Fuel cell flexible graphite bipolar plate pore sealing agent

Abstract

The application discloses a fuel cell flexible graphite bipolar plate micropore leaking stoppage agent, which comprises 30-50 parts of organic silicon double end cap agent with two (methyl) acryloyloxy groups at each end, 50-70 parts of high-Tg methacrylate monomer, 0.5-2 parts of leveling agent and 0.2-1.0 parts of free radical thermal initiator, and the total amount of the organic silicon double end cap agent and the high-Tg methacrylate monomer is 100 parts by weight. The leaking stoppage agent has excellent ethylene glycol resistance due to the organic silicon structure, the organic silicon double end cap agent has four (methyl) acryloyloxy groups capable of free radical polymerization on each molecule, has high crosslinking density, and has high heat resistance after copolymerization with the high-Tg methacrylate monomer, and meanwhile, the leaking stoppage agent has low curing shrinkage and small residual stress, and is beneficial to keeping the bipolar plate to have good bending strength at high temperature.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrogen fuel cells, and particularly relates to a heat-cured micro-pore plugging agent for flexible graphite bipolar plates of hydrogen fuel cell stacks. BACKGROUND

[0002] Fuel cell bipolar plates are the core structural support of hydrogen fuel cell stacks, and are divided into metal bipolar plates and graphite bipolar plates. Graphite bipolar plates are widely used in fuel cell stacks of commercial vehicles due to the advantages of easy availability of raw materials, low cost, good chemical corrosion resistance, and long service life. However, flexible graphite plates have a micro-porous structure and must be treated with a plugging agent for impregnation to ensure the gas tightness of the bipolar plate. After the plugging agent is cured, it must also impart sufficient mechanical strength, chemical resistance (mainly resistance to ethylene glycol) and long-term heat resistance to the flexible graphite plate.

[0003] Flexible graphite bipolar plates generally use (meth) acrylate monomers compounded into an impregnation resin solution as a plugging agent (referring to Chinese Patent CN 107706430B). Before use, a free radical thermal initiator is added, the flexible graphite plate is impregnated in the plugging agent, and vacuum or pressurized impregnation is performed to allow the plugging agent molecules to penetrate into the micro-pores of the flexible graphite bipolar plate. Then, the surface of the bipolar plate is cleaned to prevent the plugging agent from affecting the electrical conductivity of the graphite after it is cured on the surface of the bipolar plate. After that, the bipolar plate is heated and cured in a water bath, and the plugging agent forms a dense network structure after curing, thereby imparting gas tightness, compressive strength, chemical resistance and heat resistance to the bipolar plate.

[0004] After the flexible graphite bipolar plate is assembled into a stack, it must be able to withstand long-term exposure to ethylene glycol aqueous solution cooling medium at a temperature of 80-95℃ during fuel cell operation. The (meth) acrylate polymer has some solubility in ethylene glycol, which causes the plugging agent of the bipolar plate to partially dissolve in the ethylene glycol during long-term operation of the fuel cell, resulting in pore cracks and gas leakage and failure.

[0005] The Tg of the methacrylate polymer or copolymer mentioned in Chinese Patent CN 107706430B is relatively low, and few components have a Tg exceeding 100℃. The Tg of long-chain alkyl acrylate polymers is even below zero degrees, and the graphite bipolar plate has a significantly reduced bending strength in the rubber state at the operating temperature of the fuel cell, making it difficult to meet the stringent requirements for stable operation of hydrogen fuel cell vehicles at high temperatures. SUMMARY

[0006] The purpose of the present application is to provide a micro-pore plugging agent for flexible graphite bipolar plates of hydrogen fuel cells.

[0007] The technical solution to achieve the purpose of the present application is as follows:

[0008] In a first aspect, the present application provides a flexible graphite bipolar plate pore plugging agent, comprising: 30-50 parts by weight of a silicone double end cap agent with two (meth) acryloyloxy groups at each end and 50-70 parts by weight of a high Tg methacrylate monomer, the total of which is 100 parts by weight, and 0.5-2 parts by weight of a leveling agent and 0.2-1.0 parts by weight of a free radical thermal initiator;

[0009] In the formula, the silicone double end cap agent with two (meth) acryloyloxy groups at each end has the following structure:

[0010]

[0011] In the formula, R1 represents a methyl group or a hydrogen atom.

