A nickel cobalt nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure and a preparation method and application thereof

Abstract

The application discloses a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure and a preparation method thereof, and belongs to the technical field of energy materials. The method comprises the following steps: firstly, preparing Ni-Co-ZIF crystals with uniform particle sizes; then, adding polyvinylpyrrolidone spinning solution; and finally, preparing the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure through micro-flow spinning and high-temperature carbonization. The composite catalyst is a micron-level fiber membrane, which is composed of a carbon fiber substrate with a porous structure on the surface and nickel-cobalt-nitrogen co-doped carbon, wherein the nickel-cobalt-nitrogen co-doped carbon is uniformly embedded on the carbon fiber. The material has high electrocatalytic activity for oxygen evolution reaction in an alkaline medium, and the performance is superior to that of commercial RuO2.

Description

Technical Field

[0001] This invention relates to the field of energy materials technology, specifically to a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure and its preparation method. Background Technology

[0002] The escalating global energy shortage and environmental pollution have drawn widespread public attention. To meet the ever-growing energy demands, seeking sustainable, clean, and efficient new energy production methods is crucial. Water electrolysis, as an efficient and pollution-free sustainable hydrogen production pathway, is considered one of the most promising methods for the production, storage, and use of renewable energy. However, its anodic oxygen evolution reaction kinetics are slow, and the reaction barrier is large, resulting in an overpotential much higher than the theoretical decomposition voltage of water. Therefore, the development of highly efficient oxygen evolution electrocatalysts is urgently needed. Currently, the most effective oxygen evolution reaction catalysts are noble metal catalysts IrO2 and RuO2, but their scarcity, high cost, and poor electrochemical stability severely hinder their large-scale commercial application.

[0003] In recent years, transition metal-based electrocatalysts have been considered a new generation of high-performance oxygen evolution electrocatalysts due to their low cost and high intrinsic activity. Among them, zeolite imidazole ester framework (ZIFs) containing abundant carbon and nitrogen ligands and high transition metal ion content can be transformed into nitrogen-doped transition metal-based carbon materials through high-temperature pyrolysis. These carbon materials possess a unique hierarchical porous structure, which increases the specific surface area and thus enhances the electrocatalytic activity. Nevertheless, pure ZIF-derived materials still suffer from poor conductivity, poor stability, and slow mass transfer rates during electrochemical reactions. Carbon fibers, with their unique one-dimensional structure, are well-known for their high conductivity and stability, and are often used in composites with other materials for widespread application in catalysis. Therefore, the composite of ZIF-derived materials and carbon fibers can significantly enhance the conductivity of the material, and the highly graphitized carbon fiber structure can effectively suppress the shedding of metal particles during the catalytic reaction, thereby improving the catalytic stability of the material.

[0004] The present invention aims to provide a highly active nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst and its preparation method. This catalyst has a parallel array structure and exhibits excellent electrocatalytic activity for oxygen evolution. Forming the material into a parallel array structure not only promotes the directional transfer of ions and charges, improving the mass transfer rate of the composite catalyst, but also promotes electrolyte permeation and the release of post-reaction gases, further improving the electrocatalytic performance for oxygen evolution. Therefore, this invention proposes to composite Ni-Co-ZIF with PVP fibers and prepare a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite material with a parallel array structure based on microfluidic spinning technology. This composite catalyst exhibits electrocatalytic performance exceeding that of commercially available ruthenium oxide in the oxygen evolution reaction. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure, comprising the following steps:

[0007] (1) Preparation of Ni-Co-ZIF crystals: Cobalt acetate tetrahydrate (Co(CH3COO)2·4H2O) and nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O) were dissolved in ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; dimethylimidazolium (2-MIM) was dissolved in ethanol to obtain an ethanol solution of 2-MIM; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-MIM, stirred, oil bath, centrifuged, washed and vacuum dried to obtain Ni-Co-ZIF crystals.

[0008] (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: A small amount of PVP was dissolved in N,N-dimethylformamide (DMF) solution, and Ni-Co-ZIF crystals obtained in step (1) were added. The mixture was ultrasonically dispersed evenly, and an appropriate amount of PVP was added again and stirred to obtain a uniformly dispersed spinning solution. Then, the spinning solution was subjected to microfluidic spinning to prepare Ni-Co-ZIF / PVP fiber precursor.

