JP2005235548A - Solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell capable of preventing electrode peeling during long-time operation and maintaining stable power generation characteristics.
SOLUTION: In a solid oxide fuel cell including a power generation cell in which a fuel electrode layer and an air electrode layer are arranged on both surfaces of a solid electrolyte layer 3, Ni and samarium are formed at an interface between the fuel electrode layer and the solid electrolyte layer 3. The first fuel electrode layer 4a is formed by the mixture 10 of the added ceria. The first fuel electrode layer 4 a contains coarse SDC 11 having a diameter larger than the average particle diameter of the mixture 10. The anchor effect of the coarse SDC 11 improves the peel resistance of the fuel electrode layer, and excellent durability can be obtained even for a long time operation, so that stable power generation performance can be maintained.
[Selection] Figure 2

Description

  The present invention relates to a solid oxide fuel cell including a power generation cell configured by disposing a fuel electrode layer and an air electrode layer on both surfaces of a solid electrolyte layer, and in particular, aims to improve durability and power generation performance of the power generation cell. The present invention relates to an electrode structure.

  Solid oxide fuel cells are being developed as third-generation fuel cells for power generation. At present, three types of solid oxide fuel cells have been proposed: a cylindrical type, a monolith type, and a flat plate type, all of which have a solid electrolyte composed of an oxide ion conductor between an air electrode and a fuel electrode. It has a laminated structure sandwiched between. A fuel cell stack having a predetermined output can be configured by alternately laminating power generation cells and separators made of this laminate.

The power generation cell is supplied with oxygen (air) as an oxidant gas on the air electrode side and fuel gas (H ₂ , CO, CH _4, etc.) on the fuel electrode side. The air electrode and the fuel electrode are both porous so that the gas can reach the interface with the solid electrolyte. Oxygen supplied to the air electrode passes through pores in the air electrode and reaches the vicinity of the interface with the solid electrolyte, and receives electrons from the air electrode and is ionized to oxide ions (O ²⁻ ). . The oxide ions diffusely move in the solid electrolyte toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and emit electrons to the fuel electrode.

The electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
Fuel electrode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻
Overall: H ₂ +1/2 O ₂ → H ₂ O

  FIG. 3 shows the internal structure of the power generation cell 1 in a conventional solid oxide fuel cell. In the figure, reference numeral 2 denotes an air electrode layer, reference numeral 3 denotes a solid electrolyte layer, and reference numeral 4 denotes a fuel electrode layer. As described above, the power generation cell 1 having a structure in which the electrode layers 2 and 4 made of a single layer are formed on the solid electrolyte layer 3 is generally used. Each electrode layer is formed by various known methods such as a doctor blade method, a screen printing method, a curtain coating method, and a spin coating method.

  By the way, in the power generation cell 1 having the above electrode structure, the power generation characteristics due to the separation phenomenon of the solid electrolyte layer 3 and each electrode layer (especially the fuel electrode layer) in the thermal cycle during long-time operation and the diffusion of Ni into the solid electrolyte layer 3. The problem was a decline. The separation of the fuel electrode layer 4 is considered to be due to the metal such as Ni contained in the fuel electrode layer 4 being baked on the solid electrolyte layer in an oxide state and contracted by reduction during power generation.

In recent years, for example, Patent Documents 1 to 3 have been disclosed as techniques for solving problems related to durability and power generation characteristics of such power generation cells.
JP-A-8-213028 JP 2003-17073 A JP 2001-351646 A

  However, these disclosed techniques are not always sufficient to prevent electrode peeling and Ni aggregation / sintering.

  Therefore, in view of such problems of durability and power generation characteristics of the power generation cell, the present invention has a suitable electrode structure capable of maintaining stable power generation characteristics by preventing electrode peeling due to thermal cycles during long-time operation. It aims at providing the solid oxide fuel cell provided with the cell.

  That is, the present invention according to claim 1 is a solid oxide fuel cell including a power generation cell in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer, wherein the fuel electrode layer is the solid electrolyte layer. A first fuel electrode layer made of a mixture of metal particles and ceramic particles at the interface between the first fuel electrode layer and the first fuel electrode layer containing coarse ceramic particles having a diameter larger than the average particle diameter of the mixture. It is a feature.

