Micro-pore sealing agent for flexible graphite bipolar plate of ethylene glycol resistant fuel cell

Abstract

The application discloses a flexible graphite bipolar plate micro-hole plugging agent for ethylene glycol-resistant fuel cells, 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 plugging agent has excellent ethylene glycol resistance due to the organic silicon structure, and 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 plugging agent has low curing shrinkage and small residual stress, and is beneficial to keeping good bending strength of the bipolar plate at high temperature.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen fuel cells, specifically relating to a thermosetting microporous sealant for flexible graphite bipolar plates in hydrogen fuel cell stacks. Background Technology

[0002] Fuel cell bipolar plates are the core structural support components 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 availability of raw materials, low cost, good chemical corrosion resistance, and long service life. However, flexible graphite plates have a microporous structure and must be impregnated with a sealing agent to ensure the airtightness of the bipolar plate. At the same time, after the sealing agent cures, it must give the flexible graphite plate sufficient mechanical strength, chemical resistance (mainly resistance to ethylene glycol), and long-term heat resistance.

[0003] Flexible graphite bipolar plates typically use a resin solution formulated with (meth)acrylate monomers as a sealing agent (refer to Chinese Patent CN 107706430B). Before use, a free radical thermal initiator is added. The flexible graphite plate is then impregnated in the sealing agent under vacuum or pressure, allowing the sealing agent molecules to penetrate into the micropores of the flexible graphite bipolar plate. Residual sealing agent on the surface of the bipolar plate is then cleaned to prevent it from affecting the conductivity of the graphite after curing. The bipolar plate is then cured in a water bath. After curing, the sealing agent forms a dense network structure, thereby giving the bipolar plate airtightness, compressive strength, chemical resistance, and heat resistance.

[0004] After flexible graphite bipolar plates are assembled into a fuel cell stack, they are in contact with ethylene glycol aqueous solution as a cooling medium at a temperature of 80-95°C for a long time during fuel cell operation. They need to be resistant to long-term high temperature of ethylene glycol aqueous solution. However, (meth)acrylate polymers have a certain degree of solubility in ethylene glycol. As a result, after long-term operation of the fuel cell, the bipolar plate sealing agent partially dissolves in ethylene glycol, producing pores and cracks, leading to gas leakage and failure.

[0005] The methacrylate polymers or copolymers mentioned in Chinese patent CN 107706430B have relatively low Tg, with very few components having a Tg exceeding 100°C. The Tg of long-chain alkyl acrylate polymers is even below zero, placing them in a rubbery state at fuel cell operating temperatures. This significantly reduces the flexural strength of the graphite bipolar plates, making it difficult to meet the stringent requirements for stable operation of hydrogen fuel cell vehicles under long-term high temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a microporous plugging agent for flexible graphite bipolar plates in fuel cells with good heat resistance and ethylene glycol resistance.

[0007] The technical solution to achieve the purpose of this invention is:

[0008] In a first aspect, the present invention provides a microporous plugging agent for a flexible graphite bipolar plate resistant to ethylene glycol fuel cells, comprising: 30-50 parts by weight of an organosilicon dual-end capping 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, as well as 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] The organosilicon dual-end capping agent, with two (meth)acryloyloxy groups at each end, has the following structure:

[0010]

[0011] R1 represents a methyl group or a hydrogen atom.

[0012] Preferably, the organosilicon dual-end terminator with two (meth)acryloyloxy groups at each end is prepared by the following steps:

[0013] Step 1: A hydrosilylation reaction is carried out with hydrogen-containing dual-terminated agents and 4-vinylepoxycyclohexane in the presence of a platinum catalyst to generate dual-terminated agents with one epoxy group at each end.

[0014]

[0015] Step 2: A ring-opening esterification reaction is carried out between a dual-terminator containing one epoxy group at each end and excess (meth)acrylic acid in the presence of a ring-opening esterification catalyst to obtain a dual-terminator containing one hydroxyl group and one (meth)acryloyloxy group at each end.