[0009] (3) Preparation of composite catalyst of nickel cobalt nitrogen co-doped carbon / carbon fiber: The Ni-Co-ZIF / PVP fiber precursor obtained in step (2) was pre-oxidized in a muffle furnace and then carbonized at high temperature in a tube furnace under argon atmosphere to obtain a nickel cobalt nitrogen co-doped carbon / carbon fiber electrocatalyst with parallel array structure.

[0010] In step (2), the working principle of the microfluidic spinning machine is as follows: the spinning solution is brought into perpendicular contact with the receiver by the gravity of the droplets, and then the fibers are wound around the receiver by the traction effect brought by the rotation of the receiver motor. At the same time, the movement of the stepper motor drives the needle to move back and forth, so that the fibers are collected in an orderly manner on the receiver, forming a continuous microfiber with a parallel array structure. Due to the effect of gravity, all the collected fibers are vertically downward, thus forming a parallel and orderly fiber structure.

[0011] Furthermore, in steps (1), (2), and (3), Ni-Co-ZIF can also be Zn-Ni-Co-ZIF.

[0012] Furthermore, in step (1), the stirring time is 1~6 h, the oil bath temperature is 60~80℃, the oil bath time is 5~8 h, the centrifugal cleaning reagent is anhydrous ethanol and DMF, the molar ratio of cobalt acetate tetrahydrate and nickel acetate tetrahydrate is (1:2)~(2:1), and the molar ratio of the metal salt (Co(CH3COO)2·4H2O and Ni(CH3COO)2·4H2O) to 2-methylimidazole is 3:8.

[0013] Furthermore, in step (2), the microfluidic spinning machine consists of a microfluidic pump, a spinning receiver, a temperature and humidity control system, a control system, a motor, and a worktable. The parameters of the temperature and humidity control system are: temperature 20-40℃, humidity 10-30%, the parameters of the microfluidic pump are: needle push speed 0.02-0.08mL / h, needle size 20-24, the rotation speed of the receiver motor is 100-800r / min, the receiving distance between the needle and the receiver is 1-10mm, and the frequency of the stepper motor is 1000-3000Hz.

[0014] Furthermore, in step (2), the mass ratio of Ni-Co-ZIF to PVP is between (1:5) and (2:1), and the mass of PVP added for the first time is 10% to 30% of the total mass of PVP; in the spinning solution, each 1g of PVP needs to be dissolved in 3 to 5ml of DMF; the ultrasonic time is 0.5 to 5h.

[0015] Furthermore, in step (3), the pre-oxidation process is to raise the temperature to 120~180℃ at a heating rate of 1~2℃ / min, hold for 1~5h, and then raise the temperature to 220℃~280℃ at a heating rate of 1~3℃ / min, hold for 1~5h. The specific process of high-temperature carbonization is to raise the temperature to 700℃~1000℃ at a heating rate of 1~10℃ / min and hold for 1~5h. The inert gas atmosphere in the tube furnace can be high-purity argon, high-purity nitrogen or other high-purity inert gases.

[0016] This invention discloses a composite catalyst of nickel-cobalt-nitrogen co-doped carbon / carbon fiber with a parallel array structure. The composite catalyst is composed of a porous carbon fiber matrix and nickel-cobalt-nitrogen co-doped carbon in the form of micron-sized fibers, wherein the nickel-cobalt-nitrogen co-doped carbon is uniformly embedded on the carbon fiber. The diameter of the nickel-cobalt-nitrogen co-doped carbon is 0.8~1.8μm, and the diameter of the carbon fiber is 0.8~2μm. Preferably, the diameter of the nickel-cobalt-nitrogen co-doped carbon is 0.8~1.5μm, and the diameter of the carbon fiber is 1~2μm.

[0017] This invention also discloses a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure for use in oxygen evolution and hydrogen evolution reactions in alkaline media.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention provides a method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite catalyst with a parallel array structure. The method employs microfluidic spinning technology to prepare uniformly dispersed Ni-Co-ZIF PVP fibers with a parallel array structure. After high-temperature carbonization, the resulting nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite catalyst with a parallel array structure is obtained. Compared to the disordered fiber composite catalysts prepared by electrospinning, the composite catalyst prepared by this method grows uniformly along the same direction, exhibiting extremely high orientation, effectively accelerating charge transfer, and exposing more active sites, thereby improving the electrocatalytic activity of the catalyst.

