Nitrogen-doped carbon / triple cobalt tetraselenide / carbon nanotube composite material, preparation method and application thereof

Abstract

The present disclosure relates to a nitrogen-doped carbon / tricobalt tetraselenide / carbon nanotube composite material and a preparation method and application thereof, doped tricobalt tetraselenide nanoparticles on a nitrogen-doped carbon polyhedron and interconnected with carbon nanotubes as an electrode composite material to improve the charge and discharge cycle capacity, the nitrogen-doped carbon / tricobalt tetraselenide / carbon nanotube composite material provides an electron transmission channel with carbon nanotubes; dimethyl imidazole cobalt-derived nitrogen-doped carbon as a carbon support, providing a stable polyhedral structure and enhancing the electrical conductivity; tricobalt tetraselenide as a transition metal selenide, enhancing the catalytic and adsorption capacity of the composite material, which is conducive to improving the cycle stability and service life of the battery. Meanwhile, the present disclosure also provides a preparation method thereof, which has a simple production process, low cost, and the nitrogen-doped carbon / tricobalt tetraselenide / carbon nanotube prepared by the method has excellent electrochemical performance.

Description

Technical Field

[0001] This disclosure relates to the field of advanced nanocomposite material preparation technology, and in particular to nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, their preparation methods and applications. Background Technology

[0002] In recent years, lithium-sulfur batteries have become a long-term research hotspot in the field of new energy storage / conversion due to their advantages such as ultra-high specific capacity (1675 mAh / g), high theoretical energy density (2600 Wh / kg), abundant sulfur reserves, environmental friendliness, and low cost, pointing the way for the development of next-generation energy systems, especially electric vehicles. Lithium-sulfur batteries are secondary batteries that use lithium as the anode and sulfur as the cathode, converting the chemical energy provided by the breaking of sulfur-sulfur bonds into electrical energy. Therefore, designing a sulfur host with high conductivity is an effective strategy to improve the cycle performance of lithium-sulfur batteries.

[0003] Currently, extensive research is being conducted on carbonaceous materials with various nanostructures. However, most carbon-based materials contain only a few polar sites, resulting in limited binding sites for lithium polysulfides. Therefore, heteroatom doping, such as nitrogen, phosphorus, and oxygen atoms, can significantly improve the electrical conductivity, surface polarity, and adsorption capacity of lithium polysulfides in carbon-based materials. In recent years, porous carbon materials synthesized by carbonization of metal-organic frameworks have attracted much attention due to their high porosity and high specific surface area. Abundant organic ligands provide a rich carbon source, and the resulting porous carbon, due to its unique morphology and layered porous structure, is conducive to the adsorption of lithium polysulfides. Dimethylimidazolium cobalt is a class of porous zeolite-like metal-organic framework materials composed of cobalt ion centers and dimethylimidazolium ligands. Cobalt-based electrocatalysts exhibit good activity and chemical stability. Furthermore, cobalt particles on carbon-based materials significantly enhance electrocatalytic activity by increasing electronic conductivity and providing more active sites. In addition to the direct formation of cobalt-carbon bonds, there is also a strong synergistic effect between cobalt and carbon, which can further enhance catalytic activity. Furthermore, carbon nanotubes are considered promising catalysts due to their simple preparation, high electrical conductivity, and excellent electrochemical activity. Previous research has shown that metal-organic frameworks (MOFs) can yield carbon-based materials with large surface areas and provide sufficient metal active sites for electrocatalysis. Moreover, in metal-carbon composites derived from MOFs, stronger coordination between metal and carbon atoms can generate a robust framework. Uniform distribution of heteroatoms and metal species within the framework can be achieved through sintering and in-situ migration of metal nanoparticles. Cobalt-based compounds have received considerable attention in past research due to their high chemical stability and excellent electrical conductivity.

