Preparation method and application of nickel monatomic sulfur-nitrogen co-doped foam carbon monolithic catalyst

Abstract

The application belongs to the technical field of carbon material preparation, and discloses a preparation method of a nickel monatomic sulfur-nitrogen co-doped foam carbon monolithic catalyst and application thereof. The preparation method comprises the following steps: cutting, washing and drying polyurethane foam; dissolving coal liquefaction pitch in tetrahydrofuran, and then immersing the polyurethane foam in the tetrahydrofuran, and then drying; oxidizing and curing the impregnated and dried polyurethane foam, and then co-pyrolyzing the polyurethane foam with melamine to obtain nitrogen-doped foam carbon; immersing the prepared nitrogen-doped foam carbon in a nickel nitrate-containing N,N-dimethylformamide solution to obtain a nickel-containing nitrogen-doped foam carbon intermediate; co-pyrolyzing thiourea and the nickel-containing nitrogen-doped foam intermediate in a corundum boat in an inert atmosphere, and then performing acid washing and vacuum drying on the sample after cooling to obtain a target material. The application has the advantages of simple process and easy scale preparation, and the material has large current density, high carbon monoxide Faraday efficiency and good stability when applied to the electrocatalytic reduction of carbon dioxide to carbon monoxide.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalysis and relates to a method for preparing a nickel single-atom sulfur and nitrogen co-doped foamed carbon monolithic catalyst and its application. Background Technology

[0002] With the acceleration of industrialization, human demand for fossil fuels has increased dramatically, leading to a continuous rise in the consumption of resources such as coal, oil, and natural gas, and consequently, a sustained increase in CO2 levels in the Earth's atmosphere. Currently, the CO2 concentration in the Earth's atmosphere has reached 430 ppm, far exceeding the normal level in nature, thus triggering a series of environmental problems. To address the problem of excessive CO2 emissions, researchers have proposed methods to reduce CO2 into highly productive chemicals through electrochemical catalysis. However, this approach also faces many challenges, such as complex reduction products and the presence of hydrogen evolution side reactions. Therefore, there is an urgent need to develop catalysts with high activity and high selectivity. Currently, MNC catalysts are widely used in CO2 electroreduction reactions due to their high atom utilization and unique electronic structure. The M-N4 site is generally considered to be the common active center of this type of catalyst. Its high geometric and electronic symmetry leads to excessive enrichment of electrons in the metal center, increasing the energy barrier and reducing selectivity. By employing strategies such as heteroatom doping, the electronic structure of the metal center can be altered to enhance its intrinsic activity. Compared to N atoms, S atoms have a larger atomic radius, are more easily polarized, and have lower electronegativity in donating electrons, which can significantly modulate the local electron density, thereby improving the activity and selectivity of MNC catalysts.

[0003] Furthermore, as shown in "Dimensionality Engineering toward Carbon Materials for Electrochemical CO2 Reduction: Progress and Prospect," MNC catalysts are generally present in powder form. In practical applications, polymer binders (such as polytetrafluoroethylene or Nafion) are needed to fix the nanoparticles onto a conductive substrate. This inevitably increases resistance and reduces current density. Simultaneously, the active components are prone to detachment under high voltages, resulting in poor stability and severely limiting their practical application. Directly growing them on a three-dimensional conductive substrate to create a self-supporting monolithic electrode represents a new development direction. Self-supporting monolithic catalysts do not require complex coating processes or the addition of additional binders, simplifying the preparation process while ensuring rapid electron transport and electrode structural stability.

[0004] In view of this, the present invention proposes a method for preparing a nickel single-atom sulfur and nitrogen co-doped foamed carbon monolithic catalyst, which can effectively solve the problems of low current density, selectivity and stability of MNC catalysts and exhibit excellent performance in electrocatalytic CO2 reduction. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a method for preparing a nickel-monomeric single-atom sulfur-nitrogen co-doped foamed carbon catalyst and its application. This invention prepares a nickel-monomeric single-atom sulfur-nitrogen co-doped foamed carbon catalyst via a template method, impregnation method, and secondary pyrolysis. This method is simple and easy to scale up. The introduction of sulfur atoms improves the catalyst's selectivity, while the monolithic structure accelerates electron transfer and exhibits good stability. It demonstrates high current density, high Faradaic efficiency, and high stability in the electrocatalytic reduction of CO2.

