Ion solvation membrane for alkaline water electrolysis, preparation method and application thereof

Abstract

This invention provides a method for preparing an ion-solventized membrane for alkaline water electrolysis. During the preparation of the PBI casting solution, a titanate coupling agent containing pyrophosphate groups is added to eliminate the bubbling effect caused by the addition. After gradient drying, a smooth and uniform membrane sample is obtained. This method is simple, and the resulting doped membrane exhibits lower membrane resistance, higher hydroxide conductivity, and maintains good mechanical strength. The membrane of this invention is dense, possesses good gas barrier properties, good hydroxide conductivity and mechanical strength, low impedance, and good electrochemical performance, making it suitable for water electrolysis.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production by water electrolysis, specifically relating to an ion solvation membrane for alkaline water electrolysis, its preparation method, and its application. Background Technology

[0002] Amidst the consensus on "peak carbon emissions and carbon neutrality" as a development trend, the development of renewable and clean energy has received considerable attention. Renewable energy sources such as solar and wind power, due to their intermittent nature, require efficient energy carriers to drive their widespread application. Sustainable, high-energy-density hydrogen is an ideal energy carrier. Among various hydrogen production methods, water electrolysis has attracted increasing attention from the market and researchers due to its high efficiency and zero carbon emissions. The alkaline water electrolysis membrane is located between the anode and cathode chambers, allowing ions to pass through while blocking the mixing of hydrogen and oxygen. Furthermore, because the working environment is a high-concentration alkaline solution at 70-90℃, the membrane also needs to possess certain high-temperature and alkali resistance. Traditionally used membranes are asbestos cloth and PPS cloth. As porous membranes, they suffer from low gas barrier properties and high electrical resistance due to the material properties. Asbestos cloth is currently banned in most countries due to its toxicity. Researchers have improved the ion conduction performance of the membrane by adding organic polymers and hydrophilic inorganic materials to PPS cloth, but the gas barrier property remains unresolved.

[0003] Therefore, researchers investigated the application of other types of membranes in water electrolysis. Aili proposed using ion-solvent membranes in alkaline water electrolysis. Ion-solvent membranes are prepared using polybenzimidazole. Under alkaline conditions, the imidazole rings on the main chain can be deprotonated, forming a network-like negatively charged structure for ion conduction. Unlike porous membranes, ion-solvent membranes do not rely on porous structures to absorb alkaline solutions for ion transport, thus forming a dense structure. This results in excellent gas barrier properties and mechanical properties. Furthermore, polybenzimidazole is an aromatic heterocyclic polymer; the benzene rings in the main chain enhance the polymer's mechanical stability and chemical resistance. The nitrogen atoms on the imidazole rings can be deprotonated under alkaline conditions, providing the basis for hydroxide ion conduction. These characteristics make ion-solvent membranes applicable to alkaline water electrolysis. However, the hydroxide conductivity of ion-solvent membranes depends on the alkaline electrolyte. Therefore, it is necessary to improve the membrane's hydroxide conductivity and reduce its sheet resistance to enhance its electrochemical performance. In response, numerous researchers have employed various methods to optimize the performance of PBI. Diaz et al. blended polyvinyl alcohol with the membrane to increase the hydroxyl content in the polymer, thereby enhancing hydroxyl transport. However, this resulted in a reduction in the mechanical properties of the membrane, hindering its further application. Li et al. synthesized PBI using different monomers, enhancing the polymer's hydroxyl transport capacity through functionalization of the functional groups. However, this required modification during the polymer synthesis stage, making the process relatively cumbersome.

[0004] Therefore, there is an urgent need to develop a process that is simple and easy to implement, and can effectively improve the hydroxide conductivity of the membrane while maintaining good mechanical properties, so as to enhance the commercial application potential of ion-solventized membranes in the field of alkaline water electrolysis. Summary of the Invention

[0005] To address the above problems, this invention provides an ion-solventizing membrane for alkaline water electrolysis, its preparation method, and its application.

[0006] To address the aforementioned technical issues, the following solutions are proposed:

[0007] A method for preparing an ion-solvated membrane for alkaline water electrolysis, comprising:

[0008] S1. Dissolve polybenzimidazole in an organic solvent to obtain a mixed solution;

[0009] S2. Add a titanate coupling agent containing pyrophosphate groups to the mixed solution, while heating and stirring. After stirring evenly, the resulting polymer solution is subjected to bubble removal treatment. Then, the defoamed polymer solution is scraped onto the substrate and subjected to gradient vacuum drying.