  The present invention according to claim 2 is the solid oxide fuel cell according to claim 1, wherein the coarse ceramic particles have a particle size of 1 to 30 μm and the coarse ceramic particles include the first ceramic particles. The proportion of coarse ceramic particles in the total volume of the fuel electrode layer is 1 to 50 vol%.

  The configuration described in claims 1 and 2 forms an extremely thin first fuel electrode layer having a thickness of about 1 μm by a small amount of a mixture of Ni and SDC (for example, Ni: 10 vol%, SDC: 90 vol%). At the same time, coarse SDC particles are randomly placed and baked on the first fuel electrode layer by spraying. The anchor effect of the coarse SDC particles improves the peeling resistance of the fuel electrode layer and is stable even during long-time operation. Power generation performance can be obtained. A second fuel electrode layer is formed on the first fuel electrode layer using an electrode material having a suitable composition (for example, a mixture of Ni: 60 vol% and SDC: 40 vol%).

Here, the reason why the particle size of the coarse SDC particles is set to 1 to 30 μm is that when the particle size is less than 1 μm, a sufficient anchor effect cannot be obtained, and the fuel electrode layer is peeled off during a long time operation. This is because when the thickness is 30 μm or more, the overvoltage in the fuel electrode layer becomes large, and the power generation performance decreases.
Also, the ratio of the coarse ceramic particles in the total volume of the first fuel electrode layer containing the coarse ceramic particles is set to 1 to 50 vol%. If the proportion is less than 1 vol%, a sufficient anchor effect cannot be obtained, and the operation is performed for a long time. This is because the fuel electrode layer is peeled off at 50 vol% or more, and the overvoltage of the fuel electrode layer increases and power generation performance decreases.

  The invention according to claim 3 is a solid oxide fuel cell comprising a power generation cell in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer, wherein the fuel electrode layer is the solid electrolyte layer. A first fuel electrode layer made of a mixture of metal particles and ceramic particles at the interface with a coarse ceramic having a projected area larger than the average particle diameter of the mixture in the form of dots in an aligned state. It is characterized by being applied.

According to a fourth aspect of the present invention, in the solid oxide fuel cell according to the third aspect, the projected area of the coarse ceramic dots is 0.04 cm ² or less, and the number of coarse ceramic dots is It is characterized by being 100 or less / cm ² .

  The configurations according to claims 3 and 4 form an extremely thin electrode layer having a thickness of about 1 μm with a small amount of a mixture of Ni and SDC (for example, Ni: 10 vol%, SDC: 90 vol%), and Coarse SDC slurry is applied to the surface in a layered manner by screen printing or the like, and baked. The coarse SDC is formed in a dot shape in an aligned state. The anchor effect of the coarse SDC dots improves the peel resistance of the fuel electrode layer, and stable power generation performance can be obtained even during long-time power generation. A second fuel electrode layer is formed on the first fuel electrode layer with an electrode material having the same preferred composition as described above.

Here, the projected area of coarse SDC dots is set to 0.04 cm ² (corresponding to a screen pattern hole of 2 mm × 2 mm square) or less because if the projected area is larger than 0.04 cm ² , the overvoltage in the fuel electrode layer is large. This is because the power generation performance is reduced.
The number of coarse SDC dots is set to 100 or less / cm ² because when the number of coarse SDC dots per 1 cm ² is more than 100, the overvoltage in the fuel electrode layer increases and the power generation performance decreases. It is.

  The present invention according to claim 5 is the solid oxide fuel cell according to any one of claims 1 to 4, wherein the mixing ratio of the metal particles in the mixture of the metal particles and the ceramic particles is determined. It is characterized by being less than 20 vol%.

The present invention according to claim 6 is the solid oxide fuel cell according to any one of claims 1 to 5, wherein the ceramic particles of the first fuel electrode layer have a general formula: Ce ₁ It is characterized by being a ceria of _-x B _x O ₂ (wherein B is one or more of Sm, Gd, Y and Ca added).

  Further, according to a seventh aspect of the present invention, in the solid oxide fuel cell according to any one of the first to sixth aspects, the first fuel electrode layer includes Ni and samarium-added ceria (SDC). It is characterized by comprising a mixture of

  In the structure of Claims 5-7, in the 1st fuel electrode layer located in the interface with a solid electrolyte layer, the diffusion amount to the solid electrolyte layer of Ni is reduced by reducing the mixing amount of metal particles, such as Ni. Thus, the peel resistance and power generation characteristics can be further improved.

