KR101054000B1 - Separator for solid oxide fuel cell and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a separator for a solid oxide fuel cell and a method of manufacturing the same. The method for producing a separator for a solid oxide fuel cell includes (i) forming a channel on at least one surface of a substrate made of ferritic stainless steel, and ii) a mixture of (Mn, Co) ₃ O ₄ and a perovskite phase oxide. It is applied to any one side of the substrate and dried to form a protective coating layer, iii) reducing heat treatment of the protective coating layer in a reducing atmosphere, and iii) disposing a foamed metal current collector on the outer surface of the protective coating layer .

The separator for a solid oxide fuel cell according to the present invention forms a protective coating layer having excellent high temperature conductivity, and minimizes the contact resistance between the separator and the cathode through the arrangement of the foamed metal current collector, thereby improving the current collecting function.

Solid oxide, fuel cell, separator, coating layer, reduction heat treatment, foam metal, current collector

Description

Separator for solid oxide fuel cell and manufacturing method thereof {SEPARATOR FOR SOLID OXIDE FUEL CELL AND MANUFACTURING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell (SOFC), and more particularly, to a separator for a solid oxide fuel cell having improved current collector function and a method of manufacturing the same.

The solid oxide fuel cell has a structure in which a plurality of electricity generating units including a unit cell and a separator are stacked.

The unit cell includes an electrolyte membrane, an air electrode located on one side of the electrolyte membrane, and a fuel electrode located on the other side of the electrolyte membrane. When oxygen is supplied to the cathode and hydrogen is supplied to the anode, oxygen ions generated by the reduction reaction of oxygen at the cathode move through the electrolyte membrane to the anode and react with hydrogen supplied to the anode to generate water. In this case, electrons flow from the anode to the external circuit in the process of being consumed by the cathode, thereby producing electrical energy.

Separator plates are disposed on both sides of the unit cell to physically separate neighboring unit cells and form a channel for supplying hydrogen or oxygen to one surface facing the unit cell. The separator is also made of a conductive material to connect the cathode of one unit cell and the anode of a neighboring unit cell in series.

Recently, as the operating temperature of a solid oxide fuel cell is lowered to 800 ° C. or less, the material of the separator is changing from a conventional ceramic material to a metal material having excellent processability and low manufacturing cost.

However, since the metal separator and the cathode are exposed to a high temperature oxidizing atmosphere in the operating environment of the solid oxide fuel cell, an oxide is formed on the surface of the separator to reduce the conductivity of the separator. In addition, since the contact resistance between the metal separator and the cathode increases due to the oxide formation, the conductive properties of the metal separator and the cathode are reduced. As a result, the current collecting function of the separator is weakened and the efficiency of the solid oxide fuel cell is lowered.

An object of the present invention is to provide a separator for a solid oxide fuel cell and a method of manufacturing the same, which improves current collecting function by increasing conductivity and minimizing contact resistance with an air electrode.

The separator for a solid oxide fuel cell according to an embodiment of the present invention includes: (i) a channel formed on at least one surface, a substrate made of ferritic stainless steel, and ii) formed on one surface of the substrate, and (Mn, Co A protective coating layer comprising a mixture of ₃ ) O ₄ and a perovskite phase oxide, and iii) a foamed metal current collector disposed on an outer surface of the protective coating layer.

The perovskite phase oxide may be included in an amount of 0.01 wt% to 10 wt% based on (Mn, Co) ₃ O ₄ . The perovskite oxide may include any one selected from the group consisting of La-Sr-Mn oxide (LSM), La-Sr-Co oxide (LSC), and La-Sr-Co-Fe oxide (LSCF). .

The protective coating layer may have a thickness of 10 μm to 100 μm. The foam metal current collector may be an open foam metal body including Cu or a Cu alloy.

The protective coating layer is oxidized in the operating environment of the solid oxide fuel cell, and a portion of the sponge structure of the foamed metal current collector may be superimposed on the protective coating layer.

Method for producing a separator for a solid oxide fuel cell according to an embodiment of the present invention, i) forming a channel on at least one side of the substrate made of ferritic stainless steel, ii) (Mn, Co) ₃ O ₄ And applying a mixture of perovskite oxides to one side of the substrate and drying to form a protective coating layer, iii) reducing heat treatment of the protective coating layer in a reducing atmosphere, and iii) foam metal collection on the outer surface of the protective coating layer. Arranging the whole.

In the step of forming the protective coating layer, the mixture may include 0.01 wt% to 10 wt% of the perovskite phase oxide relative to (Mn, Co) ₃ O ₄ . The perovskite oxide may include any one selected from the group consisting of La-Sr-Mn oxide (LSM), La-Sr-Co oxide (LSC), and La-Sr-Co-Fe oxide (LSCF). .

