A silicon-oxygen network-containing anion exchange membrane and a preparation method thereof

Abstract

The application belongs to the technical field of fuel cell materials, and particularly relates to a preparation method of a siloxane network anion exchange membrane, which comprises the following steps: (1) preparation of a polyaryl piperidine polymer; (2) preparation of iodomethyl trimethoxysilane; (3) modification of siloxane; (4) preparation of an anion exchange membrane; and (5) hydrolysis of siloxane. In the application, the siloxane can be hydrolyzed into a siloxane network structure containing hydroxyl groups, so as to improve the water retention capacity of the membrane and improve the chemical stability of the membrane under water shortage conditions such as low humidity or high current density. Meanwhile, by changing the hydrolysis conditions of the siloxane and controlling the structure of the hydroxyl-containing siloxane network, the hydrated ion channel can be controlled, the ion transmission rate of the membrane can be optimized, the membrane has a high ion conductivity, and the application has a wide application prospect in the field of anion exchange membrane fuel cells.

Description

A silicon-oxygen network anion exchange membrane and its preparation method Technical Field

[0001] This invention belongs to the field of fuel cell systems and relates to a method for preparing an anion exchange membrane, particularly to a siloxy-containing quaternized piperidine polyaryl basic anion exchange membrane and its preparation method. Background Technology

[0002] Fuel cells possess advantages such as high efficiency, cleanliness, and sustainability, and occupy an important position in the field of new energy. Alkaline anion exchange membrane fuel cells (HEMFCs) have attracted widespread attention due to their advantages, such as the ability to use non-precious metal catalysts and inexpensive bipolar plates in an alkaline environment, which significantly reduces the cost of fuel cells.

[0003] Anion exchange membranes (HEMs) are one of the key materials in HEMFCs, constraining their development. HEMs primarily function to conduct hydroxide ions and isolate anode and cathode gases; their performance directly impacts fuel cell efficiency and lifespan. In particular, poor chemical stability is a major challenge for HEMs, a problem that researchers in this field are actively working to solve. In recent years, significant progress has been made in HEM development, with substantial improvements in various aspects of membrane performance, especially in conductivity and offline stability. Regarding conductivity, the ionic conductivity of anion exchange membranes has approached or even surpassed that of Nafion membranes. In terms of offline stability, researchers have also achieved excellent results through various strategies, including geometric optimization and substituent selection. Currently, the offline stability of anion exchange membranes reaches up to 2000 hours. For example, the poly(terphenylpiperidine) polymer developed by Zhuang et al. exhibits a stability of 210 days (Zhuang et al., Journal of Power Sources 2018, 390, 165-167). The polyarylpiperidine polymer developed by Yan et al. exhibits stability for 2000 hours (Yanetal, Nature Energy 2019, 4, 392-398). The polyfluorene-piperidine polymer developed by Lee et al. also shows stability for 2000 hours (Leeetal, Nat Commun 2021, 12, 2367). However, in practical applications, the lifetime of HEMFCs is generally below 300 hours (DRDekel, Journal of Power Sources 2018, 375, 158-169), especially under low humidity or high current density conditions. Under these conditions, the degree of hydration within the membrane decreases rapidly, leading to increased hydroxyl attack and subsequent rapid membrane degradation, ultimately resulting in a significant reduction in battery performance and lifespan. Therefore, the poor chemical stability of anion exchange membranes under low humidity or high current density operating conditions remains a key bottleneck for the further development of HEMFCs. Summary of the Invention

[0004] Currently, anion exchange membranes exhibit poor chemical stability under low humidity or high current density conditions, rapidly degrading under hydroxyl attack. This invention provides a silicon-oxygen network-containing anion exchange membrane and its preparation method. One objective is to increase the number of water molecules surrounding the piperidine ring cation by introducing a silicon-oxygen network generated in situ through the hydrolysis of silicon oxides, thereby reducing the probability of direct hydroxyl attack on the cation and improving the chemical stability of the anion exchange membrane, especially under water-deficient conditions such as low humidity or high current density. Another objective of this invention is to regulate the size of the hydrated ion channels and optimize the ion conduction rate of the anion membrane through the in-situ hydrolysis reaction of siloxanes.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] A silicon-oxygen network anion exchange membrane, wherein the structure of the anion exchange membrane is a polyaromatic piperidine copolymer, and its structure is shown in the general formula:

[0007]

[0008] Wherein, Ar is any one of the following monomers, or is copolymerized using any two of the following monomers;

[0009]

[0010] R is selected from the following structures;

[0011]

[0012] Based on the above technical solutions, preferably, the polymer backbone is an aromatic polymer and the cationic functional group is a silicon-containing piperidine cyclic quaternary ammonium salt.

