Alumina oxyhydroxide-based alkaline electrolytic water composite separator and method for preparing the same

Abstract

The application discloses a kind of hydroxyl aluminum oxide-based alkaline electrolytic water composite diaphragm and preparation method thereof, belong to diaphragm preparation technical field, the diaphragm is composed of polysulfone, polyvinylpyrrolidone, quaternary ammonium polyvinyl alcohol, gamma-AlOOH powder, by the introduction of gamma-AlOOH powder can significantly reduce surface resistance, enhance gas resistance, improve mechanical strength and dimensional stability, improve thermal stability and chemical stability, by quaternary ammonium modification can significantly enhance the permanent hydrophilicity of diaphragm, improve diaphragm ion conduction efficiency.

Description

Technical Field

[0001] This invention relates to the field of membrane preparation technology, and more specifically to a hydroxyalumina-based alkaline water electrolysis composite membrane and its preparation method. Background Technology

[0002] In alkaline water electrolysis for hydrogen production, the membrane is crucial. It isolates hydrogen and oxygen to prevent an explosion from mixing, while allowing hydroxide ions to pass through, completing the circuit. The quality of the membrane directly affects the purity of hydrogen and oxygen, as well as power consumption. Currently, commonly used membrane designs in alkaline water electrolysis for hydrogen production focus on improving mechanical strength, ionic conductivity, gas barrier properties (preventing H2 / O2 permeation), and alkali resistance. Common types include phase inversion composite membranes, multilayer coated membranes, hydrophilically modified biopolymer membranes, and ion-transfer membranes based on hydrogen bond networks.

[0003] However, the core challenge facing traditional alkaline electrolyzer diaphragms lies in the imbalance of hydrophilicity control and the bubble accumulation effect. Polyphenylene sulfide (PPS), as the mainstream base membrane material, has poor hydrophilicity, making it difficult for the electrolyte to fully wet the diaphragm pores, leading to the formation of microbubbles. These bubbles accumulate at the diaphragm-electrolyte interface, forming an insulating layer and significantly increasing ohmic resistance. More seriously, although traditional alumina-coated diaphragms improve hydrophilicity by introducing hydroxyl groups, their excessively high surface free energy easily leads to excessive liquid absorption and swelling, which in turn blocks ion channels. For example, patent CN119349610A explicitly points out that traditional alumina coatings have a "relatively high water absorption rate," the root cause of which is the excessive exposure of unsaturated aluminum ions, leading to the excessive adsorption of electrolyte solvent molecules.

[0004] Furthermore, existing strategies for enhancing the hydrophilicity of membranes generally face the serious challenge of insufficient long-term effectiveness. When using biopolymers (such as chitosan) or polar substances that are simply physically adsorbed / coated (such as ordinary alumina and titanium dioxide) as hydrophilic agents, their chemical stability is significantly insufficient under strongly alkaline (such as 6M KOH), high-temperature (60-90℃) electrolytic environments, and continuous bubble scouring. For example, although chitosan-modified (patent CN118186492A) has excellent initial hydrophilicity, its glycosidic bonds and acetyl groups are prone to hydrolytic breakage under concentrated alkali and high temperature, resulting in the loss of hydrophilic groups (-OH, -NH2), and its function usually degrades severely within 2000 hours of operation; the hydroxyl groups on the surface of ordinary γ-Al2O3 particles (patent CN119349610A, etc.) are prone to dehydroxylation reactions or complexation and deactivation with electrolyte ions during long-term operation, and physically adsorbed particles are prone to detachment from the polymer matrix.

[0005] Therefore, how to provide a diaphragm that is simple to prepare, low in cost, and has low surface resistivity and high airtightness is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a hydroxyalumina-based alkaline water electrolysis composite membrane and its preparation method. The method has the advantages of simple operation, low cost and large output, and the membrane has the characteristics of low surface resistance and high air tightness.

