A proton exchange membrane based on large-area single-layer nanoporous graphene nafion composite and a preparation method thereof

Abstract

The application discloses a kind of proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite and preparation method thereof, first by plasma etching to obtain graphene / copper foil sample;Nafion latex is spin-coated on the graphene surface of graphene / copper foil sample;Graphene / copper foil sample after spin-coating is dried and solidified, Nafion film is hot-pressed on the spin-coated surface of graphene sample, to obtain Nafion / graphene / copper foil sample;Nafion / graphene / copper foil sample is etched in etching liquid, then the sample is washed, the remaining copper foil etching is completed, and is cleaned and dried;Continue to spin-coat Nafion latex;Nafion / graphene sample after spin-coating is dried and solidified, and then hot-pressed with Nafion film to be composite;Nafion / graphene / Nafion sample is soaked in acid solution and dried, to obtain proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite.The application effectively solves the performance improvement bottleneck caused by the low proton transmission efficiency of intrinsic graphene due to the insufficient selectivity of proton exchange membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of direct methanol fuel cells, and particularly relates to a proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite and a preparation method thereof. BACKGROUND

[0002] Direct methanol fuel cells (DMFCs) have a wide application potential in portable electronic devices, backup power sources and small vehicles due to their simple structure, easy fuel supply, high energy density and renewable energy application. In the DMFC system, a proton exchange membrane (PEM) is a core component, which functions to conduct protons and prevent fuel, i.e. methanol molecules, from passing through. Perfluorosulfonic acid (PFSA) membranes, commonly known as Nafion, have been the main commercial PEM material. Nafion is composed of a hydrophobic polytetrafluoroethylene (PTFE) backbone and a hydrophilic sulfonic acid (-SO3H) side chain, which provides excellent proton conductivity, mechanical strength, chemical stability and durability. However, Nafion has poor selectivity between protons and other ions or small molecules, which hinders the further improvement of electrochemical energy systems. In fuel cells, the resulting permeation problem can cause fuel loss, reduce the cathode voltage and affect the performance of the fuel cell. In direct methanol fuel cells (DMFCs), due to the high methanol permeability of the currently commercial proton exchange membrane, about 40% of the methanol can penetrate the membrane and be lost. To reduce methanol permeation, DMFCs usually use thicker Nafion membranes, which can reduce the performance of the fuel cell. Given the excellent proton conductivity of Nafion, a large number of studies have been devoted to retaining the Nafion system and modifying it to meet application requirements. Researchers have attempted to reduce permeation by compounding and hybridizing Nafion with low-methanol-compatible polymers and inorganic nanoparticles, surface modification or multi-layer systems. The doped membranes of Nafion and nanomaterials usually significantly improve their physical and electrical properties by adding a small amount of nanoparticles or nanofillers. However, the modified Nafion membrane usually causes a slight decrease in proton conductivity, and the added nanoparticles increase the tortuosity of proton transport, which can reduce the overall performance.

[0003] In response to the growing interest in large-area two-dimensional materials, different solutions have been proposed. In 2016, Tian-Shou Zhao et al. sandwiched a layer of large-area single-layer graphene between two layers of Nafion membranes and applied it in DMFCs. They reported that the open-circuit voltage (OCV) performance was improved, while the decrease in power density was not significant, highlighting the potential of graphene in reducing methanol permeation. The introduction of large-area single-layer two-dimensional materials avoids the problem of tortuous proton conduction paths and can provide controllable selective nanopores to adapt to specific application requirements. Bukola et al. confirmed that excellent proton conduction can be achieved through the intrinsic hexagonal pores of graphene and through water molecules in the liquid phase by Grothuss and carrier mechanisms. At the same time, the excellent selectivity of single-layer graphene has been studied in the fields of organic separation, gas separation, and water desalination. Therefore, large-area two-dimensional materials such as graphene bring new opportunities for the development of new proton exchange membranes.

[0004] Although the introduction of graphene alleviates the problem of methanol permeation in DMFC applications, there is still much room for improvement in ensuring proton conductivity and improving fuel cell performance. By creating pores on the surface of large-area graphene, the proton penetration resistance can be reduced while maintaining precise selectivity, thereby improving the performance of the overall proton exchange membrane. Ion bombardment is a method of creating atomic precision nanopores by carefully controlling parameters, but its application scale is limited by equipment. In contrast, plasma can achieve large-area atomic-level pore creation. Mahurin et al. used oxygen plasma etching technology to adjust the pore size of single-layer graphene and achieved efficient ion selection and fast water transport in seawater desalination applications. Similarly, Karnik et al. used oxygen plasma etching technology to form selective pores ≤1 nm in CVD graphene, improving the selectivity of small molecules and proteins. + To break the mutual restriction between pore size and pore density in plasma pore creation, Wang et al. proposed a method that uses high-energy argon plasma to control pore density and then uses low-energy oxygen plasma to control pore size. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a proton exchange membrane based on large-area single-layer nanoporous graphene and Nafion composite and a preparation method thereof to solve the technical problem of insufficient methanol selectivity of the proton exchange membrane. The large-area single-layer graphene is introduced on the basis of the commercial Nafion membrane; and the plasma pore creation technology is combined to create fine pores on the surface of graphene, while achieving high methanol selectivity and high proton conduction performance.