[0012] Preferably, the synthesis method of the silicone double end cap agent with two (meth) acryloyloxy groups at each end comprises:

[0013] First step: performing a silicon-hydrogen addition reaction on a hydrogen-containing double end cap and a trimethylolpropane monoallyl ether in the presence of a platinum gold catalyst to generate a double end cap compound containing two hydroxyl groups at each end,

[0014]

[0015] Second step: performing an esterification and dehydration reaction on the double end cap compound containing two hydroxyl groups at each end and an excess of (meth) acrylate in the presence of an acid catalyst and a cyclohexane water-carrying agent to generate a double end cap compound with two (meth) acryloyloxy structures at each end:

[0016]

[0017] In the formula, R1 represents a methyl group or a hydrogen atom.

[0018] Specifically, in order to prevent the occurrence of acrylic acid self-polymerization during the esterification and dehydration reaction of the acrylic ester, a free radical polymerization inhibitor needs to be added to the esterification and dehydration reaction, and the amount of addition is 0.01% to 1% of the total mass of the reactants.

[0019] More specifically, the free radical polymerization inhibitor is any one or more of p-methoxyphenol, hydroquinone, 2,5-dimethylhydroquinone, and 2,6-di-tert-butyl-4-methylphenol.

[0020] Specifically, the acid catalyst for the esterification and dehydration reaction of the acrylic ester is selected from any one of concentrated sulfuric acid, sodium bisulfate, methyl sulfonic acid, methylbenzenesulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid, and preferably any one of methyl sulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid, and the amount of addition is 0.1% to 5.0% of the total mass of the reactants.

[0021] Preferably, the high Tg methacrylate monomer is selected from any one of isobornyl (meth)acrylate, o-phenylphenoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, tricyclodecanyl (meth)acrylate, dicyclopentadiene (meth)acrylate, (meth)acryloyl morpholine and N,N-dimethyl acrylamide, etc. Based on the comprehensive consideration of heat resistance and low viscosity, isobornyl (meth)acrylate, dicyclopentadiene (meth)acrylate or tricyclodecanyl (meth)acrylate is preferred.

[0022] Preferably, the leveling agent can be selected from any leveling agent that has a wetting effect on the flexible graphite bipolar plate, and the amount of the leveling agent can be determined according to the impregnation amount of the flexible graphite bipolar plate after impregnation. The higher the impregnation amount, the better the effect of the leveling agent. Preferably, the leveling agent is BYK-333 or BYK-3505 from BYK Germany, and a superdispersant such as CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9, etc.

[0023] Preferably, the free radical thermal initiator is selected from an initiator with a decomposition temperature of 80-95°C, and an azo and peroxide free radical thermal initiator is preferred. Preferably, the free radical thermal initiator is azobisisobutyronitrile, azobisisoheptyl nitrile or benzoyl peroxide.

[0024] Preferably, various antioxidants, anti-aging agents and fluorescent agents can be added to the composition based on the consideration of weather resistance, heat resistance and fluorescent identification.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The flexible graphite bipolar plate sealing agent composition of the present application comprises a silicone double end cap agent with two (meth) acryloyloxy groups at each end. Due to the hydrophobic and oleophobic properties and low surface tension of the organosiloxane structure, the silicone double end cap agent has excellent ethylene glycol resistance and will not swell or dissolve in contact with ethylene glycol aqueous solution at high temperature for a long time, and is particularly suitable for sealing the micropores of the flexible graphite bipolar plate of a hydrogen fuel cell.

[0027] (2) The flexible graphite bipolar plate sealing agent composition of the present application comprises a silicone double end cap agent compound with two (meth) acryloyloxy groups at each end. Each molecule contains four (meth) acryloyloxy groups that can be free radical polymerized. After copolymerization with a high Tg methacrylate monomer, the silicone double end cap agent compound has high heat resistance, low curing shrinkage and small residual stress, which is beneficial to maintaining good bending strength of the bipolar plate at high temperature. DETAILED DESCRIPTION

[0028] The application will be described in detail below with reference to examples.

[0029] The (meth)acrylate monomer has the advantages of low viscosity, strong permeability, and low curing temperature, and is the preferred compound for fuel cell graphite bipolar plate micropore plugging agents. Compared with acrylate compounds, methacrylate compounds are more easily subjected to free radical thermal curing reaction, and the cured product has a higher Tg (glass transition temperature), that is, has higher heat resistance, so most commercial micropore plugging agents use methacrylate monomers as the main component. However, after polymerization of the methacrylate monomer, there are very few monomers with Tg exceeding 100℃, and the heat resistance is not as good as that of epoxy resin cured product. In addition, due to the low crosslinking density and the presence of a large number of polar ester bonds, the resistance to ethylene glycol is not good.

[0030] The application introduces a tetrafunctional monomer containing a methyl siloxane structure, which has a high Tg and excellent ethylene glycol resistance.

