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CN110665526B - Nitrogen-sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof - Google Patents

Nitrogen-sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof Download PDF

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CN110665526B
CN110665526B CN201910850581.0A CN201910850581A CN110665526B CN 110665526 B CN110665526 B CN 110665526B CN 201910850581 A CN201910850581 A CN 201910850581A CN 110665526 B CN110665526 B CN 110665526B
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sulfur
carbon
nitrogen
hemispherical
based material
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CN110665526A (en
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王帅
张翔宇
肖菲
肖军武
池凯
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Huazhong University of Science and Technology
Shenzhen Huazhong University of Science and Technology Research Institute
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Shenzhen Huazhong University of Science and Technology Research Institute
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Abstract

The invention belongs to the field of synthesis of a carbon material doped with a hetero element and the field of electrocatalytic oxygen reduction, and particularly relates to a nitrogen-sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof. The invention provides a preparation method of a nitrogen-sulfur co-doped hollow hemispherical carbon-based material, which comprises the steps of obtaining hemispherical silica microspheres as a template by controlling the hydrolysis degree of tetraethoxysilane, carrying out polymerization of dopamine on the surface of the template, then carbonizing the obtained high polymer, removing the template, and finally doping sulfur in a gas phase to obtain the nitrogen-sulfur co-doped carbon-based material.

Description

Nitrogen-sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof
Technical Field
The invention belongs to the field of synthesis of a carbon material doped with a hetero element and the field of electrocatalytic oxygen reduction, and particularly relates to a nitrogen-sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof.
Background
The oxygen reduction reaction plays a crucial role in various energy conversion and storage systems, such as fuel cells and metal air cells. However, the slow kinetics of these days greatly limit the overall performance of these devices. To solve this problem, various catalysts have been widely studied. Up to now, the noble metal catalyst platinum still has an unfortunate position in the aspect of oxygen reduction performance. However, platinum-based materials are low in earth abundance and expensive. Therefore, metal-free carbon materials have been highly varied in recent years for the purpose of practical use, are inexpensive, and have good performance in electrocatalytic oxygen reduction.
Most of the prior art discloses nitrogen and sulfur doped spherical carbon-based materials or carbon nano-particle materials for oxygen reduction catalysts, however, the carbon materials have the defects of small specific surface area, incomplete reaction site exposure and the like, so that the oxygen reduction electrocatalytic performance of the carbon materials cannot achieve good effect.
Disclosure of Invention
In order to overcome the defects or the improvement requirements of the prior art, the invention provides a nitrogen and sulfur co-doped hollow hemispherical carbon-based material, and preparation and application thereof.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a method for preparing a nitrogen and sulfur co-doped hollow hemispherical carbon-based material, comprising the steps of:
(1) under the alkaline environment containing solvent, the ethyl orthosilicate is partially hydrolyzed to obtain a hemispherical silicon dioxide template;
(2) adding dopamine hydrochloride into the system of the hemispherical silicon dioxide template obtained in the step (1), so that dopamine hydrochloride is subjected to polymerization reaction on the inner surface and the outer surface of the hemispherical silicon dioxide template obtained by partial hydrolysis, performing solid-liquid separation after the reaction, and drying the obtained solid powder to obtain a dried sample;
(3) calcining the dried sample obtained in the step (2) in an inert atmosphere to carbonize a polymer obtained by polymerizing dopamine hydrochloride, so as to obtain a carbonized sample;
(4) removing the hemispherical silicon dioxide template from the carbonized sample by acid etching, washing, separating and drying to obtain a sample from which the hemispherical silicon dioxide template is removed;
(5) and (3) taking thiourea as a sulfur source, and doping sulfur element in the sample from which the hemispherical silicon dioxide template is removed by adopting a chemical vapor deposition method to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based material.
Preferably, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of the water to the ethanol is 1: 2-4.
Preferably, the alkaline environment is formed by adding ammonia water into the system in the step (1), wherein the volume ratio of the ammonia water to the solvent is 1: 10-15; the volume ratio of the ammonia water to the tetraethoxysilane is 1: 1-2.
Preferably, the dopamine hydrochloride is added in an amount of 200-600 g in 130ml of mixed solvent of water and ethanol.
