JP4876363B2 - Current collector, method for producing the same, and solid oxide fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current collector for a solid oxide fuel cell, a method for producing the current collector, and a solid oxide fuel cell using the current collector.
[0002]
[Prior art]
Solid oxide fuel cells having a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer and a fuel electrode layer are being developed as a third-generation fuel cell for power generation. In a solid oxide fuel cell, oxygen (air) is supplied to the air electrode side, and fuel gas (H ₂ , CO, etc.) is supplied to 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.
[0003]
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 layer. At this part, it receives electrons from the air electrode and converts them into oxide ions (O ²⁻ ). Ionized. The oxide ions diffuse and move in the solid electrolyte layer 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.
[0004]
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
[0005]
The solid electrolyte layer is a moving medium for oxide ions and at the same time functions as a partition for preventing direct contact between the fuel gas and air, and thus has a dense structure that is impermeable to gas. This solid electrolyte layer should have a high oxide ion conductivity, be chemically stable under conditions from the oxidizing atmosphere on the air electrode side to the reducing atmosphere on the fuel electrode side, and be made of a material that is resistant to thermal shock. There is generally used stabilized zirconia (YSZ) to which yttria is added as a material satisfying such requirements.
[0006]
On the other hand, both the air electrode (cathode) layer and the fuel electrode (anode) layer, which are electrodes, must be made of a material having high electron conductivity. Since the air electrode material must be chemically stable in a high-temperature oxidizing atmosphere around 700 ° C., the metal is inappropriate, and a perovskite-type oxide material having electron conductivity, specifically LaMnO ₃ Alternatively, LaCoO ₃ or a solid solution in which a part of these La is substituted with Sr, Ca or the like is generally used. The fuel electrode material is generally a metal such as Ni or Co, or a cermet such as Ni—YSZ or Co—YSZ.
[0007]
Solid oxide fuel cells include a high temperature operation type that operates at a high temperature of about 1000 ° C. and a low temperature operation type that operates at a low temperature of about 700 ° C. A low temperature operation type solid oxide fuel cell is a fuel cell even at low temperatures, for example, by reducing the thickness of stabilized zirconia (YSZ) to which the electrolyte yttria is added to about 10 μm to reduce the resistance of the electrolyte. Use power generation cells modified to generate electricity.
[0008]
In a high-temperature solid oxide fuel cell, ceramics having electronic conductivity such as lanthanum chromite (LaCrO ₃ ) is used as a separator. In a low-temperature solid oxide fuel cell, a metal material such as stainless steel is used. Can be used.
[0009]
Three types of solid oxide fuel cell structures have been proposed: a cylindrical type, a monolith type, and a flat plate type. Among these structures, a metal separator can be used for a low temperature operation type solid oxide fuel cell. Therefore, a flat plate type structure that is easy to give a shape to the metal separator is suitable.
[0010]
A stack of flat plate type solid oxide fuel cells has a structure in which power generation cells, current collectors, and separators are alternately stacked. A pair of separators sandwich the power generation cell from both sides, one being in contact with the air electrode via the air electrode current collector and the other being in contact with the fuel electrode via the fuel electrode current collector. A sponge-like porous body such as a Ni-based alloy can be used for the fuel electrode current collector, and a sponge-like porous body such as an Ag-based alloy can be used for the air electrode current collector. Can do. The sponge-like porous body has a current collecting function, a gas permeation function, a uniform gas diffusion function, a cushion function, a thermal expansion difference absorption function, and the like, and is therefore suitable as a multifunctional current collector material.
[0011]
The separator has a function of electrically connecting the power generation cells and supplying gas to the power generation cells. The fuel is introduced from the outer peripheral surface of the separator and discharged from the surface facing the separator fuel electrode layer. Each has a passage and an oxidant passage through which oxidant gas is introduced from the outer peripheral surface of the separator and discharged from the surface facing the oxidant electrode layer of the separator.
