Super-hydrophilic PAN-based carbon nanofiber as well as preparation method and application thereof

Abstract

The invention discloses a super-hydrophilic PAN-based carbon nanofiber as well as a preparation method and application thereof, and belongs to the technical field of carbon nanofibers. The method specifically comprises the following steps: (1) mixing and dissolving a PAN-based carbon precursor and KI in an N, N-dimethylformamide solution, and uniformly stirring; (2) spinning through an electrostatic spinning process; and (3) sequentially carrying out pre-oxidation, high-temperature carbonization and cooling, thereby obtaining the product. The prepared super-hydrophilic PAN-based carbon nanofiber has the characteristics of super-strong hydrophilicity, good conductive network, simple preparation process, excellent electrochemical performance and the like, and the capacitive performance of a capacitor can be remarkably improved when the super-hydrophilic PAN-based carbon nanofiber is applied to an electrode of a self-supporting flexible supercapacitor; the problem of poor electrochemical performance caused by insufficient surface hydrophilicity of a traditional electrospinning PAN-based carbon nanofiber flexible electrode material is successfully solved, and a new way is provided for research and development of a high-performance self-supporting flexible electrode material.

Description

Technical Field

[0001] This invention relates to the field of carbon nanofiber technology, and more specifically to a superhydrophilic PAN-based carbon nanofiber, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible portable electronics technology, the market demand for flexible energy storage devices has experienced explosive growth. As a core component of flexible energy storage devices, the research and development of flexible, wearable electrode materials has become a focus of industry attention. Carbon nanofibers (CNFs) prepared by electrospinning technology, with their unique one-dimensional nanostructure and ultra-long three-dimensional network structure formed by interwoven fibers, exhibit natural advantages in flexible device assembly, providing a highly promising material foundation for the development of flexible energy storage devices. Among them, carbon nanofibers prepared from polyacrylonitrile (PAN) through electrospinning have become the mainstream solution for the preparation of carbon nanofiber electrode materials due to their wide availability of raw materials and mature and stable preparation process.

[0003] However, current processes for preparing PAN-based carbon nanofibers mostly focus on producing high-modulus, high-strength carbon nanofibers. Carbon nanofibers obtained through these processes have significant drawbacks: low surface polarity and a scarcity of oxygen-containing functional groups, making it difficult to achieve complete wetting in aqueous electrolytes. This limits the improvement of their electrochemical performance and fails to fully meet the stringent requirements of practical applications.

[0004] In the current industry development, the large-scale preparation of hydrophilic carbon nanofibers has significant economic value and application prospects. Existing technologies mostly employ a two-step strategy combining spinning and post-processing, but the hydrophilicity of the carbon nanofiber materials actually prepared is still unsatisfactory.

[0005] Therefore, how to improve the hydrophilicity of PAN-based carbon nanofibers is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a superhydrophilic PAN-based carbon nanofiber, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing superhydrophilic PAN-based carbon nanofibers specifically includes the following steps: (1) Preparation of precursor solution The PAN-based carbon precursor was mixed with KI and dissolved in N,N-dimethylformamide solution, and stirred until homogeneous to obtain the precursor solution. (2) Electrospinning The precursor solution was spun into polymer nanofiber membranes by electrospinning. (3) High-temperature carbonization The polymer nanofiber membrane was subjected to pre-oxidation, high-temperature carbonization, and cooling in sequence to obtain superhydrophilic PAN-based carbon nanofibers.

[0008] Furthermore, in step (1) above, the PAN-based carbon precursor is a single PAN, a PAN / cellulose acetate (PAN / CA) mixture, a PAN / polyvinylpyrrolidone (PAN / PVP) mixture, or a PAN / polymethyl methacrylate (PAN / PMMA) mixture.

[0009] Furthermore, in step (1) above, when the PAN-based carbon precursor is a single PAN, the mass ratio of the single PAN to KI is (70~140):(1~10), preferably 140:5.

[0010] Furthermore, in step (1) above, when the PAN-based carbon precursor is a PAN / CA mixture, the mass ratio of PAN to CA is (1~4):(1~4), preferably 1:1; the mass ratio of PAN to KI is (70~140):(1~10), preferably 70:5.

[0011] The further beneficial effect of adopting the above is that, through the optimized KI doping content, the hydrophilicity of the two PAN-based carbon nanofibers is optimal.

[0012] Furthermore, in step (2) above, the positive electrode voltage of the electrospinning process is 10~20 kV, preferably 17 kV; the negative electrode voltage is -1~-3 kV, preferably -2 kV; the nozzle of the injection pump is 15~25 cm from the receiving plate, preferably 18 cm; and the solution flow rate is 4~20 µL / min, preferably 8 µL / min.

