A nitrogen and sulfur doped carbon-based electrocatalytic material, a preparation method and application thereof

Abstract

The application relates to the technical field of electrocatalysis, in particular to a nitrogen and sulfur doped carbon-based electrocatalytic material and a preparation method and application thereof. The application comprises the following steps: S1, obtaining silk fibroin, uniformly mixing the silk fibroin with a sulfur source, a spinning aid and an acidic solvent to form a spinning solution; S2, preparing the spinning solution into a composite nanofiber by adopting an electrostatic spinning method; S3, sequentially performing pre-oxidation treatment, carbonization treatment, pure water treatment and drying treatment on the composite nanofiber to obtain the nitrogen and sulfur doped carbon-based electrocatalytic material. The prepared nitrogen and sulfur doped carbon-based electrocatalytic material has the nanofiber structure characteristic and a large specific surface area, can significantly improve the catalytic activity, and makes the nitrogen and sulfur doped carbon-based electrocatalytic material have a wide application prospect in the fields of water electrolysis hydrogen production, oxygen production and the like.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a nitrogen- and sulfur-doped carbon-based electrocatalytic material, its preparation method, and its application. Background Technology

[0002] Metal-free carbon-based electrocatalytic materials have attracted widespread attention in the fields of energy conversion and storage in recent years due to their low cost, excellent stability, and huge catalytic potential. Especially in applications such as fuel cells and water electrolysis for hydrogen production, metal-free carbon-based electrocatalytic materials have become a research hotspot due to their excellent electrocatalytic performance. However, the actual performance of these materials still cannot meet the growing application demands, and key indicators such as catalytic activity and stability still need to be improved.

[0003] Currently, the main factors limiting the performance improvement of metal-free carbon-based electrocatalytic materials are low doping levels, uncontrollable doping sites, and uncontrollable performance when using single heteroatom doping or multiple heteroatom co-doping. Low heteroatom doping levels result in insufficient adjustment of the electronic structure, failing to fully realize the performance improvement effect. Precise control of doping sites affects electron distribution and the formation of active centers, leading to poor material performance stability and consistency. Single heteroatom doping offers limited electronic structure adjustment capabilities; multi-heteroatom co-doping allows for multi-dimensional control of the electronic structure, but faces challenges such as complex inter-element interactions and difficulty in ensuring doping uniformity. In existing technologies, most metal-free carbon-based electrocatalytic materials employ solid-phase reaction doping, which involves mixing a carbon source with a heteroatom-containing source and then pyrolyzing the mixture at high temperatures. However, solid-phase reactions have significant limitations: slow mass transfer rates and low reaction efficiency, which prolong the preparation cycle and increase energy consumption. Furthermore, uneven component contact can occur in solid-phase reactions, making it difficult to ensure doping uniformity, resulting in localized overdoping or underdoping, thus affecting the overall performance improvement of the material. Therefore, there is an urgent need to develop an efficient and controllable doping method for preparing metal-free carbon-based electrocatalytic materials with multiple functions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing nitrogen- and sulfur-doped carbon-based electrocatalytic materials, using silk fibroin as the nitrogen and carbon source to achieve high-level nitrogen doping, improve doping uniformity, and enhance its catalytic performance.

[0005] This application also provides a nitrogen- and sulfur-doped carbon-based electrocatalytic material, which has nanofiber structure characteristics.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing nitrogen- and sulfur-doped carbon-based electrocatalytic materials, comprising the following steps: S1. Obtain silk fibroin by mixing the silk fibroin with a sulfur source, a spinning aid, and an acidic solvent to form a spinning solution; wherein the sulfur source is a sulfur-containing compound, the spinning aid is a polymer, and the acidic solvent is an organic acid capable of dissolving the silk fibroin. S2. The spinning solution is prepared into composite nanofibers by electrospinning. S3. The composite nanofibers are subjected to pre-oxidation treatment, carbonization treatment, pure water treatment and drying treatment in sequence to obtain nitrogen and sulfur doped carbon-based electrocatalytic materials; wherein the pre-oxidation treatment is carried out in an air atmosphere and the carbonization treatment is carried out in an inert atmosphere.

