Modified graphene oxide nafion proton composite membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of fuel cell proton exchange membrane preparation, in particular to a modified graphene oxide nafion proton composite membrane and a preparation method and application thereof.The modified graphene oxide nafion proton composite membrane is obtained by mixing graphene oxide slurry, anhydrous cupric sulfate and N, N-dimethylformamide, heating in a water bath, dropwise adding an alcoholic solution, condensing, refluxing and filtering; adding the modified graphene oxide into the nafion solution to obtain a modified graphene oxide nafion dispersion liquid; the modified graphene oxide nafion dispersion liquid is poured into a membrane disc, vacuum drying is performed to obtain the modified graphene oxide nafion proton composite membrane, the nafion proton composite membrane is of a multi-layer sheet structure, when the nafion proton composite membrane serves as a proton exchange membrane, the barrier property of the nafion proton composite membrane is superior to that of a common nafion membrane without a sheet structure, the hydrophobicity of the nafion proton composite membrane is changed compared with that of a pure nafion membrane, and the modified graphene oxide nafion proton composite membrane has the advantages of being simple in preparation process and high in practicability. And the water-soluble polymer is not singly deviated to be more hydrophobic or more hydrophilic any more, so that the application range of the water-soluble polymer is wider.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell proton exchange membrane preparation, and particularly relates to a modified graphene oxide nafion proton composite membrane, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, environmental problems have gradually attracted wide attention. Protecting the environment, reducing emissions, and developing environmentally friendly energy are of great significance to humanity and society. Therefore, batteries have become a field that various experts compete to research. Among them, the most valuable one is fuel cells. Proton exchange membrane fuel cells have attracted the interest of researchers in the battery field in recent years due to their high energy conversion efficiency and zero emissions, and have become a hot spot in new energy research. The proton exchange membrane is the core component of a proton fuel cell, and its performance directly determines the performance of the proton fuel cell. The key to the proton exchange membrane is the proton conduction performance, because this directly affects the basic function of the proton fuel cell.

[0003] At present, proton exchange membranes are all perfluorosulfonic acid membranes represented by nafion resin. However, in the actual use process, there are still some problems with nafion membranes. One is that the strength of a pure nafion membrane itself is relatively low, and some carriers are required for use. The other is that the proton conduction efficiency of the nafion membrane can still be further improved. Therefore, the preparation of composite membranes has become a key point. However, the nafion membranes prepared by existing methods rely greatly on the water content. In a high-temperature and low-humidity environment, serious water loss occurs, and the proton conduction efficiency will decrease significantly due to the collapse of the ion cluster network dynamic channels formed by sulfonic acid groups and water molecules through dynamic hydrogen bonds. When the nafion membrane is used in a direct methanol fuel cell, a lot of methanol fuel will directly penetrate through the proton exchange membrane to the cathode, causing interference to the cathode reaction of the methanol fuel cell, resulting in a reduction in its efficiency and waste of fuel. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a modified graphene oxide nafion proton composite membrane, a preparation method thereof, and an application thereof. The present invention changes the hydrophobicity compared with a pure nafion membrane, and no longer simply tends to be more hydrophobic or more hydrophilic, making its application range wider. The nafion proton composite membrane prepared by the present invention has a multi-layered sheet structure in its microscopic morphology, and its barrier property is better than that of a common nafion membrane without a sheet structure when used as a proton exchange membrane.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A preparation method of a modified graphene oxide nafion proton composite membrane, comprising the following steps:

[0007] In N,N-dimethylformamide solvent, using graphene oxide slurry as the raw material and anhydrous copper sulfate as the catalyst, after mixing, heat in a water bath. During the heating process, dropwise add an alcohol solution for modification. The carboxyl groups in the graphene oxide slurry react with the hydroxyl groups in the alcohol solution through catalytic esterification to form ester groups. Then, carry out condensation reflux and filtration to obtain modified graphene oxide.

[0008] Disperse the modified graphene oxide into a nafion solution, stir, ultrasonicate, and perform suction filtration to obtain a modified graphene oxide nafion dispersion.

[0009] Pour the modified graphene oxide nafion dispersion evenly into a membrane tray and dry it under vacuum to obtain a modified graphene oxide nafion proton composite membrane.

