阅读说明：本技术 一种b掺杂vc纳米粒子催化剂的制备及其在合成氨中的应用 (Preparation of B-doped VC nano particle catalyst and application thereof in ammonia synthesis ) 是由 朱罕 文炎坤 陆双龙 段芳 杜明亮 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种B掺杂VC纳米粒子催化剂的制备及其在合成氨中的应用,属于复合材料制备领域。本发明利用静电纺丝法将硼源和钒源与超细纤维前驱体混合纺丝获得混合纳米纤维膜,然后经过预氧化和石墨化工艺制备得到一种B掺杂VC纳米粒子催化材料。本发明方法工艺简单、成本低廉,本发明在碳纳米纤维负载的B掺杂的VC纳米粒子上构建了V-C-B结构。V-C-B结构的构建可以引起电荷密度的重新分布,优化给电子效应,催化活性和选择性较高,可实现在中性条件下的高活性氮还原反应。(The invention discloses a preparation method of a B-doped VC (vitamin C) nanoparticle catalyst and application thereof in ammonia synthesis, belonging to the field of preparation of composite materials. According to the invention, a boron source, a vanadium source and a superfine fiber precursor are mixed and spun by using an electrostatic spinning method to obtain a mixed nanofiber membrane, and then the B-doped VC nano particle catalytic material is prepared by pre-oxidation and graphitization processes. The method has simple process and low cost, and the V-C-B structure is constructed on the B-doped VC nano particles loaded on the carbon nano fibers. The construction of the V-C-B structure can cause the redistribution of charge density, optimize electron-donating effect, have higher catalytic activity and selectivity and can realize high-activity nitrogen reduction reaction under neutral condition.)

1. A preparation method of a B-doped VC nano particle catalytic material is characterized by comprising the following steps:

(1) preparing a mixed nanofiber membrane containing a boron source and a vanadium source: adding a boron source and a vanadium source into the solution of the superfine fiber precursor, uniformly stirring, and then spinning by adopting an electrostatic spinning method to obtain a mixed nanofiber membrane;

(2) preparing a B-doped VC nanoparticle catalyst electrocatalytic nitrogen fixation material: calcining the mixed nanofiber membrane prepared in the step (1), heating to 230-280 ℃, preserving heat for 1-3 hours in the air atmosphere, pre-oxidizing, heating to 800-1000 ℃ in the inert gas atmosphere after heat preservation, preserving heat for 2-4 hours at 800-1000 ℃ for graphitization, and cooling under the protection of inert gas after heat preservation, thus obtaining the B-VC/CNFs catalytic material.

2. The preparation method according to claim 1, wherein in the step (1), the superfine fiber precursor comprises one or more of polyacrylonitrile, polyvinylpyrrolidone or polyvinyl alcohol.

3. The preparation method according to claim 2, wherein in the step (1), the concentration of the superfine fiber precursor solution is 12-15 wt%; the solvent of the solution of the superfine fiber precursor is N, N-dimethylformamide.

4. The production method according to any one of claims 1 to 3, wherein in the step (1), the boron source is one or both of boric acid and diboron trioxide; the vanadium source is one or two of vanadium chloride or vanadium acetylacetonate.

5. The production method according to claim 4, wherein the boron source and the vanadium source are added in an amount of 40 to 60% and 10 to 30%, respectively, based on the mass of the microfibrous precursor.

6. The method according to any one of claims 1 to 5, wherein in the step (1), the electrostatic spinning operation parameters are as follows: the spinning voltage is 5-40kV, the distance from the receiving device to the spinning needle is 15-30cm, and the solution flow rate is 0.10-0.60 mL/min.

7. The production method according to any one of claims 1 to 6, wherein in the step (2), the temperature increase rate is 5 to 10 ℃/min.

8. The B-doped VC nano particle catalyst material prepared by the preparation method according to any one of claims 1 to 7.

9. The preparation method of any one of claims 1 to 7 or the application of the B-doped VC nano particle catalyst material in electrocatalytic nitrogen fixation of claim 8.