[0013] The further beneficial effect of adopting the above-mentioned method is that the needle spinneret disperses in a conical shape, falls evenly and continuously onto the receiving plate, and there is no liquid accumulation, resulting in the best spinning effect.

[0014] Furthermore, in step (3) above, the pre-oxidation atmosphere is air, the heating rate is 1~10℃ / min, preferably 1℃ / min; the temperature is 200~300℃, preferably 240℃; and the holding time is 1~3 h, preferably 1 h.

[0015] Furthermore, in step (3) above, the atmosphere for high-temperature carbonization is nitrogen or argon, the heating rate is 1~10℃ / min, preferably 5℃ / min; the temperature is 700~1000℃, preferably 800℃; and the holding time is 1~3 h, preferably 1 h.

[0016] The further beneficial effect of adopting the above-mentioned method is that, during the high-temperature carbonization process, the large amount of KI volatilization not only effectively increases the specific surface area of ​​carbon nanofibers, but also significantly enhances their hydrophilicity, thereby endowing the material with excellent electrochemical performance.

[0017] Furthermore, in step (3) above, the temperature is cooled to room temperature.

[0018] This invention also claims protection for a superhydrophilic PAN-based carbon nanofiber prepared by the above-described preparation method.

[0019] This invention also claims the application of the superhydrophilic PAN-based carbon nanofibers prepared by the above-described method in the preparation of self-supporting flexible electrode materials.

[0020] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention obtains a one-dimensional polymer nanofiber membrane through electrospinning technology, and then fixes the carbon skeleton of the fiber through pre-oxidation to prevent the fiber from pulverizing during high-temperature calcination. Finally, during the high-temperature carbonization process, KI volatilizes to increase the content of oxygen-containing functional groups on the surface of the material, effectively improving the hydrophilicity of the PAN-based carbon nanofiber material.

[0021] 2. This invention employs electrospinning technology, cleverly utilizing KI to alter the oxygen-containing functional group content on the surface of PAN-based electrospun carbon nanofibers. This allows for the acquisition of superhydrophilic PAN-based carbon nanofibers without compromising the material's structural properties. The resulting fibers possess advantages such as good electrical conductivity and a simple preparation method.

[0022] 3. This invention improves the hydrophilicity of PAN-based carbon nanofibers (solid and hollow structures) by adding KI to the PAN-based carbon nanofiber electrospinning precursor solution and improving the hydrophilicity of PAN-based carbon nanofibers (solid and hollow structures) based on the volatilization of KI during high-temperature carbonization. This can efficiently and stably improve the hydrophilicity of PAN-based carbon nanofibers without damaging their bulk structure, and has the advantages of simple process and environmental friendliness.

[0023] 4. This invention utilizes the large-scale volatilization of potassium iodide (KI) to increase the content of oxygen-containing functional groups on the surface of carbon nanofibers without changing the main structure of the material or affecting its toughness and other properties. This effectively enhances the hydrophilicity of the material and thus significantly improves its electrochemical performance, providing a new solution for the development of electrode materials for flexible energy storage devices.

[0024] 5. The superhydrophilic PAN-based carbon nanofibers prepared by this invention have superhydrophilicity, good conductive network and ion transport channels, as well as flexibility, and can be applied to self-supporting flexible energy storage devices.

[0025] 6. The superhydrophilic PAN-based carbon nanofibers prepared by this invention, as electrode materials for self-supporting supercapacitors, have high specific capacitance and excellent rate performance.

[0026] 7. The superhydrophilic PAN-based carbon nanofibers prepared by this invention have the characteristics of strong hydrophilicity, good conductive network, simple preparation process and excellent electrochemical performance. When applied to the electrodes of self-supporting flexible supercapacitors, they can significantly improve the capacitance performance of the capacitor. This invention successfully solves the problem of poor electrochemical performance caused by insufficient surface hydrophilicity of traditional electrospun PAN-based carbon nanofiber flexible electrode materials, and provides a new approach for the research and development of high-performance self-supporting flexible electrode materials. Attached Figure Description

[0027] Figure 1 Scanning electron microscope (SEM) images (left) and optical micrographs (right) of carbon nanofibers in Examples 1-2; Figure 2 XPS full spectrum (left) and elemental content distribution (right) of carbon nanofibers in Example 2 and Comparative Example 2; Figure 3 A comparison diagram of the contact angles of carbon nanofibers in Examples 1-2 and Comparative Examples 1-2; Figure 4 The images show the cyclic voltammetry curves (left) and constant current charge-discharge curves (right) of carbon nanofibers at different scan rates and current densities, respectively, for Example 1. Figure 5 The cyclic voltammetry curves (left) and constant current charge-discharge curves (right) of carbon nanofibers in Examples 1-2 and Comparative Examples 1-2 at the same scan rate are shown. Detailed Implementation