[0013] A method for preparing a silicon-oxygen network anion exchange membrane includes the following steps:

[0014] (1) Preparation of iodosiloxane compounds

[0015] The iodosiloxane compound was dissolved in acetonitrile, sodium iodide was added, and the mixture was refluxed at 90-110 °C for 24-48 h. The acetonitrile was then removed by rotary evaporation, and the remaining solution was separated by vacuum distillation to obtain a colorless solution of iodomethyltrimethoxysilane.

[0016] Wherein, the chlorosiloxane compound is at least one of iodomethyltrimethoxysilane, iodomethyldimethoxymethylsilane, and iodomethylmethoxydimethylsilane; the iodosiloxane compound is at least one of iodomethyltrimethoxysilane, iodomethyldimethoxymethylsilane, and iodomethylmethoxydimethylsilane.

[0017] (2) Modification of siloxanes

[0018] The yellowish-white solid of polyarylepiperidine polymer was dissolved in dimethyl sulfoxide, and a certain proportion of the iodosiloxane compound obtained in step (1) was added. The temperature was controlled at 50-100℃, and the quaternization reaction was carried out for 24-72 hours. After the reaction was completed, a brownish-black siloxane-modified polyarylepiperidine polymer solution was obtained.

[0019] (3) Preparation of anion exchange membranes

[0020] The polymer solution obtained in step (2) is diluted with dimethyl sulfoxide at 1-20 wt%, mixed thoroughly, poured into a glass mold for casting or coating, and dried at 80°C to form a film to obtain a quaternized siloxane-modified polyarylpiperidine anion exchange membrane.

[0021] (4) Hydrolysis of siloxanes

[0022] The anion exchange membrane obtained in step (3) was immersed in potassium hydroxide solution or saturated potassium carbonate solution and hydrolyzed at 60-100℃ for 1-5 hours. After the reaction was completed, a piperidine quaternary ammonium salt anion exchange membrane containing a silicon-oxygen network was obtained.

[0023] Based on the above technical solution, preferably, the molar ratio of the chlorosiloxane compound and sodium iodide in step (1) is 1:(1-20).

[0024] Based on the above technical solutions, preferably, the molar ratio of the chlorosiloxane compound to the polyarylpiperidine polymer in step (2) is (1-10):1.

[0025] Based on the above technical solutions, preferably, the polyarylepiperidine polymer is selected from p-terphenylpiperidine polymer, polyfluorenylpiperidine polymer, and polyspirocyclic piperidine polymer; the p-terphenylpiperidine polymer can be polymerized from two monomers, p-terphenyl and N-methylpiperidine, to form a copolymer according to the literature (Zhuang et al., Journal of Power Sources 2018, 390, 165-167), and other monomers can also be achieved in the same way.

[0026] Based on the above technical solutions, preferably, in the hydrolysis of siloxane in preparation step (4), the concentration of potassium hydroxide is 1-5M.

[0027] Beneficial effects

[0028] This invention discloses a silicon-oxygen network anion exchange membrane, which is a polymer with an aromatic backbone and a silicon-oxygen network composed of piperidine cationic groups. The use of piperidine cationic groups and aromatic polymers with a conjugated backbone improves the chemical stability of the anion exchange membrane. Furthermore, the siloxane modified with piperidine cationic groups can hydrolyze into a silicon-oxygen network, increasing the number of water molecules around the cations and thus improving the hydration coefficient of the anion exchange membrane, enhancing its water retention capacity, and improving its chemical stability under low humidity or high current density conditions. By changing the chemical composition and hydrolysis conditions of the modified siloxane, the hydrophilicity and size of the silicon-oxygen network can be controlled, thereby regulating the hydrated ion channels and optimizing the ionic conductivity of the anion exchange membrane, resulting in a membrane with high ionic conductivity and broad application prospects in the field of anion exchange membrane fuel cells. In addition, this preparation method involves obtaining the polymer first and then performing silanization modification, which not only benefits the polymer's molecular weight but also facilitates control of the silicon-oxygen network system. If the monomer is silanized first and then polymerized, it will not only affect the polymer's molecular weight but also make it difficult to adjust the silicon-oxygen network system. Attached Figure Description

[0029] Figure 1 is a reaction flow chart of step 1 in Example 1.