10. An electrocatalytic nitrogen fixation method, wherein the B-doped VC nanoparticle catalyst material of claim 8 is used as an electrocatalyst.

Technical Field

The invention relates to a preparation method of a B-doped VC (vitamin C) nanoparticle catalyst and application thereof in ammonia synthesis, belonging to the field of preparation of composite materials.

Background

Ammonia is used as an important chemical raw material and an energy carrier, and is widely applied to fertilizer production and energy conversion. Currently, industrial synthesis of ammonia relies primarily on the haber process. The haber process requires pure hydrogen as a reactant and is carried out under high temperature and pressure conditions. The haber process also results in the emission of large amounts of greenhouse gases, which is inconsistent with the goal of carbon neutralization. Therefore, there is a need to develop efficient, mild and sustainable technologies for producing ammonia.

In recent years, the electrochemical nitrogen fixation reaction technology is considered to be a new method for synthesizing ammonia with great development prospect due to the advantages of low energy consumption, controllable reaction, environmental protection and the like. Because the nitrogen-nitrogen triple bond is very stable, the nitrogen adsorption capacity is weak, the intermediate generation energy is high, and the dynamic process of the electrochemical nitrogen reduction reaction is seriously hindered. During the electrochemical nitrogen reduction reaction, the hydrogen evolution reaction can also become a strong competitor of the electrochemical nitrogen reduction reaction, and the selectivity and the activity of the catalyst are further limited. Therefore, it is desirable to design an electrochemical nitrogen reduction catalyst with high selectivity and high activity.

Transition metal carbides, as an efficient electrocatalyst, have been widely used in the field of electrocatalysis due to their noble-metal-like electronic structure, high electrical conductivity and excellent stability. In nature, vanadium-based nitrogen fixation enzymes can achieve nitrogen fixation through multiple proton and electron transfer steps under ambient conditions. For this reason, scientists designed and synthesized vanadium carbide catalysts for artificial nitrogen fixation. However, the d-orbital of vanadium also participates in hydrogen evolution reactions, resulting in lower faradaic efficiency of electrochemical nitrogen reduction reactions. Therefore, it is necessary to adjust the electronic structure of vanadium carbide to obtain higher selectivity of the electrochemical nitrogen reduction reaction. The electronic structure of vanadium carbide is related to the interaction of the metal and carbon. The electron donor is introduced into the vanadium carbide matrix, so that the electronic configuration of the vanadium carbide matrix can be effectively adjusted, and the physicochemical property of the active center can be optimized. Recent studies have shown sp³Boron atoms hybridized and partially occupying the orbitals can serve as active sites for electrocatalytic nitrogen reduction. Nitrogen atoms are adsorbed on unoccupied orbitals of boron atoms, which are connectedThe charge transfer to nitrogen atom promotes the feedback of pi electrons. However, strong B-N bonds severely hinder N₂To NH₃And (5) converting the intermediate. Therefore, optimizing the degree of electron donating effect is critical to achieving excellent catalytic activity.

Disclosure of Invention

[ problem ] to

The invention aims to solve the technical problems of difficult preparation, low catalytic activity, poor selectivity and the like of the catalyst material for synthesizing ammonia in the prior art.

[ solution ]

The invention aims to provide a catalytic material capable of performing electrochemical nitrogen reduction reaction under a neutral condition.

In order to achieve the purpose, the specific technical scheme of the invention is as follows: a preparation method of a B-doped VC nano particle catalytic material comprises the following steps:

(1) preparing a mixed nanofiber membrane containing a boron source and a vanadium source: adding a boron source and a vanadium source into the solution of the superfine fiber precursor, uniformly stirring, and then spinning by adopting an electrostatic spinning method to obtain a mixed nanofiber membrane;

(2) preparing a B-doped VC nanoparticle catalyst electrocatalytic nitrogen fixation material: calcining the mixed nanofiber membrane prepared in the step (1), heating to 230-280 ℃, preserving heat for 1-3 hours in the air atmosphere, pre-oxidizing, heating to 800-1000 ℃ in the inert gas atmosphere after heat preservation, preserving heat for 2-4 hours at 800-1000 ℃ for graphitization, and cooling under the protection of inert gas after heat preservation, thus obtaining the B-VC/CNFs catalytic material.

