Crosslinking type benzoxazine water electrolysis proton exchange membrane with excellent membrane-forming property and preparation method and application of crosslinking type benzoxazine water electrolysis proton exchange membrane

Abstract

The invention provides a cross-linked benzoxazine water electrolysis proton exchange membrane with excellent membrane-forming property, and a preparation method and application of the cross-linked benzoxazine water electrolysis proton exchange membrane. The preparation method of the proton exchange membrane comprises the following steps: dissolving a benzoxazine oligomer in a solvent, adding an isocyanate compound, uniformly mixing, and forming a membrane to obtain the cross-linked benzoxazine proton exchange membrane for water electrolysis. The proton exchange membrane disclosed by the invention has good membrane-forming property, toughness and mechanical strength, high proton conductivity and low cost; the material shows excellent performance when applied to proton exchange membrane water electrolysis, and has a huge application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, a preparation method thereof, and an application thereof. Background Art

[0002] Water electrolysis powered by renewable energy is an important way to produce green hydrogen. Among various water electrolysis technologies, proton exchange membrane water electrolysis (PEM-WE) stands out due to its high current density, high-purity and high-pressure hydrogen output, and rapid response, which is conducive to perfect combination with renewable energy. In addition, using proton exchange membrane (PEM) technology for water electrolysis can also improve the purity of hydrogen because the PEM is a separation membrane that allows proton conduction while hindering the transport of oxygen (from the anode to the cathode).

[0003] Perfluorosulfonic acid polymer membranes represented by Nafion are well-known for their excellent ionic conductivity and have established themselves in the commercial PEM market. However, due to their high cost, environmental pollution caused by fluorine elements, high gas permeability (especially H2), and reduced mechanical stability at high temperatures (T>80 °C), it is still necessary to continuously explore new alternative membrane materials. When PEM-WE operates at low current density, the oxygen production rate will decrease, resulting in an increase in hydrogen contamination in oxygen. This situation will bring serious safety risks, especially during operation. If the hydrogen concentration in oxygen exceeds 4%, it will lead to fire and explosion risks. To reduce these risks, the thickness of the Nafion membrane is usually designed to be about 100 μm or greater. However, increasing the PEM thickness will lead to an increase in membrane resistance, thereby affecting the electrolysis efficiency. Therefore, there is an urgent need to develop a new electrolyte membrane with excellent gas barrier properties and low resistance.

[0004] Chinese patent document CN103044348A discloses a sulfonic acid group-containing benzoxazine resin. The invention uses a sulfonic acid group-containing phenol, amine compound, and formaldehyde as raw materials, and through the Mannich reaction, synthesizes a series of sulfonic acid group-containing benzoxazine monomers. Finally, the benzoxazine monomers are heated to undergo ring-opening polymerization to form a sulfonic acid group-containing polybenzoxazine film. This synthesis route directly introduces sulfonic acid groups onto the aromatic benzene ring, endowing the product with high thermal stability, strong acid resistance, good dimensional stability, and alcohol resistance, and has great application prospects in the field of proton exchange membrane fuel cells. However, the film-forming property and toughness of the film obtained by this invention need to be improved, and it has not been applied to the field of proton exchange membrane water electrolysis.

[0005] Therefore, it is of great significance to develop a new electrolyte membrane with excellent toughness, good film-forming property, excellent gas barrier properties, low resistance, and low cost to improve the efficiency of water electrolysis. Summary of the Invention

[0006] Aiming at the deficiencies existing in the prior art, the present invention provides a cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, and its preparation method and application. The benzoxazine oligomer containing acidic groups and the isocyanate compound are subjected to a cross-linking reaction to obtain a cross-linked polybenzoxazine film containing acidic groups. The proton exchange membrane of the present invention has good film-forming property, toughness and mechanical strength, high proton conductivity and low cost, and shows excellent performance when applied to proton exchange membrane water electrolysis, and has great application prospects.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method of a cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, comprising the steps of: dissolving the benzoxazine oligomer in a solvent, adding the isocyanate compound, mixing evenly, and forming a film to obtain a cross-linked benzoxazine proton exchange membrane for water electrolysis;

[0009] The benzoxazine oligomer has the following repeating structural units:

[0010]

[0011] Wherein, R1 is selected from -SO3Na or -COOH; R2 is selected from -CH2CH2OH, -CH2CH(CH3)OH, -CH(CH2OH)CH2OH or CH2CH2OCH2CH2OH.

[0012] Preferably according to the present invention, the solvent is one of water, N,N-dimethylacetamide, tetrahydrofuran, chloroform, acetone, toluene, N-methylpyrrolidone, dimethyl sulfoxide or dioxane; the mass ratio of the benzoxazine oligomer to the volume of the solvent is 0.1-1 g / mL.

[0013] Preferably according to the present invention, the isocyanate compound is one of hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, tetramethylxylylene diisocyanate, dicyclohexylmethane diisocyanate or xylylene diisocyanate.

