Niobium nitride reduced graphene oxide composite film, method and flexible supercapacitor

Abstract

The invention provides a niobium nitride reduced graphene oxide composite film and method and a flexible supercapacitor, and the method comprises the steps: taking Nb2AlC powder as a precursor, employing a NaF-NH4F-HF composite etching system and a segmented temperature control etching technology, and preparing a Nb2C2Tx MXene suspension with high purity and a few-layer structure; the Nb2C2Tx / rGO composite membrane is prepared by using Nb2C2Tx as a substrate, reducing GO by using hydrazine hydrate to prepare rGO suspension, compounding Nb2C2Tx and rGO by using a spin coating-hot pressing-low temperature annealing process, and forming the Nb2C2Tx / rGO composite membrane with tight interface combination by combining with hydrophilic modification treatment of the substrate. By regulating and controlling the etching temperature, the rGO compounding ratio and the hot pressing parameters, the conductivity, the mechanical property and the cycling stability of the composite film are optimized, and a new path is provided for a high-performance flexible supercapacitor electrode material.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology, specifically relating to a niobium nitride-reduced graphene oxide composite film and method, as well as a flexible supercapacitor. Background Technology

[0002] With the rapid development of flexible electronic devices (such as wearable sensors and flexible displays), higher requirements are being placed on the flexibility, high power density, and long cycle life of supporting energy storage devices. Supercapacitors, due to their fast charging and discharging speeds and good cycle stability, have become a core candidate device in the field of flexible energy storage, and their performance largely depends on the electrode materials. While traditional flexible electrode materials (such as carbon nanotubes and graphene) possess a certain degree of flexibility, they suffer from the problem of balancing conductivity and mechanical strength. Carbon nanotube films are prone to aggregation, leading to increased resistance, and graphene films have weak interlayer bonding and are prone to cracking, failing to meet the high comprehensive performance requirements of flexible supercapacitors. Therefore, the development of new high-performance flexible electrode materials is urgently needed.

[0003] MXene, as a novel type of two-dimensional layered carbide material, exhibits high electrical conductivity (resistivity as low as 10⁻⁶). -6 Nb-based MXenes (such as Nb2C2T) exhibit significant advantages in the field of flexible electrodes due to their high Ω•cm content, excellent mechanical flexibility, and abundant surface functional groups. x Due to its high electron transport rate and good electrochemical stability, Nb₂C₂T has become a research hotspot. However, existing Nb₂C₂T... x The preparation process has significant defects: it often employs a single LiF-HF etching system, Li + For F - Limited activity regulation capability can easily lead to incomplete removal of the Al layer in the Nb2AlC precursor (residual impurities affect conductivity), or excessive etching can damage Nb2C2T. x The layered structure (leading to decreased mechanical properties); moreover, the etched products are mostly multi-layered aggregates, requiring complex peeling processes to obtain fewer layers of Nb2C2T. x This increases preparation costs and process complexity.

[0004] To improve the mechanical properties of MXene film, it is a mainstream technology to composite MXene with other carbon materials (such as reduced graphene oxide rGO), but there are key problems in the existing composite process: first, the interface bonding is weak, MXene and rGO are only combined by van der Waals force, lacking of chemical bonding sites, interlayer slip easily occurs during bending, resulting in poor cycle stability of the composite film, the surface resistance change rate often exceeds 30% after 1000 times bending); second, the film forming process has low compatibility, the existing composite film is mostly prepared by vacuum filtration method, which is difficult to precisely control the film thickness and uniformity, and cannot adapt to the surface characteristics of flexible substrates such as sapphire and quartz glass, limiting its practical application in flexible supercapacitors, and it is urgent to break through the dual technical bottlenecks of preparation process and composite interface regulation. SUMMARY

[0005] In order to solve the problems in the prior art, the present application provides a niobium nitride reduced graphene oxide composite film and method and a flexible supercapacitor, using Nb2AlC powder as a precursor, using a NaF-NH4F-HF composite etching system and a segmented temperature control etching process to prepare high-purity, few-layer structure Nb2C2T x MXene suspension; at the same time, rGO suspension is prepared by reducing GO with hydrazine hydrate, and Nb2C2T x / rGO composite film is formed by combining with the hydrophilic modification treatment of the substrate, and the interface bonding of the Nb2C2T x / rGO composite film is formed by combining with the hydrophilic modification treatment of the substrate, and the interface bonding of the Nb2C2T