In one embodiment of the invention, in the step (1), the superfine fiber precursor includes one or more of polyacrylonitrile, polyvinylpyrrolidone or polyvinyl alcohol.

In one embodiment of the present invention, in the step (1), the concentration of the microfiber precursor solution is 12 to 15 wt%.

In one embodiment of the present invention, in the step (1), the solvent of the solution of the microfiber precursor is N, N-dimethylformamide.

In one embodiment of the present invention, in step (1), the boron source is one or both of boric acid or diboron trioxide.

In one embodiment of the present invention, in step (1), the vanadium source is one or both of vanadium chloride and vanadium acetylacetonate.

In one embodiment of the present invention, the boron source and the vanadium source are added in an amount of 40 to 60% and 10 to 30%, respectively, based on the mass of the microfibrous precursor.

In one embodiment of the present invention, in the step (1), the stirring is preferably magnetic stirring.

In one embodiment of the present invention, in step (1), the operating parameters of the electrostatic spinning are: the spinning voltage is 5-40kV, the distance from the receiving device to the spinning needle is 15-30cm, and the solution flow rate is 0.10-0.60 mL/min.

In one embodiment of the present invention, in step (1), the operating parameters of the electrospinning are preferably: the spinning voltage is 10-30kV, the distance from the receiving device to the spinning needle is 15-20cm, and the solution flow rate is 0.20-0.40 mL/min.

In one embodiment of the invention, in the step (2), the mixed fiber membrane is placed in a corundum boat and placed in the middle of a tube furnace to be subjected to high-temperature carbonization operation.

In one embodiment of the invention, in the step (2), the temperature rise rate is 5-10 ℃/min, preferably one or more of 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min and 10 ℃/min, and more preferably 5 ℃/min.

In one embodiment of the present invention, in the step (2), the temperature of the pre-oxidation is preferably 230 ℃.

In one embodiment of the invention, the inert gas is argon.

The invention also provides the B-doped VC nano particle catalyst material prepared by the method.

The invention also provides the preparation method or the application of the preparation method in electrocatalysis nitrogen fixation of the B-doped VC nanoparticle catalyst material.

The invention also provides an electrocatalytic nitrogen fixation method, which adopts the B-doped VC nano particle catalyst material as an electrocatalyst.

Compared with the prior art, the invention has the following remarkable advantages:

(1) the invention constructs a V-C-B structure on the B-doped VC nano particles loaded by the carbon nano fibers. The construction of the V-C-B structure can cause the redistribution of charge density and optimize electron donating effect. B and V atoms with electron-lacking surfaces can be used as active sites of electrocatalytic nitrogen fixation to adjust the adsorption behavior of key intermediates, so that the energy barrier of the reaction is reduced, and the catalyst is endowed with excellent electrocatalytic nitrogen fixation performance.

(2) The invention develops a method for carrying out in-situ nano particle doping by using a one-dimensional carbon material as a nano reactor by taking an organic polymer as a carbon source. Meanwhile, the one-dimensional carbon nanofiber prepared by the electrostatic spinning method has a strong electronic coupling effect with the nano particles, and the catalytic activity and selectivity are further improved.

(3) The catalytic material prepared by the method can be used as an integrated electrode, and other conductive materials are not needed to be coated on the surface of the electrode; the catalytic material prepared by the invention has higher electro-catalytic activity and stability under neutral conditions.

Drawings

FIG. 1 is a microscopic morphology of the B-VC/CNFs electrode material prepared in example 1, wherein (a) a field emission electron microscope image of the B-VC/CNFs; (b) transmission electron micrographs of B-VC/CNFs; (c-d) high resolution transmission electron microscopy images of B-VC/CNFs.

