JP2005174583A - Fuel electrode for solid oxide fuel cell, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel electrode for an SOFC which does not lose adhesiveness to an electrolyte even at a low temperature equal to or below 1,000°C, which can be calcined, which is superior in conductivity, which improves output performance and durability of the SOFC, and which realizes cost reduction, provide its manufacturing method, and furthermore provide the SOFC on which such a fuel electrode is mounted. <P>SOLUTION: A metal such as Ag and Al having a melting point higher than an operating temperature of the SOFC by 100°C or more, and which has a melting point equal to or below 1,000°C is added to an electrode catalyst such as Ni, Cu, Pt, and a fuel electrode material containing a solid oxide electrolyte provided with oxygen ion conductivity such as stabilized zirconia and seria series solid solution, and calcined at a temperature equal to or below 1,000°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid oxide fuel cell using a solid oxide material as an electrolyte, a fuel electrode for a solid oxide fuel cell used as a fuel electrode in the fuel cell, a method for producing the same, and The present invention relates to a fuel electrode paste used for manufacturing a fuel electrode, and further to a solid oxide fuel cell using such a fuel electrode.

  In general, fuel cells are attracting attention as a clean energy source that has high power generation efficiency, generates almost no harmful exhaust gas, and is friendly to the global environment, and has also been put into practical use as a power source for mobile objects such as automobiles. .

  Depending on the type of electrolyte used, the fuel cell may be a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a polymer electrolyte fuel cell (PEFC), or a solid oxide fuel cell (hereinafter referred to as “fuel cell”). Among these, SOFC is a solid oxide electrolyte material having ionic conductivity instead of a liquid material such as phosphoric acid aqueous solution or molten carbonate as an electrolyte material. And has higher power generation efficiency than PAFC and MCFC type fuel cells, and high temperature exhaust heat can be obtained. Therefore, application to an on-site cogeneration system is expected.

  For example, in the case of a fuel electrode, Ni cermet is used as an electrode material for such SOFC, and a slurry containing the electrode material is applied to the surface of an electrolyte made of YSZ (yttria-added stabilized zirconia). After drying, the fuel electrode layer is formed on the electrolyte by sintering at a high temperature exceeding 1000 ° C.

At this time, low-temperature sintering at less than 1000 ° C. results in insufficient sintering, resulting in insufficient adhesion to the fuel electrode electrolyte, peeling during long-term use, and cell output. On the other hand, since the sintering temperature is high, the material of the member that can be used as a component of the cell is limited from the viewpoint of heat resistance, and the reaction between the electrolyte and the fuel electrode occurs, and the reaction formed at the interface Since the product may cause a reduction in the output of the cell and further increase the production cost such as the need for a high-temperature firing furnace, it is desirable that sufficient sintering is possible at a lower temperature.
From such a viewpoint, for example, in Patent Document 1, for the purpose of low-temperature sintering of a platinum electrode film, bismuth oxide (Bi ₂ O ₃ ) and cupric oxide or copper are added to an electrode, and these are added at 1000 ° C. In the following, it is described that the electrode is formed by firing. Here, bismuth oxide is used as a sintering aid, and cupric oxide or copper is used as an anti-segregation agent for the bismuth oxide.

In Patent Document 2, core particles made of a metal having a relatively high melting point are dispersed in a reducing agent solution, a metal salt solution of a metal having a relatively low melting point is added to the dispersion, and the core particles have a melting point. It is described that conductive particles coated with a low metal are obtained.
JP-A-8-136497 JP 2002-334614 A

However, when the technique described in the above cited reference 1 is applied to the SOFC fuel electrode, bismuth oxide has low reduction resistance and may be reduced to Bi in the fuel electrode. In addition, since Bi has a melting point of about 274 ° C. and is much lower than the operating temperature of SOFC (generally 600 ° C. or higher), there is a high risk that Bi produced by reduction will melt and aggregate.
Therefore, when such a phenomenon occurs, the part from which bismuth oxide is removed becomes less sinterable and increases the risk of the fuel electrode being damaged. Further, there is a problem that the aggregated Bi not only inhibits the gas diffusion of the fuel electrode but also covers the electrode catalyst, so that the electrode catalyst does not function and the output of the cell is lowered.

  In addition, when cupric oxide or copper is added as a segregation preventing agent, cupric oxide (copper is oxidized during the firing step and finally becomes cupric oxide) itself has electronic conductivity, oxygen ion conductivity. There is a problem that the performance of the electrode is lowered, that is, the output of the cell is lowered.

