Nafion / graphene-based composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a Nafion / graphene-based composite film as well as a preparation method and application thereof. The Nafion / graphene-based composite film is of a multi-layer composite structure Nafion / Nafion (L) / graphene / Nafion (L) / graphene / Nafion; wherein the Nafion (L) is a buffer layer formed by a liquid Nafion solution; the graphene is single-layer graphene; the graphene coverage degree is 99% or above. The prepared composite membrane is used for hydrogen isotope separation in a liquid water environment, the separation ratio reaches 9 or above, and the electrolysis stability exceeds 400 hours.

Description

Technical Field

[0001] This invention relates to the field of Nafion / graphene-based composite membrane preparation technology, specifically to a Nafion / graphene-based composite membrane for efficient separation of hydrogen isotopes in liquid water environments and its preparation method, the structure of which is Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion. Background Technology

[0002] The separation of hydrogen isotopes (such as protium / deuterium) is a key technology in fields such as nuclear energy, but traditional separation methods are inefficient due to their extremely similar physicochemical properties. Graphene, with its unique single-atom-layer structure and the difference in zero-point vibrational energy when hydrogen isotopes pass through it, is considered a highly promising room-temperature separation material.

[0003] Because monolayer graphene grown using chemical vapor deposition (CVD) is only one atom thick, it is easily damaged during preparation and requires a substrate to protect its structure. Currently, most graphene-based composite films are prepared using a hot-pressing method. This method involves directly hot-pressing a solid-solid Nafion film onto a substrate such as copper foil with monolayer graphene grown on it at around 130°C under pressure at the solid-solid interface. The copper is then etched, leaving a clean Nafion / graphene composite film. This method requires appropriate pressure and a high degree of substrate flatness. Existing research mainly focuses on conductivity differences or gas separation performance in gas environments, failing to effectively address the long-term stability of the composite film in liquid water electrolysis environments.

[0004] This preparation technique requires applying pressure during the process, making it highly susceptible to damage from uneven substrates or inconsistent pressure, which can cause the monolayer graphene to break apart and compromise its integrity. Furthermore, prolonged exposure to liquid water can lead to interface failure between graphene and Nafion, resulting in graphene breakage and a sharp decline in separation performance. Therefore, a well-designed method to protect the single-atom-layer graphene is crucial for achieving more efficient ion selectivity and stability.

[0005] The applicant disclosed a method for preparing and applying a Nafion / graphene / PES liquid-Nafion hemihydrate composite membrane in CN202411809519.4. However, after testing, the protium-deuterium separation ratio was 3-6, which is not ideal. Summary of the Invention

[0006] The purpose of this invention is to provide a new method for preparing composite membranes based on the basic strategy of Nafion / graphene composite membranes, which can effectively protect the structural integrity of graphene and significantly improve its long-term operational stability in liquid water environments, so as to promote the practical application of hydrogen isotope separation technology.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A Nafion / graphene composite film has a multilayer composite structure, wherein the multilayer structure is: Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion; wherein Nafion(L) is a buffer layer formed by liquid Nafion solution; the graphene is a single layer of graphene; and the graphene coverage is above 99%.

[0009] Furthermore, the thickness of the Nafion ranges from 10 to 20 μm; the thickness of the Nafion(L) ranges from 80 to 300 nm.

[0010] The present invention also provides the application of the Nafion / graphene composite membrane in hydrogen isotope separation.

[0011] The present invention also provides a method for preparing the Nafion / graphene composite film, comprising the following steps:

[0012] (1) Provide a metal foil on which a single layer of graphene is grown, and spin-coat the surface of the graphene with Nafion solution to form an initial structure of Nafion(L) / graphene / metal foil.

[0013] (2) The initial structure is hot-pressed and composited with a solid Nafion film for the first time, so that the Nafion (L) layer is in contact with the solid Nafion film;

[0014] (3) The metal foil was removed by dry etching and wet etching in sequence to obtain Nafion / Nafion(L) / graphene composite film;

[0015] (4) Repeat step (1) to prepare the second initial structure of Nafion(L) / graphene / metal foil; and perform a second hot-pressing composite with the Nafion(L) side of the second initial structure and the graphene side of the composite film obtained in step (3). Then, remove the metal foil by dry etching and wet etching in sequence to obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene composite film.