  As described above, according to the present invention, the thin first fuel electrode layer is formed at the interface between the fuel electrode layer and the solid electrolyte layer by a mixture of metal particles such as Ni containing coarse ceramic and ceramic particles. The peeling effect of the electrode layer is improved by the anchor effect of the coarse ceramic, and the power generation cell has excellent durability even during long-time operation, and stable power generation performance can be obtained.

  In addition, by reducing the amount of Ni mixed in the first fuel electrode layer, it is possible to suppress the diffusion phenomenon of Ni to the solid electrolyte layer that occurs during operation, thereby further improving peeling resistance and power generation characteristics. Can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 shows the internal structure of a power generation cell according to the present invention. As shown in FIG. 1, the power generation cell 1 is composed of a solid electrolyte layer 3, a fuel electrode layer 4 and an air electrode layer 2 disposed on both surfaces thereof, and each of these electrode layers 2, 4 has a predetermined electrode material. It is formed by applying and laminating a slurry of mixed particles granulated from powder onto both surfaces of a solid electrolyte layer by a known doctor blade method or screen printing and firing in a high temperature atmosphere of 1000 ° C. or higher.

Since the solid electrolyte layer 3 is a moving medium for oxide ions and also functions as a partition for preventing direct contact between the fuel gas and air, the solid electrolyte layer 3 has a dense structure that is impermeable to gas. This solid electrolyte layer 3 is made of a material that has high oxide ion conductivity, is chemically stable under conditions from an oxidizing atmosphere on the air electrode side to a reducing atmosphere on the fuel electrode side, and is resistant to thermal shock. Generally, stabilized zirconia (YSZ) added with yttria is used.
In this embodiment, a lanthanum gallate material (LaGaO ₃ ) having a perovskite crystal structure is used as the oxide ion conductive material exhibiting conductivity exceeding YSZ, and an electrolyte layer having a thickness of about 200 μm is formed. . Since this material exhibits high conductivity even at a low temperature, it is suitable for realizing a solid oxide fuel cell having a lower operating temperature than the conventional temperature of about 1000 ° C.

Both the air electrode layer 2 (cathode) and the fuel electrode layer 4 (anode) must be made of a material having high electron conductivity. Since the air electrode layer 2 must be chemically stable in a high-temperature oxidizing atmosphere of around 700 ° C., the metal is inappropriate and a perovskite oxide material having electron conductivity, specifically, Are LaMnO ₃ or LaCoO ₃ , or a solid solution in which a part of these La is substituted with Sr, Ca or the like, and further a solid solution in which SmCoO ₃ or a part of Sm is substituted with Sr, Ca or the like.

On the other hand, the fuel electrode layer 4, the mixing composition Ni (or, Co, Cu) as the electrode material Ce _1-x and a ceria-based ceramic Sm _x O _2: using a mixture of (SDC samarium doped ceria), and Ni A two-layer structure of a first fuel electrode layer 4a and a second fuel electrode layer 4b is formed according to the composition ratio of SDC. The particle size of the Ni / SDC mixture is about 1 μm or less.

In the present embodiment, the first fuel electrode layer 4a in the vicinity of the interface with the solid electrolyte layer 3 has a very thin first fuel having a composition ratio of Ni (10 vol%) / SDC (90 vol%) and a thickness of about 1 μm. The electrode layer 4a was formed, and the second fuel electrode layer 4b having a thickness of about 30 μm and a composition ratio of Ni (60 vol%) / SDC (40 vol%) was formed thereon. The first fuel electrode layer 4a contains the above-described Ni / SDC mixture and coarse SDC particles having a diameter larger than the average particle diameter of the mixture.
In addition to the ceria-based ceramic material such as SDC described above, a zirconia-based material or a lanthanum gallate-based material can be used as the ceramic material.

The electrode structure shown in FIG. 2A is obtained by randomly arranging and baking coarse SDC particles 11 on the above-described Ni / SDC mixture 10 by spraying. In the present embodiment, the particle diameter of the coarse SDC particles 11 is set to 1 to 30 μm, and the ratio of the coarse SDC particles 11 to the total volume of the first fuel electrode layer 4a including the coarse SDC particles 11 is 1 It is set to ˜50 vol%.
By defining the particle size of the coarse SDC particles 11 and the amount thereof within the above range, a sufficient anchoring effect by the coarse SDC particles 11 can be obtained with respect to the solid electrolyte layer 3. Thus, the power generation cell 1 has excellent durability and stable power generation performance even in a heat cycle during long-time operation.