[0012]
[Problems to be solved by the invention]
By the way, in the conventional fuel cell, a current collector made of a porous cushion material is disposed between the electrode layer and the separator, and gas is distributed and supplied from the separator to the electrode layer through the current collector. When supplying gas to the electrode layer from the central part of the electrode via the current collector, there is a difference in power generation between the central part and the peripheral part because the gas of sufficient concentration does not reach the peripheral part of the electrode layer. In order to improve the power generation efficiency, further improvement in the performance of the current collector has been demanded.
[0013]
In view of the above circumstances, an object of the present invention is to provide a current collector capable of improving power generation efficiency, a method for manufacturing the current collector, and a solid oxide fuel cell using the current collector.
[0014]
[Means for Solving the Problems]
According to a first aspect of the present invention, a current collector disposed between a separator and an electrode layer of a solid oxide fuel cell is composed of a porous metal body having a three-dimensional skeleton structure, and an outer peripheral edge portion is formed. It is characterized in that the porosity is lower than that in the center.
[0015]
In this current collector, the porosity of the outer peripheral edge portion is set lower than that in the central portion, so that the back pressure acting on the outer peripheral end of the current collector can be increased. Therefore, even when applied to a fuel cell of a type in which a gas seal member is not provided on the outer peripheral portion of the power generation cell, gas escape from the outer peripheral portion of the current collector can be suppressed and supplied from the central portion of the separator. The gas can be distributed at a sufficient concentration to the periphery of the current collector. As a result, gas can be uniformly distributed and supplied to the electrode layer over a wide area from the center to the periphery of the current collector, eliminating the difference in power generation between the center and the periphery, and improving the overall power generation efficiency. Can be improved.
[0016]
According to a second aspect of the present invention, there is provided a method for producing a current collector disposed between a separator and an electrode layer of a solid oxide fuel cell, wherein a circle made of a metal porous body having a homogeneous three-dimensional skeleton structure as a whole. A step of forming a plate, and a step of compressing the outer peripheral edge of the disc to form a porosity of the portion lower than that of the central portion.
[0017]
As a method of lowering the porosity of the outer peripheral edge of a disk made of a metal porous body, a method of adjusting the porosity at the stage of molding the metal porous body can be adopted, but in the invention of claim 2, In the molding step of the material, the whole is formed as a metal porous body having a homogeneous three-dimensional skeleton structure, and in the subsequent steps, the peripheral edge portion of the disk is utilized by utilizing the easily crushed property of the metal porous body. By compressing and crushing, the porosity of the part is made lower than others. At that time, the thickness of the portion to be compressed and crushed can be made large in advance, and the entire thickness can be made uniform in the crushed state later. Note that the fine structure of the current collector may be a mesh, felt, foam, or the like. However, when the current collector is made of a metal foam having a three-dimensional skeleton structure, it can be easily crushed and thus can be processed extremely easily.
[0018]
According to a third aspect of the present invention, there is provided a method for producing a current collector disposed between a separator and an electrode layer of a solid oxide fuel cell, wherein a circle made of a metal porous body having a homogeneous three-dimensional skeleton structure as a whole. A step of forming a plate, a step of forming an annular upright wall by bending the outer peripheral edge of the disc over the entire circumference, and the portion by compressing the upright wall in the thickness direction of the disc And a step of forming the whole with a uniform thickness while forming a lower porosity than the central portion.
[0019]
In this invention, before compressing and crushing the outer peripheral edge of the disk, the outer peripheral edge of the disk is bent in advance to form a standing wall, and the height of the standing wall is compressed and crushed in that state. Thus, the porosity of the outer peripheral edge portion is formed to be lower than that of the central portion while making the entire thickness uniform. Therefore, the porosity can be adjusted while making the entire thickness uniform without special measures (such as forming the outer peripheral edge to be thicker) in the metal porous body forming step. In that case, the size of the porosity can be set according to the bending height of the standing wall.
