JP3230156B2 - Electrode of solid oxide fuel cell and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode structure of a solid oxide fuel cell (SOFC), which is being developed as a third generation fuel cell for power generation, and a method of manufacturing the same.

[0002]

2. Description of the Related Art SOFCs are roughly classified into a cylindrical type and a flat type. The flat type includes a bipolar type and a monolith (integral) type. In both cases, a solid electrolyte made of an oxide ion conductor is used as an air electrode. It has a laminated structure sandwiched between a (cathode) and a fuel electrode (anode). The single cells made of the laminate are connected via an interconnector (separator), and a gas supply distributor is interposed between the electrode and the interconnector as necessary, or a distributor structure is provided to the interconnector.

In an SOFC, oxygen (air) is placed on the air electrode side.
However, fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode side. When oxygen supplied to the air electrode side passes through the air electrode and reaches near the interface with the solid electrolyte, it receives electrons from the air electrode and is ionized into oxide ions (O ²⁻ ). The generated oxide ions diffuse and move in the direction of the fuel electrode in the solid electrolyte, react with the fuel gas near the interface with the fuel electrode, and form a reaction product (H ₂ O, CO ₂
Etc.) and emit electrons to the fuel electrode. These electrons are taken out as electricity.

[0004] The electrode reaction of SOFC, for example, ionization reaction of oxygen molecules to oxide ions occurring on the air electrode side (1 /
Since 2 O ₂ + 2e ⁻ → O ^2- ) involves oxygen molecules, electrons and oxide ions, (1) a solid electrolyte carrying oxide ions, and (2) an air electrode carrying electrons It is said that this occurs only at the three-phase interface of (3) the gas phase (air) that supplies oxygen molecules. Similarly, at the fuel electrode side, an electrode reaction occurs at the three-phase interface between the solid electrolyte, the fuel electrode, and the gaseous fuel gas.
BR> happens. It is therefore believed that increasing the three-phase interface (which is more precisely the "three-phase interface length" since it is one-dimensional) is advantageous to the smooth progression of the electrode reaction.

The material of the solid electrolyte must have high oxide ion conductivity, be chemically stable under conditions from an oxidizing atmosphere on the air electrode side to a reducing atmosphere on the fuel electrode side, and be resistant to thermal shock. Desired. Yttria-stabilized zirconia (YSZ) has been conventionally used as a solid electrolyte material satisfying such requirements.

On the other hand, both the air electrode and the fuel electrode, which are electrodes, need to be made of a material having high electron conductivity. Since the cathode material must be chemically stable in a high-temperature oxidizing atmosphere of about 1000 ° C., metals are unsuitable, and a perovskite oxide material having electron conductivity is suitable. Examples of such materials include LaMnO ₃ , LaCo
O ₃ , SmCoO ₃ , PrCoO ₃ , and L of these compounds
Although a, a solid solution in which a part of Sm or Pr is substituted with Sr, Ca, or the like is available, LaMnO ₃ having a thermal expansion coefficient close to that of YSZ or a solid solution thereof is mainly used. The fuel electrode material is generally a metal such as Ni or Co, or a cermet such as Ni-YSZ or Co-YSZ. Incidentally, metals such as Ni are usually NiO
Is reduced to metal during operation of the fuel cell.

[0007] The solid electrolyte is a gas impermeable dense layer because it functions as a partition for preventing direct contact between fuel gas and air, as well as a moving medium for oxide ions. On the other hand, the electrodes (the air electrode and the fuel electrode) are formed as porous layers so that the gas can pass therethrough. Each layer is formed by a thermal spraying method, an electrochemical vapor deposition (EVD) method, a sheet forming method using a slurry, a screen printing method, or the like. For example, in the case of the thermal spraying method, a dense layer can be formed by plasma spraying, and a porous layer can be formed by acetylene spraying. E
In the VD method, a dense layer is formed. In the sheet forming method, a dense layer and a porous layer can be separately formed depending on the particle size of the powder in the slurry and the presence or absence of an organic pore-forming agent.

As described above, the electrodes (air electrode and fuel electrode) of the SOFC are required to be porous and have a large three-phase interface length. In order to increase the three-phase interface length, Japanese Patent Application Laid-Open No. 1-227362 discloses that the particle size is adjusted so that fine particles are present in a portion of the electrode layer in contact with the electrolyte and coarse particles are present in other portions. Proposed. Also,
When the sheet forming method is used, the porosity of the electrode is increased by adding a powder of an organic substance which is thermally decomposed and removed during sintering (that is, solid at room temperature) as a pore-forming agent to form the sheet. (E.g., JP-A-6-251772)
No., JP-A-6-206781).

Further, in order to avoid a rapid change in the coefficient of thermal expansion mainly at the interface between the electrolyte and the electrode, it is also possible to adopt a gradient composition in which the composition change at the interface is gentle, as disclosed in JP-A-2-27863. And many other patent publications.

