Preparation method of aluminum monatomic nitrogen-doped carbon catalyst based on carbon nanotube support and application of aluminum monatomic nitrogen-doped carbon catalyst in electrocatalytic carbon dioxide reduction

Abstract

The invention discloses a preparation method of an aluminum monatomic nitrogen-doped carbon catalyst based on carbon nanotube support and application of the aluminum monatomic nitrogen-doped carbon catalyst in electrocatalytic carbon dioxide reduction.The preparation method comprises the steps that a nitrogen source, an aluminum precursor solution and carbon nanotubes are added into a solvent, stirring, heating and ultrasonic dispersion are performed to obtain a precursor solution, and the precursor solution is dried to obtain a carbon nanotube-supported aluminum monatomic nitrogen-doped carbon catalyst; the mass volume ratio of the carbon nanotubes to the aluminum precursor solution is 2-3 g / 10 mL; and drying the precursor solution, calcining, carrying out heat treatment, carrying out acid treatment, filtering, washing, and drying to obtain the aluminum monatomic nitrogen-doped carbon catalyst. According to the catalyst prepared by the preparation method, aluminum single atoms can be stably anchored and uniformly distributed in a nitrogen-doped carbon matrix by utilizing the conductivity and skeleton supporting effect of CNT, so that efficient CO2 electroreduction performance is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemistry, and particularly relates to a preparation method of an aluminum monatomic nitrogen-doped carbon catalyst based on carbon nanotube support and application of the aluminum monatomic nitrogen-doped carbon catalyst in electrocatalytic reduction of carbon dioxide. BACKGROUND

[0002] With the increasing seriousness of global warming, the increase in the emission of carbon dioxide (CO2), as one of the main greenhouse gases, has a huge impact on the environment. The electrochemical carbon dioxide reduction reaction (CO2RR) driven by renewable electricity can convert CO2 into fuels and valuable chemicals, and is a promising technology for alleviating environmental problems and energy crises. Among numerous products, carbon monoxide (CO) is of great concern due to its simple reaction path, low potential requirement, and wide use in chemical synthesis (such as Fischer-Tropsch synthesis, Monsanto method, etc.). However, due to the stable chemical properties of CO2 molecules, slow reaction kinetics, and easy competition with the hydrogen evolution reaction (HER), the design of catalysts is still a core challenge in this field.

[0003] Existing studies have shown that noble metal catalysts (such as Au and Ag) exhibit excellent CO selectivity and catalytic efficiency in CO2RR, but are limited by cost and resource scarcity, making it difficult to achieve large-scale application. Therefore, the development of efficient electrocatalysts composed of abundant non-noble metal elements in the earth's crust has become a research hotspot. Single-atom catalysts (SACs) have shown great potential due to their unique structure and high atom utilization. p-block metal single-atom catalysts have shown great prospects in promoting the conversion of CO2RR to CO due to their high overpotential for HER. Among them, aluminum (Al), as the most abundant metal element in the earth's crust, if it can be stably supported and exhibit high activity, will greatly reduce the cost and expand the application prospects.

[0004] However, relying solely on active site design still cannot solve the problems of insufficient electron transport and structural stability. Carbon nanotubes (CNTs) can improve electron transport, stabilize single-atom dispersion, and enhance the overall structure and mass transfer performance of materials due to their excellent electrical conductivity, rich surface structure, and three-dimensional skeletal characteristics. Combining the advantages of CNTs with aluminum monatomic catalysts is expected to break through existing limitations and further improve the faradic efficiency of CO2 electroreduction to CO.