[0016]

[0017] Step 3: An esterification and dehydration reaction is carried out between a dual-termining agent containing one hydroxyl group and one (meth)acryloyloxy group at each end, and excess (meth)acrylic acid in the presence of cyclohexane as a dehydrating agent and an acidic catalyst to generate a dual-termining agent containing two acryloyloxy groups at each end.

[0018]

[0019] R1 represents a methyl group or a hydrogen atom.

[0020] Specifically, the ring-opening esterification catalyst is selected from tertiary amines and quaternary ammonium salts, commonly including any one of triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylphosphine, triphenylantimony, chromium acetylacetone, chromium isooctanoate, stannous octoate, and tetraethylammonium bromide, and its amount is 0.1% to 5.0% of the reactants.

[0021] Specifically, in order to prevent the self-polymerization of (meth)acrylic acid during the esterification and dehydration reaction, a free radical polymerization inhibitor needs to be added to the esterification and dehydration reaction, and the amount added is 0.01% to 1% of the total mass of the reactants.

[0022] 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.

[0023] Specifically, the acidic catalyst is selected from any one of concentrated sulfuric acid, sodium bisulfate, methanesulfonic acid, methylbenzenesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid superacid, preferably any one of methanesulfonic acid, trifluoromethanesulfonic acid, strong acid ion exchange resin and solid superacid, and its addition amount is 0.1% to 5.0% of the total mass of the reactants.

[0024] Preferably, the high-Tg methacrylate monomer is selected from any one of isobornyl methacrylate, o-phenylphenoxyethyl methacrylate, benzyl methacrylate, phenyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofuran methacrylate, tricyclodecyl methacrylate, dicyclopentadiene methacrylate, methacryloylmorpholine, and N,N-dimethylacrylamide, etc. Considering factors such as heat resistance and low viscosity, isobornyl methacrylate, dicyclopentadiene methacrylate, or tricyclodecyl methacrylate are preferred.

[0025] Preferably, the leveling agent can be any leveling agent that has a wetting effect on the flexible graphite bipolar plate. The choice depends on the impregnation content of the sealing agent after the flexible graphite bipolar plate is impregnated; a higher impregnation content results in a better leveling effect. Preferred leveling agents include BYK-333 and BYK-3505 from BYK (Germany), as well as high-molecular-weight superdispersants such as CH-1, CH-2, CH-3, CH-5, CH-6, CH-7, CH-8, CH-9, etc.

[0026] Preferably, the free radical thermal initiator is an initiator with a decomposition temperature of 80–95°C, and azo-based or peroxide-based free radical thermal initiators are selected. Azobisisobutyronitrile, azobisisoheptanenitrile, or benzoyl peroxide are preferred free radical thermal initiators.

[0027] Preferably, considering factors such as weather resistance, heat resistance, and fluorescence recognition, various antioxidants, anti-aging agents, fluorescent agents, etc., can be added to the above-mentioned components.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) One of the components of the flexible graphite bipolar plate plugging agent of the present invention is an organosilicon double-ending agent with two (meth)acryloyloxy groups at each end. Due to the hydrophobic and oleophobic properties and low surface tension of the organosiloxane structure, it has excellent ethylene glycol resistance. It will not swell or dissolve when in contact with ethylene glycol aqueous solution at long-term high temperature, and is particularly suitable for micropore plugging of flexible graphite bipolar plates for hydrogen fuel cells.

[0030] (2) One of the components of the flexible graphite bipolar plate sealing agent of the present invention is an organosilicon double-ending 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 high Tg methacrylate monomers, it has high heat resistance, low curing shrinkage rate, and low residual stress, which is beneficial for the bipolar plate to maintain good bending strength at high temperature. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the embodiments.

