A high-nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax and a preparation method and application thereof

Abstract

This invention discloses a high-nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax, its preparation method, and its applications. Using biomass flax fabric as the carbon precursor, the membrane is first pre-carbonized at a programmed rate of 750-850℃ in an inert gas atmosphere, followed by activation treatment at 850-950℃ in a mixed atmosphere of ammonia and inert gas. This invention has the following advantages and effects: Through the aforementioned "Type IV" programmed ammonia activation strategy, this invention achieves simultaneous carbonization, activation, and nitrogen doping in a one-step process using biomass waste as raw material. The process is simple, green, and efficient.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and electrochemical energy storage technology, specifically relating to a high-nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible electronic devices, the demand for matching high-performance, flexible, and lightweight energy storage devices is becoming increasingly urgent. Flexible supercapacitors have become a research hotspot due to their high power density, long cycle life, and fast charge / discharge capabilities. Electrode materials are the core factor determining their performance, and self-supporting, binder-free carbon fiber electrodes are an ideal choice as they avoid performance losses caused by inactive additives.

[0003] Biomass-derived carbon materials are widely available, inexpensive, and sustainable. Flax fiber, in particular, has attracted attention due to its high aspect ratio and strength. However, carbon materials obtained by directly carbonizing flax have extremely low specific capacitance. While CO2 activation can increase the specific surface area, it does not provide good rate performance. To improve the electrochemical performance of carbon materials, introducing heteroatoms such as nitrogen atoms for doping is an effective strategy, as it can adjust the electronic structure, enhance wettability, and provide pseudocapacitance.

[0004] Existing nitrogen doping methods are mainly divided into in-situ synthesis and post-processing. In-situ synthesis has stringent requirements for precursors and is complex; post-processing is relatively simple, but often uses highly corrosive reagents such as nitric acid or requires multiple steps, making the process cumbersome and potentially damaging to the structural integrity of the material.

[0005] Therefore, it is of great significance to develop a simple, efficient, one-step process for activation and nitrogen doping, which can produce self-supporting carbon fiber membranes with high specific surface area, high nitrogen content, hierarchical porosity, and excellent flexibility. Summary of the Invention

[0006] The present invention aims to provide a simple and mild preparation method that can simultaneously achieve activation and doping in one step, resulting in a self-supporting nitrogen-doped porous carbon fiber membrane (PNCFs) with high specific surface area, high nitrogen content, hierarchical porous structure with coexistence of micropores and mesopores and excellent mechanical flexibility, and successfully applying it to high-performance flexible supercapacitors.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a high-nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax: using biomass flax fabric as a carbon precursor, the membrane is first pre-carbonized at 750-850℃ in an inert gas atmosphere at a programmed rate, and then activated at 850-950℃ in a mixed atmosphere of ammonia and inert gas.

[0008] In a preferred embodiment, the present invention can be further configured such that the pre-carbonization holding time is 100-140 minutes and the activation treatment holding time is 15-60 minutes.

[0009] In a preferred embodiment, the present invention can be further configured such that the temperature rise rate of the programmed temperature rise is 3-10℃ / min.

[0010] In a preferred embodiment, the present invention can be further configured such that the total flow rate of the mixed atmosphere is 150-250 mL / min, wherein the ammonia gas fraction is 20-40%.

[0011] This invention also provides a highly nitrogen-doped flexible porous carbon fiber membrane prepared according to the above preparation method: the carbon fiber membrane is a self-supporting flexible thin film with a BET specific surface area ≥1000 m². 2 / g, total pore volume ≥0.45cm³ 3 / g, nitrogen content ≥4.5at.%, and nitrogen exists mainly in pyridine nitrogen.

[0012] In a preferred embodiment, the present invention may be further configured such that the carbon fiber membrane has a hierarchical porous structure comprising micropores and mesopores, wherein the mesopore volume accounts for 5%-15% of the total pore volume.

[0013] In a preferred embodiment, the present invention may be further configured such that the pyridine nitrogen content of the carbon fiber membrane accounts for 35%-50% of the total nitrogen content.

[0014] In a preferred embodiment, the present invention can be further configured such that the carbon fiber membrane retains its structural integrity after being bent 180°, and its conductivity retention rate is above 95%.