[0014] Preferably according to the present invention, the percentage of the molar amount of the isocyanate group in the isocyanate compound to the molar amount of the hydroxyl group in the benzoxazine oligomer is 40%-70%, preferably 40%-50%, and further preferably 40%.

[0015] Preferably according to the present invention, the film-forming conditions are as follows: keep warm at 70 - 90°C for 4 - 8 h, keep warm at 90 - 110°C for 2 - 6 h, keep warm at 110 - 130°C for 1 - 3 h, keep warm at 130 - 150°C for 1 - 3 h, and keep warm at 150 - 170°C for 1 - 3 h. The film-forming conditions are as follows: keep warm at 80°C for 6 h, keep warm at 100°C for 4 h, keep warm at 120°C for 2 h, keep warm at 140°C for 2 h, and keep warm at 160°C for 2 h.

[0016] Preferably according to the present invention, the preparation method of the benzoxazine oligomer includes the steps: the benzoxazine monomer is polymerized to obtain the benzoxazine oligomer; the benzoxazine monomer has the following structure:

[0017]

[0018] Among them, R1 is selected from -SO3Na or -COOH; R2 is selected from -CH2CH2OH, -CH2CH(CH3)OH, -CH(CH2OH)CH2OH or CH2CH2OCH2CH2OH.

[0019] Preferably, the polymerization reaction temperature is 100 - 200°C, the polymerization reaction time is 10 - 20 h, and the polymerization reaction is carried out under the protection of a protective gas; the protective gas is nitrogen or argon.

[0020] Preferably, the preparation method of the benzoxazine monomer includes the steps:

[0021] The phenolic compound, amine compound and paraformaldehyde are fully dispersed in a solvent, reacted, and then precipitated, washed and rotary evaporated to obtain the benzoxazine monomer; the phenolic compound is one of sodium p-hydroxybenzenesulfonate or p-carboxyphenol; the amine compound is one of ethanolamine, 2-amino-1-propanol, serine alcohol or diethanolamine.

[0022] Further preferably, the solvent is selected from one of water, N,N-dimethylformamide, tetrahydrofuran, chloroform, acetone, toluene, N-methylpyrrolidone, dimethyl sulfoxide or dioxane; the mass ratio of the phenolic compound to the volume of the solvent is 1:4 - 6 g / mL.

[0023] Further preferably, the molar ratio of the phenolic compound, amine compound and paraformaldehyde is 1:1:2. The addition amount of paraformaldehyde can promote the forward reaction and thus improve the synthesis yield.

[0024] Further preferably, the reaction temperature is 100 - 160°C, the reaction time is 4 - 8 h, and the reaction is carried out under reflux and stirring conditions.

[0025] A crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property is prepared by the above method.

[0026] According to the present invention, the schematic structure of the proton exchange membrane is as follows:

[0027]

[0028] Wherein, R1 is selected from -SO3Na or -COOH; R3 is selected from -CH2CH-, -CH2CH(CH3)-, -CH(CH2-)CH2- or -CH2CH2OCH2CH2-;

[0029] R4 is a non-isocyanate group in the corresponding isocyanate compound.

[0030] Application of the above crosslinked benzoxazine proton exchange membrane with excellent film-forming property in electrolyzed water.

[0031] The technical features and beneficial effects of the present invention are as follows:

[0032] 1. The present invention uses phenol and amine compounds containing sulfonic acid groups or carboxyl groups and paraformaldehyde as raw materials, and successfully synthesizes a series of benzoxazine monomers containing sulfonic acid groups or carboxyl groups through the Mannich reaction. The benzoxazine monomers are prepared into oligomers by a thermal ring-opening method. The oligomers and isocyanate compounds are crosslinked to obtain a urethane bond-crosslinked benzoxazine proton exchange membrane. The raw materials used in the present invention are cheap and easily available, and it is expected to obtain high-performance and low-cost proton exchange membrane materials.

[0033] 2. The present invention crosslinks the benzoxazine oligomers by using urethane bonds, endowing the membrane with good film-forming property and mechanical properties such as toughness, making it more resistant to damage and deformation under high-pressure working conditions. Based on the flexible chain structure of hexamethylene diisocyanate, the prepared membrane can be folded and unfolded arbitrarily without damage, and the elongation at break can reach 120%, and the tensile strength can reach 36 MPa. The crosslinked structure improves the dimensional stability and mechanical strength of the membrane; in an 80°C water environment, the dimensional swelling rate is as low as 13.9%.

[0034] 3. The present invention introduces a crosslinked structure to make the molecular chains have a more compact structure, making it difficult for gases to migrate in the membrane, with a lower gas permeability, thereby improving the gas barrier property. At the same time, the proton exchange membrane of the present invention has low resistance performance.

[0035] 4. The urethane bonds introduced in the present invention are also easy to form hydrogen bonds with water, having better hydrophilic and water retention effects. In an 80°C water environment, the water absorption rate is 65%.