[0005] Currently, some patents and researches have attempted to improve performance by optimizing single-atom structure. For example, Chinese invention patent CN118563355A discloses a nickel-nitrogen-carbon electrocatalyst with high specific surface area, which significantly improves the selectivity of CO2 electroreduction; Chinese invention patent CN117448862A reports an iron single-atom catalyst suitable for reducing CO2 to CO under high current density conditions, which exhibits excellent CO selectivity and stability; Chinese invention patent CN116892030A proposes a carbon-supported cobalt single-atom catalyst with high bending structure, which has excellent electrocatalytic reduction of carbon dioxide performance in a wide voltage range. However, most of the related work focuses on transition metal systems, and the exploration of p-block element aluminum is limited, and the conductivity and support of CNT have not been fully combined. SUMMARY

[0006] The present application provides a preparation method of an aluminum single-atom nitrogen-doped carbon catalyst supported by carbon nanotubes. The catalyst prepared by the preparation method utilizes the conductivity and skeletal support of CNT to enable aluminum single atoms to be stably anchored and uniformly distributed in the nitrogen-doped carbon matrix, thereby achieving high-efficiency CO2 electroreduction performance.

[0007] To achieve the above-mentioned objectives, the present application provides a preparation method of an aluminum single-atom nitrogen-doped carbon catalyst supported by carbon nanotubes, comprising: Step one, adding a nitrogen source, an aluminum precursor solution, and carbon nanotubes into a solvent, stirring, heating, and ultrasonic dispersion to obtain a precursor solution, wherein the mass-volume ratio of the carbon nanotubes to the aluminum precursor solution is 2-3 g / 10 mL; Step two, drying and calcining the precursor solution, then performing acid treatment, filtration, washing, and drying to obtain an aluminum single-atom nitrogen-doped carbon catalyst.

[0008] By adding an appropriate amount of carbon nanotubes, the carbon nanotubes are uniformly distributed, which is beneficial to the effective diffusion and mass transfer of CO2, and the catalytically active sites distributed on the carbon nanotubes can fully exert their effectiveness, thereby achieving high-efficiency CO2 electroreduction performance and exhibiting excellent CO selectivity.

[0009] If the content of carbon nanotubes is too low, the carbon nanotubes are dispersed relatively loosely, and the carbon nanotubes are insufficiently distributed, which causes aluminum species to easily agglomerate into larger carbon nanosheet structures, thereby affecting the diffusion and mass transfer of CO2 and limiting the exertion of active sites.

[0010] If the content of carbon nanotubes is too high, the carbon nanotubes excessively accumulate and agglomerate, which causes the pores to be blocked and the mass transfer to be limited, thereby weakening the overall performance of the catalyst.

[0011] Preferably, the carbon nanotubes are one or more of multi-walled carbon nanotubes, hydroxylated multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, single-walled carbon nanotubes.

[0012] Further preferably, the carbon nanotubes are multi-walled carbon nanotubes.

[0013] Multi-walled carbon nanotubes have a multi-layer nested tubular structure, which can enhance the structural stability of the material through van der Waals forces and spatial support between the tube walls, preventing agglomeration or structural collapse during high-temperature calcination and electrocatalytic reactions. Its multi-level pore structure not only effectively increases the specific surface area, but also provides sufficient anchoring sites for aluminum single-atom active sites, thereby optimizing the diffusion and mass transfer efficiency of CO2. In addition, multi-walled carbon nanotubes provide a continuous electron conduction path with lower transmission resistance than modified carbon nanotubes, which can construct a high-efficiency three-dimensional conductive network to promote electron transfer and synergistically improve the activity and selectivity of the catalyst in the CO2 reduction reaction.

[0014] Preferably, the aluminum precursor solution is one or more of aluminum nitrate, aluminum acetate, aluminum chloride, aluminum acetylacetone, or a combination thereof, and the concentration of the aluminum precursor solution is 0.01-2 mol / L, preferably aluminum nitrate.

[0015] Preferably, the mass ratio of the nitrogen source to the carbon nanotubes is 8:1-12:1.

[0016] Preferably, the nitrogen source is one or more of dicyandiamide, melamine, urea, ammonia, preferably urea.

[0017] Preferably, the solvent is one or more of deionized water, ethanol, propanol, diethylene glycol, isopropanol, or a combination thereof, further preferably deionized water.

[0018] Preferably, the stirring rate is 100-1500 rpm.

