阅读说明：本技术 一种还原氧化石墨烯/MXene多孔柔性膜电极及其制备方法和应用 (Reduced graphene oxide/MXene porous flexible membrane electrode and preparation method and application thereof ) 是由 阙文修 罗艺佳 于 2021-08-19 设计创作，主要内容包括：本发明公开了一种还原氧化石墨烯/MXene多孔柔性膜电极及其制备方法和应用,制备方法利用交叉抽滤将氧化石墨烯和MXene分层次抽滤成多层混合膜,并通过低温退火的手段还原氧化石墨烯,利用还原阶段逸出气体造孔,既保持了二维的材料形态,又增加了电极材料的离子嵌入脱出通道,抑制了材料自堆叠现象。多孔的形貌又增加了复合膜的机械柔韧性。工艺路线简单,重复性好,无有机添加剂,原料来源广泛,价格低廉,副产物低毒易于无害化处理,具有良好的经济和环境效应,有利于大规模的工业化应用。制备的材料柔韧性好,电化学性能良好,循环性能优越,作为柔性电子储能设备和可穿戴电子储能设备的电极材料具有广泛巨大的应用潜力。(The invention discloses a reduced graphene oxide/MXene porous flexible membrane electrode and a preparation method and application thereof. The porous morphology also increases the mechanical flexibility of the composite membrane. The method has the advantages of simple process route, good repeatability, no organic additive, wide raw material source, low price, low toxicity of by-products, easy harmless treatment, good economic and environmental effects and contribution to large-scale industrial application. The prepared material has good flexibility, good electrochemical performance and excellent cycle performance, and has wide and huge application potential as an electrode material of flexible electronic energy storage equipment and wearable electronic energy storage equipment.)

1. A preparation method of a reduced graphene oxide/MXene porous flexible membrane electrode is characterized by comprising the following steps:

1) adding graphene oxide powder into ultrapure water for low-temperature ultrasonic treatment, centrifuging and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution with the concentration of 0.5-5 mg/mL, and defining the sol solution as sol solution A;

2) etching Ti by liquid phase etching using an etchant₃AlC₂Collecting a ceramic material to obtain a multilayer MXene nanosheet solution, carrying out low-temperature ultrasonic treatment on the multilayer MXene nanosheet solution in an inert atmosphere, and centrifugally collecting an upper-layer suspension to obtain a single few-layer MXene nanosheet sol solution with the concentration of 0.5-5 mg/mL, wherein the single few-layer MXene nanosheet sol solution is defined as a sol solution B;

3) preparing a sol solution A and a sol solution B on a vacuum filtration device in a cross filtration manner to obtain a mixed film C, wherein the mixed film C is of a sandwich structure, the number of cross filtration layers is limited to a singular layer of at least three layers, the middle layer is the sol solution A or a mixed solution of the sol solution A and the sol solution B, and the mass ratio of the sol solution A to the sol solution B is defined as A: b is 1: (0-0.5), the outermost layer is sol liquid B, and the mass of the graphene oxide or MXene active substances in each filtering layer is limited to 3-15 mg;

4) and drying the mixed film C, and then carrying out low-temperature annealing reduction to obtain the reduced graphene oxide/MXene porous flexible membrane electrode.

2. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein in step 1), graphite powder is used as a raw material, concentrated sulfuric acid, potassium permanganate and H₂O₂、KNO₃Or NaNO₃And preparing graphene oxide by adopting a modified Hummers method as an auxiliary material, and freeze-drying to obtain graphene oxide powder for storage.

3. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 2, wherein the particle size of the graphite powder is 200-2000 mesh.

4. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein the conditions of the low temperature ultrasound in step 1) are as follows: the temperature is 5-15 ℃, the frequency is 40KHz, and the time is 40-90 min; the centrifugation conditions were: 3000-5000 rpm for 20-45 min.

5. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein Ti in step 2) is Ti₃AlC₂The ceramic material is prepared by mixing Ti powder, TiC powder and Al powder according to the mass ratio of 1:2 (1.1-1.2) and calcining at 1350-1450 ℃ for 2h in an inert atmosphere, wherein Ti is₃AlC₂The ceramic material is ground and sieved, the grain size is less than 400 meshes, and the etching agent is HF acid or a mixed solution of HCl and LiF.

6. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein the conditions of the low temperature ultrasound in step 2) are as follows: 5-15 ℃, 40-90 min at the frequency of 40KHz, and the centrifugation conditions are as follows: 3000-4000 rpm for 20-45 min.

7. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein the mixed film C in step 4) is placed in an atmosphere tube furnace, and annealing reduction is performed at 200-500 ℃ for 1-3 h under the condition of inert atmosphere.

8. The method for preparing a reduced graphene oxide/MXene porous flexible membrane electrode according to claim 1, wherein the mixed membrane C in step 4) is dried at room temperature, freeze-dried at-40 ℃ to-20 ℃ or vacuum-dried at 35-40 ℃ for 10-15 h.

9. The reduced graphene oxide/MXene porous flexible membrane electrode is characterized by being prepared by the preparation method of the reduced graphene oxide/MXene porous flexible membrane electrode as claimed in any one of claims 1 to 8, and is of a sandwich structure, the number of layers is at least three, the middle layer is a reduced graphene oxide layer, or the reduced graphene oxide layer and the MXene layer, and the outermost layer is the MXene layer.

10. Use of the reduced graphene oxide/MXene porous flexible membrane electrode of claim 9 as an electrode material for flexible electronic energy storage devices and wearable electronic energy storage devices.

Technical Field

The invention belongs to the field of preparation of flexible energy storage materials, and particularly relates to a reduced graphene oxide/MXene porous flexible membrane electrode and a preparation method and application thereof.

Background

In the modern society, along with the development and progress of science and technology, the flexible wearable electronic device, the foldable display, the foldable mobile phone and the like have emerged, so that the requirements on the flexible energy storage device with high energy density, long cycle efficiency and rapid charge and discharge rate are urgent, and further, new requirements on the development of corresponding flexible electrodes are provided.

With Ti₃C₂Representative MXenes series materials are obtained by etching a layer of element a from MAX, where element a represents a group IIIA or IVA element (a ═ Al, Ga, In, Ti, Si, Ge, Sn, Pb). MAX phase molecular expression is M_n+1AX_nThe corresponding MXenes molecular expression is M_n+1X_n(n-1, 2 or 3). With Ti₃C₂The represented MXenes series materials have good metal conductivity and hydrophilicity, and have application reports in the fields of transparent photoelectric materials, electromagnetic absorption and shielding materials, biomedicine, electrocatalytic materials, energy storage materials and the like at present. However, as with other two-dimensional materials, MXenes as a membrane electrode material cannot overcome the self-stacking phenomenon of the material, and it is a common technical means to stably enhance the performance of the MXenes-based material by using the synergistic effect of two-phase materials through compounding with other materials.

The graphene oxide serving as a two-dimensional sheet material has a larger theoretical specific surface area (theoretical value: 2620 m)² g^-1) And good conductivity, graphene oxide with Ti₃C₂The compounding of the MXene material has a lot of research and exploration. However, graphene oxide film formation also faces severe self-stacking phenomenon, and film formation once after directly mixing two materials may not be the best choice. The synthesized graphene oxide/MXene three-dimensional aerogel or hydrogel can enlarge the specific surface area and the active sites of the material, but the three-dimensional material form is not more than that of a two-dimensional film, and the application range of the composite material in the field of flexible energy storage is narrowed.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a reduced graphene oxide/MXene porous flexible membrane electrode and a preparation method and application thereof, the preparation method is simple in process, good in repeatability, wide in raw material source, low in price, low in toxicity of byproducts and easy to treat, so that the porous flexible membrane electrode has excellent economic value and is suitable for large-scale commercial transformation application, the prepared porous flexible membrane electrode is good in flexibility, good in electrochemical performance and excellent in cycle performance, and has wide and huge application potential as an electrode material of flexible electronic energy storage equipment and wearable electronic energy storage equipment.

In order to achieve the above purpose, the invention provides a preparation method of a reduced graphene oxide/MXene porous flexible membrane electrode, which comprises the following steps:

1) adding graphene oxide powder into ultrapure water for low-temperature ultrasonic treatment, centrifuging and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution with the concentration of 0.5-5 mg/mL, and defining the sol solution as sol solution A;

2) etching Ti by liquid phase etching using an etchant₃AlC₂Collecting a ceramic material to obtain a multilayer MXene nanosheet solution, carrying out low-temperature ultrasonic treatment on the multilayer MXene nanosheet solution in an inert atmosphere, and centrifugally collecting an upper-layer suspension to obtain a single few-layer MXene nanosheet sol solution with the concentration of 0.5-5 mg/mL, wherein the single few-layer MXene nanosheet sol solution is defined as a sol solution B;

