KR100786367B1 - Gasket composition for fuel cell stack - Google Patents

Abstract

A gasket composition for a fuel cell is provided to prevent hydrolysis, to reduce the ion elution of metal oxide for preventing the catalytic poisoning of a membrane electrode assembly, to increase the lifetime of a fuel cell and to improve the compression set at a low temperature for enhancing the sealing property at a low temperature. A gasket composition for a fuel cell comprises 100 parts by weight of a polymer which comprises a vinylidene fluoride monomer, a tetrafluoroethylene monomer, and a perfluoromethyl vinyl ether monomer; 0-4 parts by weight of a pigment which comprises carbon black. Preferably the gasket composition comprises a cure site monomer. Preferably the composition comprises further 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (DBPH) as a peroxide curing agent, and triallyl isocyanurate (TAIC) as a crosslinking accelerator.

Description

Gasket composition for fuel cell stack

1 is a cross-sectional view showing an example of a fuel cell stack to which the gasket composition of the present invention is applied.

<Explanation of symbols for the main parts of the drawings>

10. Membrane-electrode assembly 11. Fuel electrode

12. Air electrode 13. Polymer electrolyte membrane

20. Separator 24. Gasket

The present invention relates to a gasket composition for a fuel cell stack, and more particularly, to prevent leakage of fuel gas and oxidant gas supplied to the electrode from the fuel cell stack to the outside or mixing of two kinds of gases. It relates to a gasket composition for fuel cell stack that is fitted around the fixed.

Unlike conventional internal combustion engine cars, which are driven by exploding fossil fuel and oxygen in the air in the engine, converting the chemical energy of the fossil fuel into mechanical energy, the fuel cell vehicle is a fuel cell that serves as an engine of the conventional internal combustion engine. The vehicle is driven by converting the electrical energy generated by supplying hydrogen and oxygen to the stack into mechanical energy.

A fuel cell stack using an electrolyte membrane, which is an example of the fuel cell, has a structure in which hundreds or more of alternating unit cells based on a membrane-electrode assembly (MEA), a gasket, and a separator are alternately stacked.

A typical unit cell is composed of a polymer electrolyte membrane for selectively transporting hydrogen ions, a fuel electrode and an air electrode, which are a pair of electrodes formed on both surfaces of the polymer electrolyte membrane.

The fuel electrode and the air electrode are usually provided with a catalyst layer formed on the surface of the polymer electrolyte membrane and an air diffusion layer formed on the outer surface of the catalyst layer and having both breathability and electron conductivity.

A gasket is disposed around the fuel electrode and the air electrode to prevent the fuel gas and the oxidant gas supplied to the electrode from leaking to the outside or to mix the two kinds of gases with each other.

The gasket is generally used a silicone rubber composition or the like, and can be assembled in advance with the electrode and the polymer electrolyte membrane. However, the conventional gasket made of a silicone rubber composition has a problem in that the hydrolysis reaction proceeds with respect to moisture generated when the fuel cell is driven, thereby deteriorating long-term durability.

On the other hand, recently, the gasket material may be made of a fluororubber composition to which a bisphenol crosslinking system using a bisphenol (bisphenol, DihydroxyDiphenyldimethylmethane) vulcanizing agent is applied. Bisphenol vulcanizing agents often include bisphenol A or bisphenol AF, and bisphenol AF is commonly used, and in this case, ammonium salts promote crosslinking reactions.

When the bisphenol crosslinks, the rubber causes a dehydrogenation reaction. In order to prevent the generation of HF as a by-product from the dehydrogenation reaction, MgO or Ca (OH) ₂ as an acid acceptor and a crosslinking aid to help crosslinking with water to form water by combining with hydrogen. Metal oxides and / or metal ions such as these need to be used, so that the metal oxides or metal ions remain in the gasket. However, the metal oxide and / or metal ions remaining in the gasket are eluted after the gasket is attached to the fuel cell, which causes poisoning of the catalyst in the membrane-electrode assembly, thereby degrading fuel cell efficiency. There is this.

In addition, the fluororubber composition using a bisphenol crosslinking system is not excellent in compression set reduction at low temperatures, thereby causing a problem in that the sealing performance is lowered at low temperature startup of the fuel cell.

An object of the present invention is to provide a gasket rubber composition for a fuel cell stack having a structure in which a hydrolysis reaction does not proceed with respect to moisture generated during driving of a fuel cell.

Another object of the present invention is to provide a gasket rubber composition for a fuel cell stack in which elution of metal oxides is reduced.

It is still another object of the present invention to provide a gasket rubber composition for fuel cell stack having excellent sealing property at low temperature startup of the fuel cell.

Accordingly, a gasket composition for a fuel cell stack according to an embodiment of the present invention is a gasket composition for a fuel cell stack comprising a polymer and a crosslinking agent, wherein the polymer is vinylidene fluoride, tetrafluoroethylene, and perfluoro. It consists of a ternary copolymer of methylvinyl ether, and a crosslinking agent consists of 2-5 weight part of peroxide vulcanizing agents with respect to 100 weight part of polymers.

