KR20070092013A - Bipolar plate and stack for the fuel cell system having the same - Google Patents

Abstract

A bipolar plate is provided to prevent fluid flow channels from being clogged by a gas diffusion layer during the assembling step of a stack by forming gas diffusion layers on the surfaces of the bipolar plate. A bipolar plate(10) comprises: a main body(12) in which fluid flow channels(12a) are processed on the surface thereof; and a gas diffusion layer(14) which comes in contact with the surface of the main body. A stack for a fuel cell system includes: an electrode-membrane assembly in which a catalyst layer is formed on the surface of an electrolyte membrane; and the bipolar plate in which fluid flow channels(12a) are formed on the surface of the main body facing the electrode-membrane assembly. The gas diffusion layer facing the catalytic layer is provided on the surface of the main body of the bipolar plate.

Description

Bipolar plate and stack for fuel cell system having same {BIPOLAR PLATE AND STACK FOR THE FUEL CELL SYSTEM HAVING THE SAME}

1 is a cross-sectional view of a bipolar plate according to the present invention;

2 is a schematic view of a stack for a fuel cell system having the bipolar plate of FIG. 1;

3 shows a three-layer structure of an electrode membrane assembly constituting a stack for a fuel cell system;

4 shows a four-layer structure of the electrode film assembly;

5 shows a five-layer structure of the electrode film assembly;

6 shows an embodiment of a fuel cell according to a conventional example;

7 is a sectional view of a fuel cell unit according to another conventional example;

8 is a sectional view of an assembly composed of a positive electrode plate and a MEA according to another conventional example;

9 is a view showing a gas diffusion channel for a bipolar plate according to another conventional example.

<Description of Symbols for Major Parts of Drawings>

10 bipolar plate

12: main body

14 gas diffusion layer

10, 120, 220, 320: electrode film assembly

100: stack

110: electricity generating unit

[Patent Document 1] Japanese Unexamined Patent Publication No. 10-12246

[Patent Document 2] Japanese Unexamined Patent Publication No. 2003-257469

[Patent Document 3] Republic of Korea Patent Publication No. 2001-71877

[Patent Document 4] US Patent Publication No. 6,649,297

The present invention relates to a stack for a fuel cell system having a bipolar plate having a gas diffusion layer provided on the surface thereof, and preferably a surface for preventing the channel formed in the bipolar plate from being clogged by the fastening pressure when the stack is fastened. The present invention relates to a stack for a fuel cell system having a bipolar plate provided with a gas diffusion layer.

In general, a fuel cell system is a power generation device that converts electricity into electrical energy by a chemical reaction between hydrogen and oxygen, and is being researched and developed as an alternative to solve the difficulty of securing power due to the increase in power demand and the increasing global environmental problems. . Such a fuel cell system basically has a stack in which a plurality of unit cells for generating electricity are stacked.

The stack has a structure in which a plurality of unit cells stacked between end plates are fastened by bolts and nuts. The unit cell includes an MEA having anode and cathode electrodes provided on both sides of an electrolyte membrane, and a separator, that is, a bipolar plate, each having a channel for fluid flow disposed on both sides of the MEA and processed on a surface thereof.

The bipolar plate supplies the reactants such as hydrogen-containing fuel and oxygen to the anode electrode and the cathode electrode, respectively, and discharges products such as carbon dioxide and water generated at the anode electrode and the cathode electrode, respectively. The anode electrode and the cathode electrode have a catalyst layer and a gas diffusion layer (GDL) that are sequentially stacked on the electrolyte membrane.

In the state where the gas diffusion layer faces the surface of the bipolar plate on which the fluid flow channel is formed, the bolt and the nut are fastened to assemble the stack.

However, when the gas diffusion layer blocks the fluid flow channel of the bipolar plate in this fastening process, the supply of reactants such as hydrogen fuel and oxygen and the discharge of products such as carbon dioxide and water are hindered. As a result, the power generation efficiency of the fuel cell system is lowered.

Japanese Patent Laid-Open No. 10-12246 (Patent Document 1) discloses a gas separation having a solid polymer electrolyte membrane, a membrane electrode composite serving as a gas diffusion electrode sandwiching it, and a plurality of convex groups forming gas separation portions on both surfaces of the base plate. A bipolar plate which also serves as a plate and a current collector is disclosed, and the plurality of convex groups are formed by injection molding of a thermoplastic resin which is a polymer having excellent fluidity (see FIG. 6).