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a preparation method of a niobium nitride reduced graphene oxide composite film, the specific steps are as follows: Nb2AlC powder is added into a NaF-NH4F-HF composite etching solution in batches, and black precipitate is collected, and after purification, the black precipitate is dispersed, ultrasonic treated, centrifuged, and the upper clear liquid is taken as Nb2C2T x MXene suspension; Hydrazine hydrate and GO suspension are mixed and reacted, then diluted and ultrasonic treated to obtain rGO suspension; Nb2C2T x MXene suspension is spin-coated on the pretreated hydrophilic flexible substrate, dried to obtain Nb2C2T x bottom film; rGO suspension is spin-coated on the Nb2C2T x bottom film, dried to obtain rGO cover layer; Nb2C2T xThe bottom layer film and the rGO cover layer are hot-pressed, annealed and cooled to obtain the Nb2C2T

[0007] Further, the Nb2C2T x The preparation method of the MXene suspension is as follows: The water bath temperature is maintained at 38-42 DEG C, and the Nb2AlC powder is slowly added into the NaF-NH4F-HF composite etching solution in batches. After the first addition, it is statically placed for 4-6 min, and after each subsequent addition, the material is dispersed by stirring for 20-40 s. After the Nb2AlC powder is completely added, the rotation speed is adjusted to 600-700 r / min, and the reaction is continued for 15-17 h, and then the temperature is raised to 42-52 DEG C and the reaction is continued for 7-9 h to obtain a black turbid etching solution. The black turbid etching solution is centrifuged, and the black precipitate is collected, purified, redispersed, ultrasonically treated, centrifuged, and the upper layer of the transparent black dispersion liquid is taken to obtain a Nb2C2T x MXene suspension; The preparation method of the rGO suspension is as follows: Hydrazine hydrate and the GO suspension are mixed and reacted at 55-65 DEG C for 1.5-2.5 h, the reaction solution is diluted and ultrasonically treated to obtain the rGO suspension.

[0008] Further, the Nb2C2T x MXene suspension is spin-coated on the pretreated hydrophilic flexible substrate. x In the step of the bottom layer film: The Nb2C2T x The MXene suspension is dropped onto the center of the pretreated hydrophilic flexible substrate, the rotation speed is adjusted to 2500-3500 r / min and maintained for 25-35 s, the drying temperature is 75-85 DEG C, the vacuum degree is controlled at -0.10 to -0.08 MPa, and the drying time is 1.5-2.5 h to obtain the Nb2C2T x bottom layer film.

[0009] Further, the Nb2C2T x In the step of spin-coating the rGO suspension on the bottom layer film and drying to obtain the rGO cover layer: The Nb2C2T xThe rGO suspension is dripped on the bottom layer film, the rotation speed is 400 r / min to 600 r / min in the low-speed pre-rotation stage, and the duration is 8 s to 12 s; then the rotation speed is adjusted to 2500 r / min to 3500 r / min, and the duration is maintained for 25 s to 35 s, the drying temperature is 75 DEG C to 85 DEG C, the vacuum degree is controlled to be -0.10 MPa to -0.08 MPa, and the drying time is 1.5 h to 2.5 h, so that the rGO cover layer is obtained.

[0010] Further, the Nb2C2T x The use amount of the MXene suspension and the rGO suspension is the same and is related to the size of the hydrophilic flexible substrate.

[0011] Further, the hot pressing is as follows: the hot pressing temperature is 110 DEG C to 130 DEG C, the pressure is 0.4 MPa to 0.6 MPa, and the hot pressing time is 25 min to 35 min.

[0012] Further, the annealing is as follows: in a protective atmosphere, the heating rate is set to be 4 DEG C / min to 6 DEG C / min, the temperature is raised to 170 DEG C to 190 DEG C, and the annealing time is 5 h to 7 h.

[0013] The application further provides a Nb2C2T reduced graphene oxide composite film prepared by the preparation method, and the surface resistance of the Nb2C2T reduced graphene oxide composite film is 7.8 Ω / sq to 15.3 Ω / sq, the breaking strength is 32.5 MPa to 45.6 MPa, and the light transmittance is 75.6% to 85.2%.