[0010]

However, the conventional adjustment of the porosity of the electrode of the SOFC by such means as adjusting the particle size of the electrode material and adding an organic powder as a pore-forming agent requires a sufficient three-phase interface length. Therefore, there was a problem that the electrode reaction was limited, the polarization was increased, and the output of the SOFC was reduced.

Further, in the conventional SOFC, since the materials of the electrode and the electrolyte are different from each other, it is difficult to completely match the thermal expansion coefficients of the two, and it is easy to cause thermal distortion. This problem can be alleviated by the gradient composition at the above interface,
The gradient composition is not a fundamental solution because it does not match the thermal expansion coefficients, and the formation of the gradient composition layer is troublesome and costly. The present invention provides an electrode and an electrode / solid electrolyte laminate of a solid oxide fuel cell and a method for producing the same, which can solve these problems.

[0012]

Means for Solving the Problems The present inventors disclosed in Japanese Patent Laid-Open No.
Attention was paid to a method for manufacturing a porous metal body disclosed in Japanese Patent No. 49002. In this method, the sheet is formed by adding a water-insoluble organic solvent having a higher vapor pressure than water to an ordinary aqueous slurry for sheet formation containing fine metal powder and a water-soluble resin binder. During the drying of the molded article, the organic solvent evaporates and turns into a gas to evaporate from the molded article, so that a large number of air bubbles are generated and the molded article has a three-dimensional network structure. When this molded body is sintered, a porous metal sintered body having a three-dimensional network structure is obtained.

This sintered body is formed by sintering a metal fine powder. Since the porous material itself forms a three-dimensional network structure, the total specific surface area including the internal surface area of the network structure is added. Is as large as 1000 cm ² / cm ³ or more, and the total porosity is 80 to 97%. As a conventional metal body having a three-dimensional network structure, there is a metal body plated with a polyurethane foam having a three-dimensional network structure, which has a porosity of 92%.
Although very large at ~ 96%, the specific surface area is 5-75 cm ² / c
not only to m ^3.

The present inventors have tried to apply the above-described method for producing a porous metal body to a ceramic material for forming an electrode, and as a result, have formed an electrode skeleton having a three-dimensional network structure by this method. However, it has been found that when the particles of the electrode material are adhered to the surface of the electrode skeleton, the surface area used for the electrode reaction becomes very large, so that the above problem can be solved.

Here, the present invention has a skeleton composed of a porous sintered body having a three-dimensional network structure made of an oxide ion conductive material and / or an oxide ion mixed conductive material, and the surface of this skeleton is provided. A solid oxide fuel cell electrode characterized in that particles made of an electron conductive material and / or mixed oxide ion conductive material adhere to the electrode. Preferably, the electrode is an electrode / electrolyte laminate or electrode / electrolyte / integrally formed on one or both sides of an oxide ion conductive dense solid electrolyte layer with an electrolyte.
It takes the form of an electrode stack.

The present invention also relates to a solid oxide fuel cell comprising an air electrode and / or a fuel electrode comprising the electrode having the above structure.

The skeleton of the electrode of the present invention is obtained by forming a sheet using an aqueous slurry containing a water-immiscible organic solvent having a higher vapor pressure than that of water. It can be formed by forming a porous sheet having a three-dimensional network structure made of a conductive material and sintering the sheet.

Before or after sintering the porous sheet having the three-dimensional network structure, the porous sheet is impregnated with a slurry of an electron conductive material and / or a mixed oxide ion conductive material and, if necessary, is heated in the thickness direction. After being compressed and then sintered, the electrode of the present invention can be manufactured. On one side of this electrode,
When a dense electrolyte layer is formed by thermal spraying or electrochemical deposition of an oxide ion conductive material, an electrode / electrolyte laminate of a solid oxide fuel cell can be manufactured.

Further, a dense solid electrolyte sheet having oxide ion conductivity is thermocompression-bonded to the unsintered three-dimensional net-structured sheet, and the obtained laminate is sintered to obtain a solid oxide fuel. A battery electrode skeleton / electrolyte laminate is obtained. Further, the obtained sintered body is impregnated with a slurry of an electron conductive material and / or a mixed oxide ion conductive material, and then sintered again to produce an electrode / electrolyte laminate for a solid oxide fuel cell. Can be.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrode of a conventional solid oxide fuel cell is usually a sintered body of fine powder of an electrode material, and has a structure in which particles and pores are simply dispersed. That is, the pores only exist between the particles of the electrode material. Even in the case of having a graded composition, the simple dispersion structure is the same except that the particles of the electrode material change in the thickness direction of the layer.