[0020] The composite catalyst prepared by the method provided in this invention has the following characteristics: (1) Compared with disordered structures, highly oriented parallel array structure fibers can promote directional charge transfer and improve charge transfer efficiency. (2) The ordered fiber structure is more conducive to electrolyte penetration and gas release after reaction, thereby exposing more active sites. In addition, the unique pore structure of carbon fibers and the porous structure of ZIFs derivatives also greatly increase the specific surface area and the number of exposed active sites. (3) The highly graphitized fiber structure can effectively reduce the migration and shedding of metal particles in electrochemical tests and improve the stability of the catalyst.

[0021] The composite catalyst prepared in this invention and a commercial RuO2 catalyst were compared in an alkaline medium to assess their electrocatalytic performance in oxygen evolution. (See attached figure.) Figure 4 The composite catalyst prepared in this invention operates at 100 mA / cm². 2 The corresponding overpotential is lower than that of disordered nickel-cobalt-nitrogen co-doped carbon / carbon fiber and commercial RuO2, demonstrating that the catalyst prepared in this invention has excellent electrocatalytic performance. Attached Figure Description

[0022] Figure 1This is a schematic diagram of a microfluidic spinning machine. 1. Temperature and humidity control system; 2. Injector; 3. Multi-axis worktable; 4. Needle; 5. Motor; 6. Roller receiver; 7. Stepper motor control system; 8. Constant temperature and humidity control system; 9. Microfluidic pump control system; 10. Motor control system.

[0023] Figure 2 The XRD pattern of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a parallel array structure prepared in Example 1;

[0024] Figure 3 The image shows the SEM image of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a parallel array structure prepared in Example 1.

[0025] Figure 4 The linear sweep voltammetry curves of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a parallel array structure prepared in Example 1, and those of disordered nickel-cobalt-nitrogen co-doped carbon / carbon fiber and commercial RuO2 in alkaline medium are shown. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0027] This invention discloses a composite catalyst of nickel-cobalt-nitrogen co-doped carbon / carbon fiber with a parallel array structure. The composite catalyst is composed of a porous carbon fiber matrix and nickel-cobalt-nitrogen co-doped carbon in the form of micron-sized fibers, wherein the nickel-cobalt-nitrogen co-doped carbon is uniformly embedded on the carbon fiber; the diameter of the nickel-cobalt-nitrogen co-doped carbon is 0.8~1.8μm, and the diameter of the carbon fiber is 0.8~2μm.

[0028] The nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure disclosed in this invention is applied to oxygen evolution and hydrogen evolution reactions in alkaline media.

[0029] A method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure, comprising the following steps:

[0030] (1) Preparation of Ni-Co-ZIF crystals: Co(CH3COO)2·4H2O and Ni(CH3COO)2·4H2O were dissolved in ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; 2-MIM was dissolved in ethanol to obtain an ethanol solution of 2-MIM; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-MIM, stirred, oil bath, centrifuged, washed and vacuum dried to obtain Ni-Co-ZIF crystals;

[0031] (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: Dissolve a small amount of PVP in DMF solution, add Ni-Co-ZIF crystals obtained in step (1), and ultrasonically disperse evenly. Add an appropriate amount of PVP again and stir to obtain a uniformly dispersed spinning solution. Select a suitable needle type, adjust the appropriate temperature, humidity and other environmental factors through the temperature and humidity control system, and set appropriate parameters such as rotation speed, injection speed and step rate. Inject the spinning solution into the syringe and use a microfluidic spinning machine to perform microfluidic spinning to obtain Ni-Co-ZIF / PVP fiber precursor with parallel array structure.

[0032] (3) Preparation of nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite catalyst: The Ni-Co-ZIF / PVP fiber precursor obtained in step (2) was pre-oxidized in a muffle furnace and then carbonized at high temperature in a tube furnace under an argon atmosphere to obtain a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure.