[0016] (5) Seal the edges of the composite membrane obtained in step (4), leaving the electrolytic region in the middle empty; there are no special restrictions on the sealing material, as long as it can seal the edges of the composite membrane and prevent protons from passing through; PDMS (polydimethylsiloxane) is preferred for sealing.

[0017] (6) The other solid Nafion film is hot-pressed with the composite film sealed in step (5) for the third time to finally obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film.

[0018] Furthermore, the metal foil is copper foil.

[0019] Furthermore, the spin coating speed in step (1) is 500-1500 rpm and the time is 10-20 seconds.

[0020] Further, the hot-pressing composite process conditions described in steps (2), (4) and (5) are as follows: first, apply a pressure of 200-500 kg at room temperature and maintain it for 1-3 minutes, then raise the temperature to 100-150°C and maintain the same pressure to continue hot pressing for 1-3 minutes.

[0021] Further, in step (3), the dry etching is oxygen plasma etching, and the etching conditions are: O2 flow rate 60-100 sccm, Ar flow rate 15-25 sccm, RF power 20-30W, and etching time 50-70 seconds; the wet etching uses 0.4-1.0 mol / L ammonium persulfate solution as etching solution, and the etching time is 2-4 hours.

[0022] The present invention also provides a method for separating hydrogen isotopes, which uses the aforementioned Nafion / graphene composite membrane to separate hydrogen isotopes in a liquid water electrolysis environment by adjusting the current density.

[0023] Furthermore, by adjusting the current density, the hydrogen-to-deuterium separation ratio of the composite membrane can be made to reach 9 or higher.

[0024] Furthermore, the composite membrane exhibits stability exceeding 400 hours in a liquid water electrolysis environment.

[0025] Compared with the prior art, this technical solution has the following advantages:

[0026] This invention provides a graphene-based composite membrane for efficient separation of hydrogen isotopes in liquid water environments, with a structure of Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion. Firstly, addressing the issue of high graphene breakage rate during hot pressing in the Nafion / graphene structure, this invention spin-coates a layer of Nafion solution onto the graphene surface, using it as a buffer to improve the adhesion between the Nafion membrane and the graphene film. Furthermore, a layer of the same Nafion(L) / graphene structure is superimposed on the other side of the graphene, preparing a Nafion / Nafion(L) / graphene / Nafion(L) / graphene structure. The two graphene layers can compensate for any minor damage to the other, thereby improving the separation performance of the composite membrane in electrolysis. Characterization demonstrates that its graphene coverage exceeds 99%. Finally, to protect the top layer of graphene, a solid Nafion film is hot-pressed on top, resulting in a Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film with a separation ratio of over 9 and an electrolytic stability of over 400 hours, enabling efficient separation of hydrogen isotopes in liquid water environments.

[0027] 1. The liquid phase interlayer Nafion (L) is a key flexible buffer and interface bonding layer. As an interlayer between graphene and the upper and lower solid Nafion support layers, it achieves a stress-free and fully wetted perfect interface bonding through its fluidity, fundamentally avoiding mechanical damage caused by hot pressing and increasing the coverage of transferred graphene to over 99%.

[0028] 2. The device edge encapsulation layer is impermeable to protons using PDMS, which solves the problems of edge leakage and low proton penetration efficiency during electrolysis.

[0029] 3. The outermost solid Nafion film provides robust mechanical support and chemical protection for the internal precision structure.

[0030] 4. The introduction of bilayer graphene can synergistically improve separation selectivity. Together with advantage 3, it enables the composite membrane to withstand long-term erosion in the liquid water environment. The electrolytic stability at high separation ratio exceeds 400 hours, realizing the long-term stability of the composite membrane in the liquid water electrolysis environment.

[0031] 5. The composite membrane prepared by this invention achieves a protium-deuterium element separation ratio of 9 or higher. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Figure 1 A schematic diagram of the composite membrane preparation process.

[0034] Figure 2Optical photographs and Raman characterization of the composite film.

[0035] Figure 3 Long-term stability test of H / D separation performance of composite membrane.

[0036] Figure 4 Optical photographs and physical images of single-layer graphene composite films and multilayer graphene composite films after testing. Detailed Implementation

[0037] In the following examples, the Nafion membrane is a commercially available 12 μm thick ePTFE-enhanced Gore proton exchange membrane (Gore 788.12). It was cut to 2 cm * 4 cm for use.