The use of an organic pore-forming agent in the form of a solid powder, which disappears during firing, as disclosed in JP-A-6-251772 or the like, creates voids in the electrode larger than the pores between the particles. As a result, the porosity of the electrode increases. However, even in this case, since these large voids are only scattered in the electrode, and the electrode does not have a three-dimensional network structure, the specific surface area is small, and it is substantially impossible to attach a large amount of another particle to the void. Impossible. As schematically shown in FIG. 1, the electrode of the present invention has a structure in which particles 2 are adhered to the surface of a skeleton 1 composed of a porous sintered body having a three-dimensional network structure. The skeleton 1 of the three-dimensional network structure has large pores A (that is, pores of the network structure) generated by the generation of bubbles due to evaporation of liquid, and small pores B (that is, pores inside the sintered body) between the particles constituting the skeleton. )). The particles 2 adhere to the surface of the skeleton 1, that is, the outer surface of the skeleton and the surface of the large pores A. Although the attached particles 2 are illustrated as being isolated from each other for the purpose of drawing, the attached particles 2 actually contact each other to form an extremely thin porous coating layer.

Accordingly, the solid electrode is different from the conventional electrode in that the solid is composed of two kinds of materials, that is, the porous skeleton 1 and the adhered particles 2, and the pores are composed of two kinds of large pores A and small pores B. Further, the skeleton has a three-dimensional network structure, which is different from the porous body formed by the above-mentioned organic pore-forming agent.

The surface of the skeleton to which the particles 2 adhere, that is, the outer surface of the skeleton and the surface of the large pores A in the network structure are the electrode surfaces. Therefore, the surface area of the electrode is dramatically increased as compared with the conventional case where only the outer surface is the electrode surface, so that the three-phase interface length is significantly increased and the electrode characteristics are greatly improved. In addition, since the porosity of the electrode skeleton is very large, the effect of alleviating thermal shock and thermal strain is large, and it is possible to prevent occurrence of destruction due to a difference in thermal expansion coefficient with the electrolyte. Furthermore, if the electrode skeleton is made of the same material or a similar material as the material of the electrolyte, the thermal shock and thermal strain are significantly reduced.

Since the skeleton 1 of the electrode serves as a path for oxide ions leading to the solid electrolyte, a certain degree of oxide ion conductivity is required. Therefore, as the material of the skeleton,
At least one selected from an oxide ion conductive material and an oxide ion mixed conductive material is used.

On the other hand, the adhering particles 2 need to have a certain degree of electron conductivity because they pass through the three-phase interface for electrons necessary for the transfer of oxide ions. Therefore, the attached particles
It is composed of at least one material selected from an electron conductive material and an oxide ion mixed conductive material. Preferably, at least a part of the attached particles is made of an electron conductive material. That is, the adhered particles are made of only the electron conductive material or a mixture of the electron conductive material and the oxide ion mixed conductive material.

In this specification, an oxide ion conductive material means an oxide ion conductive material having an ion transport number of 0.7 or more. The oxide ion mixed conductive material means an oxide ion conductive material having an ion transport number of 0.1 to 0.7. An oxide ion conductive material having an ion transport number of less than 0.1 is an electron conductive material.

The first suitable material for the skeleton 1 is an oxide ion conductive material which has been conventionally used as a solid electrolyte of a solid oxide fuel cell. That is, typically, yttria-stabilized zirconia (YSZ) having a fluorite-type crystal structure is used, but other oxide ion conductive materials known to be usable as a solid electrolyte for a fuel cell are also used. be able to.

As an oxide ion conductive material having a conductivity higher than that of YSZ, there is a lanthanum gallate-based material having a composition represented by the following formula and having a perovskite crystal structure, which was previously filed by the present applicants. Was. This material has properties suitable as a solid electrolyte for a solid oxide fuel cell,
Since it shows high conductivity even at a low temperature, it is possible to construct a solid oxide fuel cell whose operating temperature is lower than the conventional one at around 1000 ° C. This material is also very suitable as a skeletal material of the electrode in the present invention.

Ln _1-x A _x Ga _1-yz B1 _y B2 _z O ₃ ... wherein Ln is one or two of La, Ce, Pr, Nd and Sm.
A or more, preferably La and / or Nd, more preferably La; A = one or more of Sr, Ca, Ba, preferably Sr; B1 = Mg, one or more of Al, In, Preferably, Mg; B2 = one or more of Co, Fe, Ni, Cu, preferably Co or Fe, more preferably Co; x = 0.
05-0.3, preferably 0.10-0.25, more preferably 0.17
~ 0.22; y = 0.025 to 0.29, preferably 0.025 to 0.17,
More preferably 0.09 to 0.13; z = 0.01 to 0.15, preferably 0.02 to 0.15, more preferably 0.07 to 0.10; y + z ≦ 0.
3, preferably y + z = 0.10-0.25.

When the skeleton is formed from a mixed oxide ion conductor, suitable materials represented by the above formula, Ln,
A, B1, B2, and x are as described above, and y and z
Is a lanthanum gallate-based material having a perovskite structure.