[0020]
According to a fourth aspect of the present invention, a fuel electrode layer and an oxidant electrode layer are laminated on both sides of a solid electrolyte layer, and a fuel electrode current collector and an oxidant comprising a porous body outside the fuel electrode layer and the oxidant electrode layer, respectively. A fuel cell stack is formed by laminating an electrode current collector and laminating a separator on the outside of the fuel electrode current collector and the oxidant electrode current collector, and the fuel electrode current collector and the oxidant are formed from the center of the separator. 2. The current collector according to claim 1, wherein at least the fuel electrode current collector is a solid oxide fuel cell that supplies fuel gas and oxidant gas to the fuel electrode layer and the oxidant electrode layer via an electrode current collector. 3. It is characterized by using.
[0021]
The problem caused by the uneven distribution and supply of gas through the current collector occurs mainly on the fuel gas supply side. This is because the fuel gas cannot flow in a large amount like air (oxidant gas) and can flow only in a prescribed amount. Therefore, in the invention of claim 3, the current collector having a lower porosity in the outer peripheral edge portion of claim 1 is used as at least the anode current collector. By using this current collector, the fuel gas can be distributed and supplied in a uniform distribution over the entire surface of the fuel electrode layer, so that the power generation efficiency is improved.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B are configuration diagrams of a current collector, where FIG. 1A is a plan view and FIG. 1B is a cross-sectional view. FIG. 2 is a process explanatory diagram of a method of manufacturing a current collector. 3 is an exploded sectional view of the solid oxide fuel cell, and FIG. 4 is an exploded perspective view of the main part.
[0023]
First, the whole structure of the solid oxide fuel cell of embodiment is demonstrated using FIG. 3, FIG. In FIG. 3, reference numeral 1 denotes a fuel cell stack placed with its stacking direction vertical. This fuel cell stack 1 includes a power generation cell (power generation unit) 5 in which a fuel electrode layer 3 and an air electrode layer (oxidant electrode layer) 4 are arranged on both surfaces of a solid electrolyte layer 2, and a fuel electrode outside the fuel electrode layer 3. A current collector 6, an air electrode current collector (oxidant electrode current collector) 7 outside the air electrode layer 4, and a separator 8 outside each current collector 6, 7 are sequentially stacked. .
[0024]
Here, the solid electrolyte layer 2 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is composed of a metal such as Ni or Co or a cermet such as Ni—YSZ or Co—YSZ, and air. The electrode layer 4 is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector 7 is made of an Ag-based alloy or the like. The separator 8 is made of stainless steel or the like.
[0025]
The porous metal plate which comprises the electrical power collectors 6 and 7 is produced through the following process. The order of the process is slurry preparation process → molding process → foaming process → drying process → degreasing process → sintering process.
[0026]
First, in the slurry preparation step, a metal powder, an organic solvent (such as n-hexane), a surfactant (such as sodium dodecylbenzenesulfonate), a water-soluble resin binder (such as hydroxypropylmethylcellulose), a plasticizer (such as glycerin), A foam slurry is prepared by mixing water. This is formed into a thin plate shape on a carrier sheet by a doctor blade method in a forming step to obtain a green sheet. Next, in the foaming process, the green sheet is foamed in a sponge shape using the vapor pressure of the volatile organic solvent and the foaming property of the surfactant in a high-temperature and high-humidity environment, followed by a drying process, a degreasing process, A porous metal plate is obtained through a firing step.
[0027]
In this case, in the foaming process, the bubbles generated inside the green sheet receive a substantially equivalent pressure from all directions and grow in a substantially spherical shape. When the bubbles diffuse from the inside and approach the interface with the atmosphere, the bubbles grow into a thin portion of the slurry between the bubbles and the atmosphere, eventually breaking the bubbles, and the gas inside the bubbles is made small It diffuses from the hole into the atmosphere. Therefore, a porous metal plate having continuous pores opened on the surface is obtained.
[0028]
The current collectors 6 and 7 are configured by cutting the porous metal plate (metal porous body) having the three-dimensional skeleton structure thus produced into a circle. In particular, the anode current collector 6 made of a porous sintered metal plate such as a Ni-based alloy has an outer peripheral edge portion 6A that is more central than the central portion 6B, as shown in detail in FIGS. Are also formed with a low porosity.