[0006] The technical scheme adopted by the present application is as follows:

[0007] The application discloses a preparation method of a proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite.

[0008] S1, performing plasma etching on a graphene sample to obtain a porous graphene / copper foil sample;

[0009] S2, spin-coating a layer of Nafion emulsion on the graphene surface of the porous graphene / copper foil sample prepared in the step S1 and repeating the spin-coating for multiple times;

[0010] S3, drying and curing the porous graphene / copper foil sample after the spin-coating in the step S2 on a hot table, hot-pressing a Nafion film on the side of the graphene sample on which the spin-coating is performed to obtain a Nafion / porous graphene / copper foil sample;

[0011] S4, etching the Nafion / porous graphene / copper foil sample after the hot-pressing in the step S3 in an etching solution, removing the materials attached to the back of the copper foil, then flushing the back of the Nafion film, etching the remaining copper foil in the clean etching solution, cleaning and air-drying after the etching to obtain a Nafion / porous graphene sample;

[0012] S5, continuously spin-coating a layer of Nafion emulsion on the graphene side of the Nafion / porous graphene sample after the air-drying in the step S4;

[0013] S6, drying and curing the Nafion / porous graphene sample after the spin-coating in the step S5 on a hot table, then hot-pressing and compounding the Nafion / porous graphene sample with another Nafion film to obtain a Nafion / porous graphene / Nafion sample;

[0014] S7, air-drying the Nafion / porous graphene / Nafion sample prepared in the step S6 after being soaked in an acid solution to obtain a proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite.

[0015] Preferably, in the step S1, the graphene on the copper substrate obtained through chemical vapor deposition growth is flattened by a glass plate, the graphene side faces upward, and the sample is attached to the glass plate; the glass plate is placed in a cavity of a plasma cleaning agent, vacuum is drawn for 5-30 min, the argon gas pressure in the cavity is adjusted to 1.5-1.7 mbar and balanced for 5-30 min, the plasma generation power is set to 15-25 W, and the argon plasma etching time is 5-10 s; after the cavity is broken vacuum, a Faraday copper mesh is placed on the graphene sample, vacuum is drawn for 5-30 min, the oxygen gas pressure in the cavity is adjusted to 0.25-0.4 mbar and balanced for 5-30 min, and the plasma generation power is set to 5-10 W.

[0016] Preferably, in step S2, the spin-coating of a layer of Nafion emulsion is specifically as follows:

[0017] The spin-coating of a layer of Nafion emulsion is completed by spin-coating at 400-500 rpm for 10-30 s, and then spin-coating at 500-1500 rpm for 30-60 s.

[0018] Preferably, in step S3, the drying and curing temperature is 115-140℃, and the time is 10-30 min.

[0019] Preferably, the thickness of the Nafion film is 12-183 μm, the pressure for hot pressing is 2.5-4.0 MPa, the hot pressing time is 2-10 min, and the hot pressing temperature is 125-140℃.

[0020] Preferably, in step S4, the etching time is 5-10 min; the back of the copper foil is washed with deionized water, and the remaining copper foil is etched with a 0.1-0.5 M FeCl3 solution; after etching for 1-3 h, the transparent N212 / graphene film is washed in deionized water for 5-30 min, washed in a 5%-15% HCl solution for 5-30 min, and finally washed again in deionized water for 5-30 min.

[0021] Preferably, in step S5, the spin-coating of a layer of Nafion emulsion is specifically as follows:

[0022] The spin-coating of a layer of Nafion emulsion is completed by spin-coating at 400-500 rpm for 10-30 s, and then spin-coating at 500-1500 rpm for 30-60 s.

[0023] Preferably, in step S6, the drying and curing temperature is 115-140℃, and the time is 10-30 min; then a Nafion film with a thickness of 12-183 μm is selected, and the Nafion / graphene / copper foil sample is hot pressed with the Nafion film on the spin-coated surface, the hot pressing pressure is 2.5-4.0 MPa, the hot pressing time is 2-10 min, and the hot pressing temperature is 125-140℃.

[0024] Preferably, in step S7, the acid solution is a 5%-15% HCl solution, and the soaking time is 10-40 h.

[0025] Another technical solution of the present application is that, based on the large-area single-layer nano-porous graphene Nafion composite proton exchange membrane, an open-circuit voltage of 0.5 V or more and a maximum power density of 130 mW cm -2 under test conditions of 60-90℃ can be achieved.

[0026] Compared with the prior art, the present application has at least the following beneficial effects:

[0027] The application discloses a preparation method of a proton exchange membrane based on large-area single-layer nanoporous graphene Nafion composite.

[0028] Further, the large-area single-layer graphene is subjected to plasma pore forming, fine regulation of the pore diameter in the graphene is realized, the proton conduction capacity is further improved on the basis of guaranteeing the methanol selectivity, and the decline of the proton conduction capacity of the membrane caused by the introduction of the graphene is avoided.

