KR20090068632A - A fabrication method of separators for planar solid oxide fuel cells - Google Patents

Abstract

A fabrication method of separators is provided to form spinel oxides with excellent conductivity at a contact surface of an air electrode in a high temperature oxidation atmosphere, and to prevent Cr-poisoning by forming alumina oxide preventing diffusion and evaporation of chrome. A fabrication method of separators for planar solid oxide fuel cells comprises the steps of: coating a contact surface(5a) contacting an air electrode(4) of a separator with highly conductive materials; and coating the bottom(5c) and side surfaces(5b) of channels which is a site that does not contact with the air electrode with materials preventing the diffusion of the chrome component. The highly conductive materials are one material selected from nickel(Ni), cobalt(Co) and copper(Cu).

Description

A fabrication method of separators for planar solid oxide fuel cells

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal separator for a planar solid oxide fuel cell, and in detail, a connection portion contacting the cathode electrode is one of nickel (Ni), cobalt (Co), and copper (Cu). The material is coated on the material, and the bottom and side surfaces of the gas flow path which are not in contact with the cathode electrode are first coated with aluminum (Al) on the lower layer, and one of nickel (Ni), cobalt (Co) and copper (Cu) is coated. It is characterized by coating on the upper layer.

The separator used in the planar solid oxide fuel cell has three functions.

The first is the function of physically separating cells from neighboring cells in manufacturing a solid oxide fuel cell stack. The second is the function of electrically connecting the cell to the cell. The third is the function of providing a flow path of the reaction gas.

Recently, as the operating temperature is lowered to less than 800 ℃, the separator material used in the plate-type solid oxide fuel cell is changing from the conventional ceramic material to the excellent metal material in terms of processability and cost.

Among the metal materials, Fe-Cr alloys are used because the coefficient of thermal expansion is similar to that of neighboring cell materials. However, Fe-Cr alloy acts as a factor to reduce the battery performance by disturbing the normal electrochemical reaction by generating volatile Cr component in the solid oxide fuel cell operating environment. In addition, the separator should be excellent in conductivity for a long time at high temperature, it forms a chromium oxide on the surface serves to reduce the conductivity. That is, the metal separator should be free of chromium (Cr) components and at the same time form an oxide having excellent conductivity on the surface.

Fe-Cr alloys include ZMG232 developed by Hitachi Metals and Crofer22 developed by ThyssenKrupp. ZMG232 is a Ferritic Fe-22Cr alloy containing 22% Cr and added 0.04% La and 0.22% Zr. Briefly looking at the characteristics of ZMG232, the coefficient of thermal expansion is 12.8 × 10 ^-6 / ℃, reports that the oxidation resistance and electrical conductivity is superior to the existing STS430 in the temperature range of 700 ~ 1000 ℃. It is said to be related to the characteristics of oxides formed on the surface in an oxidizing atmosphere. That is, the ZMG232 alloy is said to have a structure in which the oxide structure is dense, high adhesion, and excellent electrical conductivity. Crofer22, developed by ThyssenKrupp, is a Ferritic Fe-Cr alloy originally developed for automotive APU (Auxiliary Power Unit). Looking at the characteristics of Crofer22, in order to minimize the evaporation of Cr, and to lower the coefficient of thermal expansion, a small amount of La of 0.08% is included. Mn and Ti are added thereto to form (Mn, Cr) ₂ O ₄ in the upper layer and Cr ₂ O ₃ in the lower layer in a high temperature oxidation atmosphere. The (Mn, Cr) ₂ O ₄ oxide of the spinel structure also has a function of preventing the evaporation of Cr.

However, these developed Fe-Cr-Mn alloys do not completely prevent electrical conductivity and Cr-poisoning in a solid oxide fuel cell environment, so surface treatment techniques for controlling surface characteristics may be used in parallel. Therefore, the research flow of the separator for a solid oxide fuel cell has been introduced to the surface coating to enhance the surface characteristics with the development of the alloy. In other words, research is being conducted to increase the electrical conductivity by coating a suitable component on a conventional ferritic stainless steel sheet, and to reduce the toxicity by chromium components.