FIG. 2X-ray diffraction patterns of the electrode materials of B-VC/CNFs and VC/CNFs prepared in example 1.

FIG. 3 at 0.5M K₂SO₄K in (1)₂SO₄In the solution, the solution is added with a solvent,faraday efficiencies and corresponding NH of electrode materials of B-VC/CNFs prepared in example 1 at different potentials₃And (4) a yield graph.

Detailed Description

The electrochemical performance test method of the electrode under the neutral condition comprises the following steps: electrochemical testing was performed using an H-cell at CHI660E electrochemical workstation with an electrolyte of 0.5M K₂SO₄Solution, a three electrode system was used during the test: the prepared electrode material is used as a working electrode, a platinum wire is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and the voltage ranges of electrocatalytic nitrogen fixation (NRR) tests are respectively-0.8V to-1.4V. During the test, high-purity nitrogen is continuously introduced into the anode chamber and the cathode chamber of the H-shaped electrolytic cell. After a long-time constant voltage test, the electrolyte is collected, and an indophenol blue test method is used for carrying out an ultraviolet test on the electrolyte. By comparing with a standard curve, the Faraday efficiency and NH of the catalyst are calculated₃Yield.

The present invention is further described below with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

The invention relates to a preparation method of a B-doped VC nano particle catalyst material, which comprises the following steps:

(1) adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12 wt%, adding 0.5g of vanadium acetylacetonate and 1g of boric acid into 15g of polyacrylonitrile/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance from a spinning needle to a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 230 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, after the pre-oxidation is finished, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 2 hours, carrying out graphitization (under an argon atmosphere, the same is applied below), forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in the calcining process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

FIG. 1 is a microscopic morphology of B-VC/CNFs electrode material, wherein FIG. 1a is a scanning electron microscope image of B-VC/CNFs carbonized at 900 ℃, from which it can be seen that a one-dimensional carbon nanofiber weaves a three-dimensional network and the surface of the carbon nanofiber is rough. FIG. 1B is a transmission electron micrograph of B-VC/CNFs after 900 ℃ carbonization, from which it can be seen that uniform nanocrystals are distributed on the surface of the carbon nanofibers. The size of the nanocrystals is about 5-10nm as can be seen by the high resolution transmission electron micrographs of FIGS. 1 c-d.

FIG. 2 is a powder X-ray diffraction pattern of B-VC/CNFs and VC/CNFs, and it can be seen that the diffraction peak of VC is consistent with that of (JCPDS No.73-0476) standard card, which illustrates that the nanocrystals above B-VC/CNFs and VC/CNFs consist of VC phase. And when B is introduced into the VC matrix, the phase composition of VC is not changed.

FIG. 3 is a graph at 0.5M K₂SO₄In solution, the Faraday efficiency and corresponding NH of the electrode material of B-VC/CNFs under different potentials₃And (4) a yield graph. It can be seen that the faradaic efficiency and corresponding NH of the electrode materials of B-VC/CNFs increases with increasing voltage₃The yield shows a tendency to increase first and then decrease. Wherein, at-0.6V vs RHE, NH of the B-VC/CNFs electrode material₃The Faraday efficiency and yield of (1, 46, 443) mu mol h are the highest^-1cm^-2. The B-VC/CNFs electro-catalytic material prepared by the invention can carry out electro-catalytic nitrogen fixation reaction under neutral condition, and has higher catalytic activity and selectivity.

Example 2

(1) Adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium acetylacetonate and 1g of boric acid into 15g of polyacrylonitrile/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance between a spinning needle and a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 230 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 800 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

The B-VC/CNFs electro-catalytic material prepared in the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and the catalytic activity and selectivity are similar to those of the B-VC/CNFs electro-catalytic material prepared in the embodiment 1.