  On the other hand, when the fuel electrode is formed of the conductive particles described in the cited document 2, the fuel electrode can be sintered at a temperature of 1000 ° C. or lower depending on the melting point of the “metal having a relatively low melting point”. Although it is conceivable, since the core particles (electrode catalyst) made of a high melting point metal are coated with a low melting point metal, the contact between the electrode catalyst and the electrolyte becomes difficult, so-called 3 of electrode catalyst-electrolyte-fuel gas. Formation of a phase interface becomes difficult. Therefore, it becomes difficult for the electrode catalyst to participate in the fuel cell reaction, and there is a problem that the output of the cell is lowered.

  The present invention has been made paying attention to the above-mentioned problems in the conventional fuel electrode for SOFC, and the object of the present invention is to ensure firing without impairing the adhesion with the electrolyte even at a low temperature of 1000 ° C. or lower. A fuel electrode for SOFC that can be connected, has excellent conductivity, is low in cost, and can improve output performance and durability, as well as a method for manufacturing such a fuel electrode, and also such a fuel electrode. It is to provide the SOFC.

  The fuel electrode for SOFC of the present invention includes, for example, an electrode catalyst such as Ni, Cu, and Pt, an electrolyte composed of a solid oxide having oxygen ion conductivity such as stabilized zirconia and ceria-based solid solution, and the SOFC. It is characterized by containing a metal such as Ag or Al having a melting point of 100 ° C. or higher and 1000 ° C. or lower than the operating temperature.

  The method for producing a fuel electrode for SOFC of the present invention is suitable for the fuel electrode of the present invention, wherein the electrode catalyst and electrolyte as described above and the low melting point metal as described above are formed into particles. , A step of kneading with an organic solvent and a binder to form a slurry, a step of applying the slurry on the electrolyte, or applying the slurry to a porous substrate and drying it as necessary. Further, it is characterized in that it includes a step of applying a slurry containing an electrolyte material and a step of sintering them in an inert atmosphere or a reducing atmosphere at a temperature of 1000 ° C. or lower.

Furthermore, the fuel electrode paste for SOFC of the present invention is suitably used for the production of the fuel electrode of the present invention, and contains the low melting point metal in addition to the electrode catalyst and the electrolyte. Yes.
The SOFC of the present invention includes the fuel electrode for a fuel cell of the present invention.

According to the present invention, a low melting point metal having a melting point of 100 ° C. or higher and 1000 ° C. or lower than the operating temperature of the mounted SOFC is added to the fuel electrode material comprising the electrode catalyst and the solid oxide electrolyte. Sinterability of the fuel electrode is improved, and low-temperature sintering at 1000 ° C. or lower is possible, the fuel electrode is altered, the reaction product between the fuel electrode and the electrolyte is generated, and the heat of the fuel electrode and the electrolyte is further increased. Separation of the fuel electrode due to the difference in expansion rate can be suppressed, the internal resistance of the cell is reduced, and the output and durability can be improved. Further, since the metal has electron conductivity, the electron conductivity of the fuel electrode is improved, and the cell output can be improved.
Furthermore, it is not necessary to use a member made of a heat-resistant material of 1000 ° C. or more as a cell component, the material selectivity is increased, the material cost can be reduced, and a high-temperature sintering furnace is not required. Manufacturing costs can be reduced.

  Hereinafter, the fuel electrode for SOFC of the present invention and the manufacturing method thereof will be described in more detail. In the present specification, “%” means mass percentage unless otherwise specified.

  As described above, the fuel electrode for SOFC of the present invention is obtained by adding a metal having a melting point of 100 ° C. or higher and 1000 ° C. or lower to the SOFC operating temperature to a fuel electrode material such as Ni-cermet. The metal mentioned here refers to a material different from the electrode catalyst and the electrolyte, has a low melting point as described above, and includes a single metal and an alloy composed of a plurality of metals as described later.

The fuel electrode is mainly composed of an electrode catalyst and an electrolyte. The low melting point metal is added to improve the sinterability of the fuel electrode, and the added metal is heated near the melting point during the fuel electrode firing step. As a result, it is fused to the electrode catalyst and the electrolyte to improve the sinterability of the fuel electrode. And since the melting | fusing point of the added metal is 100 degreeC or more higher than the operating temperature of SOFC, it exists as a solid metal at the time of an operation | movement.
Therefore, it has excellent electronic conductivity as a metal compared with the case where an oxide having poor electron conductivity and oxygen ion conductivity or a metal having a melting point lower than the operating temperature is added to improve sinterability. At the same time, metal agglomeration and alteration are unlikely to occur during operation of the fuel cell, so that a fuel electrode excellent in electronic conductivity and durability can be obtained. Here, the melting point of the metal to be added is at least 100 ° C. higher than the SOFC operating temperature. If the temperature is higher than the operating temperature by 100 ° C. This is because durability is obtained and the sinterability of the fuel electrode can be improved.