The object of the present invention is to solve two problems. The first is to control oxides formed on the surface in high temperature oxidizing atmospheres to form oxides with excellent conductivity. The second is to prevent the chromium component from coming out of the stainless steel sheet.

In order to solve this technical problem, the present invention chose a method of surface treatment in the flow path of the separator. In order to solve the two problems separately, the contact surface of the separator plate which meets the cathode electrode is intended to be coated with a material having excellent conductivity, and the bottom and side surfaces of the separator channel, which are not in contact with the electrode, prevent the toxic effects of chromium. In order to coat the material to prevent the diffusion of the chromium component on the surface.

In the present invention, in the manufacture of a separator used in a plate-type solid oxide fuel cell having a Fe-Cr-Mn alloy, which is a ferritic stainless steel sheet, the connection portions that meet the cathode electrode are nickel (Ni), cobalt (Co), and copper. One material (Cu) is coated, and the bottom and side surfaces of the gas flow path not contacting the cathode electrode are first coated with aluminum (Al) on the lower layer, and nickel (Ni), cobalt (Co), and copper (Cu). By coating one of the materials on the upper layer, the contact surface with the cathode, in which the electrical connection function is important, forms a highly conductive spinel oxide on the surface in a high temperature oxidizing atmosphere, as well as the surface of the chromium on the bottom and side of the gas flow path. Because it forms an alumina oxide that can prevent diffusion and evaporation, it is effective in preventing Cr-poisoning by chromium components. It is possible.

In order to achieve the above object, in the present invention, a connection portion in contact with the cathode electrode in a metal plate for a solid-state solid oxide fuel cell is coated with one of nickel (Ni), cobalt (Co), and copper (Cu), and Cathode The bottom and side surfaces of the gas flow passage not in contact with the electrode are first coated with aluminum (Al) on the lower layer, and one of nickel (Ni), cobalt (Co), and copper (Cu) is coated on the upper layer. do.

Hereinafter, the drawings will be described in more detail.

1 is a view showing a stack state of a general planar solid oxide fuel cell. The solid oxide fuel cell includes an electrolyte 3 having oxygen ion conductivity, an anode electrode 4 and an anode electrode 2 positioned on both sides thereof, and when oxygen and hydrogen are supplied to each electrode, the cathode electrode 4 Oxygen ions generated through the reduction reaction of oxygen moves through the electrolyte 3 to the anode electrode 2 and then reacts with hydrogen supplied to the anode electrode 2 to form water. At this time, since the electrons generated in the anode electrode 2 are transferred to the cathode electrode 4 and consumed, electrons flow to an external circuit, thereby producing electrical energy using the same. Therefore, the chemical reaction that occurs in solid oxide fuel cell is the same as that of hydrogen and oxygen meet and become water.

In the figure, reference numeral 1 is an anode side end plate, and 8 is an anode side end plate.

On the other hand, a fuel cell composed of an electrolyte (3), a cathode electrode (4) and a cathode electrode (2) is called a unit cell, because the amount of electrical energy produced by one unit cell is very limited, so that the fuel cell can be used for power generation. To this end, it is inevitable to form a stack structure in which several unit cells are stacked. When connecting each unit cell constituting the stack structure, the separator 5 is provided to prevent the mixing of gases while electrically connecting the anode electrode 2 and the cathode electrode 4. Accordingly, the separator 5, the anode electrode 2, the electrolyte 3, and the cathode electrode 4, which are basic units repeatedly installed to form a stack, are referred to as SOFC components.