[0014] The application further provides a flexible supercapacitor, in which the Nb2C2T reduced graphene oxide composite film is attached to the surface of a positive electrode current collector as a positive electrode active layer of the flexible supercapacitor.

[0015] Further, the cycle stability of the flexible supercapacitor is 11.2% to 25.7%.

[0016] Compared with the prior art, the application has at least the following beneficial effects: The application provides a preparation method of a Nb2C2T reduced graphene oxide composite film, in which a NaF-NH4F-HF composite etching system is used in combination with a segmented temperature control process to prepare the Nb2C2T x The MXene suspension, Na + The F - The reaction kinetics with the Al layer is accelerated, and the etching reaction rate is accelerated; the NH4 + The local etching intensity can be buffered to avoid excessive or uneven etching. The segmented temperature control process can precisely control the etching process, completely remove the Al layer, and form uniform carbon layer micropores, so that the prepared Nb2C2T xWith a high proportion of few-layer structures and complete conductive pathways, Nb2C2T effectively solves the problem of balancing efficiency and structure in traditional etching methods, laying a solid foundation for obtaining high-performance composite films. Through hot pressing, Nb2C2T... x It forms an intercalation-bonding relationship with the rGO interface. The edge groups of rGO interact with Nb2C2T. x Surface functional groups undergo chemical bonding, and rGO sheets are inserted into Nb2C2T. x Interlayer structure. This structure not only enhances the mechanical strength of the composite film, making it less prone to cracking when bent and ensuring its flexibility to meet the bending and folding requirements of flexible devices; at the same time, the stable interface structure ensures the stability of the conductive network, effectively improving the cycle performance of the composite film and extending its service life as an electrode material for flexible supercapacitors.

[0017] Using the aforementioned composite film as the positive electrode active layer of a flexible supercapacitor enhances its mechanical strength, preventing bending and cracking, ensuring the stability of the conductive network, and significantly improving cycle performance. By adjusting the etching temperature, rGO composite ratio, and hot-pressing parameters, the conductivity, mechanical properties, and cycle stability of the composite film can be further optimized, meeting the requirements of high-performance flexible supercapacitors for electrode materials. The entire fabrication process does not require high temperature and high pressure; the spin-coating parameters and rGO ratio can be flexibly adjusted; the substrate pretreatment is simple and compatible with various substrates, well adapting to the bending and folding requirements of flexible devices. The NaF and NH4F used are conventional, low-cost raw materials; residual ions from etching can be removed by centrifugation; hydrazine hydrate reduces GO efficiently without complex post-processing; the process is simple, environmentally friendly, and easily scaled up through modifications to existing production lines, demonstrating high practical application value. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] This invention provides a niobium nitride-reduced graphene oxide composite film, the preparation method of which is as follows: 1. Base fixation: Select a hydrophilic sapphire substrate and securely fix it on the vacuum suction cup of the spin coater to ensure that the substrate surface is flat and free of defects, providing uniform support for subsequent coatings.

[0020] 2. Spin coating of the underlying MXene suspension: Use a pipette to accurately pipette 1.0 mL to 2.0 mL of Nb2C2T. xThe MXene suspension was slowly dripped onto the center of the sapphire substrate to avoid air bubbles or droplet splashing. The spin coater parameters were set as follows: during the low-speed pre-spinning stage, the speed was 400 r / min to 600 r / min for 8 to 12 seconds to allow the suspension to spread initially; then, during the high-speed spin coating stage, the speed was adjusted to 2500 r / min to 3500 r / min and held for 25 to 35 seconds to form a uniform and dense underlying MXene film.

[0021] 3. Drying of the bottom membrane: The spin-coated substrate is transferred to a drying device, and the drying temperature is set to 75℃~85℃, the vacuum degree is controlled within the range of -0.10MPa~-0.08MPa, and the drying time is 1.5 h~2.5 h to completely remove the solvent and obtain a structurally stable underlying MXene film with a thickness of 5μm~8μm.