[0036] 5. The proton exchange membrane structure of the present invention contains sulfonic acid or carboxyl groups, which is beneficial to improving the proton conductivity. The proton conductivity of the thin film can reach 90 mS / cm at 80°C and 100% relative humidity, and at 100°C, its conductivity is as high as 115 mS / cm.

[0037] 6. The proton exchange membrane of the present invention exhibits excellent performance in water electrolysis and has great application prospects in the field of water electrolysis. The test results of water electrolysis with this membrane as a component show that under the test conditions of 80 °C, the open circuit voltage of a single electrolytic cell is 1.55 V, and the maximum output current density at 1.95 V is 1.29 A / cm 2 , higher than 1.02 A / cm 2 of the commercial Nafion 115 membrane; the lowest concentration of H2 in O2 during its 24-hour operation is 563 ppm, far lower than 965 ppm of the commercial Nafion 115 membrane; at a current of 0.5 A, the prepared proton exchange membrane can operate stably for more than 240 hours. Description of the Drawings

[0038] Figure 1 HNMR spectrum of the benzoxazine monomer obtained in Example 1 1 ;

[0039] Figure 2 FT-IR spectrum of the benzoxazine monomer obtained in Example 1

[0040] Figure 3 HNMR spectrum of the benzoxazine oligomer obtained in Example 1 1 ;

[0041] Figure 4 FT-IR spectrum of the benzoxazine oligomer obtained in Example 1

[0042] Figure 5 Digital photo of the proton exchange membrane obtained in Example 1

[0043] Figure 6 FT-IR spectrum of the proton exchange membrane obtained in Example 1

[0044] Figure 7 DMA spectrum of the proton exchange membrane obtained in Example 1

[0045] Figure 8 TGA spectrum of the proton exchange membrane obtained in Example 1

[0046] Figure 9 Stress-strain curve of the proton exchange membrane obtained in Example 1

[0047] Figure 10 Polarization curve of the proton exchange membrane obtained in Example 1 and the commercial Nafion 115 membrane

[0048] Figure 11 H2 barrier property diagram of the proton exchange membrane obtained in Example 1.

[0049] Figure 12Electrolytic water durability test chart of the proton exchange membrane obtained in Example 1. Detailed implementation manners

[0050] The present invention will be further described below through specific examples, but the protection scope of the present invention is not limited thereto.

[0051] Example 1

[0052] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, comprising the steps:

[0053] (1) The sodium p-hydroxybenzenesulfonate-diethanolamine type benzoxazine monomer has the following structure:

[0054]

[0055] The preparation method is as follows: Dissolve sodium p-hydroxybenzenesulfonate, diethanolamine, and paraformaldehyde in toluene according to a molar ratio of 1:1:2. The mass ratio of sodium p-hydroxybenzenesulfonate to the volume of the solvent toluene is 1:5 g / mL, and reflux and stir the reaction at 100 °C for 6 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a yellow powder. (Yield 85%)

[0056] Test the 1 1H NMR of the sulfonic acid group-containing benzoxazine monomer obtained in this example, 1 The 1H NMR spectrum is as Figure 1 shown, and the NMR data are as follows:

[0057] 1 1H NMR (400 MHz, DMSO-d6, ppm): 4.85 (N-CH2-O), 3.98 (Ar-CH2-N), 3.57 (CH2-CH2-OH), 3.48 (CH2-OH), 3.41 (O-CH2-CH2), 2.82 (N-CH2-CH2).

[0058] Test the FT-IR of the sulfonic acid group-containing benzoxazine monomer obtained in this example. The FT-IR spectrum is as Figure 2 shown, and the FT-IR data are as follows:

[0059] IR (KBr, cm -1 ) 930 cm -1 (oxazine ring), 1195 cm -1 (C-O-C), 1488 cm -1 (trisubstituted benzene).

[0060] (2) The benzoxazine oligomer based on sodium p - hydroxybenzenesulfonate and diethanolamine has the following structure:

[0061]

[0062] The preparation method is as follows:

[0063] Add 25 g of sodium p - hydroxybenzenesulfonate - diethanolamine - type benzoxazine monomer to a 50 - mL four - necked flask. Under an Ar atmosphere and with mechanical stirring, gradually heat up to 150 °C and react at this temperature for 12 h. After the reaction is completed, cool to room temperature to obtain a yellow - brown solid, which is the benzoxazine oligomer.

[0064] Test the sulfonic - acid - group - containing benzoxazine oligomer obtained in this example for its 1 1H NMR spectrum as Figure 3 shown. The NMR data are as follows:

[0065] 1 1H NMR (400 MHz, DMSO - d6, ppm): 3.42 (CH2 - CH2 - OH), 3.36 (CH2 - OH), 3.25 (O - CH2 - CH2), 2.73 (N - CH2 - CH2).