Reduction heat treatment may be performed for 3 hours to 24 hours in a reducing atmosphere of 700 ℃ to 900 ℃. The foam metal current collector may be an open foam metal body including Cu or a Cu alloy.

In the method for manufacturing a separator for a solid oxide fuel cell, after disposing a foamed metal current collector, oxidizing a protective coating layer in an operating environment of the solid oxide fuel cell, and superposing a portion of the sponge structure of the foamed metal current collector on the protective coating layer. It may further include.

The separator for a solid oxide fuel cell according to the present invention forms a protective coating layer having excellent high temperature conductivity, and minimizes contact resistance with an air electrode by arranging a foamed metal current collector. Therefore, the current collecting function of the separator may be improved to maximize the electricity generation efficiency of the solid oxide fuel cell.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

1 is a process flowchart illustrating a manufacturing process of a separator for a solid oxide fuel cell (hereinafter, referred to as SOFC) according to an embodiment of the present invention.

Referring to FIG. 1, the method for manufacturing a separator for SOFC may include a first step S100 of forming a channel on at least one surface of the substrate, a second step S200 of forming a protective coating layer on one surface of the substrate, A third step (S300) for reducing heat treatment of the protective coating layer in a reducing atmosphere, and a fourth step (S400) for disposing a foamed metal current collector on the outer surface of the protective coating layer.

In addition, the method for manufacturing a separator for SOFC may further include a fifth step S500 of oxidizing the protective coating layer in the operating environment of the SOFC to superimpose a part of the sponge structure of the foamed metal current collector on the protective coating layer.

FIG. 2 is a partial cross-sectional view showing the substrate of the first step shown in FIG. 1.

Referring to FIG. 2, the substrate 10 is made of ferritic stainless steel. Substrate 10 forms channel 12 on one side that will face the cathode and one side that will face the anode when applied as a separator in SOFC. The channel 12 on the surface facing the cathode serves to supply oxygen to the cathode, and the channel 12 on the surface facing the anode serves to supply hydrogen to the anode.

In SOFC, the separator plate positioned between two adjacent unit cells forms the channel 12 on both sides, and the outermost separator plate forms the channel 12 only on the inner side. In FIG. 2, the substrate 10 having the channel 12 formed on one surface to face the cathode is illustrated.

3 is a partial cross-sectional view showing the substrate and the protective coating layer of the second step shown in FIG.

Referring to FIG. 3, the protective coating layer 14 is formed on one surface of the substrate 10 to face the cathode. The protective coating layer 14 comprises a mixture of (Mn, Co) ₃ O ₄ and Perovskite phase oxides. (Mn, Co) ₃ O ₄ is a spinel phase oxide having excellent conductivity, and exhibits conductivity of up to 60 S / cm at about 800 ° C., which is an operating temperature of a fuel cell. The protective coating layer 14 improves the current collecting performance of the separator by increasing the conductivity of the substrate 10 by the (Mn, Co) ₃ O ₄ component.

The perovskite phase oxide includes any one selected from the group consisting of La-Sr-Mn oxide (LSM), La-Sr-Co oxide (LSC), and La-Sr-Co-Fe oxide (LSCF). The rare earth metal contained in the perovskite phase oxide increases the oxidation resistance of the ferritic stainless steel to improve high temperature conductivity. Therefore, the protective coating layer 14 can increase the oxidation resistance of the substrate 10 by the perovskite oxide component. The perovskite phase oxide also serves to dense the structure of the protective coating layer 14.

The perovskite phase oxide may be included in an amount of 0.01 wt% to 10 wt% based on (Mn, Co) ₃ O ₄ . When the content of the perovskite phase oxide is less than 0.01% by weight, it is not possible to obtain an increase in oxidation resistance, and when the content of the perovskite phase oxide is more than 10%, it is not preferable because only the material consumption increases without improving the performance.

The effect of increasing the oxidation resistance by the rare earth metal can also be realized by adding a rare earth metal to the ferritic stainless steel itself. In this case, however, a vacuum atmosphere is required, which makes the manufacturing process difficult and increases the manufacturing cost. In this embodiment, as the protective coating layer 14 including the rare earth metal is formed on one surface of the substrate 10, the manufacturing process of the separator may be simplified while obtaining an effect of increasing oxidation resistance by adding the rare earth metal.