[0010] In the present invention, adding modified graphene oxide makes the composite membrane structure have a multi-layer flaky shape, increasing the proton conduction channels and thus improving the conductivity. Moreover, the nafion membrane added with modified graphene oxide becomes more durable in structure due to the addition of inorganic substances, strengthening the membrane strength, solving the problem of low proton conduction efficiency of the nafion membrane prepared by existing methods. When the modified graphene oxide nafion proton composite membrane prepared by the present invention is used in a direct methanol fuel cell, the barrier property of the proton exchange membrane is better than that of a common nafion membrane without a lamellar structure, solving the problem that methanol fuel directly penetrates through the proton exchange membrane to the cathode, causing interference to the cathode reaction of the methanol fuel cell, resulting in reduced efficiency and wasted dye.

[0011] In a preferred embodiment of the present invention, the mass percentage of modified graphene oxide in the nafion solution is 0.5% - 1%.

[0012] In a preferred embodiment of the present invention, the mass ratio of graphene oxide slurry to the alcohol solution is 6:10 - 15.

[0013] In a preferred embodiment of the present invention, the mass ratio of graphene oxide slurry to anhydrous copper sulfate is 30 - 35:1.

[0014] In a preferred embodiment of the present invention, the mass ratio of graphene oxide slurry to N,N-dimethylformamide is 1:10 - 20.

[0015] In a preferred embodiment of the present invention, the mass fraction of the graphene oxide slurry is 1%, and the solvent in the graphene oxide slurry is N,N-dimethylformamide.

[0016] In a preferred embodiment of the present invention, the alcohol solution is anhydrous ethanol.

[0017] In a preferred embodiment of the present invention, the water bath heating temperature is 85°C - 95°C.

[0018] In a preferred embodiment of the present invention, the condensation reflux temperature is 85°C to 95°C, and the condensation reflux time is 6h to 10h.

[0019] Another object of the present invention is to provide a modified graphene oxide nafion proton composite membrane prepared by the preparation method described in any one of the above.

[0020] The third object of the present invention is to provide an application of the modified graphene oxide nafion proton composite membrane described above in a fuel cell.

[0021] Adding some inorganic substances to the nafion solution and mixing them to obtain better performance has become a new direction. However, there is currently no report on using graphene oxide as a composite material to improve proton conduction, alcohol resistance, and mechanical strength. There is even less report on using ethanol as a modifier to modify graphene oxide to make it partially hydrophobic and then composite with nafion to prepare a nafion composite membrane.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. In the present invention, the nafion proton composite membrane uses graphene oxide as a raw material, anhydrous copper sulfate as a catalyst in a nitrogen-nitrogen dimethylformamide solvent, and an alcohol solution is added dropwise during the water bath process for modification. The carboxyl group in graphene oxide reacts with the hydroxyl group in the alcohol solution to generate an ester group through a catalytic esterification reaction, obtaining modified graphene oxide. Then, the modified graphene oxide is dispersed in the nafion solution to obtain a modified graphene oxide nafion dispersion. The modified graphene oxide nafion dispersion is evenly poured into a membrane tray and vacuum dried to obtain a modified graphene oxide nafion proton composite membrane. The addition of modified graphene oxide in the present invention makes the composite membrane structure have a multi-layer flaky shape, increasing the proton conduction channels and thus improving the conductivity. Moreover, the nafion membrane with the addition of modified graphene oxide becomes more durable due to the addition of inorganic substances in terms of structure, strengthening the membrane strength, and solving the problem of low proton conduction efficiency of the nafion membrane prepared by the existing method. When the modified graphene oxide nafion proton composite membrane prepared in the present invention is used in a direct methanol fuel cell, the barrier property of the proton exchange membrane is better than that of a common nafion membrane without a lamellar structure, solving the problem that methanol fuel directly penetrates through the proton exchange membrane to the cathode, interfering with the cathode reaction of the methanol fuel cell, resulting in a reduction in its efficiency and waste of dyes.

[0024] 2. The hydrophobicity of the present invention has changed compared to the pure Nafion membrane, and it no longer simply tends to be more hydrophobic or more hydrophilic. The modified graphene oxide Nafion proton composite membrane prepared in the present invention exhibits a multi-layer flaky structure. When used as a proton exchange membrane, its barrier property is better than that of the ordinary Nafion membrane without a flaky structure. In the present invention, the conductivity of the Nafion membrane added with 1% modified graphene oxide increases by 34.84%, and the membrane strength increases. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the contact angle diagram of the Nafion membrane added with 0.5% modified graphene oxide of the present invention.