[0028] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0029] The preparation method of superhydrophilic PAN-based carbon nanofibers specifically includes the following steps: (1) Preparation of precursor solution Weigh 1.4 g PAN and 50 mg KI, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, superhydrophilic PAN-based carbon nanofibers were obtained. Example 2

[0030] The preparation method of superhydrophilic PAN-based carbon nanofibers differs from that of Example 1 only in that 0.7 g of PAN, 0.7 g of cellulose acetate, and 50 mg of KI are weighed in step (1). The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 0.7 g PAN, 0.7 g cellulose acetate and 50 mg KI, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, superhydrophilic PAN-based carbon nanofibers were obtained. Example 3

[0031] The preparation method of superhydrophilic PAN-based carbon nanofibers differs from that of Example 1 only in step (1) where 0.7 g of PAN, 0.7 g of cellulose acetate, and 25 mg of KI are weighed. The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 0.7 g PAN, 0.7 g cellulose acetate and 25 mg KI, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, superhydrophilic PAN-based carbon nanofibers were obtained. Example 4

[0032] The preparation method of superhydrophilic PAN-based carbon nanofibers differs from that of Example 1 only in that 0.7 g of PAN, 0.7 g of cellulose acetate, and 35 mg of KI are weighed in step (1). The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 0.7 g PAN, 0.7 g cellulose acetate and 35 mg KI, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, superhydrophilic PAN-based carbon nanofibers were obtained. Example 5

[0033] The preparation method of superhydrophilic PAN-based carbon nanofibers differs from that of Example 1 only in that 0.7 g of PAN, 0.7 g of cellulose acetate, and 75 mg of KI are weighed in step (1). The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 0.7 g PAN, 0.7 g cellulose acetate and 75 mg KI, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, superhydrophilic PAN-based carbon nanofibers were obtained. Comparative Example 1

[0034] The preparation method of hydrophilic unmodified PAN-based solid carbon nanofibers differs from Example 1 only in that 1.4 g of PAN is weighed in step (1), and KI is not added. The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 1.4 g PAN and place it in 10 mL of N,N-dimethylformamide solution. Stir magnetically for 12 h at room temperature (25℃) to fully dissolve and obtain the precursor solution. (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min in air and held for 1 h. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, hydrophilic unmodified PAN-based solid carbon nanofibers were obtained. Comparative Example 2

[0035] The preparation method of hydrophilic unmodified PAN-based hollow carbon nanofibers differs from Example 1 only in that 0.7 g of PAN and 0.7 g of cellulose acetate are weighed in step (1), and KI is not added. The rest is the same as in Example 1, specifically including the following steps: (1) Preparation of precursor solution Weigh 0.7 g PAN and 0.7 g cellulose acetate, place them in 10 mL N,N dimethylformamide solution, and stir magnetically for 12 h at room temperature (25℃) to fully dissolve them and obtain the precursor solution; (2) Electrospinning The positive electrode voltage was set to 17 kV, the negative electrode voltage to -2 kV, the distance between the syringe nozzle and the receiving plate to 18 cm, and the solution flow rate to 8 μL / min. The precursor solution was spun by electrospinning to obtain a polymer nanofiber membrane. (3) High-temperature carbonization The polymer nanofiber membrane was placed in a tube furnace for pre-oxidation. The temperature was increased to 240°C at a rate of 1°C / min and held for 1 h in an air atmosphere. Then, nitrogen gas was introduced for high-temperature carbonization. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 h. After cooling to room temperature, hydrophilic unmodified PAN-based hollow carbon nanofibers were obtained. Performance testing

[0036] 1. Morphological characteristics The superhydrophilic PAN-based carbon nanofibers prepared in Examples 1-2 were subjected to scanning electron microscopy (SEM) to obtain SEM images, see [link to SEM]. Figure 1 (Left).

[0037] Bending tests on the superhydrophilic PAN-based carbon nanofibers prepared in Examples 1-2 showed that they exhibited good flexibility. (See [link to relevant documentation]). Figure 1 (right).

[0038] Depend on Figure 1 It can be seen that Examples 1-2 still maintain an ultra-long fiber structure, with relatively uniform fiber diameter and good mechanical flexibility.

[0039] 2. X-ray photoelectron spectroscopy test X-ray photoelectron spectroscopy (XPS) was performed on the superhydrophilic PAN-based carbon nanofibers prepared in Example 2 and the unmodified hydrophilic PAN-based hollow carbon nanofibers prepared in Comparative Example 2. The elemental composition comparison before and after hydrophilic modification was obtained (see [reference]). Figure 2 .

