside the matrix 11 which is an anode, and an oxidant gas 16 is flowed outside the cathode 13.

Such a solid oxide fuel cell is prepared as follows. The matrix 11 that is the anode will be described later. The solid electrolyte body 12 is a yttria-stabilized dense zirconia (thickness 40 to 200 μm) and has a YSZ powder having a particle size range of 7 to 50 μm (PC-YZ ₁₄ W / F: manufactured by Nippon Polishing Industry Co., Ltd.). Was deposited on the matrix 11 as the anode by the low pressure plasma spraying method.

The cathode 13 is a perovskite complex oxide having a thickness of 50 to 200 μm. For example, alkaline earth or rare earth doped or undoped oxide or a mixture of oxides, such as lanthanum manganite LaMnO ₃ , lanthanum nickelite LaNiO ₃ , lanthanum cobaltite LaCoO ₃ , lanthanum chromite LaCrO ₃ etc. It consists of oxides and combinations thereof. Preferred dopants are strontium, calcium and the like. For example, strontium-doped lanthanum manganite L
The case of using a _0.85 Sr _0.15 MnO ₃ will be described. Lanthanum oxide La ₂ O ₃ , manganese carbonate MnCO ₃ and strontium carbonate SrCO ₃ were used as starting materials for the synthesis using the powder mixing method, and weighed so that the composition was La _0.85 Sr _0.15 MnO ₃ . Water was added to this, and the mixture was wet-mixed, dried, and then crushed, and then calcined in air at a temperature of 1250 ° C for 6 hours to obtain La _0.85 Sr.
_A calcined powder of _0.15 MnO ₃ is obtained. The powder obtained by crushing the calcined powder was confirmed to be a perovskite single phase by X-ray diffraction. The obtained powder is added with polyvinyl butyral as a binder, polyethylene glycol as a wetting agent, and dioctyl phthalate as a plasticizer in a mixed solvent (60:40 wt%) of toluene and isopropyl alcohol, and wet mixed for 12 hours with a ball mill. The obtained slurry was defoamed in a vacuum glove box at a pressure of about 160 mmHg for 10 to 30 minutes. This slurry was applied and baked on the already formed solid electrolyte body 12 using a coating method.

Each unit cell is connected at least in series with an adjacent unit cell. For example, electrical connections are made along the entire electrochemically active length in selected axial directions of the unit cell. Here, a mask is applied to a predetermined portion in the lengthwise direction of the outer peripheral surface of the matrix 11 which is the anode when the solid electrolyte body is formed, and the interconnection 14 is attached to this portion. The interconnection 14 extending over the entire active length of this unit cell is
Conductivity must be maintained under both reducing and oxidizing atmospheres. Therefore, the preferred interconnection material is LaCr doped with alkaline earth or rare earth.
O ₃ . Preferred dopants are strontium, calcium, magnesium and the like. For example, the case of using calcium-doped La _0.7 Ca _0.3 CrO ₃ will be described. As the starting material when synthesizing using the powder mixing method,
Lanthanum oxide La ₂ O ₃ , chromium oxide Cr ₂ O ₃ and calcium carbonate CaCO ₃ were mixed with a predetermined amount of each powder, and the mixture was mixed in air 12
It was calcined at a temperature of 00 ° C. for 5 hours and crushed with a ball mill for 8 hours. The synthesized calcined powder was subjected to X-ray diffraction and confirmed to be a perovskite single phase. This was classified into a particle size range of 44 μm to 74 μm, and a dense interconnection 14 having a thickness of 40 to 100 μm was formed by reduced pressure plasma spraying.

Next, the relationship between the average pore diameter of the matrix and the gas diffusibility will be described below. The matrix was prepared by a known method using yttria-stabilized zirconia. The average pore diameter of the matrix was arbitrarily controlled by combining the type and addition amount of the binder, the firing method, the particle size of the raw material powder, and the like. The matrix thickness was 2.0 to 3.0 mm, and the pore size distribution of the matrix was measured by the mercury porosimetry. The gas permeability coefficient of the matrix that is the anode was calculated from the amount of N ₂ permeation at room temperature.

FIG. 3 is a diagram showing the relationship between the average pore diameter of the matrix and the gas permeation coefficient. The gas permeation coefficient is 10 ^-2 [cm ² · s ^-1 so that the diffusion of the reaction gas does not rate-limit the electrode reaction under high temperature operation of the solid oxide fuel cell.
It can be seen that an average pore diameter of 2 μm or more is required to obtain [cmH ₂ O ^-1 ]. This corresponds to the average particle size of zirconia powder granules of 50 μm. On the other hand, as the gas permeability coefficient of the matrix increases, the gas diffusivity improves, but the mechanical strength decreases as the average pore diameter increases, and cracks easily occur due to thermal shock during operation. In the study range of the present invention, it was found that the strength was extremely reduced when the average pore diameter was 20 μm or more. Therefore,
The upper limit of the average pore size was set to 15 μm. This corresponds to an average particle size of zirconia powder granules of 300 μm.