[0029] Further, the Nafion emulsion is spin-coated on the surface of the porous graphene, the interface affinity during subsequent hot pressing of the porous graphene and the Nafion film is enhanced, the interface gap between the Nafion and the graphene is effectively reduced, the stability of the composite film is improved, and the transmission path of the protons at the interface is shortened.

[0030] Further, after the surface spin-coating of the porous graphene, heating is performed to promote surface solidification, which is helpful to the stable combination of the spin-coating layer and the porous graphene, and provides a surface protection layer for the porous graphene, so that damage of the porous graphene caused by local stress during subsequent hot pressing is prevented.

[0031] Further, by selecting the Nafion film with the thickness of 12-183 mu m, sufficient mechanical support can be provided for the porous graphene, and the thickness of the Nafion does not cause negative influence on the performance of the whole film. The Nafion film with the thickness in the range has multiple commercial specifications to be selected. The temperature of the hot pressing is close to the glass transition temperature of the Nafion film, which is beneficial to the good adhesion of the Nafion film and the Nafion emulsion layer; the selection of the hot pressing time and the pressure considers that appropriate pressure is provided to realize the good adhesion of the Nafion interface, and the pressure is prevented from being too large or the pressing time from being too long to cause damage of the porous graphene.

[0032] Further, first etching the back of the porous graphene on the copper substrate helps to remove the graphene on the back of the copper substrate for subsequent film preparation. Since the copper foil back surface needs to be etched first, the graphene attached to the back surface is loosened, making it easier to remove with deionized water for subsequent washing, so a shorter back etching time is selected. If the etching time is too long, the sample will lose the support of the copper foil substrate and cannot be washed with deionized water. Since the etching solution may come into contact with the Nafion membrane during the etching process, using a traditional ammonium persulfate solution may simultaneously corrode the Nafion membrane, so a high-concentration FeCl3 solution is selected in the present application. After completing the etching of the copper foil, the surface of the porous graphene is cleaned repeatedly with deionized water and a high-concentration hydrochloric acid solution to remove ion residues.

[0033] Further, multiple spin coating on the surface of the porous graphene can effectively reduce the interfacial stress between the first layer of spin coating film and the graphene, and reduce the possibility of graphene damage due to local stress concentration in the subsequent preparation process.

[0034] Further, repeating the spin coating and hot pressing process on the other side of the porous graphene ensures that both sides of the porous graphene can be well attached to the Nafion and have sufficient mechanical support.

[0035] Further, soaking the prepared composite membrane in a high-concentration acid solution is beneficial for ion exchange in the Nafion, so that there is a sufficient amount of protons in the microstructure, which helps to improve the proton conduction ability in subsequent battery applications.

[0036] In summary, the present application proposes a new type of proton exchange membrane with a Nafion / large-area single-layer nano-porous graphene / Nafion composite structure, which ensures excellent proton conduction ability and methanol selectivity. The composite membrane has stable interface attachment at the interface and good mechanical properties as a whole.

[0037] The technical solutions of the present application will be further described in detail below with the aid of the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings used in the following comparative example description are briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and other accompanying drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1The preparation flow chart of the proton exchange membrane involved in the present application: a) is the graphene prepared by CVD on copper substrate; b) is the plasma treatment; c) is the Nafion spin coating; d) is the secondary hot pressing; e) is the etching of copper; f) is the porous graphene on the Nafion film; g) is the spin coating again on the graphene surface; h) is the hot pressing composite;

[0040] Figure 2 The interface comparison chart of the composite film before and after the spin coating process: a) is the interface of the composite film without introducing the spin coating process; b) is the interface of the composite film after introducing the spin coating process;

[0041] Figure 3 The characterization results of the CVD prepared graphene and the composite film: a) is the scanning electron microscope (SEM) image of the graphene on the SiO2 / Si substrate; b) is the Raman spectrum of the graphene on the copper substrate; c) is the SEM image of the graphene on the N212 substrate; d) is the cross-section SEM image of the N212 / graphene / N212 film; e) is the contact angle measurement chart of the N212 film; f) is the contact angle measurement chart of the N212 film after transferring the graphene; g) is the photo of the synthesized N212 / graphene / N212 film; h) is the photo of the synthesized MEA;

[0042] Figure 4 The characterization of the nanoporous graphene: a) is the photo of the plasma treatment process; b) is the Raman spectrum of the graphene obtained by different pore-forming time;

[0043] Figure 5 The performance test of the N212 / nanoporous graphene / N212 series film: a) proton conductivity test; b) methanol permeability test; c) selectivity performance results;

[0044] Figure 6 The direct methanol fuel cell (DMFC) performance test results of the N212 / nanoporous graphene / N212 series film. DETAILED DESCRIPTION

[0045] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0046] In the present application, all the embodiments and preferred implementation methods mentioned in the present application can be combined to form new technical solutions, if not specially stated.

[0047] In the present application, all the technical features and preferred features mentioned in the present application can be combined to form new technical solutions, if not otherwise specified.

[0048] In the present application, percentage (%) or part refers to the percentage by weight or weight parts of the composition, if not otherwise specified.

[0049] In the present application, each component or its preferred component involved can be combined to form new technical solutions, if not otherwise specified.

