Sulfonic acid-functionalized covalent organic frameworks / nafion proton exchange materials, methods of making, and uses thereof

Abstract

The application discloses a kind of sulfonic acid group covalent organic framework / Nafion composite material for proton conduction and preparation method and application thereof, belong to fuel cell technical field.The application first utilizes double sulfonic acid group organic aromatic amine ligand and aldehyde group ligand to construct a kind of sulfonic acid functional two-dimensional covalent organic framework material COF-(SO3H)2 by condensation reaction.COF-(SO3H)2 is compounded with Nafion polymer to prepare proton exchange membrane, and the proton exchange membrane material has excellent proton conduction, and the proton conductivity is 1.338*10 ‑1 S·cm ‑1 (80ºC).The proton exchange membrane material of the application is prepared by solvothermal process and casting method, and the preparation method is simple and easy to operate, which provides a new choice for proton conduction material in fuel cell, and expands the application value of covalent organic framework material.

Description

Technical Field

[0001] This invention belongs to the field of fuel electronics technology, specifically relating to the synthesis of a sulfonic acid functionalized covalent organic framework / Nafion composite material and its application in proton transport. Background Technology

[0002] Fuel cells can directly convert the chemical energy of fuel into electrical energy, and are green and pollution-free, making them one of the most promising energy conversion devices. In the design and research of fuel cells, developing suitable proton-conducting materials is crucial to obtaining high-performance fuel cells. Currently, DuPont's Nafion proton exchange membrane is widely used. However, proton conductivity is generally dependent on the presence of water, and high humidity can easily lead to liquid water clogging the gas transport channels. Studies have shown that the introduction of functionalized nanofillers (SiO2, MOFs, graphene, etc.) can improve the water content and water retention capacity of proton exchange membranes, potentially improving the continuity of proton transfer channels and enhancing proton transfer. Covalent organic frameworks (COFs) possess advantages such as high specific surface area, tunable periodic porosity, and ordered structure. Ordered nanopores can provide regular transport channels for protons, increasing the proton carrier capacity within the pores and achieving high proton conductivity. Compared with other materials, COFs exhibit excellent stability and compatibility due to their relatively stable covalent bonds. Furthermore, introducing sulfonate groups into the COF framework can provide additional proton transfer sites, thereby improving the ion exchange capacity of the material. Combining with polymers can further form interfacial proton transfer channels while increasing mechanical properties. This holds promise for addressing the shortcomings of existing materials and designing and developing high-performance materials. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a sulfonic acid-functionalized covalent organic framework / Nafion composite material, its preparation method, and its application. First, a highly crystalline sulfonic acid-functionalized COF material (COF-(SO3H)2) is constructed by condensing 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 2,5-diamino-1,4-benzenedisulfonic acid organic ligands with aldehydes and amines. Then, an ion exchange membrane is prepared by composite bonding with Nafion using a mixed casting method. This membrane material exhibits excellent proton transport performance; the proton conductivity of COF-(SO3H)2 is 2.212 × 10⁻⁶ under 80% humidity conditions. -2 S·cm -1 Under the same conditions, the proton conductivity of the commercial product Nafion is 5.566 × 10⁻⁶. -2 S·cm -1 The proton conductivity of the COF-(SO3H)2 / Nafion composite material reaches 1.338 × 10⁻⁶. -1 S·cm-1 It is 2.4 times that of commercial products.

[0004] To solve the above problems, the present invention adopts the following technical solution:

[0005] A method for preparing a sulfonic acid-functionalized covalent organic framework / Nafion proton exchange material includes the following steps:

[0006] (1) Dissolve 2,4,6-trihydroxytriphenylmethane and 2,5-diaminobenzene-1,4-disulfonic acid in a mixed solution of trimethylbenzene and 1,4-dioxane, add acetic acid solution, stir at room temperature for 15 minutes to make the system uniformly mixed; transfer to liquid nitrogen, freeze solidify for 3 minutes, and vacuum the reaction system.