[0010] S3. Soak the dried ion-solventized membrane in an alkaline solution for 3-14 days to obtain the final product.

[0011] Preferably, in step S1, the organic solvent is at least one of methyl sulfoxide, DMF (N,N-dimethylformamide), DMAc (N,N-dimethylacetamide), and NMP (N-methylpyrrolidone); and the concentration of polybenzimidazole in the mixed solution is 2-6 wt%.

[0012] Preferably, in step S2, the titanate coupling agent containing pyrophosphate groups is titanate coupling agent HY-311, HY-311w, or HY-201; the amount of titanate coupling agent containing pyrophosphate groups added is 1-15% of the mass of polybenzimidazole.

[0013] Preferably, in step S2, the gradient vacuum drying includes: first drying at 30-100 ℃ and a vacuum of 0.03-0.09 MPa for 0.5-2 h, then drying at 110-150 ℃ and a vacuum of 0.03-0.09 MPa for 1-4 h, and finally drying at 110-150 ℃ and a vacuum of 0.09-0.1 MPa for 1-4 h.

[0014] Preferably, in step S1, dissolving polybenzimidazole in an organic solvent includes: adding polybenzimidazole to an organic solvent, then heating and stirring to dissolve the polybenzimidazole in the organic solvent, thereby obtaining a homogeneous mixed solution.

[0015] Preferably, in step S1, the heating temperature is 25-100℃, and the stirring time is 2-3 h.

[0016] Preferably, in step S2, the stirring time is 3-4 hours and the heating temperature is 25-100 °C.

[0017] Preferably, in step S2, the bubble elimination treatment involves ultrasonic treatment of the polymer solution to eliminate bubbles; the ultrasonic treatment time is 10-60 min.

[0018] The substrate is a glass plate, aluminum plate, polytetrafluoroethylene plate or stainless steel plate, etc.; the temperature of the substrate is 30-100℃.

[0019] As a general inventive concept, the present invention also provides an ion-solventized membrane, which is prepared by the aforementioned preparation method.

[0020] As a general inventive concept, the present invention also provides an application of an ion-solventizing membrane in water electrolysis.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention involves adding a titanate coupling agent containing pyrophosphate groups during the preparation of the PBI casting solution, eliminating the bubbling effect caused by the addition, thus obtaining a smooth and uniform membrane sample. This method is simple, and the resulting doped membrane exhibits lower membrane resistance, higher hydroxide conductivity, and maintains good mechanical strength. Compared to porous membranes, the ion-solventized membrane prepared by this invention has improved gas barrier properties due to its dense membrane structure, and compared to pure PBI membranes, it has lower impedance and superior electrochemical performance. The dense membrane of this invention possesses excellent gas barrier properties, good hydroxide conductivity, and mechanical strength, meeting the requirements for use in water electrolysis and can be applied to water electrolysis. Attached Figure Description

[0023] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The polarization curves are for the ion-solventized films prepared in Examples 1-2 and Comparative Example 1.

[0025] Figure 2The mechanical strength diagrams are for the ion-solventized films prepared in Examples 1-3 and Comparative Examples 1-2.

[0026] Figure 3 The diagram shows the combined surface resistivity, conductivity, and mechanical strength of the ion-solventized films prepared in Examples 1-3 and Comparative Examples 1-2. Detailed Implementation

[0027] A method for preparing an ion-solvated membrane for alkaline water electrolysis, comprising:

[0028] S1. Dissolve polybenzimidazole in an organic solvent to obtain a mixed solution;

[0029] S2. Add a titanate coupling agent containing pyrophosphate groups to the mixed solution, while heating and stirring. After stirring evenly, the resulting polymer solution is subjected to bubble removal treatment. Then, the defoamed polymer solution is scraped onto the substrate and subjected to gradient vacuum drying.

[0030] S3. Soak the dried ion-solventized membrane in an alkaline solution for 3-14 days to obtain the final product.

[0031] In some embodiments, in step S1, the organic solvent is at least one of methyl sulfoxide, DMF (N,N-dimethylformamide), DMAc (N,N-dimethylacetamide), and NMP (N-methylpyrrolidone).