Y = 0 to 0.29, preferably 0.025 to 0.17,
More preferably 0.09 to 0.13; 0.15 <z ≦ 0.3, preferably 0.15 <z ≦ 0.25; y + z ≦ 0.3, preferably y + z =
0.10-0.25. That is, when the lanthanum gallate-based material having the composition represented by the above formula has az value of 0.15 or less, the ion transport number increases and the oxide ionic conductor is formed.
When the value exceeds 0.15, the ion transport number is lowered, and the oxide-ion mixed conductor is obtained.

Another mixed oxide ion conductor suitable for the framework material is a material of the perovskite type crystal structure, also represented by the following formula: A '_1-x' Ca _{x '} Ga _1-y' B _'y' O ₃ · · · wherein, a '= trivalent ions 8 coordination ionic radius 1.05.
15% of one or more lanthanoid metals; B '
= One or more of Co, Fe, Ni and Cu, preferably
Cox '= 0.05-0.3, preferably 0.05-0.2; y' = 0.05
~ 0.3, preferably 0.08-0.2.

Examples of the A ′ metal include Nd, Pr, Sm, Ce, Eu, and Gd.
Etc., among which Nd is particularly preferred. The material represented by the above formula can exhibit higher conductivity than the material represented by the formula.

When the electrode is a fuel electrode (anode), it is not preferable that the skeleton is made of the above-mentioned mixed oxide ion conductor, because the total conductivity is reduced in a reducing atmosphere to which the fuel electrode is exposed. When the electrode is an air electrode (cathode), the above problem does not occur even if the skeleton is a mixed oxide ion conductor. Therefore, the framework material of the air electrode may be an oxide ion conductor, an oxide ion mixed conductor, or a mixture of both.

The surface of the skeleton 1 having this three-dimensional network structure
(Including the voids of the network structure, that is, the surface of large pores A)
The particles 2 adhered to are made of an electron conductive material and / or an oxide ion mixed conductive material as described above. The adhered particles may be made of a material conventionally used for a fuel electrode or an air electrode.

As the material of the particles attached to the fuel electrode, Ni, C
o, Ce_1-mC_mO_Two (C is one of Sm, Gd, Y, Ca or
At least one selected from two or more, m = 0 to 0.4)
Can be used. Of these, Ce_1-mC_mO_Two(this is
CeO if m = 0_TwoIs mixed oxide ion conduction
The body, and the metal is, of course, the electronic conductor. Preferred
One is at least one metal selected from Ni and Co (preferably
Ni) and Ce _1-mC_mO_TwoIs a mixture with

As a material of the particles attached to the air electrode, La which is an electron conductive material or an oxide ion mixed conductive material is used.
At least one material of MnO ₃ , LaCoO ₃ , SmCoO ₃ , and PrCoO ₃ can be used. Here, for example, LaMn
The O ₃ -based material includes a material in which La or Mn is partially replaced with another metal, and the same applies to the other materials. For example, a conventionally known material in which a part of La is replaced with Sr and / or Ca can be used.

The electrodes of the solid oxide fuel cell are used in a form integrated with the solid electrolyte layer. The electrode in which the particles of the electrode material are adhered to the skeleton surface of the porous sintered body having the three-dimensional network structure according to the present invention is, as described later, an electrolyte material for the thermocompression-bonded or sintered electrode before sintering. Can be integrated with the electrolyte material by a method such as thermal spraying.

In order to eliminate or minimize thermal distortion at the electrolyte / electrode interface, which is a problem when integrated with the solid electrolyte, the electrode skeleton is made of the same or similar material as the solid electrolyte layer. May be. The term “similar material” means a material having the same crystal structure as the main component.

For example, when the solid electrolyte is YSZ,
The skeleton of the electrode can also be composed of YSZ. Also,
The solid electrolyte is an oxide ion conductor represented by the above formula.
(I.e., when the z value is 0.15 or less), the skeleton of the electrode is also composed of the same oxide ion conductor,
Alternatively, a material of the same formula, but with a z-value greater than 0.15, which is a mixed oxide ion mixed conductor, can be used. Further, the compound represented by the above formula is also a common material in terms of a rare earth gallate having a perovskite structure, and thus can be sufficiently used as an electrode skeleton.

When the material of the skeleton occupying most of the electrodes is made of the same material or a material similar to that of the solid electrolyte, the problem of thermal distortion at the electrolyte / electrode interface can be eliminated or significantly reduced. However, in the present invention, the electrode skeleton has a three-dimensional network structure having a large surface area, and since this structure has a relaxing effect against thermal shock and thermal stress, the electrolyte and the electrode skeleton are different materials. However, the occurrence of destruction due to the difference in the coefficient of thermal expansion between the two is unlikely to occur.

Next, the method for producing the electrode, the skeleton thereof, and the electrode / electrolyte laminate according to the present invention will be described. An electrode skeleton made of a porous sintered body having a three-dimensional network structure was obtained by forming a foam sheet using a water-insoluble organic solvent according to the method described in JP-A-8-49002. If necessary, the sheet can be manufactured by thermally compressing the sheet in the thickness direction and then sintering the sheet. However,
Instead of the metal powder described therein, a powder of a ceramic (that is, an oxide ion conductive material and / or a mixed oxide ion conductive material) serving as a framework material of the electrode is used.