[0038] Nafion solution (L) was commercially available under the brand Adamas; CAS: 31175-20-9; Nafion perfluorinated resin; D521, 5 wt.% in a mixture of lower aliphatic alcohols and water, containing 45% water; RG.

[0039] Example 1

[0040] 1. Use a desiccant to evacuate the Nafion solution for 30 seconds to eliminate surface air bubbles. Spin-coat a layer of Nafion solution onto the graphene surface grown on copper foil at a spin speed of 1000 rpm for 15 seconds to completely cover the surface graphene film.

[0041] 2. Place a solid Nafion film on a PET backing, and attach the above-mentioned Nafion(L) / graphene onto the Nafion film, wherein the Nafion film is in contact with Nafion(L);

[0042] 3. Place the composite film on a hot press and press it at room temperature for 2 minutes under a pressure of 300 kg, then heat it to 130 ℃ and press it for 2 minutes.

[0043] 4. The hot-pressed composite film was etched using a dry etching method. The graphene on the other side of the copper foil that was not in contact with the Nafion film was etched away using oxygen plasma. The etching conditions were 80 sccm O2, 20 sccm Ar atmosphere, 25W power RF for 60s.

[0044] 5. Perform wet etching on the composite film after dry etching. Invert it in a 0.5 mol / L ammonium persulfate solution. After 3 hours, when the copper foil is completely etched, wash it three times in deionized water and soak it for 30 minutes to remove the ammonium persulfate on the surface of the composite film.

[0045] 6. After drying at room temperature, the Nafion / Nafion(L) / graphene composite film is finally obtained;

[0046] 7. Repeat step 1; then attach the Nafion (L) side of the Nafion (L) / graphene from step 1 to the graphene side of the Nafion / Nafion (L) / graphene from step 5.

[0047] 8. Repeat steps 3, 4, and 5, and after drying at room temperature, obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene composite film;

[0048] 9. Lay the composite film obtained in step 8 onto PDMS around the edges, seal the edges, and leave the middle area empty; the middle electrolytic area after sealing is 1cm * 2cm;

[0049] 10. The composite film sealed in step 9 is hot-pressed with solid Nafion (1cm * 2cm area). The 1cm * 2cm solid Nafion is adhered to the middle area of ​​the composite film, resulting in a Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film. The hot-pressing conditions are the same as in step 3.

[0050] Example 2

[0051] 1. Use a desiccant to evacuate the Nafion solution for 30 seconds to eliminate surface air bubbles. Spin-coat a layer of Nafion solution onto the graphene surface grown on copper foil at a spin speed of 500 rpm for 10 seconds to completely cover the surface graphene film.

[0052] 2. Place a solid Nafion film on a PET backing, and attach the above-mentioned Nafion(L) / graphene onto the Nafion film, wherein the Nafion film is in contact with Nafion(L);

[0053] 3. Place the composite film on a hot press and press it at room temperature for 3 minutes under a pressure of 200 kg, then heat it to 100 ℃ and press it for 3 minutes.

[0054] 4. The hot-pressed composite film was etched using a dry etching method. The graphene on the other side of the copper foil that was not in contact with the Nafion film was etched away using oxygen plasma. The etching conditions were 80 sccm O2, 20 sccm Ar atmosphere, 30W power RF for 50s.

[0055] 5. Perform wet etching on the composite film after dry etching. Invert it in a 0.5 mol / L ammonium persulfate solution. After 3 hours, when the copper foil is completely etched, wash it three times in deionized water and soak it for 30 minutes to remove the ammonium persulfate on the surface of the composite film.

[0056] 6. After drying at room temperature, the Nafion / Nafion(L) / graphene composite film is finally obtained;

[0057] 7. Repeat step 1, and then attach the Nafion (L) side of the Nafion (L) / graphene from step 1 to the graphene side of the Nafion / Nafion (L) / graphene from step 5.

[0058] 8. Repeat steps 3, 4, and 5, and after drying at room temperature, obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene composite film;

[0059] 9. Lay the composite film obtained in step 8 onto PDMS around the edges, seal the edges, and leave the middle area empty; the middle electrolytic area after sealing is 1cm * 2cm;

[0060] 10. The composite film sealed in step 9 is hot-pressed with solid Nafion (1cm * 2cm area). The 1cm * 2cm solid Nafion is adhered to the middle area of ​​the composite film, resulting in a Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film. The hot-pressing conditions are the same as in step 3.