Conventionally, porosity has been used as an index as a control factor of gas diffusivity, but as a result of examination, it was found that the magnitude of porosity and the gas permeation coefficient do not necessarily correspond uniquely. Even if the porosity is large, this does not necessarily mean that there are many through holes connecting the inside and outside of the matrix. That is, it is considered that the average pore diameter is more dominant than the porosity as a control factor of gas diffusivity.

Next, the matrix 1 which is the anode of the present invention
1 will be described in detail. FIG. 2 is a sectional view of an essential part showing a unit cell of a solid oxide fuel cell according to an embodiment of the present invention. The matrix is a porous body obtained by impregnating a flexible polyurethane foam with a slurry of yttria-stabilized zirconia YSZ, then drying and firing at a temperature of 1400 ° C. for 3 hours. The matrix comprises a fine pore layer 20 having a pore diameter of 2 μm and a coarse pore layer 19 having a pore diameter of 15 μm. The pore layer has a thickness of 500μ
m is the outer layer and the coarse pore layer is the inner layer having a thickness of 2 mm. The length of the matrix is 50 cm and the thickness is 2.5 mm.

Nickel oxide and yttria-stabilized zirconia YSZ were weighed in a ratio of 3: 1 as an anode material, distilled water was added as a solution, and polycarboxylic acid ammonium salt was added as a dispersant, and the mixture was mixed for a predetermined time in a ball mill to prepare a slurry. And Although various solvents can be used in preparing the slurry, water that is nonflammable and does not cause environmental pollution is preferable. Pour the obtained slurry into a matrix,
It was suction filtered and impregnated. The slurry-impregnated matrix was dried in an oven at a temperature of 60 ° C. for 8 h, then held at 110 ° C. for 8 h, and then in air for 130 h.
It was baked for 2 hours at a temperature of 0 ° C.

Then, at a temperature of 1000 ° C. in a hydrogen stream, 1
The nickel oxide was reduced to nickel by heating for h. The obtained electrode did not peel off and no cracks in the matrix were observed. The solid electrolyte that can be used as the matrix may be the same yttria-stabilized zirconia YSZ as the solid electrolyte body, or may be zirconia partially stabilized by other stabilizing dopants such as magnesia, calcia, and ceria, or completely stabilized. The same effect as above can be obtained by adding carbides or nitrides in addition to mullite, alumina, etc., which can be added as a reinforcing material.

Nickel is preferred as the anode material from the viewpoint of oxidation resistance, but other electron conductors such as cobalt,
Iron, ruthenium or alloys or mixtures of these can be used. Since the inner layer of the matrix is a coarse pore layer, the gas permeability coefficient of the matrix is almost 10
^A value close to ^-1 [cm ² · s ^-1 · cmH ₂ O ^-1 ] is obtained. Further, since the outer layer of the matrix is a pore layer, the mechanical strength of the matrix is large. In this way, a matrix excellent in both gas permeability and mechanical strength can be obtained. Example 2 A cathode matrix is prepared as a flat plate. The matrix is composed of a fine pore layer and a coarse pore layer in the same manner as in Example 1.
La _0.85 Sr _0.15 MnO ₃ is used as the cathode material. Lanthanum oxide La ₂ O ₃ , manganese carbonate MnCO ₃ and strontium carbonate SrCO ₃ were used as starting materials for the synthesis using the powder mixing method, and weighed so that the composition was La _0.85 Sr _0.15 MnO ₃ . Water was added to this, and the mixture was wet-mixed, dried, and then crushed, then calcined in air at a temperature of 1250 ° C for 6 hours, and La _0.85 Sr
_A calcined powder of _0.15 MnO ₃ is obtained. The powder obtained by crushing the calcined powder was confirmed to be a perovskite single phase by X-ray diffraction. The obtained powder is wet-mixed in a ball mill for 10 hours using polyacrylonitrile as a binder. The obtained slurry was defoamed in a vacuum glove box at a pressure of about 160 mmHg for 10 to 30 minutes. This slurry was impregnated into a matrix composed of yttria-stabilized zirconia YSZ and dried, and then dried in air at a temperature of 1300 ° C. for 2 hours.
Baked. The obtained cathode matrix (not shown) is effective as a cathode. In the above example, strontium-doped lanthanum manganite LaMnO ₃
Other perovskite-based complex oxides such as alkaline earth or rare earth doped or undoped oxides or mixtures of oxides, such as lanthanum manganite LaMnO ₃ , lanthanum nickelite LaNi.
O ₃ , lantern cobaltite LaCoO ₃ , lanthanum chromite
Oxides such as LaCrO ₃ and combinations thereof have the same effects as above.