[0026] Figure 2 It is the contact angle diagram of the Nafion membrane added with 0.5% unmodified graphene oxide of the present invention.

[0027] Figure 3 It is the contact angle diagram of the Nafion membrane without added modified graphene oxide of the present invention.

[0028] Figure 4 It is the three-efficiency diagram of the Nafion membrane added with 0.5% modified graphene oxide.

[0029] Figure 5 Among them, (a) is the microscopic structure diagram of the Nafion membrane without added graphene oxide, and (b) is the microscopic structure diagram of the Nafion membrane added with modified graphene oxide. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following combines the embodiments of the present invention and uses preferred embodiments and accompanying drawings for detailed description. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0031] It should be noted that all the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through the market or prepared by existing methods.

[0032] Example 1

[0033] A preparation method of a modified graphene oxide Nafion proton composite membrane includes the following steps:

[0034] (1) Mix 15 g of graphene oxide slurry with a mass fraction of 1%, 150 g of N,N-dimethylformamide, and 0.5 g of catalyst anhydrous copper sulfate, add them to a container, heat in a water bath at 95 °C, slowly dropwise add 25 g of anhydrous ethanol during this period, carry out condensation reflux at 95 °C for 8 h, and filter the treated solution to obtain modified graphene oxide.

[0035] (2) Add the modified graphene oxide to the nafion solution for dispersion. The mass percentage of the modified graphene oxide in the nafion solution is 0.5%. Stir mechanically for 12 h and sonicate for 1.5 h. Filter the solution after sonication treatment, and obtain the modified graphene oxide nafion dispersion after suction filtration.

[0036] (3) Pour the modified graphene oxide nafion dispersion evenly into a membrane tray, place it in a vacuum oven and dry at 120 °C for 2 h to obtain the modified graphene oxide nafion proton composite membrane.

[0037] Example 2

[0038] A preparation method of a modified graphene oxide nafion proton composite membrane, comprising the following steps:

[0039] (1) Mix 15 g of graphene oxide slurry with a mass fraction of 1%, 150 g of N,N-dimethylformamide, and 0.5 g of catalyst anhydrous copper sulfate, add them to a container, heat in a water bath at 95 °C, slowly dropwise add 25 g of anhydrous ethanol during this period, carry out condensation reflux at 95 °C for 8 h, and filter the treated solution to obtain modified graphene oxide.

[0040] (2) Add the modified graphene oxide to the nafion solution for dispersion. The mass percentage of the modified graphene oxide in the nafion solution is 1%. Stir mechanically for 12 h and sonicate for 1.5 h. Filter the solution after sonication treatment, and obtain the modified graphene oxide nafion dispersion after suction filtration.

[0041] (3) Pour the modified graphene oxide nafion dispersion evenly into a membrane tray, place it in a vacuum oven and dry at 120 °C for 2 h to obtain the modified graphene oxide nafion proton composite membrane.

[0042] Example 3

[0043] A preparation method of a modified graphene oxide nafion proton composite membrane, comprising the following steps:

[0044] (1) Mix 15 g of graphene oxide slurry with a mass fraction of 1%, 300 g of N,N-dimethylformamide, and 0.5 g of catalyst anhydrous copper sulfate, add them to a container, heat in a water bath at 85 °C, slowly drip 30 g of absolute ethanol during this period, and carry out condensation reflux at 85 °C for 6 h. After filtering the treated solution, modified graphene oxide is obtained.

[0045] (2) Add the modified graphene oxide to the nafion solution for dispersion. The mass percentage of the modified graphene oxide in the nafion solution is 1%. Stir mechanically for 12 h and ultrasonicate for 1.5 h. Filter the ultrasonically treated solution and obtain the modified graphene oxide nafion dispersion after suction filtration.

[0046] (3) Pour the modified graphene oxide nafion dispersion evenly into a membrane tray, place it in a vacuum oven and dry at 120 °C for 2 h to obtain the modified graphene oxide nafion proton composite membrane.