[0050] In the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "6~22" represents that all the real numbers between "6~22" have been listed herein, and "6~22" is only a shorthand notation for these numerical combinations.

[0051] The lower limit and upper limit of the range disclosed in the present application can be one or more lower limits and one or more upper limits, respectively.

[0052] In the present application, the term "and / or" used herein means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0053] In the present application, unless otherwise specified, each reaction or operation step can be carried out sequentially or according to the sequence. Preferably, the reaction method herein is carried out sequentially.

[0054] Unless otherwise specified, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied in the present application.

[0055] The present application provides a proton exchange membrane based on large-area single-layer nano-porous graphene and Nafion composite and a preparation method thereof. On the basis of the prior art, large-area single-layer nano-porous graphene is introduced, which can effectively utilize the atomic-level selectivity of graphene, improve the methanol blocking ability while basically maintaining the proton conduction ability of Nafion membrane. For the interface treatment of the composite structure, the present application optimizes multiple spin coating on both sides of graphene, ensuring good adhesion of the Nafion and graphene two-phase interface, so that the proton can be stably and efficiently transmitted.

[0056] Please refer to Figure 1 The present application provides a preparation method of a proton exchange membrane based on large-area single-layer nano-porous graphene and Nafion composite, comprising the following steps:

[0057] S1, plasma etching the porous graphene sample to obtain a porous graphene / copper foil sample;

[0058] The graphene on the copper substrate obtained by chemical vapor deposition (CVD) is fixed on a clean glass plate with the graphene facing up, and the four corners are fixed with adhesive tape. The glass plate is placed in the cavity of the plasma cleaning agent, vacuumed for 5-30 minutes, and then the argon gas pressure in the cavity is adjusted to 1.5-1.7 mbar and balanced for 5-30 minutes. The plasma generation power is set to 15-25 W, and the argon plasma etching time is 5-10 seconds. After the cavity is broken, a self-made Faraday copper mesh is placed on the graphene sample, vacuumed for 5-30 minutes, and then the oxygen gas pressure in the cavity is adjusted to 0.25-0.4 mbar and balanced for 5-30 minutes. The plasma generation power is set to 5-10 W, and the oxygen etching time is adjusted according to the target screen aperture.

[0059] The Faraday copper mesh is connected by 5-20 mesh copper mesh to protect the graphene sample on the copper foil from four sides and the top, and appropriately weaken the plasma intensity in the copper mesh.

[0060] S2, spin-coating a layer of Nafion emulsion on the graphene surface of the porous graphene / copper foil sample, and repeating the above steps to form a relatively thick Nafion support layer on the surface of the porous graphene;

[0061] A few drops of Nafion emulsion are added on the surface of the copper substrate porous graphene, so that it completely covers the graphene surface. Spin-coating at 400-500 rpm for 10-30 seconds, and then spin-coating at 500-1500 rpm for 30-60 seconds. Repeat several times.

[0062] S3, drying and curing the spin-coated porous graphene / copper foil sample on the hot table, and hot-pressing the Nafion film on the spin-coated side of the graphene sample to obtain a Nafion / porous graphene / copper foil sample;

[0063] The spin-coated side of the porous graphene / copper foil sample is facing up, the hot table temperature is set to 115-140℃, and the curing time is 10-30 minutes.

[0064] The thickness of the Nafion film used is 10-183 μm, the pressure used for hot pressing is 2.5-4.0 MPa, the hot pressing time is 2-10 minutes, and the hot pressing temperature is 125-140℃.

[0065] S4, etching the hot-pressed Nafion / porous graphene / copper foil sample in an etching solution to remove the material attached to the back of the copper foil, then rinsing the back of the film, placing the sample in clean etching solution to etch the remaining copper foil, after etching, cleaning the Nafion / porous graphene sample to remove the etching solution residue, and air-drying the Nafion / porous graphene sample to obtain a Nafion / graphene sample;

[0066] The etching solution is selected to be 0.1-0.5M FeCl3 solution, the copper foil is faced downward during etching, the sample is floated on the surface of the etching solution, and the etching time is 5-10 minutes; the surface of the copper foil is rinsed with deionized water (deionized water) to remove surface impurities, and then clean 0.1-0.5M FeCl3 solution is used to etch the remaining copper foil; after etching for 1-3 hours, the transparent Nafion / porous graphene film is sequentially cleaned in deionized water for 5-30 minutes, 5%-15% HCl solution for 5-30 minutes, and finally deionized water for 5-30 minutes; the graphene side of the Nafion / porous graphene sample is placed flat on the dust-free paper, and air-dried overnight.

[0067] S5, spin-coating a layer of Nafion emulsion on the graphene side of the air-dried Nafion / porous graphene sample to enhance the interfacial adhesion;

[0068] Nafion emulsion is added to the graphene side of the Nafion / porous graphene sample, so that the emulsion completely covers the sample, spin-coating at 400-500 rpm for 10-30 seconds, and then spin-coating at 500-1500 rpm for 30-60 seconds; repeat several times.