On the other hand, the separation plate 5 basically uses a Fe-Cr-Mn stainless steel sheet, and the gas flow path 6 toward the cathode and the gas flow path 7 toward the anode should be provided. However, since the separator 5 which meets the cathode electrode 4 meets high temperature air, not only the oxide is formed on the surface, but also the electrical conductivity is reduced, and the performance of the cell is reduced due to the evaporation of the chromium component. Therefore, there is a need to coat the surface of the separator plate 5 that meets the cathode electrode 4.

FIG. 2 is an enlarged explanatory view of a portion A of FIG. 1, illustrating a surface treated separator according to the present invention. FIG.

First, the periphery of the cathode side separation plate gas flow path 9 includes: an electrode contact portion 5a in direct contact with the cathode electrode 4, a channel side portion 5b not directly contacting the electrode, and a channel bottom portion 5c. Consists of However, the required functions of the portions 5a which directly meet the electrodes and the portions 5b and 5c which do not directly meet the electrodes differ greatly. That is, the contact surface that meets the cathode electrode 4 should have excellent electrical conductivity because the cell should be electrically connected to the cell, and the bottom and side surfaces of the separator gas flow path 9, which is not part of the electrode, are formed of chromium. Since the battery performance is reduced by evaporation, it should be a material to prevent evaporation of chromium components. First, when Fe-Cr alloy is used as a separator, a method for preventing evaporation of chromium components should use an alloy or a suitable material coated to prevent the formation of chromium-based oxide on the surface.

In order to solve this problem, in the present invention, the contact surface contacting the cathode electrode 4 in the metal separator plate for fuel cell is a contact surface coating layer coated with one of nickel (Ni), cobalt (Co), and copper (Cu) ( 11), aluminum coating layers 10a and 10b are coated on the bottom and side surfaces of the gas flow passage not in contact with the cathode electrode 4, and the upper layers are nickel (Ni), cobalt (Co), and copper ( Cu) is composed of a two-layer coating layer coated with one of the materials. In order to prevent volatilization of the chromium component, the formation of the chromium oxide formed on the surface should be fundamentally prevented. In addition, there must be a dense and uniform film to prevent the diffusion of chromium to the surface, which can play this role is alumina (Al ₂ O ₃ ). Therefore, the present invention was designed to coat aluminum on the bottom and side of the gas flow path. However, the alumina formed on the surface should not be formed on the surface in contact with the cathode electrode 4. Because alumina is insulated and has very high resistance, it does not have electrical connection. Therefore, the present invention selectively coats only the bottom and side surfaces of the gas flow path except for the electrode contact surface. The thickness of aluminum coated on the surface is sufficient to form a uniform and stable oxide film at the temperature at which the solid oxide fuel cell is operated. According to the experimental results, 5㎛ or more is enough in the air atmosphere at 800 ℃. However, in the coating process, a coating layer of nickel (Ni), cobalt (Co), copper (Cu), etc. is formed on the aluminum coating layer. However, this upper coating layer is not a problem. This is because not only Al ₂ O ₃ but also oxides such as NiAl ₂ O ₄ , CoAl ₂ O ₄ and CuAl ₂ O ₄ are formed on the surface through the high temperature oxidation process. That is, since formation of chromium oxide can be prevented, there is no problem. On the other hand, the cathode contact surface is preferably coated with a material such as nickel (Ni), cobalt (Co), copper (Cu). Because coating these materials, NiCr ₂ O ₄ and NiMn ₂ O ₄ with good electrical conductivity are formed on the surface of nickel (Ni), and CoCr ₂ O ₄ and CoMn ₂ O ₄ with excellent electrical conductivity in the case of cobalt (Co). Is formed, and in the case of Cu, CuCr ₂ O ₄ and CuMn ₂ O ₄ having excellent electrical conductivity are formed. These spinel oxides have higher electrical conductivity than Cr ₂ O ₃ or MnCr ₂ O ₄ when using existing Fe—Cr—Mn alloys.