Japanese Patent Laid-Open No. 2003-257469 (Patent Document 2) discloses a unit cell including an electrode membrane assembly, a reaction layer, a gas supply layer, a conductive bipolar plate, and a gasket. (See FIG. 7).

Korean Laid-Open Patent Publication No. 2001-71877 (Patent Document 3) discloses an assembly composed of a positive electrode plate and a MEA positioned with a sealing bead higher than the gas diffusion layer so that the gaps between the seal and the gas diffusion layers are avoided. )

U.S. Patent No. 6,649,297 (Patent Document 4) discloses a bipolar plate having a convex quadrilateral structure in the form of a channel (see Fig. 9).

However, in the above-mentioned patent documents, a structure for fundamentally preventing the phenomenon in which the channel formed in the bipolar plate is blocked by the gas diffusion layer in the assembly process of the stack is not disclosed.

The present invention has been proposed to solve the conventional problems as described above, in order to prevent the fluid flow channel of the bipolar plate is blocked by the gas diffusion layer constituting the anode electrode or the cathode electrode in the stack assembly process. It is an object of the present invention to provide a bipolar plate having a gas diffusion layer on its surface and a stack for a fuel cell system having the same.

In order to achieve the above object, according to the present invention, the bipolar plate is characterized in that the fluid flow channel is processed on the surface, the gas diffusion layer is provided on the surface.

Pores having a size of 100 nm to 10 μm are formed in the gas diffusion layer, and the gas diffusion layer has a thickness of 50 to 200 μm. The gas diffusion layer is made of a carbon material.

In addition, the stack for a fuel cell system according to the present invention comprises an electrode membrane assembly having a catalyst layer formed on the surface of an electrolyte membrane, and a bipolar plate having a fluid flow channel formed on a surface facing the electrode membrane assembly. The surface of the plate is characterized in that the gas diffusion layer is provided.

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

1 is a cross-sectional view of a bipolar plate according to the present invention, FIG. 2 is a schematic diagram of a stack for a fuel cell system having the bipolar plate of FIG. 1, and FIG. 3 is a three-layer structure of an electrode membrane assembly constituting the stack for a fuel cell system. 4 shows a four-layer structure of the electrode film assembly, and FIG. 5 shows a five-layer structure of the electrode film assembly.

Referring to FIG. 1, a bipolar plate 10 according to the present invention includes a main body 12 having a fluid flow channel 12a formed on a surface thereof, and a gas diffusion layer 14 provided on a surface of the main body 12. Have The gas diffusion layer 14 is made of the same or similar material as that of the body 12.

The manufacturing process of the main body 12 is as follows. That is, the main body 12 is manufactured by mixing and molding an electrically conductive powder, for example, carbon powder and a polymer resin, preparing the carbon block, and pressing the carbon block to form a channel for fluid flow on the surface thereof. This body 12 is referred to as a composite bipolar plate. However, the material of the main body 12 is not limited thereto, and may be made of metal or graphite.

The manufacturing process of the gas diffusion layer 14 is as follows. First, similarly to the manufacturing process of the main body 12, an electrically conductive powder, for example, carbon powder and a polymer resin is mixed and molded to prepare a carbon block. The gas diffusion layer 14 is produced by cutting such a carbon block into a thickness of about 50 to 200 mu m. At this time, in the gas diffusion layer 14, the pores have a size of about 100nm ~ 10㎛. This is to facilitate the supply of the reactants to be supplied to the anode electrode and the cathode electrode of the electrode membrane assembly and the discharge of the product generated therefrom as described below.

The bipolar plate 10 according to the present invention is manufactured by bonding the gas diffusion layer 14 and the main body 12 produced through the above-described process. In this case, since the gas diffusion layer 14 and the main body 12 use similar or identical polymer resins, the polymer resin is integrated in the bonding process so that the gas diffusion layer 14 is bonded to the surface of the main body 12. As a result, the fluid flow channel formed in the main body 12 is maintained in a good state without clogging caused by the gas diffusion layer 14.

Referring to FIG. 2, the stack 100 for a fuel cell system includes an electricity generator 110 generating electricity through a chemical reaction between hydrogen and oxygen, and a pair of end plates provided on both sides of the electricity generator 110. Has 102.

