A high-temperature proton exchange membrane containing an imidazole-containing long-chain crosslinking agent and a preparation method thereof

Abstract

The present invention provides a long-chain imidazole-containing crosslinking agent, a high-temperature proton exchange membrane, and a preparation method thereof. The structural formula of the long-chain imidazole-containing crosslinking agent is: The polybenzimidazole high-temperature proton exchange membrane crosslinked with this crosslinking agent not only has good thermodynamic properties, mechanical properties, and high proton conductivity, but also has excellent antioxidant stability and durability, and has good application prospects in the field of high-temperature proton exchange membrane fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and particularly relates to a polybenzimidazole high-temperature proton exchange membrane cross-linked with an imidazole long-chain cross-linking agent, a membrane electrode and a preparation method thereof. Background Art

[0002] Fuel cells have attracted considerable attention due to their clean, pollution-free nature. High-temperature proton exchange membrane fuel cells (HT-PEMFCs) operate at temperatures between 140°C and 200°C. High temperatures enable faster electrode reaction kinetics, a simpler electrode interface, and increased resistance to CO poisoning, making the integration of reforming hydrogen production and fuel cell power generation feasible. HT-PEMFCs have become a research hotspot in the industry.

[0003] Polybenzimidazole (PBI) primarily refers to linear heterocyclic polymers containing benzimidazole groups in their repeating units. There are numerous types of PBI, including ABPBI, OPBI, s-PBI, p-PBI, m-PBI, and py-PBI. PBI exhibits excellent thermal stability and is a preferred matrix material for HT-PEMs due to its unique thermal stability. However, conventional polybenzimidazole high-temperature proton exchange membranes currently suffer from insufficient proton conductivity, low mechanical strength, and the tendency for phosphate loss, making them still far from practical engineering applications.

[0004] Therefore, the preparation of PBI membranes with good mechanical properties, high proton conductivity and high phosphoric acid retention capacity has received increasing attention. Summary of the Invention

[0005] To address the problems of insufficient mechanical properties and proton conductivity of PBI as a high-temperature proton exchange membrane, as well as its low phosphate retention capacity, the inventors conducted intensive research and provided a high-temperature proton exchange membrane containing a long-chain imidazole crosslinker and a preparation method thereof. The polybenzimidazole high-temperature proton exchange membrane cross-linked with this crosslinker not only has good thermodynamic properties, mechanical properties, and high proton conductivity, but also has excellent antioxidant stability and durability, and has good application prospects in the field of high-temperature proton exchange membrane fuel cells.

[0006] The technical solutions provided by the present invention are as follows:

[0007] In the first aspect, a long-chain imidazole crosslinking agent has the following structural formula:

[0008]

[0009] In a second aspect, a method for preparing an imidazole-containing long-chain crosslinking agent comprises:

[0010] reacting 3,3'-4,4'-diaminobenzidine and 2,2-bis(4-carboxyphenyl)hexafluoropropane under an inert atmosphere to obtain a crosslinker precursor;

[0011] 4-Hydroxymethylbenzoic acid was further added to the reaction system, and the reaction was continued under the same conditions to synthesize a cross-linking agent;

[0012] After the reaction is completed, the reaction solution is mixed with deionized water, and the precipitated solid is neutralized with an inorganic weak base, washed, and dried to obtain a solid cross-linking agent.

[0013] In a third aspect, a high-temperature proton exchange membrane is obtained by cross-linking with an imidazole-containing long-chain cross-linking agent, wherein the substrate of the high-temperature proton exchange membrane is a polybenzimidazole material selected from one or more of OPBI, F6PBI, m-PBI, and p-PBI.

[0014] In a fourth aspect, a method for preparing a high-temperature proton exchange membrane obtained by cross-linking with an imidazole-based long-chain cross-linking agent comprises:

[0015] dissolving the cross-linking agent and polybenzimidazole powder in a polar aprotic organic solvent respectively;

[0016] The crosslinking agent solution and the polybenzimidazole solution are mixed evenly, and a film is formed by a casting method, the solvent is evaporated and a crosslinking reaction is carried out to obtain a high-temperature proton crosslinked membrane dry film;

[0017] The high-temperature proton cross-linked membrane dry film is immersed in phosphoric acid to obtain a high-temperature proton exchange membrane immersed in phosphoric acid.