Next, a coating process for manufacturing the metal separator 5 having such a configuration will be described. The present invention will be divided into two types according to the method of implementing gas flow paths in the Fe-Cr-Mn alloy disc, which is a flat metal separator substrate. Considering the case where a gas flow path is made by using an etching process, the separation plate manufacturing process is as follows. First, a gas flow path is formed through an etching process, and then aluminum is coated on the bottom and side surfaces of the flow path. In this case, in order to prevent the aluminum from being coated on the contact surface that meets the cathode electrode 4, a mask plate for preventing coating is used. Next, one of nickel (Ni), cobalt (Co), and copper (Cu) is coated on the contact surface of the metal separator to contact the cathode electrode 4. When coating the electrode contact surface, the coating is also performed on the bottom and side surfaces of the flow path at the same time during the coating process, which does not matter much in the function of the separator. That is, the bottom surface of the flow path is made of aluminum, and the upper layer is composed of a double coating layer coated with one of nickel (Ni), cobalt (Co), and copper (Cu).

Secondly, considering the case of making a gas flow path using a press process, the separation plate manufacturing process is as follows. First, aluminum is coated on the bottom and side portions of the gas passage. In this case, in order to prevent the aluminum from being coated on the contact surface that meets the cathode electrode 4, a mask plate for preventing coating is used. Next, the aluminum partially coated substrate is pressed to form a flow path of the separator. Finally, one of nickel (Ni), cobalt (Co) and copper (Cu) is coated. After this process, the electrode contact surface is coated with one of nickel (Ni), cobalt (Co), and copper (Cu), and the bottom and side surfaces of the flow path are made of aluminum, and the upper layer is nickel ( Ni), cobalt (Co), copper (Cu) is composed of a double coating layer coated with one of the materials.

As described above, the present invention has a Fe-Cr alloy, a ferritic stainless steel sheet, in the manufacture of a separator used in a plate-type solid oxide fuel cell, the connecting portion that meets the cathode electrode in order to form a good conductivity of the spinel oxide One of nickel (Ni), cobalt (Co), and copper (Cu) is coated, and the bottom and side surfaces of the gas flow path which are not in contact with the cathode electrode have a lower layer of aluminum (Al) to prevent volatilization of the chromium component. First, the coating is performed on one of nickel (Ni), cobalt (Co), and copper (Cu).

1 is a schematic view showing a stack state of a general planar solid oxide fuel cell

FIG. 2 is an enlarged explanatory view of a portion A of FIG. 1 and is a cross-sectional view showing a part of the surface-treated separator plate according to the present invention. FIG.

※ Explanation of code for main part of drawing

1: End plate (fuel electrode side) 2: Fuel electrode electrode 3: Electrolyte

4: cathode electrode 5: separator

5a: electrode contact portion 5b: flow passage side portion 5c: flow passage bottom portion

6: cathode gas flow path 7. anode gas flow path

8: End plate (air pole side) 9: Separation plate gas flow path (air pole side)

10a: aluminum coating layer (bottom) 10b: aluminum coating layer (side)

11: electrode contact surface coating layer

Claims (2)

In manufacturing a metal separator for a flat solid oxide fuel cell, The contact surface that meets the cathode electrode of the separator plate is coated with a highly conductive material, The bottom surface and the side surface of the flow path that is a portion that does not contact the cathode electrode, the method for manufacturing a separator for a flat plate type solid oxide fuel cell, characterized in that the coating on the surface to prevent the diffusion of chromium components. In manufacturing a metal separator for a flat solid oxide fuel cell, The connecting portion that meets the cathode electrode of the separator plate based on the Fe-Cr-Mn alloy substrate is coated with one of nickel (Ni), cobalt (Co), and copper (Cu), The bottom and side surfaces of the gas flow passage not contacting the cathode electrode are first coated with aluminum (Al) on the lower layer, and one of nickel (Ni), cobalt (Co), and copper (Cu) is coated on the upper layer. A method of manufacturing a separator for a plate-type solid oxide fuel cell.

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