[0015] The present invention also provides an electrode whose active material comprises the aforementioned highly nitrogen-doped flexible porous carbon fiber membrane.

[0016] The present invention also provides a supercapacitor, wherein at least one of its positive and negative electrodes is an electrode containing the aforementioned highly nitrogen-doped flexible porous carbon fiber membrane, the supercapacitor is a flexible supercapacitor, and its electrolyte is an aqueous electrolyte or a quasi-solid gel electrolyte.

[0017] Compared with the prior art, the beneficial effects of the embodiments of the present invention are: 1. Green, simple, and low-cost process: Using flax, a biomass waste, as raw material, ammonia is used as both an activator and a nitrogen source. Carbonization, activation, and nitrogen doping are achieved in one step. The process route is simple and efficient, avoiding multi-step processing and the use of highly corrosive reagents. It has the advantages of being environmentally friendly and low-cost.

[0018] 2. Excellent Material Structure and Synergistic Performance: Through a unique "Type IV" activation procedure, the physical and chemical properties of the material are synergistically controlled. The prepared carbon fiber membrane simultaneously possesses high specific surface area, high nitrogen content, hierarchical porous structure, and excellent intrinsic flexibility. In the porous structure, micropores provide energy storage sites, while mesopores promote ion transport.

[0019] 3. Excellent electrochemical performance: As a supercapacitor electrode, this material exhibits high specific capacitance, excellent rate performance, and long-term cycling stability in a three-electrode system. The assembled symmetrical flexible device demonstrates high areal energy density and excellent mechanical flexibility, with almost no change in capacitance after bending 180°.

[0020] 4. Broad application prospects: This self-supporting flexible electrode material does not require additional current collectors and binders, and can be directly used to construct flexible supercapacitors, simplifying device processes and reducing manufacturing costs. It has good application potential in wearable electronic devices, flexible displays and other fields. Attached Figure Description

[0021] Figure 1 Here is a SEM image of PNCF-IV-900-45 obtained in Example 1; Figure 2 The nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the products obtained in Comparative Example 1 and Example 1 are shown. Figure 3 This is the XPS N1s high-resolution spectrum of PNCF-IV-900-45 obtained in Example 1; Figure 4 The CV curves of the symmetrical flexible supercapacitor assembled from the materials prepared in Example 1 at different bending angles are shown. Detailed Implementation

[0022] The technical solutions described in this invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described in this specification are only some feasible technical solutions of this invention. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without any creative effort should be considered to fall within the scope of protection of this invention.

[0023] This application successfully prepared a highly nitrogen-doped flexible porous carbon fiber membrane with excellent comprehensive performance through an optimized "pre-carbonization + high-temperature ammonia activation" procedure. This method is simple and efficient, and the material shows great application potential in flexible supercapacitors.

[0024] A method for preparing a highly nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax uses biomass flax fabric as the sole carbon precursor. In a mixed atmosphere of ammonia and inert gas, the carbonization, activation, and nitrogen doping processes are completed in one step by precisely controlling the activation parameters. Specific steps include: S1. Pretreatment: The linen fabric used as raw material is washed sequentially in sodium hydroxide solution and deionized water to remove surface impurities and some hemicellulose components. After washing, the fabric is dried in an oven to obtain clean pretreated raw material; S2. Programmed Ammonia Activation and Carbonization: The pretreated linen fabric is placed in a tube furnace and subjected to programmed temperature rise treatment under a flowing atmosphere. The activation program is a specially designed "Type IV" program, which specifically includes three stages: The first stage: pre-carbonization. In a pure inert gas atmosphere such as nitrogen, the furnace temperature is raised to 750-850℃ at a certain heating rate and held at this temperature for 100-140 minutes. The main purpose of this stage is to carbonize the linen fabric, forming a preliminary carbon skeleton structure. The second stage: activation and doping. The atmosphere is switched to a mixture of ammonia and an inert gas, such as an NH3 / N2 mixture, and the temperature is further increased to a higher target activation temperature of 850-950℃. At this target temperature, activation is carried out for 15 to 60 minutes. During this process, ammonia acts as an activator, etching the carbon framework to create pores, and also as a nitrogen source, doping nitrogen atoms into the carbon framework, thus completing activation and doping in one step.