Preferably, step (1) allows partial hydrolysis of the tetraethoxysilane for no more than 1 hour.
Preferably, the calcination temperature in the step (3) is 400-700 ℃, the flow rate of the inert atmosphere is 40-120 sccm, the temperature rise rate is 2-5 ℃/min, and the calcination time is 1-4 h.
Preferably, the acid of step (4) is hydrofluoric acid.
Preferably, in the chemical vapor deposition process in the step (5), the mass ratio of the sample from which the hemispherical silica template is removed to thiourea is 1: 200-800.
Preferably, the chemical vapor deposition is carried out in a tube furnace, the heating rate is 2-10 ℃/min, the heat preservation time is 1-4 h, and the annealing temperature is 600-1000 ℃.
According to another aspect of the invention, the nitrogen and sulfur co-doped hollow hemispherical carbon-based material prepared by the preparation method is provided.
According to another aspect of the present invention, there is provided a use of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material as an oxygen reduction catalyst.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) the invention provides a preparation method of a nitrogen-sulfur co-doped hollow hemispherical carbon-based material, which comprises the steps of obtaining hemispherical silica microspheres as a template by controlling the hydrolysis degree of tetraethoxysilane, carrying out polymerization of dopamine on the surface of the template, then carbonizing the obtained high polymer, removing the template, and finally doping sulfur in a gas phase to obtain the nitrogen-sulfur co-doped carbon-based material.
(2) The preparation method of the nitrogen-sulfur co-doped hollow hemispherical carbon-based material provided by the invention is simple and time-saving, the experimental conditions are mild, and the obtained material is uniform in appearance and easy to synthesize.
(3) The nitrogen-sulfur co-doped porous carbon prepared by the method well reduces the adsorption energy of oxygen and an active intermediate in the reaction process, and the excellent hollow hemispherical structure greatly promotes the exposure of the reactive active site and the contact of the active site and an electrolyte. The nitrogen and sulfur co-doped hollow hemispherical carbon-based material prepared by the invention can be applied to the field of electrocatalysis.
(4) The method successfully prepares the nitrogen-sulfur co-doped hollow hemispherical carbon-based catalyst by using dopamine as a carbon source and a nitrogen source, using silicon dioxide as a template, using ammonia water to provide an alkaline environment, and using thiourea as a nitrogen source and a sulfur source through polymerization of dopamine under an alkaline condition.
Drawings
Fig. 1 is a scanning electron micrograph of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material prepared in example 1.
Fig. 2 is a transmission electron micrograph of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material prepared in example 2.
Fig. 3 is a raman spectrum picture of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material prepared in example 3.
Fig. 4 is a picture of X-ray diffraction spectrum of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material of example 1.
Fig. 5 is a cyclic voltammogram of the nitrogen and sulfur co-doped hollow hemisphere carbon-based material prepared in example 1 under an oxygen atmosphere.
Fig. 6 is a polarization curve of the nitrogen and sulfur co-doped hollow hemisphere carbon-based material prepared in example 2 under an oxygen atmosphere.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a preparation method of a nitrogen and sulfur co-doped hollow hemispherical carbon-based material, which comprises the following steps:
(1) under the alkaline environment containing solvent, the ethyl orthosilicate is partially hydrolyzed to obtain a hemispherical silicon dioxide template;
(2) adding dopamine hydrochloride into the system of the hemispherical silicon dioxide template obtained in the step (1), so that dopamine hydrochloride is subjected to polymerization reaction on the inner surface and the outer surface of the hemispherical silicon dioxide template obtained by partial hydrolysis, performing solid-liquid separation after the reaction, and drying the obtained solid powder to obtain a dried sample;
(3) calcining the dried sample obtained in the step (2) in an inert atmosphere to carbonize a polymer obtained by polymerizing dopamine hydrochloride, so as to obtain a carbonized sample;
(4) removing the hemispherical silicon dioxide template from the carbonized sample by acid etching, washing, separating and drying to obtain a sample from which the hemispherical silicon dioxide template is removed;
(5) and (3) taking thiourea as a sulfur source, and doping sulfur element in the sample from which the hemispherical silicon dioxide template is removed by adopting a chemical vapor deposition method to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based material.