[0030] Figure 2 is a reaction flow chart of step 2 in Example 1.

[0031] Figure 3 is a reaction flow chart of step 4 in Example 1.

[0032] Figure 4 is an infrared characterization image.

[0033] Figure 5 shows the moisture content. Detailed Implementation

[0034] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0035] Example 1

[0036] A method for preparing a silicon-oxygen network anion exchange membrane is as follows:

[0037] (1) Preparation of polyaryl polymers

[0038] The copolymer of p-terphenyl and N-methylpiperidone (QAPPT) was prepared according to the literature (Zhuang et al., Journal of Power Sources 2018, 390, 165-167). The process flow diagram for this step is shown in Figure 1.

[0039] (2) Preparation of iodomethyltrimethoxysilane

[0040] 20 g of chloromethyltrimethoxysilane was dissolved in 100 ml of acetonitrile, sodium iodide was added, and the mixture was refluxed at 90 °C for 24 h. The molar ratio of sodium iodide to chloromethyltrimethoxysilane was 10:1. Acetonitrile was then removed by rotary evaporation, and the remaining solution was separated by vacuum distillation to obtain iodomethyltrimethoxysilane.

[0041] (3) Modification with siloxanes

[0042] 1g of the polyarylpiperidine polymer obtained in step (1) and 10ml of dimethyl sulfoxide solvent were added to a single-necked flask and dissolved by magnetic stirring. Iodomethyltrimethoxysilane obtained in step (2) was added, and the temperature was controlled at 80℃. The quaternization reaction was carried out for 24h. After the reaction was completed, a brownish-black siloxane-modified polyarylpiperidine polymer solution was obtained. The molar ratio of iodomethyltrimethoxysilane to polyarylpiperidine polymer was 1:1. The process flow diagram of this step is shown in Figure 2.

[0043] (4) Preparation of anion exchange membranes

[0044] Take 3 ml of the polymer solution obtained in step (2) with a pipette and place it in a sample tube. Add 7 ml of dimethyl sulfoxide to dilute it. After mixing thoroughly, pour it into a 10 cm × 10 cm glass mold and cast it. Dry it in a drying oven at 80 °C to form a film and obtain a siloxane-modified polyarylpiperidine anion exchange membrane.

[0045] (5) Hydrolysis of siloxanes

[0046] The glass mold with the film already formed was removed and immersed in a saturated potassium carbonate solution for hydrolysis at 80°C for 1 hour to obtain a piperidine quaternary ammonium salt anion exchange membrane (TOSi-1) containing a silicon-oxygen network. The process flow diagram for this step is shown in Figure 3. Figure 4 shows its infrared spectrum, which contains an infrared absorption peak of Si-O-Si, indicating successful introduction of siloxane. Furthermore, as shown in Figure 5, its water content is higher than that of the poly(terphenyl piperidine) copolymer.

[0047] Example 2

[0048] A method for preparing a silicon-oxygen network anion exchange membrane is as follows:

[0049] (1) Preparation of polyaryl polymers

[0050] A copolymer of p-terphenyl and N-methylpiperidone (QAPPT) was prepared according to the literature (Zhuang et al., Journal of Power Sources 2018, 390, 165-167).

[0051] (2) Preparation of iodomethyltrimethoxysilane

[0052] 20 g of chloromethyltrimethoxysilane was dissolved in 100 ml of acetonitrile, sodium iodide was added, and the mixture was refluxed at 90 °C for 24 h. The molar ratio of sodium iodide to chloromethyltrimethoxysilane was 10:1. Acetonitrile was then removed by rotary evaporation, and the remaining solution was separated by vacuum distillation to obtain iodomethyltrimethoxysilane.

[0053] (3) Modification with siloxanes

[0054] 1g of the polyarylpiperidine polymer obtained in step (1) and 10ml of dimethyl sulfoxide solvent were added to a single-necked flask and dissolved by magnetic stirring. Iodomethyltrimethoxysilane obtained in step (2) was added, and the temperature was controlled at 80℃. The quaternization reaction was carried out for 24h. After the reaction was completed, a brownish-black siloxane-modified polyarylpiperidine polymer solution was obtained. The molar ratio of iodomethyltrimethoxysilane to polyarylpiperidine polymer was 2:1. The process flow diagram of this step is shown in Figure 2.

