JP2013149349A - Laminated solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an external electrode in which over-sintering of a sintered compact can be prevented without causing any structural defect of a laminated solid oxide fuel cell, and degradation of power generation performance or yield loss can be minimized.SOLUTION: A fuel electrode side external electrode 6 and an air electrode side internal electrode 7 connected, respectively, with a fuel electrode 2 and an air electrode 3 of a laminated solid oxide fuel cell 1, where the fuel electrode 2 and the air electrode 3 are laminated alternately with an electrolyte 4 interposed therebetween and sintered, are formed using any one or two kinds of conductive materials of Ag and Au. Consequently, the baking temperature of the fuel electrode side external electrode 6 and air electrode side internal electrode 7 is lowered, over-sintering of a sintered compact is prevented, damage (defect such as cracking) on the laminated solid oxide fuel cell 1 is minimized, and a high power density can be obtained without causing degradation of power generation performance or yield loss.

Description

The present invention relates to a stacked solid oxide fuel cell.

Fuel cells are attracting attention as energy creation technology in a low-carbon society, and are expected to be put to practical use for a wide range of applications such as fuel cell vehicles, household cogeneration systems, and small power supplies for portable devices. There are various types of fuel cells. Among them, solid oxide fuel cells have advantages such as high energy conversion efficiency and high reliability because they are composed of inorganic all solids. In a solid oxide fuel cell, a voltage obtained by one power generation cell in which an air electrode and a fuel electrode are arranged to face each other through a solid electrolyte (hereinafter simply referred to as an electrolyte) is as low as about 1V. For this reason, conventionally, as shown in Patent Document 1, a plurality of power generation cells are electrically connected in series using an electrical conductor such as a separator, and the obtained voltage and power have been increased. On the other hand, Patent Document 2 discloses a monolithic sintered multi-layer solid oxide that has a plurality of electrolytes, air electrodes, and fuel electrodes in a single element without using a separator, and is electrically connected in parallel by an interconnector. A physical fuel cell is disclosed.

Further, in Patent Document 3, in a stacked solid oxide fuel cell having a plurality of electrolytes, air electrodes, and fuel electrodes in a single sintered body, the external electrode is sintered using platinum as the first electrode and the second electrode. A technique is disclosed that is configured on a combined end face and is electrically connected to a fuel electrode and an air electrode, respectively.

International Publication No. 2009/119971 JP 2003-297387A JP 2011-34688 A

Since the stacked solid oxide fuel cell is used in a high-temperature oxidizing atmosphere of 300 to 900 ° C., the characteristics required for the external electrode material for electrically connecting a plurality of fuel electrodes and air electrodes respectively are The conductivity is ¹ Scm ⁻¹ or more. Platinum is one of the preferred materials as a conductive material that satisfies this characteristic. However, in order to bring the platinum electrode into close contact with the surface of the stacked solid oxide fuel cell, which is a sintered body, a baking temperature of about 1600 ° C. is required with respect to 1769 ° C., which is the melting point of platinum. However, since the stacked solid oxide fuel cell is sintered at 1500 ° C. or lower, if the baking of platinum is performed at a baking temperature higher than the sintering temperature of the stacked solid oxide fuel cell, the stacked solid oxide fuel cell This may cause structural defects such as cracks in the fuel cell and cause oversintering of the sintered body, leading to a decrease in power generation performance, leading to a decrease in yield.

  The present invention has been made in view of the above, and without causing structural defects of the stacked solid oxide fuel cell, further prevents oversintering of the sintered body, and reduces power generation performance and yield. It is an object to form an external electrode without causing any problems.

In order to solve the above-described problems and achieve the object, the stacked solid oxide fuel cell according to the present invention includes an external electrode made of one or two kinds of conductive materials of Ag and Au. It is characterized by. As a result, the baking temperature of the external electrode can be made lower than the sintering temperature of the stacked solid oxide fuel cell, and it is possible to prevent a decrease in power generation performance and yield.

As a desirable aspect of the present invention, the external electrode is preferably made of a mixed material obtained by mixing ceramics with one or two kinds of conductive materials of Ag and Au. Thereby, aggregation of Ag and Au of the conductive material can be suppressed, the difference in thermal expansion between the stacked solid oxide fuel cell and the external electrode can be reduced, and peeling can be suppressed.

As a desirable aspect of the present invention, Y ₂ O ₃ stabilized ZrO ₂ , Sc ₂ O ₃ stabilized ZrO ₂ , Sm ₂ O ₃ added CeO ₂ , Gd ₂ O ₃ added CeO ₂ , ZrO ₂ , Al It is preferable to use at least one selected from ₂ O ₃ , SiO ₂ , and MgO. As a result, the stacked solid oxide fuel cell and the external electrode are firmly bonded, and peeling can be suppressed.

  As a desirable mode of the present invention, it is preferable that the mixed material has a mixing ratio of the ceramic to the conductive material of 10 to 70 vol%. Thereby, it is possible to maintain electronic conductivity without obstructing the network of conductive materials.