[0007] (2) After the system obtained in step (1) is melted-frozen-vacuumed three times, it is sealed and transferred to an oven for solvothermal reaction;

[0008] (3) After the reaction was complete, the sample was cooled to room temperature to obtain a crystalline sample. It was washed with tetrahydrofuran and N,N-dimethylformamide and then dried to obtain a sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material.

[0009] (4) The sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material prepared in step (3) is dispersed in a DMF-treated Nafion d-521 solution and ultrasonically stirred for 6 hours to obtain a casting solution. The casting solution is then poured into a glass culture dish with an inner diameter of 9 cm and dried to obtain the sulfonic acid-functionalized covalent organic framework / Nafion proton exchange material.

[0010] Furthermore, the structural units of the sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material are 2,4,6-trihydroxytribenzaldehyde and 2,5-diaminobenzene-1,4-disulfonic acid.

[0011] Furthermore, such as Figure 2 As shown, the sulfonic acid-functionalized COF-(SO3H)2 material is monoclinic with unit cell parameters a=22.86 Å, α=90°, b=22.86 Å, β=90°, c=3.6 Å, and γ=120°. The COF-(SO3H)2 material has a two-dimensional supramolecular structure, with layers forming a three-dimensional structure through π-π interactions. The entire network structure exhibits hexagonal channels with a side length of 10.33 Å.

[0012] Furthermore, in step (1), the molar ratio of 2,4,6-trihydroxytriphenylmethane and 1,4-disulfonic acid-p-phenylenediamine is 2:3; the volume ratio of trimethylbenzene and 1,4-dioxane in the mixed solution of trimethylbenzene and 1,4-dioxane is 1:1; and the concentration of the acetic acid solution is 6 mol / L.

[0013] Furthermore, in step (2), the solvothermal reaction temperature is 120°C and the solvothermal reaction time is 3 days.

[0014] Furthermore, in step (3), the temperature is reduced to room temperature at a rate of 10°C / h.

[0015] Furthermore, in step (4), the mass fraction of the sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material is 5%-20%, preferably 10%.

[0016] Furthermore, the drying temperature in step (4) is 80°C and the drying time is 10 h.

[0017] The application of the sulfonic acid-functionalized COF-(SO3H)2 material described in this invention in proton conductivity: COF-(SO3H)2 / Nafion proton exchange membrane material is prepared into a disc with a diameter of 5 mm using a mold, and the proton conductivity of the material in the humidity range of 60%-90% is measured by electrochemical impedance spectroscopy in a constant temperature and humidity chamber.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The proton-conducting material of the present invention can be prepared by hydrothermal method and casting process. The preparation method is simple and easy to implement, providing a new choice for proton-conducting materials and expanding the application value of crystalline COFs materials.

[0020] 2. The covalent organic framework material of the present invention has a high density of sulfonate loading, with a sulfonate loading as high as 4.76 mmol / g.

[0021] 3. The COF-(SO3H)2 / Nafion proton exchange membrane material of the present invention exhibits excellent proton conductivity, with a proton conductivity reaching 0.1338 S·cm. -1 Under the same conditions, it is 2.4 times that of commercial proton exchange membranes. Attached Figure Description

[0022] Figure 1 These are the molecular formulas of the aldehyde and amino monomers used in material preparation.

[0023] Figure 2 This is the crystal structure diagram of COF-(SO3H)2 material.

[0024] Figure 3 This is a thermogravimetric analysis diagram of COF-(SO3H)2 material.

[0025] Figure 4 This is the PXRD pattern of COF-(SO3H)2 material.

[0026] Figure 5 This is the water vapor adsorption curve of COF-(SO3H)2 material.

[0027] Figure 6 This is the infrared spectrum analysis of the COF-(SO3H)2 / Nafion proton exchange membrane.