The end plate 102 provided on one side of the stack 100 includes, but is not limited to, a fuel inlet through which hydrogen-containing fuel flows, and DC electricity generated by the electricity generator 110 inside the stack 100 to the outside. An output terminal for supplying power is provided. The end plate 102 provided on the other side of the stack 100 is provided with an air inlet through which air is introduced and a discharge part for discharging carbon dioxide (CO ₂ ) and water (H ₂ O) to the outside, respectively.

The electricity generating unit 110 of the stack 100 includes a polymer film 22 and an electrode membrane assembly 20 (MEA; Membrane Electrode Assembly) composed of electrodes 24 provided on both sides of the polymer film 22.

The polymer membrane 22 has a function of preventing ion permeation of hydrogen-containing fuel together with the function of ion exchange to transfer hydrogen ions generated in the catalyst layer of the anode electrode 24 to the catalyst layer of the cathode electrode 24 as described below. A conductive polymer electrolyte membrane having a thickness of about 50 ~ 200㎛. As the polymer membrane 22, for example, a resin solution such as perfluorinated sulfonic acid is coated on a perfluorofluorofluoride resin film made of perfluoro uroselfonate resin (Nafion) or a porous polytetrafluoroethylene thin film support. And membranes in which cation exchange resins and inorganic silicates are coated on porous membranes and porous non-conductive polymer supports.

The electrode 24 of the electrode membrane assembly 20 is manufactured by applying a catalyst material on the polymer membrane 22, and the electrode 24 oxidizes hydrogen gas contained in the hydrogen-containing fuel to oxidize hydrogen ions (H ⁺ ) and electrons. (e ^-) to the produced water such chemical reaction results as such the anode electrode of the carbon dioxide produced as a by-product discharged to the outside of the oxidation process and the chemical reaction of oxygen and hydrogen ions are conducted while generating a cathode electrode for discharging to the outside Are distinguished.

As shown in FIGS. 3 to 5, the electrode membrane assembly may be classified into a three-layer structure, a four-layer structure, and a five-layer structure according to the stacked structure. First, referring to FIG. 3, the electrode membrane assembly 120 may have a three-layer structure including a polymer membrane 122 and a catalyst layer 124 formed on both sides of the polymer membrane 122. Referring to FIG. 4, the electrode membrane assembly 220 includes a polymer membrane 222, a catalyst layer 224 formed on both sides of the polymer membrane 222, and a carbon layer 226 formed on at least one catalyst layer 224. It consists of a four-layer structure. In addition, referring to FIG. 5, the electrode membrane assembly 320 includes a polymer layer 322, a catalyst layer 324 formed on both sides of the polymer membrane 322, and a carbon layer 326 formed on the catalyst layer 224. It consists of a layer structure.

At this time, in the electrode film assembly having a four-layer structure and a five-layer structure, the carbon layers 226 and 326 are provided with fine pores, for example, pores having a size of less than 100 nm.

In addition, the stack 100 is disposed to face each other between adjacent electrode film assemblies 20 to supply hydrogen and oxygen to the anode electrode 24 and the cathode electrode 24 of the electrode film assembly 20, respectively. Bipolar plate 10. In this case, the stack 100 is provided with a plurality of unit cells including the electrode film assembly 20 and the bipolar plates 10 positioned at both sides thereof to form the electricity generating unit 110.

As described above, the bipolar plate 10 interposed between the adjacent electrode membrane assemblies 20 includes a main body 12 in which a fluid flow channel 12a is formed, and a gas diffusion layer provided on the surface of the main body 12. 12) The fluid flow channel may be divided into a fuel supply channel for supplying hydrogen-containing fuel to the anode electrode 24 and an oxygen supply channel for supplying oxygen to the cathode electrode 24 in the stack 100.

Thereafter, the stack 100 is assembled by firmly fastening the electricity generating unit 110 between the end plates 102 through the fastening operation of the bolt and nut (not shown). At this time, as described above, the fluid flow channel 12a formed in the main body 12 of the bipolar plate 10 is provided in a good state without the blockage caused by the gas diffusion layer 14, and thus the assembled stack 100 In the fuel supply passage and the oxygen supply passage, the fluid flow is maintained in a good state.