  As a desirable mode of the present invention, it is preferable that the external electrode is formed in a plurality of layers with a gradient composition by changing a mixing ratio of the conductive material and the ceramic. Thereby, the difference in thermal expansion between the stacked solid oxide fuel cell and the external electrode can be further relaxed, and peeling can be suppressed.

  As a desirable mode of the present invention, it is preferable that the external electrode reduce the mixing ratio of ceramics toward the outside of the stacked solid oxide fuel cell. Thereby, it is possible to maintain the electronic conductivity of the external electrode and to suppress peeling.

  As a desirable aspect of the present invention, the external electrode preferably has a porosity of 10 to 80%. Thereby, it is possible to ensure gas permeability and to maintain electronic conductivity without impeding the network of the conductive material.

The present invention can suppress structural defects of a stacked solid oxide fuel cell and oversintering of a sintered body, and can suppress a decrease in power generation performance. Thereby, a yield can be improved.

It is the schematic explaining the operating principle of a fuel cell with a flat type solid oxide fuel cell. 1 is a cross-sectional view showing a structure of a stacked solid oxide fuel cell according to an embodiment of the present invention. It is a flowchart which shows the manufacturing process of the lamination type solid oxide fuel cell which concerns on this invention. It is sectional drawing which shows the structure of the lamination type solid oxide fuel cell which concerns on another embodiment of this invention. It is sectional drawing which shows the structure of the lamination type solid oxide fuel cell which concerns on another embodiment of this invention. It is the schematic explaining the evaluation method of the lamination type solid oxide fuel cell concerning the present invention.

FIG. 1 is a schematic diagram illustrating the operation principle of a fuel cell using a flat solid oxide fuel cell. The general operating principle of the fuel cell will be described with reference to FIG. A fuel cell is a power generation device that converts the chemical energy of a fuel directly into electrical energy by electrochemically reacting hydrogen and oxygen of the fuel on the reverse principle of water electrolysis. In the air electrode 63, oxygen receives electrons from an external circuit, becomes oxide ions, travels through the electrolyte 64, and moves to the fuel electrode 62. In the fuel electrode 62, the oxide ions transmitted through the electrolyte 64 react with hydrogen to release electrons to an external circuit. If this is expressed by a chemical reaction formula,
Air electrode: (1/2) O ₂ + 2e ⁻ → O ²⁻ (1)
Fuel electrode: O ² + H ₂ → H ₂ O + 2e ⁻ (2)
Overall: (1/2) O ₂ + H ₂ → H ₂ O (3)
It becomes. The fuel cell according to the present invention is a solid oxide fuel cell (SOFC). In addition to H ₂ , for example, CO can also be used as fuel for SOFC.

SOFC is characterized by high power generation efficiency compared to other fuel cells. On the other hand, the SOFC has a low ion conductivity of about 10 ⁻¹ Scm ^{−1 at} a high temperature operation of 500 ° C. to 1000 ° C., and the electrode area of the fuel electrode 62 and the air electrode 63 is sufficient for taking out current sufficiently. There is a need to increase the thickness of the electrolyte 64 and to make the electrolyte 64 thinner. Therefore, the stacked solid oxide fuel cell according to the present invention attempts to extract a large current by increasing the effective electrode area per unit area as compared with the conventional flat plate and cylindrical SOFC. is there. For this reason, the stacked solid oxide fuel cell according to the present invention has a structure in which electrodes (fuel electrode or air electrode) and an electrolyte are alternately stacked and integrally sintered without using a separator. As a result, the electrode area per unit volume can be increased and the size can be reduced.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.

<Laminated Solid Oxide Fuel Cell 1>
FIG. 2 is a cross-sectional view showing the structure of a stacked solid oxide fuel cell according to an embodiment of the present invention. The stacked solid oxide fuel cell 1 includes a plurality of fuel electrodes 2, a plurality of air electrodes 3, an electrolyte 4 disposed between at least the fuel electrode 2 and the air electrode 3, and adjacent electrolytes 4. The partition part 5 arrange | positioned between is included.

  In the present embodiment, the fuel electrode 2, the air electrode 3, the electrolyte 4, and the partition portion 5 are integrally configured to form the stacked solid oxide fuel cell 1. Here, in this embodiment, in order to electrically connect the plurality of fuel electrodes 2 and the air electrode 3, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 are further provided. As described above, the stacked solid oxide fuel cell 1 includes the fuel electrode side external electrode 6 and the air electrode side external electrode 7.

<Fuel electrode 2>
The fuel electrode 2 is an electrode that generates electrons at the interface between the electrolyte 4 and the externally supplied fuel (hydrogen) by the reaction expressed by the following equation (4) with the oxide ions that have passed through the electrolyte 4. is there.
O ²⁻ + H ₂ → H ₂ O + 2e ⁻ (4)
In the present embodiment, the fuel electrode 2 is a porous electrode formed so that a plurality of voids (holes) communicate with each other in order to allow hydrogen to reach the three-phase interface and promote the reaction represented by the above formula (4). Made of quality material.