[0007] Further, in step S1, the silk fibroin protein in the spinning solution has a mass fraction of 6.7wt% to 8wt%, the spinning aid has a mass fraction of 1.1wt% to 1.5wt%, and the sulfur source has a mass fraction of 1wt% to 10wt%.

[0008] Furthermore, the average molecular weight of the spinning aid is any value between 300kDa and 600kDa.

[0009] Furthermore, the spinning aid is polyoxyethylene or polyvinylpyrrolidone, and the sulfur source is any one of anhydrous potassium sulfate, sodium sulfate, and magnesium sulfate.

[0010] Furthermore, in step S2, the applied voltage is any value between 15kV and 20kV, the receiving distance is limited to any value between 15cm and 20cm, the temperature is limited to any value between 10℃ and 30℃, and the relative humidity is limited to any value between 25% and 35%.

[0011] Furthermore, in step S3, during the pre-oxidation treatment, the treatment temperature is increased from room temperature to a range of 200℃ to 300℃, and the heating rate is any value between 1℃ / min and 5℃ / min.

[0012] Furthermore, in step S3, during the carbonization process, the temperature is increased from room temperature to any value between 750°C and 1000°C, and the heating rate is any value between 1°C / min and 5°C / min.

[0013] Further, in step S3, the purification process includes: washing the composite nanofibers after carbonization treatment with an acidic solution, and then washing the composite nanofibers with pure water; the acidic solution is any one of hydrochloric acid, sulfuric acid, and nitric acid.

[0014] This application provides a nitrogen- and sulfur-doped carbon-based electrocatalytic material, which is prepared by the above-described preparation method.

[0015] This application also provides the application of the above-mentioned nitrogen and sulfur doped carbon-based electrocatalytic materials in the catalytic reactions of hydrogen and oxygen evolution in water electrolysis.

[0016] The beneficial effects of this invention are as follows: The preparation method provided in this application can effectively achieve a high level of nitrogen doping by using silk fibroin as both a nitrogen and carbon source. Simultaneously, by employing electrospinning, the uniform mixing of components such as the carbon, nitrogen, and sulfur sources can be promoted, which facilitates contact between the components during pyrolysis, thereby achieving uniform doping of nitrogen and sulfur elements and further improving the doping level.

[0017] The nitrogen- and sulfur-doped carbon-based electrocatalysts prepared by this method possess nanofiber structure characteristics and a large specific surface area, providing abundant active sites for catalytic reactions. The nanofiber structure also endows these nitrogen- and sulfur-doped carbon-based electrocatalysts with excellent electron and mass transport properties, significantly improving their catalytic activity and thus enhancing their electrocatalytic performance. This makes these nitrogen- and sulfur-doped carbon-based electrocatalysts promising for applications in water electrolysis for hydrogen and oxygen production.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 The image shows a scanning electron microscope image of the nitrogen- and sulfur-doped carbon-based electrocatalytic material as shown in Example 1 of this invention. Figure 2 The elemental distribution of the nitrogen- and sulfur-doped carbon-based electrocatalytic material shown in Example 1 of this invention is obtained by high-angle annular dark-field scanning transmission electron microscopy. Figure 3 The image shows a scanning electron microscope image of the nitrogen- and sulfur-doped carbon-based electrocatalytic material as shown in Example 2 of this invention. Figure 4 The hydrogen evolution catalytic polarization curves obtained by applying the nitrogen- and sulfur-doped carbon-based electrocatalytic material shown in Example 1 of this invention to 0.5M H2SO4 electrolyte are shown. Figure 5 The oxygen evolution catalytic polarization curves obtained by applying the nitrogen- and sulfur-doped carbon-based electrocatalytic material shown in Example 1 of this invention to 1M KOH electrolyte are shown. Figure 6 The hydrogen evolution catalytic polarization curves obtained by applying the nitrogen- and sulfur-doped carbon-based electrocatalytic material shown in Example 2 of this invention to 0.5 M H2SO4 electrolyte are shown. Figure 7The oxygen evolution catalytic polarization curves of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials shown in Example 2 of this invention, applied to 1M KOH electrolyte. Detailed Implementation