3) preparing a sol solution A and a sol solution B on a vacuum filtration device in a cross filtration manner to obtain a mixed film C, wherein the mixed film C is of a sandwich structure, the number of cross filtration layers is limited to a singular layer of at least three layers, the middle layer is the sol solution A or a mixed solution of the sol solution A and the sol solution B, and the mass ratio of the sol solution A to the sol solution B is defined as A: b is 1: (0-0.5), the outermost layer is sol liquid B, and the mass of the graphene oxide or MXene active substances in each filtering layer is limited to 3-15 mg;

4) and drying the mixed film C, and then carrying out low-temperature annealing reduction to obtain the reduced graphene oxide/MXene porous flexible membrane electrode.

Preferably, in the step 1), graphite powder is used as a raw material, and concentrated sulfuric acid, potassium permanganate and H are used₂O₂、KNO₃Or NaNO₃And preparing graphene oxide by adopting a modified Hummers method as an auxiliary material, and freeze-drying to obtain graphene oxide powder for storage.

Preferably, the particle size of the graphite powder is 200-2000 meshes.

Preferably, the conditions of the low-temperature ultrasound in the step 1) are as follows: the temperature is 5-15 ℃, the frequency is 40KHz, and the time is 40-90 min; the centrifugation conditions were: 3000-5000 rpm for 20-45 min.

Preferably, it is characterized in that Ti in the step 2)₃AlC₂The ceramic material is prepared by mixing Ti powder, TiC powder and Al powder according to the mass ratio of 1:2 (1.1-1.2) and calcining at 1350-1450 ℃ for 2h in an inert atmosphere, wherein Ti is₃AlC₂The ceramic material is ground and sieved, the grain size is less than 400 meshes, and the etching agent is HF acid or a mixed solution of HCl and LiF.

Preferably, the low-temperature ultrasound in the step 2) is performed under the following conditions: 5-15 ℃, 40-90 min at the frequency of 40KHz, and the centrifugation conditions are as follows: 3000-4000 rpm for 20-45 min.

Preferably, the mixed film C in the step 4) is placed in an atmosphere tube furnace, and annealing reduction is carried out at the temperature of 200-500 ℃ for 1-3 h under the condition of inert atmosphere.

Preferably, the drying of the mixed film C in the step 4) adopts drying at room temperature, freeze drying at-40 to-20 ℃ or vacuum drying at 35 to 40 ℃, and the drying time is 10 to 15 hours.

The invention also provides a reduced graphene oxide/MXene porous flexible membrane electrode which is prepared by the preparation method of the reduced graphene oxide/MXene porous flexible membrane electrode and has a sandwich structure, the number of layers is at least three single layers, the middle layer is a reduced graphene oxide layer or a reduced graphene oxide + MXene layer, and the outermost layer is an MXene layer.

The invention also provides application of the reduced graphene oxide/MXene porous flexible membrane electrode as an electrode material of flexible electronic energy storage equipment and wearable electronic energy storage equipment.

Compared with the prior art, the preparation method disclosed by the invention has the advantages that the graphene oxide and MXene are subjected to layered suction filtration to form the multilayer mixed film by using a cross suction filtration process means, the graphene oxide is reduced by using a low-temperature annealing means, and the pores are formed by using the escaping gas in the reduction stage, so that the two-dimensional material form is kept, the ion embedding and extracting channel of the electrode material is increased, and the self-stacking phenomenon of the material is inhibited. The porous morphology also increases the mechanical flexibility of the composite membrane. Therefore, the method has the advantages of simple process route, good repeatability, no organic additive, wide raw material source, low price, low toxicity of by-products, easy harmless treatment, good economic and environmental effects and contribution to large-scale industrial application. The prepared porous flexible membrane electrode material has good flexibility, good electrochemical performance and excellent cycle performance, and has wide and huge application potential as an electrode material of flexible electronic energy storage equipment and wearable electronic energy storage equipment.

Drawings

FIG. 1 is an optical photograph of a reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of the present invention;

fig. 2 is a scanning electron microscope image of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of the present invention;

fig. 3 is a constant current charge and discharge performance diagram of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in embodiment 1 of the present invention;

fig. 4 is a graph of the cycle performance and coulombic efficiency of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of the present invention.