According to the embodiment of the present invention, the fluid flow channel 12a formed in the bipolar plate body 12 is hydrophobicized or hydrophilic treated according to the type of the electrode facing. For example, one channel, i.e., the fuel supply passage facing the anode electrode 24, is hydrophobic so that hydrogen-containing fuel easily moves to the catalyst layer 24 of the anode electrode 24, thereby producing a by-product at the anode electrode 24. The carbon dioxide generated by is easily discharged through the fuel supply passage. On the other hand, by hydrophilic treatment of the other channel, that is, the oxygen supply passage facing the cathode electrode 24, the water generated as a by-product from the cathode electrode 24 is a channel for fluid flow of the body 12a from the cathode electrode 24 It is discharged to the outside while easily moving to 12a.

Hereinafter, the operation of the fuel cell system according to the present invention will be described.

Hydrogen-containing fuel supplied from a fuel supply unit (not shown) is supplied through the fuel supply passage of the bipolar plate 10 and the gas diffusion layer 14 in the stack 100 to the anode of the electric generator 110, in particular the electrode membrane assembly 20. It is easily supplied to the electrode 24. Oxygen supplied from an oxygen supply unit (not shown) passes through the oxygen supply passage of the bipolar plate 10 and the gas diffusion layer 14 in the stack 100, and thus the cathode electrode of the electrode generator assembly 20, in particular, the electrode membrane assembly 20. 24).

Hydrogen ions and carbon dioxide are produced by the hydrogen oxidation reaction at the anode electrode 24, wherein the hydrogen ions move to the cathode electrode 24 through the polymer membrane 22 and the carbon dioxide is a gas diffusion layer 14 of the bipolar plate 10. And discharged to the outside through the fuel supply passage. Water generated by the oxygen reduction reaction at the cathode electrode 24 is easily moved from the cathode electrode 24 to the bipolar plate 10 side and then discharged to the outside through the gas diffusion layer 14 and the hydrogen supply passage. On the other hand, electricity is generated by electrons generated at the anode electrode 24 moving to the cathode electrode 24. At this time, the electricity generated from the individual unit cells of the electricity generating unit 110 is fed to the external load through the output terminal provided to the end plate 102 via the bipolar plate 10 which is connected to each other so that the electricity can be connected to each other. .

According to the present invention, by forming a gas diffusion layer on the surface of the bipolar plate it is possible to prevent the fluid flow channel formed in the bipolar plate is blocked by the gas diffusion layer during assembly of the stack to improve the power generation efficiency of the fuel cell system.

Claims (14)

The main body with a fluid flow channel on its surface, A bipolar plate comprising a gas diffusion layer in contact with the surface of the main body. The method of claim 1, The gas diffusion layer is a bipolar plate, characterized in that the pores of 100nm ~ 10㎛ size is formed. The method of claim 1, The gas diffusion layer is a bipolar plate, characterized in that having a thickness of 50 ~ 200㎛. The method of claim 1, The gas diffusion layer is a bipolar plate, characterized in that made of a carbon material. The method of claim 1, The gas diffusion layer is a bipolar plate, characterized in that made of the same material as the main body. An electrode membrane assembly having a catalyst layer formed on the surface of the electrolyte membrane; It consists of a bipolar plate having a body in which a fluid flow channel is processed on the surface facing the electrode membrane assembly, The gas diffusion layer facing the catalyst layer is provided on the surface of the body of the bipolar plate, the fuel cell system stack. The method of claim 6, The gas diffusion layer is a stack for a fuel cell system, characterized in that the pores of 100nm ~ 10㎛ size is formed. The method of claim 6, The gas diffusion layer is a stack for a fuel cell system, characterized in that having a thickness of 50 ~ 200㎛. The method of claim 6, The gas diffusion layer is a stack for a fuel cell system, characterized in that made of a carbon material. The method of claim 6, The gas diffusion layer is a stack for a fuel cell system, characterized in that made of the same material as the main body. The method of claim 7, wherein And a carbon layer interposed between the at least one catalyst layer and the gas diffusion layer. The method of claim 7, wherein And a carbon layer interposed between the catalyst layer and the gas diffusion layer. The method according to claim 11 or 12, wherein The carbon layer is a stack for a fuel cell system, characterized in that the fine size pores are formed. The method of claim 14, The pores formed in the gas diffusion layer is larger than the pores formed in the carbon layer.

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