[0006] The technical solution of this invention:

[0007] A method for preparing a nickel-monolithic single-atom sulfur-nitrogen co-doped foamed carbon catalyst includes the following steps:

[0008] (1) Cut the polyurethane foam into pieces of (0.5~1.0)×(0.5~1.0)×(1.0~2.0)cm. 3 The rectangular blocks were washed 3 to 5 times with deionized water and anhydrous ethanol to remove surface impurities, and then placed in a forced-air drying oven to dry at 60 to 100°C for 6 to 12 hours.

[0009] (2) Add coal liquefaction pitch to tetrahydrofuran solution, stir and sonicate for 0.5 to 2 hours to obtain a uniformly mixed pitch solution; immerse the dried polyurethane foam from step (1) into the pitch solution, squeeze repeatedly to remove excess pitch solution, and dry the impregnated polyurethane foam at room temperature for 48 to 96 hours.

[0010] (3) The polyurethane foam loaded with asphalt in step (2) is oxidized and cured at 300-500°C for 0.5-2 hours in an air atmosphere. After cooling to room temperature, it is co-pyrolyzed with melamine in an inert atmosphere to obtain nitrogen-doped foam carbon.

[0011] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in N,N-dimethylformamide solution containing nickel nitrate for 12-24 hours at room temperature. After immersion, it is taken out and placed in a forced-air drying oven to dry at 60-100℃ for 12-24 hours to obtain nickel-doped nitrogen foam carbon intermediate.

[0012] (5) Thiourea and nickel-nitrogen-doped foamed carbon intermediates are mixed and pyrolyzed under an inert atmosphere. After cooling to room temperature, they are soaked in 0.5-2 mol / L HCl for 12-24 h, then washed with deionized water until neutral, and dried in a vacuum drying oven at 60-100 °C for 12-24 h to obtain a nickel single-atom sulfur-nitrogen co-doped foamed carbon monolithic catalyst.

[0013] Preferably, the pore size of the polyurethane foam in step (1) is 40 to 60 PPI.

[0014] Preferably, the mass ratio of coal liquefaction pitch to tetrahydrofuran in the pitch solution in step (2) is 1:2 to 1:4.

[0015] Preferably, the oxidative curing heating rate in step (3) is 1 to 3 °C / min.

[0016] Preferably, the pyrolysis conditions in step (3) are: heating from room temperature to 700-900°C at a heating rate of 1-5°C / min, and holding at that temperature for 1-3 hours.

[0017] Preferably, the concentration of the N,N-dimethylformamide solution containing nickel nitrate in step (4) is 0.02 to 0.05 mol / L.

[0018] Preferably, the pyrolysis conditions in step (5) are: heating from room temperature to 800-1000℃ at a heating rate of 3-7℃ / min, and holding at that temperature for 1-3 hours.

[0019] Application of the nickel single-atom sulfur and nitrogen co-doped foamed carbon monolithic catalyst prepared by the above method in CO2 electrocatalytic reduction.

[0020] The beneficial effects of this invention are: (a) By introducing S atoms, this method forms a Ni-N3S coordination structure with Ni and N atoms, changing the coordination of Ni-N and altering the surface chemical state of Ni atoms, thus regulating the local electron density at the Ni atom center and improving the selectivity of the catalyst; (b) The three-dimensional porous self-supporting integral structure can provide a larger three-phase contact area, which is beneficial for the dispersion of active components, while also promoting mass transfer, accelerating electron transport, and ensuring the stability of the electrode structure; (c) Compared with traditional metal substrates, carbon foam has advantages such as low cost, good thermal stability, good mechanical properties, low density, and strong processability; (d) The preparation method provided is simple, the raw materials are readily available, and it is easy to scale up production. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of nickel single-atom sulfur-nitrogen co-doped foam carbon prepared in Example 1.