Detailed Description

The present invention will be further explained with reference to the drawings and specific examples in the specification, and it should be understood that the examples described are only a part of the examples of the present application, and not all examples. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The invention provides a preparation method of a reduced graphene oxide/MXene porous flexible membrane electrode, which comprises the following steps:

1) adding ultrapure water into graphene oxide powder obtained by freeze drying to prepare a solution with a certain concentration, performing low-temperature ultrasound, and centrifugally collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution, which is defined as sol solution A;

2) carrying out low-temperature ultrasonic treatment on the multilayer MXene nanosheet solution collected after etching under the condition of introducing inert gas, and centrifugally collecting the upper-layer suspension to obtain single few-layer MXene nanosheet sol solution, wherein the single few-layer MXene nanosheet sol solution is defined as sol solution B;

3) preparing a material A and material B mixed film C by the sol solution A and the sol solution B prepared in the above way on a vacuum filtration device in a cross filtration mode;

4) and (3) drying the film C, placing the film C in an atmosphere tube furnace, setting the temperature range of 200-500 ℃ and the time range of 1-3 h under the condition of introducing inert atmosphere, and annealing and reducing the film to obtain a composite film D, namely the reduced graphene oxide/MXene porous flexible film electrode.

Specifically, the graphene oxide powder in the step 1) is prepared by a modified Hummers method, graphite powder is used as a raw material, and concentrated sulfuric acid, potassium permanganate and H are added₂O₂、KNO₃Or NaNO₃Preparing graphene oxide as an auxiliary material, and freeze-drying to obtain powder for storage. Wherein the particle size of the graphite powder is 200-2000 meshes, and the auxiliary material is an analytical reagent.

Specifically, the low-temperature ultrasonic condition for preparing the single-few-layer graphene oxide nanosheet sol solution A in the step 1) is 5-15 ℃, the frequency is 40KHz and 40-90 min, and the centrifugal condition is 3000-5000 rpm and 20-45 min. The concentration of the sol solution is limited to 0.5-5 mg/mL.

Specifically, in the step 2), the multilayer MXene nanosheet solution is etched by a liquid phase etching method to form Ti₃AlC₂And (3) preparing a ceramic material. Wherein Ti₃AlC₂The ceramic material is prepared from Ti powder, TiC powder and Al powder according to the mass ratio of 1:2 (1.1-1.2) under the inert atmosphere and the calcining conditions of 1350-1450 ℃ for 2 hours, the ceramic material is ground and sieved to have the particle size smaller than 400 meshes, and the etching agent can be HF acid or a mixed solution of HCl and LiF.

Specifically, the low-temperature ultrasonic condition for preparing the single-few-layer MXene nanosheet sol solution B in the step 2) is 5-15 ℃, the frequency is 40KHz and 40-90 min, meanwhile, inert gas is blown into the system, and the centrifugal condition is 3000-4000 rpm and 20-45 min. The concentration of the sol solution is limited to 0.5-5 mg/mL.

Specifically, in the step 3), a 0.22 micron pore size water system filter membrane is used for vacuum filtration. The prepared mixed film C is limited to be a sandwich structure, the number of the cross suction filtration layers is limited to be a single layer of at least three layers, the middle layer can be sol solution A or a mixed solution of the sol solution A and the sol solution B, wherein the mixed solution mass ratio of the sol solution A to the sol solution B is limited to be A: b is 1: (0-0.5), the outermost layer component is limited to sol solution B. The mass of the graphene oxide or MXene active substance in each suction filtration layer is limited within the range of 3-15 mg. It is understood that the outermost layer means the outermost two layers, and the intermediate layer means the remaining layers except for the outermost two layers.

Specifically, the drying treatment means of the mixed film C in the step 4) can be drying at room temperature, freezing and drying at-40 to-20 ℃ or drying at vacuum 35 to 40 ℃ for 10 to 15 hours. The inert gas introduced in the above step is limited to argon.

The invention also provides a reduced graphene oxide/MXene porous flexible membrane electrode which is prepared by the preparation method and has a sandwich structure, the number of layers is at least three, the middle layer is a reduced graphene oxide layer or a reduced graphene oxide + MXene layer, and the outermost layer is an MXene layer, the surface of the membrane electrode has obvious porous morphology, and the composite membrane can be bent by 180 degrees, has good mechanical flexibility, good electrochemical performance and excellent cycle performance, and has wide and huge application potential as an electrode material of flexible and wearable electronic energy storage equipment.