[0033] In step (1), Ni-Co-ZIF can also be Co-ZIF; the molar ratio of cobalt acetate tetrahydrate and nickel acetate tetrahydrate is (1:2) to (2:1), and the molar ratio of the metal salt (Co(CH3COO)2·4H2O and Ni(CH3COO)2·4H2O) to 2-methylimidazole is 3:8.

[0034] In step (2), the mass ratio of Ni-Co-ZIF to PVP is between (1:5) and (2:1), and the mass of PVP added for the first time is 10% to 30% of the total mass of PVP; each 1g of PVP needs to be dissolved in 3 to 5ml of DMF.

[0035] In step (3), the pre-oxidation process involves heating to 120-180℃ at a heating rate of 1-2℃ / min, holding for 1-5 hours, and then heating to 220-280℃ at a heating rate of 1-3℃ / min, holding for 1-5 hours; the high-temperature carbonization process involves heating to 700-1000℃ at a heating rate of 1-10℃ / min and holding for 1-5 hours.

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0037] Example 1

[0038] The steps for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a Co:Ni molar ratio of 2:1 and a parallel array structure are as follows:

[0039] (1) Preparation of Ni-Co-ZIF crystals: 3984 mg (16 mmol) of Co(CH3COO)2·4H2O and 1992 mg (8 mmol) of Ni(CH3COO)2·4H2O were dissolved in 180 mL of ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; 5248 mg (64 mmol) of 2-MIM was dissolved in 20 mL of ethanol to obtain an ethanol solution of 2-MIM; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-MIM, stirred for 1 h, and then heated at 80 °C. o Ni-Co-ZIF crystals were obtained by oil bath for 5 hours, centrifugation, washing, and vacuum drying.

[0040] (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: Dissolve 0.8g PVP in 10mL LMF solution, add 0.8g Ni-Co-ZIF crystal from step (1), sonicate for 2h, then add 1.2g PVP and stir for 12h to obtain a uniformly dispersed spinning solution. Set temperature and humidity control parameters: temperature 30℃, humidity 20% and other environmental factors. Set microfluidic pump parameters: select a No. 21 needle, needle injection speed 0.3mL / h, set receiver motor speed 200r / min, stepper motor frequency 2000Hz, and receiving distance between needle and receiver 5mm. Inject the spinning solution into the syringe and use a microfluidic spinning machine to perform microfluidic spinning to obtain a Ni-Co-ZIF / PVP fiber precursor with a parallel array structure.

[0041] (3) Preparation of nickel cobalt nitrogen co-doped carbon / carbon fiber composite catalyst: The precursor obtained in step (2) was placed in a muffle furnace and heated to 150°C at a rate of 1°C / min and held for 1 h. Then it was pre-oxidized and heated to 250°C at a rate of 1°C / min and held for 1 h. Then it was carbonized at 800°C at a rate of 3°C / min in a tube furnace under argon atmosphere for 2 h. After that, it was cooled with the furnace to obtain a nickel cobalt nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure.

[0042] Figure 1 This is a schematic diagram of the microfluidic spinning machine used in this embodiment.

[0043] Figure 2 The image shows the XRD pattern of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array prepared in Example 1. As can be seen from the image, the cobalt and nickel elements doped in the composite catalyst disclosed in this invention exist in the form of a CoNi alloy.

[0044] Figure 3 The image shows the SEM image of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a parallel array structure prepared in Example 1. As can be seen from the image, the micron fiber membrane has high orientation, with all fibers arranged in parallel along the same direction. The diameter of a single fiber is 1~2μm, and the nickel-cobalt-nitrogen co-doped carbon is uniformly distributed on the fiber with a diameter of 0.8~1.5μm.

[0045] The composite catalyst prepared in this embodiment and the commercial RuO2 catalyst were respectively placed in an alkaline medium for oxygen evolution reaction testing. The obtained linear sweep voltammetric curves are shown below. Figure 4 As shown, the electrolyte solution was 1.0 M KOH; the scanning voltage was 1.0 V to 2.0 V. The figure shows that the composite catalyst prepared in this invention has a flux of 100 mA / cm². 2 The overpotential corresponding to the current density is superior to that of disordered nickel-cobalt-nitrogen co-doped carbon / carbon fiber and commercial RuO2, indicating that the composite catalyst prepared in this invention has excellent electrocatalytic activity in alkaline media.