[0055] (4) Preparation of anion exchange membranes

[0056] Take 3 ml of the polymer solution obtained in step (2) with a pipette and place it in a sample tube. Add 7 ml of dimethyl sulfoxide to dilute it. After mixing thoroughly, pour it into a 10 cm × 10 cm glass mold and cast it. Dry it in a drying oven at 80 °C to form a film and obtain a siloxane-modified polyarylpiperidine anion exchange membrane.

[0057] (5) Hydrolysis of siloxanes

[0058] The glass mold with the film already formed was removed and immersed in a saturated potassium carbonate solution for hydrolysis at 80°C for 1 hour to obtain a piperidine quaternary ammonium salt anion exchange membrane (TOSi-2) containing a silicon-oxygen network. The process flow diagram for this step is shown in Figure 3. Figure 4 shows its infrared spectrum, which contains an infrared absorption peak of Si-O-Si, indicating successful introduction of siloxane. Furthermore, as shown in Figure 5, its water content is higher than that of the poly(terphenyl piperidine) copolymer.

[0059] Example 3

[0060] A method for preparing a silicon-oxygen network anion exchange membrane is as follows:

[0061] (1) Preparation of polyaryl polymers

[0062] A copolymer of p-terphenyl and N-methylpiperidone (QAPPT) was prepared according to the literature (Zhuang et al., Journal of Power Sources 2018, 390, 165-167).

[0063] (2) Preparation of iodomethyltrimethoxysilane

[0064] 20 g of chloromethyltrimethoxysilane was dissolved in 100 ml of acetonitrile, sodium iodide was added, and the mixture was refluxed at 90 °C for 24 h. The molar ratio of sodium iodide to chloromethyltrimethoxysilane was 10:1. Acetonitrile was then removed by rotary evaporation, and the remaining solution was separated by vacuum distillation to obtain iodomethyltrimethoxysilane.

[0065] (3) Modification with siloxanes

[0066] 1g of the polyarylpiperidine polymer obtained in step (1) and 10ml of dimethyl sulfoxide solvent were added to a single-necked flask and dissolved by magnetic stirring. Iodomethyltrimethoxysilane obtained in step (2) was added and the temperature was controlled at 80℃. The quaternization reaction was carried out for 24h. After the reaction was completed, a brownish-black siloxane-modified polyarylpiperidine polymer solution was obtained. The molar ratio of iodomethyltrimethoxysilane to polyarylpiperidine polymer was 4:1. The process flow diagram of this step is shown in Figure 2.

[0067] (4) Preparation of anion exchange membranes

[0068] Take 3 ml of the polymer solution obtained in step (2) with a pipette and place it in a sample tube. Add 7 ml of dimethyl sulfoxide to dilute it. After mixing thoroughly, pour it into a 10 cm × 10 cm glass mold and cast it. Dry it in a drying oven at 80 °C to form a film and obtain a siloxane-modified polyarylpiperidine anion exchange membrane.

[0069] (5) Hydrolysis of siloxanes

[0070] The glass mold with the film already formed was removed and immersed in a saturated potassium carbonate solution for hydrolysis at 80°C for 1 hour to obtain a piperidine quaternary ammonium salt anion exchange membrane (TOSi-4) containing a silicon-oxygen network. The process flow diagram for this step is shown in Figure 3. Figure 4 shows its infrared spectrum, which contains an infrared absorption peak of Si-O-Si, indicating successful introduction of siloxane. Furthermore, as shown in Figure 5, its water content is higher than that of the poly(terphenyl piperidine) copolymer.

[0071] Example 4

[0072] A method for preparing a silicon-oxygen network anion exchange membrane is as follows:

[0073] (1) Preparation of polyaryl polymers

[0074] A copolymer of p-terphenyl and N-methylpiperidone (QAPPT) was prepared according to the literature (Zhuang et al., Journal of Power Sources 2018, 390, 165-167).

[0075] (2) Preparation of iodomethylmethoxydimethylsilane

[0076] 20 g of chloromethylmethoxydimethylsilane was dissolved in 100 ml of acetonitrile, sodium iodide was added, and the mixture was refluxed at 90 °C for 24 h. The molar ratio of sodium iodide to iodomethylmethoxydimethylsilane was 10:1. Acetonitrile was then removed by rotary evaporation, and the remaining solution was separated by vacuum distillation to obtain iodomethylmethoxydimethylsilane.