The method has the advantages of simple and clear process flow, strong process design, controllable factors, stable process flow, good product repeatability and low requirement on equipment. The invention has the advantages of wide raw material source, low cost, easy obtainment, no need of any organic additive, and easy harmless treatment of waste water and waste materials generated in the process. Has the advantages of environmental protection, economy and environmental protection. According to the reduced graphene oxide/MXene prepared by the method, the process step of annealing in the atmosphere furnace is utilized, on one hand, the reduction of the graphene oxide is realized without adding additional chemical additives, on the other hand, the phenomenon that hydrothermal steam and other oxygen-containing gases are released in the reduction stage of the graphene oxide is utilized to promote the pore formation of the film, the self-stacking phenomenon of a two-dimensional material is inhibited, more channels for embedding and releasing ions are manufactured, and the electrochemical performance of the film electrode is facilitated. The composite film of the invention can be combined in a diversified way, and the prepared composite film can be independently supported, has excellent mechanical flexibility and is easy for mass production and industrial application.

The present invention will be described in detail with reference to specific examples.

Example 1:

1) preparing the graphene oxide powder obtained by freeze drying into a solution with a certain concentration, carrying out ultrasonic treatment for 60min at a low temperature of 5 ℃, carrying out high-speed centrifugation for 30min at a rotating speed of 3500rpm, and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution A with a concentration of 2 mg/mL;

2) subjecting the multilayer MXene nanosheet solution collected after etching to ultrasonic treatment at a low temperature of 5 ℃ for 60min under the condition of introducing inert gas, performing high-speed centrifugal collection at a rotating speed of 3500rpm for 30min, and collecting the upper suspension to obtain a single-few-layer MXene nanosheet sol solution B with a concentration of 1.5 mg/mL;

3) sequentially pumping 10mg of MXene, 5mg of graphene oxide and 10mg of MXene in a cross pumping filtration mode by using a 0.22-micron-aperture water-based filter membrane to prepare a sandwich-structure mixed film C taking the graphene oxide layer as a sandwich;

4) and drying the film C at room temperature overnight, transferring the film C into an atmosphere tube furnace, setting the temperature of 250 ℃ for reaction for 2 hours under the condition of argon atmosphere, and annealing and reducing the film C to obtain a composite film D, namely the reduced graphene oxide/MXene porous flexible film electrode.

Referring to an optical photograph of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of fig. 1, it can be seen from a top view that the surface of the composite membrane presents an obvious porous morphology, and the composite membrane can be bent by 180 degrees, which proves that the composite membrane has good flexibility. After a series of electrochemical performance tests, the prepared electrode plate still has good bending performance after being taken off, and the composite membrane prepared by the invention has excellent mechanical flexibility as a flexible membrane electrode.

Referring to a scanning electron microscope image of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of fig. 2, it is observed from (a) that the surface of the composite membrane exhibits a porous wrinkle morphology at a low magnification, and from (b) that the composite membrane is formed by stacking parallel two-dimensional nano-layer sheets, and because a membrane preparation method of cross-filtration is adopted, the inter-layer sheet distance is successfully expanded, the inter-layer sheet stacking is effectively prevented, and a channel more favorable for ion insertion and extraction is formed.

Referring to the constant current charge and discharge performance diagram of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of FIG. 3, wherein the constant current charge and discharge performance diagram is 1A g^-1The specific mass capacity of the composite membrane electrode prepared in example 1 reaches 322F g at the current density^-1。

Referring to the cycle performance diagram of the reduced graphene oxide/MXene porous flexible membrane electrode prepared in example 1 of FIG. 4, it can be seen that the cycle performance is 10A g^-1After 32000 charge-discharge cycles under the current density, the capacity retention rate and the discharge coulombic efficiency of the composite membrane electrode are about 100 percent, which reflects that the prepared composite membrane electrode has excellent cycle stability and is an ideal electrode of a flexible electronic device with longer service life.

Example 2:

1) preparing the graphene oxide powder obtained by freeze drying into a solution with a certain concentration, performing ultrasonic treatment at a low temperature of 10 ℃ for 45min, performing high-speed centrifugation at a rotating speed of 4000rpm for 25min, and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution A with a concentration of 2 mg/mL;

2) subjecting the multilayer MXene nanosheet solution collected after etching to ultrasonic treatment at the low temperature of 10 ℃ for 45min under the condition of introducing inert gas, performing high-speed centrifugal collection at the rotating speed of 4000rpm for 25min, and collecting the upper suspension to obtain a single few-layer MXene nanosheet sol solution B with the concentration of 2 mg/mL;

3) and (3) sequentially pumping 4mg of MXene and 6mg of A in total amount by using a 0.22-micron-aperture water-based filter membrane to prepare the sol solution A and the sol solution B in a cross-pumping filtration mode: b is 1: repeatedly filtering the mixed solution with the mass ratio of 0.5 for five layers to prepare a mixed film C with a sandwich structure;

4) and (3) freeze-drying the film C at-40 ℃ for 15h, transferring the film C into an atmosphere tube furnace, reacting at 200 ℃ for 3h under the argon atmosphere, and annealing and reducing the film to obtain a composite film D.