[0066] Test the FT - IR of the sulfonic - acid - group - containing benzoxazine oligomer obtained in this example. The FT - IR spectrum is as Figure 4 shown. The FT - IR data are as follows:

[0067] IR (KBr, cm -1 ) 3450 cm -1 (- OH), and 1470 cm -1 (tetrasubstituted benzene).

[0068] (3) Use hexamethylene diisocyanate as a cross - linker to cross - link the benzoxazine oligomer based on sodium p - hydroxybenzenesulfonate and diethanolamine to prepare a proton exchange membrane

[0069] Hexamethylene diisocyanate has the following structure:

[0070]

[0071] The preparation method is as follows:

[0072] Take 3.2 g (20 mmol -OH) of the benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and diethanolamine in a 25 mL glass bottle, add 10 mL of DMAc, dissolve the oligomer into a yellowish-brown transparent solution, add 0.67 g (8 mmol -CNO) of hexamethylene diisocyanate thereto, mix evenly, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h. Finally, a yellow transparent film is obtained, as Figure 5 shown. Based on the flexible chain structure of hexamethylene diisocyanate, the prepared film can be folded and unfolded arbitrarily without damage.

[0073] The IR spectrum of the transparent film PUBZ obtained in this example is as Figure 6 shown. The characteristic peak of -CNO in HDI is at 2250 cm -1 ; for the final cured product PUBZ, the characteristic peak of -CNO at 2250 cm -1 almost disappears, and the hydroxyl peak weakens significantly at 3200 - 3600 cm -1 ; meanwhile, a strong band belonging to the carbonyl characteristic peak in urethane appears at 1703 cm -1 , indicating that urethane bonds have been formed.

[0074] The DMA of the transparent film obtained in this example is as Figure 7 shown. As Figure 7 can be seen, the glass transition temperature corresponding to the maximum value of Tanδ is 40 °C,

[0075] The TGA curve of the transparent film obtained in this example is as Figure 8 shown. As Figure 8 can be seen, T d5 is 280 °C, T d10 is 300 °C, and the char yield at 800 °C under N2 atmosphere is 21%. It has good thermal stability.

[0076] The stress-strain curve of the transparent film obtained in this example is as Figure 9 shown. As can be seen from the figure, the film has excellent mechanical properties, with an elongation at break of up to 120% and a tensile strength of 36 MPa.

[0077] The proton conductivity of the transparent thin film obtained in this example can reach 90 mS / cm at 80 °C and 100% relative humidity, and its conductivity is as high as 115 mS / cm at 100 °C.

[0078] Detection of water absorption rate (WU) and swelling rate (SR): Before the test, the membrane was dried in a vacuum oven at 120 °C until a consistent weight was reached. Then, the initial mass and dimensions of the membrane in the dry state were recorded. Subsequently, the membrane was immersed in deionized water for 24 hours (at 25 °C and 80 °C). After the immersion time ended, the residual water on the membrane surface was immediately removed, and the resulting mass and dimensions were recorded. The calculations of WU and SR were performed using the following formulas respectively:

[0079]

[0080] Above, W wet and W dry represent the mass of the dry membrane and the wet membrane respectively. L dry and L wet represent the dimensions of the dry membrane and the wet membrane respectively.

[0081] In terms of reliability and durability, the proton exchange membrane must have excellent dimensional stability. This is particularly important for proton exchange membrane water electrolysis because excessive water absorption may cause unpredictable changes in the dimensions of the proton exchange membrane. During actual operation, the membrane is in direct contact with high-temperature liquid water (80 °C), and the membrane will undergo excessive swelling, and delamination will occur between the membrane layer and the catalyst layer, thereby reducing the durability of the proton exchange membrane. Therefore, the proton exchange membrane must balance its water absorption and swelling properties. At 80 °C, the water absorption rate of the proton exchange membrane of the present invention is 65%, while that of Nafion 115 is 21%. The dimensional swelling rate of the proton exchange membrane of the present invention is as low as 13.9%, while that of Nafion 115 is 38.6%. At 80 °C, the dimensional stability of the proton exchange membrane of the present invention is significantly better than that of commercial Nafion 115. This characteristic is very beneficial for the application of the proton exchange membrane of the present invention in proton exchange membrane water electrolysis. In practical applications, proton exchange membrane water electrolysis usually operates at 80 °C.

[0082] Example 2

[0083] A preparation method of a cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property is as described in Example 1, except that: in step (3), the dosage of hexamethylene diisocyanate is such that the content of -CNO is 10 mmol; other steps and conditions are the same as in Example 1.

[0084] Example 3

[0085] A preparation method of a cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property is as described in Example 1, except that: in step (3), the dosage of hexamethylene diisocyanate is such that the content of -CNO is 12 mmol; other steps and conditions are the same as in Example 1.

[0086] Example 4

[0087] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, as described in Example 1, except that in step (3), the amount of hexamethylene diisocyanate is such that the content of -CNO is 14 mmol; other steps and conditions are the same as in Example 1.