  In addition, the phenomenon of Ni diffusing into the solid electrolyte layer 3 during operation can be suppressed by reducing the amount of Ni mixed in the vicinity of the interface of the solid electrolyte layer 3 as in the first fuel electrode layer 4a. The power generation characteristics of the cell 1 are improved.

  In addition, in the first fuel electrode layer 4a and the second fuel electrode layer 4b, the Ni / SDC mixture as the electrode material can be given a composition gradient in the stacking direction. For example, the first fuel electrode layer 4a In this case, the composition ratio of Ni is preferably 1 vol% or more and less than 20 vol%, and the composition ratio of Ni is preferably 20 to 70% in the second fuel electrode.

  Next, in the electrode structure shown in FIG. 2B, the slurry containing coarse SDC 11 was applied to the Ni / SDC mixture 10 layer in the above-described manner in a layered manner by, for example, screen printing, and baked. Therefore, the coarse SDC is formed in a dot shape in an aligned state over the entire surface of the first fuel electrode layer 4a.

In the present embodiment, setting the projected area of the coarse SDC dots 11 (corresponding to the screen pattern holes of 2mm × 2mm square) 0.04 cm ² below, and within 100 the number of coarse SDC dots 11 / cm ² It is set to.
In this way, by defining the projected area and the number of coarse SDC dots 11 within the above range, the peeling resistance of the fuel electrode layer 4 is improved by the anchor effect of the coarse SDC dots 11, and the power generation performance in long-time power generation. Can be stabilized. Further, by arranging the coarse SDC dots 11 uniformly on the first fuel electrode layer 4a, the residual stress between the electrode layer and the electrolyte layer during the sintering is relaxed, and the warping and bending of the power generation cell 1 are reduced. Has merit.

The figure which shows the internal structure of the electric power generation cell to which this invention was applied. The figure which shows the internal structure of a 1st fuel electrode layer. The figure which shows the internal structure of the conventional power generation cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power generation cell 2 Air electrode layer 3 Solid electrolyte layer 4 Fuel electrode layer 4a 1st fuel electrode layer 10 Mixture 11 Coarse ceramic (coarse SDC particle, coarse SDC dot)

Claims (7)

In a solid oxide fuel cell comprising a power generation cell in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer,
The fuel electrode layer has a first fuel electrode layer made of a mixture of metal particles and ceramic particles at an interface with the solid electrolyte layer, and the first fuel electrode layer has a diameter larger than the average particle diameter of the mixture. A solid oxide fuel cell comprising coarse ceramic particles. The coarse ceramic particles have a particle size of 1 to 30 μm, and the proportion of the coarse ceramic particles in the total volume of the first fuel electrode layer containing the coarse ceramic particles is 1 to 50 vol%. The solid oxide fuel cell according to claim 1. In a solid oxide fuel cell comprising a power generation cell in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer,
The fuel electrode layer has a first fuel electrode layer made of a mixture of metal particles and ceramic particles at the interface with the solid electrolyte layer, and the projected area of the first fuel electrode layer is larger than the average particle size of the mixture. A solid oxide fuel cell, characterized in that large coarse ceramics are applied in the form of dots in an aligned state. The projected area of the coarse ceramic dots with a 0.04 cm ² or less, the solid oxide fuel cell according to claim 3, characterized in that the number of the coarse ceramic dots is 100 or less / cm ^2. 5. The solid oxide fuel cell according to claim 1, wherein a mixing ratio of the metal particles in the mixture of the metal particles and the ceramic particles is less than 20 vol%. The ceramic particles of the first fuel electrode layer are ceria of the general formula: Ce _1-x B _x O ₂ (wherein B is one or more of Sm, Gd, Y, and Ca are added). The solid oxide fuel cell according to any one of claims 1 to 5, wherein: 7. The solid oxide fuel cell according to claim 1, wherein the first fuel electrode layer is made of a mixture of Ni and samarium-added ceria (SDC).

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