[0019] Preferably, the drying temperature is 25-120°C, and the drying time is 6-12 h.

[0020] Preferably, the calcination heat treatment temperature is 600-1100°C, the heat treatment atmosphere is nitrogen or argon, the heating rate is 0.5-10°C / min, the calcination time is 30-200 min, and the gas flow rate is 50-150 mL / min.

[0021] Further preferably, the heat treatment atmosphere is nitrogen.

[0022] Preferably, the acid solution for acid treatment is one or more of sulfuric acid, hydrochloric acid, nitric acid, or a combination thereof.

[0023] Further preferably, the acid solution is sulfuric acid.

[0024] Preferably, the concentration of the acid solution is 0.1-2M, the acid treatment time is 2-24h, and the acid treatment time is 20-80℃.

[0025] The present application removes the unloaded aluminum component by controlling the concentration, time and treatment temperature of the acid solution, thereby obtaining an Al-NC catalyst uniformly dispersed.

[0026] Preferably, the filtering method is centrifugation or suction filtration.

[0027] Further preferably, the filtering method is centrifugation, and the centrifugation speed is 3000-12000rpm.

[0028] Preferably, the washing is 3-10 times of washing with ethanol or deionized water alternately.

[0029] Preferably, the drying temperature is 25-120℃, and the drying time is 6-12h.

[0030] In another aspect, the present application also provides the application of the Al-NC catalyst prepared by the preparation method of the carbon nanotube supported Al single-atom nitrogen-doped carbon catalyst in the catalytic reduction of carbon dioxide to carbon monoxide.

[0031] Compared with the prior art, the present application has the following beneficial effects: The present application introduces an appropriate amount of carbon nanotubes, which synergistically improves the structure and function of the catalyst. The carbon nanotubes not only provide a continuous conductive channel to improve electron transport, but also provide stable anchoring sites for the dispersion and fixation of aluminum single atoms, avoiding their clustering and deactivation. At the same time, the three-dimensional skeleton constructed by the carbon nanotubes effectively supports the overall structure of the material, ensuring the smoothness of the porous channel and promoting the mass transfer of gas and electrolyte. Aluminum, as an abundant metal on earth, reduces the cost of the catalyst, making it more economical and environmentally friendly. Compared with traditional catalysts that rely solely on material composition design, the present application reveals a new mechanism for structure-property optimization from the perspective of carrier function, with the advantages of low cost, scalability and long-term stable operation. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 SEM image of the Al-NC-1 single-atom catalyst prepared in Comparative Example 1; Figure 2 SEM image of the Al-NC-2 single-atom catalyst prepared in Example 1; Figure 3 SEM image of the Al-NC-3 single-atom catalyst prepared in Comparative Example 2; Figure 4Faraday efficiency plot of the catalyst prepared for Comparative Example 1 at different current; Figure 5 Faraday efficiency plot of the catalyst prepared for Example 1 at different current; Figure 6 Faraday efficiency plot of the catalyst prepared for Comparative Example 2 at different current; Figure 7 Faraday efficiency plot of the catalyst prepared for Example 2 at different current; Figure 8 Faraday efficiency plot of the catalyst prepared for Example 3 at different current; Figure 9 Faraday efficiency plot of the catalyst prepared for Comparative Example 3 at different current. DETAILED DESCRIPTION

[0033] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with the embodiments of the present application.

[0034] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application, however, can be practiced in a variety of ways beyond the specific embodiments described herein without departing from the scope of the present application, and it is understood that it is not intended to limit the present application to the described specific embodiments.

[0035] Secondly, the "one embodiment" or "an embodiment" as used herein means that a specific feature, structure, or characteristic described can be included in at least one implementation of the present application. The appearances of "in one embodiment" or "in an embodiment" at various places in the specification do not necessarily refer to the same embodiment, nor do they necessarily refer to a single implementation, although they can.