[0007] To achieve the above objectives, the present invention provides a method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane, characterized by comprising the following steps:

[0008] S1, slowly add polysulfone resin powder to N-methylpyrrolidone and stir to obtain an N-methylpyrrolidone solution of polysulfone resin;

[0009] S2, under stirring, add quaternized polyvinyl alcohol to the N-methylpyrrolidone solution of polysulfone resin to completely dissolve it and form a homogeneous mixed solution;

[0010] S3, add γ-AlOOH powder to the mixed solution, stir continuously to make it evenly dispersed, and then remove air bubbles by vacuum to obtain the casting solution;

[0011] S4. Pour the casting solution onto a clean, flat substrate and use a scraper to scrape it at a uniform speed to form a uniform liquid film. Immediately immerse the entire substrate with the liquid film into the coagulation bath and keep it submerged to allow the solvent and non-solvent to exchange, causing the polymer to precipitate and form a wet composite membrane with a microporous structure.

[0012] S5, the wet composite membrane is removed from the coagulation bath, rinsed with deionized water to remove solvent and impurities from the membrane surface, then wiped to remove surface moisture, and dried to obtain the hydroxyalumina-based alkaline electrolytic water composite membrane.

[0013] The mass ratio of polysulfone resin to N-methylpyrrolidone in step S1 is 9.0~9.8:36~50.

[0014] In step S2, the mass ratio of quaternized polyvinyl alcohol to polysulfone resin is 0.3:9.8.

[0015] The method for preparing the quaternized polyvinyl alcohol is as follows:

[0016] Polyvinyl alcohol was dissolved in distilled water at 85°C and stirred until homogeneous. Then, the mixture was cooled to 65°C, and glycidyl trimethylammonium chloride and KOH were added while stirring to carry out a quaternization reaction. After the reaction was completed, the resulting viscous polymer mixture was washed with anhydrous ethanol to obtain a yellow precipitate. The precipitate was dried at 65°C to obtain the quaternized polyvinyl alcohol.

[0017] The ratio of polyvinyl alcohol to distilled water is 10g:90mL;

[0018] The mass ratio of polyvinyl alcohol to glycidyl trimethylammonium chloride is 10:15;

[0019] The molar ratio of glycidyltrimethylammonium chloride and KOH is 1:1;

[0020] The quaternization reaction time is 4 hours.

[0021] The mass ratio of γ-AlOOH powder to polysulfone resin in step S3 is 40:9.8;

[0022] The preparation method of the γ-AlOOH powder is as follows:

[0023] 20 mmol of aluminum sulfate octahydrate was dissolved in 60 mL of ethanol solution, 80 mmol of urea was added, the mixture was stirred evenly, transferred to a high-pressure reactor, and subjected to hydrothermal reaction. The mixture was then cooled to room temperature to obtain a white precipitate. The precipitate was washed three times by centrifugation with high-purity water and anhydrous ethanol, and dried to obtain γ-AlOOH powder sample.

[0024] The ethanol solution is prepared by mixing ethanol and high-purity water in a volume ratio of 1:2.

[0025] The ratio of aluminum sulfate octahydrate to ethanol is 20 mmol: 60 mL;

[0026] The molar ratio of aluminum sulfate octahydrate to urea is 20:80;

[0027] The hydrothermal reaction was carried out at a temperature of 140°C for 24 hours.

[0028] The drying temperature is 60°C.

[0029] The present invention also provides a hydroxyalumina-based alkaline water electrolysis composite membrane prepared by the method described above.

[0030] As can be seen from the above technical solution, the present invention provides a hydroxyalumina-based alkaline water electrolysis composite membrane and its preparation method, the beneficial effects of which are:

[0031] 1) Significantly reduced sheet resistivity and improved electrolysis efficiency: Based on the hydrophilic network constructed by AlOOH, quaternized PVA further introduces a large number of positively charged quaternary ammonium groups. These groups generate strong electrostatic interactions in an alkaline environment, which can efficiently attract and enrich OH groups. - The ions significantly promote the migration of hydroxide ions in the membrane. Compared with AlOOH that relies solely on physical adsorption, quaternized PVA constructs a more continuous and efficient ion transport channel through charge guidance, thereby further reducing the membrane surface resistivity and improving electrolysis efficiency at the same AlOOH content.