[0028] Figure 7 This is an electron micrograph of the COF-(SO3H)2 / Nafion proton exchange membrane.

[0029] Figure 8 These are the AC impedance spectra of the COF-(SO3H)2 / Nafion proton exchange membrane at different temperatures.

[0030] Figure 9 This is an Arrhenius fitting plot of proton conductivity in different proton exchange membranes.

[0031] Figure 10 This is a graph showing the relationship between the conductivity of different proton exchange membranes and temperature.

[0032] Figure 11 This is a graph showing the relationship between the conductivity of a 10% COF-(SO3H)2 / Nafion proton exchange membrane and humidity. Detailed Implementation

[0033] The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0034] Example 1

[0035] The preparation method of the sulfonic acid-functionalized COF-(SO3H)2 / Nafion proton exchange membrane in this embodiment is as follows:

[0036] 2,4,6-Trihydroxytribenzaldehyde (0.1 mmol, 0.0210 g) and 2,5-diaminobenzene-1,4-disulfonic acid (0.15 mmol, 0.0402 g) were dissolved in 2 mL of a 1:1 mixture of trimethylbenzene and 1,4-dioxane. 0.2 mL of a 6 mol / L acetic acid solution was added, and the mixture was stirred at room temperature for 15 minutes to ensure homogeneity. The container was then transferred to liquid nitrogen and frozen for 3 minutes. This freezing-vacuuming-thawing cycle was repeated three times before the mixture was sealed and transferred to an oven at 120°C for 3 days. The mixture was then cooled to room temperature at a rate of 10°C / h to obtain a crystalline sample. After washing with tetrahydrofuran and N,N-dimethylformamide and drying, sulfonic acid-functionalized COF-(SO3H)2 material was obtained and dispersed in DMF-treated Nafion at a total mass fraction of 5%-20%. In d-521 solution, stir for 6 hours and ultrasonically stir for 1 hour to obtain casting solution. Pour into a glass culture dish with an inner diameter of 9 cm and store at 80℃ for 10 h to obtain COF-(SO3H)2 / Nafion proton exchange membrane, which is then soaked in water for later use.

[0037] 1. Thermogravimetric analysis of COF-(SO3H)2 material in Example 1

[0038] Weigh 5 mg of COF-(SO3H)2 material from Example 1 and test the material using a thermogravimetric analyzer. Figure 3 As shown, the weight loss that occurs before 297°C corresponds to the departure of free guest molecules in the material, while the large weight loss above 300°C corresponds to the decomposition of ligands.

[0039] 2. PXRD analysis of COF-(SO3H)2 material in Example 1

[0040] The COF-(SO3H)2 material from Example 1 was dried in air and then ground in a mortar for 0.5 h to obtain a uniform powder. The powder X-ray diffraction pattern was obtained using a PANalytical X'Pert PRO powder diffractometer under Cu-Kα ray irradiation for 5 min, and compared with a simulated pattern. Figure 4 As shown, the sample exhibits good stability.

[0041] 3. Water adsorption analysis of COF-(SO3H)2 material in Example 1

[0042] The COF-(SO3H)2 material from Example 1 was ground in a mortar for 0.5 h to obtain a uniform powder. 58 mg of the sample was weighed and ground at 25°C. o C. The water vapor adsorption isotherm was tested using a Konta VSTAR vapor adsorption instrument. For example... Figure 5As shown, the sample exhibited a strong water retention capacity during the desorption process, still having a water absorption capacity of 72 mg / g even when the pressure dropped to 0.1.

[0043] 4. Infrared spectral analysis of the COF-(SO3H)2 / Nafion proton exchange membrane in Example 1

[0044] The COF-(SO3H)2 / Nafion proton exchange membrane material from Example 1 was subjected to temperatures of 400-4000 cm⁻¹. -1 Within the specified range, the sample powder was analyzed by FI-IR spectroscopy using a Thermo iS50 FT-IR spectrometer. Infrared images were obtained, such as... Figure 6 As shown, the significant characteristic peaks indicate that the composite material was successfully prepared.