Further, since the melting point of the metal is 1000 ° C. or lower, the fuel electrode can be sintered even near the melting point, that is, 1000 ° C. or lower.
When the electrode catalyst particles and the electrolyte are sintered at a high temperature exceeding 1000 ° C., the electrode particles and the electrolyte particles may react to form a reaction product that becomes a resistance component of the cell. In the invention, since the sintering at a low temperature of 1000 ° C. or less is possible, this risk can be reduced, and the internal resistance of the cell is reduced and the output is improved.
In addition, when the thermal expansion coefficients of the electrolyte and the fuel electrode are different, the higher the firing temperature, the more the degree of shrinkage appears, and the risk of separation of the fuel electrode and the electrolyte increases. Lowering the following not only reduces the risk, but it is also possible to use a relatively inexpensive metal material such as stainless steel that could not be applied to the cell components from the viewpoint of heat resistance. As a result, the selectivity of the constituent materials is expanded, and the cost of SOFC can be reduced.

  On the other hand, referring to the lower limit of the melting point of the metal, recently, the operating temperature of SOFC has been lowered, and operation at about 600 ° C. has become possible. Although a metal having a melting point in the range can be used, it goes without saying that a metal having a lower melting point can be used if the operating temperature is further lowered.

  As for the firing time of the fuel electrode, a suitable firing time is set according to conditions such as the electrode catalyst and the particle size of the electrolyte particles. For example, when the fuel electrode paste as shown in the examples described later is used Can be baked in about 1 to 2 hours.

In the present invention, examples of the low melting point metal include silver (Ag), aluminum (Al), magnesium (Mg), zinc (Zn), tellurium (Te), copper (Cu), nickel (Ni), and cobalt (Co ), Iron (Fe), gold (Au), platinum (Pt), or any combination thereof.
However, among these metals, Ag, Al, Mg, Zn and Te have melting points of 1000 ° C. or lower and can be used as single metals, whereas Cu, Ni, Co, Fe, Mn, About Au and Pt, since each of them has a melting point of 1000 ° C. or more, it is necessary to use an alloy of two or more of these. Of course, even an alloy between the first group and an alloy between metals straddling both groups can be used as long as it is an alloy having a melting point of 1000 ° C. or lower and SOFC operating temperature + 100 ° C. or higher. Needless to say.

Examples of the electrode catalyst include nickel (Ni), platinum (Pt), copper (Cu), palladium (Pd), ruthenium (Ru), cobalt (Co), iron (Fe), silver (Ag), and chromium (Cr). Etc. can be used.
In addition, as an electrolyte, an oxide having oxygen ion conductivity, for example, SDC (Samaria Doped Ceria), YSZ (Yttria Stabilized Zirconia), CeO ₂ (Ceria) solid solution, lanthanum gallate oxide, etc. These may be used alone or in combination of two or more of these oxides.

  About content of the said low melting metal, it is desirable to add 0.5-20% of low melting point oxide with respect to a fuel electrode main component, ie, the said electrode catalyst, and electrolyte. That is, if the added amount of the metal is less than 0.5%, the effect of improving the sinterability of the fuel electrode cannot be sufficiently obtained, and if it exceeds 20%, the sintering proceeds excessively and the fuel electrode is increased. There is a tendency that the gas diffusibility of the electrode catalyst decreases, or the electrode catalyst is covered with the metal and the function of the electrode catalyst is impaired.

  The particle diameter of the metal is preferably 5 μm or less, more preferably 1 μm or less. That is, when the particle diameter of the metal exceeds 5 μm, the dispersibility of the low melting point metal particles in the fuel electrode is deteriorated, and the effect of sintering the fuel electrode may not be sufficient.