[0032] 2) Enhanced gas barrier properties, improving gas purity and safety: The "maze effect" formed by the AlOOH nanosheets provides the physical basis for gas barrier properties. Quaternized PVA, as a functional polymer matrix, not only uniformly disperses and stabilizes the AlOOH nanosheets, but its own cross-linked dense structure further enhances the overall compactness of the membrane. The synergistic effect of both enhances the diffusion barrier capability of hydrogen and oxygen in the membrane, more effectively suppressing gas cross-linking and improving gas purity and system safety.

[0033] 3) Improved mechanical strength and dimensional stability, extending service life: AlOOH acts as a rigid nanofiller to enhance the mechanical properties of the membrane. The quaternized PVA matrix further enhances the membrane's toughness, swelling resistance, and overall structural stability through intermolecular chain forces and potential cross-linking structures. In hot alkaline environments, quaternized PVA effectively inhibits excessive matrix swelling and synergistically maintains membrane dimensional stability with AlOOH, thereby extending the membrane's service life under harsh alkaline electrolysis conditions.

[0034] 4) Quaternization modification significantly enhances OH- - Ion conductivity further reduces surface resistivity: Unlike AlOOH, which relies solely on physical hydrophilicity to adsorb electrolytes, the permanent positively charged groups introduced by quaternized PVA can form a directional electrostatic guiding effect in alkaline electrolytes, significantly reducing OH- ions. - The ion migration energy barrier. This characteristic allows the membrane to establish a highly efficient ion conduction path while possessing the physical hydrophilic channels of AlOOH, thereby achieving a "dual enhancement" in ion conduction capacity, more effectively reducing membrane resistance, and optimizing water electrolysis performance. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 These are SEM images of Embodiment 1 and Comparative Example 1 of this application.

[0037] Figure 2 The water contact angle is shown in Example 1.

[0038] Figure 3 The water contact angle is shown in Comparative Example 1.

[0039] Figure 4 The contact angle of the 30% alkali solution in Example 1 is shown.

[0040] Figure 5 The contact angle of the 30% alkaline solution in Comparative Example 1 is shown. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] S1, 20 mmol of aluminum sulfate octahydrate was dissolved in 60 mL of ethanol solution (the ethanol solution was prepared by mixing ethanol and high-purity water in a volume ratio of 1:2). After complete dissolution, 80 mmol of urea was added and stirred until completely dissolved. The solution was then transferred to a 100 mL high-pressure reactor, sealed, and placed in an electric heating drying oven. The reactor was kept at 140 °C for 24 h and cooled to room temperature to obtain a white precipitate. The precipitate was washed three times by centrifugation with high-purity water and anhydrous ethanol, and then dried in a 60 °C oven to obtain γ-AlOOH powder sample.

[0044] S2, 10 g of polyvinyl alcohol polymer (PVA) was dissolved in 90 mL of distilled water at 85 °C. The resulting solution was stirred for 3 hours until the mixture became homogeneous and had a viscous, transparent appearance. The viscous mixture was cooled to 65 °C, and an appropriate amount of glycidyltrimethylammonium chloride (GTMAC) (15 g) and KOH (GTMAC to KOH molar ratio 1:1) were added to the PVA solution with continuous stirring. The mixture was then stirred for another 4 hours. The resulting viscous polymer mixture was washed with anhydrous ethanol to obtain a yellow precipitate. The resulting quaternized poly(vinyl alcohol) precipitate (denoted as Q-PVA) was then dried at 65 °C.