In this embodiment, the fuel electrode 2 is composed of a composite material (hereinafter referred to as Pt / YSZ) of platinum (hereinafter referred to as Pt) and Y ₂ O ₃ stabilized ZrO ₂ (hereinafter referred to as YSZ). In addition, a material having electron conductivity in a high-temperature reducing atmosphere and exhibiting catalytic activity can be used as the material of the fuel electrode 2. As such a material, there is a metal material using one or more of Pt, Ni, Co, and Cu. Each of them can be used only with a metal material, but in order to promote electrode reaction and catalytic reaction, and further to suppress aggregation / sintering between metal materials, YSZ which is an oxide ion conductor, It can be used as a composite with Sc ₂ O ₃ stabilized ZrO ₂ (hereinafter referred to as ScSZ), Gd ₂ O ₃ added CeO ₂ (hereinafter referred to as GDC), Sm ₂ O ₃ added CeO ₂ (hereinafter referred to as SDC), or the like.

When the length of the fuel electrode 2 in the direction in which the fuel electrode 2, the air electrode 3, and the electrolyte 4 are laminated is the thickness of the fuel electrode 2, the thickness is preferably 10 to 1000 μm, more preferably 20 to 200 μm. . By setting the thickness of the fuel electrode 2 in the above range, gas diffusibility is maintained and high power generation performance is obtained.

<Air electrode 3>
In the air electrode 3, when oxygen in the air reaches the interface (three-phase interface) with the electrolyte 4, electrons moving from the fuel electrode 2 side and oxygen react as shown in the following formula (5).
1 / 2O ₂ + 2e ⁻ → O ²⁻ (5)
The oxide ions generated by the reaction shown in the above formula (5) move through the electrolyte 4. In the present embodiment, the air electrode 3 is a porous formed so that a plurality of voids (holes) communicate with each other in order to allow oxygen to reach the three-phase interface and promote the reaction represented by the above formula (5). Made of quality material.

In the present embodiment, the air electrode 3 is composed of a composite material of Pt and YSZ. In addition, a material having electron conductivity in a high-temperature oxidizing atmosphere and exhibiting catalytic activity can be used as the material of the air electrode 3. Examples of such materials include Ag, (LaSr) CoO ₃ (hereinafter referred to as LSC), (LaSr) (CoFe) O ₃ (hereinafter referred to as LSCF), and (LaSr) MnO ₃ (hereinafter referred to as LSM). There are materials that use one type or two or more types. Each of these materials can be used alone, but in order to promote electrode reactions and catalytic reactions, and to suppress aggregation / sintering between the materials, oxide ion conductors YSZ and ScSZ are used. , GDC, SDC, etc. can be used as a composite.

  When the length of the air electrode 3 in the direction in which the fuel electrode 2, the air electrode 3, and the electrolyte 4 are laminated is the thickness of the air electrode 3, the thickness is preferably 10 to 1000 μm, more preferably 20 to 200 μm. . By setting the thickness of the air electrode 3 in the above range, gas diffusibility is maintained and high power generation performance is obtained.

<Electrolyte 4>
The electrolyte 4 is preferably dense YSZ, ScSZ, GDC, SDC, or (LaSr) (GaMg) O ₃ (hereinafter referred to as LSGM) having an oxide ion transport number of 0.96 (96%) or more.

  Such an oxide is preferable because of its high oxide ion transport number and high oxide ion conductivity. The upper limit of the oxide ion transport number is 1, that is, it is preferable that the oxide ion bears all of the electrical conduction, but it is about 0.995 in the current technology.

The YSZ, it is preferable that yttrium (Y) was dissolved 3-15 mole% zirconia (ZrO _2). As ScSZ, scandium (Sc) is preferably dissolved in zirconia (ZrO ₂ ) in an amount of 5 to 10 mol%. As GDC, gadolinium (Gd) is preferably dissolved in ceria (CeO ₂ ) at 10 to 20 mol%. As the SDC, samarium (Sm) dissolved in 10 to 20 mol% in ceria (CeO ₂ ) is preferable. The _LSGM, in _{(La 1-X Sr X)} (Ga 1-Y Mg Y) O 3, preferably those with 0.1 ≦ X ≦ 0.4,0.1 ≦ Y ≦ 0.4.

  When the length of the electrolyte 4 in the direction in which the fuel electrode 2, the air electrode 3 and the electrolyte 4 are laminated is the thickness of the electrolyte 4, the thickness is preferably 1 to 50 μm, more preferably 1 to 10 μm. By setting the thickness within the above range, there is an advantage that the strength as the electrolyte 4 can be secured and the power generation performance can be kept high.

<Partition 5>
As described above, in the present embodiment, the partition portion 5 is between the adjacent electrolytes 4 and connects the electrolytes 4 to each other. When leakage of electrons or gas occurs between the fuel electrode 2 and the air electrode 3, the power generation performance of the stacked solid oxide fuel cell 1 is degraded. For this reason, in the partition part 5, it is desirable not to cause insulation between the fuel electrode 2 and the air electrode 3 and gas leakage.

By making the partition part 5 and the electrolyte 4 the same material, there exists an advantage that manufacture of the lamination type solid oxide fuel cell 1 becomes easy. In particular, YSZ, ScSZ, GDC, SDC, or LSGM used for the electrolyte 4 is preferable.