[0045] 5. Electron microscopy analysis of the COF-(SO3H)2 / Nafion proton exchange membrane material in Example 1

[0046] The COF-(SO3H)2 / Nafion proton exchange membrane material from Example 1 was dispersed on a silicon wafer using methanol, dried, and then fixed onto a conductive adhesive. Gold was then sputtered onto the substrate for 120 seconds. The process was performed using a Zeiss Merlin compact field emission scanning electron microscope (FE-SEM) to obtain high-resolution scanning electron microscopy images, as shown below. Figure 7 As shown, the composite membrane has a smooth surface, indicating that the composite is very uniform.

[0047] Example 2: Proton conductivity test of commercially available pure Nafion proton exchange membrane material in an 80% humidity environment.

[0048] Pure Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The constant temperature and humidity chamber was adjusted to 80% humidity, and the AC impedance spectrum of the material was measured using electrochemical impedance spectroscopy within a temperature range of 30℃-80℃ (e.g., ...). Figure 8 As shown), the proton conductivity is 5.566 × 10⁻⁶. -2 S·cm -1 And the Arrhenius equation was used to fit and calculate the proton transport activation barrier (e.g., Figure 9 As shown in the figure, the activation energy is 0.12 eV.

[0049] Following the method described above, the proton conductivity of COF-(SO3H)2 under 80% humidity conditions is 2.212 × 10⁻⁶. -2 S·cm -1 .

[0050] Example 3 The 5% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing in an 80% humidity environment.

[0051] The 5% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The constant temperature and humidity chamber was adjusted to 80% humidity, and the AC impedance spectrum of the material was measured using electrochemical impedance spectroscopy within a temperature range of 30℃-80℃ (e.g., ...). Figure 8 As shown), the proton conductivity is 1.012 × 10⁻⁶. -1 S·cm -1 And the proton transport activation barrier (e.g., using the Arrhenius equation) was fitted to calculate the energy level. Figure 9 As shown in the figure, the activation energy is 0.10 eV.

[0052] Example 4 The 10% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing in an 80% humidity environment.

[0053] A 10% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The discs were then subjected to electrochemical impedance spectroscopy (EIS) at 80% humidity within a temperature range of 30℃-80℃. The proton conductivity was found to be 1.338 × 10⁻⁶. -1 S·cm -1 And the proton transport activation barrier (e.g., using the Arrhenius equation) was fitted to calculate the energy level. Figure 9 As shown in the figure, the activation energy is 0.086 eV. The relatively small energy barrier indicates that proton transport in this material follows a transport mechanism.

[0054] Example 4 The 20% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing in an 80% humidity environment.

[0055] 20% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The discs were then subjected to electrochemical impedance spectroscopy (EIS) at 80% humidity in a constant temperature and humidity chamber within a temperature range of 30℃-80℃. The proton conductivity was found to be 6.367 × 10⁻⁶. -2 S·cm -1 And the proton transport activation barrier (e.g., using the Arrhenius equation) was fitted to calculate the energy level. Figure 9 As shown in the figure, the activation energy is 0.089 eV. The relatively small energy barrier indicates that proton transport in this material follows a transport mechanism.

[0056] Example 5 The 10% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing under 60% humidity.

[0057] A 10% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The discs were then subjected to electrochemical impedance spectroscopy (EIS) at 30℃-80℃ with the humidity set to 60%. The proton conductivity was found to be 5.782 × 10⁻⁶. -2 S·cm -1 (like Figure 11 As shown in the figure, the activation energy barrier for proton transport was calculated using the Arrhenius equation, and the activation energy was found to be 0.154 eV. The relatively small energy barrier indicates that proton transport in this material follows a transport mechanism.