[0022] Figure 2This is a high-resolution XPS S2p spectrum of the nickel single-atom sulfur-nitrogen co-doped foam carbon prepared in Example 1.

[0023] Figure 3 This is a graph showing the CO2 electroreduction performance of nickel single-atom sulfur-nitrogen co-doped foam carbon prepared in Example 1.

[0024] Figure 4 This is a potentiostatic electrolysis diagram of nickel single-atom sulfur-nitrogen co-doped foam carbon prepared in Example 1. Detailed Implementation

[0025] The specific embodiments of the present invention are further described below with reference to the accompanying drawings and technical solutions.

[0026] Example 1

[0027] (1) Cut polyurethane foam with a pore size of 50 PPI into pieces of 1.0 × 0.5 × 2.0 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 80°C for 12 hours.

[0028] (2) Weigh 4g of coal liquefaction pitch and add it to 12g of tetrahydrofuran solution. Stir and sonicate for 1h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 72h.

[0029] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 350°C at a heating rate of 1°C / min in air atmosphere and kept for 1h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 3g of melamine and heated from room temperature to 900°C at a heating rate of 5°C / min in inert atmosphere and kept for 2h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0030] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.03 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 80 °C for 12 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0031] (5) Weigh 3g of thiourea and place it in a corundum boat. Put in the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4). Under an inert atmosphere, heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 80℃ for 12h to obtain the target material.

[0032] The obtained samples were observed using a scanning electron microscope, such as Figure 1 As shown, it retains the interconnected pore structure in the polyurethane template, has a more continuous conductive network, can provide a larger three-phase contact area, accelerate the rapid diffusion of CO2 gas in the CO2RR process, promote its full contact with the electrolyte for material exchange, and accelerate the reaction rate. Figure 2 The high-resolution XPS S2p spectrum of the obtained sample shows that the introduced S atoms formed a coordination structure with Ni atoms and simultaneously altered the surface chemical state of the Ni atoms. The CO2 electrocatalytic reduction test of the sample yielded the following results: Figure 3 As shown, at -1.4V vs. RHE, the CO Faraday efficiency can reach 97.8%, and the CO local current density is 57.8 mA cm⁻¹. -2 Furthermore, in the voltage range of -1.0 to -1.8V vs. RHE, the CO Faraday efficiency is above 90%. Figure 4 To test the stability of the sample, constant potential electrolysis was performed for 8 hours at -1.4V vs. RHE. The current density remained stable and the CO Faraday efficiency remained above 90%, indicating that it has good stability.

[0033] Example 2

[0034] (1) Cut polyurethane foam with a pore size of 40 PPI into pieces of 1.0 × 0.8 × 1.5 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 100°C for 8 hours.

[0035] (2) Weigh 5g of coal liquefaction pitch and add it to 15g of tetrahydrofuran solution. Stir and sonicate for 1.5h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 84h.

[0036] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 300°C at a heating rate of 1.5°C / min in air atmosphere and held for 1.5h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 3.5g of melamine and heated from room temperature to 800°C at a heating rate of 5°C / min in inert atmosphere and held for 3h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0037] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.04 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 100 °C for 8 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0038] (5) Weigh 3.5g of thiourea and place it in a corundum boat. Put in the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4). Under an inert atmosphere, heat the temperature from room temperature to 800℃ at a heating rate of 5℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 100℃ for 8h to obtain the target material.

[0039] The obtained sample was subjected to electrocatalytic CO2 reduction tests, and its CO Faraday efficiency reached 88.2% at -1.8V vs. RHE, with a CO local current density of 48.6 mA cm⁻¹. -2 Furthermore, in the voltage range of -1.4 to -1.8V vs. RHE, the CO Faraday efficiency is above 80%.

[0040] Example 3

[0041] (1) Cut polyurethane foam with a pore size of 50 PPI into pieces of 0.8 × 0.5 × 1.5 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 80°C for 8 hours.