In some embodiments, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of the water to the ethanol is 1: 2-4. The solvent water and ethanol selected by the invention can control the hydrolysis rate of the tetraethoxysilane, thereby determining the size of the formed silicon dioxide microspheres; on the other hand, for the polymerization of dopamine hydrochloride in the step (2), water can well dissolve dopamine, but dopamine is polymerized in water too fast to be coated on the surface of silicon dioxide, and the polymerization speed of dopamine can be slowed down by adding ethanol. So that the coating can be well coated on the surface of the silicon dioxide.
In some embodiments, the alkaline environment is formed by adding ammonia water into the system in the step (1), wherein the volume ratio of the ammonia water to the solvent is 1: 10-15; the volume ratio of the ammonia water to the tetraethoxysilane is 1: 1-2.
In some embodiments, the dopamine hydrochloride is added in an amount of 200-600 g per 130ml of the solvent.
In some embodiments, step (1) partially hydrolyzes the tetraethoxysilane for no more than 1 hour. The step (1) of partial hydrolysis of the tetraethoxysilane refers to that the tetraethoxysilane is not completely reacted by controlling the time, and when the hydrolysis is not yet available to form complete spherical silicon dioxide, dopamine hydrochloride is added to enable the dopamine hydrochloride to be coated on the surface of the incomplete spherical silicon dioxide.
According to the invention, the hydrolysis degree of the silicon source is controlled to ensure that the obtained silicon dioxide microspheres do not form complete spheres, and the dopamine interacts with dopamine, so that the dopamine can be polymerized and deposited on the inner surface and the outer surface of the incomplete spherical silicon dioxide microspheres simultaneously to obtain the carbon material, and the obtained carbon material has the following advantages: 1. the obtained metal-free carbon catalyst has controllable specific surface area, and hemispheres with different specific surface areas can be obtained by controlling the polymerization time of the tetraethoxysilane. 2. The excellent hollow hemisphere structure greatly facilitates the exposure of the reactive active sites and the contact of the active sites with the electrolyte. 3. The nitrogen and sulfur co-doping well changes the electron cloud density of carbon in the carbon material, and the change well reduces the adsorption energy of oxygen and active intermediates in the reaction process, so that the oxygen reduction performance of the catalyst is greatly improved.
In some embodiments, the inert atmosphere in the step (3) is argon or nitrogen, the calcination temperature is 400-700 ℃, the flow rate of the inert atmosphere is 40-120 sccm, the temperature rise rate is 2-5 ℃/min, the calcination time is 1-4 h, and the purity of the inert gas is greater than 99.999%. In the step, the high molecular polymer obtained after dopamine polymerization is subjected to carbonization reaction, and the carbon material with improved conductivity and crystallinity compared with the high molecular polymer is obtained.
In some embodiments, the acid of step (4) is hydrofluoric acid. In some embodiments, the volume ratio of water to hydrofluoric acid in this step is 1: (1-5), the reaction time is 2-6 h, and the reaction temperature is 25-80 ℃. And etching to remove the hemispherical silicon dioxide template to obtain the hollow hemispherical carbon material.
In some embodiments, the mass ratio of the sample from which the hemispherical silica template is removed to thiourea in the chemical vapor deposition process in step (5) is 1: 200-800.
In some embodiments, the chemical vapor deposition is performed in a tube furnace, the temperature rise rate is 2-10 ℃/min, the heat preservation time is 1-4 h, and the annealing temperature is 600-1000 ℃.
The invention also provides the nitrogen-sulfur co-doped hollow hemispherical carbon-based material prepared by the preparation method. The carbon-based material mainly contains carbon element, contains a small amount of nitrogen element and sulfur element, is doped on a carbon matrix consisting of the carbon element, and has the nitrogen element content of 5-10 wt% and the sulfur element content of 4-12 wt%; the carbon-based material is porous, hollow and hemispherical.
The invention also provides application of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material as an oxygen reduction catalyst.