[0031] The silicone double sealing agent with two (meth) acryloyloxy groups at both ends of the application is first subjected to a silicon-hydrogen addition reaction in the presence of a platinum catalyst using a hydrogen-containing double sealing agent and trimethylolpropane monoallyl ether to generate a double sealing compound containing two hydroxyl groups at both ends. Then, the double sealing compound containing two hydroxyl groups at both ends and excess (meth) acrylic acid are subjected to an esterification and dehydration reaction in the presence of an acid catalyst and cyclohexane water-carrying agent to generate a double sealing compound ATH containing two (meth) acryloyloxy structures at both ends.

[0032] If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased on the market.

[0033] Synthesis of double-hydroxyl double sealing agent:

[0034] A three-necked glass flask with an oil bath and a condenser device was added with 100 g of trimethylolpropane monoallyl ether and 0.01 g of chloroplatinic acid, and stirred to warm up to 70℃. 42 g of hydrogen-containing double sealing agent (1,1,3,3-tetramethyldisiloxane) was added dropwise, and the addition was completed within one hour. Then, the temperature was raised to 80℃ and the reaction was continued for 4 h. The unreacted hydrogen-containing double sealing agent was removed by vacuumization to obtain a colorless transparent double sealing agent containing two hydroxyl groups at both ends (double-hydroxyl double sealing agent). The molecular weight was 482.7.

[0035] Synthesis of double-acryloyloxy double sealing agent (ATH-1 synthesis):

[0036] A three-necked glass flask with oil bath and condenser was charged with 100 g of dihydroxy end-capper, 66 g of acrylic acid, 6.0 g of methanesulfonic acid, 0.06 g of MeHQ radical inhibitor, 150 g of cyclohexane water-carrying agent, and stirred to elevate the temperature to 85°C and refluxed. The water carried out was periodically discharged by a separatory funnel. The amount of water trapped in the separatory funnel was carefully observed until no more water was distilled out, which indicated that the reaction was completed. The temperature was lowered to room temperature. Excess sodium carbonate was added to neutralize the residual acrylic acid and acidic catalyst. The precipitate was filtered and washed with water for several times. Then, it was vacuum dried to obtain a light yellow transparent di-end-capper with two acrylic acryloxy groups at each end, which was abbreviated as ATH-1, with a viscosity of 420 mPas and a molecular weight of 698.7.

[0037] Synthesis of dimethacryloxy end-capper (ATH-2 synthesis)

[0038] A three-necked glass flask with oil bath and condenser was charged with 100 g of dihydroxy end-capper, 79 g of methacrylic acid, 1.0 g of trifluoromethanesulfonic acid, 0.07 g of MeHQ radical inhibitor, 180 g of cyclohexane water-carrying agent, and stirred to elevate the temperature to 85°C and refluxed. The water carried out was periodically discharged by a separatory funnel. The amount of water trapped in the separatory funnel was carefully observed until no more water was distilled out, which indicated that the reaction was completed. The temperature was lowered to room temperature. Excess sodium carbonate was added to neutralize the residual methacrylic acid and acidic catalyst. The precipitate was filtered and washed with water for several times. Then, it was vacuum dried to obtain a light yellow transparent di-end-capper with two methacryloxy groups at each end, which was abbreviated as ATH-2, with a viscosity of 487 mPas and a molecular weight of 754.7.

[0039] The sealant formulations in the examples and comparative examples were prepared by mixing the components and stirring until the solids were dissolved to form a clear solution.

[0040] The formulations of the examples and comparative examples are shown in Table 1 below.

[0041] Table 1

[0042]

[0043] The evaluation method for ethylene glycol resistance is as follows:

[0044] The sealant 10 g was poured into a Teflon mold with a diameter of 4.0 cm and a height of 2.0 cm, and placed in a 80°C drying oven for 2 h, and then the temperature was raised to 120°C and heated for another 2 h to obtain a colorless transparent cylindrical cured product. The cylindrical cured product was placed in a glass bottle containing 50% wt ethylene glycol aqueous solution and sealed, and then transferred to a 90°C oven and kept for 1000 h. The solubility of the cured product and the turbidity of the ethylene glycol aqueous solution were observed to evaluate the ethylene glycol resistance of the sealant.