[0018] In the fifth aspect, a membrane electrode comprises a gas diffusion layer, a catalytic layer, and a proton exchange membrane in sequence from both sides to the middle. The proton exchange membrane is the high-temperature proton exchange membrane obtained by cross-linking the long-chain imidazole cross-linking agent described in the third aspect.

[0019] In a sixth aspect, a fuel cell comprises the membrane electrode according to the fifth aspect.

[0020] The present invention provides an imidazole-containing long-chain crosslinking agent, a high-temperature proton exchange membrane, and a preparation method thereof, which have the following beneficial effects:

[0021] (1) The present invention provides an imidazole-containing long-chain crosslinking agent, which introduces additional basic groups into the crosslinking structure, effectively increasing the phosphate adsorption capacity of the polybenzimidazole membrane and thus improving the proton conductivity;

[0022] (2) The present invention provides an imidazole-containing long-chain crosslinking agent, which introduces additional fluorine-containing groups into the crosslinking structure, effectively improving the antioxidant stability and durability of the polybenzimidazole film;

[0023] (3) The imidazole-containing long-chain crosslinking agent provided by the present invention has a long chain structure and a large group volume, which can improve the problem of poor solubility of cross-linked polybenzimidazole;

[0024] (4) The high-temperature proton exchange membrane provided by the present invention is modified by cross-linking and introducing a long-chain imidazole cross-linking agent into polybenzimidazole, thereby greatly improving the mechanical properties and dimensional stability of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 to 3 and the tensile stress-strain curves of Examples 1 to 3 and Comparative Examples 1 to 3;

[0026] Figure 2 is the proton conductivity of Examples 1 to 3 and Comparative Examples 1 to 3;

[0027] Figure 3 The performance of the membrane electrode cells assembled from Examples 1 to 3 and Comparative Examples 1 to 3 was tested;

[0028] Figure 4 The following are the Fenton test data of the antioxidant stability of Example 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0029] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0030] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0031] For HT-PEM, traditional cross-linking can improve the mechanical properties of PBI membranes due to the strong bonds between PBI molecules. However, this strong bond also hinders the absorption of PA, resulting in a decrease in proton conductivity.

[0032] Introducing additional alkaline phosphate affinity sites into the crosslinker can effectively improve phosphate absorption, increasing proton conductivity and phosphate retention. Furthermore, introducing fluorinated sites into the crosslinker can enhance the antioxidant stability and durability of the crosslinked membrane. The long-chain crosslinker structure and large group volume can improve the poor solubility of crosslinked polybenzimidazole.

[0033] Based on this, the present invention provides an imidazole-containing long-chain crosslinking agent, which contains a benzimidazole ring, a trifluoromethyl group, and a long-chain aromatic ring structure, and the terminal group is p-hydroxymethylbenzene; the structure is shown in Formula 1:

[0034]

[0035] The preparation method of the imidazole-containing long-chain cross-linking agent comprises the following steps:

[0036] Step S1: using 3,3'-4,4'-diaminobenzidine and 2,2-bis(4-carboxyphenyl)hexafluoropropane as raw materials and polyphosphoric acid (PPA) as a reaction solvent, reacting at 180-200° C., such as 190° C., under an inert atmosphere, such as nitrogen, to obtain a crosslinker precursor, as shown in the following formula:

[0037]

[0038] Step S2: After step S1 is completed, 4-hydroxymethylbenzoic acid (capping agent) is added to the reaction system and the reaction is continued under the same conditions, as shown in the following formula:

[0039]

[0040] Step S3: After the reaction is completed, the reaction solution is slowly poured into deionized water to precipitate solids. In order to neutralize excess acid, an inorganic weak base such as a saturated sodium bicarbonate aqueous solution is used for neutralization reaction; the neutralized solids are washed several times and placed in an oven for drying.

[0041] As a preferred embodiment, in step S1, the molar ratio of the reactants 3,3'-4,4'-diaminobenzidine to 2,2-bis(4-carboxyphenyl)hexafluoropropane is (2-2.2):1, such as 2:1.