It is preferable that the composition for gaskets contains a cure site monomer.

On the other hand, the gasket composition further comprises a pigment, the pigment preferably comprises 0 to 4 parts by weight of carbon black with respect to 100 parts by weight of the polymer.

In addition, the peroxide vulcanizing agent is DBPH (2,5-dimethyl-2,5-di ( t -butylperoxy) hexane), the composition for the gasket may further include a cross-linking accelerator that is TAIC (triallylisocyanurate).

Hereinafter, a gasket composition for a fuel cell stack according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a fuel cell stack using an electrolyte membrane, which is an example of a fuel cell stack to which the present invention is adopted. Referring to FIG. 1, the fuel cell stack has a structure in which unit cells having a membrane-electrode assembly (MEA) 10, a gasket 24, and a separator plate 20 are alternately stacked.

The membrane-electrode assembly (MEA) 10 includes a polymer electrolyte membrane 13 for selectively transporting hydrogen ions, a fuel electrode 11 and an air electrode 12 which are a pair of electrodes formed on both surfaces of the polymer electrolyte membrane 13. It is composed of The fuel electrode 11 and the air electrode 12 generally comprise a catalyst layer formed on the surface of the polymer electrolyte membrane 13 and a gas diffusion layer formed on the outer surface of the catalyst layer and having both breathability and electron conductivity.

Around the fuel electrode 11 and the air electrode 12, a gasket 24 fixed to prevent the fuel gas and the oxidant gas supplied to the electrode from leaking out or the two kinds of gases are not mixed with each other is provided. Is placed.

A conductive separator plate 20 may be disposed outside the membrane-electrode assembly 10. The separator 20 mechanically fixes the membrane-electrode assembly 10 and simultaneously connects the adjacent membrane-electrode assemblies 10 to each other electrically in series, in some cases in parallel.

A gasket composition for a fuel cell stack according to a preferred embodiment of the present invention applied to a fuel cell stack including the above structure comprises a polymer, a filler, and a crosslinking agent.

The polymer consists of a vinylidene fluoride monomer, a tetrafluoroethylene monomer, and a perfluoromethylvinylether monomer. In this case, each monomer is ternary copolymerized into a polymer.

Typically, the fuel cell stack operates in a strong acid atmosphere of about pH 2, and its operating temperature is also high. Accordingly, the gasket provided in the fuel cell stack is preferably excellent in heat resistance and chemical resistance. Each monomer applied to the present invention has a C-F bond and a high content of fluorine. As the content of fluorine increases, chemical resistance and heat resistance are improved, and according to the present invention, heat resistance and chemical resistance increase as a result.

In addition, the perfluoromethyl vinyl ether maintains the flexibility of the molecular chain even at low temperatures. Therefore, the polymer containing the perfluoromethyl vinyl ether has improved low temperature and maintains excellent sealability even at low temperature startup of the fuel cell.

Carbon black may be used as the pigment. The carbon black is a material made by incomplete combustion or pyrolysis of a carbon-containing material such as natural gas, petroleum, or coal tar-based heavy oil, and has excellent reinforcement and chemical resistance. The carbon black preferably has 0 to 4 parts by weight based on 100 parts by weight of the polymer. In this case, the carbon black may be MT black included in N900 in the case of ASTM classification.

The crosslinking agent functions to cross-link each of the monomers. The crosslinking agent applied to the present invention comprises a peroxide vulcanizing agent. That is, the present invention uses a peroxide crosslinking system. Peroxide vulcanizing agents are excellent in resistance to amine compounds and resistance to methanol.

In the present invention, DBPH (2,5-dimethyl-2,5-di ( t -butylperoxy) hexane) may be used as a crosslinking agent, and TAIC (triallylisocyanurate) may be used as a crosslinking accelerator.

As mentioned above, in the bisphenol crosslinking system, a dehydrogenation reaction must occur, so a metal oxide needs to be used as a hydroxyl agent in order to prevent HF generation, but in the case of a peroxide crosslinking system, there is no need to use a hydroxylant to absorb HF gas. . Small amounts of metal oxides can be used, but they are used as crosslinking aids and not as oxalates. Therefore, ion dissolution generated from the metal oxide can be minimized, thereby preventing poisoning from occurring in the catalyst in the membrane-electrode assembly, thereby improving fuel cell efficiency and lifespan.

In this case, the peroxide vulcanizing agent has 2 to 5 parts by weight based on 100 parts by weight of the polymer.

On the other hand, the gasket composition of the present invention preferably contains a cure site monomer in the polymer. As an example of the curesite monomer, a compound such as trifluoro-monobromo-ethylene (-CF 2 -CFBr-) may be used.

The effect on the peroxide vulcanizing agent in the gasket composition according to the invention can be more clearly understood by the following examples.