[0077] (3) Modification with siloxanes

[0078] 1g of the polyarylpiperidine polymer obtained in step (1) and 10ml of dimethyl sulfoxide solvent were added to a single-necked flask and dissolved by magnetic stirring. Iodomethylmethoxydimethylsilane obtained in step (2) was added, and the temperature was controlled at 80℃. The quaternization reaction was carried out for 24h. After the reaction was completed, a brownish-black siloxane-modified polyarylpiperidine polymer solution was obtained. The molar ratio of iodomethylmethoxydimethylsilane to polyarylpiperidine polymer was 4:1.

[0079] (4) Preparation of anion exchange membranes

[0080] Take 3 ml of the polymer solution obtained in step (2) with a pipette and place it in a sample tube. Add 7 ml of dimethyl sulfoxide to dilute it. After mixing thoroughly, pour it into a 10 cm × 10 cm glass mold and cast it. Dry it in a drying oven at 80 °C to form a film and obtain a siloxane-modified polyarylpiperidine anion exchange membrane.

[0081] (5) Hydrolysis of siloxanes

[0082] The glass mold with the film already formed was taken out and immersed in a saturated potassium carbonate solution. It was hydrolyzed at 80°C for 1 hour to obtain a piperidine quaternary ammonium salt anion exchange membrane (Si-4) containing a silicon-oxygen network.

[0083] All the raw materials listed in this invention, as well as the upper and lower limits and ranges of the raw materials and process parameters (such as time), can be used to test this invention. Examples are not listed here.

Claims

1. A silicon-oxygen network anion exchange membrane, characterized in that, The anion exchange membrane is a polyaromatic piperidine copolymer, and its structure is shown in the general formula: Wherein, Ar is any one of the following monomers, or is copolymerized using any two of the following monomers; R is selected from the following structures; The preparation method of the silicon-oxygen network anion exchange membrane includes the following steps: (1) Preparation of iodosiloxane compound: Dissolve chlorosiloxane compound in acetonitrile, add sodium iodide, and reflux at 90-110℃ for 24-48 h; then remove acetonitrile by rotary evaporation, and separate the remaining solution by vacuum distillation to obtain iodosiloxane compound; wherein, the chlorosiloxane compound is at least one of chloromethyltrimethoxysilane, chloromethyldimethoxymethylsilane and chloromethylmethoxydimethylsilane; the iodosiloxane compound is at least one of iodomethyltrimethoxysilane, iodomethyldimethoxymethylsilane and iodomethylmethoxydimethylsilane; (2) Modification of siloxane: Dissolve polyarylpiperidine polymer in dimethyl sulfoxide, add the iodosiloxane compound obtained in step (1), control the temperature at 50-100℃, and carry out the quaternization reaction for 24-72 h. h, after the reaction was completed, a polyarylpiperidine polymer solution modified with siloxane was obtained; (3) Preparation of anion exchange membrane The polymer solution obtained in step (2) was diluted with dimethyl sulfoxide. After dilution, the polymer solution concentration was 2-20wt%. After thorough mixing, it was poured into a mold for casting or scraping. After drying, a quaternized siloxane-modified polyarylpiperidine anion exchange membrane was obtained; (4) Hydrolysis of siloxane The anion exchange membrane obtained in step (3) was immersed in potassium hydroxide solution or saturated potassium carbonate solution and hydrolyzed at 60-100℃ for 1-5 h. After the reaction was completed, a piperidine quaternary ammonium salt anion exchange membrane containing a silicon-oxygen network was obtained.

2. The silicon-oxygen network anion exchange membrane according to claim 1, characterized in that, The polymer backbone is an aromatic polymer, and the cationic functional group is a silicon-containing piperidine cyclic quaternary ammonium salt.

3. The silicon-oxygen network anion exchange membrane as described in claim 1, characterized in that, The molar ratio of the chlorosiloxane compound and sodium iodide in step (1) is 1:1-20.

4. The silicon-oxygen network anion exchange membrane as described in claim 1, characterized in that, The molar ratio of the iodosiloxane compound to the polyarylpiperidine polymer in step (2) is 1-10:

1.

5. The silicon-oxygen network anion exchange membrane as described in claim 1, characterized in that, The concentration of the diluted polymer solution in step (3) is 1-20 wt%.

6. The silicon-oxygen network anion exchange membrane as described in claim 1, characterized in that, The concentration of the potassium hydroxide solution in step (4) is 1-5 M.

7. The silicon-oxygen network anion exchange membrane as described in claim 1, characterized in that, The polyarylpiperidine polymer is selected from p-terphenylpiperidine polymer, polyfluorenylpiperidine polymer, and polyspirocyclic piperidine polymer.

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