[0042] As a preferred embodiment, in step S1, the mass of the reactants accounts for 0.5% to 1.5% of the mass of the polyphosphoric acid.

[0043] As a preferred embodiment, in step S2, the molar ratio of the added 4-hydroxymethylbenzoic acid to 2,2-bis(4-carboxyphenyl)hexafluoropropane is (2-2.2):1, such as 2:1.

[0044] As a preferred embodiment, in step S3, the drying temperature is 60-100° C., and the drying time is 12-24 hours.

[0045] As a preferred embodiment, in step S2, 4-hydroxymethylbenzoic acid is used as the end-capping agent. Compared with the use of 4-chloromethylbenzoic acid, the reaction product generates Cl - Caused by Cl - Ionic pollution, whose product is water, is easy to remove.

[0046] The present invention also provides a high-temperature proton exchange membrane obtained by cross-linking the above-mentioned imidazole-containing long-chain cross-linking agent. The substrate of the high-temperature proton exchange membrane is a polybenzimidazole material (PBI), including but not limited to one or more of OPBI, F6PBI, m-PBI, and p-PBI.

[0047] The method for preparing a high-temperature proton exchange membrane obtained by cross-linking with an imidazole-containing long-chain cross-linking agent comprises the following steps:

[0048] Step S1, dissolving a cross-linking agent and polybenzimidazole powder in a polar aprotic organic solvent respectively;

[0049] In this step, the aprotic organic solvent is at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF).

[0050] In this step, the molar fraction of the cross-linking agent in the polybenzimidazole repeating unit is 5% to 15%.

[0051] Step S2, mixing the crosslinker solution and the polybenzimidazole solution evenly, and forming a film by a casting method, such as forming a film on a clean glass plate;

[0052] Step S3, placing the glass plate coated with the proton membrane solution in an oven to evaporate the solvent and perform a cross-linking reaction to obtain a high-temperature proton cross-linked membrane dry film;

[0053] In this step, the oven treatment temperature is 60-100° C. for 12-24 hours, such as 80° C. for 12 hours for drying, and 150-180° C. for 0.5-3 hours, such as 160° C. for 1 hour, to complete the cross-linking reaction.

[0054] Step S4: soaking the high-temperature proton cross-linked membrane dry film in 65wt% to 85wt% phosphoric acid at 80 to 120° C. for 3 to 5 hours to obtain a high-temperature proton exchange membrane soaked in phosphoric acid.

[0055] The present invention also provides a membrane electrode, which includes a gas diffusion layer, a catalytic layer, and a proton exchange membrane in sequence from both sides to the middle. The proton exchange membrane is the high-temperature proton exchange membrane obtained by cross-linking the above-mentioned imidazole-containing long-chain crosslinking agent.

[0056] The present invention also provides a fuel cell comprising the membrane electrode described above.

[0057] Example

[0058] Example 1

[0059] 1 mmol of 3'3-4'4-diaminobenzidine (DAB) and 0.5 mmol of 2,2-bis(4-carboxyphenyl)hexafluoropropane monomer were added to a three-necked flask, followed by 50 g of PPA. After nitrogen protection, the mixture was heated to 190°C and allowed to react for 12 hours to obtain a crosslinker precursor. 1 mmol of 4-hydroxymethylbenzoic acid was then added to the reaction solution, and the reaction continued for 6 hours. After the reaction was complete, the hot reaction solution was poured into deionized water. The precipitated solid was neutralized with saturated sodium bicarbonate aqueous solution to a neutral pH, then rinsed several times with deionized water and methanol, and dried in an oven at 80°C for 24 hours to obtain a long-chain imidazole-containing crosslinker.

[0060] Take 0.25mmol of the above cross-linker, add 5g of NMP, and heat to 80℃ to dissolve. Take 5mmol of OPBI powder, add 25g of NMP, and heat to 80℃ to dissolve. Mix the cross-linker solution and OPBI solution and stir evenly. Use a sliding scraper on a glass plate to form a uniform film, and dry it completely in an 80℃ oven. Then treat it in a vacuum oven at 160℃ for 1h to complete the reaction between OPBI and the cross-linker. The resulting composite cross-linked membrane was soaked in 85wt% phosphoric acid at 100℃ for 3h and then taken out to obtain the desired composite high-temperature proton exchange membrane named cl5%-OPBI.