[0045] S3, add 36 g of N-methylpyrrolidone (NMP) to a 100 mL three-necked flask, then slowly add 9.8 g of polysulfone resin (PSF) powder to the NMP and stir at 55 °C for 3 h. Transfer the polysulfone to a mechanical stirrer, and add 0.3 g of quaternized poly(vinyl alcohol) (Q-PVA) at a stirring speed of 300 rpm, and continue stirring until completely dissolved to form a homogeneous solution.

[0046] S4. Add 40 g of γ-AlOOH powder to the above solution, adjust the stirring speed to an appropriate intensity (to ensure sufficient dispersion and avoid introducing excessive air bubbles), and continue stirring for 12 hours to ensure that the γ-AlOOH powder is uniformly dispersed in the polymer solution. Transfer to a suitable container and place in a vacuum drying oven. Vacuum the solution at room temperature for 12 hours to ensure that there are no obvious air bubbles in the casting solution.

[0047] S5. Pour the fully degassed casting solution onto a clean, flat substrate (such as a glass plate or polyester film). Use a 200-500 μm doctor blade to uniformly coat the substrate, forming a uniform liquid film. Immediately immerse the entire substrate with the wet film into a coagulation bath (deionized water or a non-solvent aqueous solution of a certain concentration, at 25°C). Maintain immersion for 30 minutes to allow the solvent (NMP) and non-solvent (water) to exchange, causing polymer precipitation and forming a wet composite membrane with a microporous structure.

[0048] S6. Carefully remove the solidified wet membrane from the coagulation bath. Rinse the membrane surface thoroughly with plenty of deionized water to completely remove residual solvent and possible impurities. Place the cleaned wet membrane on clean filter paper or absorbent cloth to remove excess surface moisture, then transfer it to a vacuum drying oven and dry at 60°C for 24 hours to completely remove moisture from the membrane, obtaining the final composite microporous membrane for alkaline water electrolysis.

[0049] Comparative Example 1

[0050] S1, 20 mmol of aluminum sulfate octahydrate was dissolved in 60 mL of ethanol solution (the ethanol solution was prepared by mixing ethanol and high-purity water in a volume ratio of 1:2). After complete dissolution, 80 mmol of urea was added, stirred evenly, and transferred to a 100 mL high-pressure reactor. After sealing, it was placed in an electric heating drying oven and kept at 140 ℃ for 24 h. After cooling to room temperature, a white precipitate was obtained. It was washed three times by centrifugation with high-purity water and anhydrous ethanol, respectively, and dried in an oven at 60 ℃ to obtain γ-AlOOH powder sample.

[0051] S2, add 55 g of N-methylpyrrolidone (NMP) to a 100 mL three-necked flask. Then slowly add 14.7 g of polysulfone (PSF) powder to the NMP and stir at 55 °C for 3 h. Transfer the polysulfone to a mechanical stirrer and add 0.3 g of polyvinyl alcohol (PVA) at a stirring rate of 300 rpm, continuing to stir until completely dissolved to form a homogeneous solution.

[0052] S3, add 45 g of AlOOH powder to the homogeneous solution described in step 2. Adjust the stirring speed to an appropriate intensity (ensuring sufficient dispersion without introducing excessive air bubbles), and continue stirring for 12 hours to ensure that the AlOOH nanoparticles are uniformly dispersed in the polymer solution. Transfer the solution to a suitable container and place it in a vacuum drying oven. Vacuum the solution at room temperature for 12 hours to ensure that there are no obvious air bubbles in the casting solution.

[0053] S4. Pour the fully degassed casting solution onto a clean, flat substrate (such as a glass plate or polyester film). Use a 200-500 μm doctor blade to uniformly coat the substrate, forming a uniform liquid film. Immediately immerse the entire substrate with the wet film into a coagulation bath (usually deionized water or a non-solvent aqueous solution of a certain concentration, at a temperature such as 25 °C). Maintain immersion for 30 minutes to allow the solvent (NMP) to exchange with the non-solvent (water), causing the polymer to precipitate and forming a wet composite membrane with a microporous structure.