[0047] Example 4

[0048] A preparation method of a modified graphene oxide nafion proton composite membrane, comprising the following steps:

[0049] (1) Mix 15 g of graphene oxide slurry with a mass fraction of 1%, 200 g of N,N-dimethylformamide, and 0.5 g of catalyst anhydrous copper sulfate, add them to a container, heat in a water bath at 90 °C, slowly drip 37.5 g of absolute ethanol during this period, and carry out condensation reflux at 90 °C for 10 h. After filtering the treated solution, modified graphene oxide is obtained.

[0050] (2) Add the modified graphene oxide to the nafion solution for dispersion. The mass percentage of the modified graphene oxide in the nafion solution is 1%. Stir mechanically for 12 h and ultrasonicate for 1.5 h. Filter the ultrasonically treated solution and obtain the modified graphene oxide nafion dispersion after suction filtration.

[0051] (3) Pour the modified graphene oxide nafion dispersion evenly into a membrane tray, place it in a vacuum oven and dry at 120 °C for 2 h to obtain the modified graphene oxide nafion proton composite membrane.

[0052] Comparative Example 1

[0053] A preparation method of a graphene oxide nafion proton composite membrane, comprising the following steps:

[0054] (1) Add the graphene oxide slurry with a mass fraction of 1% to the nafion solution. The mass percentage of the modified graphene oxide in the nafion solution is 0.5%. Stir mechanically for 12 h and ultrasonicate for 1.5 h. Filter the ultrasonically treated solution and obtain the graphene oxide nafion dispersion after suction filtration.

[0055] (2) Pour the graphene oxide nafion dispersion evenly onto the membrane tray, and place it in a vacuum oven at 120 °C for drying for 2 h to obtain a modified graphene oxide nafion proton composite membrane.

[0056] Comparative Example 2

[0057] Pour the nafion solution evenly onto the membrane tray, and place it in a vacuum oven at 120 °C for drying for 2 h to obtain a nafion membrane without added graphene oxide.

[0058] Result analysis

[0059] Figures 1 to 3 The contact angle diagrams of the nafion membranes with 0.5% added modified graphene oxide, 0.5% added unmodified graphene oxide, and no added graphene oxide are shown respectively. It can be seen that the hydrophobicity of the modified graphene oxide nafion proton composite membrane prepared in the present invention has changed compared with the pure nafion membrane, and it no longer simply tends to be more hydrophobic or more hydrophilic.

[0060] Figure 4 The three-efficiency diagrams of the nafion membrane with 0.5% added modified graphene oxide are shown. From Figure 4 it can be seen that the three broken lines extend smoothly, and it can be concluded that the membrane has good stability and reliability during use.

[0061] Figure 5 Among them, (a) is the microscopic structure diagram of the nafion membrane without added graphene oxide, and (b) is the microscopic structure diagram of the nafion membrane with added modified graphene oxide. It can be seen from the figure that the nafion composite membrane with added modified graphene oxide presents a multi-layer flaky structure, and its barrier property is better than that of the ordinary nafion membrane without a flaky structure when used as a proton exchange membrane.

[0062] Table 1 Conductivity comparison

[0063]

[0064] Table 1 shows the conductivity comparison results of the nafion membrane without added GO, the nafion membrane with 0.5% added unmodified GO, the nafion membrane with 0.5% added modified GO, and the nafion membrane with 1% added modified GO. It can be seen that in the conductivity test, the conductivity of the nafion membrane with 1% added modified GO has increased by 34.84% compared with the conductivity of the nafion membrane without added GO, proving that the conductivity of the nafion membrane with 1% added modified GO is more excellent and its use situation is better when used as a proton exchange membrane.