[0020] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Please see Figure 1 A preferred embodiment of this application illustrates a method for preparing a nitrogen- and sulfur-doped carbon-based electrocatalytic material, comprising the following steps: S1. Obtain silk fibroin by mixing silk fibroin with a sulfur source, a spinning aid, and an acidic solvent to form a spinning solution; wherein the sulfur source is a sulfur-containing compound, the spinning aid is a polymer, and the acidic solvent is an organic acid that can dissolve silk fibroin. S2. Composite nanofibers are prepared from the spinning solution using an electrospinning method. S3. The composite nanofibers are subjected to pre-oxidation and carbonization treatments in sequence. Then, the carbonized composite nanofibers are subjected to purification and drying treatments in sequence to obtain nitrogen and sulfur doped carbon-based electrocatalytic materials. The pre-oxidation treatment is carried out in an air atmosphere, and the carbonization treatment is carried out in an inert atmosphere.

[0022] Compared to traditional methods, the preparation method provided in this embodiment, by using silk fibroin as both nitrogen and carbon sources, facilitates high-level nitrogen doping and improves doping uniformity, solving problems such as uneven doping and low doping levels caused by adding an additional nitrogen source. Furthermore, silk fibroin, as a raw material, is widely available, environmentally friendly, and harmless, meeting the requirements of green chemistry and sustainable development. In step S2 of the preparation method provided in this embodiment, the use of electrospinning promotes uniform mixing of the components, namely the carbon source, nitrogen source, sulfur source, and spinning aid. This facilitates contact between components during subsequent carbonization and pyrolysis, making the formation of composite nanofibers more efficient and controllable, thereby achieving uniform doping of nitrogen and sulfur elements and further improving the doping level, which is beneficial for enhancing its catalytic performance. In step S3, the combination of pre-oxidation and carbonization treatments endows the final nitrogen- and sulfur-doped carbon-based electrocatalytic material with nanofiber structural characteristics and effectively maintains the material's pore structure, giving it excellent electron transport and mass transport properties, enhancing its stability and activity, and thus promoting its catalytic performance.

[0023] This preparation method is simple to operate and highly efficient, capable of producing carbon-based electrocatalysts with high levels of nitrogen and sulfur doping. The resulting carbon-based electrocatalysts possess a large specific surface area, fully exposing active sites. Simultaneously, the porous structure between the nanofibers facilitates ion diffusion and mass transport, further enhancing the material's catalytic performance. Consequently, this carbon-based electrocatalyst exhibits excellent hydrogen evolution and oxygen evolution catalytic performance, showing broad application potential in energy conversion and storage fields such as water electrolysis.

[0024] In one embodiment, in step S1, the spinning solution contains 6.7 wt%–8 wt% silk fibroin, 1.1 wt%–1.5 wt% spinning aid, and 1 wt%–10 wt% sulfur source. By precisely controlling the mass fraction range of each component, the doping amounts of nitrogen and sulfur can be effectively adjusted, thereby achieving precise control over the electronic structure and surface properties of the electrocatalytic material. This helps to improve the catalytic activity of the electrocatalytic material and optimize its performance in catalytic reactions. In this embodiment or other embodiments, the average molecular weight of the spinning aid is limited to any value between 300 kDa and 600 kDa. By limiting the average molecular weight of the spinning aid, the viscosity and rheological properties of the spinning solution can be optimized, thereby helping to form uniform composite nanofibers and providing a good foundation for the subsequent preparation of high-performance electrocatalytic materials. In some embodiments, the spinning aid can be a polymer such as polyethylene oxide or polyvinylpyrrolidone, and the sulfur source can be anhydrous sulfate, such as any one of anhydrous potassium sulfate, sodium sulfate, and magnesium sulfate, preferably anhydrous magnesium sulfate. By clearly defining the specific types of sulfur source and spinning aid, it is helpful to precisely control the reaction system, thereby ensuring that nitrogen and sulfur elements are doped into carbon-based materials as expected, improving the accuracy and stability of doping, and thus ensuring the consistency of the performance of electrocatalytic materials.