[0022] 4. Spin coating of rGO suspension: On the dried MXene film, use a pipette to draw 1.0 mL to 2.0 mL of rGO (reduced graphene oxide) suspension again, and spin coat it using the same parameters as the base layer: low speed 400 r / min to 600 r / min for 8 to 12 seconds, high speed 2500 r / min to 3500 r / min for 25 to 35 seconds to form an rGO coating layer with a thickness of 2 μm to 4 μm.

[0023] 5. Drying the rGO layer: The substrate coated with rGO suspension was placed under the same drying conditions (75℃~85℃, -0.10MPa~-0.08MPa) and dried for 1.5h~2.5h to ensure that the rGO layer was tightly bonded to the underlying MXene membrane and that there was no residual solvent.

[0024] 6. Hot-pressing composite: The bilayer film was placed in a hot press, with the hot pressing temperature set to 110℃~130℃, the pressure to 0.4MPa~0.6MPa, and the hot pressing time to 25min~35min. Through hot pressing, the interfacial bonding between MXene and rGO was further enhanced, forming a well-composite NR composite film precursor; Nb2C2T was further processed through hot pressing. x An intercalation-bonding effect is formed at the rGO interface. The edge groups of rGO interact with Nb2C2T. x The surface functional groups are chemically bonded and the layers are inserted between them, which not only improves the mechanical strength of the composite film to avoid bending and cracking, but also ensures the stability of the conductive network and improves the cycle performance.

[0025] 7. Annealing treatment: The hot-pressed composite membrane precursor was placed in a tube furnace and annealed under an argon protective atmosphere. The heating rate was set to 4℃ / min~6℃ / min, the temperature was raised to 170℃~190℃, and the annealing time was 5h~7h. The annealing process helps to eliminate internal stress, optimize the crystal structure, and improve the overall performance of the composite membrane.

[0026] 8. Cooling and Finished Product Acquisition: After annealing, turn off the heating power and allow the composite film to cool naturally to room temperature in the tube furnace. Then remove it to obtain high-performance Nb2C2T. x / rGO composite membrane, the total thickness of the composite membrane is 7μm ~12μm.

[0027] 9. Fabrication of flexible symmetrical supercapacitors The composite membrane was peeled from the sapphire substrate and transferred to a flexible polyimide (PI) substrate, then connected to a copper foil current collector. Combined with a gel electrolyte and a cellulose separator, it was assembled into a flexible symmetrical supercapacitor. This device exhibits stability with a capacity retention of ≥90% after 10,000 cycles and shows no significant performance degradation within a bending angle range of 0° to 180°, making it suitable for wearable electronic devices.

[0028] In step 2, Nb2C2T x The MXene suspension was prepared as follows: Step 1: Preparation of composite etching solution Weigh 2.0-2.2 g of NaF and 0.8-1.0 g of NH4F and mix thoroughly. Slowly add the mixture to 45-55 mL of HF solution diluted to 6.5-7.5 mol / L and stir for 8-12 min. Transfer the mixture to a polytetrafluoroethylene reactor and place it in a constant temperature water bath with a stirrer set to 350-450 r / min and 40-45℃. Stir for 20-30 min, observing the dissolution state every 5 min to form a homogeneous and stable NaF-NH4F-HF composite etching solution.

[0029] Step 2: Nb2AlC etching reaction Maintain a water bath temperature of 38℃~42℃. Weigh 1.4g~1.6g of Nb2AlC powder and slowly add it to the etching solution in 7~9 portions (0.15~0.20g each time, with an interval of 1~3min). After the first addition, let it stand for 4min~6min to start the reaction (the solution should be slightly turbid as an indicator). After each subsequent addition, stir for 20s~40s to disperse the material. After all the material has been added, adjust the rotation speed to 600r / min~700r / min and react at 42℃ for 15h~17h. Then, raise the temperature to 42℃~52℃ and continue the reaction for 7h~9h to obtain a black, turbid etching solution.

[0030] Step 3: Nb2C2T xPurification and Dispersion Centrifuge the etching solution (4000-5000 rpm, 8-10 min), collect the black precipitate, wash with deionized water and repeat centrifugation (4500-5500 rpm, 8-12 min) until the supernatant pH ≥ 7.0. Add 40-50 mL of deionized water to the purified precipitate, sonicate (350-450 W, 12-18 min), then centrifuge (3500-4500 rpm, 1-2 h), and collect the upper transparent black dispersion to obtain Nb₂C₂T with a mass concentration of 12-18 mg / mL. x MXene suspension.