[0025] Third stage: Cooling. After the reaction is complete, the atmosphere is switched back to pure inert gas, and the sample is allowed to cool naturally to room temperature under the protection of the inert gas to prevent the high-temperature material from being oxidized during the cooling process.

[0026] In step S2, the heating rate is 3-10℃ / min. The total flow rate of the inert gas and the mixed gas is 150-250 mL / min. During the mixed gas stage, the ammonia fraction accounts for 20%-40% of the total volume.

[0027] S3. Product Collection: After the program is completed, remove the material from the tube furnace. The obtained product is a black, flexible, self-supporting thin film material, namely a highly nitrogen-doped flexible porous carbon fiber membrane, which can be used directly as an electrode material.

[0028] This invention systematically optimizes the "activation procedure type." Unlike the simple activation processes commonly found in existing technologies, which are performed in a single atmosphere or temperature, this invention designs a two-step procedure: "pre-carbonization plus specific high-temperature ammonia activation," or "Type IV" procedure. In this procedure, the pre-carbonization step is carried out in a purely inert atmosphere. Its function is to allow flax fibers to form a preliminary thermally stable carbon skeleton under relatively mild conditions and to remove most of the volatiles, thereby providing a structurally stable carbon substrate with a surface rich in defect sites for subsequent steps. The subsequent ammonia activation step is carried out at a higher temperature, where the introduced NH3 decomposes to generate active free radicals, such as ·NH2 and ·NH, which can react efficiently with the carbon skeleton. This process synergistically achieves two key functions: first, selective etching on the carbon skeleton, which not only develops abundant micropores but also creatively introduces a certain proportion of mesopores, forming a hierarchical pore structure conducive to ion transport; second, in-situ doping of nitrogen atoms into the carbon matrix in an electrochemically active form. This program, through step design and parameter control, cleverly and synergistically optimizes the pore structure and surface chemistry of materials, resulting in excellent comprehensive properties, including but not limited to 1152 μm. 2 Specific surface area per g, 0.502 cm² 3 The core process achieves a total pore volume of / g and a nitrogen content of 5.56 at.%.

[0029] Secondly, this invention provides a highly nitrogen-doped flexible porous carbon fiber membrane prepared by the above method. This material is a self-supporting flexible film composed of an interwoven network structure of carbon fibers. The carbon fibers have a diameter ranging from 5 to 10 μm, with a rough surface exhibiting abundant hierarchical porosity. The material possesses a hierarchical porous structure, with a BET specific surface area between 1000 and 1200 m². 2 The total pore volume is between 0.45 and 0.55 cm³ / g. 3 / g, of which mesopore volume accounts for 5%-15% of the total pore volume. Chemically, the material contains 4.5-6.0 at.%, primarily in the form of highly electrochemically active pyridine nitrogen, accounting for approximately 35%-50% of the total nitrogen content. The material exhibits both good mechanical flexibility and structural integrity, maintaining its structure without damage after bending 180°, and retaining over 95% of its conductivity, meeting the mechanical and electrical requirements of flexible devices for the substrate.

[0030] Thirdly, this invention provides the application of the aforementioned highly nitrogen-doped flexible porous carbon fiber membrane as an electrode active material in energy storage devices, particularly in flexible supercapacitors. Due to its self-supporting properties, high specific surface area, high nitrogen doping content, and excellent flexibility, the material can be directly used as an electrode without the need for additional current collectors, binders, or conductive agents, thus simplifying the electrode fabrication process.

[0031] Fourthly, the present invention provides a flexible supercapacitor, wherein at least one of its positive and negative electrodes is composed of the aforementioned highly nitrogen-doped flexible porous carbon fiber membrane. The electrolyte may be selected from an aqueous electrolyte such as a 6M KOH solution or a quasi-solid-state gel electrolyte such as PVA / KOH gel.

[0032] The flexible supercapacitor has a symmetrical structure, meaning that both its positive and negative electrodes are composed of highly nitrogen-doped flexible porous carbon fiber membranes of the same specification. This structure fully utilizes the inherent good conductivity and structural stability of the material, eliminating the need for any binders or conductive additives, thereby simplifying the electrodes and increasing the overall energy density of the device.

