JP2007173055A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell capable of preventing degradation accompanying oxidation and reduction of an interconnector, and maintaining stable cell characteristics even with a long-period operation, as to one of non-diaphragm type. <P>SOLUTION: For the solid oxide fuel cell provided with an integrated cell structure in which a plurality of unit cells are formed each having a pair of a fuel electrode 3 and an air electrode 4 on the same plane of solid electrolyte 2, and electrodes of different unit cells are connected with each other by an interconnector 5, the interconnector 5 is coated with a protective layer 6 for protecting it 5 from reaction gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a solid oxide fuel cell that stably generates power in a reaction gas mainly composed of a mixed gas of fuel gas and air.

  As a cell design of a fuel cell, a flat plate type (stack type), a cylindrical type (tube type), and the like have been proposed.

  In such a cell, a fuel electrode and an air electrode are respectively disposed on the front surface and the back surface of the electrolyte, and power generation is performed by separately supplying fuel gas and oxidant gas using the electrolyte as a partition wall. .

  In order to improve the performance of such a partition-type cell, it is necessary to reduce the thickness of the electrolyte, and it is necessary to reduce the internal resistance of the electrolyte material. However, if the electrolyte is too thin, it becomes brittle, There was a problem that durability deteriorated.

  For this reason, as a fuel cell that replaces the partition type cell described above, the fuel electrode and the air electrode are arranged on the same surface of the substrate made of a solid electrolyte, and power is generated by supplying a mixed gas of fuel gas and oxidant gas. A possible non-membrane type solid oxide fuel cell has been proposed (for example, Patent Document 1). According to this fuel cell, since it is not necessary to separate the fuel gas and the oxidant gas, the separator and the gas seal are not required, and the structure and the manufacturing process can be greatly simplified.

Further, in this non-membrane type solid oxide fuel cell, the conduction of oxygen ions occurs near the surface layer of the solid electrolyte, and the fuel electrode and the air electrode are formed close to each other on the same surface of the solid electrolyte. The thickness of the electrolyte does not directly affect the performance of the battery as in the case of the cylinder type. Therefore, the thickness of the electrolyte can be increased while maintaining the performance of the battery, thereby improving the vulnerability.
JP-A-8-264195 (page 2-3, FIG. 1)

  However, in the conventional non-membrane type solid electrolyte fuel cell, the oxidation proceeds in part of the interconnector by flowing a mixed gas of fuel gas and oxidant gas. As a result, a chemical change (forms a resistance component) and a physical change (film deterioration due to volume expansion) occur in the interconnector, thereby increasing the resistance, thereby causing a problem that the battery performance is lowered.

  Accordingly, the present invention provides a solid oxide fuel cell capable of preventing deterioration due to oxidation and reduction of an interconnector and maintaining stable battery characteristics even in long-term operation in a non-membrane type solid electrolyte fuel cell. An object is to provide a battery.

  In order to achieve the above object, a solid oxide fuel cell according to the present invention comprises a plurality of single cells each having a pair of fuel electrodes and air electrodes formed on the same plane of a solid electrolyte, and the electrodes between different single cells. A solid oxide fuel cell having an integrated cell structure in which the interconnectors are connected by an interconnector, wherein the interconnector is covered with a protective layer for protecting the interconnector from a reaction gas.

  The protective layer preferably has a gas barrier property against a reactive gas.

  In addition, when the interconnector is formed of a material that is easily oxidized, the protective layer is preferably formed of a material that has oxidation resistance to the reaction gas.

  The protective layer may have a single layer structure or a multi-layer structure.

  A preferred embodiment of a solid oxide fuel cell according to the present invention will be described below with reference to FIGS. 1 is a plan view, FIG. 2 is an AA longitudinal sectional view of FIG. 1, and FIG. 3 is a BB longitudinal sectional view of FIG. Throughout the drawings, the same components are denoted by the same reference numerals.

  In the solid oxide fuel cell 1, a plurality of single cells in which a pair of fuel electrodes 3 and air electrodes 4 are formed on the same plane of the solid electrolyte 2 are formed, and electrodes of different single cells are connected by an interconnector 5. The interconnector 5 has an integrated cell structure and is covered with a protective layer 6 that protects the interconnector 5 from reaction gas. In the illustrated example, an example in which single cells are connected in series by the interconnector 5 is shown.

As the material of the solid electrolyte 2, those known as electrolytes for solid oxide fuel cells can be used. For example, ceria-based oxides such as (Ce, Sm) O ₃ and (Ce, Gd) O ₃ , Examples include ceramic materials such as lanthanum galide oxides such as (La, Sr) (Ga, Mg) O ₃ , zirconia oxides such as scandium stabilized zirconia (ScSZ) and yttria stabilized zirconia (YSZ). be able to.