Dopamine is a biological neurotransmitter, can perform oxidation-crosslinking reaction by using oxygen dissolved in water solution under the condition of aqueous solution or alkaline, can form a thin layer which is tightly attached to the surface of a solid material after polymerization and can almost cover the surfaces of all materials, the polymerization reaction has good controllability and strong molecule designability, secondary reaction can be performed, and the high-conductivity carbon-based material can be obtained through high-temperature pyrolysis. The method fully utilizes the characteristic of dopamine, controls the hydrolysis degree of a silicon source to obtain hemispherical rather than spherical silicon dioxide microspheres, and takes the hemispherical silicon dioxide microspheres as a template, and carries out polymerization on the surface of the hemispherical silicon dioxide microspheres, including the inner surface and the outer surface, to obtain the macromolecular carbon material. And then further carrying out carbonization, template removal and vapor deposition to co-dope sulfur to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based material.
The following are examples:
example 1
Uniformly mixing 100ml of ethanol and 25ml of water in a 200ml beaker, adding 5ml of ammonia water into a mixed system of the water and the ethanol, uniformly mixing, adding 5ml of tetraethyl orthosilicate, stirring for 10 minutes, adding 300mg of dopamine hydrochloride, reacting for 24 hours at a stirring speed of 500 rpm to obtain a polydopamine-silicon dioxide compound, centrifugally washing and drying the obtained material, calcining in a tubular furnace in an argon (flow of 120sccm) atmosphere, heating at a heating rate of 5 ℃ per minute, keeping the temperature at 500 ℃, keeping the temperature for 1 hour, and then putting the material into a reactor with a volume ratio of hydrofluoric acid to water of 1: 4, removing acid for 5 hours in the mixed solvent, filtering and drying the obtained sample, finally putting the sample into a tube furnace in the atmosphere of argon (the flow is 120sccm) for annealing, and weighing the sample and thiourea in a mass ratio of 1: 400, heating rate of 10 ℃ per minute, heat preservation temperature of 800 ℃ for 1h, and naturally cooling to room temperature to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based catalyst. The scanning electron micrograph of the apparent morphology of the sample is shown in figure 1.
As can be seen from fig. 1, the catalyst described in the examples has a very pronounced hollow hemisphere characteristic, with a hemisphere diameter of about 200nm, demonstrating the successful synthesis of the material.
The carbon-based material is mainly composed of carbon elements and contains a small amount of nitrogen elements and sulfur elements, wherein the small amount of nitrogen elements and sulfur elements are doped on a carbon matrix composed of the carbon elements, and the content of the nitrogen elements is 9.1 wt% and the content of the sulfur elements is 6.9 wt%; the carbon-based material is porous, hollow and hemispherical.
Example 2
Uniformly mixing 62.5ml of ethanol and 62.5ml of water in a 200ml beaker, adding 10ml of ammonia water into a mixed system of the water and the ethanol, uniformly mixing, adding 10ml of tetraethyl orthosilicate, stirring for 10 minutes, adding 400mg of dopamine hydrochloride, reacting for 6 hours at a stirring speed of 500 revolutions per minute to obtain a polydopamine-silicon dioxide compound, centrifugally washing and drying the obtained material, then calcining in a tubular furnace under an argon atmosphere (the flow is 60sccm), the heating rate is 2 ℃ per minute, the heat preservation temperature is 700 ℃, the heat preservation time is 4 hours, and then putting the material into a reactor with the volume ratio of hydrofluoric acid to water being 1: 4, removing acid for 2 hours in the mixed solvent, filtering and drying the obtained sample, finally putting the sample into a tube furnace in an argon (flow is 60sccm) atmosphere for annealing, and weighing the sample and thiourea in a mass ratio of 1:200, heating rate is 5 ℃ per minute, heat preservation temperature is 1000 ℃, heat preservation time is 3 hours, and natural cooling is carried out to room temperature, thus obtaining the nitrogen-sulfur co-doped hollow hemispherical carbon-based catalyst. The transmission electron micrograph of this sample is shown in FIG. 2.
As can be seen from fig. 2, the crystallinity of the carbon catalyst carbon obtained in the examples was good, and it can be seen that the carbon catalyst carbon has a distinct hemispherical boundary in the figure, confirming the successful synthesis of the material.
The carbon-based material is mainly made of carbon element and contains a small amount of nitrogen element and sulfur element, the small amount of nitrogen element and sulfur element are doped on a carbon matrix consisting of the carbon element, and the content of the nitrogen element is 4 wt% and the content of the sulfur element is 12 wt%; the carbon-based material is porous, hollow and hemispherical.
