JP2005085522A - Supporting membrane type solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the breakage of a power generating cell by increasing the strength of an electrode supporter and enhance power generating performance by thinning a solid electrolyte. <P>SOLUTION: A supporting membrane type solid oxide fuel cell has a power generating cell 5 in which a fuel electrode 3 having electrode supporting structure is arranged on one side of the solid electrolyte 2 and an air electrode 4 is arranged on the other side of the solid electrolyte 2. The solid electrolyte 2 has a thickness of 5-100 μm, and porous ceramic having a thickness of 0.2-3 mm obtained by compressing and/baking a molded body having three-dimensional skeletal structure is used as the fuel electrode supporter. Particles 22 of an electrode material are attached to the surface of a ceramic skeleton and in of pores 23. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a support membrane type solid oxide fuel cell in which an electrode is used as a support, and more particularly to a solid oxide fuel cell with improved cell reliability and power generation performance.

  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 side passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte, where it receives electrons from the air electrode and is ionized to oxide ions (O ²⁻ ). The 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

  By the way, flat-stacked solid oxide fuel cells can be roughly classified into a self-supporting membrane type in which the solid electrolyte layer is thickened and a support membrane type in which strength is provided by an electrode support.

In the self-supporting membrane type solid oxide fuel cell, the thickness of the solid electrolyte is increased to about 200 to 500 μm in order to increase the strength of the power generation cell. When the electrolyte layer is thickened, its resistance increases and it becomes difficult to obtain a high output. Therefore, in order to obtain sufficient power generation characteristics, the operating temperature of the battery is usually set at a high temperature of about 1000 ° C. This is because the ionic conductivity of the solid electrolyte depends on the temperature, and the conductivity decreases as the temperature decreases.
However, since the battery constituent material uses ceramics at such a high temperature, its durability greatly affects the life and performance of the battery.

  On the other hand, a support membrane type solid oxide fuel cell has a structure in which an electrolyte membrane is formed on a thick electrode support (for example, Ni / YSZ cermet as a fuel electrode support). By obtaining strength, the thickness of the solid electrolyte can be reduced. By reducing the thickness of the solid electrolyte, the operating temperature of the battery can be lowered to around 700 ° C.

  However, since the electrode support is a porous body having gas permeability for supplying the fuel gas to the boundary with the solid electrolyte, the electrode support itself has a low mechanical strength. In the membrane type solid oxide fuel cell, the power generation cell is easily broken and lacks reliability. Increasing the thickness of the electrode support increases the strength. However, the gas diffusibility decreases and the battery output decreases accordingly. Therefore, it is necessary to avoid increasing the thickness of the fuel electrode support unnecessarily.

  In view of the above-described conventional problems, the present invention improves the power generation performance by improving the strength of the electrode support to prevent cracking of the power generation cell and reducing the thickness of the solid electrolyte to improve the power generation performance. An object of the present invention is to provide an oxide fuel cell.

  That is, the present invention described in claim 1 is a support membrane type solid oxide fuel cell including a power generation cell in which an electrode having an electrode support structure is disposed on one surface of a solid electrolyte. 100 μm and a porous sintered body having a thickness of 0.2 to 3 mm obtained by compressing and firing a molded body having a three-dimensional skeleton structure as an electrode support, and the surface of the porous sintered body and It is characterized in that particles of the electrode material are adhered in the pores.

  The present invention described in claim 2 is characterized in that, in the support membrane type solid oxide fuel cell described in claim 1, a lanthanum gallate material is used as the solid electrolyte.

  Further, the present invention described in claim 3 uses a ceria-based ceramic as the porous sintered body in the support membrane type solid oxide fuel cell according to claim 1 or 2. It is characterized by that.

  According to a fourth aspect of the present invention, there is provided the support membrane type solid oxide fuel cell according to any one of the first to third aspects, wherein the particles of the fuel electrode material are Ni and samarium-added ceria (SDC). In addition, the amount of Ni mixed at the interface of the skeleton is less than that of SDC, and the Ni mixing ratio is increased toward the surface.

In the structure according to any one of claims 1 to 3, by using the porous ceramic having the three-dimensional skeleton structure described above as the electrode support, the strength of the electrode support is improved, and the power generation cell can be obtained even if the solid electrolyte is thinned. Sufficient mechanical strength can be obtained. As a result, the power generation cell is difficult to break and the reliability of the solid oxide fuel cell is improved. In addition, by reducing the thickness of the solid electrolyte as described above, the resistance of the solid electrolyte is reduced, and the power generation performance can be improved.
Further, in the configuration according to claim 4, by providing the composition gradient to the fuel electrode material particles, it is possible to avoid a rapid change in the coefficient of thermal expansion at the interface between the ceramic skeleton and the electrode material in the fuel electrode support, Electrode peeling can be prevented.