[0042] (2) Weigh 2.5g of coal liquefaction pitch and add it to 7.5g of tetrahydrofuran solution. Stir and sonicate for 0.5h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 60h.

[0043] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 300°C at a heating rate of 1°C / min in air atmosphere and held for 1.5h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 2g of melamine and heated from room temperature to 800°C at a heating rate of 5°C / min in inert atmosphere and held for 3h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0044] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.02 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0045] (5) Weigh 2g of thiourea and place it in a corundum boat. Put in the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4). Under an inert atmosphere, heat the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and maintain it for 1h. After cooling to room temperature, soak it in 1mol / L HCl for 12h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 100℃ for 12h to obtain the target material.

[0046] The obtained sample was subjected to electrocatalytic CO2 reduction tests, and its CO Faraday efficiency reached 89.8% at -1.8V vs. RHE, with a local CO current density of 57.8 mA cm⁻¹. -2 Furthermore, in the voltage range of -1.2 to -1.8V vs. RHE, the CO Faraday efficiency is above 80%.

[0047] Example 4

[0048] (1) Cut polyurethane foam with a pore size of 60 PPI into pieces of 1.0 × 0.5 × 1.0 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 60°C for 12 hours.

[0049] (2) Weigh 2g of coal liquefaction pitch and add it to 5g of tetrahydrofuran solution. Stir and sonicate for 1h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 48h.

[0050] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 400°C at a heating rate of 2°C / min in air atmosphere and held for 0.5h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 2g of melamine and heated from room temperature to 700°C at a heating rate of 5°C / min in inert atmosphere and held for 2h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0051] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.04 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 80 °C for 18 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0052] (5) Weigh 2g of thiourea and place it in a corundum boat. Put the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4) into the boat. Under an inert atmosphere, heat the temperature from room temperature to 1000℃ at a heating rate of 7℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1.5mol / L HCl for 18h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 100℃ for 12h to obtain the target material.

[0053] Electrocatalytic CO2 reduction tests were conducted on the obtained samples. The CO Faraday efficiency reached 94.6% at -1.4V vs. RHE, with a local CO current density of 44.8 mA cm⁻¹. -2 Furthermore, in the voltage range of -1.0 to -1.8V vs. RHE, the CO Faraday efficiency is above 90%.

[0054] Example 5

[0055] (1) Cut polyurethane foam with a pore size of 40 PPI into pieces of 1.0 × 0.5 × 1.5 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 60°C for 24 hours.

[0056] (2) Weigh 3.5g of coal liquefaction pitch and add it to 10g of tetrahydrofuran solution. Stir and sonicate for 2 hours to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 96 hours.

[0057] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 400°C at a heating rate of 1.5°C / min in air atmosphere and kept for 1h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 4g of melamine and heated from room temperature to 800°C at a heating rate of 4°C / min in inert atmosphere and kept for 3h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0058] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.03 mol / L nickel nitrate for 24 h at room temperature. After immersion, it is taken out and placed in a forced-air drying oven to dry at 80 °C for 18 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0059] (5) Weigh 3g of thiourea and place it in a corundum boat. Put in the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4). Under an inert atmosphere, heat the temperature from room temperature to 900℃ at a heating rate of 5℃ / min and maintain it for 3h. After cooling to room temperature, soak it in 2mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 100℃ for 12h to obtain the target material.

[0060] Electrocatalytic CO2 reduction tests were conducted on the obtained samples. The CO Faraday efficiency reached 92.4% at -1.4V vs. RHE, with a local CO current density of 48.5 mA cm⁻¹. -2Furthermore, in the voltage range of -1.2 to -1.8V vs. RHE, the CO Faraday efficiency is above 90%.

[0061] Comparative Example 1

[0062] (1) Cut polyurethane foam with a pore size of 50 PPI into pieces of 1.0 × 0.5 × 2.0 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 80°C for 12 hours.

[0063] (2) Weigh 4g of coal liquefaction pitch and add it to 12g of tetrahydrofuran solution. Stir and sonicate for 1h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 72h.