[0029]
As a method of setting only the porosity of the outer peripheral edge portion 6A of the disk made of a metal porous body to be lower than that of the central portion 6B, a method of adjusting the porosity at the stage of forming the metal porous body may be adopted. Although it is possible, here, in the material forming stage, the whole is formed as a porous metal plate having a homogeneous three-dimensional skeleton structure, and in the step after cutting it into a circle, the porous metal plate By utilizing the property of being easily crushed, the outer peripheral edge portion 6A of the disk is compressed and crushed so that the porosity of the portion is made lower than others.
[0030]
The specific manufacturing method will be described with reference to FIG.
In this method, first, in a first step, a disk 21 made of a porous metal body having a homogeneous three-dimensional skeleton structure is formed and set in a press machine 30 as shown in FIG. To do. The press machine 30 includes an upper mold 33 including a core 31 and an outer ring 32, and a lower mold 36 including a core 34 and an outer ring 35.
[0031]
After setting the disk 21 on the lower mold 36, in the second step, the upper and lower cores 31, 34 are moved downward relative to the upper and lower rings 32, 35 as shown in FIG. By doing so, the outer peripheral edge of the disc 21 is bent over the entire circumference, and the annular upright wall 22 is formed.
[0032]
Next, in the third step, as shown in (c), the ring 32 of the upper mold 33 is moved downward, and the upright wall 22 is compressed in the thickness direction of the disk 21, thereby making the whole uniform. Form to thickness. By doing so, the current collector 6 is obtained in which the porosity of the outer peripheral edge portion (the portion where the standing wall 22 was present) 6A is lower than that of the central portion 6B. Thereafter, as shown in (d), the upper mold 33 and the lower mold 36 may be opened to take out the molded product (current collector 6).
[0033]
By forming the current collector 6 through these processes, the entire structure can be obtained without special measures (such as forming the outer peripheral edge to be thick) at the metal porous body forming stage. The porosity of the outer peripheral edge portion 6A can be set low while making the thickness of each of them uniform.
[0034]
3 and 4, the overall configuration will be described. The separator 8 has a function of electrically connecting the power generation cells 5 and supplying gas to the power generation cells 5. A fuel passage 11 introduced from the outer peripheral surface of the separator 8 and discharged from the substantially central portion of the surface of the separator 8 facing the anode current collector 6, and an oxidant gas introduced from the outer peripheral surface of the separator 8 Each has an oxidant passage 12 to be discharged from a surface facing the air electrode current collector 7. However, the separators 8 (8A, 8B) at both ends have only one of the passages 11 and 12.
[0035]
On the other hand, as shown in FIG. 3, on the side of the fuel cell stack 1, a fuel manifold 15 that supplies fuel gas to the fuel passages 11 of the separators 8 through the connection pipes 13, and an oxidant passage 12 of each separator 8. An oxidant manifold 16 for supplying an oxidant gas through the connection pipe 14 extends in the stacking direction of the power generation cells 5.
[0036]
In the fuel cell having the above-described configuration, the anode current collector 6 is configured such that the porosity of the outer peripheral edge portion 6A shown in FIG. 1 is set lower than that of the central portion 6B. The fuel gas to be distributed can be distributed with good distribution over the entire surface of the fuel electrode layer 3 through the fuel electrode current collector 6.
[0037]
In other words, since the conventional current collector has a uniform porosity, the gas escapes from the outer peripheral edge, so that the gas concentration decreases from the central part to the peripheral part. However, the anode current collector 6 has a lower porosity in the outer peripheral edge portion 6A than that in the central portion 6B. The back pressure acting on the outer peripheral end can be increased. Therefore, even when applied to a fuel cell of a type in which no gas seal member is provided on the outer peripheral portion of the power generation cell (sealless type), the escape of gas from the outer peripheral end of the current collector 6 can be suppressed, and the separator 8 The fuel gas supplied from the central portion of the current collector can be distributed to the peripheral portion of the current collector 6 at a sufficient concentration. As a result, the fuel gas can be evenly distributed and supplied to the entire surface of the fuel electrode layer 3 over a wide area from the central portion to the peripheral portion of the current collector 6, and the difference in power generation amount between the central portion and the peripheral portion can be reduced. Without it, the overall power generation efficiency can be improved.