  The fuel electrode 3 and the air electrode 4 can be formed of ceramic powder. The particle size of the powder is usually 10 nm to 100 μm, preferably 100 nm to 10 μm.

As the fuel electrode 3, for example, a mixture of a metal catalyst and a ceramic powder material made of an oxide ion conductor can be used. As the metal catalyst used at this time, a material that is stable in a reducing atmosphere, such as nickel, iron, cobalt, or a noble metal (platinum, ruthenium, palladium, etc.) and has hydrogen oxidation activity can be used. In addition, as the oxide ion conductor, one having a fluorite structure or a perovskite structure can be preferably used. Examples of those having a fluorite structure include ceria-based oxides such as (Ce, Sm) O ₃ and (Ce, Gd) O ₃ , scandium-stabilized zirconia (ScSZ), and yttria-stabilized zirconia (YSZ). A zirconia-type oxide can be mentioned. In addition, examples of those having a perovskite structure include lanthanum galide oxides such as (La, Sr) (Ga, Mg) O ₃ . Among the above materials, it is preferable to form the fuel electrode 3 with a mixture of an oxide ion conductor and nickel. The mixed form of the ceramic material made of the oxide ion conductor and nickel may be a physical mixed form or a form of powder modification to nickel. Moreover, the ceramic material mentioned above can be used individually by 1 type or in mixture of 2 or more types. Moreover, the fuel electrode 3 can also be comprised using a metal catalyst alone.

The ceramic powder material forming the air electrode 4 can be formed of, for example, a metal oxide having a perovskite structure. Specifically, (Sm, Sr) CoO ₃ , (La, Sr) MnO ₃ , (La, Sr) CoO ₃ , (La, Sr) (Fe, Co) O ₃ , (La, Sr) (Fe, Co , Ni) O _{3 and the} like. These ceramic powders can be used singly or in combination of two or more. Note that it is preferable to form the air electrode 4 with a perovskite-type metal oxide containing cobalt, since both electron conductivity and ion conductivity are improved.

  The interconnector 5 can be formed of at least one material selected from the group consisting of metals and conductive ceramics. Examples of such a material for the interconnector 5 include Pt, Au, Ag, Ni, Cu, stainless steel, and lanthanum chromite materials.

  The protective layer 6 preferably has a gas barrier property against the reactive gas in order to prevent the reactive gas from coming into contact with the interconnector 5. Examples of the protective layer 6 having a gas barrier property include non-conductive metal oxides such as alumina, silica, zirconia, titania, lanthanum, and ceria. By using such a material, the heat resistance and oxidation resistance required for the protective layer 6 are also satisfied. Examples of particularly excellent heat resistance and oxidation resistance include alumina and zirconia.

The protective layer 6 can have a single layer structure or a multilayer structure of a plurality of layers. When peeling may occur between the interconnector 5 and the protective layer 6 during firing, a material obtained by mixing both the interconnector forming material and the protective layer forming material may be laminated as an intermediate layer. is there. For example, when the interconnector is Ni and the protective layer is alumina (Al ₂ O ₃ ), a layer made of a material obtained by mixing them by 50% may be formed between the interconnector and the protective layer.

  The solid oxide fuel cell 1 having the above-described configuration can be manufactured as follows.

  First, using the solid electrolyte 2 as a substrate, the fuel electrode 3 and the air electrode 4 are applied or deposited on the solid electrolyte 2 by a wet method or a dry method. As a wet method, a powder material, which is a material for forming the fuel electrode 3 and the air electrode 4, is mixed with a resin binder and pasted into a paste, and is applied to a predetermined pattern by a screen printing method or a spray coating method. A slurry in which a powder material, which is a material for forming the fuel electrode 3 and the air electrode 4, is dispersed in a solvent such as isopropanol, a method of forming a thin film by a lithography method, a doctor blade method, or the like, or a slurry by an electrophoretic electrodeposition method There is a method of electrodepositing in a predetermined pattern, and a dry method includes a method of depositing in a predetermined pattern by CVD, EVD, sputtering or the like.

  In the case of a wet method, the fuel electrode paste is dried at 60 to 150 ° C. for about 5 to 120 minutes.

  Either the fuel electrode 3 or the air electrode 4 may be applied, dried or deposited first, but in the case of a ceramic material, one of the fuel electrode 3 and the air electrode 4 is applied, dried or deposited, and then one of them is fired and sintered. Thereafter, the other may be applied, dried, or deposited, and the other may be fired and sintered, or both electrodes may be fired simultaneously.