[0032] In some preferred embodiments, the concentration of polybenzimidazole in the mixed solution is 2-6 wt%. Too low a concentration will prolong the drying time of the membrane and increase the amount of solvent used; too high a concentration will hinder the stirring and dissolution of the polymer and lead to excessively high viscosity, affecting the preparation of the membrane.

[0033] In some preferred embodiments, in step S2, the titanate coupling agent containing pyrophosphate groups is titanate coupling agent HY-311, HY-311w, or HY-201.

[0034] In some preferred embodiments, the amount of the titanate coupling agent containing pyrophosphate groups added is 1-15% of the mass of polybenzimidazole, more preferably 1-12%, and even more preferably 2-10%.

[0035] In a preferred embodiment, step S2, the gradient vacuum drying includes: first drying at 30-100℃ and a vacuum of 0.03-0.09 MPa for 0.5-2 h, then drying at 110-150℃ and a vacuum of 0.03-0.09 MPa for 1-4 h, and finally drying at 110-150℃ and a vacuum of 0.09-0.1 MPa for 1-4 h. This preferred gradient vacuum drying method is beneficial for obtaining membrane samples with a smooth and uniform surface, free from bubble defects and wrinkles.

[0036] In some embodiments, step S1, dissolving polybenzimidazole in an organic solvent, includes: adding polybenzimidazole to an organic solvent, then heating and stirring to dissolve the polybenzimidazole in the organic solvent, obtaining a homogeneous mixed solution. In some preferred embodiments, in step S1, the heating temperature is 25-100 °C; and the stirring time is 2-3 h.

[0037] In some preferred embodiments, in step S2, the stirring time is 3-4 hours; and the heating temperature is 25-100°C.

[0038] In some preferred embodiments, in step S2, the bubble elimination treatment involves ultrasonic treatment of the polymer solution to eliminate bubbles; the ultrasonic treatment time is 10-60 min.

[0039] In some embodiments, the substrate is a glass plate, an aluminum plate, a polytetrafluoroethylene plate, or a stainless steel plate, etc.; in some preferred embodiments, the temperature of the substrate is 30-100 ℃.

[0040] As a general inventive concept, the present invention also provides an ion-solventized membrane, which is prepared by the aforementioned preparation method.

[0041] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0042] Example 1

[0043] Polymer polybenzimidazole (PBI) was added to DMSO, and the concentration of PBI was controlled at 4 wt%. Then, the mixture was heated to 70 °C in an oil bath and magnetically stirred for 3 h to completely dissolve PBI in DMSO to obtain a mixed solution. Then, bis(dioctyloxypyrophosphate) ethylene titanate (titanium ester coupling agent HY-311) was added at a mass ratio of 5% to HY-311 / (polybenzimidazole + titanate coupling agent HY-311). The mixture was stirred for 3 hours to ensure homogeneity. The polymer solution was then sonicated for 30 minutes to eliminate air bubbles. It was then coated onto a glass plate at 70°C using an 800 μm doctor blade and placed in a vacuum drying oven for drying. The drying process involved first drying at 70°C and 0.08 MPa for 0.5 hours, then at 120°C and 0.08 MPa for 2 hours, and finally at 120°C and 0.1 MPa for 2 hours (the temperature was increased from 70°C to 120°C, and the vacuum was maintained at 0.08 MPa for 2 hours before being increased to 0.1 MPa). After drying, the film was immersed in KOH solution for 7 days to obtain an ion-solventized film doped with 5% bis(dioctyloxypyrophosphate) ethylene titanate.

[0044] Observation revealed that the obtained ion-solventized film had a dense and uniform surface, free of residual bubbles or pores. The solvent evaporated uniformly, and no adverse solvent effects were observed during film formation. Furthermore, the prepared ion-solventized film did not exhibit significant delamination, which is presumably due to the fact that the organic phase in the bis(dioctyloxypyrophosphate) ethylene titanate coupling agent is a long-chain alkane, capable of entanglement with the molecular chains of PBI, effectively enhancing the bonding between the two.

[0045] Example 2

[0046] The only difference between this embodiment and Example 1 is the amount of titanate coupling agent HY-311 added. In this embodiment, the titanate coupling agent HY-311 is added at a mass ratio of 10% (HY-311 / (polybenzimidazole + titanate coupling agent HY-311)). The resulting membrane surface is dense and uniform, without residual bubbles or pores.