[0032] (Meth)acrylate monomers possess advantages such as low viscosity, strong permeability, and low curing temperature, making them the preferred compounds for microporous plugging agents in graphite bipolar plates for fuel cells. Compared to acrylate compounds, methacrylate compounds undergo free radical thermosetting reactions more easily, and the cured products have a higher Tg (glass transition temperature), meaning they exhibit higher heat resistance. Therefore, most commercial microporous plugging agents use methacrylate monomers as the main component. However, after polymerization, methacrylate monomers rarely have a Tg exceeding 100℃, resulting in lower heat resistance compared to epoxy resin cured products. Furthermore, due to insufficient crosslinking density and the presence of numerous polar ester bonds, their resistance to ethylene glycol is not ideal.

[0033] This invention introduces a tetrafunctional monomer containing a methylsiloxane structure, which has high Tg and excellent resistance to ethylene glycol.

[0034] The organosilicon dual-terminator of the present invention, with two (meth)acryloyloxy groups at each end, first undergoes a hydrosilylation reaction with a hydrogen-containing dual-terminator and AGE (allyl glycidyl ether) in the presence of a platinum catalyst to generate a dual-terminator compound with one epoxy group at each end. Then, it undergoes an epoxy ring-opening reaction with excess (meth)acrylic acid in the presence of a catalyst. The generated hydroxyl group further undergoes an esterification and dehydration reaction with excess (meth)acrylic acid and a cyclohexane dehydrating agent in the presence of an acidic catalyst to generate a dual-terminator compound with two (meth)acryloyloxy groups at each end.

[0035] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] Synthesis of epoxy-based dual-capping agents

[0037] 160g of 4-vinylepoxycyclohexane and 0.01g of chloroplatinic acid were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 70°C. 100g of hydrogen-containing double-ended head (1,1,3,3-tetramethyldisiloxane) was added dropwise over one hour. The mixture was then heated to 80°C and the reaction continued for 4 hours. Unreacted hydrogen-containing double-ended head was removed under vacuum to obtain a colorless and transparent double-ended head agent with one epoxy group at each end (referred to as epoxy double-ended head agent), with a molecular weight of 382.7.

[0038] Synthesis of hydroxyacryloyloxy bicapsulant

[0039] 100g of epoxy-based dual-heading agent, 0.5g of tetraethylammonium bromide, and 0.05g of MeHQ free radical inhibitor were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 70°C, and 50g of acrylic acid was added dropwise over one hour. The temperature was then raised to 80°C and the reaction continued for 6 hours. Excess sodium carbonate was added to neutralize the residual acrylic acid and tetraethylammonium bromide. The precipitate was filtered, washed with water several times, and then dried under vacuum to obtain a pale yellow, transparent dual-heading agent containing one hydroxyl group and one acryloxy group at each end (referred to as hydroxyacryloyloxy dual-heading agent), with a molecular weight of 526.8.

[0040] Synthesis of bisacryloyloxy dicapping agent-1

[0041] In a three-necked glass flask equipped with an oil bath and condenser, 100g of hydroxyacryloyloxy dual-terminant, 0.05g of MeHQ free radical inhibitor, 0.05g of BHT free radical inhibitor, 0.5g of trifluoromethanesulfonic acid, and 100g of cyclohexane dehydrating agent were added. The mixture was stirred and heated to 85°C under reflux. 35g of acrylic acid was added dropwise, completing the addition within one hour. The water carried over was periodically released using a separatory tube. The amount of water retained in the separatory tube was carefully observed until no more excess water was distilled out, indicating that the reaction was complete. The mixture was cooled to room temperature, and excess sodium carbonate was added to neutralize the residual acrylic acid and trifluoromethanesulfonic acid. The precipitate was filtered, washed repeatedly with water, and then vacuum dried to obtain a pale yellow, transparent dual-terminant containing two acryloyloxy groups at each end (referred to as bisacryloyloxy dual-terminant-1), with a viscosity of 387 mPas and a molecular weight of 634.9.