Moreover, you may comprise the partition part 5 and the electrolyte 4 with a different material. The material of the partition part 5 can also suppress the performance degradation of the stacked solid oxide fuel cell 1 more effectively by using a material having an electron conductivity lower than that of the electrolyte 4 or a material that can ensure gas tightness. Is possible. As a material that can be used for the partition portion 5, ZrO ₂ , Al ₂ O ₃ , SiO ₂ , and MgO can be used.

<Fuel electrode side external electrode 6, air electrode side external electrode 7>
In this embodiment, in order to electrically connect the plurality of fuel electrodes 2 and the plurality of air electrodes 3 stacked in the stacked solid oxide fuel cell 1, the fuel electrode side external electrode 6 and the air The pole side external electrode 7 is required. By having the fuel electrode side external electrode 6 and the air electrode side external electrode 7, the voltage and power output from the stacked solid oxide fuel cell 1 can be taken out. Further, a plurality of stacked solid oxide fuel cells 1 can be connected in series and in parallel, and the output voltage and power can be improved. The fuel electrode side external electrode 6 must be a conductive material capable of maintaining electronic conductivity in a high temperature reducing atmosphere and the air electrode side external electrode 7 in a high temperature oxidizing atmosphere.

  As a conductive material that can be used for the fuel electrode side external electrode 6 and the air electrode side external electrode 7, Ag and Au having a relatively low melting point among noble metals are preferable.

Moreover, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 are good to be comprised with a porous body. This is because the fuel gas supplied from the fuel electrode side external electrode 6 side is distributed inside each anode 2 and the oxygen supplied from the air electrode side external electrode 7 side is distributed inside each cathode 3. Further, in order to make the fuel electrode side external electrode 6 and the air electrode side external electrode 7 porous, the fuel electrode side external electrode paste and the air electrode side external electrode paste include a void forming agent in addition to the conductive powder particles. Good to include. As the void forming agent, for example, an acrylic polymer or the like that disappears upon firing can be used. Thus, by using the void forming agent that disappears during baking, the fuel electrode-side external electrode 6 and the air electrode-side external electrode 7 of a porous body can be easily produced.

Further, the fuel electrode-side external electrode 6 and the air electrode-side external electrode 7 can be used only with a conductive material, but are preferably composed of a composite material of a conductive material and ceramics. In order to suppress aggregation / sintering between conductive materials, composites such as YSZ, ScSZ, GDC, SDC, etc. that can be used for the electrolyte 4 and ZrO ₂ , Al ₂ O ₃ , SiO ₂ , MgO, etc. that can be used for the partition part 5 Turn into.

<Method for Producing Multilayer Solid Oxide Fuel Cell>
The method for producing the stacked solid oxide fuel cell according to this embodiment is not particularly limited, and a known method may be employed. In the following, a method for producing an electrolyte green sheet by forming an electrolyte into a sheet, and forming electrodes and partitions for a fuel electrode and an air electrode on the electrolyte green sheet using screen printing and laminating them is described. This will be specifically described.

  FIG. 3 is a flowchart showing manufacturing steps of the stacked solid oxide fuel cell according to the present embodiment. An electrode green layer for forming the fuel electrode 2 and the air electrode 3 and a blank layer for forming the partition portion 5 are formed on the electrolyte green sheet for forming the electrolyte 4 shown in FIG. . Next, a plurality of sheets are laminated so that the fuel electrode 2 and the air electrode 3 are alternately exposed at different end faces after cutting to form a sheet laminate. Next, this sheet laminated body is cut into the size of one part unit of the laminated solid oxide fuel cell. And debuying and firing. A post-treatment is performed as necessary, and the fuel electrode side external electrode 6 and the air electrode side external electrode 7 are formed, whereby the stacked solid oxide fuel cell 1 is manufactured.

  First, an electrolyte slurry for forming the electrolyte 4 and an electrode slurry for forming the fuel electrode 2 and the air electrode 3 are prepared. The electrolyte slurry is obtained by putting the powder as the raw material of the electrolyte 4 into a plastic pot together with grinding balls, adding a solvent, a binder and a plasticizer thereto and mixing for 10 to 20 hours. Although there is no restriction | limiting in content of a solvent, a binder, and a plasticizer, For example, content of a solvent is 10 mass% or more and 50 mass% or less, and content of a binder is set in the range of about 1 mass% or more and 10 mass% or less. can do. In the slurry for electrolyte, you may contain a dispersing agent etc. in 10 mass% or less as needed. Thereby, sheet formability, structure retainability, and drying can be ensured.

  The electrode slurry is prepared by mixing 10 to 80 vol% of a void forming material with respect to the conductive powder and adding a solvent and a binder to the conductive powder in order to maintain electronic conduction without hindering the network of the conductive powder. . Although there is no restriction | limiting in content of a solvent and a binder, For example, content of a solvent is 10 mass% or more and 50 mass% or less, and content of a binder can be set in the range of about 1 mass% or more and 10 mass% or less. it can. Thereby, printability, structure retention, and drying properties can be ensured. If necessary, the electrode slurry may contain a dispersant or the like in a range of 10% by mass or less in order to improve the dispersibility of the conductive powder. These raw material powders, solvents, and the like were mixed by a three roll to obtain an electrode slurry.