[0036] Comparative Example 1 A solution of aluminum nitrate with a concentration of 25 mg / mL was prepared as an aluminum source and was ready for use. In the following steps, 0.1 g of urea, 0.01 g of multi-walled carbon nanotubes, and 2 mL of the solution of aluminum nitrate were taken and added to 150 mL of deionized water. This solution was stirred at room temperature for 5 hours to ensure that the components in the solution were uniformly dispersed. Subsequently, the uniformity of the mixture was further promoted by ultrasonic treatment for 15 minutes. After the treatment, the solution was placed in a rotary evaporation device and was subjected to rotary evaporation at a temperature of 61°C to remove the water in the solution until the sample was concentrated to a dry state. The sample after rotary evaporation was placed in a vacuum drying oven at 60°C and was dried overnight to ensure that all the water was completely removed.

[0037] Next, the dried sample powder will be subjected to high-temperature heat treatment. The treatment process will be carried out in a nitrogen atmosphere, with an annealing temperature set at 900°C, a heating rate of 2°C / min, and an annealing time of 1 hour. This step helps to promote the formation of a stable structure of the aluminum and nitrogen-doped carbon material. After the annealing is completed, the sample will be subjected to acid treatment using a 0.5 M sulfuric acid solution to remove the unloaded aluminum components. During the acid treatment process, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution can effectively remove all excess aluminum components. The sample after acid treatment will be filtered to remove the acid solution and washed with deionized water and ethanol alternately for more than 3 times to ensure the purity of the sample. The wet filter cake after washing will be placed in a vacuum drying oven with a temperature set at 60°C for drying for 6 hours, and then naturally cooled to room temperature to obtain the catalyst Al-NC-1.

[0038] The electrode slurry is configured by taking 700 μL of isopropyl alcohol, 250 μL of deionized water, and 50 μL of a 5% Nafion film solution, and mixing them uniformly. 10 mg of the catalyst Al-NC-1 is added and ultrasonically dispersed for 30 min. The electrode slurry is sprayed on a carbon paper with a model number of 28 BC, and the carbon paper has a size of 2.5*2.5 cm 2 , to make a gas diffusion electrode. The gas diffusion electrode is placed in a flow electrolysis cell to act as a cathode for the electrocatalytic reduction of carbon dioxide reaction, and an iridium-plated titanium sheet is used as the anode. Both the cathode and the anode electrolyte use 1M potassium hydroxide solution, and the cathode and anode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are hydrogen and carbon monoxide.

[0039] The electrochemical test is carried out by using a constant current method, and the current density is 200, 400, 600, and 800 mA cm -2 .

[0040] Comparative Example 2 An aluminum nitrate solution with a concentration of 25 mg / mL is prepared as an aluminum source and is ready for use. In the following steps, 10 g of urea, 1 g of multi-walled carbon nanotubes, and 2 mL of the aluminum nitrate solution are added to 150 mL of deionized water. The solution is stirred at room temperature for 5 hours to ensure that the components in the solution are uniformly dispersed. Then, the uniformity of the mixture is further promoted by ultrasonic treatment for 15 minutes. After the treatment, the solution is placed in a rotary evaporation device and is subjected to rotary evaporation at a temperature of 61°C to remove the water in the solution until the sample is concentrated to a dry state. The sample after rotary evaporation is placed in a vacuum drying oven at 60°C and is dried overnight to ensure that all the water is completely removed.

[0041] Next, the dried sample powder will be subjected to high-temperature heat treatment. The treatment process will be carried out in a nitrogen atmosphere, with an annealing temperature set at 900°C, a heating rate of 2°C / min, and an annealing time of 1 hour. This step helps to promote the formation of a stable structure of the aluminum and nitrogen-doped carbon material. After the annealing is completed, the sample will be subjected to acid treatment using a 0.5 M sulfuric acid solution to remove the unloaded aluminum components. During the acid treatment process, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution can effectively remove all excess aluminum components. After acid treatment, the sample will be filtered to remove the acid solution and washed with deionized water and ethanol alternately for more than 3 times to ensure the purity of the sample. The wet filter cake after washing will be placed in a vacuum drying oven with a temperature set at 60°C for drying for 6 hours, and then naturally cooled to room temperature to obtain the final catalyst Al-NC-3.