The skeletal material powder (hereinafter, also referred to as raw material powder) used for molding the foamed sheet can be obtained by a known method when a commercially available product cannot be used. For example, when the skeletal material is a material having a composition represented by the above formula, an oxide of each metal (i.e., Ln, A, Ga, B1, and B2) or a precursor that is thermally decomposed into an oxide (e.g., (Carbonate, carboxylic acid, etc.) are mixed at a ratio so as to have a predetermined composition ratio, calcined, and then pulverized by a ball mill or the like to prepare a raw material powder. The average particle size of the raw material powder is preferably in the range of 0.5 to 500 μm, more preferably 0.5 to 200 μm.

The raw material powder for the electrode skeleton is mixed with a water-insoluble organic solvent having a higher vapor pressure than water, a surfactant, a water-soluble resin binder, a plasticizer, and water to prepare a slurry for sheet molding. I do. This slurry is the same as an aqueous slurry used in a normal sheet forming method except that it contains a water-insoluble organic solvent serving as a foaming agent.

The water-insoluble organic solvent is not particularly limited as long as it has a vapor pressure higher than that of water.
Is a hydrocarbon solvent. Specific examples include neopentane, hexane, isohexane, heptane, isoheptane, octane, benzene, toluene and the like.
The surfactant is not particularly limited, and may be used as a neutral detergent for dishes. Examples of the water-soluble resin binder include methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose ammonium, ethylcellulose,
There are polyvinyl alcohol and the like. The plasticizer may be used as needed, and can be selected from polyhydric alcohols, oils, fats, ethers and esters. Specific examples include polyethylene glycol, olive oil, petroleum ether, di-n-butyl phthalate, sorbitan monooleate, and glycerin.

The mixing ratio of the above components is expressed in% by weight, for example, as follows. Raw material powder constituting electrode skeleton: 5 to 80%, water-insoluble organic solvent: 0.05 to 10%, water-soluble resin binder: 0.5 to 20%, surfactant: 0.05 to 10%, plasticizer: 15% or less ( 0 may be used), rest: water.

This aqueous slurry is mixed well, formed into a sheet by a known doctor blade method, slip casting method, or the like. When the obtained sheet is dried, the vapor pressure of the water is higher than that of water before the water evaporates. Large water-insoluble organic solvents evaporate and evaporate. For example, when the water-insoluble organic solvent is the above-mentioned hydrocarbon solvent, the organic solvent evaporates at a temperature of 5 ° C. or higher. Drying is preferably performed at a relatively low temperature, for example, 50 ° C. or less, so that evaporation of water does not occur rapidly. Since the solvent to be evaporated is dispersed and confined in the slurry, large bubbles remain on the sheet after the solvent is evaporated due to volume expansion when the solvent evaporates. When the water is evaporated and the drying is completed, a porous foam sheet having a three-dimensional network structure due to generation of many large bubbles is obtained. As shown in FIG. 1, these large bubbles are significantly larger than the particle diameter of the skeletal material powder used for forming the slurry, but are relatively well-sized.
Since this sheet contains a resin binder and a plasticizer, it has a handleable strength even if its porosity is large.

When this porous foam sheet is sintered,
Even after sintering, the three-dimensional network structure is maintained, and a porous electrode skeleton having the three-dimensional network structure is obtained. Sintering conditions are appropriately set according to the type of the raw material powder so that sintering occurs sufficiently. Prior to sintering, the sheet may be heated to a temperature lower than the sintering temperature to remove organic matter (eg, binder, plasticizer, surfactant) from the sheet.

FIG. 2 shows an example of a scanning electron micrograph of an electrode skeleton having a three-dimensional network structure obtained after sintering. Pores significantly larger than the particle size of the raw material powder constituting the skeleton
It can be seen that many (voids) are generated and the sintered body has a three-dimensional network structure. In addition to the surface formed by the large pores (pores A in FIG. 1), the sintered body itself constituting the three-dimensional network structure is a porous body formed by sintering powder and has fine pores inside. (Pore B in FIG. 1),
This electrode skeleton has a very large overall specific surface area (external pore A
And the surface of the internal pores B). The overall specific surface area will generally be greater than 1000 cm ² / cm ³ .

When the particles 2 are adhered to the surface of the porous sintered body having a three-dimensional network structure (that is, the electrode skeleton 1), the electrode of the present invention is obtained. This adhesion may be performed by impregnating the electrode skeleton with the slurry containing the particles 2 and then sintering the electrode skeleton. The slurry to be used may be either an aqueous type or an organic solvent type, and the particles 2 (that is, the powder of the electrode material) are
It can be prepared by dispersing in water containing a water-soluble resin binder and a surfactant as described above, or in an organic solvent containing a resinous binder and a surfactant soluble in an organic solvent. The preferred powder concentration of this slurry is 20-70% by weight
It is. Average particle size of powder in slurry is 0.5 ~ 200μm
Is preferably within the range.