[0033] Example 1: Preparation of highly nitrogen-doped flexible porous carbon fiber membrane PNCF-IV-900-45 This embodiment provides a typical process for preparing highly nitrogen-doped flexible porous carbon fiber membranes using a "Type IV" activation procedure. The specific steps are as follows: S1. Raw material pretreatment Commercially available linen fabric was cut to appropriate sizes and then soaked in a 1 mol / L sodium hydroxide aqueous solution at room temperature for 24 hours to remove wax, gum, and other impurities from the fiber surface. After soaking, the fabric was removed and repeatedly washed with deionized water until the washing solution was neutral. The washed fabric was then placed in an oven and dried at 80°C to constant weight to obtain the pretreated linen fabric.

[0034] S2. Programmed ammonia activation, i.e., Type IV programmable activation. Weigh approximately 1.0g of pretreated linen fabric and lay it flat in a quartz boat within a tube furnace. Push the quartz boat into the central constant-temperature zone of the furnace. The specific activation procedure is as follows: Pre-carbonization stage: Under a pure nitrogen atmosphere, the gas flow rate is set to 200 mL / min. The furnace temperature is increased from room temperature to 800℃ at a heating rate of 5℃ / min, and held at 800℃ for 120 minutes to fully carbonize the linen fabric and form a preliminary carbon skeleton structure.

[0035] Activation and Doping Stage: After pre-carbonization, the furnace atmosphere is switched to an ammonia / nitrogen mixture, with an ammonia flow rate of 60 mL / min and a nitrogen flow rate of 140 mL / min, maintaining a total flow rate of 200 mL / min. Under the same atmosphere, the furnace temperature is increased from 800℃ to 900℃ at a rate of 5℃ / min, and then held at 900℃ for 45 minutes for activation. In this stage, ammonia acts as an activator, etching the carbon framework to create pores, and also as a nitrogen source, doping nitrogen atoms into the carbon framework.

[0036] Cooling stage: After activation, switch the atmosphere back to pure nitrogen and allow the sample to cool naturally to room temperature under nitrogen protection.

[0037] S3. Product Collection After the furnace temperature cooled to room temperature, the quartz boat was removed, yielding a black, flexible, self-supporting carbon fiber membrane. The resulting sample was designated PNCF-IV-900-45.

[0038] Example 2: Preparation of PNCF-IV-900-30 with different activation times This embodiment aims to investigate the effect of activation and holding time on the structure and properties of the product. The preparation steps are basically the same as in Example 1, except that in step S2, the holding time at 900°C is shortened from 45 minutes to 30 minutes. The obtained sample is designated as PNCF-IV-900-30.

[0039] Example 3: Preparation of PNCF-IV-850-45 at different activation temperatures This embodiment aims to investigate the effect of activation temperature on the structure and properties of the product. The preparation steps are basically the same as in Example 1, except that in step S2, the activation and doping stage, the final activation temperature is reduced from 900℃ to 850℃, while the holding time remains 45 minutes. The resulting sample is designated HPCMT-1100-4.

[0040] Comparative Example 1: Directly carbonized unactivated sample This comparative example provides a direct carbonization process without ammonia activation, used to illustrate the necessity of the ammonia activation step for porous structures and nitrogen doping.

[0041] S1. Raw material pretreatment: Same as step S1 in Example 1.

[0042] S2. Carbonization treatment: The pretreated linen fabric was placed in a tube furnace and heated directly to 900°C at a heating rate of 5°C / min under a pure nitrogen atmosphere of 200 mL / min. The temperature was then maintained at 900°C for 120 minutes. No atmosphere was changed or ammonia was introduced during the entire process.

[0043] S3. Product collection: After cooling, the sample is taken out, and the resulting black carbonized fiber membrane is obtained.

[0044] The comparative sample was a pure carbonized material, not activated by ammonia, and theoretically did not possess a high nitrogen doping content or abundant porous structure. The resulting sample was labeled CF-1100-6.

[0045] Comparative Example 2: Different activation procedures based on literature methods—one-step ammonia activation This comparative example provides a sample prepared using a "one-step activation procedure" commonly found in the literature, for comparison with the "Type IV" two-step activation procedure of this invention.

[0046] S1. Raw material pretreatment: Same as step S1 in Example 1.