Example 3
Uniformly mixing 80ml of ethanol and 40ml of water in a 200ml beaker, adding 10ml of ammonia water into a mixing system of the water and the ethanol, uniformly mixing, adding 5ml of tetraethyl orthosilicate, stirring for 10 minutes, adding 200mg of dopamine hydrochloride, reacting for 12 hours at a stirring speed of 500 rpm to obtain a polydopamine-silicon dioxide compound, centrifugally washing and drying the obtained material, calcining in a tubular furnace under the atmosphere of argon (the flow is 40sccm), wherein the heating rate is 4 ℃ per minute, the heat preservation temperature is 400 ℃, the heat preservation time is 2 hours, and then putting the material into a reactor with the volume ratio of hydrofluoric acid to water being 1: 4, removing acid for 4 hours, filtering and drying the obtained sample, finally putting the sample into a tube furnace in an argon (flow is 40sccm) atmosphere for annealing, and weighing the sample and thiourea in a mass ratio of 1: 300, heating rate of 2 ℃ per minute, heat preservation temperature of 700 ℃ for 2 hours, and naturally cooling to room temperature to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based catalyst.
The carbon-based material is mainly composed of carbon elements and contains a small amount of nitrogen elements and sulfur elements, wherein the small amount of nitrogen elements and sulfur elements are doped on a carbon matrix composed of the carbon elements, and the content of the nitrogen elements is 8.2 wt% and the content of the sulfur elements is 5.7 wt%; the carbon-based material is porous, hollow and hemispherical.
The Raman spectrum of this sample is shown in FIG. 3. From FIG. 3As can be seen, the Raman spectrum has 1356cm-1And 1578cm-1Two large peaks, corresponding to the D peak and the G peak of carbon, well illustrate that carbon in the catalyst has good catalytic activity and conductivity.
Example 4
Uniformly mixing 96ml of ethanol and 24ml of water in a 200ml beaker, adding 7.5ml of ammonia water into a mixed system of the water and the ethanol, uniformly mixing, adding 7.5ml of tetraethyl orthosilicate, stirring for 10 minutes, adding 300mg of dopamine hydrochloride, reacting for 24 hours at a stirring speed of 500 revolutions per minute to obtain a polydopamine-silicon dioxide compound, centrifugally washing and drying the obtained material, then calcining in a tubular furnace under the atmosphere of argon (the flow is 80sccm), the heating rate is 3 ℃ per minute, the heat preservation temperature is 500 ℃, the heat preservation time is 1 hour, and then putting the material into a reactor with the volume ratio of hydrofluoric acid to water being 1: 5, removing acid for 2 hours in the mixed solvent, filtering and drying the obtained sample, finally putting the sample into a tube furnace in the atmosphere of argon (the flow is 80sccm) for annealing, and weighing the sample and thiourea in a mass ratio of 1:200, heating rate of 10 ℃ per minute, heat preservation temperature of 600 ℃ for 4 hours, and naturally cooling to room temperature to obtain the nitrogen-sulfur co-doped hollow hemispherical carbon-based catalyst.
The carbon-based material is mainly made of carbon element and contains a small amount of nitrogen element and sulfur element, the small amount of nitrogen element and sulfur element are doped on a carbon matrix consisting of the carbon element, the content of the nitrogen element is 10 wt%, and the content of the sulfur element is 4 wt%; the carbon-based material is porous, hollow and hemispherical.
Example 5
The sample of example 1 was characterised by an X-ray diffractometer (Philips PW-1830) and the XRD characterisation is shown in figure 4. As can be seen from figure 4, the XRD has a diffraction peak at 24 deg. which corresponds to the carbon peak, indicating the presence of crystalline carbon in the catalyst.
Example 6
Weighing 5mg of the sample obtained in the example 1, adding 490ul of N, N-dimethylformamide, then adding 10 mul of naphthol aqueous solution with the mass fraction of 5%, ultrasonically dispersing uniformly, taking out 5 mul of the uniformly dispersed sample, loading the sample on a ring disc electrode, drying by using an infrared lamp, taking the electrode as a working electrode, a carbon rod as a counter electrode, a mercury/mercury oxide electrode as a reference electrode, using 0.1 mol of potassium hydroxide aqueous solution as electrolyte, and testing the oxygen reduction performance of the material by using a rotating disc electrode and an electrochemical workstation. The cyclic voltammogram of the material in oxygen is shown in figure 5.