  As described above, according to the present invention, the strength of the electrode support can be improved, and sufficient mechanical strength as a power generation cell can be obtained even if the solid electrolyte is thinned. Thereby, it becomes difficult to break a power generation cell, and the reliability of a solid oxide fuel cell is improved. In addition, by reducing the thickness of the solid electrolyte, the resistance of the solid electrolyte can be reduced, and the power generation performance can be improved.

  Moreover, according to this invention, electrode peeling in a fuel electrode support body can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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 5 includes a solid electrolyte 2, a fuel electrode 3 and an air electrode 4 disposed on both surfaces thereof.

Since the solid electrolyte 2 functions as a partition wall for preventing the fuel gas and the air from being brought into direct contact with each other, it has a dense structure that is impermeable to gas. The solid electrolyte 2 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 80 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 (cathode) 4 and the fuel electrode (anode) 3 that are electrodes must be made of a material having high electron conductivity. As for the air electrode material, it must be chemically stable in a high-temperature oxidizing atmosphere of around 700 ° C., so that the metal is inappropriate and a perovskite oxide material having electron conductivity, specifically, 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 a part of SmCoO ₃ or Sm is substituted with Sr, Ca or the like are used.

On the other hand, as shown in FIG. 1, the fuel electrode 3 has an electrode support structure in which particles 22 of an electrode material are attached to a skeleton 21 (electrode skeleton) made of a porous sintered body having a three-dimensional skeleton structure. The skeleton 21 of this three-dimensional skeleton structure has large pores 23 generated by the generation of bubbles by evaporation of liquid, particles 22 adhere to the outer surface of the skeleton 21, and the internal space of the large pores 23 The particles 22 are baked in a filled state.
Incidentally, the thickness of this electrode support is about 0.5 mm, the thickness of the skeleton is about 0.05 mm, and the porosity is about 60%.

  In such a fuel electrode support, the outer surface of the skeleton 21 to which the particles 22 are attached and the large pores 23 in the skeleton structure filled with the particles 22 serve as electrode surfaces, and a reaction layer is formed at the interface between the electrode surfaces and the solid electrolyte 2. It is formed. Incidentally, the area ratio of the reaction layer is 20% or less.

  Usually, when a porous body is used for the electrode support, the solid electrolyte 2 and the electrode support are subjected to a solid solution reaction in the firing process, the composition of the solid electrolyte is changed, and the performance of the solid electrolyte is deteriorated. In the present embodiment, this problem is solved by using a porous body having a three-dimensional skeleton structure as the electrode support and reducing the area ratio of the reaction layer at the interface between the electrode surface and the solid electrolyte 2 as described above. doing.

  In addition, since the porosity of the skeleton 21 is very large, the mitigating action against thermal shock and thermal strain is also large, and therefore cracking of the power generation cell 5 due to the difference in thermal expansion coefficient with the solid electrolyte 2 in the thermal cycle during operation. Can be prevented.

Here, since the electrode skeleton 21 becomes a passage for oxide ions leading to the solid electrolyte 2, some degree of oxide ion conductivity is required. Therefore, an oxide ion conductive material is used as a skeleton material. In this embodiment, samarium-added ceria (SDC: CeSmO ₂ ) is used as the ceria-based ceramic, and Ni is dispersed therein.
As other skeleton materials, zirconia materials and lanthanum gallate materials can be used.

  On the other hand, the adhering particle 22 becomes a passage of electrons necessary for the delivery of oxide ions at the three-phase interface, and therefore requires a certain degree of electron conductivity, and a mixture of an electron conductive material and an oxide ion conductive material. Is used. The particle size is about 1 μm.

In this embodiment, a mixture of Ni (or Co, Cu) and SDC is used, and the electrode material Ni / SDC has a composition gradient. That is, at the interface with the skeleton 21, the amount of Ni mixed is made smaller than SDC, and the Ni mixing ratio is gradually increased toward the surface side, so that Ni is formed on the outermost surface.
By providing the Ni / SDC composition with the inclination as described above, a rapid change in the coefficient of thermal expansion at the interface between the skeleton and the electrode material in the electrode support can be avoided, and electrode peeling can be prevented.
In addition to the above, as the oxide ion conductive material, the same material as the solid electrolyte 2 such as a zirconia material or a lanthanum gallate material is used.