[0026]

According to the first aspect of the present invention, according to the first aspect of the present invention, there is provided a support membrane type solid oxide fuel cell,
The matrix has (1) a matrix, (2) a single cell, and (3) an electron conductor, and the matrix supports the single cell on one main surface through a solid electrolyte body and carries the electron conductor in its pores. The single cell is a solid electrolyte body and electrodes of a predetermined polarity arranged on one main surface thereof, and the matrix is a porous body having the same main component as the solid electrolyte body, and the pore diameter is a unit cell. It is assumed that the electron conductor increases from the supporting main surface toward the opposite main surface, and the electron conductor is carried by the matrix and functions as an electrode having a polarity opposite to that of the electrode, so that the matrix and the solid electrolyte body are thermally aligned. The nature is enhanced.
Since the electron conductor functioning as an electrode is supported on the matrix, the electrode does not peel off from the solid electrolyte body. Furthermore, a solid oxide fuel cell having excellent gas diffusivity and mechanical strength can be obtained by the pore distribution of the matrix.

According to a second aspect of the present invention, there is provided a method for manufacturing a solid oxide fuel cell of a supporting membrane system, which comprises (1) a matrix preparing step and (2) an electron conductor supporting step.
The matrix preparation process is a process of preparing a matrix by impregnating a porous plastic sheet with a slurry of powder having the same main component as the solid electrolyte and then heat treating it, and the supporting process of the electron conductor is carried out by mixing the slurry of the electron conductor. Since it is a step of impregnating the matrix and carrying out a heat treatment to support the electron conductor on the matrix, a solid oxide fuel cell excellent in thermal compatibility, gas permeability, and mechanical strength against thermal shock can be obtained. Easily obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a unit cell of a solid oxide fuel cell according to an embodiment of the present invention.

FIG. 2 is a sectional view of an essential part showing a unit cell of a solid oxide fuel cell according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an average pore diameter of a matrix and a gas permeation coefficient.

FIG. 4 is a perspective view showing a unit cell of a conventional solid oxide fuel cell.

[Explanation of symbols]

 11 Matrix that is an anode 12 Solid electrolyte body 13 Cathode 14 Interconnection 15 Fuel gas 16 Oxidant gas 17 Porous support tube 18 Anode 19 Coarse pore layer 20 Pore layer

Claims (9)

[Claims] 1. A solid oxide fuel cell of a supporting membrane system, comprising: (1) matrix, (2) single cell, (3) electron conductor, and the matrix has a solid electrolyte on one main surface thereof. A single cell is supported through a body and an electron conductor is carried in its pores. The single cell is a solid electrolyte body and electrodes of a predetermined polarity arranged on one main surface of the solid electrolyte body, and the matrix is the solid electrolyte body. And the diameter of the pores increases from the main surface supporting the single cell to the main surface facing the porous body having the same main component as that of the electron conductor supported on the matrix to A solid oxide fuel cell, which functions as an electrode of opposite polarity. 2. The solid oxide fuel cell according to claim 1, wherein the pore size of the matrix is in the range of 2 to 15 μm. 3. The solid oxide fuel cell according to claim 1, wherein the matrix is zirconia partially or completely stabilized by yttria, magnesia, calcia or ceria. 4. The solid oxide fuel cell according to claim 1, wherein the electron conductor is nickel, cobalt, ruthenium, or an alloy or mixture thereof. 5. The solid oxide fuel cell according to claim 1, wherein the electron conductor is lanthanum manganite LaMnO ₃ , lanthanum chromite LaCrO ₃ , lanthanum nickelite LaNiO ₃ , lanthanum cobaltite doped with alkaline earth or rare earth. A solid oxide fuel cell, which is LaCoO ₃ or a mixture thereof. 6. The solid oxide fuel cell according to claim 1, wherein the solid electrolyte body is yttria-stabilized zirconia. 7. The solid electrolyte fuel cell according to claim 1, wherein the solid electrolyte body of the single cell is provided with an electrode having the same function as an electron conductor on the main surface in contact with the matrix. battery. 8. A method for manufacturing a support membrane type solid oxide fuel cell, comprising: (1) a matrix preparing step and (2) an electron conductor supporting step, wherein the matrix preparing step is a porous plastic. The step of impregnating the sheet with a slurry of powder having the same main component as the solid electrolyte and then heat treating to prepare a matrix, the step of supporting the electron conductor impregnating the matrix with the slurry of the electron conductor, and A method for producing a solid oxide fuel cell, which comprises a step of carrying out heat treatment to support an electron conductor on a matrix. 9. The method for producing a solid oxide fuel cell according to claim 8, wherein the porous plastic sheet is a flexible polyurethane foam.