Example 3:

1) preparing the graphene oxide powder obtained by freeze drying into a solution with a certain concentration, carrying out ultrasonic treatment for 60min at a low temperature of 15 ℃, carrying out high-speed centrifugation for 20min at a rotating speed of 3000rpm, and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution A with a concentration of 1.5 mg/mL;

2) subjecting the multilayer MXene nanosheet solution collected after etching to ultrasonic treatment at the low temperature of 15 ℃ for 60min under the condition of introducing inert gas, performing high-speed centrifugal collection at the rotating speed of 3000rpm for 20min, and collecting the upper suspension to obtain a single few-layer MXene nanosheet sol solution B with the concentration of 2 mg/mL;

3) sequentially pumping 4mg of MXene and 3mg of graphene oxide by using a 0.22-micron-aperture water-based filter membrane, and repeatedly pumping seven layers to prepare a sandwich-structure mixed film C taking the graphene oxide layer as a sandwich;

4) and (3) drying the film C in vacuum at the temperature of 40 ℃ for 12h, transferring the film C to an atmosphere tube furnace, reacting for 1.5h at the temperature of 300 ℃ under the condition of argon atmosphere, and annealing and reducing the film to obtain a composite film D.

Example 4:

1) preparing the graphene oxide powder obtained by freeze drying into a solution with a certain concentration, carrying out ultrasonic treatment for 60min at a low temperature of 10 ℃, carrying out high-speed centrifugation for 40min at a rotating speed of 5000rpm, and collecting an upper-layer suspension to obtain a single-few-layer graphene oxide nanosheet sol solution A with a concentration of 0.5 mg/mL;

2) subjecting the multilayer MXene nanosheet solution collected after etching to ultrasonic treatment at a low temperature of 10 ℃ for 60min under the condition of introducing inert gas, performing high-speed centrifugal collection at a rotating speed of 5000rpm for 40min, and collecting the upper suspension to obtain a single-few-layer MXene nanosheet sol solution B with a concentration of 0.5 mg/mL;

3) sequentially pumping 3mg of MXene and 3mg of graphene oxide by using a 0.22-micron-aperture water-based filter membrane, and repeatedly pumping nine layers of graphene oxide layers to prepare a sandwich-structure mixed film C taking the graphene oxide layers as a sandwich;

4) the film C was vacuum dried at 35 ℃ for 10h and transferred to an atmospheric tube furnace. And (3) reacting for 1h at 500 ℃ under the condition of argon atmosphere, and annealing and reducing the film to obtain a composite film D.

Example 5:

1) preparing graphene oxide powder obtained by freeze drying into a solution with a certain concentration, performing ultrasonic treatment at a low temperature of 5 ℃ for 60min, performing high-speed centrifugation at a rotating speed of 3000rpm for 45min, collecting an upper-layer suspension, and performing high-speed centrifugation on the upper-layer suspension at a rotating speed of 8000rpm for 30min for concentration to obtain a single-few-layer graphene oxide nanosheet sol solution A with a concentration of 5 mg/mL;

2) subjecting the multilayer MXene nanosheet solution collected after etching to ultrasonic treatment at a low temperature of 5 ℃ for 60min under the condition of introducing inert gas, performing high-speed centrifugal collection at a rotating speed of 3000rpm for 45min, collecting the upper suspension, and continuously performing high-speed centrifugal collection on the upper suspension at a rotating speed of 8000rpm for 30min for concentration to obtain a single few-layer MXene nanosheet sol solution B with a concentration of 5 mg/mL;

3) sequentially pumping 15mg of MXene and 15mg of graphene oxide by using a 0.22-micron-aperture water-based filter membrane, and repeatedly pumping and filtering the three layers to prepare a sandwich-structure mixed film C taking the graphene oxide layer as a sandwich;

4) film C was dried at room temperature for 15h and transferred to an atmospheric tube furnace. And (3) reacting for 3h at 200 ℃ under the condition of argon atmosphere, and annealing and reducing the film to obtain a composite film D.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.