As can be seen from FIGS. 1 and 2, the voids in the electrode skeleton are much larger and communicate with the particle size of the powder in the slurry. It penetrates not only into the outer surface of the skeleton but also into the void inside the electrode, and adheres to the surface. After impregnation, the particles are sintered at an appropriate temperature to bond the attached particles to the surface of the skeleton or to each other.

The obtained electrode can be used as a fuel electrode if the deposited particles are a material suitable for the fuel electrode, and can be used as an air electrode if the material is suitable for the air electrode. When the electrode is integrated with the solid electrolyte, the electrode cannot be press-bonded to the solid electrolyte formed by the sheet forming method because the electrode is already sintered. However, when a layer of an oxide ion conductive material is formed on one side of the electrode by thermal spraying or electrochemical vapor deposition, a dense electrolyte layer integrated with the sintered electrode can be formed.

When integrated with the solid electrolyte formed by the sheet forming method, the solid electrolyte may be integrated at a stage before sintering. That is, as described above, the raw material powder for the electrode skeleton is formed into a foam sheet to obtain a non-sintered porous sheet for an electrode skeleton having a three-dimensional network structure. In this porous sheet,
A separately prepared unsintered solid electrolyte sheet densely formed by a sheet forming method is thermocompression-bonded using, for example, a hot press, and the obtained laminate is sintered to obtain an electrode skeleton / electrolyte laminate. Is manufactured. The unsintered porous sheet serving as an electrode skeleton has a three-dimensional network structure and a very high porosity, but has a mechanical strength that can withstand thermocompression bonding with a resin binder and a plasticizer.

The electrode skeleton of the electrode skeleton / electrolyte laminate obtained by sintering is then impregnated with a slurry containing adhered particles, and the surface of the electrode skeleton (including the outer surface and the surface of large pores as described above) Attach particles to After impregnation, the laminate is sintered again to bind the attached particles to the skeleton, producing an electrode / electrolyte laminate.

As described above, the porous sheet for the cathode skeleton and the porous sheet for the anode skeleton, and the separately prepared densely-formed electrolyte sheet are thermocompression-bonded with a hot press to obtain a laminate. Is burned to produce a three-layer laminate of an air electrode skeleton / electrolyte / fuel electrode skeleton. The slurry containing the adhering particles is impregnated next to the air electrode skeleton and the fuel electrode skeleton of the three-layer laminate obtained by sintering, particles are adhered to the surface of the electrode skeleton, and the laminate is sintered again. When the attached particles are bonded to the skeleton, a single cell of a flat solid oxide fuel cell having a three-layer structure of an air electrode / electrolyte / fuel electrode is obtained. Of course, only one of the air electrode and the fuel electrode may be manufactured by any of the above methods. A bipolar or monolithic solid oxide fuel cell can be manufactured using the single cell of the flat solid oxide fuel cell.

[0056]

[Example] La _0.8 Sr _0.2 Ga _0.8 Mg _0.115 Co _0.085 O ₃ (hereinafter referred to as LS
The powder of each metal oxide was mixed in a ball mill so as to have a composition of GMC. After calcining this mixed powder at 1100 ° C., it is mixed again with a ball mill, and has an average particle size of about 1.5 μm.
LSGMC raw material powder was obtained.

48.8% by weight of the raw material powder, 2.4% of a water-immiscible organic solvent (hexane), 9.8% of a surfactant (neutral dishwashing detergent), 4.9% of a water-soluble resin binder (methylcellulose), An aqueous slurry containing 4.9% of a plasticizer (glycerin) and water in water was prepared, and a sheet having a thickness of 2 mm was formed from the slurry by a doctor blade method. While the formed sheet was left at room temperature at about 30 ° C for 1 hour, a number of relatively uniform bubbles were generated in the sheet,
A green foam sheet having a three-dimensional network structure with a thickness of about 6 mm was obtained.

After the porous foamed sheet is dried, it is thermocompressed by a hot press with a dense electrolyte sheet separately formed in advance by a doctor blade method to obtain an unsintered laminate serving as an electrolyte / electrode skeleton. Was. The electrolyte sheet used is a raw material powder composed of LSGMC having the same composition as described above. The raw material powder is 61% by weight, the surfactant (maleic acid ester) 0.6%, the binder (polyvinyl butyral) 1.8%, It was obtained by preparing a solvent-based slurry containing 1.8% of a plasticizer (di-n-butyl phthalate) in an organic solvent and shaping the slurry by a doctor blade method, and having a thickness of 0.25 mm. Was.

The above laminate was fired at 1500 ° C. in the air for 3 hours and sintered to obtain an electrolyte / electrode skeleton laminate. FIG. 2 shows a scanning electron micrograph (magnification: 40,000 times) of the surface of the laminate on the electrode skeleton side. As can be seen from this figure, the electrode skeleton had a three-dimensional network structure. Separately, a sintered body having only the electrode skeleton was similarly prepared, and its porosity and specific surface area were measured. As a result, the porosity was about 50%, and the overall specific surface area was 1000 cm ² 1 / cm ³ . The size of the void was in the range of about 20 to 1000 μm.

