Preparation method of proton exchange membrane with MXene directionally arranged along membrane thickness direction

Abstract

The invention relates to the field of fuel cells, and discloses a preparation method of a proton exchange membrane with MXene directionally arranged along the membrane thickness direction, and the preparation method comprises the following steps: 1, depositing a Ti3AlC2 film on the surface of a substrate through direct current magnetron sputtering; step 2, etching the Ti3AlC2 thin film by using an NH4HF2 solution, so as to prepare an MXene film; 3, the MXene film is cut in the radial direction; 4, carboxylating the MXene film obtained in the step 3, and modifying the MXene film by using a polymer containing amido to form an N-Ti bond; and step 5, soaking the modified MXene membrane in a Nafion solution, and carrying out drying, hot pressing and heat treatment to prepare the proton exchange membrane in which MXene is directionally arranged along the membrane thickness direction. The proton exchange membrane disclosed by the invention is based on Nafion and MXene, and the MXene is orderly and directionally arranged along the membrane thickness direction, so that the proton transmission curvature can be effectively reduced; and the modified MXene has a large amount of proton exchange capacity, and the thermal stability of the Nafion matrix can be improved.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and in particular to a method for preparing a proton exchange membrane in which MXene is oriented along a membrane thickness direction. Background Art

[0002] With the rapid development and maturity of hydrogen storage and production technologies, hydrogen energy has emerged in people's vision and is considered to be one of the most promising renewable energy sources. As one of the ways to achieve efficient use of hydrogen energy, proton exchange membrane fuel cells (PEMFC) have become one of the important alternative energy sources in automobiles, industry and other fields.

[0003] As the core component of proton exchange membrane fuel cells, proton exchange membrane (PEM) directly determines the performance of the battery. Taking the most mature commercial Nafion membrane as an example, it has a considerable proton exchange rate (r) of 10 at 60-80°C and RH = 98%. -2 -10 -1 S / cm. However, when Nafion membrane is operated at such low temperature for a long time, certain problems often occur, such as catalyst poisoning, slow electrode reaction, complex water management and low water vapor utilization. At present, the solutions to these technical problems generally require increasing the operating temperature. However, when the temperature is raised to above 80°C, the defects of poor thermal stability and poor water retention of Nafion membrane are exposed again. At high temperature, due to the rapid loss of internal water, it will directly lead to the weakening or even failure of Grotthuss mechanism and carrier mechanism, resulting in a rapid decrease in its r value, and holes will appear in the structure, leading to fuel penetration. In addition, the proton transmission channels in the Nafion membrane are not arranged continuously, resulting in low proton transmission efficiency. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a proton exchange membrane with MXene arranged in a directional manner along the membrane thickness direction. The proton exchange membrane of the present invention is based on Nafion and MXene, wherein MXene is orderly and directional arranged along the membrane thickness direction, which can effectively reduce the proton transmission curvature; and the modified MXene has a large amount of proton exchange capacity and can improve the thermal stability of the Nafion matrix.

[0005] The specific technical solution of the present invention is: a method for preparing a proton exchange membrane in which MXene is oriented along the thickness direction of the membrane, which comprises the following steps:

[0006] Step 1: Depositing Ti3AlC2 thin film on the substrate surface by DC magnetron sputtering.

[0007] Step 2: Etch the Al layer in the Ti3AlC2 film with an NH4HF2 solution to obtain an MXene film. After etching, the MXene film presents a multi-layer flaky morphology at the microscale.

[0008] Step 3: Cut the MXene film radially to obtain a thinner MXene film.

[0009] Step 4: First, carboxylate the MXene film obtained in Step 3, and then modify the MXene film with a polymer containing carboxyl or amine groups.

[0010] Step 5: Immerse the modified MXene film in a Nafion solution, and after drying, hot pressing, and heat treatment, a proton exchange membrane with MXene arranged in a lamellar orientation along the film thickness direction (i.e., the single layers of MXene are perpendicular to the film thickness direction) is prepared.

[0011] The Nafion membrane has poor thermal stability and water retention performance, and its internal water is easily lost at high temperatures. In addition, the arrangement of proton transport channels in the Nafion membrane is discontinuous, resulting in low proton transport efficiency. The proton exchange membrane of the present invention is a composite membrane based on MXene and Nafion. Among them, MXene has hydroxyl groups on its surface and has natural hydrophilicity, which is crucial for effective proton conduction. The -OH groups can not only improve the moisture retention but also provide a continuous path for proton transport to promote proton movement. In addition, by arranging MXene along the film thickness direction in the present invention, a straight-through proton transport channel can be formed, which can effectively reduce the curvature of proton transport and thus improve the fuel cell efficiency.