As can be seen from FIG. 5, the cyclic voltammogram has a reduction peak at 0.87V, which proves that the catalyst obtained in the example has oxygen reduction catalytic activity equivalent to 20% of commercial platinum-carbon material, and shows excellent oxygen reduction electrocatalytic performance.
Example 7
Weighing 5mg of the sample obtained in the example 2, adding 490ul of N, N-dimethylformamide, then adding 10 mul of naphthol aqueous solution with the mass fraction of 5%, ultrasonically dispersing uniformly, taking out 5 mul of the uniformly dispersed sample, loading the sample on a ring disc electrode, drying by using an infrared lamp, taking the electrode as a working electrode, a carbon rod as a counter electrode, a mercury/mercury oxide electrode as a reference electrode, using 0.1 mol of potassium hydroxide aqueous solution as electrolyte, and testing the oxygen reduction performance of the material by using a rotating disc electrode and an electrochemical workstation. The polarization curve of the material in oxygen is shown in figure 6.
As can be seen from fig. 6, the polarization curve shows that the catalyst in this example has a half-wave potential of 0.85V, comparable to the performance of a 20% commercial platinum carbon catalyst, showing good oxygen reduction electrocatalytic activity of the catalyst.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. The preparation method of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material is characterized by comprising the following steps of:
(1) under the alkaline environment containing solvent, the ethyl orthosilicate is partially hydrolyzed to obtain a hemispherical silicon dioxide template;
(2) adding dopamine hydrochloride into the system of the hemispherical silicon dioxide template obtained in the step (1), so that dopamine hydrochloride is subjected to polymerization reaction on the inner surface and the outer surface of the hemispherical silicon dioxide template obtained by partial hydrolysis, performing solid-liquid separation after the reaction, and drying the obtained solid powder to obtain a dried sample;
(3) calcining the dried sample obtained in the step (2) in an inert atmosphere to carbonize a polymer obtained by polymerizing dopamine hydrochloride, so as to obtain a carbonized sample;
(4) removing the hemispherical silicon dioxide template from the carbonized sample by acid etching, washing, separating and drying to obtain a sample from which the hemispherical silicon dioxide template is removed;
(5) taking thiourea as a sulfur source, and doping sulfur element in the sample from which the hemispherical silicon dioxide template is removed by adopting a chemical vapor deposition method to obtain a nitrogen-sulfur co-doped hollow hemispherical carbon-based material; the solvent is a mixed solution of water and ethanol, wherein the volume ratio of the water to the ethanol is 1: 2-4.
2. The preparation method of claim 1, wherein the alkaline environment is formed by adding ammonia water to the system in the step (1), wherein the volume ratio of the ammonia water to the solvent is 1: 10-15; the volume ratio of the ammonia water to the tetraethoxysilane is 1: 1-2.
3. The method according to claim 1, wherein the dopamine hydrochloride is added in an amount of 200 to 600 g per 130ml of the mixed solvent of water and ethanol.
4. The method of claim 1, wherein step (1) partially hydrolyzes the tetraethoxysilane for a period of time not more than 1 hour.
5. The method according to claim 1, wherein the calcination temperature in step (3) is 400 to 700 ℃, the flow rate of the inert gas is 40 to 120sccm, the temperature rise rate is 2 to 5 ℃/min, and the calcination time is 1 to 4 hours.
6. The preparation method according to claim 1, wherein the mass ratio of the sample from which the hemispherical silica template is removed to thiourea in the chemical vapor deposition in the step (5) is 1:200 to 800.
7. The preparation method according to claim 1, wherein the chemical vapor deposition is carried out in a tube furnace, the temperature rise rate is 2-10 ℃/min, the heat preservation time is 1-4 h, and the annealing temperature is 600-1000 ℃.
8. The nitrogen-sulfur-codoped hollow hemispherical carbon-based material prepared by the preparation method according to any one of claims 1 to 7.
9. The use of the nitrogen and sulfur co-doped hollow hemispherical carbon-based material according to claim 8 as an oxygen reduction catalyst.
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