[0088] Example 5

[0089] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, comprising the steps:

[0090] (1) The sodium p-hydroxybenzenesulfonate-ethanolamine type benzoxazine monomer has the following structure:

[0091]

[0092] The preparation method is as follows: Dissolve sodium p-hydroxybenzenesulfonate, ethanolamine, and paraformaldehyde in toluene at a molar ratio of 1:1:2. The mass ratio of sodium p-hydroxybenzenesulfonate to the volume of the solvent toluene is 1:5 g / mL. Stir and react under reflux at 100 °C for 8 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield 82%)

[0093] (2) The benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and ethanolamine has the following structure:

[0094]

[0095] The preparation method is as follows:

[0096] Add 25 g of sodium p-hydroxybenzenesulfonate-ethanolamine type benzoxazine monomer to a 50 mL four-necked flask. Under an Ar atmosphere and mechanical stirring, gradually heat to 150 °C and react at this temperature for 12 h. After the reaction, cool to room temperature to obtain the benzoxazine oligomer.

[0097] (3) Crosslink the benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and ethanolamine with toluene diisocyanate to prepare a proton exchange membrane

[0098] Toluene diisocyanate has the following structure:

[0099]

[0100] The preparation method is as follows:

[0101] Take the benzoxazine oligomer (20 mmol -OH) based on sodium p-hydroxybenzenesulfonate and ethanolamine in a glass bottle, add 10 mL of DMAc to dissolve the oligomer, add toluene diisocyanate (8 mmol -CNO) thereto, mix evenly, and pour into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h, and finally obtain a brown transparent film.

[0102] Example 6

[0103] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, comprising the steps:

[0104] (1) The sodium p-hydroxybenzenesulfonate-2-amino-1-propanol type benzoxazine monomer has the following structure:

[0105]

[0106] The preparation method is as follows: Dissolve sodium p-hydroxybenzenesulfonate, 2-amino-1-propanol, and paraformaldehyde in toluene according to a molar ratio of 1:1:2. The mass ratio of sodium p-hydroxybenzenesulfonate to the volume of the solvent toluene is 1:5 g / mL, and reflux and stir the reaction at 100 °C for 8 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield 84%)

[0107] (2) The benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and 2-amino-1-propanol

[0108]

[0109] The preparation method is as follows:

[0110] Add 25 g of sodium p-hydroxybenzenesulfonate-2-amino-1-propanol type benzoxazine monomer to a 50 mL four-necked flask. Under an Ar atmosphere and mechanical stirring conditions, gradually heat up to 150 °C and react at this temperature for 14 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0111] (3) Crosslink the benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and 2-amino-1-propanol with isophorone diisocyanate to prepare a proton exchange membrane

[0112] Isophorone diisocyanate has the following structure:

[0113]

[0114] The preparation method is as follows:

[0115] Take the benzoxazine oligomer (20 mmol -OH) based on sodium p-hydroxybenzenesulfonate and 2-amino-1-propanol in a glass bottle, add 10 mL of DMAc, dissolve the oligomer, add isophorone diisocyanate (8 mmol -CNO) to it, mix well, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h, and finally obtain a brown transparent film.

[0116] Example 7

[0117] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, comprising the steps:

[0118] (1) Sodium p-hydroxybenzenesulfonate-serinol type benzoxazine has the following structure:

[0119]

[0120] The preparation method is as follows: Dissolve sodium p-hydroxybenzenesulfonate, serinol, and paraformaldehyde in toluene at a molar ratio of 1:1:2. The mass ratio of sodium p-hydroxybenzenesulfonate to the volume of the solvent toluene is 1:5 g / mL, and reflux and stir the reaction at 100 °C for 6 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield 88%)

[0121] (2) The benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and serinol has the following structure:

[0122]

[0123] The preparation method is as follows:

[0124] Add 25 g of sodium p-hydroxybenzenesulfonate-serinol type benzoxazine monomer to a 50 mL four-necked flask. Under an Ar atmosphere and mechanical stirring conditions, gradually heat up to 160 °C and react at this temperature for 12 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0125] (3) Use cyclohexylmethane diisocyanate as a crosslinking agent to crosslink the benzoxazine oligomer based on sodium p-hydroxybenzenesulfonate and serinol to prepare a proton exchange membrane

[0126] Cyclohexylmethane diisocyanate has the following structure:

[0127]

[0128] The preparation method is as follows:

[0129] Take the benzoxazine oligomer (20 mmol -OH) based on sodium 4-hydroxybenzenesulfonate and serine in a glass bottle, add 10 mL of DMAc, dissolve the oligomer, add hexamethylene diisocyanate (8 mmol -CNO) thereto, mix evenly, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h, and finally obtain a brown transparent film.