[0058] Example 6 The 10% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing under 70% humidity.

[0059] A 10% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The discs were then subjected to electrochemical impedance spectroscopy (EIS) at 30℃-80℃ with the humidity set to 70%. The proton conductivity was found to be 7.899 × 10⁻⁶. -2 S·cm -1 (like Figure 11 As shown in the figure, the activation energy barrier for proton transport was calculated using the Arrhenius equation, and the activation energy was found to be 0.104 eV. The relatively small energy barrier indicates that proton transport in this material follows a transport mechanism.

[0060] Example 7 The 10% COF-(SO3H)2 / Nafion proton exchange membrane material prepared in Example 1 was subjected to proton conductivity testing in an environment with 90% humidity.

[0061] A 10% COF-(SO3H)2 / Nafion proton exchange membrane material was prepared into 5 mm diameter discs using a mold. The discs were then subjected to electrochemical impedance spectroscopy (EIS) at 30℃-80℃ with the humidity set to 90%. The proton conductivity was found to be 1.329 × 10⁻⁶. -1 S·cm -1 (like Figure 11As shown in the figure, the activation energy barrier for proton transport was calculated using the Arrhenius equation, and the activation energy was found to be 0.089 eV. The relatively small energy barrier indicates that proton transport in this material follows a transport mechanism.

[0062] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. The application of sulfonic acid-functionalized covalent organic frameworks / Nafion proton exchange materials in proton transport in fuel cells, characterized by: Sulfonic acid-functionalized covalent organic framework / Nafion proton exchange materials were fabricated into 5 mm diameter discs using a mold. The proton conductivity of the material was measured by electrochemical impedance spectroscopy in a constant temperature and humidity chamber within a humidity range of 60%–90%. Under 80% humidity conditions, the proton conductivity of the sulfonic acid-functionalized covalent organic framework / Nafion proton exchange material with a COF-(SO3H)2 mass fraction of 10% reached 1.338 × 10⁻⁶. -1 S·cm -1 ; The structural units of the sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material are 2,4,6-trihydroxytribenzaldehyde and 2,5-diaminobenzene-1,4-disulfonic acid. The sulfonic acid-functionalized covalent organic framework COF-(SO3H)2 material is monoclinic with cell parameters a=22.86 Å α=90, b=22.86 Å β=90, c=3.6 Å γ=120; The COF-(SO3H)2 material is a two-dimensional supramolecular structure. The layers form a three-dimensional structure through π-π interactions. The entire grid structure presents hexagonal channels with a side length of 10.33 Å. The preparation method of the sulfonic acid-functionalized covalent organic framework / Nafion proton exchange material is as follows: 0.1 mmol of 2,4,6-trihydroxytriphenylmethane and 0.15 mmol of 2,5-diaminobenzene-1,4-disulfonic acid were dissolved in 2 mL of a 1:1 mixture of trimethylbenzene and 1,4-dioxane. 0.2 mL of a 6 mol / L acetic acid solution was added, and the mixture was stirred at room temperature for 15 minutes to ensure homogeneity. The container was then transferred to liquid nitrogen and frozen for 3 minutes. This freezing-vacuuming-thawing cycle was repeated three times before sealing and transferring the mixture to an oven at 120°C for 3 days. The mixture was then cooled to room temperature at a rate of 10°C / h to obtain a crystalline sample. After washing with tetrahydrofuran and N,N-dimethylformamide and drying, sulfonic acid-functionalized COF-(SO3H)2 material was obtained. This material was dispersed at a total mass fraction of 10% in a DMF-treated Nafion d-521 solution, stirred for 6 hours, and ultrasonically stirred for 1 hour to obtain a casting solution. This solution was then poured into a container with an inner diameter of 9 mm. The COF-(SO3H)2 / Nafion proton exchange membrane was obtained by storing it in a glass culture dish at 80℃ for 10 h and then soaking it in water for later use.

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