[0012] Furthermore, the present invention also performs modification treatment on MXene. First, one of the purposes of carboxylating MXene is to enhance the reaction activity of MXene with imino groups, increase surface active sites, and thus improve the compatibility and stability with Nafion. On this basis, due to the large specific surface area and the presence of active sites (carboxyl groups) of MXenes, the amine groups of the polymer react with the active groups on the MXene surface to form stable chemical bonds. The energy of these bonds is greater than the energy of π-π interactions and hydrogen bonds in the MXene layer, which can effectively stabilize the MXene layer and increase the binding force between layers. In addition, the sulfonic acid groups in Nafion can also combine with amine groups to form acid-base pairs, so the formed structure will be more stable and the activation energy of proton transport will be lower (acid-base interaction between amine groups and sulfonic acid protons).

[0013] Preferably, in Step 1, in the direct current magnetron sputtering, the diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0014] Preferably, in step one, the thickness of the Ti3AlC2 film is 4 - 6 cm.

[0015] Preferably, in step one, before deposition, the substrate is cleaned with acetone, rinsed with isopropanol, dried with nitrogen, and finally preheated in a deposition chamber at 750 - 800 °C for 50 - 70 min. The deposition is carried out at 750 - 800 °C.

[0016] Preferably, in step two, the concentration of the NH4HF2 solution is 0.8 - 1.2 M, and the etching time is 1 - 3 h.

[0017] Preferably, in step three, the thickness of the MXene film after cutting is 50 - 200 μm.

[0018] Preferably, in step four, the carboxylation is as follows: The MXene film is mixed with a 25 - 35% H2O2 solution at a solid - liquid ratio of 3 - 5 mg / mL, heated and stirred at 75 - 85 °C for 4 - 8 h, and centrifuged and washed 2 - 4 times.

[0019] Preferably, in step four, the modification of the MXene film with an amine - containing polymer is as follows: The MXene film is mixed with an aqueous solution of an amine - containing polymer at a concentration of 4 - 6% at a solid - liquid ratio of 3 - 5 mg / mL, and stirred at 45 - 55 °C for 10 - 15 h under nitrogen protection. The amine - containing polymer is branched polyethyleneimine or polydopamine.

[0020] The present invention finds that the dosage between the amine - containing polymer and the MXene film is crucial for the modification effect. If the dosage of the amine - containing polymer is too small, there are insufficient receptors for proton conduction, and continuous channels cannot be formed, which will hinder the proton conduction ability; while if the dosage of the amine - containing polymer is too large, it is easy to block the transport channels, resulting in a decline in performance.

[0021] Preferably, in step five, the concentration of the Nafion solution is 4 - 6%, the solid - liquid ratio of the MXene film to the Nafion solution is (0.5 - 1.5) mg / mL, and the soaking time is 10 - 15 h.

[0022] The present invention finds that the dosage between the Nafion solution and the MXene film is crucial for the film performance. If the proportion of MXene is too large, the mechanical properties will decline; if the proportion of MXene is too small, the optimization effect is not obvious.

[0023] Preferably, in step five, the drying temperature is 25 - 30 °C; the conditions for hot pressing are a temperature of 95 - 105 °C, a pressure of 0.08 - 0.12 MPa, and a time of 5 - 15 min; the heat treatment temperature is 95 - 105 °C, and the time is 4 - 8 h.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The proton exchange membrane of the present invention is a composite membrane based on MXene and Nafion. Arranging MXene along the membrane thickness direction can form a straight-through proton transport channel, which can effectively reduce the curvature of proton transport and thus improve the efficiency of fuel cells. Moreover, MXene has hydroxyl groups on its surface, which can not only improve the moisture retention property, but also provide a continuous path for proton transport to promote proton movement.

[0026] (2) The present invention performs modification treatment on MXene. Carboxylation treatment of MXene can not only enhance the reactivity of MXene with imino groups, but also increase the surface active sites, thereby improving the compatibility and stability with Nafion. The amine groups of the polymer react with the active groups on the surface of MXene to form stable chemical bonds, which can effectively stabilize the MXene layer and increase the binding force between layers. In addition, the sulfonic acid groups in Nafion can also combine with amine groups to form acid-base pairs, resulting in a more stable structure and a lower activation energy for proton transport.

[0027] (3) The proton exchange membrane of the present invention can maintain the proton exchange rate and thermal stability of the proton exchange membrane under the operating conditions of a fuel cell at high temperatures (above 100 °C). Detailed Embodiments

[0028] The present invention will be further described below in conjunction with embodiments.