[0025] In one embodiment, in step S2, during the process of preparing composite nanofibers from the spinning solution using electrospinning, the applied voltage is any value between 15kV and 20kV, the receiving distance is limited to any value between 15cm and 20cm, the temperature is limited to any value between 10℃ and 30℃, and the relative humidity is limited to any value between 25% and 35%. By limiting the parameters such as voltage, receiving distance, temperature, and relative humidity during electrospinning, the diameter, morphology, and structure of the composite nanofibers can be precisely controlled, forming nanofibers with high specific surface area and good pore structure. This helps to increase the electrocatalytic reaction active sites of the final electrocatalytic material and improve its catalytic efficiency. In this embodiment or other embodiments, in step S3, during the pre-oxidation treatment, the treatment temperature is increased from room temperature to the range of 200℃ to 300℃, and the heating rate is any value between 1℃ / min and 5℃ / min. By defining the temperature range and heating rate of the pre-oxidation treatment, the organic components in the composite nanofibers can undergo appropriate oxidation reactions to form a stable carbon framework structure, while avoiding excessive oxidation that could lead to structural damage, thus providing a good precursor for subsequent carbonization. Furthermore, the pre-oxidation treatment time is preferably controlled within the range of 1 to 3 hours. In some embodiments, in step S3, during the carbonization process, the temperature is increased from room temperature to any value between 750°C and 1000°C, with a heating rate of 1°C / min to 5°C / min. By limiting the temperature range and heating rate of the carbonization treatment, the degree of carbonization can be precisely controlled, allowing nitrogen and sulfur elements to be uniformly doped into the carbon-based material, forming a stable doped structure and improving the stability and conductivity of the electrocatalytic material. Simultaneously, the carbonization treatment time is preferably controlled within the range of 1.5 to 3 hours. In other embodiments, in step S3, the purification treatment includes: washing the carbonized composite nanofibers with an acidic solution, followed by washing the composite nanofibers with pure water; the acidic solution is any one of hydrochloric acid, sulfuric acid, and nitric acid. By washing the composite nanofibers sequentially with acidic solution and pure water, impurities and residues on the surface after carbonization can be effectively removed, improving the purity of the electrocatalytic material, thereby enhancing its catalytic performance and reducing the occurrence of side reactions during the catalytic reaction.

[0026] This application also provides a nitrogen- and sulfur-doped carbon-based electrocatalytic material, which is prepared using the above-described preparation method. The carbon-based electrocatalytic material possesses uniform nitrogen and sulfur doping characteristics, high specific surface area, and a good pore structure, thus exhibiting excellent electrocatalytic performance, such as high catalytic activity and good stability.

[0027] This application also provides the application of this nitrogen- and sulfur-doped carbon-based electrocatalytic material in the catalytic reactions of hydrogen and oxygen evolution in water electrolysis. Its high catalytic activity can reduce the overpotential of the water electrolysis reaction and improve energy conversion efficiency; its good stability ensures that its performance does not decay during long-term catalytic reactions, reducing equipment maintenance costs; thus, it has broad application prospects in the fields of hydrogen and oxygen production through water electrolysis.

[0028] Example 1 S1. Obtain 0.67g of silk fibroin. At the same time, weigh 0.13g of polyethylene oxide with an average molecular weight of 30kDa, 0.4g of anhydrous magnesium sulfate, and 8.8g of anhydrous formic acid. Mix the weighed silk fibroin, polyethylene oxide, anhydrous magnesium sulfate, and anhydrous formic acid, and stir to make them evenly mixed to obtain a spinning solution.

[0029] S2. The spinning solution is prepared into composite nanofibers by electrospinning. Specifically, the spinning solution is transferred into a 10mL syringe, and an 18G needle is used as the spinning needle. At the same time, a voltage of 18kV is applied, and the receiving distance is set to 16cm. The flow rate of the spinning solution is controlled to 1mL / h by using an injection pump. The silk fibroin / polyethylene oxide / magnesium sulfate composite nanofibers are obtained by spinning.