[0042] Synthesis of hydroxymethacryloyloxy dual-capping agent

[0043] 100g of epoxy-based bi-capping agent, 0.5g of tetraethylammonium bromide, and 0.05g of MeHQ free radical inhibitor were added to a three-necked glass flask equipped with an oil bath and condenser. The mixture was stirred and heated to 70°C, and 60g of methacrylic acid was added dropwise over one hour. The temperature was then raised to 80°C and the reaction continued for 6 hours. Excess sodium carbonate was added to neutralize the residual methacrylic acid and tetraethylammonium bromide. The precipitate was filtered, washed repeatedly with water, and then vacuum dried to obtain a pale yellow, transparent bi-capping agent containing one hydroxyl group and one methacryloyloxy group at each end (referred to as hydroxymethacryloyloxy bi-capping agent), with a molecular weight of 554.8. Synthesis of bismethacryloyloxy bi-capping agent-2

[0044] In a three-necked glass flask equipped with an oil bath and condenser, 100g of hydroxymethacryloxy dual-heading agent, 0.05g of MeHQ free radical inhibitor, 0.05g of BHT free radical inhibitor, 0.5g of trifluoromethanesulfonic acid, and 150g of cyclohexane dehydrating agent were added. The mixture was stirred and heated to 85°C under reflux. 42g of methacrylic acid was added dropwise, completing the addition within one hour. The water carried over was periodically released using a separatory tube. The amount of water retained in the separatory tube was carefully observed until no more excess water was distilled out, indicating that the reaction was complete. The mixture was cooled to room temperature, and excess sodium carbonate was added to neutralize the residual acrylic acid and trifluoromethanesulfonic acid. The precipitate was filtered, washed repeatedly with water, and then vacuum dried to obtain a pale yellow, transparent dual-heading agent containing two methacryloxy groups at each end (referred to as bismethacryloxy dual-heading agent-2), with a viscosity of 412 mPas and a molecular weight of 690.9.

[0045] The sealant formulations in the examples and comparative examples are prepared by mixing all components and stirring until all solid substances are dissolved into a transparent liquid.

[0046] The formulations of the examples and comparative examples are shown in Table 1 below.

[0047] Table 1

[0048] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example-1 Comparative Example-2 Comparative Example-3 Diacryloyloxy Bi-capping Agent-1 30 45 35 10 Dimethacryloyloxy Bi-capping Agent-2 40 35 Isoborneol acrylate 70 90 Isoborneol methacrylate 60 55 50 50 Dicyclopentadiene acrylate 65 Tricyclodecyl methacrylate 65 50 Dipropylene glycol diacrylate 50 Azobisisobutyronitrile thermal initiator 0.5 0.5 0.5 0.5 0.5 Benzoyl peroxide thermal initiator 0.5 0.5 0.5 BYK-333 leveling agent 1.0 1.0 1.0 1.0 1.0 1.0 BYK-3505 leveling agent 1.0 1.0 Tg(DMA, tanδ peak value) ℃ 125 174 149 171 182 106 166 89 Resistance to ethylene glycol ○ ◎ ◎ ◎ ◎ △ × ×

[0049] The evaluation method for ethylene glycol resistance is as follows:

[0050] 10g of the sealant was poured into a Teflon mold with a diameter of 4.0cm and a height of 2.0cm. The mold was then placed in an 80℃ drying oven and heated for 2 hours, followed by heating to 120℃ for another 2 hours, resulting in a colorless, transparent cylindrical cured product. This cylindrical cured product was placed in a glass bottle containing a 50% wt ethylene glycol aqueous solution, sealed, and placed in a 90℃ oven for 1000 hours. The solubility of the cured product and the turbidity of the ethylene glycol aqueous solution were then examined to evaluate the sealant's resistance to ethylene glycol.

[0051] Ethylene glycol resistance is classified into four levels:

[0052] 1. Excellent ◎ (The solidified material is intact and undamaged; the ethylene glycol aqueous solution is clear, free of foreign matter, and not cloudy)

[0053] 2. Good (No obvious dissolution of the solidified material; the ethylene glycol aqueous solution is slightly turbid)

[0054] 3. Generally △ (The solidified material shows obvious dissolution, and the ethylene glycol aqueous solution becomes cloudy)

[0055] 4. Very poor × (The solidified material swells and dissolves; the ethylene glycol aqueous solution is slightly very turbid).