[0029] Example 1

[0030] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit a Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches a thickness of 5 cm. The gas during the sputtering process is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm respectively.

[0031] (2) Etch the Ti3AlC2 thin film with a 1 M NH4HF2 solution at room temperature for 2 h.

[0032] (3) Cut the obtained Ti3AlC2 MXene material radially to make a MXene membrane with a thickness of 100 μm.

[0033] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 5 ml of 5% aqueous solution of branched polyethyleneimine BPEI (Lupasol FG from BASF) and stir at 50 °C for 12 h under nitrogen protection.

[0034] (5) Immerse the modified MXene film in 20 ml of 5% Nafion solution for 12 h. After drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h, a proton exchange membrane is made.

[0035] Example 2

[0036] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit a Ti3AlC2 film from Ti, Al, and C targets using direct current magnetron sputtering technology in an ultra-high vacuum system until it reaches 5 cm thick. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0037] (2) Etch the Ti3AlC2 film with 1 M NH4HF2 solution at room temperature for 2 h.

[0038] (3) Cut the Ti3AlC2 MXene material longitudinally to make an MXene film with a thickness of 100 μm.

[0039] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 5 ml of 5% aqueous solution of polydopamine (PDA) and stir at 50 °C for 12 h under nitrogen protection.

[0040] (5) Immerse the modified MXene film in 20 ml of 5% Nafion solution for 12 h. After drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h, a proton exchange membrane is made.

[0041] Comparative Example 1 (1) Clean the substrate with acetone, rinse with isopropyl alcohol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit the Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches 5 cm thick. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0042] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0043] (3) Cut the Ti3AlC2 MXene material longitudinally to make a MXene film with a thickness of 100 μm.

[0044] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 5 ml of 5% aqueous polyacrylamide (PAM) solution and stir at 50 °C for 12 h under nitrogen protection.

[0045] (5) Immerse the modified MXene film in 20 ml of 5% Nafion solution for 12 h. After drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h, a proton exchange membrane is made. Comparative Example 2 (using a pure Nafion membrane)

[0046] Use a pipette to aspirate 3 ml of 5 wt% Nafion solution, evenly drop it in the center of a glass substrate, and scrape the solution evenly with a spatula. Dry in an oven at 80 °C for 12 h, and make a proton exchange membrane after the vacuum degree ≤ 0.1 MPa.

[0047] Comparative Example 3 (the difference from Example 1 is only that the MXene film is not modified)

[0048] (1) Clean the substrate with acetone, rinse with isopropyl alcohol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit the Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches 5 cm thick. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0049] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0050] (3) Cut the Ti3AlC2 MXene material longitudinally to make an MXene film with a thickness of 100 μm.

[0051] (4) Immerse 20 mg of the MXene film in 20 ml of 5% Nafion solution for 12 h, and then make a proton exchange membrane after drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h. Comparative Example 4 (the only difference from Example 1 is that when modified with branched polyethyleneimine, the amount of branched polyethyleneimine is too low)

[0052] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit a Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches a thickness of 5 cm. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm respectively.

[0053] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0054] (3) Cut the Ti3AlC2 MXene material longitudinally to make an MXene film with a thickness of 100 μm.

[0055] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 2 ml of 5% aqueous solution of BPEI (Lupasol FG from BASF) and stir at 50 °C for 12 h under nitrogen protection.

[0056] (5) Immerse the modified MXene film in 20 ml of 5% Nafion solution for 12 h, and then make a proton exchange membrane after drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h. Comparative Example 5 (the only difference from Example 1 is that when modified with branched polyethyleneimine, the amount of branched polyethyleneimine is too high)

[0057] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit the Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches a thickness of 5 cm. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0058] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0059] (3) Cut the Ti3AlC2 MXene material longitudinally to make a MXene film with a thickness of 100 μm.

[0060] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 10 ml of 5% aqueous solution of BPEI (Lupasol FG from BASF) and stir at 50 °C for 12 h under nitrogen protection.

[0061] (5) Immerse the modified MXene film in 20 ml of 5% Nafion solution for 12 h, and then make a proton exchange membrane after drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h. Comparative Example 6 (the difference from Example 1 is only that the amount of MXene film used in the last step is too low)

[0062] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit the Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches a thickness of 5 cm. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0063] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0064] (3) Cut the Ti3AlC2 MXene material longitudinally to make a MXene film with a thickness of 100 μm.