[0054] S5. Carefully remove the solidified wet membrane from the coagulation bath. Rinse the membrane surface thoroughly with plenty of deionized water to completely remove residual solvent and any possible impurities. Place the rinsed wet membrane on clean filter paper or absorbent cloth to remove excess surface moisture, then transfer it to a vacuum drying oven and dry at 60 °C for 24 hours to completely remove moisture from the membrane, obtaining the final composite microporous membrane for alkaline water electrolysis. The dried membrane should be stored in a desiccator for later use.

[0055] Characterization and performance testing

[0056] SEM characterization

[0057] The products of the examples and comparative examples were observed using scanning electron microscopy, and the results are shown in the figure. Figure 1 Where a and b are the surface and cross-section of the membrane prepared in Example 1, respectively, and c and d are the surface and cross-section of the membrane prepared in Comparative Example 1, respectively. The comparison shows that the membrane in Example 1 is more dense, without large through-pores, thus reducing hydrogen permeation.

[0058] Mechanical property testing

[0059] A 0.14 cm × 4 cm strip of composite diaphragm was cut and subjected to tensile strength testing. The test results are as follows:

[0060]

[0061] The data in the table show that the quaternization modification of AlOOH and PVA both help to enhance the mechanical properties of the composite membrane.

[0062] airtightness test

[0063] A 0.14 cm × 4 cm strip of composite diaphragm was cut for airtightness testing. The test results are as follows:

[0064]

[0065] The airtightness of Example 1 is significantly higher than that of Comparative Example 1, indicating that the quaternization modification enhances the airtightness of the membrane, thereby effectively blocking the cross-permeation of hydrogen and oxygen gases and improving safety.

[0066] Hydrophilicity test

[0067] The contact angles of the diaphragm with pure water and 30% alkaline solution were measured, and the results are as follows:

[0068]

[0069] The comparison shows that the contact angle of Example 1 is smaller than that of Comparative Example 1, indicating that the addition of Q-PVA improves the hydrophilicity and alkali-loving properties of the composite membrane.

[0070] Alkali absorption rate test

[0071] The alkali absorption rate was determined as follows: A 30 wt% KOH solution was prepared, and a 1 cm × 1 cm composite diaphragm sample was cut and weighed to obtain the sample mass m1. After drying, the sample was immersed in the 30 wt% KOH solution. After the sample was immersed in the alkali for 4 h, it was removed from the alkali by holding one corner with clamps and suspended in the air for 30 ± 2 s to drip off the alkali solution. The mass m2 was then measured on a balance. (Note: If less than 1 drop of alkali solution did not drip off, the corner of the sample containing the droplet was touched against the wall of the container to allow the droplet to fall off before weighing.) The alkali absorption rate A of the diaphragm was calculated using the following formula:

[0072]

[0073] Where: A--diaphragm alkali absorption rate, %; m1--sample mass before alkali immersion, g; m2--sample mass after alkali immersion, g.

[0074] The experiment was repeated three times, and the results are as follows:

[0075]

[0076] As shown in the figure, the alkali absorption rate of the membrane prepared in Example 1 of this application is greater than 200%, indicating that the membrane has extremely high porosity or extremely strong hydrophilicity. A high alkali absorption rate means that the pores inside the membrane are fully filled with electrolyte, forming continuous and abundant ion transport channels.

[0077] Surface resistance test

[0078] The sheet resistance test was performed using a Chenhua electrochemical workstation. Before conducting the diaphragm sheet resistance test, a 4cm² effective area without a diaphragm was first used. 2The resistance of the fixture was measured twice in a 30 wt% KOH solution at 60℃, and recorded as blank group 1 and blank group 2. A 2 cm × 2 cm composite diaphragm was cut, installed in the fixture, and its resistance was measured twice in a 30 wt% KOH solution at 60℃. The average of the two measurements was taken, and the data is as follows.