[0038]
Note that the current collector similar to the fuel electrode current collector 6 in which the porosity of the outer peripheral edge portion is lower than that of the central portion can be used for the air electrode current collector 7. Further, as the porous structure of the current collectors 6 and 7, a mesh, felt, or the like can be used in addition to the foam.
[0039]
In the above-described embodiment, the solid oxide fuel cell using stabilized zirconia (YSZ) in which yttria is added to the electrolyte of the power generation cell has been shown. However, the present invention is not limited to other solid oxide fuel cells, for example, The present invention can also be applied to a solid oxide fuel cell using a ceria-based electrolyte and a gallate electrolyte.
[0040]
【Effect of the invention】
As described above, the current collector of the first aspect of the invention has a lower porosity at the outer peripheral edge portion than that at the central portion, so that the back pressure acting on the outer peripheral end of the current collector is increased. The gas supplied from the central portion of the separator can be spread to the peripheral portion of the current collector at a sufficient concentration. Therefore, gas can be uniformly distributed and supplied to the electrode layer over a wide area from the center to the periphery of the current collector, eliminating the difference in power generation between the center and the periphery, and improving the overall power generation efficiency. Can be up.
[0041]
According to the manufacturing method of the invention of claim 2, the whole is formed as a metal porous body having a homogeneous three-dimensional skeleton structure at the material forming stage, and the outer peripheral edge of the disk is compressed in the subsequent process. By crushing, the porosity of the portion is made lower than others, so the porosity can be easily adjusted. According to the third aspect of the present invention, the porosity can be easily adjusted while making the entire thickness uniform without special measures in the metal porous body forming step.
[0042]
According to the invention of claim 4, since the current collector is used as at least the fuel electrode current collector, the fuel gas can be distributed and supplied in a uniform distribution over the entire surface of the fuel electrode layer. Is up.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a current collector according to an embodiment of the present invention, where (a) is a plan view and (b) is a cross-sectional view.
FIGS. 2A to 2D are process diagrams for explaining a method of manufacturing a current collector.
FIG. 3 is an exploded cross-sectional view showing a main configuration of a solid oxide fuel cell according to an embodiment of the present invention.
FIG. 4 is an exploded perspective view showing a main configuration of the fuel cell.

Claims (4)

The current collector disposed between the separator and the electrode layer of the solid oxide fuel cell is composed of a metal porous body having a three-dimensional skeleton structure, and the outer peripheral edge is formed to have a lower porosity than the center. A solid oxide fuel cell current collector. In the method for producing a current collector disposed between a separator and an electrode layer of a solid oxide fuel cell, a step of forming a disk made of a metal porous body having a homogeneous three-dimensional skeleton structure as a whole; A method of manufacturing a current collector for a solid oxide fuel cell, comprising compressing an outer peripheral edge of the disk to form a porosity of the portion lower than that of the central portion. In the method for producing a current collector disposed between a separator and an electrode layer of a solid oxide fuel cell, a step of forming a disk made of a metal porous body having a homogeneous three-dimensional skeleton structure as a whole; The step of forming an annular standing wall by bending the outer peripheral edge of the disc over the entire circumference, and the porosity of the portion from the center by compressing the standing wall in the thickness direction of the disc And a step of forming the whole with a uniform thickness, and a method for producing a current collector for a solid oxide fuel cell, characterized by comprising: A fuel electrode layer and an oxidant electrode layer are stacked on both sides of the solid electrolyte layer, and a fuel electrode current collector and an oxidant electrode current collector made of a porous material are stacked outside the fuel electrode layer and the oxidant electrode layer, respectively. A fuel cell stack is configured by laminating a separator on the outside of the fuel electrode current collector and the oxidant electrode current collector, and the fuel electrode current collector and the oxidant electrode current collector are interposed from the central portion of the separator. A solid oxide fuel cell for supplying a fuel gas and an oxidant gas to a fuel electrode layer and an oxidant electrode layer, wherein the current collector according to claim 1 is used as at least the fuel electrode current collector. Solid oxide fuel cell.

Images