[0046] Example 2

[0047] The steps for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a Co:Ni molar ratio of 1:1 and a parallel array structure are as follows:

[0048] (1) Preparation of Ni-Co-ZIF crystals: 2988 mg (12 mmol) of Co(CH3COO)2·4H2O and 2988 mg (12 mmol) of Ni(CH3COO)2·4H2O were dissolved in 180 mL of ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; 5248 mg (64 mmol) of 2-MIM was dissolved in 20 mL of ethanol to obtain an ethanol solution of 2-MIM; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-MIM, stirred for 1 h, and then heated at 80 °C. o Ni-Co-ZIF crystals were obtained by oil bath for 5 hours, centrifugation, washing, and vacuum drying.

[0049] (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: Dissolve 0.8g PVP in 10mL LMF solution, add 0.8g Ni-Co-ZIF crystal from step (1), sonicate for 2h, then add 1.2g PVP and stir for 12h to obtain a uniformly dispersed spinning solution. Set temperature and humidity control parameters: temperature 30℃, humidity 20% and other environmental factors. Set microfluidic pump parameters: select a No. 21 needle, needle injection speed 0.3mL / h, set receiver motor speed 200r / min, stepper motor frequency 2000Hz, and receiving distance between needle and receiver 5mm. Inject the spinning solution into the syringe and use a microfluidic spinning machine to perform microfluidic spinning to obtain a parallel array structure Ni-Co-ZIF / PVP fiber precursor.

[0050] (3) Preparation of nickel cobalt nitrogen co-doped carbon / carbon fiber composite catalyst: The fiber precursor obtained in step (2) was placed in a muffle furnace and heated to 150°C at a rate of 1°C / min and held for 1 h. Then it was pre-oxidized and heated to 250°C at a rate of 1°C / min and held for 1 h. Then it was carbonized at 800°C at a rate of 3°C / min in a tube furnace under argon atmosphere for 2 h. After that, it was cooled with the furnace to obtain a nickel cobalt nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure.

[0051] Example 3

[0052] The steps for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber electrocatalyst with a Co:Ni molar ratio of 1:2 and a parallel array structure are as follows:

[0053] (1) Preparation of Ni-Co-ZIF crystals: 1992 mg (8 mmol) of Co(CH3COO)2·4H2O and 3984 mg (16 mmol) of Ni(CH3COO)2·4H2O were dissolved in 180 mL of ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; 5248 mg (64 mmol) of 2-MIM was dissolved in 20 mL of ethanol to obtain an ethanol solution of 2-MIM; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-MIM, stirred for 1 h, and then heated at 80 °C. o Ni-Co-ZIF crystals were obtained by oil bath for 5 hours, centrifugation, washing, and vacuum drying.

[0054] (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: Dissolve 0.8g PVP in 10mL LMF solution, add 0.8g Ni-Co-ZIF crystal from step (1), sonicate for 2h, then add 1.2g PVP and stir for 12h to obtain a uniformly dispersed spinning solution. Set temperature and humidity control parameters: temperature 30℃, humidity 20% and other environmental factors. Set microfluidic pump parameters: select a No. 21 needle, needle injection speed 0.3mL / h, set receiver motor speed 200r / min, stepper motor frequency 2000Hz, and receiving distance between needle and receiver 5mm. Inject the spinning solution into the syringe and use a microfluidic spinning machine to perform microfluidic spinning to obtain a parallel array structure Ni-Co-ZIF / PVP fiber precursor.

[0055] (3) Preparation of nickel cobalt nitrogen co-doped carbon / carbon fiber composite catalyst: The fiber precursor obtained in step (2) was placed in a muffle furnace and heated to 150°C at a rate of 1°C / min and held for 1 h. Then it was pre-oxidized and heated to 250°C at a rate of 1°C / min and held for 1 h. Then it was carbonized at 800°C at a rate of 3°C / min in a tube furnace under argon atmosphere for 2 h. After that, it was cooled with the furnace to obtain a nickel cobalt nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure.