[0042] The electrode slurry was prepared by mixing 700 μL of isopropyl alcohol, 250 μL of deionized water, and 50 μL of a 5% Nafion film solution. 10 mg of catalyst Al-NC-3 was added and ultrasonically dispersed for 30 min. The electrode slurry was sprayed onto a carbon paper with a model number of 28 BC, and the carbon paper had a size of 2.5*2.5 cm 2 , to form a gas diffusion electrode. The gas diffusion electrode was placed in a flow electrolysis cell to act as a cathode for the electrocatalytic reduction of carbon dioxide, and an iridium-plated titanium sheet was used as the anode. Both the cathode and the anode electrolyte used 1 M potassium hydroxide solution, and the cathode and anode electrode chambers were separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurred at the cathode, and the main products were hydrogen and carbon monoxide.

[0043] The electrochemical test was carried out using the constant current method, and the current density was 200, 400, 600, and 800 mA cm -2 .

[0044] Example 1 An aluminum nitrate solution with a concentration of 25 mg / mL was prepared as an aluminum source and was ready for use. In the following steps, 5 g of urea, 0.5 g of multi-walled carbon nanotubes, and 2 mL of aluminum nitrate solution were added to 150 mL of deionized water. The solution was stirred at room temperature for 5 hours to ensure that the components in the solution were uniformly dispersed. Subsequently, ultrasonic treatment for 15 minutes was used to further promote the uniformity of the mixture. After treatment, the solution was subjected to rotary evaporation at a temperature of 61°C to remove the water in the solution until the sample was concentrated to a dry state. The sample after rotary evaporation was placed in a vacuum drying oven at 60°C and dried overnight to ensure that all the water was completely removed.

[0045] Next, the dried sample powder will be subjected to high-temperature heat treatment. This process will be carried out in a nitrogen atmosphere, with an annealing temperature set at 900°C, a heating rate of 2°C / min, and an annealing time of 1 hour. This step helps to promote the formation of a stable structure of the aluminum and nitrogen-doped carbon material. After the annealing is complete, the sample will be subjected to acid treatment using a 0.5 M sulfuric acid solution to remove the unloaded aluminum cluster components. During the acid treatment, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution can effectively remove all excess aluminum components. The sample after acid treatment will be filtered to remove the acid solution and washed with deionized water and ethanol alternately for 5 times to ensure the purity of the sample. The wet filter cake after washing will be placed in a vacuum drying oven with a temperature set at 60°C for drying for 6 hours, and then naturally cooled to room temperature to obtain the catalyst Al-NC-2.

[0046] The electrode slurry is configured by taking 700 μL of isopropyl alcohol, 250 μL of deionized water, and 50 μL of a 5% Nafion film solution, and mixing them uniformly. 10 mg of the catalyst Al-NC-2 is added and ultrasonically dispersed for 30 min. The electrode slurry is sprayed on a carbon paper with a model number of 28 BC, and the size of the carbon paper is 2.5*2.5 cm 2 , to make a gas diffusion electrode. The gas diffusion electrode is placed in a flow electrolysis cell to act as a cathode for the electrocatalytic reduction of carbon dioxide reaction, and an iridium-plated titanium sheet is used as the anode. Both the cathode and the anode electrolyte use 1 M potassium hydroxide solution, and the cathode and anode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are hydrogen and carbon monoxide.

[0047] The electrochemical test is carried out by using the constant current method, and the current density is 200, 400, 600, 800 mA cm -2 .

[0048] Example 2 An aluminum nitrate solution with a concentration of 25 mg / mL is prepared as an aluminum source and is ready for use. In the following steps, 5 g of dicyandiamide, 0.5 g of multi-walled carbon nanotubes, and 2 mL of the aluminum nitrate solution are added to 150 mL of deionized water. This solution is stirred at room temperature for 5 hours to ensure that the components in the solution are uniformly dispersed. Subsequently, ultrasonic treatment for 15 minutes is used to further promote the uniformity of the mixture. After the treatment, the solution is subjected to rotary evaporation at a temperature of 61°C to remove the water in the solution until the sample is concentrated to a dry state. The sample after rotary evaporation is placed in a vacuum drying oven at 60°C and dried overnight to ensure that all the water is completely removed.