  As a solvent used for preparation of the slurry for electrolyte and the slurry for electrodes, organic solvents, such as acetone, toluene, isobutyl alcohol, methyl ethyl ketone, terpineol, can be used, for example. Moreover, as a binder, a butyral resin, an acrylic resin, etc. can be used, for example. The powder that is a raw material for the electrolyte is the powder of the electrolyte material described above, and the conductive powder is the powder of the fuel electrode material and the air electrode material described above. In this embodiment, YSZ powder was used as the electrolyte raw material powder, and Pt / YSZ powder was used as the conductive powder for both the fuel electrode and the air electrode. In addition, as the void forming material used in the electrode slurry, for example, a material that disappears upon firing, such as an acrylic polymer, can be used. Thus, a porous fuel electrode and an air electrode can be easily produced by using the void forming material that disappears during firing.

  After the electrolyte slurry and the electrode slurry are obtained, an electrolyte green sheet is prepared using the electrolyte slurry. For example, an electrolyte green sheet having a thickness of 1 μm to 100 μm is manufactured by applying a slurry for electrolyte by a doctor blade method or the like and then drying it.

  Next, an electrode layer for a fuel electrode or an air electrode is formed on the obtained electrolyte green sheet. For example, the electrode slurry is subjected to pattern printing by screen printing or the like and then dried to form an electrode layer having a thickness of 10 μm to 200 μm. In the present embodiment, the blank layer that becomes the partition portion 5 is formed in the reverse pattern of the screen printing that forms the above-described electrode layer using the electrolyte slurry.

In addition, when the partition part 5 is comprised with the material different from the electrolyte 4, the slurry for blanks is produced separately from the slurry for electrolyte. In this case, the blank slurry is prepared by adding a solvent and a binder to the raw material powder particles of the partition portion 5. Although there is no restriction | limiting in content of a solvent and a binder, For example, content of a solvent is 10 mass% or more and 50 mass% or less, and content of a binder can be set in the range of about 1 mass% or more and 10 mass% or less. it can. Thereby, printability, structure retention, and drying properties can be ensured. The solvent and binder used for preparing the blank slurry may be the same as those used for preparing the electrolyte slurry.

In this way, a sheet in which an electrode layer and a blank layer are formed on the electrolyte green sheet is produced. Here, a plurality of sheets are produced. Next, as shown in FIG. 2, this sheet is laminated so that the fuel electrode 2 and the air electrode 3 are alternately overlapped. Further, the fuel electrode 2 and the air electrode 3 are laminated so as to be exposed to different end faces after cutting the sheet laminate.

Next, it pressurizes toward the lamination direction. Thereby, a plurality of sheets are pressure-bonded and integrated. After that, the sheet stack is cut in parts, that is, in one unit of the stacked solid oxide fuel cell 1. In this way, a component unit laminate is obtained.

Next, a binder removal process is performed on the cut component unit laminate. Furthermore, the sintered body of a component unit laminated body is obtained by baking this. In the sintered body of the component unit laminate, the fuel electrode 2, the air electrode 3, the electrolyte 4, and the partition portion 5 are integrated.

The binder removal treatment and firing conditions of the component unit laminate are different depending on the electrolyte material and electrode layer material used. For example, when the component unit laminate is fired using Pt / YSZ particles as the electrode layer, the component unit The laminate is heated and held in the atmosphere at 400 to 600 ° C. for 1 to 2 hours to remove the binder from the component unit laminate. Thereafter, the component unit laminate is fired at 1350 ° C. to 1500 ° C. for 3 hours to 5 hours in the air to obtain a sintered body. As a result, as shown in FIG. 2, the fuel electrodes 2, the electrolytes 4 and the air electrodes 3 are alternately stacked, and the partition portions 5 provided between the electrolytes 4 adjacent thereto are integrated by sintering. Thus, the stacked solid oxide fuel cell 1 having the stacked structure is completed.