[0004] Cobalt-based chalcogenides exhibit excellent cycle performance in lithium-sulfur battery systems due to their good catalytic activity. Generally, transition metal selenides have higher conductivity than their sulfides and show greater application potential as catalysts in lithium-sulfur batteries. For example, the existing technology “'Ultrafine Co3Se4Nanoparticles in Nitrogen-Doped 3D Carbon Matrix for High-Stable and Long-Cycle-Life Lithium Sulfur Batteries', Cai D, Liu BK, Zhu DH, et al. Advanced Energy Materials, 2020, 10(19): 1904273” mentions that by doping highly conductive and catalytically active cobalt tetraselenide nanoparticles into a nitrogen-doped three-dimensional interconnected carbon matrix, dissolved lithium polysulfides diffuse and migrate to the lithium anode under the competition of concentration gradient and electric field force, and are captured by active n-doped sites and Co3Se4 centers. Adsorbed lithium polysulfides can accept and release electrons at these polar sites via adjacent conductive carbon, and the exposed carbon / Co3Se4 / electrolyte interface can accelerate the conversion reactions of these sulfur compounds, endowing them with good electrochemical performance. However, the confinement and catalysis of lithium polysulfides by transition metal selenides as electrocatalysts are still in their early stages. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this disclosure provides a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, its preparation method, and its application.

[0006] According to a first aspect of this disclosure, a method for preparing a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material is provided, characterized by comprising the following steps:

[0007] Step 1: Preparation of cobalt dimethylimidazolium. Cobalt source and dimethylimidazolium are dissolved in methanol solution in a certain proportion and mixed after thorough stirring to obtain a mixed solution. The mixed solution is placed in a beaker and aged at 25 degrees Celsius. After aging, it is washed, filtered, and dried to obtain a purple powder, which is cobalt dimethylimidazolium powder.

[0008] Step 2: Prepare nitrogen-doped carbon / cobalt / carbon nanotubes. Place the dimethylimidazolium cobalt obtained in Step 1 in a beaker, add a carbon source and stir thoroughly in an ethanol solution. After stirring, dry the powder. Place the dried powder in a tube furnace and carbonize it under an inert atmosphere to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0009] The carbon nanotubes in step two are derived from melamine, and the mass ratio of cobalt dimethylimidazolium to melamine is 1:1-1:2; the carbonization conditions are as follows: first carbonize at 500-570 degrees Celsius for 2 hours, and then carbonize at 700-810 degrees Celsius for 2 hours.

[0010] Step 3: Prepare nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes. After thoroughly grinding and mixing the nitrogen-doped carbon / cobalt / carbon nanotubes obtained in Step 2 with the selenium source in a certain proportion, place them in a tube furnace and heat-treat them under an inert atmosphere to obtain nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0011] Preferably, the dimethylimidazole cobalt in step one is a metal-organic structural material, the cobalt source is cobalt nitrate, and the molar ratio of the cobalt source to dimethylimidazole is 1:3-1:7.

[0012] Preferably, the aging time in step one is 24 hours.

[0013] Preferably, in step three, the selenium source is elemental selenium powder, and the mass ratio of the nitrogen-doped carbon / cobalt / carbon nanotube material to the selenium powder is 1:1-1:2.

[0014] Preferably, the heat treatment temperature in step three is 600-680 degrees Celsius, and the heat treatment time is 5 hours.

[0015] According to a second aspect of this disclosure, a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material is provided.

[0016] According to a third aspect of this disclosure, an application of a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material is provided.

[0017] The principle of this disclosed technical solution is:

[0018] This disclosure provides a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, its preparation method, and its applications. The method utilizes carbon nanotubes to connect the nitrogen-doped carbon framework, improving the charge-discharge cycle performance of cobalt tetraselenide. The carbon nanotubes provide electron transport channels, the nitrogen-doped carbon acts as a carbon scaffold and provides nitrogen doping sites, and cobalt tetraselenide serves as a catalytic and adsorbent material, thereby enhancing the charge-discharge cycle performance of the composite material. The charge-discharge cycle performance is suitable for batteries using lithium, sodium, or potassium as the anode. Specifically, a nitrogen-doped carbon framework is obtained by carbonizing dimethylimidazolium cobalt. The porous carbon framework exhibits high porosity and high specific surface area, while nitrogen doping improves the polarity and chalcophilic affinity of the carbon framework. Carbon nanotubes are obtained by carbonizing melamine coated on dimethylimidazolium cobalt. The numerous carbon nanotubes provide electron transport channels. The cobalt on the carbonized surface is then selenized to obtain cobalt tetraselenide, which serves as a cobalt-based chalcogenide catalyst, enhancing the catalytic and adsorption capabilities of the composite material and improving the cycle stability and lifespan of the battery.