[0061] Example 2

[0062] The polybenzimidazole high-temperature proton exchange membrane cross-linked with an imidazole long-chain cross-linking agent in this embodiment is different from that in Example 1 in that the amount of the cross-linking agent added is 0.5 mmol, and the obtained cross-linked membrane is named cl10%-OPBI.

[0063] Example 3

[0064] The polybenzimidazole high-temperature proton exchange membrane cross-linked with an imidazole long-chain cross-linking agent in this embodiment is different from that in Example 1 in that the amount of the cross-linking agent added is 0.75 mmol, and the obtained cross-linked membrane is named cl15%-OPBI.

[0065] Comparative Example 1

[0066] 0.5 mmol of 3'3-4'4-diaminobenzidine (DAB) and 0.5 mmol of dicarboxydiphenyl ether monomer were added to a three-necked flask, and 50 g of polyphosphoric acid (PPA) was added. After nitrogen protection, the mixture was heated to 140°C and reacted for 4 hours to obtain a polyether benzimidazole (OPBI) solution. The hot solution was poured into deionized water, and the precipitated solid was neutralized with saturated sodium bicarbonate aqueous solution to a neutral pH, then rinsed several times with deionized water and methanol, and dried in an oven at 80°C for 24 hours to obtain OPBI solid.

[0067] 0.5 g of the above OPBI solid was taken, 25 g of N-methylpyrrolidone (NMP) was added, and the mixture was heated to 70° C. to dissolve the mixture, thereby obtaining an OPBI polymer solution.

[0068] The OPBI polymer was formed into a film on a glass plate and placed in an oven to evaporate the solvent to obtain an OPBI proton exchange membrane.

[0069] Comparative Example 2

[0070] The polybenzimidazole high-temperature proton exchange membrane in this comparative example is different from that in Example 1 in that p-dichloromethylbenzene is used as a cross-linking agent.

[0071] Comparative Example 3

[0072] The polybenzimidazole high-temperature proton exchange membrane in this comparative example differs from that in Example 1 in that 4-chloromethylbenzoic acid is used as an end-capping agent to prepare a cross-linking agent, and the cross-linking agent has the following structural formula:

[0073]

[0074] Test example

[0075] The composite membranes with different doping amounts obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were treated with phosphoric acid and then subjected to the following tests.

[0076] With reference to GB / T 20042.3-2022, the proton conductivity of the obtained high-temperature proton exchange membrane was tested. The specific operating conditions were: at a temperature of 110°C to 180°C and a humidity of 0%, a conductivity test device was connected to an electrochemical impedance spectroscopy (EIM) instrument.

[0077] With reference to GB / T 20042.5-2009, polarization curve tests were conducted on the obtained high-temperature proton exchange membrane fuel cell. The specific operating conditions were: single cell operating temperature of 160°C, pure hydrogen feed for the anode, atmospheric pressure air feed for the cathode, and a cathode / anode feed ratio of 4 / 1.

[0078] Figure 1 are the tensile stress-strain curves of Examples 1 to 3 and Comparative Examples 1 to 3; Figure 1 It can be seen that the mechanical properties of the cross-linked film increase with the increase of the cross-linking degree. When the cross-linking degree is 15%, the maximum tensile strength is 12.9 MPa. The tensile strengths of Comparative Examples 1 to 3 are all lower than those of Examples 1-3.

[0079] Figure 2 is the proton conductivity of Examples 1 to 3 and Comparative Examples 1 to 3; Figure 2It can be seen that after using the conventional cross-linking agent, the proton conductivity of Comparative Example 2 actually decreases, and is only 57.6 mS / cm at 160°C, which is lower than the uncross-linked membrane of Comparative Example 1 (75.1 mS / cm). The proton conductivities of Comparative Examples 1 to 3 are all lower than those of Examples 1 to 3, among which Example 1 has the highest proton conductivity at 160°C, which is 143.1 mS / cm, indicating that the cross-linking agent has the effect of improving the proton conductivity of the proton membrane, and the proton conductivity of Examples 1 to 3 has a similar improvement.