[0049] Next, the dried sample powder will be subjected to high-temperature heat treatment. This process will be carried out in a nitrogen atmosphere, with an annealing temperature set at 900°C, a heating rate of 2°C / min, and an annealing time of 1 hour. This step helps to promote the formation of a stable structure of the aluminum and nitrogen-doped carbon material. After the annealing is complete, the sample will be subjected to acid treatment using a 0.5 M sulfuric acid solution to remove the unloaded aluminum cluster components. During the acid treatment, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution can effectively remove all excess aluminum components. After acid treatment, the sample will be filtered to remove the acid solution and washed with deionized water and ethanol alternately for 5 times to ensure the purity of the sample. The wet filter cake after washing will be placed in a vacuum drying oven with a temperature setting of 60°C for drying for 6 hours, and then naturally cooled to room temperature to obtain the catalyst Al-NC-4.

[0050] The electrode slurry is configured by taking 700 μL of isopropyl alcohol, 250 μL of deionized water, and 50 μL of a 5% Nafion film solution, and mixing them uniformly. 10 mg of the above-mentioned catalyst Al-NC-4 is added and ultrasonically dispersed for 30 min. The electrode slurry is sprayed onto a carbon paper with a model number of 28BC, and the carbon paper has a size of 2.5*2.5 cm 2 , to make a gas diffusion electrode. The gas diffusion electrode is placed in a flow electrolysis cell to act as a cathode for the electrocatalytic reduction of carbon dioxide reaction, and an iridium-plated titanium sheet is used as the anode. Both the cathode and the anode electrolyte use 1 M potassium hydroxide solution, and the cathode and anode electrode chambers are separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurs at the cathode, and the main products are hydrogen and carbon monoxide.

[0051] The electrochemical test is carried out by using the constant current method, and the current density is 200, 400, 600, 800 mA cm -2 .

[0052] Example 3 An aluminum nitrate solution with a concentration of 25 mg / mL is prepared as an aluminum source and is ready for use. In the following steps, 4 g of urea, 0.4 g of multi-walled carbon nanotubes, and 1.7 mL of aluminum nitrate solution are added to 150 mL of deionized water. This solution is stirred at room temperature for 5 hours to ensure that the components in the solution are uniformly dispersed. Subsequently, ultrasonic treatment for 15 minutes is used to further promote the uniformity of the mixture. After treatment, the solution is subjected to rotary evaporation at a temperature of 61°C to remove the water in the solution until the sample is concentrated to a dry state. The sample after rotary evaporation is placed in a vacuum drying oven at 60°C and dried overnight to ensure that all the water is completely removed.

[0053] Next, the dried sample powder will be subjected to high-temperature heat treatment. This process will be carried out in a nitrogen atmosphere, with an annealing temperature set at 900°C, a heating rate of 2°C / min, and an annealing time of 1 hour. This step helps to promote the formation of a stable structure of the aluminum and nitrogen-doped carbon material. After the annealing is complete, the sample will be subjected to acid treatment using a 0.5 M sulfuric acid solution to remove the unloaded aluminum cluster components. During the acid treatment, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution can effectively remove all excess aluminum components. The sample after acid treatment will be filtered to remove the acid solution and washed with deionized water and ethanol alternately 5 times to ensure the purity of the sample. The wet filter cake after washing will be placed in a vacuum drying oven with a temperature set at 60°C for drying for 6 hours, and then naturally cooled to room temperature to obtain the catalyst Al-NC-5.