[0019] The beneficial effects of this disclosed technical solution are as follows:

[0020] 1. This disclosure provides a method for improving the charge-discharge cycle capability of cobalt tetraselenide by connecting a nitrogen-doped carbon framework with carbon nanotubes. The preparation method is low-cost, simple, and produces a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material with excellent electrochemical performance. In this composite material, carbon nanotubes provide electron transport channels; nitrogen-doped carbon acts as a carbon scaffold, providing a stable polyhedral structure and enhancing conductivity; and cobalt tetraselenide, as a transition metal selenide, enhances catalytic and adsorption capabilities. When assembled into a lithium-sulfur battery, its initial discharge capacity reaches 1413 mAh / g, and after 100 cycles, it reaches 1039 mAh / g. It can also sustain 1000 cycles at a 1 C current density, with a capacity decay rate of 0.034% per cycle. Furthermore, its rate performance is also good at different current densities.

[0021] 2. This disclosure provides a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material. It utilizes a nitrogen-doped carbon skeleton obtained by carbonizing dimethylimidazolium cobalt as a three-dimensional matrix material. The resulting porous carbon skeleton exhibits high porosity and high specific surface area. Nitrogen doping enhances the polarity and chalcophilic affinity of the carbon skeleton, ensuring excellent electrochemical performance of the composite material. Carbon nanotubes are obtained by carbonizing melamine coated on dimethylimidazolium cobalt. The numerous carbon nanotubes provide electron transport channels, improving the battery's electrochemical performance. The cobalt on the carbonized surface, after selenization, yields cobalt tetraselenide, which acts as a cobalt-based chalcogenide catalyst, enhancing the composite material's catalytic and adsorption capabilities. This plays a crucial role in the battery's cycle stability and lifespan.

[0022] 3. This disclosure provides a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, which are prepared by precipitation, high-temperature carbonization, and high-temperature melting. Specifically, dimethylimidazolium cobalt is synthesized through an aging reaction, then mixed with melamine and subjected to high-temperature carbonization, and finally melted with selenium powder at high temperature to obtain the composite material. The overall preparation method is simple, low-cost, and effectively reduces the experimental difficulty. Attached Figure Description

[0023] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. The drawings are provided for a better understanding of the present invention and are not intended to limit the scope of this disclosure. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein: Figure 1 This is a schematic diagram illustrating the synthesis of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material prepared according to the embodiments of this disclosure;

[0024] Figure 2 Scanning electron microscope (SEM) images of (a) cobalt dimethylimidazolium, (b) nitrogen-doped carbon / cobalt / carbon nanotube composites, (c) nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composites, and (d) nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composites prepared for embodiments of this disclosure.

[0025] Figure 3 Raman spectra of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes, nitrogen-doped carbon / cobalt tetraselenide, and nitrogen-doped carbon / cobalt / carbon nanotube composites prepared according to embodiments of this disclosure;

[0026] Figure 4 X-ray diffraction patterns of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes, nitrogen-doped carbon / cobalt tetraselenide, and nitrogen-doped carbon / cobalt / carbon nanotube composite materials prepared according to embodiments of this disclosure;

[0027] Figure 5 The X-ray photoelectron spectra of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material prepared for the embodiments of this disclosure are shown in (a) as the full spectrum; (b) as the high-resolution spectrum of carbon; (c) as the high-resolution spectrum of nitrogen; (d) as the high-resolution spectrum of cobalt; and (e) as the high-resolution spectrum of selenium.

[0028] Figure 6 Cycle curves of lithium electrodes and lithium-sulfur batteries with nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur electrodes according to embodiments of this disclosure.

[0029] Figure 7 The rate performance curves of a lithium-sulfur battery using a lithium electrode and a prepared nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur electrode at different current densities are shown in the embodiments of this disclosure.

[0030] Figure 8 This is a long-cycle cycling curve of a lithium electrode and a lithium-sulfur battery using nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur as electrodes, according to embodiments of this disclosure. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0032] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items. It should be understood that, unless otherwise specified, all the materials used in this disclosure are commercially available.

[0033] Example 1

[0034] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0035] Step 1: Preparation of cobalt dimethylimidazolium. 3.4933 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 3.947 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. The mixture was then aged at room temperature for 24 hours. The aged solution was centrifuged three times in ethanol solution to collect the precipitate. The precipitate was dried in a 60°C oven for 12 hours to remove moisture, yielding dry purple cobalt dimethylimidazolium powder.