[0064] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 350°C at a heating rate of 1°C / min in air atmosphere and kept for 1h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 3g of melamine and heated from room temperature to 900°C at a heating rate of 5°C / min in inert atmosphere and kept for 2h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0065] (4) Weigh 3g of thiourea and place it in a corundum boat. Put the nitrogen-doped foam carbon intermediate obtained in step (3) into the boat. Under an inert atmosphere, raise the temperature from room temperature to 900℃ at a rate of 5℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 80℃ for 12h to obtain the target material.

[0066] Electrocatalytic CO2 reduction tests were conducted on the obtained samples. The CO Faraday efficiency was only 35.2% at -1.4V vs. RHE, and the local CO current density was only 9.6 mA cm⁻¹. -2 Compared to Example 1, Comparative Example 1 did not include a nickel source during preparation, thus obtaining sulfur-nitrogen co-doped foamed carbon. The results show that the current density and CO Faradaic efficiency of the sulfur-nitrogen co-doped foamed carbon during electrocatalysis are significantly reduced, because it does not form Ni-Nx and Ni-S structures.

[0067] Comparative Example 2

[0068] (1) Cut polyurethane foam with a pore size of 50 PPI into pieces of 1.0 × 0.5 × 2.0 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 80°C for 12 hours.

[0069] (2) Weigh 4g of coal liquefaction pitch and add it to 12g of tetrahydrofuran solution. Stir and sonicate for 1h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 72h.

[0070] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 350°C at a heating rate of 1°C / min in air atmosphere and kept for 1h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 3g of melamine and heated from room temperature to 900°C at a heating rate of 5°C / min in inert atmosphere and kept for 2h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0071] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.03 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 80 °C for 12 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0072] (5) Weigh 3g of melamine and place it in a corundum boat. Put the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4) into the boat. Under an inert atmosphere, heat the temperature from room temperature to 900℃ at a rate of 5℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 80℃ for 12h to obtain the target material.

[0073] The obtained sample was subjected to electrocatalytic CO2 reduction tests. The CO Faraday efficiency was 75.0% at -1.4 V vs. RHE, and the local CO current density was 32.1 mA cm⁻¹. -2 In Comparative Example 2, the nickel-doped nitrogen foam carbon obtained by replacing thiourea with melamine showed a significant decrease in current density and CO Faraday efficiency during electrocatalysis compared to Example 1. This is because the absence of S atoms resulted in the formation of a Ni-N4 coordination structure between N and Ni atoms. The high geometric and electronic symmetry of this structure led to excessive enrichment of electrons in the metal center, increasing the energy barrier and reducing selectivity.

[0074] Comparative Example 3

[0075] (1) Cut polyurethane foam with a pore size of 50 PPI into pieces of 1.0 × 0.5 × 2.0 cm. 3 The rectangular block was rinsed three times with deionized water and anhydrous ethanol and then placed in a forced-air drying oven and dried at 80°C for 12 hours.

[0076] (2) Weigh 4g of coal liquefaction pitch and add it to 12g of tetrahydrofuran solution. Stir and sonicate for 1h to form a uniform pitch solution. Immerse the dried polyurethane foam from step (1) into it and repeatedly squeeze to remove excess pitch solution. Place the impregnated polyurethane foam at room temperature and dry for 72h.

[0077] (3) The polyurethane foam loaded with asphalt in step (2) was heated to 350°C at a heating rate of 1°C / min in air atmosphere and kept for 1h to oxidize and cure it. After cooling to room temperature, it was placed in a corundum boat containing 3g of melamine and heated from room temperature to 900°C at a heating rate of 5°C / min in inert atmosphere and kept for 2h. After cooling to room temperature, nitrogen-doped foam carbon was obtained.

[0078] (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in 30 mL of N,N-dimethylformamide solution containing 0.03 mol / L nickel nitrate and immersed for 12 h at room temperature. After the immersion is completed, it is taken out and placed in a forced-air drying oven and dried at 80 °C for 12 h to obtain nickel-doped nitrogen foam carbon intermediate.