[0031] In the NaF-NH4F-HF composite etching system, Na + It can promote F - Reaction kinetics with Al layer, NH 4+ By buffering the intensity of localized etching and employing a segmented temperature-controlled process, the Al layer can be completely removed, forming uniform carbon layer micropores, thus preparing Nb2C2T. x With a high proportion of few-layer structures and complete conductive pathways, it solves the problem of the traditional etching process where efficiency and structure cannot be simultaneously achieved. In step 4, the GO suspension is prepared as follows: Take 45-55 mL of GO suspension with a concentration of 7-9 mg / mL, add 4-6 mL of 4%-6% hydrazine hydrate solution, and stir in a water bath at 55-65℃ for 1.5-2.5 h. After the reaction is complete, dilute with deionized water to a concentration of 2.5-3.5 mg / mL, transfer to an ultrasonic cleaner and sonicate at 450-550 W for 1-2 h to obtain a uniformly dispersed rGO suspension.

[0032] In steps 2 and 4, the amount of suspension used is closely related to the substrate size. Taking 1.5 mL of suspension for a 30 mm × 30 mm substrate as an example, this amount can form a sufficient initial liquid film to ensure that the film layer is uniform and there is no substrate exposure during high-speed spin coating. When the substrate size increases or decreases, the amount of suspension used needs to be adjusted proportionally. Specifically, for every ±10% change in substrate size, the amount of suspension used should be adjusted by ±8% to 12%.

[0033] Example 1 Nb2C2T x The preparation of the / rGO composite membrane involves the following steps: Step 1: Weigh 2.1g of sodium fluoride (NaF) and 0.9g of ammonium fluoride (NH4F) into a dry 50mL beaker and mix thoroughly. Slowly add the mixture to 50mL of diluted 7mol / L hydrofluoric acid (HF) while stirring with a glass rod for 10min. Transfer the mixture to a 100mL PTFE reactor, then place the reactor in a constant temperature water bath with a magnetic stirrer. Set the stirring speed to 400r / min and the water bath temperature to 42℃, and continue stirring for 25min. During this period, observe the dissolution status every 5min to ensure that NaF and NH4F are completely dissolved, forming a uniform and stable NaF-NH4F-HF composite etching solution without obvious particles.

[0034] Step 2: Maintain a stable water bath temperature of 42℃ (temperature difference ≤ ±1℃). Weigh 1.5g of Nb2AlC powder using an electronic analytical balance and slowly add it to the composite etching solution in 8 portions, approximately 0.1875g each time, with 2-minute intervals between additions. After the first addition, turn off the stirrer and let it stand for 5 minutes to initiate the etching reaction (a slight turbidity in the solution indicates the start of the reaction). From the second addition onwards, turn on the stirrer for 30 seconds after each addition to disperse the material and prevent localized overheating that could cause splashing. After all the material has been added, adjust the stirring speed to 650 rpm and continue stirring and reacting at a constant temperature of 42℃ for 16 hours. Then, raise the water bath temperature to 50℃ and continue stirring and reacting for another 8 hours. After the reaction is complete, a black, turbid etching reaction solution is obtained.

[0035] Step 3: Transfer the etching reaction solution to a 50mL centrifuge tube and place it in a high-speed centrifuge. Set the speed to 4500 rpm and the centrifugation time to 8 minutes. After centrifugation, a black precipitate will be visible at the bottom of the tube. Pour off the supernatant into a new centrifuge tube. Add 10mL of deionized water to the new centrifuge tube, shake well, and then set the speed to 5000 rpm and the centrifugation time to 10 minutes. After centrifugation, collect the black Nb2C2T precipitate from the bottom of the tube. x Coarse precipitate. Add 20 mL of deionized water to the coarse precipitate, vortex for 1 min, and centrifuge again (4500 r / min, 6 min). Pour off the supernatant. Repeat the water addition-vortexing-centrifugation operation. After each centrifugation, use a pH meter to check the pH value of the supernatant until pH ≥ 7.0, so as to completely remove residual fluoride ions and ammonium ions.