[0130] Example 8

[0131] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, comprising the steps:

[0132] (1) The carboxyphenol - diethylene glycolamine type benzoxazine has the following structure:

[0133]

[0134] The preparation method is as follows: Dissolve carboxyphenol, diethylene glycolamine, and paraformaldehyde in toluene according to a molar ratio of 1:1:2. The mass ratio of carboxyphenol to the volume of the solvent toluene is 1:5 g / mL, and reflux and stir the reaction at 100 °C for 7 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield 82%)

[0135] (2) The benzoxazine oligomer based on carboxyphenol and diethylene glycolamine has the following structure:

[0136]

[0137] The preparation method is as follows: Add 25 g of carboxyphenol - diethylene glycolamine type benzoxazine monomer to a 50 mL four-necked flask. Under an Ar gas atmosphere and mechanical stirring conditions, gradually heat up to 160 °C and react at this temperature for 16 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0138] (3) Use hexamethylene diisocyanate as a crosslinking agent to crosslink the benzoxazine oligomer based on carboxyphenol and diethylene glycolamine to prepare a proton exchange membrane

[0139] The preparation method is as follows:

[0140] Take the benzoxazine oligomer (20 mmol -OH) based on carboxyphenol and diethylene glycolamine in a glass bottle, add 10 mL of DMAc, dissolve the oligomer, add hexamethylene diisocyanate (8 mmol -CNO) thereto, mix evenly, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h, and finally obtain a transparent film.

[0141] Example 9

[0142] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, comprising the steps:

[0143] (1) The carboxyphenol-ethanolamine type benzoxazine has the following structure:

[0144]

[0145] The preparation method is as follows: Dissolve carboxyphenol, ethanolamine, and paraformaldehyde in toluene at a molar ratio of 1:1:2. The mass ratio of carboxyphenol to the volume of the solvent toluene is 1:5 g / mL. Reflux and stir the reaction at 100 °C for 6 hours. Subsequently, pour the solution into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield 85%)

[0146] (2) The benzoxazine oligomer based on carboxyphenol and ethanolamine has the following structure:

[0147]

[0148] The preparation method is as follows:

[0149] Add 25 g of carboxyphenol-ethanolamine type benzoxazine monomer to a 50 mL four-necked flask. Under an Ar atmosphere and mechanical stirring, gradually heat up to 160 °C and react at this temperature for 14 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0150] (3) Use toluene diisocyanate as a crosslinking agent to crosslink the benzoxazine oligomer based on carboxyphenol and ethanolamine to prepare a proton exchange membrane

[0151] The preparation method is as follows:

[0152] Take the benzoxazine oligomer based on carboxyphenol and ethanolamine (20 mmol -OH) in a glass bottle, add 10 mL of DMAc, dissolve the oligomer, add toluene diisocyanate (8 mmol -CNO) to it, mix evenly, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h to finally obtain a transparent membrane.

[0153] Example 10

[0154] A preparation method of a crosslinked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming property, comprising the steps:

[0155] (1) p - Carboxyphenol - 2 - amino - 1 - propanol - type benzoxazine has the structure shown below:

[0156]

[0157] The preparation method is as follows: p - Carboxyphenol, 2 - amino - 1 - propanol, and paraformaldehyde are dissolved in toluene in a molar ratio of 1:1:2. The mass ratio of p - carboxyphenol to the volume of the solvent toluene is 1:5 g / mL. The mixture is refluxed and stirred at 100 °C for 8 hours. Subsequently, the solution is poured into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield: 88%)

[0158] (2) The benzoxazine oligomer based on p - carboxyphenol and 2 - amino - 1 - propanol has the structure shown below:

[0159]

[0160] The preparation method is as follows:

[0161] Add 25 g of p - carboxyphenol - 2 - amino - 1 - propanol - type benzoxazine monomer to a 50 - mL four - necked flask. Under an Ar atmosphere and mechanical stirring, gradually heat up to 150 °C and react at this temperature for 14 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0162] (3) Use diphenylmethane diisocyanate as a cross - linker to cross - link the benzoxazine oligomer based on p - carboxyphenol and 2 - amino - 1 - propanol to prepare a proton exchange membrane

[0163] The preparation method is as follows:

[0164] Take the benzoxazine oligomer based on p - carboxyphenol and 2 - amino - 1 - propanol (20 mmol - OH) in a glass bottle, add 10 mL of DMAc to dissolve the oligomer, add diphenylmethane diisocyanate (8 mmol - CNO) to it, mix well, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h to finally obtain a transparent membrane.

[0165] Example 11

[0166] A preparation method of a cross - linked benzoxazine proton exchange membrane for water electrolysis with excellent film - forming properties, including the steps:

[0167] (1) p - Carboxyphenol - serine alcohol - type benzoxazine has the structure shown below:

[0168]

[0169] The preparation method is as follows: p-carboxyphenol, serine alcohol, and paraformaldehyde are dissolved in toluene in a molar ratio of 1:1:2. The mass ratio of p-carboxyphenol to the volume of the solvent toluene is 1:5 g / mL. The mixture is stirred and reacted at 100 °C for 8 hours. Subsequently, the solution is poured into cold methanol for precipitation, washing, and rotary evaporation to obtain a powder. (Yield: 81%)

[0170] (2) The benzoxazine oligomer based on p-carboxyphenol and serine alcohol has the following structure:

[0171]

[0172] The preparation method is as follows:

[0173] Add 25 g of p-carboxyphenol-serine alcohol-based benzoxazine monomer to a 50 mL four-necked flask. Under an Ar atmosphere and mechanical stirring, gradually heat up to 150 °C and react at this temperature for 14 h. After the reaction is completed, cool to room temperature to obtain the benzoxazine oligomer.