(Example)

Table 1 shows the components and blending composition ratios of the examples and comparative examples used in this experiment. The embodiment includes 3 parts by weight of black carbon in 100 parts by weight of the ternary raw material rubber, and the comparative example includes 1 part by weight of black carbon and 7 parts by weight of oxalic acid in 100 parts by weight of the binary raw material rubber.

Component (parts by weight) Comparative Example Example Raw material rubber Binary system copolymer ¹ 100 - Ternary terpolymer ² - 100 Filling reinforcement N990 ³ One 3 Crosslinking agent Bisphenol crosslinking agent Peroxide Crosslinker ⁴ Crosslinking aid TAIC ⁵ - - Processing aid Wax ⁶ 2 2 Oxalic acid MgO ⁷ 7 - 1. Binary copolymer: FOR 801HS, Solvay solexis pre-compound (contains crosslinking agent and accelerator) 2. Tertiary terpolymer: GF series, Dupont Performance Elastomer law-gum (crosslinking agent and promoter not included) 3. N990: MT, Cancarb 4 peroxide crosslinker: DBPH-50, RT Vanderbilt 5.TAIC: triallylisocyanurate, Japan Mars 6.Wax: VPA # 2, Dupont 7.MgO: MgO # 150

Table 2 shows the results of the permanent compression test, the internal copper solution test, and the acid resistance test of the peroxide vulcanizing agent contained in the gasket composition according to the embodiment of the present invention and the bisphenol vulcanizing agent as a comparative example. In this case, the compressive permanent shrinkage test was conducted in accordance with KS M 6518, Clause 11, and the internal copper test and acid resistance test were conducted in accordance with KS, KS M 6518, Clause 13.

Test Items Comparative example Example Compressive permanent shrinkage test  Compressed permanent reduction rate (%) 25 13 Internal Copper Test  Hardness point -2 -2  Tensile Strength Change Rate (%) +13 -12  Elongation rate of change (%) -21 -8  Volume change rate (%) +2.1 +1.2 Acid resistance test  Hardness point -2 -2  Tensile Strength Change Rate (%) +4 -5  Elongation rate of change (%) -10 -5  Volume change rate (%) +0.4 -0.1

As shown in Table 2, compared to the comparative example in which 25% compression permanent shrinkage occurred, the embodiment of the present invention produced 13% compression permanent shrinkage, which is half the level of the comparative example, and thus the compressive permanent shrinkage property at low temperature. It can be seen that it is excellent. In addition, it can be seen that the embodiment of the present invention in the internal copper test has no significant difference between the comparative example and the hardness change and the tensile strength change rate, and the internal copper property is improved by decreasing the elongation change rate volume change rate. In addition, it can be seen that the elongation change rate and volume change rate of the embodiment of the present invention in the acid resistance test are improved than the comparative example.

Table 3 shows the results of the ion dissolution test of the peroxide vulcanizing agent contained in the gasket composition according to the embodiment of the present invention and the bisphenol vulcanizing agent as a comparative example. In this case, the tensile test specimen dumbbell type 3 used in the general rubber test was used. 2 ml of ultrapure water per 1 cm 3 of the specimen sample was deposited at 80 ° C. for 500 hours, and the filtrate was analyzed using ICP.

As a result, Mg, Ca, Na, P ions are eluted in the comparative example, it can be seen that the ions are not eluted in the embodiment of the present invention. That is, according to the embodiment of the present invention, ion dissolution of the metal oxide is greatly reduced, and catalyst poisoning in the membrane-electrode assembly due to the metal ions can be reduced.

Test Items unit Comparative example Example Mg ppm 0.8 0 Ca ppm 1.3 0 Na ppm 2.7 0 P ppm 2.1 0

 According to the present invention, by using a fluorine-based monomer, the hydrolysis reaction does not proceed with respect to moisture, and as a result, the long-term durability is excellent.

In addition, by using the peroxide vulcanizing agent as a crosslinking system material, ion dissolution of the metal oxide is reduced, thereby preventing catalyst poisoning in the membrane-electrode assembly, thereby increasing the life of the fuel cell and improving its efficiency. .

In addition, the compressive permanent shrinkage is improved, particularly at low temperatures, so that the sealing property is excellent at startup at low temperatures.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and any person skilled in the art to which the present invention pertains may have various modifications and equivalent other embodiments. Will understand. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (4)

In the gasket composition for a fuel cell stack comprising a polymer and a crosslinking agent, The polymer is obtained by tertiary copolymerization of a vinylidene fluoride monomer, a tetrafluoroethylene monomer, and a perfluoromethyl vinyl ether monomer; And a pigment comprising 0 to 4 parts by weight of carbon black based on 100 parts by weight of the polymer. The method of claim 1, The gasket composition is a fuel cell stack gasket composition, characterized in that it contains a cure site monomer (cure site monomer). delete The method of claim 1, The peroxide vulcanizing agent is DBPH (2,5-dimethyl-2,5-di ( t -butylperoxy) hexane), A gasket composition for a fuel cell stack, further comprising a TAIC (triallylisocyanurate) crosslinking accelerator.

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