[0065] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 5 ml of 5% aqueous solution of BPEI (Lupasol FG from BASF) and stir at 50 °C for 12 h under nitrogen protection.

[0066] (5) Immerse the modified MXene film in 40 ml of 5% Nafion solution for 12 h, and then make a proton exchange membrane after drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h. Comparative Example 7 (only different from Example 1 in that the dosage of the MXene film in the last step is too high)

[0067] (1) Clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 760 °C for 60 min. Deposit a Ti3AlC2 thin film from Ti, Al, and C targets using DC magnetron sputtering technology in an ultra-high vacuum system until it reaches 5 cm thick. The sputtering process gas is Ar (purity 99.9999%), the constant gas pressure is 4.8 mbar, and the deposition temperature is 760 °C. The diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm, respectively.

[0068] (2) Etch the Ti3AlC2 thin film with 1 M NH4HF2 solution at room temperature for 2 h.

[0069] (3) Cut the Ti3AlC2 MXene material longitudinally to make a MXene film with a thickness of 100 μm.

[0070] (4) Mix 20 mg of the MXene film with 5 ml of 30% H2O2 solution and heat and stir at 80 °C for 6 h, and finally centrifuge and wash 3 times. Mix the activated MXene with 5 ml of 5% aqueous solution of BPEI (Lupasol FG from BASF) and stir at 50 °C for 12 h under nitrogen protection.

[0071] (5) Immerse the modified MXene film in 10 ml of 5% Nafion solution for 12 h, and then make a proton exchange membrane after drying at room temperature (25 °C), hot pressing at 100 °C / 0.1 MPa for 10 min, and heat treatment at 100 °C for 6 h.

[0072] Performance test

[0073] (1) Proton exchange capacity (IEC): Take a 5 cm × 5 cm dry proton exchange membrane sample and weigh the sample weight as W using an electronic balance. d, Immerse the proton exchange membrane sample in saturated sodium chloride solution for 12 h, take out the sample, rinse it with deionized water and soak it. Mix the washing solution and the soaking solution, titrate the mixed solution with 0.1 M sodium hydroxide solution, add phenolphthalein as an indicator during the titration process, and observe the change in the color of the solution. Record the volume of sodium hydroxide consumed, V, when the solution is completely neutralized. NaOH .

[0074] The ion exchange capacity (IEC) of the sample membrane can be calculated by the following formula:

[0075]

[0076] where, V NaOH is the volume of NaOH consumed, and W d is the mass of the dry membrane.

[0077] Table 1: Proton exchange capacity (IEC)

[0078]

[0079]

[0080] The proton exchange capacity is related to the density of sulfonic acid groups. Generally, the higher the density, the higher the proton exchange capacity. From the comparison of the data in the above table, it can be seen that compared with the pure Nafion membrane of Comparative Example 1, the proton exchange membranes obtained in Examples 1-2, Comparative Examples 1-2, and Comparative Examples 4-6 of the present invention do not show a significant decrease in proton exchange capacity data. In Comparative Example 7, the low dosage of Nafion led to a decrease in proton exchange capacity.

[0081] (2) Proton exchange rate (PC) Take a dry proton exchange membrane sample of 5 cm × 5 cm, immerse the sample in deionized water for 24 h, use an alternating current impedance spectrometer to build a test platform, clamp the hydrated sample between two electrodes to ensure good contact between the electrodes and the membrane, and set the test frequency range of the alternating current impedance spectrometer from 0.01 Hz to 100 Hz with an amplitude of 10 mV. According to the impedance data, establish an equivalent circuit model, obtain the resistance R of the membrane by fitting the impedance data, and then calculate the proton conductivity according to the following formula.

[0082]

[0083] where, L is the distance between the electrodes, A is the cross-sectional area of the membrane, and R is the membrane resistance characterized by electrochemical impedance spectroscopy (EIS).

[0084] Table 2: Proton exchange rate (PC) (100 °C, 100% RH)

[0085] Case Proton exchange rate (PC) Example 1 0.257 S / cm Example 2 0.218 S / cm Comparative Example 1 0.181 S / cm Comparative Example 2 0.124 S / cm Comparative Example 3 0.098 S / cm Comparative Example 4 0.186 S / cm Comparative Example 5 0.177 S / cm Comparative Example 6 0.201 S / cm Comparative Example 7 0.213 S / cm

[0086] It can be seen from the data comparison in the above table that:

[0087] In Example 2, when using PDA, the amine group content is less and the reaction activity is lower compared with BPEI. It cannot react fully with the carboxyl group of MXene, and the interlayer is loose, resulting in a lower proton exchange rate than that in Example 1. In Comparative Example 1, PAM contains amide groups and no free amine groups, so it cannot form acid-base pairs with sulfonic acid groups and only relies on physical adsorption to bind. Compared with Example 1, the MXene layers are prone to stacking disorder and the proton transport path is tortuous.