[0030] S3. The obtained silk fibroin / polyethylene oxide / magnesium sulfate composite nanofibers were transferred to a muffle furnace, and the temperature in the muffle furnace was increased from room temperature to 240°C at a heating rate of 2°C / min for pre-oxidation treatment. After 2 hours of pre-oxidation treatment, the pre-oxidized silk fibroin / polyethylene oxide / magnesium sulfate composite nanofibers were transferred to a tube furnace, and the temperature in the tube furnace was increased from room temperature to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere for carbonization treatment. After 2 hours of carbonization treatment, the tube furnace was allowed to cool naturally to room temperature, and a black solid product was collected. Subsequently, the black solid product was washed successively with excess dilute hydrochloric acid and pure water, and then dried to obtain nitrogen and sulfur doped carbon-based electrocatalytic material, i.e., NSCNF.

[0031] The structural characteristics, elemental distribution, and content of each element of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Example 1 were analyzed. The results are as follows: Figure 1 and Figure 2 As shown in Table 1. Furthermore, X-ray photoelectron spectroscopy was used to analyze the elemental content of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials shown in Example 1. The results are shown in Table 1, where BE stands for binding energy, which is the energy required to remove an electron from an atom or molecule.

[0032] Table 1. Elemental content of nitrogen- and sulfur-doped carbon-based electrocatalysts in Example 1 based on X-ray photoelectron spectroscopy. Depend on Figure 1 and Figure 2 As can be seen, the nitrogen- and sulfur-doped carbon-based electrocatalytic material prepared in Example 1 exhibits a nanofiber network structure, with the doped nitrogen and sulfur elements uniformly distributed on the nanofibers. This structure has a large specific surface area, providing abundant active sites for electrocatalytic reactions. The uniform doping of nitrogen and sulfur elements in this carbon-based electrocatalytic material helps to improve its electronic conductivity and catalytic activity. Furthermore, as shown in Table 1, the atomic percentage of nitrogen in this carbon-based electrocatalytic material is 8.69%, and the atomic percentage of sulfur is 3.45%, both indicating a high doping level, which endows the carbon-based electrocatalytic material with excellent electrocatalytic performance.

[0033] Example 2 The difference between this embodiment and Embodiment 2 is that in step S1, 0.67g of silk fibroin is obtained, and simultaneously, 0.13g of polyethylene oxide with an average molecular weight of 30kDa, 0.3g of anhydrous magnesium sulfate, and 8.9g of anhydrous formic acid are weighed. Finally, a nitrogen- and sulfur-doped carbon-based electrocatalytic material is obtained.

[0034] The structural characteristics of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Example 2 were examined, and the results are as follows: Figure 3 As shown in Table 2. Furthermore, X-ray photoelectron spectroscopy was used to analyze the elemental content of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials shown in Example 2, and the results are shown in Table 2.

[0035] Table 2. Elemental content of nitrogen- and sulfur-doped carbon-based electrocatalysts in Example 2 based on X-ray photoelectron spectroscopy. Depend on Figure 3 It can be seen that the nitrogen and sulfur doped carbon-based electrocatalytic materials prepared in Example 2 also exhibit a nanofiber network structure. As shown in Table 2, the atomic percentage of nitrogen in the nitrogen and sulfur doped carbon-based electrocatalytic materials prepared in Example 2 is 4.95%, and the atomic percentage of sulfur is 3.13%, both with relatively high doping levels.

[0036] The electrocatalytic performance of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Examples 1 and 2 was tested and analyzed. Specifically, the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Examples 1 and 2 were respectively applied to 0.5M H2SO4 solution and 1M KOH solution. Using a three-electrode system, under 85% solution resistance compensation, and a voltage scan rate of 5 mV / s, the hydrogen evolution and oxygen evolution reactions of water electrolysis were carried out, and the polarization curves were obtained, as shown in the figure. Figures 4-7 As shown.