  As described above, by using the porous ceramic having the above-described three-dimensional skeleton structure for the fuel electrode support, the strength of the fuel electrode support itself can be improved, and even if the solid electrolyte is thinned (5 to 100 μm), the power generation cell As a result, sufficient mechanical strength can be obtained. Thereby, the power generation cell 5 becomes difficult to break, and the reliability of the solid oxide fuel cell is improved. Further, by reducing the thickness of the solid electrolyte 2, the resistance of the solid electrolyte 2 is reduced, and the power generation performance can be improved.

Next, the manufacturing process of the power generation cell 5 having the above-described configuration will be described. First, the raw material powder of the electrode skeleton 21 is formed into a foam sheet to form a porous sheet for an unsintered electrode skeleton having a three-dimensional skeleton structure. obtain. An unsintered solid electrolyte sheet, which is densely formed by a sheet forming method, is thermocompression-bonded to the porous sheet using, for example, a hot press (compressibility is about 90%). When sintered, an electrode skeleton / solid electrolyte laminate can be produced.
Next, the electrode skeleton of the electrode skeleton / electrolyte laminate obtained by sintering is impregnated with a slurry containing fuel electrode material particles 22 (for example, a mixture of Ni / SDC), so that the surface of the skeleton 21 and the pores 23 are formed. The particles 22 are adhered inside. After the impregnation, the laminate is sintered again, and the adhered particles are bonded to the skeleton 21 to produce the fuel electrode support. On the other hand, the air electrode 4 can be formed by conventional screen printing.

As described above, in the present embodiment, the fuel electrode 3 side is a support body made of a porous body having a three-dimensional skeleton structure, but the support body can also be applied to the air electrode side. As described above, electron-conductive materials such as LaMnO ₃ , LaCoO _3, and SmCoO ₃ are used. Of course, both the fuel electrode 3 and the air electrode 4 may be electrode support structures. In any configuration, it is possible to realize a highly reliable support membrane type solid oxide fuel cell that greatly improves the electrolyte characteristics and prevents the cell from being cracked due to thermal shock or thermal strain.

Next, the configuration of a solid oxide fuel cell to which the present invention is applied will be described with reference to FIG.
In FIG. 2, reference numeral 1 denotes a fuel cell stack, a power generation cell 5 in which a fuel electrode 3 and an air electrode 4 are arranged on both surfaces of a solid electrolyte 2, a fuel electrode current collector 6 outside the fuel electrode 3, and an air electrode. The air electrode current collector 7 outside the layer 4 and the separator 8 outside the current collectors 6 and 7 are sequentially stacked.
Further, on the side of the fuel cell stack 1, a fuel manifold 15 that supplies fuel gas to the fuel passage 11 of each separator 8 through the connection pipe 13, and an oxidant gas through the connection pipe 14 to the oxidant passage 12 of each separator 8. An oxidant manifold 16 is provided to extend in the stacking direction of the power generation cells 5.

The figure which shows the structure of the support membrane type power generation cell which concerns on this invention. The figure which shows the structure of the solid oxide fuel cell to which this invention is applied.

Explanation of symbols

2 Solid Electrolyte 3 Fuel Electrode 4 Air Electrode 21 Skeleton 22 Particles 23 Inside Space

Claims (4)

In a support membrane type solid oxide fuel cell comprising a power generation cell in which an electrode having an electrode support structure is disposed on one surface and / or the other surface of a solid electrolyte,
The solid electrolyte has a thickness of 5 to 100 μm, and uses a porous sintered body having a thickness of 0.2 to 3 mm obtained by compressing and firing a molded body having a three-dimensional skeleton structure as an electrode support. A support membrane type solid oxide fuel cell, characterized in that particles of an electrode material adhere to the surface and pores of a porous sintered body. The support membrane solid oxide fuel cell according to claim 1, wherein a lanthanum gallate material is used as the solid electrolyte. 3. The support membrane solid oxide fuel cell according to claim 1, wherein ceria-based ceramic is used as the porous sintered body. The anode material particles are a mixture of Ni and samarium-added ceria (SDC), and the amount of Ni mixed at the interface of the skeleton is less than SDC and the Ni mixing ratio is increased toward the surface. The support membrane type solid oxide fuel cell according to any one of claims 1 to 3, wherein the support membrane type solid oxide fuel cell is provided.

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