  The interconnector 5 and the protective layer 6 can also be formed by the same wet method or dry method as the fuel electrode 3 and the air electrode 4, and the interconnector is applied, dried or deposited in a predetermined pattern, and fired as necessary. Then, after the sintering, the protective layer 6 may be applied, dried or deposited so as to cover the interconnector 5, fired and sintered, or both electrodes may be fired simultaneously. Thus, a solid oxide fuel cell is obtained.

  In the solid oxide fuel cell having the above configuration, the interconnector 5 is protected from the reaction gas by the protective layer, so that stable battery performance can be maintained and deterioration of the battery performance is prevented. Can do.

  The present invention will be further clarified by the following examples.

NiO powder (0.01 to 10 μm, average 1 μm) and SDC ((Ce _0.8 , Sm _0.2 ) O _1.9 ) powder (particle size 0.01 to 10 μm, average particle size 0.1 μm) are used as fuel electrode materials. Using a mixture in which the ratio of NiO powder: SDC powder = 7: 3 was used, a cellulosic varnish was further mixed with this mixture to prepare a fuel electrode paste. The viscosity of the fuel electrode paste was 5 × 10 ⁵ mPa · s suitable for screen printing.

Moreover, SSC ((Sm _0.5 , Sr _0.5 ) Co _1.0 O ₃ ) powder (particle size 0.1 to 10 μm, average particle size 3 μm) is used as the air electrode material, and cellulose varnish is mixed with this SSC powder Thus, an air electrode paste was prepared. The viscosity of the air electrode paste was 5 × 10 ⁵ mPa · s suitable for screen printing.

In addition, as a material for forming the interconnector, Ni powder (particle size 0.1 to 5 μm, average particle size 2.5 μm) is used, and a cellulose-based varnish is mixed with the Ni powder to produce an interconnector paste. did. The viscosity of the interconnector paste was 5 × 10 ⁵ mPa · s suitable for screen printing.

Further, alumina (Al ₂ O ₃ ) powder was used as a protective layer, and a cellulose varnish was mixed therewith to prepare a protective layer paste. The viscosity of the protective layer paste was 5 × 10 ⁵ mPa · s suitable for screen printing.

  The fuel electrode paste was applied onto the solid electrolyte by screen printing so that the line width was 500 μm and the coating thickness was 50 μm, and then dried at 130 ° C. for 15 minutes. Then, it baked and sintered at 1450 degreeC for 1 hour, and formed the fuel electrode. The thickness of the fuel electrode after sintering was 30 μm.

  Next, the air electrode paste was applied onto the solid electrolyte by screen printing so that the line width was 500 μm and the coating thickness was 50 μm, and then dried at 130 ° C. for 15 minutes. Then, it baked and sintered at 1200 degreeC for 1 hour, the air electrode was formed, and the several single cell was formed. The thickness of the air electrode after sintering was 30 μm.

  Further, the interconnector paste is screen-printed to electrically connect the air electrode and fuel electrode of different single cells by screen printing so that the line width is 3 mm and the coating thickness is 30 μm, and then at 130 ° C. for 15 minutes. Dried. Then, it was fired at a temperature of 1000 ° C. for 1 hour and sintered to form an interconnector.

  Next, the protective layer paste was printed by screen printing so as to cover the interconnector so as to have a line width of 4 mm and a thickness of 30 μm, and then dried at 130 ° C. for 15 minutes. Thereafter, it was fired at a temperature of 1000 ° C. for 1 hour and sintered to produce a two integrated cell.

1 is a plan view showing an embodiment of a solid oxide fuel cell according to the present invention. It is AA longitudinal cross-sectional view of FIG. It is BB longitudinal cross-sectional view of FIG.

Explanation of symbols

1 Solid Oxide Fuel Cell 2 Solid Electrolyte 3 Fuel Electrode 4 Air Electrode 5 Interconnector 6 Protective Layer

Claims (4)

A solid oxide fuel cell having an integrated cell structure in which a plurality of single cells each having a pair of fuel electrodes and air electrodes formed on the same plane of a solid electrolyte are formed, and electrodes of different single cells are connected by an interconnector. A solid oxide fuel cell, wherein the interconnector is covered with a protective layer for protecting the interconnector from the reaction gas. The solid oxide fuel cell according to claim 1, wherein the protective layer has a gas barrier property against a reactive gas. The solid oxide fuel cell according to claim 2, wherein the protective layer has oxidation resistance against a reactive gas. 2. The solid oxide fuel cell according to claim 1, wherein the protective layer has a single layer structure or a multi-layer laminated structure.

Images