[0088] In Comparative Example 2, the pure Nafion membrane relies on its own sulfonic acid groups to form randomly distributed proton channels. The channel arrangement is discontinuous and the transport curvature is large. In Comparative Example 3, the hydroxyl groups on the surface of MXene are not converted into carboxyl groups, resulting in insufficient reaction activity with the amine groups of BPEI and unable to form stable chemical bonds. It only binds through physical interaction, and the interfacial compatibility is poor, resulting in a proton exchange rate even lower than that in Comparative Example 2. In Comparative Example 4, due to the too low dosage of BPEI, the number of amine groups is insufficient, the surface modification coverage rate of MXene is low, and the interlayer binding is loose. In Comparative Example 5, due to the excessive dosage of BPEI, the excessive BPEI blocks the interlayer voids of MXene and hinders the proton transport path. In Comparative Example 6, the content of MXene is insufficient and cannot form sufficient oriented channels. The Nafion matrix dominates the transport and the performance is close to that of the pure Nafion membrane. In Comparative Example 7, the excessive MXene layers are stacked densely, the permeability of Nafion is insufficient, the interfacial binding is weak, the mechanical properties decline and the proton channels are blocked.

[0089] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0090] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a proton exchange membrane with MXene oriented along the membrane thickness direction, characterized in that Including: Step 1: Deposit a Ti3AlC2 film on the surface of a substrate by DC magnetron sputtering; Step 2: Etch the Ti3AlC2 film with an NH4HF2 solution to obtain a MXene film; Step 3: Cut the MXene film radially; Step 4: First carboxylate the MXene film obtained in Step 3, and then modify the MXene film with an amine-containing polymer; Step 5: Immerse the modified MXene film in a Nafion solution, and after drying, hot pressing, and heat treatment, obtain a proton exchange membrane with MXene arranged in a lamellar orientation along the film thickness direction.

2. The preparation method according to claim 1, characterized in that, In Step 1, in the DC magnetron sputtering, the diameters of the Ti target, Al target, and C target are 75 mm, 50 mm, and 75 mm respectively.

3. The preparation method according to claim 1 or 2, characterized in that, In Step 1, the thickness of the Ti3AlC2 film is 4 - 6 cm.

4. The preparation method according to claim 1 or 2, characterized in that, In Step 1, before deposition, clean the substrate with acetone, rinse with isopropanol, dry with nitrogen, and finally preheat in a deposition chamber at 750 - 800 °C for 50 - 70 min, and the deposition is carried out at 750 - 800 °C.

5. The preparation method according to claim 1, characterized in that, In Step 2, the concentration of the NH4HF2 solution is 0.8 - 1.2 M, and the etching time is 1 - 3 h.

6. The preparation method according to claim 1, characterized in that, In Step 3, the thickness of the cut MXene film is 50 - 200 µm.

7. The preparation method according to claim 1, characterized in that, In Step 4, The carboxylation is as follows: Mix the MXene film with a 25 - 35% H2O2 solution at a solid-liquid ratio of 3 - 5 mg / mL, heat and stir at 75 - 85 °C for 4 - 8 h, and centrifuge and wash 2 - 4 times.

8. The preparation method according to claim 1 or 7, characterized in that, In Step 4, the modification of the MXene film with an amine-containing polymer is as follows: Mix the MXene film with a 4 - 6% aqueous solution of the amine-containing polymer at a solid-liquid ratio of 3 - 5 mg / mL, and stir under nitrogen protection at 45 - 55 °C for 10 - 15 h; The amine-containing polymer is branched polyethyleneimine or polydopamine.

9. The preparation method according to claim 1, wherein In Step 5, the concentration of the Nafion solution is 4 - 6%; the solid-liquid ratio of the MXene film to the Nafion solution is (0.5 - 1.5) mg / mL, and the immersion time is 10 - 15 h.

10. The preparation method according to claim 1 or 9, characterized in that, In Step 5, the drying temperature is 25 - 30 °C; the hot pressing conditions are a temperature of 95 - 105 °C, a pressure of 0.08 - 0.12 MPa, and a time of 5 - 15 min; the heat treatment temperature is 95 - 105 °C, and the time is 4 - 8 h.

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