Next, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 are formed at the sintered body exposed end portion where the fuel electrode 2 and the air electrode 3 of the stacked solid oxide fuel cell 1 are exposed. As the material paste for the external electrode, for example, the above-mentioned electrode slurry can be used. Among the noble metals, a material composed of one or two kinds of conductive materials of Ag and Au having a relatively low melting point. Use paste. As in the electrode slurry, the external electrode material paste is mixed with 10-80 vol% of void forming material with respect to the conductive powder in order to maintain the electron conduction without hindering the network of the conductive powder, and the solvent. And a binder is added. Although there is no restriction | limiting in content of a solvent and a binder, For example, content of a solvent is 10 mass% or more and 50 mass% or less, and content of a binder can be set in the range of about 1 mass% or more and 10 mass% or less. it can. Thereby, printability, structure retention, and drying properties can be ensured. In the material paste, if necessary, a dispersant or the like may be contained in a range of 10% by mass or less in order to improve the dispersibility of the conductive powder. These raw material powders, solvents and the like are mixed by a three roll to obtain a material paste. This external electrode material paste is applied to both sides of the sintered body of the stacked solid oxide fuel cell 1, dried and debindered, and then fired under predetermined conditions. The firing temperature may be lower than the sintering temperature of the stacked solid oxide fuel cell, for example, about 850 ° C. By doing so, there is no occurrence of structural defects such as cracks in the stacked solid oxide fuel cell, or oversintering of the sintered body, resulting in a decrease in power generation performance. Thereby, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 for electrically connecting each of the plurality of fuel electrodes 2 and the plurality of air electrodes 3 are integrated by sintering, and the fuel electrode side The stacked solid oxide fuel cell 1 having the external electrode 6 and the air electrode side external electrode 7 is completed. According to the method for manufacturing a stacked solid oxide fuel cell according to the present embodiment, the manufacturing process is relatively simple, and a small device is easy to manufacture. The fuel cell 1 can be manufactured. In addition to any one or two of Ag and Au as the conductive material, it is also possible to use a combination with a material having a baking temperature lower than the sintering temperature of the stacked solid oxide fuel cell. .

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

  First, each material for manufacturing a stacked solid oxide fuel cell was prepared.

As a raw material for the material constituting the electrolyte, 8 mol% Y ₂ O ₃ stabilized ZrO ₂ (hereinafter referred to as 8YSZ) powder was prepared. 8YSZ powder: 100 parts by mass, butyral as binder resin: 10 parts by mass, benzylbutyl phthalate (BBP) as plasticizer: 5 parts by mass, alcohol as solvent: 80 parts by mass To obtain a paste for electrolyte. Using the obtained electrolyte paste, an electrolyte green sheet was formed by a doctor blade method so that the thickness after firing was 15 μm.

  Next, Pt / 8YSZ mixed powder in which Pt and 8YSZ were mixed at a volume ratio of 50:50 was prepared as a raw material for the material constituting the fuel electrode and the air electrode. Pt / 8YSZ raw material powder: 100 parts by mass, acrylic beads as a void forming agent: 17 parts by mass, butyral as a binder resin: 10 parts by mass, benzyl butyl phthalate (BBP) as a plasticizer: 5 parts by mass Then, alcohol as a solvent: 80 parts by mass was mixed and dispersed with a three roll to obtain an electrode paste. Using the obtained electrode paste, an electrode layer serving as a fuel electrode and an air electrode was formed on the electrolyte green sheet by screen printing so that the thickness after firing was 50 μm. The partition part was formed by screen printing in a pattern obtained by inverting the above-described electrolyte paste with respect to the electrode printing pattern.

  Next, four green sheets on which the electrode layers were printed were alternately laminated to obtain a laminated sheet of a stacked solid oxide fuel cell having two fuel electrodes and two air electrodes. The sheet laminate was pressed at a temperature of 60 ° C., a pressure of 10 Pa, and a holding time of 30 minutes.

  Next, the sheet laminate produced above was cut out to a size of 4.5 mm × 3.2 mm after firing to obtain a component unit laminate.

  The obtained component unit laminate was debindered at 500 ° C., and then fired at a firing temperature of 1400 ° C., a holding time of 5 hours, and a firing atmosphere of air, and a laminated solid oxide fuel cell. A sintered body was obtained.

Example 1
Next, the material which comprises the fuel electrode side external electrode 6 and the air electrode side external electrode 7 was prepared with the raw material shown in Table 1. Ag as a conductive material, acrylic beads as a void forming agent: 15 parts by weight, butyral as a burner: 5 parts by weight, dioctyl adipate (DOA) as a plasticizer: 2 parts by weight, alcohol as a solvent: 80 Part by weight was mixed and dispersed with three rolls to obtain an external electrode paste. The obtained external electrode paste was applied to the end face where the fuel electrode 2 and the air electrode 3 were exposed, and baked at 850 ° C. for baking.

(Example 2)
The same operation as in Example 1 was performed except that Au was used instead of Ag of the conductive material.

(Example 3)
In the case of using a mixture of two conductive materials, the same procedure as in Example 1 was performed except that Ag and Au were mixed at a mass ratio of 50/50.

Example 4
In the case of mixing a conductive material and ceramics, the same procedure as in Example 1 was performed except that a mixed powder in which Ag and 8YSZ were mixed at a composite ratio of 50/50 by volume (vol%) was prepared.

(Examples 5 to 11)
The case of mixing the conductive material and the ceramic was the same as in Example 4 except that various ceramics were used.

(Examples 12 to 14)
The same procedure as in Example 4 was performed except that the volume ratio (vol%) in the case of mixing the conductive material and the ceramic was changed.

(Example 15)
As the gradient composition of the fuel electrode side external electrode 6 and the air electrode side external electrode 7, the inner layer is formed so that the volume ratio (vol%) when the conductive material and ceramics are mixed is different as shown in FIG. The mixing ratio of the ceramics 6a and 7a was 30/70, and the mixing ratio of the ceramics of the outer layers 6b and 7b was 60/40. Except for the above, there was no exposure, and the same procedure as in Example 4 was performed.