[0069] S6, drying and curing the spin-coated Nafion / porous graphene sample on a hot stage, and then hot-pressing with another Nafion film to obtain a Nafion / porous graphene / Nafion sample;

[0070] The spin-coated side of the Nafion / porous graphene sample is placed upward, heated and cured on a hot stage at 115-140℃ for 10-30 minutes; then a Nafion film with a thickness of 12-183μm is selected, and the spin-coated side of the Nafion / porous graphene sample is hot-pressed with the Nafion film, with a hot-pressing pressure of 2.5-4.0 MPa, a hot-pressing time of 10 minutes, and a hot-pressing temperature of 125-140℃, to obtain a Nafion / porous graphene / Nafion sample.

[0071] S7, the prepared Nafion / graphene / Nafion sample is soaked in an acid solution and then dried to obtain a proton exchange membrane based on a large-area single-layer nano-porous graphene Nafion composite, which is used for the assembly of a membrane electrode assembly (MEA).

[0072] The acid solution is a 5%-15% HCl solution, the soaking time is 10-40 hours, and the drying condition is to place the sample on a dust-free paper and dry it in air overnight.

[0073] The proton exchange membrane based on a single-layer large-area nano-porous graphene / Nafion composite structure prepared by the method of the application can achieve an open-circuit voltage of more than 0.5 V and a maximum power density of 130 mW cm -2 The above maximum power density is better than that of a commercial Nafion film of the same thickness.

[0074] To make the purpose, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. The components of the embodiments of the application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. All other embodiments obtained by a person of ordinary skill in the art without creative work on the basis of the embodiments in the application belong to the scope of protection of the application.

[0075] Embodiment 1

[0076] S1, the CVD obtained copper substrate graphene is gently flattened with two clean glass plates, the graphene surface faces upward, and is fixed on a clean glass plate with tape on four corners, and is moved into the cavity of a plasma cleaning machine. After the cavity of the plasma cleaning agent is vacuumed for 5 minutes, the argon gas pressure in the cavity is adjusted to 1.5 mbar and balanced for 5 minutes, the plasma generation power is set to 15 W, and the argon plasma etching time is 5 seconds. After the cavity is broken, a self-made Faraday copper mesh is placed on the graphene sample, vacuumed for 5 minutes, the oxygen gas pressure in the cavity is adjusted to 0.25 mbar and balanced for 5 minutes, the plasma generation power is set to 5 W, and the oxygen etching time is 10 seconds;

[0077] S2, a few drops of Nafion emulsion are added on the surface of the copper substrate graphene after plasma etching, so that the graphene surface can be completely covered, and then spin-coated at 400 rpm for 10 seconds, followed by spin-coating at 500 rpm for 30 seconds;

[0078] S3, repeat the spin-coating step once to form a thicker Nafion support layer;

[0079] S4, spin-coat the sample with the spin-coated side facing up on a hot plate at 115 °C for 30 minutes;

[0080] S5, after the curing is complete, hot-press a piece of Gore M778.12 membrane to the spin-coated side of the sample at a pressure of 2.5 MPa and a temperature of 125 °C for 2 minutes;

[0081] S6, after the hot-pressing, float the sample with the copper foil side facing down in a 0.1 M FeCl3solution for 10 minutes to etch the material attached to the back of the copper foil;

[0082] S7, after the etching is complete, rinse the copper foil side with deionized water (Dl water) and then place it on the surface of another clean 0.1 M FeCl3solution to complete the etching of the copper foil;

[0083] S8, after 3 hours of etching, the sample is transparent. Rinse the sample sequentially with Dl water for 5 minutes, 5% HC1 solution for 5 minutes, and Dl water again for 5 minutes;

[0084] S9, dry the sample with the graphene side facing up in air overnight;

[0085] S10, then, drop Nafion emulsion on the graphene side of the sample to completely cover the sample and spin-coat the membrane with the same spin-coating parameters as in step S2; repeat the spin-coating twice;

[0086] S11, place the sample with the spin-coated side facing up on a hot plate at 115 °C for 30 minutes to dry and cure;

[0087] S12, after the drying is complete, hot-press the sample with the spin-coated side facing up with another piece of Gore M778.12 membrane at a pressure of 2.5 MPa and a temperature of 125 °C for 2 minutes;

[0088] S13, after the hot-pressing, immerse the sample in 5% HC1 solution for 40 hours and then dry it in air;

[0089] S14, immerse the sample in 2.0 mg cm -2 Pt black loading (cathode) / 4.0 mg cm -2 PtRu loading (anode) gas diffusion electrode at a pressure of 3.0 MPa and a temperature of 135 °C for 3 minutes to complete the membrane electrode preparation.