[0037] like Figure 4 , Figure 5 As shown, the nitrogen- and sulfur-doped carbon-based electrocatalytic material prepared in Example 1 exhibits a performance of 10 mA / cm². 2 The overpotentials at these locations are 273 mV (hydrogen evolution) and 234 mV (oxygen evolution), respectively. This low overpotential indicates that the material exhibits excellent catalytic performance under both acidic and alkaline conditions, effectively reducing the energy consumption of the water electrolysis reaction. Figure 6 and Figure 7 As shown, the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Example 2 exhibit overpotentials of 355 mV and 439 mV for the hydrogen evolution and oxygen evolution reactions, respectively, under the same conditions. These overpotentials are higher than those in Example 1, indicating a slight decrease in catalytic performance, but the materials still possess certain catalytic activity. Therefore, it can be concluded that the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared using the method provided in this application all possess good overall performance. The high doping concentration and uniformity of the doping elements in this carbon-based electrocatalytic material significantly improve its catalytic performance, stability, and consistency.

[0038] Furthermore, by comparing the characteristics and performance of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials prepared in Example 1 with those in Example 2, it can be seen that the amount of anhydrous magnesium sulfate has a significant impact on the elemental content and catalytic performance of the nitrogen- and sulfur-doped carbon-based electrocatalytic materials. Increasing the amount of anhydrous magnesium sulfate helps to improve the nitrogen doping level, thereby enhancing the electrocatalytic performance of the material.

[0039] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0040] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a nitrogen- and sulfur-doped carbon-based electrocatalytic material, characterized in that, Includes the following steps: S1. Obtain silk fibroin by mixing the silk fibroin with a sulfur source, a spinning aid, and an acidic solvent to form a spinning solution; wherein the sulfur source is a sulfur-containing compound, the spinning aid is a polymer, and the acidic solvent is an organic acid capable of dissolving the silk fibroin. S2. The spinning solution is prepared into composite nanofibers by electrospinning. S3. The composite nanofibers are subjected to pre-oxidation treatment, carbonization treatment, pure water treatment and drying treatment in sequence to obtain nitrogen and sulfur doped carbon-based electrocatalytic materials; wherein the pre-oxidation treatment is carried out in an air atmosphere and the carbonization treatment is carried out in an inert atmosphere.

2. The preparation method according to claim 1, characterized in that, In step S1, the silk fibroin protein in the spinning solution has a mass fraction of 6.7wt% to 8wt%, the spinning aid has a mass fraction of 1.1wt% to 1.5wt%, and the sulfur source has a mass fraction of 1wt% to 10wt%.

3. The preparation method according to claim 2, characterized in that, The average molecular weight of the spinning aid is any value between 300kDa and 600kDa.

4. The preparation method according to claim 2, characterized in that, The spinning aid is polyoxyethylene or polyvinylpyrrolidone, and the sulfur source is any one of anhydrous potassium sulfate, sodium sulfate, and magnesium sulfate.

5. The preparation method according to claim 2, characterized in that, In step S2, the applied voltage is any value between 15kV and 20kV, the receiving distance is limited to any value between 15cm and 20cm, the temperature is limited to any value between 10℃ and 30℃, and the relative humidity is limited to any value between 25% and 35%.

6. The preparation method according to claim 1, characterized in that, In step S3, during the pre-oxidation treatment, the treatment temperature is increased from room temperature to a range of 200℃ to 300℃, and the heating rate is any value between 1℃ / min and 5℃ / min.

7. The preparation method according to claim 1, characterized in that, In step S3, during the carbonization process, the temperature is increased from room temperature to any value between 750°C and 1000°C, and the heating rate is any value between 1°C / min and 5°C / min.

8. The preparation method according to claim 1, characterized in that, In step S3, the purification process includes: washing the composite nanofibers after carbonization with an acidic solution, and then washing the composite nanofibers with pure water; the acidic solution is any one of hydrochloric acid, sulfuric acid, and nitric acid.

9. A nitrogen- and sulfur-doped carbon-based electrocatalytic material, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the nitrogen- and sulfur-doped carbon-based electrocatalytic material as described in claim 9 in the catalytic reaction of hydrogen and oxygen evolution in water electrolysis.

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