The fuel electrode of the present invention can be applied to various types of SOFC, and a high-performance SOFC excellent in durability at low cost can be obtained.
That is, as an SOFC, generally, as shown in FIG. 1, an electrolyte support type in which a dense electrolyte 2 is used as a support substrate and a fuel electrode 3 and an air electrode 4 are laminated on both sides, as shown in FIG. The fuel electrode 2 having permeability is used as a support substrate, and an electrode (fuel electrode) support type in which the electrolyte 3 and the air electrode 4 are laminated thereon, and further, as shown in FIG. 3, is made of a metal having gas permeability. A porous substrate support type in which a battery element composed of a fuel electrode 2, an electrolyte 3 and an air electrode 4 is laminated in this order or the reverse order on the porous substrate 5 is conceivable. The fuel electrode 3 is not limited to these types and can be applied to any type of SOFC.

As the solid oxide electrolyte 2 of the SOFC 1, SDC (Samaria Doped Ceria), YSZ (Yttria Stabilized Zirconia), CeO ₂ (Ceria) solid solution, lanthanum gallate oxide, etc. are used alone or Two or more of these can be mixed and used.
The air electrode 4 may be made of a metal material such as Pt or Ag, or a perovskite such as a lanthanum-cobalt oxide, a lanthanum-manganese oxide, a lanthanum-iron oxide, or a samarium-cobalt oxide. A type oxide or the like can be used.

In such a fuel electrode 3 for SOFC, first, the electrode catalyst, the electrolyte material, and the low melting point metal as described above are formed into particles and kneaded with an organic solvent and a binder to form a slurry, and the slurry is supported. After coating on the electrolyte 2 as the substrate or the electrolyte 2 formed on the porous substrate 5 via the air electrode 4, sintering is performed at a temperature of 1000 ° C. or less in an inert atmosphere or a reducing atmosphere. Can be manufactured.
Further, the slurry is directly applied to the porous substrate 5 and dried, and then a slurry containing an electrolyte material is further applied thereon, and these are heated to a temperature of 1000 ° C. or lower in an inert atmosphere or a reducing atmosphere. Can be manufactured by sintering.

  Since the fuel electrode paste for SOFC of the present invention contains the low melting point metal in addition to the electrode catalyst and the electrolyte, it is applied on the porous substrate 5 and the solid oxide electrolyte 2 and then 1000 ° C. By sintering at the following temperature, the fuel electrode 3 for SOFC of the present invention can be easily obtained.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples.

(Example 1)
First, an electrolyte substrate 2 made of 8YSZ (8 mol% yttria-stabilized zirconia) having a thickness of 500 μm and a diameter of 30 mm is prepared, and LSM (lanthanum-strontium-manganese complex oxide) is formed on one surface according to a conventional method. An air electrode 4 having a thickness of 20 μm and having a diameter of 20 mm was formed.

Next, NiO-8YSZ (NiO: 8YSZ = 6: 4) as a fuel electrode raw material powder is added with 5% brass powder (Cu-40% Zn, melting point: about 900 ° C.) having a particle diameter of 1 μm and an appropriate amount of terpineol. It knead | mixed and the fuel electrode slurry was obtained.
Next, the fuel electrode slurry was applied to a range of a diameter of 20 mm at the center position on the other surface of the electrolyte substrate 2 provided with an air electrode on one surface using a screen printing method.

  Then, the fuel electrode slurry applied to the electrolyte substrate 2 is fired in an inert atmosphere of Ar at 900 ° C. for 2 hours to form a fuel electrode 3 having a thickness of 20 μm and a diameter of 20 mm, as shown in FIG. An electrolyte-supported SOFC1 was obtained.

(Example 2)
First, NiO-8YSZ (NiO: 8YSZ = 6: 4) as a fuel electrode raw material powder is added and kneaded with 10% Ag powder (melting point: about 960 ° C.) having a particle diameter of 1 μm and an appropriate amount of terpineol, and kneaded. Got.

  Next, a 35 mm diameter fuel electrode green sheet was produced by the doctor blade method.

  Subsequently, an electrolyte material made of SSZ (Samaria Stabilized Zirconia) was applied to the entire surface of the obtained fuel electrode green sheet by screen printing, and baked at 1000 ° C. for 5 hours, whereby an electrolyte membrane 2 having a thickness of 8 μm. And a 30 mm diameter fuel electrode-electrolyte laminate was obtained.

  Then, an air electrode material made of LSC (lanthanum-strontium-cobalt composite oxide) is applied to the center position of the electrolyte membrane 2 within a diameter range of 20 mm using a screen printing method, followed by baking at 1000 ° C. for 1 hour. Thus, an air electrode 4 having a thickness of 20 μm and a diameter of 20 mm was formed, and a fuel electrode supported SOFC 1 as shown in FIG. 2 was obtained.