[0061] Example 3

[0062] 1. Use a desiccant to evacuate the Nafion solution for 30 seconds to eliminate surface air bubbles. Spin-coat a layer of Nafion solution onto the graphene surface grown on copper foil at a spin speed of 1500 rpm for 20 seconds to completely cover the surface graphene film.

[0063] 2. Place a solid Nafion film on a PET backing, and attach the above-mentioned Nafion(L) / graphene onto the Nafion film, wherein the Nafion film is in contact with Nafion(L);

[0064] 3. Place the composite film on a hot press and press it at 500 kg pressure for 1 min at room temperature, then heat it to 150 ℃ and press it for 1 min.

[0065] 4. The hot-pressed composite film was etched using a dry etching method. The graphene on the other side of the copper foil that was not in contact with the Nafion film was etched away using oxygen plasma. The etching conditions were 80 sccm O2, 20 sccm Ar atmosphere, 20W power RF for 70s.

[0066] 5. Perform wet etching on the composite film after dry etching. Invert it in a 0.5 mol / L ammonium persulfate solution. After 3 hours, when the copper foil is completely etched, wash it three times in deionized water and soak it for 30 minutes to remove the ammonium persulfate on the surface of the composite film.

[0067] 6. After drying at room temperature, the Nafion / Nafion(L) / graphene composite film is finally obtained;

[0068] 7. Repeat step 1, and then attach the Nafion (L) side of the Nafion (L) / graphene from step 1 to the graphene side of the Nafion / Nafion (L) / graphene from step 5.

[0069] 8. Repeat steps 3, 4, and 5, and after drying at room temperature, obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene composite film;

[0070] 9. Lay the composite film obtained in step 8 onto PDMS around the edges, seal the edges, and leave the middle area empty; the middle electrolytic area after sealing is 1cm * 2cm;

[0071] 10. The composite film sealed in step 9 is hot-pressed with solid Nafion (1cm * 2cm area). The 1cm * 2cm solid Nafion is adhered to the middle area of ​​the composite film, resulting in a Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film. The hot-pressing conditions are the same as in step 3.

[0072] Comparative Example 1

[0073] Preparation method of single-layer graphene composite film

[0074] 1. Use a desiccant to evacuate the Nafion solution for 30 seconds to eliminate surface air bubbles. Spin-coat a layer of Nafion solution onto the graphene surface grown on copper foil at a spin speed of 1000 rpm for 15 seconds to completely cover the surface graphene film.

[0075] 2. Place a solid Nafion film on a PET backing, and attach the above-mentioned Nafion(L) / graphene onto the Nafion film, wherein the Nafion film is in contact with Nafion(L);

[0076] 3. Place the composite film on a hot press and press it at room temperature for 2 minutes under a pressure of 300 kg, then heat it to 130 ℃ and press it for 2 minutes.

[0077] 4. The hot-pressed composite film was etched using a dry etching method. The graphene on the other side of the copper foil that was not in contact with the Nafion film was etched away using oxygen plasma. The etching conditions were 80 sccm O2, 20 sccm Ar atmosphere, 25W power RF for 60s.

[0078] 5. Perform wet etching on the composite film after dry etching. Invert it in a 0.5 mol / L ammonium persulfate solution. After 3 hours, when the copper foil is completely etched, wash it three times in deionized water and soak it for 30 minutes to remove the ammonium persulfate on the surface of the composite film.

[0079] 6. After drying at room temperature, the Nafion / Nafion(L) / graphene composite film is finally obtained;

[0080] 7. Lay the composite film obtained in step 6 onto PDMS around the edges, seal the edges, and leave the middle area empty; the middle electrolytic area after sealing is 1cm * 2cm;

[0081] 8. The composite film sealed in step 7 is hot-pressed with solid Nafion (1cm * 2cm area). The 1cm * 2cm solid Nafion is adhered to the middle area of ​​the composite film, resulting in a Nafion / Nafion(L) / graphene / Nafion composite film. The hot-pressing conditions are the same as in step 3.

[0082] Taking the composite membrane prepared in Example 1 as an example

[0083] 1. Add 50 mL of D2O electrolyte with an initial concentration of 1% to the PEM electrolytic cell system and electrolyze under a current of 0.6 A. When the remaining electrolyte volume is less than 5 mL, add electrolyte and continue electrolysis.

[0084] 2. During the electrolysis process, in order to determine the actual enrichment progress of D2O, the electrolyte was sampled and NMRS was performed. Each sample was 0.375 mL.