[0047] Example 3

[0048] The only difference between this embodiment and Example 1 is that in this embodiment, the titanate coupling agent HY-311 is added at a mass ratio of HY-311 / (polybenzimidazole + titanate coupling agent HY-311) of 15%. The resulting film is dense and uniform, without residual bubbles or pores.

[0049] Example 4

[0050] The only difference between this embodiment and Embodiment 1 is that gradient vacuum drying was not used. In this embodiment, the glass plate with the coated film was placed in a vacuum drying oven. The vacuum drying conditions were: a vacuum degree of 0.1 MPa, drying at 70°C for 2 hours, and then drying at 120°C for 2 hours. The resulting film had bubble defects and poor surface uniformity and low flatness.

[0051] Comparative Example 1

[0052] The only difference between this comparative example and Example 1 is that the titanate coupling agent HY-311 is not added. Instead, PBI is completely dissolved in DMSO to obtain a mixed solution, which is then subjected to bubble elimination treatment and subsequent operations to obtain an ion-solventized film.

[0053] Comparative Example 2

[0054] The only difference between this comparative example and Example 1 is the amount of titanate coupling agent HY-311 added. In this comparative example, the titanate coupling agent HY-311 was added at a mass ratio of HY-311 / (polybenzimidazole + titanate coupling agent HY-311) of 20%. The resulting membrane was dense, without residual bubbles or pores. However, due to the excessive amount of HY-311 added, it failed to disperse uniformly in the solution, resulting in a distribution of tiny particles on the membrane surface, and the membrane surface was not smooth and uniform.

[0055] The performance of the ion-solvated films prepared in each embodiment and comparative example was tested, as follows:

[0056] I. Alkali absorption rate test:

[0057] After soaking the membrane sample in 2M KOH solution at room temperature for 7 days, remove it, wipe the surface dry with filter paper, and weigh it using an analytical balance, recording the mass as m1. Dry the sample in a vacuum drying oven at 120℃ for more than 12 hours, and weigh it again, recording the mass as m2. Wash the sample thoroughly with deionized water to remove KOH from the sample, and then place it in a vacuum drying oven at 120℃ for more than 12 hours, weighing the mass as m3.

[0058] m1 = polymer + alkali + water

[0059] m2 = polymer + alkali

[0060] m3 = polymer

[0061] The formula for calculating the alkali absorption rate can be derived from the above:

[0062] Alkali absorption rate = (m2-m3) / m1

[0063] Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Doping amount / % 0 5 10 15 20 Alkali absorption rate / % 11.6 14.0 15.7 16.3 16.4

[0064] The data in the table above show that the alkali uptake rate of the membrane increases with the increase of doping amount. It is speculated that this may be because the pyrophosphate groups in the structure have a certain interaction with the alkali, which can enhance the conductivity of the membrane, reduce the sheet resistance, and promote the conduction of hydroxide ions in the membrane, which is beneficial to the improvement of the membrane's electrochemical performance. Therefore, the increase of pyrophosphate group content increases the alkali uptake rate. The alkali uptake rate does not change significantly under high doping amount because the excessive amount of addition cannot be well dispersed in the casting solution, and the interaction with the alkali tends to the upper limit.

[0065] II. Electrochemical Testing:

[0066] Membrane test area 25cm² 2 Commercially available nickel foam was used as the anode and cathode, assembled into the test assembly, and tested in 6MKOH solution at 80°C. The solution was circulated between the two flow channels at a flow rate of 50 mL / min. The system was held at 1.7 V for 30 min to reach a steady state before recording the first polarization curve. The membrane resistance was analyzed using electrochemical impedance spectroscopy (EIS), with a frequency range of 10 kHz–0.1 Hz.

[0067] Conductivity is calculated using a formula.

[0068]

[0069] σ is the conductivity, L is the film thickness, A is the test area, R1 is the component resistance with film, and R2 is the component resistance without film.

[0070] Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Doping amount / % 0 5 10 15 20 Surface resistance / mΩ·cm2 206 157.6 212.5 432.5 / Conductivity / mS / cm 29.1 31.7 23.5 11.6 /

[0071] Note: / indicates insufficient uniformity of the membrane, and no test was conducted.

[0072] In the table above, the lowest sheet resistance and highest conductivity were achieved at a doping concentration of 5%. Compared to undoped films, the sheet resistance decreased by 23.9%, and the conductivity increased by 8.9%. It can also be seen that a higher doping concentration is not necessarily better; excessively high concentrations lead to a significant increase in sheet resistance and a decrease in conductivity. This is because an increase in doping concentration may affect the dispersion of the coupling agent in the casting solution and the film, thus affecting the continuity and rate of hydroxide ion transport within the film.