The protective coating layer 14 may be formed by preparing a paste in which (Mn, Co) ₃ O ₄ and a perovskite phase oxide are mixed, and drying the paste after screen printing on one surface of the substrate 10. On the other hand, the protective coating layer 14 is prepared by preparing a solution in which (Mn, Co) ₃ O ₄ and a perovskite phase oxide are mixed, and drying the solution after spray coating on one surface of the substrate 10. can do. Drying can be performed at normal temperature or below 200 degreeC.

The protective coating layer 14 may have a thickness of 10 μm to 100 μm. When the thickness of the protective coating layer 14 is less than 10 μm, the characteristics of the protective coating layer 14 may be quickly lost due to the reaction with the substrate 10 or the penetration of external oxygen during prolonged exposure. If the thickness of the protective coating layer 14 exceeds 100㎛ the area resistivity increases, the conductivity is lowered and the manufacturing cost is increased.

In a third step (S300), the protective coating layer 14 is reduced heat treatment in a reducing atmosphere. The phase of the protective coating layer 14 temporarily changes to Mn oxide and Co by reduction heat treatment. At this time, the perovskite phase oxide contained in a small amount in the protective coating layer 14 does not change. The reduction heat treatment is performed at 1000 ° C. or less to prevent deformation and transformation at high temperature, and may be performed for 3 hours to 24 hours in a reducing atmosphere of 700 ° C. to 900 ° C. The higher the heat treatment temperature, the shorter the run time.

4 is an electron micrograph of a foamed metal current collector.

Referring to FIG. 4, the metal foam current collector is an open cell type metal foam, and is made of a sponge structure having numerous bubbles therein. Such a foamed metal current collector has an advantage of easily passing gas, and can be easily absorbed by a small external force, thereby easily absorbing mechanical tolerances of various components in manufacturing SOFCs.

The foam metal current collector may be formed of Cu foam metal or Cu alloy foam metal. Cu is susceptible to formation of oxides such as Cu ₂ O on the surface in high temperature oxidizing atmospheres, with Cu ₂ O oxides exhibiting a conductivity of about 1 to 2 S / cm at about 800 ° C., the operating temperature of the SOFC. This is a very high value compared to the conductivity of Cr ₂ O ₃ .

FIG. 5 is a partial cross-sectional view illustrating the substrate, the protective coating layer, and the foamed metal current collector in the fourth step shown in FIG. 1.

Referring to FIG. 5, the foamed metal current collector 16 is disposed on the protective coating layer 14. The foamed metal current collector 16 is located between the protective coating layer 14 and the cathode, and serves to minimize the contact resistance between the separator and the cathode by enlarging the contact area therewith. In addition, since the foamed metal current collector 16 is easily deformed, it serves to absorb mechanical tolerances of the SOFC as described above.

The foamed metal current collector 16 including Cu or Cu alloy has a high conductivity spinel phase (Cu, Mn) ₃ O ₄ or (Cn) by reacting with (Mn, Co) ₃ O ₄ included in the protective coating layer 14 or ( A reaction layer such as Cu, Co, Mn) ₃ O ₄ can be formed.

The separator plate 20 for SOFC is manufactured through the first to fourth steps described above, and the separator plate 20 is alternately stacked with a unit cell to form an SOFC.

6 is a partial cross-sectional view showing a substrate, a protective coating layer and a foamed metal current collector in a fifth step shown in FIG.

Referring to FIG. 6, the protective coating layer 14 is oxidized in the operating environment of the SOFC, and a portion of the sponge structure of the foamed metal current collector 16 is buried in the protective coating layer 14. That is, part of the sponge structure of the foamed metal current collector 16 overlaps the protective coating layer 14.

The operation operation of the SOFC is performed at 900 ° C. or lower, usually 700 ° C. to 900 ° C., and oxygen is introduced into the cathode through the channel 12 of the separator 20, and hydrogen is supplied to the anode. During operation of the SOFC, the protective heat-treated protective coating layer of the separator 20 is restored to the (Mn, Co) ₃ O ₄ structure again through an oxidation process. At this time, a part of the sponge structure of the foamed metal current collector 16 facing the protective coating layer 14 is naturally buried into the protective coating layer 14.

Therefore, in the fifth step S500, the contact area between the protective coating layer 14 and the foamed metal current collector 16 may be increased to improve a current collecting function of the separator 20.

7 is a schematic perspective view of an SOFC according to an embodiment of the present invention.

Referring to FIG. 7, the SOFC 100 includes a plurality of electricity generating units, and each electricity generating unit includes a unit cell 30 and a separator plate 20. The unit cell 30 includes an electrolyte membrane 32, an air electrode 34 positioned on one surface of the electrolyte membrane 32, and a fuel electrode 36 positioned on the other surface of the electrolyte membrane 32. The separator 20 is positioned between the unit cells 30 to physically separate the unit cells 30. The separation plate 20 forms a channel 12 on one surface facing the cathode 34 and one surface facing the fuel electrode 36.