[0036] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes. 200 mg of the dimethylimidazolium cobalt powder obtained in Step 1 and 200 mg of melamine were placed in a beaker, and 50 mL of ethanol was added. The mixture was stirred at 25°C for 12 hours. After stirring, it was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat and then placed in a tube furnace. The temperature program was set, and an inert gas was used for protection. The furnace was heated at 550°C for 2 hours, followed by a thermal reaction at 700°C for 2 hours, yielding black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0037] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:2 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 650 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0038] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0039] Figure 1 This is a schematic diagram illustrating the synthesis of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material prepared according to embodiments of this disclosure.

[0040] Figure 2The images show (a) a scanning electron microscope (SEM) image of cobalt dimethylimidazolium, (b) a scanning electron microscope (SEM) image of a nitrogen-doped carbon / cobalt / carbon nanotube composite material, (c) a scanning electron microscope (SEM) image of a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, and (d) a transmission electron microscope (TEM) image of a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material prepared according to embodiments of this disclosure. Scanning characterization shows that cobalt dimethylimidazolium has a dodecahedral structure. Figure (b) shows the nitrogen-doped carbon / cobalt / carbon nanotube composite material obtained by carbonization after melamine coating. It has a polyhedral structure similar to the precursor, with surface wrinkling and carbon nanotube formation. Figure (c) shows the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material obtained by selenization. It has a polyhedral structure with many interconnected microtubular structures and fine nanoparticles on the surface. Figure (d) is a TEM image of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, showing a large number of carbon nanotubes and fine nanoparticles covering the polyhedral surface.

[0041] Figure 3 Raman spectra of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes, nitrogen-doped carbon / cobalt tetraselenide, and nitrogen-doped carbon / cobalt / carbon nanotube composites prepared according to embodiments of this disclosure; as can be seen from the figures, the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composites exhibit obvious graphite peaks and amorphous carbon peaks, and I D / I G The highest ratio indicates that this composite material has the most defects compared to the other two materials.

[0042] Figure 4 X-ray diffraction patterns of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes, nitrogen-doped carbon / cobalt tetraselenide, and nitrogen-doped carbon / cobalt / carbon nanotube composites prepared for embodiments of this disclosure are shown in the figures. As can be seen from the figures, all peaks of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes and nitrogen-doped carbon / cobalt tetraselenide correspond well to the characteristic peaks of cobalt tetraselenide, while the characteristic peaks of nitrogen-doped carbon / cobalt / carbon nanotubes correspond well to elemental cobalt. Furthermore, nitrogen-doped carbon / cobalt / carbon nanotubes exhibit (111), (200), and (220) crystal planes, while nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes exhibit (111), (311), and (31-3) crystal planes. For these three samples, due to the low carbon content and amorphous state, no obvious carbon peaks were observed.

[0043] Figure 5(a) is the full X-ray photoelectron spectroscopy (XPS) spectrum of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material prepared in this embodiment. As shown in the figure, the material contains carbon, nitrogen, oxygen, cobalt, and selenium. Figures 5(b) to (e) are the high-resolution spectra of carbon, nitrogen, cobalt, and selenium in the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, respectively. Figure 5(b) shows that carbon exists in the forms of CC / C=C (284.6 eV), CN / C-Se (285.4 eV), and CO (286.6 eV). Nitrogen exists in the forms of pyridine nitrogen (398.1 eV), pyrrolidine nitrogen (400.1 eV), graphitic nitrogen (400.8 eV), and nitrogen oxides (403.9 eV). According to the high-resolution spectrum of cobalt, the binding energies of the divalent and trivalent states of cobalt are located at 781.6 and 778.7 eV, respectively. In the high-resolution photoelectron spectrum of selenium, the fitted peaks with binding energies at 56.1 and 55.3 eV were attributed to the 3d phases of selenium, respectively. 3 / 2 and 3D 5 / 2 track.

[0044] Figure 6 The cycling curves of the lithium-sulfur battery using lithium electrodes and the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur electrodes prepared in Example 1 are shown. Under charge-discharge cycling at a current density of 0.12 C, the initial discharge capacity is 1413 mAh / g, and the discharge capacity after 100 cycles is 1039 mAh / g. It also exhibits good cycling stability, with a capacity retention of 74% after 100 cycles and a coulombic efficiency as high as 99.4% after cycling.