[0040] Depend on Figure 2 It can be seen that, compared with Comparative Example 2, the oxygen-containing functional groups in Example 2 are significantly increased, which will effectively improve its hydrophilicity.

[0041] 3. Contact Angle Test Contact angle tests were performed on the superhydrophilic PAN-based carbon nanofibers prepared in Examples 1-2, the hydrophilic unmodified PAN-based solid carbon nanofibers prepared in Comparative Example 1, and the hydrophilic unmodified PAN-based hollow carbon nanofibers prepared in Comparative Example 2. Comparison charts of contact angles at 0 s, 3 s, and 7 s were obtained. (See attached chart). Figure 3 .

[0042] Depend on Figure 3It can be seen that, thanks to the contribution of KI to the oxygen-containing functional groups of PAN-based carbon fibers, the hydrophilicity of Examples 1-2 is significantly higher than that of Comparative Example 1.

[0043] 4. Electrochemical performance testing Electrochemical performance tests were conducted on the superhydrophilic PAN-based carbon nanofibers prepared in Examples 1-2, the hydrophilic unmodified PAN-based solid carbon nanofibers prepared in Comparative Example 1, and the hydrophilic unmodified PAN-based hollow carbon nanofibers prepared in Comparative Example 2. In a three-electrode system, the prepared materials were used as the working electrode, a platinum sheet as the counter electrode, mercury / mercuric oxide as the reference electrode, and 6 mol / L potassium hydroxide as the electrolyte. The tests were conducted in a voltage range of -1 to 0 V.

[0044] Example 1: Cyclic voltammetry curves of carbon nanofibers at different scan rates and constant current charge-discharge curves at different current densities are shown in the figure. Figure 4 For the cyclic voltammograms of carbon nanofibers in Examples 1-2 and Comparative Examples 1-2 at the same scan rate and the constant current charge-discharge curves at the same current density, please refer to [the provided text]. Figure 5 .

[0045] Depend on Figure 4-5 It can be seen that, based on the effective improvement in hydrophilicity, Examples 1-2 exhibit superior electrochemical performance compared to Comparative Examples 1-2.

[0046] The above experiments demonstrate that, compared to the carbon nanofibers prepared in the comparative examples, the present invention, based on KI, significantly enhances the hydrophilicity of PAN-based carbon fibers by increasing the content of oxygen-containing functional groups on the surface of PAN-based electrospun carbon nanofibers without compromising the basic structural properties of the material. Based on these characteristics, Examples 1-2 exhibit superior electrochemical performance compared to Comparative Examples 1-2.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing superhydrophilic PAN-based carbon nanofibers, characterized in that, Specifically, the following steps are included: (1) Preparation of precursor solution The PAN-based carbon precursor was mixed with KI and dissolved in N,N-dimethylformamide solution, and stirred until homogeneous to obtain the precursor solution. (2) Electrospinning The precursor solution was spun into polymer nanofiber membranes by electrospinning. (3) High-temperature carbonization The polymer nanofiber membrane was sequentially pre-oxidized, carbonized at high temperature, and cooled to obtain the superhydrophilic PAN-based carbon nanofiber.

2. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 1, characterized in that, In step (1), the PAN-based carbon precursor is a single PAN, a PAN / CA mixture, a PAN / PVP mixture, or a PAN / PMMA mixture.

3. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 2, characterized in that, When the PAN-based carbon precursor is a single PAN, the mass ratio of the single PAN to KI is (70~140):(1~10).

4. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 2, characterized in that, When the PAN-based carbon precursor is a PAN / CA mixture, the mass ratio of PAN to CA is (1~4):(1~4), and the mass ratio of PAN to KI is (70~140):(1~10).

5. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 1, characterized in that, In step (2), the positive electrode voltage of the electrospinning process is 10~20 kV, the negative electrode voltage is -1~-3 kV, the nozzle of the injection pump is 15~25 cm away from the receiving plate, and the solution flow rate is 4~20 µL / min.

6. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 1, characterized in that, In step (3), the pre-oxidation atmosphere is air, the heating rate is 1~10℃ / min, the temperature is 200~300℃, and the holding time is 1~3 h.

7. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 1, characterized in that, In step (3), the atmosphere for high-temperature carbonization is nitrogen or argon, the heating rate is 1~10℃ / min, the temperature is 700~1000℃, and the holding time is 1~3 h.

8. The method for preparing superhydrophilic PAN-based carbon nanofibers according to claim 1, characterized in that, In step (3), the cooling is performed to room temperature.

9. A superhydrophilic PAN-based carbon nanofiber prepared by the preparation method according to any one of claims 1 to 8.

10. The application of a superhydrophilic PAN-based carbon nanofiber prepared by any one of claims 1 to 8 in the preparation of self-supporting flexible electrode materials.

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