[0085] 3. The H / D separation ratio can be calculated by sampling the remaining electrolyte volume and concentration. During the entire 400-hour continuous electrolysis test, the separation ratio of the single-layer graphene composite membrane and the multilayer graphene composite membrane device obtained in Example 1 as a function of time is shown in the curves below. Figure 3As shown in the figure, the results indicate that the separation ratio of the comparative monolayer graphene device is not only low initially, but its performance also shows a downward trend after a certain period, indicating that its structure is unstable. In contrast, the separation ratio of the multilayer graphene composite film remains consistently above 9.0 throughout the process, and the curve does not show a significant decay trend.

[0086] 4. Key Comparison of Membrane Structure Integrity. After the test, the monolayer graphene composite film and the multilayer graphene composite film prepared in this invention were compared. The surface of the monolayer graphene composite film showed obvious wrinkles and damaged areas, indicating that the integrity of the graphene had been compromised. In contrast, the surface of the multilayer graphene composite film remained uniform and smooth, with no visible signs of damage.

[0087] In summary, the multilayered graphene composite membrane prepared by this invention greatly protects the structural integrity of graphene in a liquid water environment, possesses excellent and durable separation performance, and meets the requirements of long-term stability for practical applications.

[0088] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A Nafion / graphene composite film, characterized in that, It has a multilayer composite structure of Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion; wherein Nafion(L) is a buffer layer formed by liquid Nafion solution; the graphene is a single layer of graphene; and the graphene coverage is above 99%.

2. The Nafion / graphene composite film as described in claim 1, characterized in that, The thickness of the Nafion is 10-20 μm; the thickness of the Nafion(L) is 80-300 nm.

3. The application of the Nafion / graphene composite membrane as described in claim 1 or 2 in hydrogen isotope separation.

4. A method for preparing a Nafion / graphene composite film as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Provide a metal foil on which a single layer of graphene is grown, and spin-coat the surface of the graphene with Nafion solution to form an initial structure of Nafion(L) / graphene / metal foil. (2) The initial structure is hot-pressed and composited with a solid Nafion film for the first time, so that the Nafion (L) layer is in contact with the solid Nafion film; (3) The metal foil was removed by dry etching and wet etching in sequence to obtain Nafion / Nafion(L) / graphene composite film; (4) Repeat step (1) to prepare the second initial structure of Nafion(L) / graphene / metal foil; and perform a second hot-pressing composite with the Nafion(L) side of the second initial structure and the graphene side of the composite film obtained in step (3). Then, remove the metal foil by dry etching and wet etching in sequence to obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene composite film. (5) Seal the edges of the composite membrane obtained in step (4) and leave the middle electrolysis area empty; (6) The other solid Nafion film is hot-pressed with the composite film sealed in step (5) for the third time to finally obtain the Nafion / Nafion(L) / graphene / Nafion(L) / graphene / Nafion composite film.

5. The preparation method according to claim 4, characterized in that, The spin coating speed in step (1) is 500-1500 rpm and the time is 10-20 seconds.

6. The preparation method according to claim 4, characterized in that, The hot-pressing composite process conditions described in steps (2), (4) and (5) are as follows: first, apply a pressure of 200-500 kg at room temperature and maintain it for 1-3 minutes, then raise the temperature to 100-150℃ and maintain the same pressure to continue hot pressing for 1-3 minutes.

7. The preparation method according to claim 4, characterized in that, In step (3), the dry etching is oxygen plasma etching, and the etching conditions are: O2 flow rate 60-100 sccm, Ar flow rate 15-25 sccm, RF power 20-30W, and etching time 50-70 seconds; the wet etching uses 0.4-1.0 mol / L ammonium persulfate solution as etching solution, and the etching time is 2-4 hours.

8. A method for separating hydrogen isotopes, characterized in that, Using the Nafion / graphene composite membrane as described in claim 1 or 2, hydrogen isotopes can be separated by adjusting the current density in a liquid water electrolysis environment.

9. The hydrogen isotope separation method as described in claim 8, characterized in that, By adjusting the current density, the hydrogen-to-deuterium separation ratio of the composite membrane can be made to reach over 9.

10. The hydrogen isotope separation method as described in claim 8 or 9, characterized in that, The composite membrane exhibits stability exceeding 400 hours in a liquid water electrolysis environment.

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