[0047] S2. One-step ammonia activation: The pretreated linen fabric was placed in a tube furnace and heated directly to 900℃ at a heating rate of 5℃ / min under a pure nitrogen atmosphere of 200mL / min.

[0048] When the temperature reaches 900℃, immediately switch the atmosphere to an ammonia / nitrogen mixture, with an ammonia flow rate of 60 mL / min and a nitrogen flow rate of 140 mL / min, and keep it at 900℃ for 45 minutes for activation.

[0049] After the heat preservation is completed, switch back to a pure nitrogen atmosphere and allow it to cool naturally to room temperature.

[0050] S3. Product collection: The obtained sample is designated as PNCF-III-900-45.

[0051] The key difference between this comparative example and the present invention is that the present invention sets up an independent "pre-carbonization" stage before ammonia activation, with inert atmosphere and low temperature heat preservation, while comparative example 2 adopts a "one-step method" of directly heating to the target temperature and then introducing ammonia.

[0052] Material characterization and performance testing: To verify the effectiveness of the preparation method described in this invention and the excellent performance of the obtained materials, the samples obtained in Examples 1-3 and Comparative Examples 1-2 were systematically characterized in terms of microstructure, pore structure, surface chemical composition and electrochemical performance. The specific results are as follows.

[0053] 1. Microstructure and pore structure characteristics The surface morphology of the samples was observed using scanning electron microscopy. The results showed that the surface of the PNCF-IV-900-45 fiber sample prepared in Example 1 of this invention was rough and uneven, exhibiting a distinct and dense pore structure, indicating that ammonia activation had a significant etching effect on the carbon skeleton. In contrast, the CF-C-900-120 sample of Comparative Example 1 had a smooth fiber surface with almost no obvious pores, confirming that the pure carbonization process without ammonia activation cannot effectively create pores.

[0054] The specific surface area, pore volume, and pore size distribution of the samples were analyzed using nitrogen adsorption-desorption testing. (See [reference needed]). Figure 2 Test results show that the BET specific surface area of ​​the sample in Example 1 is as high as 1152 m². 2 / g, total pore volume is 0.502cm³ 3The pore size distribution ( / g) was the highest among all tested samples. The pore size distribution curves showed that the sample simultaneously contained micropores concentrated below 2 nm and mesopores distributed between 2 and 50 nm, exhibiting a typical hierarchical porous structure. This micropore-mesopore coexistence configuration is beneficial for simultaneously providing abundant charge storage sites and promoting rapid transport of electrolyte ions.

[0055] 2. Surface chemical composition and elemental state analysis X-ray photoelectron spectroscopy was used to characterize the elemental composition and chemical state of nitrogen species on the sample surface. (See [reference needed]) Figure 3 The results showed that the nitrogen content of the sample in Example 1 was as high as 5.56 at.%, significantly higher than that of Comparative Example 1 (0.19 at.%) and Comparative Example 2 (4.91 at.%). The relative content of pyridine nitrogen in the sample of Example 1 accounted for 47.8% of the total nitrogen, the highest among all nitrogen species, and also significantly higher than the corresponding proportion in Comparative Example 2. Pyridine nitrogen is considered to provide pseudocapacitive active sites and improve the electron donor properties of carbon materials, and is one of the key factors in improving the specific capacitance of electrodes. The above results indicate that the "Type IV" two-step activation procedure of this invention can significantly improve nitrogen doping efficiency and effectively control the nitrogen species configuration.

[0056] 3. Evaluation of electrochemical performance In the three-electrode testing system, the prepared sample was used as the working electrode, and 6 mol / L KOH aqueous solution was used as the electrolyte for testing.

[0057] Specific capacitance and rate performance: At a current density of 0.5 A / g, the mass specific capacitance of the sample in Example 1 reached 204.1 F / g, significantly better than that of Comparative Example 1 (112.5 F / g) and Comparative Example 2 (190.3 F / g). When the current density was increased to 10 A / g, the capacitance retention of the sample in Example 1 was 83.3%, demonstrating excellent rate performance. This is attributed to the ample adsorption sites provided by its high specific surface area, the rapid ion transport promoted by its mesoporous structure, and the additional pseudocapacitive contribution introduced by the high pyridine nitrogen content.