(Example 3)
First, a porous substrate 5 made of SUS 430 steel (17% Cr stainless steel) and made porous by a technique such as wet etching and having gas permeability and a thickness of 200 μm and a diameter of 30 mm was prepared.
On the other hand, a fuel electrode slurry was obtained by adding 5% Ag powder having a particle size of 0.5 μm and an appropriate amount of terpineol to NiO-8YSZ (NiO: 8YSZ = 6: 4) as a fuel electrode raw material powder and kneading them.

Next, after applying the obtained fuel electrode slurry to the entire surface of the porous substrate 5 made of stainless steel by using a screen printing method, the substrate 5 is put together with the fuel electrode slurry in a reducing atmosphere (Ar-3%). In H ₂ ), the fuel electrode 3 was formed to a thickness of 100 μm on the substrate 5 by firing at 970 ° C. for 1 hour.
Next, an electrolyte membrane 2 made of 8YSZ was formed to a thickness of 10 μm on the entire surface of the fuel electrode 3 formed on the porous substrate 5 by using the SPD method (thermal spray decomposition method).

  Then, an air electrode layer 4 made of SSC (samarium-strontium-cobalt composite oxide) is formed to a thickness of 10 μm in the range of 20 mm diameter of the center position of the electrolyte membrane 2 made of 8YSZ by the same SPD method. A porous substrate-supported SOFC 1 as shown in FIG.

It is a schematic sectional drawing explaining the cell structure of an electrolyte support type solid oxide fuel cell. It is a schematic sectional drawing explaining the cell structure of a fuel electrode support type solid oxide fuel cell. It is a schematic sectional drawing explaining the cell structure of a porous substrate support type solid oxide fuel cell.

Explanation of symbols

1 Solid oxide fuel cell 3 Fuel electrode (Fuel electrode for solid oxide fuel cell)

Claims (8)

  A fuel electrode of a solid oxide fuel cell, comprising an electrode catalyst, an electrolyte composed of a solid oxide, and a metal having a melting point of 100 ° C. or higher and 1000 ° C. or lower than the operating temperature of the fuel cell. A fuel electrode for a solid oxide fuel cell.   2. The metal according to claim 1, wherein the metal includes at least one selected from the group consisting of Ag, Al, Mg, Zn, Te, Cu, Ni, Co, Fe, Au, and Pt. Fuel electrode for solid oxide fuel cells.   3. The fuel electrode for a solid oxide fuel cell according to claim 1, wherein the metal is contained in a mass ratio of 0.5 to 20% with respect to the main component of the fuel electrode.   The fuel electrode for a solid oxide fuel cell according to any one of claims 1 to 3, wherein a particle diameter of the metal is 5 µm or less. A method for producing a fuel electrode for a fuel cell according to any one of claims 1 to 4,
An electrode catalyst, an electrolyte composed of a solid oxide, and a metal having a melting point of 100 ° C. or higher and 1000 ° C. or lower than the operating temperature of the fuel cell are made into particles and kneaded with an organic solvent and a binder to form a slurry. And a process of
A step of applying the slurry onto the substrate and then applying an electrolyte slurry thereon;
A method for producing a fuel electrode for a solid oxide fuel cell, comprising a step of sintering the slurry at a temperature of 1000 ° C. or lower in an inert atmosphere or a reducing atmosphere. A method for producing a fuel electrode for a fuel cell according to any one of claims 1 to 4,
An electrode catalyst, an electrolyte composed of a solid oxide, and a metal having a melting point of 100 ° C. or higher and 1000 ° C. or lower than the operating temperature of the fuel cell are made into particles and kneaded with an organic solvent and a binder to form a slurry. And a process of
Applying the slurry onto the electrolyte;
A method for producing a fuel electrode for a solid oxide fuel cell, comprising a step of sintering the slurry at a temperature of 1000 ° C. or lower in an inert atmosphere or a reducing atmosphere.   A paste for producing the fuel electrode for a fuel cell according to any one of claims 1 to 4, wherein the paste is an electrode catalyst, an electrolyte composed of a solid oxide, and 100 times higher than an operating temperature of the fuel cell. A fuel electrode paste for a solid oxide fuel cell, comprising a metal having a melting point of not less than 1000C and not more than 1000 ° C.   A solid oxide fuel cell comprising the fuel electrode for a fuel cell according to any one of claims 1 to 4.

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