On the electrode skeleton side of the electrolyte / electrode skeleton laminate, an aqueous slurry or a solvent slurry of a mixture of NiO and CeO ₂ (the average particle diameter of the powder is 1.0 μm, containing a resin binder and a surfactant) And baked at 1200 ° C. for 3 hours in the air to bind the particles adhered to the electrode skeleton by the impregnation. In this way, the fuel electrode, which has a three-dimensional network structure made of LSGMC and has a very large specific surface area, and NiO and CeO ₂ attached uniformly and in a highly dispersed state on its surface, was integrated with the electrolyte. It could be manufactured in a state. Note that among the adhered particles, NiO is reduced to Ni when exposed to a high-temperature reducing atmosphere during operation of the solid oxide fuel cell.

In the case of the air electrode, La
Manufacturing an electrode / electrolyte laminate by impregnating with a slurry containing a powder of a suitable material such as a MnO ₃ , LaCoO ₃ , SmCoO ₃ or PrCoO ₃ system and baking it at 1200 ° C. for 3 hours in the atmosphere, for example; Can be. As a conventional air electrode material, LaMnO 2 has a small difference in thermal expansion coefficient from YSZ despite its low conductivity.
_{Class 3} materials have been mainly used. In the present invention, since this material is attached to the electrode skeleton, the material is less susceptible to thermal distortion. Therefore, a material having high conductivity can be selected without considering the coefficient of thermal expansion, and the electrode characteristics are improved.

Further, as for the electrode skeleton, instead of LSGMC, the same LSGMC (that is, having the composition represented by the above formula) is used, and the oxide ion mixed conductor having a high Co content or the composition represented by the above formula is used. An NdGaO ₃ -based mixed oxide ion conductor having the following, YSZ, which has been conventionally used, and the like are also effective.

[0063]

As described above, the electrode of the solid oxide fuel cell according to the present invention is composed of a porous skeleton having a three-dimensional network structure having a large specific surface area and particles of an electrode material attached thereto. The three-phase interface length is greatly increased, and the electrode characteristics are significantly improved.

Further, since the porous skeleton of the electrode has an extremely large specific surface area, the electrode has a relaxing effect against thermal shock and thermal strain, and it is possible to prevent the electrode from being broken due to a difference in coefficient of thermal expansion with the electrolyte. . Furthermore, the porous skeleton of the electrode can be made of the same material as the electrolyte. In this case, there is no difference in the coefficient of thermal expansion between the electrode and the electrolyte, and the occurrence of thermal distortion itself can be eliminated. Since the attached particles of the electrode are attached to a skeleton having a large specific surface area, they are also less likely to be subjected to thermal stress. As a comprehensive result, it is possible to construct an SOFC with significantly improved output characteristics and reliability.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a structure of an electrode of the present invention.

FIG. 2 is a scanning electron micrograph of an electrode skeleton produced in an example.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/86 H01M 4/88 H01M 8/12

Claims (18)