[0079] (5) Weigh 3g of thiourea and place it in a corundum boat. Put in the nickel-nitrogen-doped foamed carbon intermediate obtained in step (4). Under an inert atmosphere, raise the temperature from room temperature to 500℃ at a heating rate of 5℃ / min and maintain it for 2h. After cooling to room temperature, soak it in 1mol / L HCl for 24h. Then wash it with deionized water until neutral. Place it in a vacuum drying oven and dry it at 80℃ for 12h to obtain the target material.

[0080] The obtained sample was subjected to electrocatalytic CO2 reduction tests. The CO Faraday efficiency was 52.8% at -1.4 V vs. RHE, and the local CO current density was 23.5 mA cm⁻¹. -2 In Comparative Example 3, the pyrolysis temperature in step (5) was reduced to 500 degrees Celsius. Compared with Example 1, the current density and CO Faradaic efficiency during electrocatalysis were significantly reduced. This is because the thiourea was not completely decomposed at the low temperature and did not form a sufficient coordination structure with Ni atoms.

Claims

1. A method for preparing a nickel-monolithic single-atom sulfur-nitrogen co-doped foamed carbon catalyst, characterized in that, Includes the following steps: (1) Cut the polyurethane foam, remove impurities, and dry it; (2) Add coal liquefaction pitch to tetrahydrofuran solution, stir and sonicate for 0.5 to 2 h to obtain a uniformly mixed pitch solution; after immersing the dried polyurethane foam in step (1) into the pitch solution, repeatedly squeeze to remove excess pitch solution, and dry the impregnated polyurethane foam at room temperature for 48 to 96 h to obtain pitch-loaded polyurethane foam. (3) The polyurethane foam loaded with asphalt in step (2) is oxidized and cured at 300 ~ 500 ℃ for 0.5 ~ 2 h in an air atmosphere. After cooling to room temperature, it is co-pyrolyzed with melamine in an inert atmosphere to obtain nitrogen-doped foam carbon. (4) The nitrogen-doped foam carbon obtained in step (3) is immersed in N,N-dimethylformamide solution containing nickel nitrate for 12 to 24 h at room temperature. After immersion, it is taken out and placed in a forced-air drying oven and dried at 60 to 100 °C for 12 to 24 h to obtain nickel-doped nitrogen foam carbon intermediate. (5) Thiourea and nickel-nitrogen-doped foamed carbon intermediates are mixed and pyrolyzed under an inert atmosphere. After cooling to room temperature, they are soaked in 0.5-2 mol / L HCl for 12-24 h, then washed with deionized water until neutral, and dried in a vacuum drying oven at 60-100 °C for 12-24 h to obtain a nickel single-atom sulfur-nitrogen co-doped foamed carbon monolithic catalyst. The pyrolysis conditions are as follows: the temperature is increased from room temperature to 800-1000℃ at a heating rate of 3-7℃ / min, and held at that temperature for 1-3 hours.

2. The preparation method according to claim 1, characterized in that, The specific implementation process of step (1) is as follows: cut polyurethane foam into cuboids, wash with deionized water and anhydrous ethanol 3 to 5 times to remove surface impurities, and then put it into a forced-air drying oven to dry at 60 to 100 ℃ for 6 to 12 h; wherein, the pore size of polyurethane foam is 40 to 60 PPI.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of coal liquefaction pitch to tetrahydrofuran in the pitch solution is 1:2 to 1:

4.

4. The preparation method according to claim 1, characterized in that, In step (3), the heating rate of the oxidation curing is 1 ~ 3 ℃ / min; The pyrolysis conditions are as follows: the temperature is increased from room temperature to 700-900℃ at a heating rate of 1-5℃ / min, and then held at that temperature for 1-3 hours.

5. The preparation method according to claim 1, characterized in that, In step (4), the concentration of the N,N-dimethylformamide solution containing nickel nitrate is 0.02 ~ 0.05 mol / L.

6. The application of the nickel single-atom sulfur-nitrogen co-doped foamed carbon monolithic catalyst obtained by any of the preparation methods described in claims 1-5 in the electrocatalytic reduction of CO2.

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