[0065] Table 2 Contact Angles of Nafion Membranes with 0.5% Modified Graphene Oxide Added

[0066] Left contact angle (°) Right contact angle (°) Differential contact angle (°) Average contact angle (°) 1 92.348 92.344 0.004 92.346 2 90.06 90.051 0.009 90.055 3 90.261 90.259 0.002 90.26

[0067] Table 3 Contact Angles of Nafion Membranes with 0.5% Unmodified Graphene Oxide Added

[0068] Left contact angle (°) Right contact angle (°) Differential contact angle (°) Average contact angle (°) 1 80.341 80.331 0.01 80.336 2 77.41 77.392 0.018 77.401 3 75.453 75.445 0.008 75.449

[0069] Table 4 Contact Angles of Nafion Membranes without Modified Graphene Oxide Added

[0070] Left contact angle (°) Right contact angle (°) Differential contact angle (°) Average contact angle (°) 1 97.783 96.46 1.322 97.121 2 94.59 92.741 1.849 93.665 3 92.01 89.328 2.682 90.669

[0071] Tables 2 - 4 are respectively the test results of the contact angles of Nafion membranes with 0.5% modified graphene oxide added, Nafion membranes with 0.5% unmodified graphene oxide added, and Nafion membranes without modified graphene oxide added, each tested 3 times. In the comparison of contact angles, compared with the Nafion membrane with 0.5% unmodified GO added, the contact angle of the Nafion membrane with 0.5% modified GO added increased by an average of 13.16°. Compared with the Nafion membrane without GO added, the contact angle decreased by an average of 2.93°. Therefore, it can be concluded that the modified GO changes the hydrophobicity after being compounded with Nafion to form a membrane, no longer simply tending to be more hydrophobic or more hydrophilic, making its application range wider.

[0072] Table 5 Tensile Property Test

[0073]

[0074] Table 5 shows the test results of tensile properties. In the tensile property test, the tensile strength of the Nafion membrane with modified GO added is generally higher than that of the Nafion membrane without modified GO added. It can be concluded that its strength has been further increased, and it is more suitable for some usage occasions that require greater strength compared to ordinary Nafion membranes.

[0075] In summary, the addition of modified graphene oxide in the present invention makes the composite membrane structure have a multi - layer flaky shape, increases the proton conduction channels, thereby improving the conductivity. Moreover, the Nafion membrane with modified graphene oxide added becomes more durable due to the addition of inorganic substances in its structure, strengthening the membrane strength, solving the problem of low proton conduction efficiency of Nafion membranes prepared by existing methods. When the modified graphene oxide Nafion proton composite membrane prepared in the present invention is used in a direct methanol fuel cell, the barrier property of the proton exchange membrane is better than that of an ordinary Nafion membrane without a lamellar structure, solving the problem that methanol fuel directly penetrates through the proton exchange membrane to the cathode, interfering with the cathode reaction of the methanol fuel cell, resulting in a reduction in its efficiency and waste of dyes.

[0076] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the adopted step methods are the same as those in the embodiments, in order to prevent redundancy, the present invention describes preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0077] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for preparing a modified graphene oxide nafion proton composite membrane, characterized in that: The following steps are involved: In a nitrogen-nitrogen dimethylformamide solvent, graphene oxide slurry is used as a raw material and anhydrous copper sulfate is used as a catalyst. After mixing, the mixture is heated in a water bath. During the heating process, an alcohol solution is added dropwise for modification. The carboxyl groups in the graphene oxide slurry react with the hydroxyl groups in the alcohol solution to generate ester groups. The ester groups are then condensed, refluxed, and filtered to obtain modified graphene oxide. Dispersing the modified graphene oxide in a nafion solution, stirring, ultrasonicating, and filtering to obtain a modified graphene oxide nafion dispersion; The modified graphene oxide nafion dispersion is evenly poured into a membrane tray, and vacuum dried to obtain a modified graphene oxide nafion proton composite membrane.

2. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that, The mass percentage of modified graphene oxide in the nafion solution is 0.5%~1%.

3. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that, The mass ratio of graphene oxide slurry to alcohol solution is 6:10~15.

4. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that, The mass ratio of graphene oxide slurry to anhydrous copper sulfate is 30~35:

1.

5. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that, The mass ratio of graphene oxide slurry to N-N-dimethylformamide is 1:10-20.

6. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that: The alcohol solution is anhydrous ethanol.

7. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that: The water bath heating temperature is 85℃~95℃.

8. The method for preparing the modified graphene oxide nafion proton composite membrane according to claim 1, characterized in that: The condensation reflux temperature is 85℃~95℃, and the condensation reflux time is 6 h~10 h.

9. A modified graphene oxide nafion proton composite membrane obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the modified graphene oxide nafion proton composite membrane according to claim 9 in a fuel cell.

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