[0079] The sheet resistance of the diaphragm in Example 1 was tested, and the results are as follows:

[0080]

[0081] The sheet resistance of the diaphragm in Example 1 was tested, and the results are as follows:

[0082]

[0083] The comparison shows that the sheet resistance of Example 1 is less than that of Comparative Example 1, indicating that the addition of Q-PVA helps to reduce the sheet resistance of the composite membrane, thereby improving the electrochemical performance of water electrolysis.

[0084] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane, characterized in that, Specifically, the steps include the following: S1, slowly add polysulfone resin powder to N-methylpyrrolidone and stir to obtain an N-methylpyrrolidone solution of polysulfone resin; S2, under stirring, add quaternized polyvinyl alcohol to the N-methylpyrrolidone solution of polysulfone resin to completely dissolve it and form a homogeneous mixed solution; S3, add γ-AlOOH powder to the mixed solution, stir continuously to make it evenly dispersed, and then remove air bubbles by vacuum to obtain the casting solution; S4. Pour the casting solution onto a clean, flat substrate and use a scraper to scrape it at a uniform speed to form a uniform liquid film. Immediately immerse the entire substrate with the liquid film into the coagulation bath and keep it submerged to allow the solvent and non-solvent to exchange, causing the polymer to precipitate and form a wet composite membrane with a microporous structure. S5, the wet composite membrane is removed from the coagulation bath, rinsed with deionized water to remove solvent and impurities from the membrane surface, then wiped to remove surface moisture, and dried to obtain the hydroxyalumina-based alkaline electrolytic water composite membrane.

2. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 1, characterized in that, The mass ratio of polysulfone resin to N-methylpyrrolidone in step S1 is 9.0~9.8:36~50.

3. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 1, characterized in that, In step S2, the mass ratio of quaternized polyvinyl alcohol to polysulfone resin is 0.3:9.

8.

4. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 3, characterized in that, The method for preparing the quaternized polyvinyl alcohol is as follows: Polyvinyl alcohol was dissolved in distilled water at 85°C and stirred until homogeneous. Then, the mixture was cooled to 65°C, and glycidyl trimethylammonium chloride and KOH were added while stirring to carry out a quaternization reaction. After the reaction was completed, the resulting viscous polymer mixture was washed with anhydrous ethanol to obtain a yellow precipitate. The precipitate was dried at 65°C to obtain the quaternized polyvinyl alcohol.

5. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 4, characterized in that, The ratio of polyvinyl alcohol to distilled water is 10g:90mL; The mass ratio of polyvinyl alcohol to glycidyl trimethylammonium chloride is 10:15; The molar ratio of glycidyltrimethylammonium chloride and KOH is 1:1; The quaternization reaction time is 4 hours.

6. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 1, characterized in that, The mass ratio of γ-AlOOH powder to polysulfone resin in step S3 is 40:9.8; The preparation method of the γ-AlOOH powder is as follows: 20 mmol of aluminum sulfate octahydrate was dissolved in 60 mL of ethanol solution, 80 mmol of urea was added, and the mixture was stirred until completely dissolved. The solution was then transferred to a high-pressure reactor for hydrothermal reaction. After cooling to room temperature, a white precipitate was obtained. The precipitate was washed three times by centrifugation with high-purity water and anhydrous ethanol, and then dried to obtain γ-AlOOH powder sample. The ethanol solution is prepared by mixing ethanol and high-purity water in a volume ratio of 1:

2.

7. The method for preparing a hydroxyalumina-based alkaline water electrolysis composite membrane according to claim 6, characterized in that, The hydrothermal reaction was carried out at a temperature of 140°C for 24 hours. The drying temperature is 60°C.

8. A hydroxyalumina-based alkaline water electrolysis composite membrane prepared by the method according to any one of claims 1-7.

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