[0080] Figure 3 The performance of the membrane electrode cells assembled from Examples 1 to 3 and Comparative Examples 1 to 3 was tested; Figure 3 It can be seen that the cross-linked membranes have higher battery discharge performance. The peak power densities of Examples 1 to 3 reach 579.2, 531.3 and 529.1 mW / cm, respectively. 2 , which is due to its high mechanical strength and reduced ohmic internal resistance brought about by proton conductivity.

[0081] Figure 4 The antioxidant stability Fenton test of Example 3 and Comparative Examples 1 to 3 is as follows; Figure 4 It can be seen that the stronger the antioxidant stability of the membrane, the greater the remaining mass after the Fenton test. The cross-linking agent containing F elements can effectively improve the antioxidant stability of the proton membrane, and it increases with the increase of the degree of cross-linking. Example 3 retains 87.6% of the mass after 96h of the Fenton test, while Comparative Example 1 only has 68.2%, and the antioxidant capacity is significantly improved. The present invention is described in detail above with reference to specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, the technical solution of the present invention and its implementation methods can be subjected to a variety of equivalent replacements, modifications or improvements, which all fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the appended claims.

[0082] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. An imidazole-containing long-chain crosslinking agent, characterized in that: The structural formula is as follows:

2. A method for preparing the imidazole-containing long-chain crosslinking agent according to claim 1, characterized in that: include: reacting 3,3'-4,4'-diaminobenzidine and 2,2-bis(4-carboxyphenyl)hexafluoropropane under an inert atmosphere to obtain a crosslinker precursor; 4-Hydroxymethylbenzoic acid was further added to the reaction system, and the reaction was continued under the same conditions to synthesize a cross-linking agent; After the reaction is completed, the reaction solution is mixed with deionized water, and the precipitated solid is neutralized with an inorganic weak base, washed, and dried to obtain a solid cross-linking agent.

3. The method for preparing an imidazole-containing long-chain crosslinking agent according to claim 2, wherein: The molar ratio of the 3,3'-4,4'-diaminobenzidine to 2,2-bis(4-carboxyphenyl)hexafluoropropane is (2-2.2):

1.

4. The method for preparing an imidazole-containing long-chain crosslinking agent according to claim 2, wherein: The molar ratio of the added 4-hydroxymethylbenzoic acid to 2,2-bis(4-carboxyphenyl)hexafluoropropane is (2-2.2):

1.

5. A high-temperature proton exchange membrane obtained by cross-linking with an imidazole-containing long-chain cross-linking agent according to claim 1, characterized in that: The substrate of the high-temperature proton exchange membrane is a polybenzimidazole material, which is selected from one or more of OPBI, F6PBI, m-PBI, and p-PBI.

6. A method for preparing a high-temperature proton exchange membrane obtained by cross-linking with an imidazole-containing long-chain cross-linking agent according to claim 1, characterized in that: include: dissolving the cross-linking agent and polybenzimidazole powder in a polar aprotic organic solvent respectively; The crosslinking agent solution and the polybenzimidazole solution are mixed evenly, and a film is formed by a casting method, the solvent is evaporated and a crosslinking reaction is carried out to obtain a high-temperature proton crosslinked membrane dry film; The high-temperature proton cross-linked membrane dry film is immersed in phosphoric acid to obtain a high-temperature proton exchange membrane immersed in phosphoric acid.

7. The method for preparing a high-temperature proton exchange membrane according to claim 6, characterized in that: The aprotic organic solvent is at least one of NMP, DMAc, DMSO, and DMF.

8. The method for preparing a high-temperature proton exchange membrane according to claim 6, characterized in that: The mole fraction of the cross-linking agent in the polybenzimidazole repeating unit is 5% to 15%.

9. A membrane electrode, characterized in that From both sides to the middle, it includes a gas diffusion layer, a catalytic layer, and a proton exchange membrane in sequence. The proton exchange membrane is the high-temperature proton exchange membrane obtained by cross-linking with an imidazole-containing long-chain cross-linking agent as claimed in claim 6.

10. A fuel cell, characterized in that: A membrane electrode according to claim 9.

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