[0174] (3) Crosslink the benzoxazine oligomer based on p-carboxyphenol and serine alcohol with naphthalene diisocyanate to prepare a proton exchange membrane

[0175] The preparation method is as follows:

[0176] Take the benzoxazine oligomer based on p-carboxyphenol and serine alcohol (20 mmol -OH) in a glass bottle, add 10 mL of DMAc to dissolve the oligomer, add naphthalene diisocyanate (8 mmol -CNO) to it, mix well, and pour it into a tetrafluoro mold. Place the mold in an oven, keep it at 80 °C for 6 h, 100 °C for 4 h, 120 °C for 2 h, 140 °C for 2 h, and 160 °C for 2 h to finally obtain a transparent membrane.

[0177] Application Example

[0178] Electrolysis performance and durability tests. A catalyst-coated membrane (CCM) based on the proton exchange membranes prepared in Examples 1-4 was prepared by the thermal transfer method. The PEM and the cathode and anode catalyst layers (CLs) were dried at 150 °C for 10 minutes, and then hot-pressed at 150 °C and 0.5 Mpa for 10 minutes to obtain a CCM with an active area of 25 cm 2 The platinum loading of the cathode CL is 0.1 mg cm -2 , and the IrO2 loading of the anode CL is 1.0 mg cm -2 . The electrolysis performance of the membrane electrode assembly (MEA) based on the proton exchange membrane was tested by the constant current method at 80 °C. The effective area of the MEA is 1.0 cm 2。Then, the fabricated MEA was assembled into a proton exchange membrane water electrolysis cell, where the end plates with embedded flow channels were made of corrosion-resistant titanium. All electrochemical measurements were carried out on an electrochemical workstation (AMETEK Princeton Applied Research VersaSTAT-3). Preheated deionized water was used as the reactant and maintained at a constant current of 0.5 A cm -2 for 240 hours at 80 °C to test the stability of proton exchange membrane water electrolysis.

[0179] Hydrogen permeation in proton exchange membrane water electrolysis. The hydrogen concentration in oxygen (H2 in O2) was obtained using a gas chromatograph (GC-APCI); 20 mL of the mixed gas from the anode of the electrolysis cell was injected into the gas chromatograph, and then the hydrogen concentration was analyzed using the thermal conductivity detector of the gas chromatograph. The hydrogen content was calculated based on the peak area in the gas chromatograph spectrum and the working curve. Water from the anode to the cathode was obtained using a gas / water separator.

[0180] The I-V characteristics of the proton exchange membrane of the present invention were evaluated in an 80 °C water electrolysis cell. During these evaluations, a Nafion 115 membrane (about 125 μm) was used as a reference. To avoid the influence of membrane thickness on proton conductivity, a proton exchange membrane with a thickness of about 120 μm was used. To ensure high-purity H2 production at the cathode, no external input was introduced during performance evaluation, and only water was fed to the anode. Nafion ionomer was used as the electrode binder for both the anode and the cathode. Figure 10 The results in 2 showed that the open-circuit voltage of the membrane electrode assembly assembled with the proton exchange membrane prepared in Example 1 was 1.55 V. At a voltage of 1.95 V, the cell current density of the proton exchange membrane of the present invention was 1.29 A / cm 2 ; the cell current density of the Nafion 115 membrane was 1.02 A / cm 2 , because of its higher degree of sulfonation in the molecular design and higher water absorption. The open-circuit voltages of the membrane electrode assemblies assembled with the proton exchange membranes prepared in Examples 2-4 were 1.55, 1.57, and 1.55 V, respectively. At a voltage of 1.95 V, the cell current densities of the proton exchange membranes were 1.16, 1.0, and 0.85 A / cm

[0181] Figure 11 shows the results obtained by gas chromatography for Example 1 (PUBZ 40％ ), Example 2 (PUBZ 50％ ), Example 3 (PUBZ 60％ ), and Example 4 (PUBZ 70％)The hydrogen content in oxygen in the obtained proton exchange membrane. In the proton exchange membrane of the present invention, the H2 content in oxygen is low because the smaller size swelling ensures the tightness of the molecular chains, making it difficult for H2 to easily pass through the membrane from the cathode side to the anode side. As Figure 11 shown, the lowest H2 content in O2 is 563 ppm, and PUBZ 40％ is 655 ppm. Under the same test conditions, the H2 content of the Nafion 115 membrane in O2 is 965 ppm, which is much higher than that of the proton exchange membrane of the present invention. This is because the Nafion 115 has a larger size swelling, resulting in fluffy molecular chains and reduced tightness between molecules. The cross-linked structure designed in the present invention has obvious advantages in preventing hydrogen crossover, and this conclusion has also been verified in the above tests.