[0090] Example 2

[0091] S1, the copper substrate graphene obtained by CVD is gently flattened with two clean glass plates, the graphene surface faces up, and the four corners are fixed on a clean glass plate with tape, and then moved into the plasma cleaning chamber. After the plasma cleaning chamber is vacuumed for 30 minutes, the argon gas pressure in the chamber is adjusted to 1.7 mbar and balanced for 30 minutes, the plasma generation power is set to 25 W, and the argon plasma etching time is 10 seconds. After the chamber is broken, a self-made Faraday copper mesh is placed on the graphene sample, vacuumed for 30 minutes, the oxygen gas pressure in the chamber is adjusted to 0.4 mbar and balanced for 30 minutes, the plasma generation power is set to 10 W, and the oxygen etching time is 10 seconds;

[0092] S2, a few drops of D520 latex are added to the surface of the copper substrate graphene after plasma etching, so that the graphene surface can be completely covered, and then spin-coated at 500 rpm for 30 seconds, followed by spin-coating at 1500 rpm for 60 seconds;

[0093] S3, repeat the above spin-coating step once to form a thicker Nafion support layer;

[0094] S4, the spin-coated sample is placed on a hot stage at 140℃ and cured for 10 minutes;

[0095] S5, after curing, a piece of N117 film is hot-pressed on the spin-coated surface of the sample, the hot-pressing pressure is 4.0 MPa, the temperature is 140℃, and the duration is 10 minutes;

[0096] S6, the sample after hot-pressing is placed with the copper foil face down in a 0.5M FeCl3 solution for etching for 5 minutes to etch the material attached to the back of the copper foil;

[0097] S7, after etching, the copper foil is washed with deionized water (deionized water), and then placed on the surface of another clean 0.5M FeCl3 solution to complete the etching of the copper foil;

[0098] S8, after 1 hour of etching, the sample is transparent. The sample is sequentially washed with deionized water for 30 minutes, then with 15% HCl solution for 30 minutes, and finally with deionized water for 30 minutes;

[0099] S9, the sample graphene surface faces up and is dried in air overnight;

[0100] S10, then, D520 latex is added to the graphene surface of the sample to completely cover the sample, and spin-coated on the film with the same spin-coating parameters as in S2; repeat spin-coating once;

[0101] S11, the sample spin-coated surface faces up and is placed on a hot stage at 140℃ and dried for 10 minutes;

[0102] S12, the dried sample was hot-pressed with another piece of N117 film at a pressure of 4.0 MPa and a temperature of 140 °C for 10 minutes;

[0103] S13, the hot-pressed sample was immersed in a 15% HC1 solution for 10 hours and then dried in air;

[0104] S14, the sample was hot-pressed with 2.0 mg cm -2 Pt black loading (cathode) / 4.0 mg cm -2 The gas diffusion electrode with PtRu loading (anode) was hot-pressed with the sample at a pressure of 3.0 MPa and a temperature of 135 °C for 3 minutes to complete the membrane electrode preparation.

[0105] Example 3

[0106] S1, the CVD obtained copper substrate graphene was gently flattened with two clean glass plates, the graphene surface was upward, and the four corners were fixed on a clean glass plate with tape and moved into the plasma cleaning machine cavity. After the cavity was vacuumed for 10 minutes, the argon gas pressure in the cavity was adjusted to 1.6 mbar and balanced for 5 minutes, the plasma generation power was set to 20 W, and the argon plasma etching time was 6 seconds. After the cavity was broken, a self-made Faraday copper mesh was placed on the graphene sample, vacuumed for 10 minutes, the oxygen gas pressure in the cavity was adjusted to 0.3 mbar and balanced for 5 minutes, the plasma generation power was set to 7 W, and the oxygen etching time was 20 seconds;

[0107] S2, a few drops of D520 latex were added on the surface of the copper substrate graphene after plasma etching, so that it could completely cover the surface of the graphene, and then spin-coated at 450 rpm for 15 seconds, followed by spin-coating at 1000 rpm for 45 seconds;

[0108] S3, the above spin-coating step was repeated once to form a thicker Nafion support layer;

[0109] S4, the spin-coated sample was cured on a hot stage at 120 °C for 20 minutes with the spin-coated surface upward;

[0110] S5, after curing, a piece of N212 film was hot-pressed on the spin-coated surface of the sample at a pressure of 3.0 MPa and a temperature of 135 °C for 3 minutes;

[0111] S6, the hot-pressed sample was etched in a 0.3 M FeCl3 solution for 7 minutes with the copper foil surface downward to etch the material attached to the back of the copper foil;

[0112] S7, after etching is completed, the copper foil surface is rinsed with deionized water (deionized water), and then the copper foil is placed on the surface of another clean 0.3M FeCl3 solution to complete the etching of the copper foil;

[0113] S8, after 2 hours of etching, the sample is transparent. The sample is sequentially cleaned with deionized water for 10 minutes, then with 10% HC1 solution for 10 minutes, and finally with deionized water again for 10 minutes;

[0114] S9, the sample graphene surface is dried overnight in air;

[0115] S10, then, D520 latex is added dropwise on the graphene surface of the sample, so that it completely covers the sample, and is spin-coated on the film with the same spin-coating parameters in S2; spin-coating is repeated twice;

[0116] S11, the sample spin-coating surface is placed upward on a hot stage at 120°C and dried and cured for 20 minutes;

[0117] S12, the dried sample spin-coating surface is placed upward, and another piece of N212 film is hot-pressed at a pressure of 3.0 MPa and a temperature of 135°C for 10 minutes;

[0118] S13, the hot-pressed sample is soaked in 10% HC1 solution for 24 hours, and then dried in air;

[0119] S14, the sample is hot-pressed with 2.0 mg cm -2 platinum black loading (cathode) / 4.0 mg cm -2 The gas diffusion electrode with PtRu loading (anode) is hot-pressed with the sample at a pressure of 3.0 MPa and a temperature of 135°C for 3 minutes to complete the preparation of the membrane electrode.