[0058] 4. Performance evaluation of flexible devices To investigate the application potential of the material of the present invention in practical flexible energy storage devices, two PNCF-IV-900-45 samples from Example 1 were used directly as positive and negative electrodes, and PVA / KOH gel polymer was used as electrolyte to assemble a symmetrical all-solid-state flexible supercapacitor.

[0059] Energy / Power Density: This device achieves a power density of 500 μW / cm². 2 At that time, the areal energy density reached 174.7 μWh / cm². 2 It exhibits good energy output capability.

[0060] Mechanical flexibility: The device was subjected to bending tests at different angles, such as 0°, 90°, and 180°. The cyclic current-voltage (CV) curves under the corresponding conditions almost completely overlapped. See [reference needed]. Figure 4 This indicates that the device maintains stable electrochemical performance under severe deformation conditions, with almost no capacitance decay. This result fully confirms that the carbon fiber film obtained in this invention possesses both excellent structural flexibility and electrochemical stability, and can be directly used in the power systems of wearable and foldable electronic devices.

[0061] In summary, this invention, through a unique two-step process of "pre-carbonization followed by high-temperature ammonia activation," successfully prepared a porous carbon fiber membrane with high specific surface area, high nitrogen doping content, hierarchical porous structure, and intrinsic flexibility using biomass waste flax fabric as a precursor. This material significantly outperforms directly carbonized samples and comparative samples prepared using a one-step activation process in terms of microstructure, surface chemistry, electrochemical performance, and flexible device characteristics. The method of this invention is simple, environmentally friendly, and the resulting self-supporting electrode material can be directly assembled into high-performance flexible supercapacitors without any additives, showing broad application prospects in wearable electronics, smart packaging, and flexible displays.

[0062] The parameters such as temperature, time, gas flow rate, and heating rate described in Examples 1-3 and Comparative Examples 1-2 are all exemplary specific values, and those skilled in the art can adjust them within the range defined in the claims according to actual needs.

[0063] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a highly nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax, characterized in that: Using biomass flax fabric as a carbon precursor, the material is first pre-carbonized at a programmed rate of 750-850℃ in an inert gas atmosphere, and then activated at 850-950℃ in a mixed atmosphere of ammonia and inert gas.

2. The method for preparing a highly nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax according to claim 1, characterized in that: The pre-carbonization holding time is 100-140 minutes, and the activation treatment holding time is 15-60 minutes.

3. The method for preparing a highly nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax according to claim 2, characterized in that: The temperature rise rate of the programmed temperature rise is 3-10℃ / min.

4. The method for preparing a highly nitrogen-doped flexible porous carbon fiber membrane based on ammonia-activated flax according to claim 1, characterized in that: The total flow rate of the mixed atmosphere is 150-250 mL / min, of which the ammonia gas fraction is 20-40%.

5. The highly nitrogen-doped flexible porous carbon fiber membrane prepared by the preparation method according to any one of claims 1-4, characterized in that: The carbon fiber membrane is a self-supporting flexible film with a BET specific surface area ≥ 1000 m². 2 / g, total pore volume ≥0.45cm³ 3 / g, nitrogen content ≥4.5at.%, and nitrogen exists mainly in pyridine nitrogen.

6. The high-nitrogen-doped flexible porous carbon fiber membrane according to claim 5, characterized in that: The carbon fiber membrane has a hierarchical porous structure comprising micropores and mesopores, wherein the mesopore volume accounts for 5%-15% of the total pore volume.

7. The high-nitrogen-doped flexible porous carbon fiber membrane according to claim 6, characterized in that: The carbon fiber membrane has a pyridine nitrogen content of 35%-50% of the total nitrogen content.

8. The high-nitrogen-doped flexible porous carbon fiber membrane according to claim 6, characterized in that: The carbon fiber membrane retains its structural integrity after being bent 180°, and its conductivity is maintained at over 95%.

9. An electrode, characterized in that, Its active material comprises the highly nitrogen-doped flexible porous carbon fiber membrane as described in any one of claims 5-8.

10. A supercapacitor, characterized in that, At least one of its positive and negative electrodes is the electrode as described in claim 9, the supercapacitor is a flexible supercapacitor, and its electrolyte is an aqueous electrolyte or a quasi-solid gel electrolyte.

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