[0054] The electrode slurry was configured by taking 700 μL of isopropyl alcohol, 250 μL of deionized water, and 50 μL of a 5% Nafion film solution, and mixing them uniformly. 10 mg of the above-mentioned catalyst Al-NC-4 was added and ultrasonically dispersed for 30 min. The electrode slurry was sprayed onto a carbon paper with a model number of 28BC, and the size of the carbon paper was 2.5*2.5 cm 2 , to make a gas diffusion electrode. The gas diffusion electrode was placed in a flow electrolysis cell to act as a cathode for the electrocatalytic reduction of carbon dioxide, and an iridium-plated titanium sheet was used as the anode. Both the cathode and the anode electrolyte used 1 M potassium hydroxide solution, and the cathode and anode electrode chambers were separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurred in the cathode, and the main products were hydrogen and carbon monoxide.

[0055] The electrochemical test was carried out by the constant current method, and the current density was 200, 400, 600, 800 mA cm -2 .

[0056] Comparative Example 3 5 g of urea and 0.5 g of multi-walled carbon nanotubes were taken and added to 150 mL of deionized water. This solution was stirred at room temperature for 5 hours to ensure that the components in the solution were uniformly dispersed. Then, the uniformity of the mixture was further promoted by ultrasonic treatment for 15 minutes. After the treatment, the solution was placed in a rotary evaporation device and rotary evaporated at a temperature of 61°C to remove the water in the solution until the sample was concentrated to a dry state. The sample after rotary evaporation was placed in a vacuum drying oven at 60°C and dried overnight to ensure that all the water was completely removed.

[0057] Next, the dried sample powder will undergo high-temperature heat treatment. This process will be carried out in a nitrogen atmosphere, with the annealing temperature set at 900℃, a heating rate of 2℃ / min, and an annealing time of 1 hour. This step helps promote the formation of a stable structure in the aluminum and nitrogen-doped carbon material. After annealing, the sample will undergo acid treatment using a 0.5 M sulfuric acid solution to remove unloaded aluminum components. During acid treatment, the sample needs to be continuously stirred for 8 hours to ensure that the acid solution effectively removes all excess aluminum components. The acid-treated sample will be filtered to remove the acid solution and washed with deionized water and ethanol alternately at least three times to ensure sample purity. The washed wet filter cake will be placed in a vacuum drying oven at 60℃ for 6 hours, and then naturally cooled to room temperature to obtain Al-NC-6.

[0058] Prepare the electrode slurry by mixing 700 μL isopropanol, 250 μL deionized water, and 50 μL 5% Nafion membrane solution until homogeneous. Add 10 mg of Al-NC-6 catalyst and sonicate for 30 min to disperse evenly. Spray the electrode slurry onto carbon paper (model 28 BC, 2.5 x 2.5 cm). 2 A gas diffusion electrode was fabricated. This electrode was placed in a flowing electrolytic cell as the cathode to perform the electrocatalytic reduction of carbon dioxide, while the anode was an iridium-plated titanium sheet. Both the cathode and anode electrolytes used a 1M potassium hydroxide solution, and the anode and cathode chambers were separated by a cation exchange membrane. The carbon dioxide catalytic reaction occurred at the cathode, with the main products being hydrogen and carbon monoxide.

[0059] Electrochemical tests were performed using the galvanostatic method at current densities of 200, 400, 600, and 800 mA cm⁻¹. -2 .

[0060] like Figure 1 As shown in (a) and (b), the SEM images of the Al-NC-1 catalyst reveal a relatively loose structure with insufficient carbon nanotube distribution, leading to the easy aggregation of some aluminum species into larger carbon nanosheet structures. This structural defect hinders the effective diffusion and mass transfer of CO2, thus limiting the full utilization of catalytic active sites.

[0061] like Figure 2 As shown in (a) and (b), the SEM images of Al-NC-2 demonstrate that carbon nanotubes are uniformly distributed throughout the material, forming a continuous three-dimensional conductive framework that effectively supports the overall structure and prevents aluminum species aggregation. This structure ensures efficient electron transport and improves mass transfer conditions during the reaction process, providing a material basis for achieving excellent CO2 reduction performance.