Example 3

(1) Adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium acetylacetonate and 1g of boric acid into 15g of polyacrylonitrile/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance between a spinning needle and a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 230 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 1000 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

The B-VC/CNFs electro-catalytic material prepared in the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and the catalytic activity and selectivity are similar to those of the B-VC/CNFs electro-catalytic material prepared in the embodiment 1.

Example 4

(1) Adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium acetylacetonate and 1g of boric acid into 15g of polyacrylonitrile/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance between a spinning needle and a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 280 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 900 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

The B-VC/CNFs electro-catalytic material prepared in the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and the catalytic activity and selectivity are similar to those of the B-VC/CNFs electro-catalytic material prepared in the embodiment 1.

Example 5

(1) Adding organic high-molecular polyvinylpyrrolidone powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium chloride and 1g of boron trioxide into 15g of polyvinylpyrrolidone/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 25kV, controlling the distance between a spinning needle and a receiving device to be 20cm, controlling the solution flow rate to be 0.3mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 280 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 900 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

The B-VC/CNFs electro-catalytic material prepared in the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and the catalytic activity and selectivity are similar to those of the B-VC/CNFs electro-catalytic material prepared in the embodiment 1.

Example 6

(1) Adding organic polymer polyvinyl alcohol powder into a solvent of N, N-dimethylformamide and deionized water to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium acetylacetonate and 1g of boron trioxide into 15g of a polyvinyl alcohol/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance from a spinning needle to a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 280 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 900 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a carbon nanofiber loaded B-doped VC nanoparticle catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the obtained B-VC/CNFs catalytic material.

The B-VC/CNFs electro-catalytic material prepared in the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and the catalytic activity and selectivity are similar to those of the B-VC/CNFs electro-catalytic material prepared in the embodiment 1.

Comparative example 1

(1) Adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 0.5g of vanadium acetylacetonate into 15g of 12 wt% polyacrylonitrile/N, N-dimethylformamide solution, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance from a spinning needle head to a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 230 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, after the pre-oxidation is finished, heating to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 2 hours, carrying out graphitization, forming a VC nano particle catalyst material loaded by carbon nanofibers in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the VC/CNFs catalytic material.

The VC/CNFs electro-catalytic material prepared by the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and has higher catalytic activity and selectivity. NH of VC/CNFs electrode material at-0.6V vs RHE₃The faradaic efficiency and yield of up to 2.1% and 0.015. mu. mol h^-1cm^-2。

Comparative example 2

(1) Adding organic polymer polyacrylonitrile powder into an N, N-dimethylformamide solvent to prepare a spinning solution with the mass concentration of 12%, adding 1g of boric acid into 15g of polyacrylonitrile/N, N-dimethylformamide solution with the mass fraction of 12 wt%, magnetically stirring for 6 hours to obtain a uniformly mixed solution, spinning the solution by adopting an electrostatic spinning method, controlling the spinning voltage range to be 16kV, controlling the distance from a spinning needle to a receiving device to be 16cm, controlling the solution flow rate to be 0.2mL/min, and continuously spinning for 15 hours to obtain a precursor mixed nanofiber membrane;

(2) and (2) putting 0.2g of the mixed nanofiber membrane prepared in the step (1) into a corundum boat, placing the corundum boat in the middle of a tubular furnace of a chemical vapor deposition system, heating to 230 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours in an air atmosphere, carrying out pre-oxidation, heating to 900 ℃ at a heating rate of 5 ℃/min after the pre-oxidation is finished, preserving heat for 2 hours, carrying out graphitization, forming a B-doped carbon nanofiber catalyst material in situ in a calcination process, and cooling to normal temperature under the protection of argon after the heat preservation is finished, thus preparing the B/CNFs catalytic material.

The B/CNFs electro-catalytic material prepared by the embodiment can also carry out electro-catalytic nitrogen fixation reaction under a neutral condition, and has high catalytic activity and selectivity. NH of B/CNFs electrode material at-0.7V vs RHE₃The Faraday efficiency and yield of the method reach 8.4 percent and 0.062 mu mol h at most^-1cm^-2。

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.