[0182] Another purpose of designing the cross-linked structure in the present invention is to improve the long-term operation performance. To evaluate the long-term performance of the proton exchange membrane prepared in Example 1, a constant current of 0.5 A / cm 2 was maintained at a temperature of 80 °C for 240 hours. Under the condition of 0.5 A / cm 2 , the voltage of the proton exchange membrane gradually increased from 1.7 V to 1.75 V within 40 hours and remained stable within 240 hours. The possible reasons are: (1) The cross-linked structure has good dimensional stability and can resist the membrane failure problem caused by water swelling. (2) The cross-linked intertwined structure is tighter, so the gas permeability is weakened and fewer free radicals are formed, which makes it more difficult for the molecular structure of the proton exchange membrane to be damaged.

[0183] Although the specific implementation manners of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, comprising the steps of: dissolving a benzoxazine oligomer in a solvent, adding an isocyanate compound, mixing uniformly, and forming a film to obtain a cross-linked benzoxazine proton exchange membrane for water electrolysis; The benzoxazine oligomer has the following repeating structural units: in, R1 is selected from -SO3Na or -COOH; R2 is selected from -CH2CH2OH, -CH2CH(CH3)OH, -CH(CH2OH)CH2OH or CH2CH2OCH2CH2OH.

2. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 1, characterized in that: Includes one or more of the following conditions: i. The solvent is one of water, N,N-dimethylacetamide, tetrahydrofuran, chloroform, acetone, toluene, N-methylpyrrolidone, dimethyl sulfoxide or dioxane; the mass ratio of the benzoxazine oligomer to the volume ratio of the solvent is 0.1-1 g / mL; ii. The molar amount of the isocyanate group in the isocyanate compound accounts for 40% to 70% of the molar amount of the hydroxyl group in the benzoxazine oligomer, preferably 40% to 50%, and more preferably 40%.

3. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 1, characterized in that: The film forming conditions are as follows: keep warm at 70-90℃ for 4-8h, keep warm at 90-110℃ for 2-6h, keep warm at 110-130℃ for 1-3h, keep warm at 130-150℃ for 1-3h, keep warm at 150-170℃ for 1-3h; the film forming conditions are as follows: keep warm at 80℃ for 6h, keep warm at 100℃ for 4h, keep warm at 120℃ for 2h, keep warm at 140℃ for 2h, keep warm at 160℃ for 2h.

4. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 1, characterized in that: The isocyanate compound is one of hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, tetramethylxylylene diisocyanate, dicyclohexylmethane diisocyanate or xylylene diisocyanate.

5. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 1, characterized in that: The preparation method of benzoxazine oligomer comprises the steps of: obtaining benzoxazine oligomer by polymerization of benzoxazine monomer; the benzoxazine monomer has the structure shown below: Wherein, R1 is selected from -SO3Na or -COOH; R2 is selected from -CH2CH2OH, -CH2CH(CH3)OH, -CH(CH2OH)CH2OH or CH2CH2OCH2CH2OH.

6. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 5, characterized in that: The polymerization reaction temperature is 100-200° C., the polymerization reaction time is 10-20 hours, and the polymerization reaction is carried out under the protection of a protective gas; the protective gas is nitrogen or argon.

7. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 5, characterized in that: The method for preparing benzoxazine monomer comprises the steps of: The phenolic compound, the amine compound and the polyformaldehyde are fully dispersed in a solvent, reacted, and then precipitated, washed and rotary evaporated to obtain a benzoxazine monomer; the phenolic compound is one of sodium p-hydroxybenzenesulfonate or p-carboxyphenol; the amine compound is one of ethanolamine, 2-amino-1-propanol, serinol or diglycolamine.

8. The method for preparing a cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties according to claim 7, characterized in that: Includes one or more of the following conditions: i. The solvent is selected from one of water, N,N-dimethylformamide, tetrahydrofuran, chloroform, acetone, toluene, N-methylpyrrolidone, dimethyl sulfoxide or dioxane; the mass ratio of the phenolic compound to the volume ratio of the solvent is 1:4-6 g / mL; ii. the molar ratio of the phenolic compound, the amine compound and the paraformaldehyde is 1:1:2; iii. The reaction temperature is 100-160°C, the reaction time is 4-8h, and the reaction is carried out under reflux and stirring conditions.

9. A cross-linked benzoxazine proton exchange membrane for water electrolysis with excellent film-forming properties, prepared by the method according to any one of claims 1 to 8.

10. Use of the cross-linked benzoxazine proton exchange membrane for water electrolysis having excellent film-forming properties as claimed in claim 9 in electrolyzed water.

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