[0056] The foregoing has provided a detailed description of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite catalyst with a parallel array structure and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these examples are merely illustrative of the methods and core ideas of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure, comprising the following steps: (1) Preparation of Ni-Co-ZIF crystals: Co(CH3COO)2·4H2O and Ni(CH3COO)2·4H2O were dissolved in ethanol to obtain an ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O; 2-methylimidazole was dissolved in ethanol to obtain an ethanol solution of 2-methylimidazole; the ethanol solution of Co(CH3COO)2·4H2O / Ni(CH3COO)2·4H2O was mixed with the ethanol solution of 2-methylimidazole, stirred, oil bath, centrifuged, washed and vacuum dried to obtain Ni-Co-ZIF crystals; (2) Preparation of Ni-Co-ZIF / PVP fiber precursor: Dissolve a small amount of PVP in DMF solution, add Ni-Co-ZIF crystals obtained in step (1), disperse evenly by ultrasonication, add an appropriate amount of PVP again and stir to obtain a uniformly dispersed spinning solution; then perform micro-flow spinning on the spinning solution to prepare Ni-Co-ZIF / PVP fiber precursor. (3) Preparation of nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst: The Ni-Co-ZIF / PVP fiber precursor obtained in step (2) was pre-oxidized in a muffle furnace and then carbonized at high temperature in a tube furnace under an argon atmosphere to obtain a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure.

2. The method for preparing the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure according to claim 1, characterized in that: In step (1), the stirring time is 1-6 h, the oil bath temperature is 60-80℃, the oil bath time is 5-8 h, the cleaning reagent is anhydrous ethanol and DMF, and the molar ratio of Co(CH3COO)2·4H2O to Ni(CH3COO)2·4H2O is (1:2) to (2:1).

3. The method for preparing the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure according to claim 1, characterized in that: The molar ratio of cobalt acetate tetrahydrate and nickel acetate tetrahydrate is (1:2) to (2:1), and the molar ratio of the sum of the amounts of Co(CH3COO)2·4H2O and Ni(CH3COO)2·4H2O to the amount of 2-methylimidazole is 3:

8.

4. The method for preparing the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure according to claim 1, characterized in that: In step (2), a microfluidic spinning machine is used to perform microfluidic spinning of the spinning solution: a suitable needle model is selected, and the appropriate temperature and humidity environmental factors are adjusted through the temperature and humidity control system. Appropriate rotation speed, injection speed, and stepping rate parameter values ​​are set. The spinning solution is injected into the syringe, and microfluidic spinning is performed using the microfluidic spinning machine. The microfluidic spinning machine consists of a microfluidic pump, a spinning receiver, a temperature and humidity control system, a control system, a motor, and a worktable. The parameters of the temperature and humidity control system are: temperature 20-40℃, humidity 10-50%, the parameters of the microfluidic pump are: needle push speed 0.02-0.08mL / h, needle model 20-24, the rotation speed of the receiver motor is 100-800r / min, the receiving distance between the needle and the receiver is 1-10mm, and the stepping motor frequency is 1000-3000Hz.

5. The method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure according to claim 1, characterized in that: In step (2), the total mass ratio of Ni-Co-ZIF to PVP is 1:5 to 2:1, the mass of PVP added for the first time is 10 to 30% of the total mass of PVP, and in the spinning solution, each 1g of PVP needs to be dissolved in 3 to 5mL of DMF, and the ultrasonic time is 0.5 to 5h.

6. The method for preparing a nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure according to claim 1, characterized in that: In step (3), the pre-oxidation process involves heating to 120-180°C at a heating rate of 1-2°C / min, holding for 1-5 hours, and then heating to 220-280°C at a heating rate of 1-3°C / min, holding for 1-5 hours. The specific high-temperature carbonization process involves heating to 700-1000°C at a heating rate of 1-10°C / min and holding for 1-5 hours. The inert gas atmosphere in the tube furnace is high-purity argon, high-purity nitrogen, or other high-purity inert gases.

7. The nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The composite electrocatalyst is composed of a carbon fiber matrix with a porous surface and nickel-cobalt-nitrogen co-doped carbon, which is uniformly embedded on the carbon fiber. The diameter of the nickel-cobalt-nitrogen co-doped carbon is 0.8~1.8μm, and the diameter of the carbon fiber is 0.8~2μm.

8. The application of the nickel-cobalt-nitrogen co-doped carbon / carbon fiber composite electrocatalyst with a parallel array structure as described in claim 7 in the oxygen evolution reaction in an alkaline medium.

Images