[0036] To purified Nb2C2T x Add 45 mL of deionized water to the precipitate, transfer it to a 100 mL beaker, place it in an ultrasonic cleaner, set the power to 400 W and the ultrasonic time to 15 min, and obtain a black suspension (not the final usable dispersion).

[0037] Transfer the suspension to centrifuge tubes and centrifuge at 4000 rpm for 1.5 h. After centrifugation, take the upper transparent black dispersion, which has a mass concentration of approximately 15 mg / mL.-1 Nb2C2T x MXene suspension.

[0038] Step 4: Preparation of rGO suspension Take 50 mL of 8 mg / mL GO suspension, add 5 mL of 5% hydrazine hydrate, stir in a 60℃ water bath for 2 h; dilute to 3 mg / mL, sonicate at 500 W for 1.5 h to obtain a homogeneous rGO suspension.

[0039] Step 5: Sapphire substrate pretreatment A 30mm × 30mm × 1.0mm sapphire substrate was sequentially ultrasonically cleaned with trichloroethylene, isopropanol, and deionized water for 20 minutes each, dried with nitrogen, and then treated with ultraviolet ozone for 40 minutes to ensure a surface water contact angle ≤ 6°. Sapphire (Al₂O₃) has high chemical inertness and will not react with Nb₂C₂T during spin coating, drying, hot pressing, and annealing at 180℃. x Even if rGO undergoes a chemical reaction, it will not release impurity ions to contaminate the film layer, ensuring the chemical purity of the composite film; and the surface roughness can be controlled below 0.5nm, which is much lower than that of glass or silicon wafers, and can accurately replicate the flatness of the substrate to the surface of the composite film, meeting the requirements of film layer consistency for subsequent device assembly.

[0040] Step Six: Nb2C2T x / rGO composite film preparation and annealing treatment The hydrophilic sapphire substrate was fixed on the spin coater suction cup, and 1.5 mL of Nb2C2T was pipetted into the substrate. x MXene suspension was dropped onto the center of the substrate, pre-spun at 500 rpm for 10 s, spin-coated at 3000 rpm for 30 s, and dried at 80℃ and -0.09 MPa for 2 h to obtain the bottom film. Then, 1.5 mL of rGO suspension was spin-coated, dried under the same conditions, and hot-pressed at 120℃ and 0.5 MPa for 30 min. Finally, the film was annealed in a tube furnace under an argon atmosphere, heated to 180℃ at 5℃ / min for 6 h, and cooled to obtain the composite film NR-30.

[0041] Example 2: Nb2C2T x / rGO composite film (NR-30, sapphire substrate, etched at 38℃→45℃) The preparation process was completely consistent with that of Example 1, except that the segmented etching temperature in step 2 was adjusted: the reaction was first carried out at a constant temperature of 38°C for 18 hours, and then the temperature was increased to 45°C and the reaction was continued for 6 hours. All other parameters remained unchanged. The final composite film was named NR-30 (38→45°C).

[0042] Example 3: Nb2C2T x / rGO composite film (NR-15, sapphire substrate, etched at 42℃→50℃) The preparation process was completely consistent with that of Example 1, except that the amount of rGO suspension in step six was adjusted: when spin-coating the upper layer of rGO suspension, the amount was changed from 1.5 mL to 0.8 mL (rGO mass percentage 15%), and all other parameters remained unchanged. The final composite membrane was named NR-15.

[0043] Example 4: Nb2C2T x / rGO composite film (NR-30, quartz glass substrate, etched at 42℃→50℃) The preparation process is completely consistent with that of Example 1, except that the substrate type in step five is replaced: the sapphire substrate is replaced with a quartz glass substrate with a size of 30mm×30mm×1.0mm. The substrate pretreatment process and other parameters remain unchanged. The final composite film is named NR-30 (quartz substrate).

[0044] Example 5: Pure Nb2C2T x Film (sapphire substrate, etched at 42℃→50℃) Compared with the preparation process in Example 1, step four (rGO suspension preparation) and step six (rGO spin coating and hot pressing) are omitted: only 1.5 mL of Nb2C2T is spin-coated onto the hydrophilic sapphire substrate. x The MXene suspension (with parameters unchanged in step six) was dried and then directly annealed, while all other parameters remained unchanged, ultimately yielding pure Nb₂C₂T. x The membrane was named N-pure.