(57) [Claims] 1. The method according to claim 1 , wherein the foam is made of an oxide ion conductive material and / or an oxide ion mixed conductive material.
It has a skeleton composed of a formed porous sintered body having a three-dimensional network structure, and it is confirmed that particles made of an electron conductive material and / or an oxide ion mixed conductive material adhere to the surface of the skeleton. An electrode of a solid oxide fuel cell, characterized by: 2. An oxide ion conductive material and / or
Three-dimensional network composed of mixed conductive oxide ions
It has a skeleton composed of a porous sintered body.
Mixed surface of electron conductive material and / or oxide ion
And adhering made of electrically resistant material particles, wherein the porous sintered body is made of a material having a composition represented by the following formula
Of a solid oxide fuel cell. Ln _1-x A _x Ga _1-yz B1 _y B2 _z O _{3 In the} formula, Ln = La, Ce, Pr, Nd, and / or Sm; A = Sr, Ca, Ba, or B1 = one or more of Mg, Al, In; B2 = one or more of Co, Fe, Ni, Cu; x = 0.05 to 0.3; y = 0.025 to 0.29; z = 0.01 to 0.15; y + z ≦ 0.3. 3. The electrode for a solid oxide fuel cell according to claim 1, wherein said porous sintered body is made of yttria-stabilized zirconia. 4. An oxide ion conductive material and / or
Three-dimensional network composed of mixed conductive oxide ions
It has a skeleton composed of a porous sintered body.
Mixed surface of electron conductive material and / or oxide ion
An electrode of a solid oxide fuel cell , wherein particles made of a conductive material are attached, the porous sintered body is made of a material having a composition represented by the following formula, and the electrode is an air electrode. . Ln _1-x A _x Ga _1-yz B1 _y B2 _z O _{3 In the} formula, Ln = La, Ce, Pr, Nd, and / or Sm; A = Sr, Ca, Ba, or B1 = one or more of Mg, Al, In; B2 = one or more of Co, Fe, Ni, Cu; x = 0.05 to 0.3; y = 0 to 0.29; 0.15 < z ≦ 0.3; y + z ≦ 0.3. 5. An oxide ion conductive material and / or
Three-dimensional network composed of mixed conductive oxide ions
It has a skeleton composed of a porous sintered body.
Mixed surface of electron conductive material and / or oxide ion
An electrode of a solid oxide fuel cell , wherein particles made of a conductive material are attached, the porous sintered body is made of a material having a composition represented by the following formula, and the electrode is an air electrode. . A ′ _{1-x ′} Ca _{x ′} Ga _{1-y ′} B ′ _{y ′} O _{3 In the} formula, A ′ = one or two or more lanthanoid metals whose 8-coordinate ionic radius of a trivalent ion is 1.05 to 1.15 ° B ′ = one or more of Co, Fe, Ni and Cu; x ′ = 0.05 to 0.3; y ′ = 0.05 to 0.3. 6. The method according to claim 1, wherein the particles are Ni, Co, Ce _1-m C _m O ₂ (C
Represents one or more of Sm, Gd, Y, and Ca, and m = 0 to 0.
The electrode of a solid oxide fuel cell according to any one of claims 1 to 3, comprising at least one of 4), wherein the electrode is a fuel electrode. 7. The method according to claim 1, wherein the particles are LaMnO ₃ , LaCoO ₃ , SmCoO
_3, and PrCoO consists of at least one material of ₃ system, the electrode is an air electrode, according to claim 1 to a solid oxide fuel cell electrode according to any of the 5. 8. A solid oxide fuel, wherein the electrode according to any one of claims 1 to 7 is integrally formed on one surface of a dense solid oxide electrolyte layer having oxide ion conductivity. Battery electrode / electrolyte laminate. 9. A solid oxide fuel wherein the electrode according to claim 1 is integrally formed on both surfaces of a dense solid oxide electrolyte layer having oxide ion conductivity. Battery electrode / electrolyte laminate. 10. The electrode according to claim 1, wherein the electrode is integrally formed on one surface of a dense solid electrolyte layer having oxide ion conductivity, and the electrode is formed on the other surface.
7. An electrode / electrolyte laminate for a solid oxide fuel cell, wherein the electrode according to any one of 6 to 6 is integrally formed. 11. A solid oxide fuel cell comprising an air electrode and / or a fuel electrode comprising the electrode according to claim 1. Description: 12. A solid oxide fuel cell comprising the electrode / electrolyte laminate according to any one of claims 8 to 10. 13. A three-dimensional sheet made of an oxide ion conductive material and / or an oxide ion mixed conductive material by sheet forming using an aqueous slurry containing a water-immiscible organic solvent having a higher vapor pressure than water. Forming a porous sheet having a network structure, and sintering the sheet;
A method for producing an electrode skeleton of a solid oxide fuel cell. 14. A three-dimensional sheet made of an oxide ion conductive material and / or an oxide ion mixed conductive material by sheet forming using an aqueous slurry containing a water-immiscible organic solvent having a higher vapor pressure than water. A porous sheet having a network structure is formed, and a dense solid electrolyte sheet having oxide ion conductivity is thermocompression-bonded to the sheet, and the obtained laminate is sintered to obtain a solid oxide fuel cell. A method for producing an electrode skeleton / electrolyte laminate. 15. A three-dimensional sheet comprising an oxide ion conductive material and / or an oxide ion mixed conductive material by sheet forming using an aqueous slurry containing a water-immiscible organic solvent having a higher vapor pressure than water. Forming a porous sheet having a network structure, impregnating the sheet with a slurry of an electron conductive material and / or an oxide ion mixed conductive material,
A method for producing an electrode of a solid oxide fuel cell, comprising sintering. 16. The method of claim 15, wherein the porous sheet is sintered prior to impregnating the slurry with the electronically conductive material. 17. A solid electrolyte, wherein a dense electrolyte layer is formed on one surface of an electrode produced by the method according to claim 14 by thermal spraying or electrochemical vapor deposition of an oxide ion conductive material. Electrodes for oxide fuel cells /
A method for producing an electrolyte laminate. 18. A three-dimensional sheet comprising an oxide ion conductive material and / or an oxide ion mixed conductive material by sheet forming using an aqueous slurry containing a water-immiscible organic solvent having a higher vapor pressure than water. A porous sheet having a network structure is formed, a dense solid electrolyte sheet having oxide ion conductivity is thermocompression-bonded to the sheet, and the obtained laminate is sintered, and the electronically conductive material and / or Alternatively, the electrode of a solid oxide fuel cell is impregnated with a slurry of a mixed conductive material of oxide ions and sintered again.
A method for producing an electrolyte laminate.