[0120] Example 4

[0121] S1, the CVD obtained copper substrate graphene is gently flattened with two clean glass plates, the graphene surface is upward, and the four corners are fixed on a clean glass plate with adhesive tape, and then the glass plate is moved into the cavity of the plasma cleaning machine. After the cavity is vacuumed for 10 minutes, the argon gas pressure in the cavity is adjusted to 1.5 mbar and balanced for 10 minutes, the plasma generation power is set to 20W, and the argon plasma etching time is 6 seconds. After the cavity is broken, a self-made Faraday copper mesh is placed on the graphene sample, vacuumed for 20 minutes, the oxygen gas pressure in the cavity is adjusted to 0.35 mbar and balanced for 5 minutes, the plasma generation power is set to 7W, and the oxygen etching time is 10 seconds;

[0122] S2, a few drops of D520 latex were added on the surface of the copper substrate graphene which was etched by plasma, so that it could completely cover the graphene surface, and then it was spin-coated at 450 rpm for 20 seconds, and then spin-coated at 1500 rpm for 45 seconds;

[0123] S3, the above spin-coating step was repeated once to form a thicker Nafion support layer;

[0124] S4, the spin-coated sample was placed on a hot stage with the spin-coated surface facing up, and was cured at 130°C for 20 minutes;

[0125] S5, after the curing was completed, a piece of N212 film was hot-pressed on the spin-coated surface of the sample, the hot-pressing pressure was 3.0 MPa, the temperature was 135°C, and the duration was 5 minutes;

[0126] S6, the sample after hot-pressing was placed with the copper foil surface facing down, and was etched in a 0.3M FeCl3 solution for 7 minutes to etch the material attached to the back of the copper foil;

[0127] S7, after the etching was completed, the copper foil surface was washed with deionized water (deionized water), and then the copper foil was placed on the surface of another clean 0.3M FeCl3 solution to complete the etching of the copper foil;

[0128] S8, after 2 hours of etching, the sample was transparent. The sample was sequentially washed with deionized water for 20 minutes, 10% HCl solution for 20 minutes, and deionized water again for 20 minutes;

[0129] S9, the sample graphene surface was dried in air overnight;

[0130] S10, then, D520 latex was added on the graphene surface of the sample to completely cover the sample, and was spin-coated on the film with the same spin-coating parameters as in S2; the spin-coating was repeated twice;

[0131] S11, the sample was placed with the spin-coated surface facing up on a hot stage at 130°C and dried for 20 minutes;

[0132] S12, the dried sample was placed with the spin-coated surface facing up, and another piece of N212 film was hot-pressed at a pressure of 3.0 MPa and a temperature of 135°C for 10 minutes;

[0133] S13, the sample after hot-pressing was immersed in a 10% HCl solution for 30 hours, and then was dried in air;

[0134] S14, the sample was combined with 2.0 mg cm -2 platinum black loading (cathode) / 4.0 mg cm -2The gas diffusion electrode with PtRu loading (anode) was prepared by hot-pressing the sample at 3.0 MPa and 135℃ for 3 minutes.

[0135] Through the scanning electron microscope characterization of the section, it can be seen that after the introduction of the two-sided spin coating process, the close fit of graphene and Nafion film at the interface can be effectively realized.

[0136] Through preliminary experimental characterization, as shown in Figure 3 (a) and Figure 3 (b), the CVD graphene used in the experiment is large-area single-layer continuous, and the Raman characterization basically does not appear obvious material defects, avoiding the influence of the material itself on the subsequent experimental results. Figure 3 (c) can observe the obvious interface of Nafion and graphene material on Nafion, combined with Figure 3 (e) and Figure 3 (f) contact angle test results, which proves the successful transfer of graphene on the Nafion film in a large area. Figure 3 (g) and Figure 3 (h) gives the real picture of the prepared film and MEA.

[0137] Figure 4 The process and result characterization of the plasma pore-forming treatment of graphene on copper foil are shown. Through Raman spectrum characterization, as shown in Figure 4 (b), adjusting the treatment time of oxygen plasma can effectively control the defect situation of the graphene surface, and realize different pore-forming effects.

[0138] Figure 5 The proton exchange membrane conductivity tested by four-electrode scanning voltammetry in pH=1 hydrochloric acid solution (a), the methanol permeation of the proton exchange membrane installed between 0.5M methanol solution and deionized water cavity (b), and the selectivity of the proton exchange membrane calculated according to the proton conductivity and methanol permeability (c) are shown. It can be seen that the oxygen plasma pore-forming can effectively improve the conductivity performance of the proton exchange membrane as shown in Figure 5 a; compared with the commercial Nafion film, the methanol permeation is significantly reduced after introducing nanoporous graphene as shown in Figure 5 b; the oxygen treatment time has little effect on the methanol permeability, mainly affecting the proton conductivity, thereby dominating the change of the selectivity of the proton exchange membrane as shown in Figure 5 c.