[0073] Increasing the alkali absorption rate can indeed improve its electrochemical performance, but there is a suitable amount to add. The module is then used for performance testing.

[0074] Figure 1 The graph shows the polarization curves. It can be seen that the 5% doped film achieves a higher current density than the undoped film. This is consistent with the sheet resistance and conductivity test results. A polarization curve could not be obtained for the 20% doped sample due to its excessively high resistance.

[0075] Mechanical strength:

[0076] The prepared ion-solvated membrane was subjected to mechanical strength testing according to the test standard GB / T 1040.3-2006, and the data are shown in Figure 3 below:

[0077] Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Doping amount / % 0 5 10 15 20 Mechanical strength / MPa 106 96 56 44 20 Elongation at break / % 34.0 11.3 7.5 7.8 9.2

[0078] Figure 2 To assess the mechanical strength and elongation at break of each membrane, a universal testing machine was used to determine the effect of doping on the membrane's mechanical strength. It was found that increasing the doping amount reduces the membrane's strength and affects its elongation at break. However, when the doping amount is only 5%, the decrease in mechanical strength is only 9.4%, still close to 100 MPa, which fully meets the application requirements.

[0079] Figure 3 The data summary chart is shown above. The test results indicate that doping with titanate coupling agents containing pyrophosphate groups has a positive effect on alkali uptake. Furthermore, electrochemical tests, including sheet resistance, conductivity, and polarization curves, confirm that a 5% doping concentration improves the membrane's performance to some extent. Mechanical property characterization also confirms that the 5% doping concentration has minimal impact on the membrane's mechanical strength, which remains at a high level.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an ion-solvated membrane for alkaline water electrolysis, characterized in that, include: S1. Dissolve polybenzimidazole in an organic solvent to obtain a mixed solution; S2. Add a titanate coupling agent containing pyrophosphate groups to the mixed solution, while heating and stirring. After stirring until homogeneous, perform bubble removal treatment on the resulting polymer solution. Then, coat the defoamed polymer solution onto a substrate and perform gradient vacuum drying. The titanate coupling agent containing pyrophosphate groups is titanate coupling agent HY-311, HY-311w, or HY-201. The amount of titanate coupling agent containing pyrophosphate groups added is 1-15% of the mass of polybenzimidazole. S3. Soak the dried ion-solventized membrane in an alkaline solution for 3-14 days to obtain the final product.

2. The method for preparing the ion-solvated film as described in claim 1, characterized in that, In step S1, the organic solvent is at least one of methyl sulfoxide, DMF, DMAc, and NMP; and the concentration of polybenzimidazole in the mixed solution is 2-6 wt%.

3. The method for preparing the ion-solvated film as described in claim 1 or 2, characterized in that, In step S2, the gradient vacuum drying includes: first drying at 30-100℃ and a vacuum of 0.03-0.09 MPa for 0.5-2 h, then drying at 110-150℃ and a vacuum of 0.03-0.09 MPa for 1-4 h, and finally drying at 110-150℃ and a vacuum of 0.09-0.1 MPa for 1-4 h.

4. The method for preparing the ion-solvated film as described in claim 1 or 2, characterized in that, In step S1, dissolving polybenzimidazole in an organic solvent includes: adding polybenzimidazole to an organic solvent, then heating and stirring to dissolve the polybenzimidazole in the organic solvent and obtain a uniform mixed solution.

5. The method for preparing the ion-solvated film as described in claim 4, characterized in that, In step S1, the heating temperature is 25-100℃; the stirring time is 2-3 h.

6. The method for preparing the ion-solvated film as described in claim 1 or 2, characterized in that, In step S2, the stirring time is 3-4 hours; the heating temperature is 25-100 ℃.

7. The method for preparing the ion-solvated film as described in claim 1 or 2, characterized in that, In step S2, the bubble elimination process involves ultrasonically treating the polymer solution to eliminate bubbles; the ultrasonic treatment time is 10-60 min. The substrate is a glass plate, an aluminum plate, a polytetrafluoroethylene plate, or a stainless steel plate; the temperature of the substrate is 30-100 ℃.

8. An ion-solventized membrane, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the ion-solventized membrane as described in claim 8 in water electrolysis.

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