[0045] Example 6: Nb2C2T x / rGO composite film (NR-30, sapphire substrate, 42℃ isothermal etching) The preparation process was completely consistent with that of Example 1, except that the etching method in step two was adjusted: the segmented temperature control was cancelled, and the reaction was carried out under constant temperature of 42°C for 24 hours. All other parameters remained unchanged, and the final composite film was named NR-30 (42°C constant temperature).

[0046] Comparative Example 1: Nb2C2T prepared by conventional single etchant x / rGO composite membrane Compared with the preparation process of Example 1, only the etching solution system in step one was changed: 2.5g LiF was used to replace NaF and NH4F, and the etching solution was a LiF-HF system (50mL of 7mol / L HF). The remaining steps (etching reaction, centrifugal purification, membrane preparation and annealing process) were the same as in Example 1. The final composite membrane was named Comparative Example 1 (LiF-HF).

[0047] Comparative Example 2: Nb2C2T composite without hot pressing x / rGO composite membrane The preparation process was completely consistent with that of Example 1, except that the hot pressing treatment in step six was omitted: the double-layer film was directly annealed after drying, without the hot pressing step at 120°C and 0.5MPa. All other parameters remained unchanged, and the final composite film was named Comparative Example 2 (without hot pressing).

[0048] The Nb2C2T prepared in Examples 1-6 and Comparative Examples 1-2 of this invention x The basic physical and mechanical properties of the / rGO composite membrane were tested. Simultaneously, the composite membrane was used as the positive electrode of a supercapacitor to test its cycling stability in flexible application scenarios, as detailed in the table below.

[0049] As can be seen from the table data, the NaF-NH4F-HF composite etching system and segmented temperature control process used in this invention can improve Nb2C2T through synergistic etching. x Layered structure integrity and surface activity, thereby optimizing the overall material performance: Example 1 (segmented etching from 42℃ to 50℃, sapphire substrate, hot-pressing composite) has a sheet resistivity of only 8.2Ω / sq and a fracture strength of 45.6MPa. Due to segmented temperature control, the Al layer can be gently removed first (42℃) and then the holes can be formed by moderate etching (50℃), reducing carbon layer damage. At the same time, hot pressing strengthens Nb2C2T. x Due to the strong interfacial bonding with rGO, the resistance change rate after 1000 bends is only 12.5%; Example 3 (rGO mass percentage 15%) has a slightly lower sheet resistance (7.8 Ω / sq) because a small amount of rGO can form a conductive network, and the resistance increase caused by excessive rGO agglomeration is avoided. However, the reduced rGO content weakens the interfacial bonding effect, so the fracture strength drops to 40.1 MPa; Example 5 (pure Nb2C2T) x Without rGO composites, the membrane lacks conductive and mechanically reinforcing phases, resulting in significantly deteriorated sheet resistivity (15.3 Ω / sq) and bending stability (change rate 25.7%), confirming the relationship between rGO and Nb2C2T. x The synergistic effect. Compared with Example 6 (42°C isothermal etching), its sheet resistivity (12.7Ω / sq) is higher than that of Example 1, because isothermal etching makes it difficult to simultaneously achieve Al removal and carbon layer protection, and some Nb2C2T... x Layer structure collapse leads to a reduction in conductive pathways; Comparative Example 1 (single LiF-HF etching) exhibits a sheet resistivity as high as 23.5 Ω / sq, due to the low efficiency of single LiF etching, resulting in increased residual Al impurities and carbon layer defects, hindering electron transport; Comparative Example 2 (without hot pressing) shows a fracture strength of only 28.9 MPa and a resistivity change rate of 45.3% after bending, due to the lack of a tight interface bond formed by hot pressing, resulting in Nb2C2T x The rGO layer is easily delaminated, resulting in a significant decrease in mechanical and cyclic stability.