[0139] After the graphene films with different pore-forming time were combined with Nafion films to prepare MEA, the performance test of direct methanol fuel cell was carried out. The methanol fuel was 5.0M methanol aqueous solution, and the test temperature was 60℃. After the MEA was assembled into a cell, it was activated at constant current for 5 hours, and then the performance test of the cell was carried out, and the test results are shown in Figure 5 The sample treated by oxygen plasma for 10s showed the best cell performance, and the open circuit voltage was 0.532 V, and the highest power density reached 134.56mW cm -2 .

[0140] In summary, the proton exchange membrane based on large-area single-layer nano-porous graphene Nafion composite and the preparation method thereof proposed by the present application can effectively improve the methanol selectivity and proton conductivity of the proton exchange membrane simultaneously, and realize the simultaneous improvement of the open circuit voltage and power density of the cell in the application of direct methanol fuel cell compared with the existing commercial proton exchange membrane with the same thickness.

[0141] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite, characterized in that, Includes the following steps: S1. Plasma etching is performed on the graphene sample to obtain a porous graphene / copper foil sample. The porous graphene on the copper substrate is grown by chemical vapor deposition. The copper foil is flattened with a glass plate, with the porous graphene side facing up, so that the sample is attached to the glass plate. The glass plate is placed in the cavity of plasma cleaning agent, and a vacuum is drawn for 5~30 min. The argon gas pressure in the cavity is adjusted to 1.5~1.7 mbar and then balanced for 5~30 min. The plasma generation power is set to 15~25W and the argon plasma etching time is 5~10 s. After the vacuum in the cavity is broken, a Faraday copper mesh is placed on the porous graphene sample. After a vacuum is drawn for 5~30 min, the oxygen gas pressure in the cavity is adjusted to 0.25~0.4 mbar and then balanced for 5~30 min. The plasma generation power is set to 5~10W. S2. Spin-coat a layer of Nafion latex onto the graphene surface of the porous graphene / copper foil sample prepared in step S1, and repeat this process multiple times. S3. Dry and cure the porous graphene / copper foil sample after spin coating in step S2 on a hot stage, and hot-press the Nafion film onto one side of the spin-coated graphene sample to obtain the Nafion / porous graphene / copper foil sample. S4. The Nafion / porous graphene / copper foil sample after hot pressing in step S3 is etched in an etching solution to remove the material attached to the back of the copper foil. Then the back of the copper foil is rinsed, and the sample is placed back into a clean etching solution to etch the remaining copper foil. After etching, it is cleaned and dried to obtain the Nafion / graphene sample. S5. After drying in step S4, a layer of Nafion latex is spin-coated onto the graphene surface of the Nafion / porous graphene sample. S6. The Nafion / graphene sample after spin coating in step S5 is dried and cured on a hot stage, and then hot-pressed with another Nafion film to obtain a Nafion / porous graphene / Nafion sample. S7. The Nafion / porous graphene / Nafion sample prepared in step S6 is immersed in an acid solution and then dried to obtain a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite.

2. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S2, the spin-coating of a layer of Nafion latex specifically involves: Spin coat at 400-500 rpm for 10-30 seconds, then spin coat at 500-1500 rpm for 30-60 seconds to complete one layer of Nafion latex.

3. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S3, the drying and curing temperature is 115~140℃ and the time is 10~30min.

4. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 3, characterized in that, The thickness of the Nafion film is 12~183μm, the pressure used for hot pressing is 2.5~4.0 MPa, the hot pressing time is 2~10min, and the hot pressing temperature is 125~140℃.

5. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S4, the etching time is 5-10 min; rinse the back of the copper foil with deionized water, and then etch the remaining copper foil with 0.1-0.5 M FeCl3 solution; after etching for 1-3 h, the transparent Nafion film is rinsed in deionized water for 5-30 min, then in 5%-15% HCl solution for 5-30 min, and finally rinsed again with deionized water for 5-30 min.

6. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S5, the next layer of Nafion latex is spin-coated as follows: Spin coat at 400-500 rpm for 10-30 seconds, then spin coat at 500-1500 rpm for 30-60 seconds.

7. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S6, the drying and curing temperature is 115~140℃ and the time is 10~30min. Then, a Nafion film with a thickness of 12~183μm is selected, and the Nafion / porous graphene / copper foil sample with the spin-coated side facing up is hot-pressed. The hot-pressing pressure is 2.5~4.0 MPa, the hot-pressing time is 2~10min, and the hot-pressing temperature is 125~140℃.

8. The method for preparing a proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite according to claim 1, characterized in that, In step S7, the acid solution is a 5%~15% HCl solution, and the soaking time is 10~40 hours.

9. A proton exchange membrane based on a large-area monolayer nanoporous graphene Nafion composite prepared by the method according to any one of claims 1 to 8, characterized in that, Under testing conditions of 60~90℃, it achieves an open-circuit voltage of over 0.5V and a power consumption of 130 mW / cm². -2 The above refers to the maximum power density.

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