[0045] Figure 7 The graphs show the rate performance curves of lithium-sulfur batteries using lithium electrodes and the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur electrodes prepared in Example 1 at different current densities. At current densities of 0.1, 0.3, 0.5, 1, and 2 C, the initial discharge capacities are 1414, 1150, 1052, 966, and 758 mAh / g, respectively. When the current density decreases from 2 C to 0.1 C, the reversible discharge capacity returns to 1202 mAh / g, indicating good rate performance.

[0046] Figure 8 Long-cycle cycling curves of a lithium-sulfur battery using lithium electrodes and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube-doped sulfur electrodes prepared in Example 1 are shown. 1000 charge-discharge cycles were performed at a current density of 1 C. The initial discharge capacity was 1095 mAh / g, and after 1000 cycles, the discharge capacity remained at 629 mAh / g, with a capacity decay rate of 0.034% per cycle.

[0047] Example 2

[0048] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0049] Step 1: Preparation of cobalt dimethylimidazolium: 3.516 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 5.978 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. The mixture was then aged at room temperature for 24 hours. The aged solution was collected by centrifugation three times in ethanol solution to obtain the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry, purple cobalt dimethylimidazolium powder.

[0050] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 148 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 152 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat, placed in a tube furnace, the temperature program was set, and an inert gas was used for protection. The mixture was heated at 500°C for 2 hours, followed by a thermal reaction at 700°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0051] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:2 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 650 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0052] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0053] Example 3

[0054] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0055] Step 1: Preparation of cobalt dimethylimidazolium: 1.749 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 1.876 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. Then, the mixture was aged at room temperature for 24 hours. The aged solution was centrifuged three times in ethanol solution to collect the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry purple cobalt dimethylimidazolium powder.

[0056] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 124 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 250 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat, placed in a tube furnace, the temperature program was set, and an inert gas was used for protection. The mixture was heated at 520°C for 2 hours, followed by a thermal reaction at 750°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0057] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:2 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 600 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0058] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0059] Example 4

[0060] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0061] Step 1: Preparation of cobalt dimethylimidazolium: 3.478 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 3.876 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. The mixture was then aged at room temperature for 24 hours. The aged solution was collected by centrifugation three times in ethanol solution to obtain the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry, purple cobalt dimethylimidazolium powder.

[0062] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 136 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 278 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat, placed in a tube furnace, the temperature program was set, and an inert gas was used for protection. The mixture was heated at 530°C for 2 hours, followed by a thermal reaction at 800°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0063] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:2 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 630 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0064] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0065] Example 5

[0066] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0067] Step 1: Preparation of cobalt dimethylimidazolium: 1.728 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 2.987 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. Then, the mixture was aged at room temperature for 24 hours. The aged solution was collected by centrifugation three times in ethanol solution to obtain the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry purple cobalt dimethylimidazolium powder.

[0068] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 217 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 226 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat and placed in a tube furnace. The temperature program was set, and an inert gas was used for protection. The mixture was heated at 515°C for 2 hours, followed by a thermal reaction at 740°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0069] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:1 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 610 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0070] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0071] Example 6

[0072] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0073] Step 1: Preparation of cobalt dimethylimidazolium: 3.684 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 6.103 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. The mixture was then aged at room temperature for 24 hours. The aged solution was collected by centrifugation three times in ethanol solution to obtain the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry, purple cobalt dimethylimidazolium powder.

[0074] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 167 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 341 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat, placed in a tube furnace, the temperature program was set, and an inert gas was used for protection. The mixture was heated at 560°C for 2 hours, followed by a thermal reaction at 780°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0075] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:2 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 670 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0076] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0077] Example 7

[0078] The embodiments of this disclosure provide a method for preparing nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite materials, including the following steps:

[0079] Step 1: Preparation of cobalt dimethylimidazolium: 1.776 g of cobalt nitrate hexahydrate was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. 2.135 g of dimethylimidazolium was placed in a beaker, and 100 mL of methanol was added. The mixture was magnetically stirred for half an hour. The dimethylimidazolium solution was poured into the cobalt nitrate hexahydrate solution, and the mixture was stirred for 10 minutes. Then, the mixture was aged at room temperature for 24 hours. The aged solution was collected by centrifugation three times in ethanol solution to obtain the precipitate. The precipitate was dried in an oven at 60°C for 12 hours to remove moisture, yielding dry purple cobalt dimethylimidazolium powder.