[0045] The ethylene glycol resistance was divided into four grades:

[0046] 1. Excellent (Cured product intact, no foreign matter and no turbidity in the glycol aqueous solution)

[0047] 2. Good (Cured product has no obvious dissolution, and the glycol aqueous solution is slightly turbid)

[0048] 3. Fair (Cured product has obvious dissolution, and the glycol aqueous solution becomes turbid)

[0049] 4. Very poor (Cured product has swelling and dissolution, and the glycol aqueous solution is very turbid)

[0050] According to Table 1, by comparing Example 1 and Comparative Example 1, it is found that the addition amount of ATH bis-acryloxy double sealing agent has a crucial influence on the glycol resistance, and the addition amount of ATH bis-acryloxy double sealing agent needs to be more than 30 phr (Parts per hundred) to achieve good resistance, and when the addition amount of ATH bis-acryloxy double sealing agent is 10 phr, the cured product has obvious dissolution after aging, the glycol aqueous solution becomes turbid, and the Tg of the obtained cured product is also relatively low, and the heat resistance is also poor.

[0051] The composition of Comparative Example 2 is all high-Tg methacrylate, and the Tg of the cured product is relatively high, but because it does not contain organosiloxane structure, the glycol resistance is poor, the cured product has swelling and dissolution after aging, and the glycol aqueous solution is very turbid.

[0052] Comparative Example 3 contains low-Tg bis-acrylate in the formula, and the Tg of the obtained cured product is relatively low, the heat resistance is poor, the glycol resistance is also relatively poor, the cured product has swelling and dissolution after aging, and the glycol aqueous solution is also very turbid.

Claims

1. A fuel cell flexible graphite bipolar plate microporous plugging agent characterized by, Comprise: 30~50 parts by weight of a silicone double-sealant with two (meth) acryloyloxy groups at both ends and 50~70 parts by weight of a high-Tg methacrylate monomer, both totaling 100 parts by weight, and 0.5~2 parts by weight of a leveling agent and 0.2~1.0 parts by weight of a free radical thermal initiator; Wherein, the silicone double-sealant with two (meth) acryloyloxy groups at both ends has the following structure: ； Wherein, R1 represents a methyl group or a hydrogen atom; The high-Tg methacrylate monomer is selected from any one of isobornyl methacrylate, o-phenylphenoxyethyl methacrylate, benzyl methacrylate, phenyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, tricyclodecanyl methacrylate, dicyclopentadiene methacrylate, and methacryloyl morpholine.

2. The lost circulation material of claim 1, wherein, The silicone double-sealant with two (meth) acryloyloxy groups at both ends is prepared by the following steps: Step 1: a silicon-hydrogen addition reaction is carried out with a hydrogen-containing double-sealant and trimethylolpropane monoallyl ether in the presence of a platinum gold catalyst to generate a double-sealant compound with two hydroxyl groups at both ends, ； Step 2: an esterification and dehydration reaction is carried out with the double-sealant compound with two hydroxyl groups at both ends and excess (meth) acrylic acid in the presence of an acidic catalyst and cyclohexane water-carrying agent to generate a double-sealant compound with two (meth) acryloyloxy structures at both ends: ； Wherein, R1 represents a methyl group or a hydrogen atom.

3. The lost circulation material of claim 2, wherein, A free radical polymerization inhibitor is added in the esterification and dehydration reaction, and the amount of addition is 0.01%~1% of the total mass of the reactants.

4. The lost circulation material of claim 3, wherein, The free radical polymerization inhibitor is any one or more of p-methoxyphenol, hydroquinone, 2,5-dimethyl hydroquinone, and 2,6-di-tert-butyl-4-methylphenol.

5. The lost circulation material of claim 2, wherein, The acidic catalyst for the esterification and dehydration reaction is selected from any one of concentrated sulfuric acid, sodium bisulfate, methyl sulfonic acid, methylbenzenesulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid.

6. The lost circulation material of claim 2, wherein, The acidic catalyst for the esterification and dehydration reaction is selected from any one of methyl sulfonic acid, triflic acid, a strongly acidic ion exchange resin, and a solid superacid.

7. The lost circulation material of claim 2, wherein, The amount of addition of the acidic catalyst for the esterification and dehydration reaction is 0.1%~5.0% of the total mass of the reactants.

8. The lost circulation material of claim 1, wherein, The high-Tg methacrylate monomer is selected from any one of isobornyl methacrylate, dicyclopentadiene methacrylate, or tricyclodecanyl methacrylate.

9. The lost circulation material of claim 1, wherein, The leveling agent is selected from any one of Germany BYK leveling agent BYK-333, BYK-3505, and tri-normal high-molecular superdispersant CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, and CH-9.

10. The lost circulation material of claim 1, wherein, The free radical thermal initiator is selected from any one of azobisisobutyronitrile, azobisisoheptyl nitrile, or benzoyl peroxide.

11. The lost circulation material of claim 1, wherein, The plugging agent also includes any one or more of an antioxidant or a fluorescent agent.

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