(Example 16)
As the gradient composition of the fuel electrode side external electrode 6 and the air electrode side external electrode 7, the inner layer is formed so that the volume ratio (vol%) in the case of mixing a conductive material and ceramics is different, as shown in FIG. 6a and 7a except that the mixing ratio of the ceramics is 30/70, the mixing ratio of the ceramics of the intermediate layers 6c and 7c is 50/50, and the mixing ratio of the ceramics of the outer layers 6b and 7b is 60/40. This was carried out in the same manner as in Example 4.

(Examples 17 and 18)
The same operation as in Example 4 was performed except that the porosity of the fuel electrode side external electrode 6 and the air electrode side external electrode 7 was changed.

(Comparative Examples 1-5)
In addition, the conductive material is Pt (Comparative Example 1), the composite ratio of the conductive material and the ceramic is 95/5 (Comparative Example 2), the composite ratio of the conductive material and the ceramic is 20/80 (Comparative Example 3), and the gap The same procedure as in each example was performed except that the rate was 5% (Comparative Example 4) and the porosity was 90% (Comparative Example 5).

  As shown in Table 1, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 were coated with a paste for external electrodes using various conductive materials on the sintered body, and both were fired at 850 ° C. The stacked solid oxide fuel cells of Sample Nos. 1 to 23 (Examples 1 to 18 and Comparative Examples 1 to 5) were obtained.

<Power generation test>
FIG. 6 is a diagram for explaining an evaluation method for a stacked solid oxide fuel cell according to the present embodiment. The stacked solid oxide fuel cell 1 according to this embodiment described above is operated by disposing the fuel electrode side external electrode 6 and the air electrode side external electrode 7 in different spaces. The stacked solid oxide fuel cell 1 is attached to a specimen support plate 50. A fuel electrode side cover 52 and an air electrode side cover 54 are attached to the specimen support plate 50. The fuel electrode side cover 52 and the air electrode side cover 54 are partitioned by a specimen support plate 50. The fuel electrode side is a fuel supply space 51, and the air electrode side is an oxygen supply space 53. In addition, a heater 55 is disposed outside the stacked solid oxide fuel cell 1, and the stacked solid oxide fuel cell 1 is heated by the heater 55 during a power generation test. A platinum lead wire 56 is extended from the fuel electrode side external electrode 6 and the air electrode side external electrode 7 of the stacked solid oxide fuel cell 1 attached to the specimen support plate 50, connected to the measuring instrument 57, and external electrode The voltage V and current I between are measured.

Before the test, first, 50 ml of He gas was circulated per minute to raise the atmospheric temperature of the stacked solid oxide fuel cell 1 to 900 ° C., and the stacked solid oxide fuel cell 1 and the specimen support plate 50 were And the fuel electrode side of the stacked solid oxide fuel cell 1 were gas sealed. After monitoring the gas composition on the fuel electrode side with a quadrupole gas mass spectrometer and confirming that the leakage from the air electrode side is 100 ppm or less for confirmation of gas sealing properties, the stacked solid oxide form The ambient temperature (equal to the operating temperature) of the fuel cell 1 was lowered to the test temperature of 800 ° C. After reaching the test temperature, hydrogen is supplied as fuel to the fuel electrode side at 100 ml / min, and air is supplied to the air electrode side at 100 ml / min, between the external electrodes of the stacked solid oxide fuel cell 1. (Between fuel electrode and air electrode) Voltage V and current I were measured.

A platinum lead wire 56 is connected to each of the fuel electrode side external electrode 6 and the air electrode side external electrode 7 of the stacked solid oxide fuel cell 1, and the fuel electrode-air electrode voltage V and current I are measured by a measuring instrument 57. Measured. As the measuring instrument 57, a potentiogalvanostat was used. In actual measurement, open circuit electromotive force (electromotive force in a state where no current is taken out) was measured first, and then the current value was increased stepwise under a constant current condition, and the voltage at each current value was measured. . The test temperature was set to 800 ° C., and the value at which the power P obtained by multiplying the current I and the voltage V obtained above was the maximum at the initial value was measured. In the shape, the number of layers, and the material of this example, when the initial value is 4000 μW or more as a reference and a value higher than that is shown, the stacked solid oxide fuel cell can be manufactured without structural defects such as cracks. It was judged. In order to evaluate the reliability, the initial maximum power described above was measured and compared with the maximum power after the tenth power generation test was repeated. In 10 repetitions, the maximum power decrease was 0.98 (2% decrease) as an allowable value and used as an evaluation criterion. This evaluation standard assumes a decrease of 20% or less in 3650 repeated power generations, and is a provisional evaluation standard.

  From Table 1, in Comparative Example 1 (Sample No. 1), the initial performance is as low as 3653 μW, and the repeatability is also low as 0.93. This is because, as the baking temperature of the external electrode material paste using Pt as the conductive material, 850 ° C. is too low, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 and the fuel electrode 2 or the air electrode 3 This is because the desired power generation performance cannot be obtained. Furthermore, by repeating the power generation test, it was confirmed that peeling progressed and power generation performance decreased.