[0062] like Figure 3As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0063] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 4 As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0064] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 5 As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0065] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 6 As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0066] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 7 As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0067] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 8 As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst.

[0068] As shown in (a) and (b), the SEM image of Al-NC-3 shows that the content of carbon nanotubes is too high, which leads to excessive accumulation of carbon nanotubes in the material and agglomeration, and part of the channels are blocked, resulting in limited mass transfer. Such unreasonable structure distribution weakens the overall performance of the catalyst. Figure 9As shown, the comparative sample Al-NC-6 (without aluminum single-atom active sites) showed a clear disadvantage under the same test conditions, with FECO always below 20% and no significant improvement with increasing current density. In contrast, the Al-NC catalysts prepared in Examples 1, 2, and 3 all significantly suppressed the hydrogen evolution side reaction and maintained high CO selectivity, further demonstrating the importance of the synergistic effect of aluminum single atoms and CNTs.

[0069] It should be noted that the above examples only illustrate the technical solutions of the present application rather than limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application, and all modifications and equivalent replacements should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon catalyst with aluminum single atom support based on carbon nanotubes, characterized in that, include: Step 1: Add nitrogen source, aluminum precursor solution and carbon nanotubes to solvent, stir, heat and ultrasonically disperse to obtain precursor solution, wherein the mass-to-volume ratio of carbon nanotubes to aluminum precursor solution is 2–3 g / 10 mL. Step 2: After drying the precursor solution, calcination heat treatment is performed, followed by acid treatment, filtration, washing, and drying to obtain an aluminum single-atom nitrogen-doped carbon catalyst.

2. The method for preparing the nitrogen-doped carbon catalyst based on carbon nanotube support for aluminum single atoms according to claim 1, characterized in that, The carbon nanotubes are one or more of the following: multi-walled carbon nanotubes, hydroxylated multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes, and single-walled carbon nanotubes.

3. The method for preparing the nitrogen-doped carbon catalyst based on carbon nanotube support for aluminum single atoms according to claim 2, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes.

4. The method for preparing the nitrogen-doped carbon catalyst of aluminum single atom supported by carbon nanotubes according to claim 1, characterized in that, The aluminum precursor solution is one or more of aluminum nitrate, aluminum acetate, aluminum chloride, aluminum acetylacetone, or a combination thereof, and the concentration of the aluminum precursor solution is 0.01-2 mol / L.

5. The method for preparing the nitrogen-doped carbon catalyst of aluminum single atom supported by carbon nanotubes according to claim 1, characterized in that, The mass ratio of the nitrogen source to carbon nanotubes is 8:1 to 12:

1.

6. The method for preparing the nitrogen-doped carbon catalyst of aluminum single atom supported by carbon nanotubes according to claim 1, characterized in that, The nitrogen source is one or more of dicyandiamide, melamine, urea, and ammonia.

7. The method for preparing the nitrogen-doped carbon catalyst based on carbon nanotube support for aluminum single atoms according to claim 1, characterized in that, The solvent is one or more of deionized water, ethanol, propanol, diethylene glycol, isopropanol, or combinations thereof.

8. The method for preparing a nitrogen-doped carbon catalyst based on carbon nanotube support for aluminum single atoms according to claim 1, characterized in that, The stirring speed is 100-1500 rpm.

9. The method for preparing the nitrogen-doped carbon catalyst of aluminum single atom supported by carbon nanotubes according to claim 1, characterized in that, The calcination heat treatment temperature is 600-1100℃, the heat treatment atmosphere is nitrogen or argon, the heating rate is 0.5-10℃ / min, the calcination time is 30-200 min, and the gas flow rate is 50-150 mL / min.

10. The application of an aluminum single-atom nitrogen-doped carbon catalyst prepared by the method of preparing an aluminum single-atom nitrogen-doped carbon catalyst based on carbon nanotube support according to any one of claims 1-9 in the catalytic reduction reaction of carbon dioxide to carbon monoxide.

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