Claims

1. A method for preparing a niobium nitride-reduced graphene oxide composite film, characterized in that, The specific steps are as follows: Nb2C2T was obtained by etching Nb2AlC powder with NaF-NH4F-HF composite etching solution. x MXene suspension; rGO suspension was obtained by reducing GO with hydrazine hydrate; Nb2C2T was spin-coated onto a pretreated hydrophilic flexible substrate. x MXene suspension, dried, yields Nb2C2T x Substratum membrane; In Nb2C2T x An rGO suspension was spin-coated onto the bottom membrane and dried to obtain an rGO coating layer. Nb2C2T on hydrophilic flexible substrate x The bottom film and the rGO capping layer are hot-pressed, annealed, and cooled to obtain a niobium nitride reduced graphene oxide composite film.

2. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, Nb2C2T x The specific method for preparing MXene suspension is as follows: Maintain the water bath temperature at 38℃~42℃, and slowly add Nb2AlC powder to the NaF-NH4F-HF composite etching solution in portions. After the first addition, let it stand for 4min~6min. After each subsequent addition, stir for 20s~40s to disperse the material. After all the Nb2AlC powder has been added, adjust the rotation speed to 600r / min~700r / min and react for 15h~17h. Then, raise the temperature to 42℃~52℃ and continue the reaction for 7h~9h to obtain a black turbid etching solution. The black, turbid etching solution was centrifuged, the black precipitate was collected and purified, then redispersed, sonicated, and centrifuged again. The upper transparent black dispersion was collected to obtain Nb₂C₂T with a mass concentration of 12 mg / mL~18 mg / mL. x MXene suspension; The specific method for preparing rGO suspension is as follows: Hydrazine hydrate and GO suspension were mixed and reacted at 55℃~65℃ for 1.5h~2.5h. After diluting the reaction solution, the mixture was ultrasonically treated to obtain rGO suspension.

3. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, Nb2C2T was spin-coated onto a pretreated hydrophilic flexible substrate. x MXene suspension, dried, yields Nb2C2T x In the process of making the bottom layer membrane: Nb2C2T x MXene suspension was dropped onto the center of a pretreated hydrophilic flexible substrate. During the low-speed pre-spinning stage, the rotation speed was 400-600 r / min for 8-12 s. The speed was then adjusted to 2500-3500 r / min and maintained for 25-35 s. The drying temperature was 75-85℃, the vacuum degree was controlled at -0.10 MPa to -0.08 MPa, and the drying time was 1.5-2.5 h to obtain Nb₂C₂T. x The underlying membrane.

4. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, In Nb2C2T x In the step of spin-coating an rGO suspension onto the bottom membrane and drying it to obtain an rGO coating layer: In the dried Nb2C2T x An rGO suspension was dripped onto the bottom membrane. During the low-speed pre-spinning stage, the rotation speed was 400 r / min to 600 r / min for 8 to 12 seconds. Then, the rotation speed was adjusted to 2500 r / min to 3500 r / min and maintained for 25 to 35 seconds. The drying temperature was 75℃ to 85℃, the vacuum degree was controlled at -0.10 MPa to -0.08 MPa, and the drying time was 1.5 to 2.5 hours to obtain the rGO coating layer.

5. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, Nb2C2T x The amounts of MXene suspension and rGO suspension were the same, and the amount was related to the size of the hydrophilic flexible substrate.

6. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, The hot pressing is performed at a temperature of 110℃~130℃, a pressure of 0.4MPa~0.6MPa, and a time of 25min~35min.

7. The method for preparing a niobium nitride-reduced graphene oxide composite film according to claim 1, characterized in that, The annealing is carried out in a protective atmosphere, with a heating rate of 4℃ / min to 6℃ / min, heating to 170℃ to 190℃, and holding for annealing for 5h to 7h.

8. A niobium nitride-reduced graphene oxide composite film, characterized in that, The niobium nitride reduced graphene oxide composite film prepared by any one of claims 1 to 7 has a sheet resistivity of 7.8 Ω / sq to 15.3 Ω / sq, a tensile strength of 32.5 MPa to 45.6 MPa, and a light transmittance of 75.6% to 85.2%.

9. A flexible supercapacitor, characterized in that, The niobium nitride reduced graphene oxide composite film described in claim 8 is attached to the surface of the positive current collector to serve as the positive active layer of the supercapacitor.

10. A flexible supercapacitor according to claim 9, characterized in that, The cycle stability of the flexible supercapacitor is 11.2%~25.7%.

Images