  In Comparative Example 1 (Sample No. 13), in the production of the external electrode material paste, the amount of ceramic mixed with the conductive material is small, and the fuel electrode side external electrode 6 and the air electrode side external electrode 7 and the sintered body The effect of relieving the difference in thermal expansion was not manifested, and it was confirmed that performance was lowered by repeated power generation.

  In Comparative Example 1 (Sample No. 17), in the production of the external electrode material paste, the amount of ceramic mixed with the conductive material was large, the Ag network structure could not be sufficiently formed, and a decrease in initial performance could be confirmed. .

  In Comparative Example 4 (Sample No. 20), since the porosity of the fuel electrode side external electrode 6 and the air electrode side external electrode 7 was low, the gas could not be sufficiently diffused and the initial performance could not be obtained.

  In Comparative Example 5 (Sample No. 23), since the porosity of the fuel electrode side external electrode 6 and the air electrode side external electrode 7 was high, an Ag network structure could not be formed, and initial performance could not be obtained.

  Examples 1 to 18 (Sample Nos. 2 to 12, 14 to 16, 18, 19, 21, and 22) are stacked solid oxide fuel cells that have sufficiently high initial performance and repeatability that satisfies standard values. Was confirmed.

  Example 15 (Sample No. 18) is an example in which the fuel electrode side external electrode 6 and the air electrode side external electrode 7 have a gradient composition configuration. As shown in FIG. 4, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 have a two-layer structure, and the mixing ratio of the conductive material and the ceramic is different in each layer, and the inner layers 6a and 7a have different mixing ratios. The gradient composition is such that the mixing ratio of ceramics is larger than the mixing ratio of ceramics of the outer layers 6b and 7b. By adopting such a configuration, the difference in thermal expansion between the sintered body of the stacked solid oxide fuel cell, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 can be further alleviated, and peeling is prevented. It is possible to suppress.

Example 16 (Sample No. 19) is another example in which the fuel electrode side external electrode 6 and the air electrode side external electrode 7 have a gradient composition configuration. As shown in FIG. 5, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 have a three-layer structure, and the mixing ratio of the conductive material and the ceramic is different in each layer, and the inner layers 6a, 7a The gradient composition is such that the mixing ratio of ceramics is larger than the mixing ratio of ceramics of the intermediate layers 6c and 7c, and the mixing ratio of ceramics of the intermediate layers 6c and 7c is larger than the mixing ratio of ceramics of the outer layers 6b and 7b. By adopting such a configuration, the difference in thermal expansion between the sintered body of the stacked solid oxide fuel cell, the fuel electrode side external electrode 6 and the air electrode side external electrode 7 can be further alleviated, and peeling is prevented. It is possible to suppress.

As described above, the stacked solid oxide fuel cell according to the present invention reduces the size of the solid oxide fuel cell, and further sinters without causing structural defects of the stacked solid oxide fuel cell. It is useful because it can prevent over-sintering of the body and can obtain a high power density without causing a decrease in power generation performance or yield.

1 Stacked Solid Oxide Fuel Cell 2, 62 Fuel Electrode 3, 63 Air Electrode 4, 64 Electrolyte 5 Partition 6 Fuel Electrode Side External Electrode 7 Air Electrode Side External Electrode 6a, 7a Inner Layer 6b, 7b Outer Layer 6c, 7c Intermediate layer

Claims (7)

In a stacked solid oxide fuel cell in which a fuel electrode and an air electrode are alternately stacked via an electrolyte, the fuel cell includes an external electrode connected to each of the fuel electrode and the air electrode, and the external electrode is made of Ag and Au. A stacked solid oxide fuel cell comprising any one or two kinds of conductive materials. 2. The stacked solid oxide fuel cell according to claim 1, wherein the external electrode is made of a mixed material in which ceramics are mixed with one or two kinds of conductive materials of Ag and Au. The ceramics are Y ₂ O ₃ stabilized ZrO ₂ , Sc ₂ O ₃ stabilized ZrO ₂ , Gd ₂ O ₃ added CeO ₂ , Sm ₂ O ₃ added CeO ₂ , ZrO ₂ , Al ₂ O ₃ , SiO ₂ , MgO. 3. The stacked solid oxide fuel cell according to claim 2, comprising at least one selected from the group consisting of.   4. The stacked solid oxide fuel cell according to claim 2, wherein the mixed material has a mixing ratio of the ceramic to the conductive material of 10 to 70 vol%. 5.   5. The stacked solid oxide fuel cell according to claim 1, wherein the external electrode includes a plurality of layers having different mixing ratios of the conductive material and the ceramic.   The external electrode includes a plurality of layers having different mixing ratios of the conductive material and the ceramic, and the mixing ratio of the ceramics in each layer decreases toward the outside of the external electrode. The stacked solid oxide fuel cell according to claim 5.   7. The stacked solid oxide fuel cell according to claim 1, wherein the external electrode has a porosity of 10 to 80%.

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