[0056] According to Table 1, by comparing Example 1 and Comparative Example 1, it was found that the amount of bisacryloyloxy dual-end agent added has a crucial impact on the ethylene glycol resistance. A good resistance can only be achieved when the amount of bisacryloyloxy dual-end agent added exceeds 30 phr (parts per hundred). When the amount of bisacryloyloxy dual-end agent added is 10 phr, the cured product shows obvious dissolution after aging, the ethylene glycol aqueous solution becomes turbid, and the Tg of the resulting cured product is relatively low, and the heat resistance is also poor.

[0057] Comparative Example 2 consists of high-Tg methacrylates. The cured product has a relatively high Tg, but because it does not contain organosiloxane structures, it has poor resistance to ethylene glycol. After aging, the cured product swells and dissolves, and the ethylene glycol aqueous solution is slightly very turbid.

[0058] The formulation of Comparative Example 3 contains a low-Tg difunctional acrylate, resulting in a cured product with a relatively low Tg, poor heat resistance, and poor resistance to ethylene glycol. After aging, the cured product swells and dissolves, and the ethylene glycol aqueous solution is also very turbid.

Claims

1. A flexible graphite bipolar plate microporous plugging agent for ethylene glycol resistant fuel cells, characterized by, Comprise: 30~50 parts by weight of a silicone double end cap agent with two (meth) acryloxy groups at each end 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 end cap agent with two (meth) acryloxy groups at each end 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 (meth) acrylate, o-phenylphenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, tricyclodecanyl (meth) acrylate, dicyclopentadiene (meth) acrylate.

2. The lost circulation material of claim 1, wherein, The silicone double end cap agent with two (meth) acryloxy groups at each end is prepared by the following steps: First step: hydrogen-containing bis-capper and 4-vinyl cyclohexene oxide in the presence of a platinum catalyst to form a bis-capper having two terminal epoxy groups steps; Second step: a double end-capper with two epoxy groups at each end and excess (meth)acrylic acid in the presence of a ring-opening esterification catalyst to obtain a double end-capper with one (meth)acryloyloxy group and one hydroxyl group at each end . Step 3: esterification of the di-epoxide of formula (III) with excess (meth)acrylic acid in the presence of a basic catalyst to form the di-sealant of formula (IV) and excess (meth)acrylic acid in the presence of a basic catalyst to form the di-sealant of formula (IV) Step 3: esterification of the di-epoxide of formula (III) with excess (meth)acrylic acid in the presence of a basic catalyst to form the di-sealant of formula (IV) 3. The lost circulation material of claim 2, wherein, A free radical polymerization inhibitor is added in the esterification 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 ring-opening esterification catalyst is selected from any one of tertiary amine, quaternary ammonium salt, triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, trimethylbenzylammonium chloride, triphenylphosphine, triphenylantimony, chromium acetylacetate, chromium isooctanoate, and tetraethylammonium bromide, and the amount of use is 0.1%~5.0% of the reactants.

6. The lost circulation material of claim 2, wherein, The acid catalyst is selected from any one of concentrated sulfuric acid, sodium bisulfate, methylsulfonic acid, methylbenzenesulfonic acid, triflic acid, strongly acidic ion exchange resin, and solid superacid.

7. The lost circulation material of claim 2, wherein, The acid catalyst is selected from any one of methylsulfonic acid, triflic acid, strongly acidic ion exchange resin, and solid superacid.

8. The lost circulation material of claim 2, wherein, The amount of addition of the acid catalyst is 0.1%~5.0% of the total mass of the reactants.

9. The lost circulation material of claim 1, wherein, The high Tg methacrylate monomer is isobornyl (meth) acrylate, dicyclopentadiene (meth) acrylate, or tricyclodecanyl (meth) acrylate.

10. The lost circulation material of claim 1, wherein, The leveling agent is selected from any one of German 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.

11. 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.

12. 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.

13. The lost circulation material of claim 1, wherein, The plugging agent further comprises one or more of an antioxidant and a fluorescent agent.

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