The separator 20 forms the above-described protective coating layer 14 (see FIG. 6) on one surface of the substrate 10 facing the cathode 34, and the foamed metal current collector between the protective coating layer 14 and the cathode 34. Place (16). The protective coating layer 14 is oxidized in the operating environment of the SOFC 100, and a part of the sponge structure of the foamed metal current collector 16 is buried into the protective coating layer 14 to protect the protective coating layer 14 and the foamed metal current collector ( 16) the contact area is enlarged.

The SOFC 100 forms a protective coating layer 14 having excellent high temperature conductivity on the separator 20, and minimizes contact resistance between the separator 20 and the cathode 34 by arranging the foamed metal current collector 16. As a result, the current collecting function of the separator 20 can be improved. As a result, the electricity generation efficiency of the SOFC 100 may be maximized.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

1 is a process flowchart illustrating a manufacturing process of a separator plate for a solid oxide fuel cell according to an exemplary embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing the substrate of the first step shown in FIG. 1.

3 is a partial cross-sectional view showing the substrate and the protective coating layer of the second step shown in FIG.

4 is an electron micrograph of a foamed metal current collector.

FIG. 5 is a partial cross-sectional view of the substrate, the protective coating layer, and the foamed metal current collector in the fourth step shown in FIG. 1.

6 is a partial cross-sectional view showing a substrate, a protective coating layer and a foamed metal current collector in a fifth step shown in FIG.

7 is a schematic perspective view of a solid oxide fuel cell according to an embodiment of the present invention.

Claims (12)

A substrate formed of at least one surface and made of ferritic stainless steel; A protective coating layer formed on one surface of the substrate and including a mixture of (Mn, Co) ₃ O ₄ and a perovskite phase oxide; And Including a foamed metal current collector in close contact with the outer surface of the protective coating layer and formed of an open cell foamed metal body, The foamed metal current collector includes Cu or a Cu alloy, and forms a reaction layer including any one of (Cu, Mn) ₃ O ₄ and (Cu, Co, Mn) ₃ O _{4 on} one surface in contact with the protective coating layer. Separation plate for a solid oxide fuel cell. The method of claim 1, The perovskite phase oxide is a solid oxide fuel cell separator comprising 0.01 to 10% by weight based on the (Mn, Co) ₃ O ₄ . The method of claim 2, The perovskite oxide is a solid comprising any one selected from the group consisting of La-Sr-Mn oxide (LSM), La-Sr-Co oxide (LSC), and La-Sr-Co-Fe oxide (LSCF). Separators for oxide fuel cells. The method of claim 1, The protective coating layer is a solid oxide fuel cell separator having a thickness of 10㎛ to 100㎛. delete The method of claim 1, The protective coating layer is oxidized in an operating environment of the solid oxide fuel cell, and a portion of the sponge structure of the foamed metal current collector overlaps the protective coating layer. Forming a channel on at least one side of the substrate made of ferritic stainless steel; Applying a mixture of (Mn, Co) ₃ O ₄ and a perovskite phase oxide to either side of the substrate and drying to form a protective coating layer; Reducing heat treating the protective coating layer in a reducing atmosphere; Disposing a foamed metal current collector including Cu or a Cu alloy on the outer surface of the protective coating layer and formed of an open cell foamed metal; The foamed metal current collector is a separator for a solid oxide fuel cell, which forms a reaction layer including any one of (Cu, Mn) ₃ O ₄ and (Cu, Co, Mn) ₃ O _{4 on} one surface of the foamed current collector. Manufacturing method. The method of claim 7, wherein In the forming of the protective coating layer, the mixture comprises 0.01% by weight to 10% by weight of the perovskite phase oxide with respect to the (Mn, Co) ₃ O ₄ Method for producing a separator for a solid oxide fuel cell. The method of claim 8, The perovskite oxide is a solid comprising any one selected from the group consisting of La-Sr-Mn oxide (LSM), La-Sr-Co oxide (LSC), and La-Sr-Co-Fe oxide (LSCF). Method for producing a separator plate for an oxide fuel cell. The method of claim 7, wherein The reduction heat treatment is a method for producing a separator for a solid oxide fuel cell that is performed for 3 to 24 hours in a reducing atmosphere of 700 ℃ to 900 ℃. delete The method of claim 7, wherein After placing the foamed metal current collector, Oxidizing the protective coating layer in an operating environment of the solid oxide fuel cell, and superposing a portion of the sponge structure of the foamed metal current collector on the protective coating layer.

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