[0080] Step 2: Preparation of nitrogen-doped carbon / cobalt / carbon nanotubes; 237 mg of dimethylimidazolium cobalt powder obtained in Step 1 and 483 mg of melamine were placed in a beaker, 50 mL of ethanol was added, and the mixture was stirred at 25°C for 12 hours. After stirring, the mixture was dried in an oven at 60°C until all moisture was evaporated. The dried solid powder was placed in a ceramic boat, placed in a tube furnace, the temperature program was set, and an inert gas was used for protection. The mixture was heated at 570°C for 2 hours, followed by a thermal reaction at 810°C for 2 hours to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder.

[0081] Step 3: Preparation of nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes; The nitrogen-doped carbon / cobalt / carbon nanotube powder obtained in Step 2 is placed in a mortar and ground with selenium powder at a mass ratio of 1:1 for 20 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 680 degrees Celsius under inert gas protection for 5 hours to carry out the thermal reaction, thereby obtaining nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0082] In some embodiments, sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes are prepared. The nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder obtained in step three is mixed with sublimed sulfur in a mortar at a mass ratio of 1:3 and ground for 30 minutes to ensure uniform mixing. The mixed powder is then placed in a ceramic boat and placed in a tube furnace. The temperature program is set, and the furnace is heated at 155 degrees Celsius under inert gas protection for 12 hours to undergo a thermal reaction, thereby obtaining sulfur-doped and nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

[0083] The foregoing has shown and described the basic principles, main features, and advantages of this disclosure. It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0084] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material, characterized in that, Includes the following steps: Step 1: Preparation of cobalt dimethylimidazolium. Cobalt source and dimethylimidazolium are dissolved in methanol solution in a certain proportion and mixed after thorough stirring to obtain a mixed solution. The mixed solution is placed in a beaker and aged at 25 degrees Celsius. After aging, it is washed, filtered, and dried to obtain a purple powder, which is cobalt dimethylimidazolium powder. Step 2: Prepare nitrogen-doped carbon / cobalt / carbon nanotubes. Place the dimethylimidazolium cobalt obtained in Step 1 in a beaker, add a carbon source and stir thoroughly in an ethanol solution. After stirring, dry the powder. Place the dried powder in a tube furnace and carbonize it under an inert atmosphere to obtain black nitrogen-doped carbon / cobalt / carbon nanotube powder. The carbon nanotubes in step two are derived from melamine, and the mass ratio of cobalt dimethylimidazolium to melamine is 1:1-1:2; the carbonization conditions are as follows: first carbonize at 500-570 degrees Celsius for 2 hours, and then carbonize at 700-810 degrees Celsius for 2 hours. Step 3: Prepare nitrogen-doped carbon / cobalt tetraselenide / carbon nanotubes. After thoroughly grinding and mixing the nitrogen-doped carbon / cobalt / carbon nanotubes obtained in Step 2 with the selenium source in a certain proportion, place them in a tube furnace and heat-treat them under an inert atmosphere to obtain nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube powder.

2. The method for preparing the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material according to claim 1, characterized in that, The dimethylimidazole cobalt in step one is a type of metal-organic structural material, the cobalt source is cobalt nitrate, and the molar ratio of the cobalt source to dimethylimidazole is 1:3-1:

7.

3. The method for preparing the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material according to claim 1, characterized in that, The aging time in step one is 24 hours.

4. The method for preparing the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material according to claim 1, characterized in that, In step three, the selenium source is elemental selenium powder, and the mass ratio of the nitrogen-doped carbon / cobalt / carbon nanotube material to the selenium powder is 1:1-1:

2.

5. The method for preparing the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material according to claim 1, characterized in that, The heat treatment temperature in step three is 600-680 degrees Celsius, and the heat treatment time is 5 hours.

6. A nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material obtained by the preparation method according to any one of claims 1-5.

7. The application of the nitrogen-doped carbon / cobalt tetraselenide / carbon nanotube composite material according to claim 6.

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