Monatomic carbon-based catalyst with reticular cross-linked structure as well as preparation method and application of monatomic carbon-based catalyst

Abstract

The invention relates to the field of electrocatalysis CO2 reduction reaction catalysts, and discloses a net-shaped cross-linked structure monatomic carbon-based catalyst and a preparation method and application thereof.The preparation method comprises the steps that carrageenan and soluble zinc salt are added into a urea solution, and continuous heating and stirring are conducted till sol is formed; freeze-drying the obtained sol to obtain aerogel; and calcining the obtained aerogel in an inert atmosphere, cooling, and carrying out acid pickling treatment to obtain the net-shaped cross-linked structure monatomic carbon-based catalyst. According to the invention, carrageenan, urea and zinc salt are used as raw materials to prepare the nitrogen-sulfur co-doped zinc monatomic carbon-based catalyst with a net-shaped cross-linked structure, and the catalyst has the advantages of high efficiency and controllable cost; and the obtained nitrogen-doped carbon-based monatomic catalyst has high catalytic activity.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic CO2 reduction reaction catalysts, and in particular to a single-atom carbon-based catalyst with a network cross-linked structure, and a preparation method and application thereof. Background Art

[0002] The core advantage of electrocatalytic CO2 reduction (CO2RR) technology lies in its efficient utilization of renewable energy. Another major advantage is its diverse product range. By selecting appropriate catalysts and adjusting reaction conditions, CO2 can be selectively reduced to a variety of chemicals and fuels, including carbon monoxide (CO), formic acid (HCOOH), acetic acid (CH3COOH), hydrocarbons, and alcohols.

[0003] The development of efficient, stable and low-cost electrocatalysts is the key to the advancement of CO2RR technology. Currently, many efficient catalysts are based on precious metals, which are not only expensive but also resource-limited. Therefore, researchers are actively exploring catalysts based on non-precious metals, such as transition metals, metal oxides and carbon-based catalysts, in order to achieve higher catalytic efficiency and lower costs. Among them, metal single-atom nanocarbon-based catalysts are considered to be materials with development potential due to their controllable active site coordination environment, good chemical stability, excellent conductivity, huge specific surface area, controllable porous structure and low-cost and feasible preparation. The microstructure and surface state of the carbon-based skeleton play a key role in regulating the catalytic reaction. In recent years, the three-dimensional network structure in polymer compounds has attracted widespread attention.

[0004] For example, in Chinese patent publication CN102166518B, the method involves first adding ethylene glycol, a precious metal precursor, and a surfactant to a reactor and stirring them evenly; then adding formaldehyde to the reactor and stirring them evenly; sealing the reactor and placing it in an oven for reaction; finally, naturally cooling the reactor to room temperature and centrifuging to wash the mixture, thereby obtaining a three-dimensional network structured precious metal nano-electrocatalytic palladium material. Another example is Chinese patent publication CN113463112B, which describes a method in which an acrylic acid / potassium acrylate neutralizing solution is first prepared; then, the neutralizing solution, an initiator, a crosslinking agent, and cobalt nitrate are uniformly mixed to form a mixed solution; the mixed solution is irradiated under ultraviolet light to obtain a hydrogel, which is then washed and dried; finally, the dried hydrogel is heated and then cooled naturally to obtain a transition metal catalyst with a three-dimensional network structure.

[0005] However, the current synthesis of three-dimensional network structure catalysts involves difficulties such as precise control of the multi-component system and removal of surfactants, which can easily affect the precision and accuracy of the synthesis. The synthesis steps such as ultraviolet light initiation, hydrogel treatment and heat treatment are complex and can easily lead to problems such as insufficient material stability and uneven metal dispersion. Therefore, the development of a method for synthesizing nitrogen-doped carbon-based materials with a network cross-linked structure that can accurately control the doping of single metal atoms, is highly efficient, cost-effective, and suitable for large-scale production has become a problem that needs to be solved. Summary of the Invention

[0006] The present invention aims to overcome the above-mentioned problems existing in the electrocatalytic CO2 reduction reaction catalysts in the prior art and provides a network-crosslinked structured single-atom carbon-based catalyst and its preparation method and application. Carrageenan, urea and zinc salt are used as raw materials to prepare a network-crosslinked structured nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst, which has the advantages of high efficiency and controllable cost; the obtained nitrogen-doped carbon-based single-atom catalyst has high catalytic activity.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a network cross-linked single-atom carbon-based catalyst, comprising the following steps: (1) Add carrageenan and soluble zinc salt to the urea solution, and continue heating and stirring until a sol is formed; wherein the mass ratio of carrageenan to urea is 1:2~2:1, and the mass ratio of carrageenan to soluble zinc salt is 5:1~50:1; (2) freeze-drying the obtained sol to obtain an aerogel; (3) The obtained aerogel is calcined in an inert atmosphere, cooled, and then acid-washed to obtain the network-crosslinked structure single-atom carbon-based catalyst.

[0008] The preparation principle of the catalyst provided by the present invention is as follows: at a suitable temperature, carrageenan is dissolved in water to form a gel, and the added urea and zinc salt are uniformly dispersed in the gel network during heating and stirring, providing good conditions for subsequent heteroatom doping; then, the formed gel is freeze-dried to remove moisture to obtain an aerogel containing urea and zinc elements; wherein, carrageenan is a polysaccharide sulfate ester composed of galactose and dehydrated galactose, which provides a sulfur source for the material; urea has a nitrogen content of 46 wt.%, which provides a sufficient nitrogen source for the material; during high-temperature calcination, the aerogel is transformed into a stable carbon skeleton, wherein the zinc element coordinates with the sulfur and nitrogen elements in the carbon skeleton to achieve heteroatom doping, and nitrogen-sulfur co-doping can optimize the electron transport path, enhance the charge transfer ability, improve the electrochemical reduction catalytic activity and stability, and ensure that the catalyst remains efficient and stable during long-term reaction; after calcination, acid treatment is performed to etch and remove potassium sulfide, calcium sulfide and excess zinc, and finally a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network cross-linked structure is formed. The present invention controls the elemental composition of the product by regulating the ratio of carrageenan, urea and zinc salt, adopts inert atmosphere protection and high-temperature calcination to promote the coordination and uniform dispersion of metal elements with nitrogen and sulfur, and prepares a network-crosslinked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst. The Zn-NS coordination active center is well fixed in the nano-carbon structure, thereby improving the selectivity of electrocatalytic CO2 reduction to produce CO.

[0009] The network cross-linked structure can significantly improve the mechanical strength and thermal stability of the catalyst, making it less susceptible to structural collapse or wear under high temperature, high pressure or shear conditions, thereby extending its service life. The excellent mechanical properties of the network cross-linked structure can solve the problem of structural degradation in long-term strain cycles of electrocatalysts, and can resist solvent swelling, acid-base corrosion or oxidative degradation. It remains stable under harsh reaction conditions (such as strong acid, strong base or polar solvent systems) to avoid catalyst deactivation. In addition, the network cross-linked structure can provide a larger specific surface area, increase the exposure of active sites, increase surface defects and adsorption energy, and enhance catalytic performance. At the same time, the high specific surface area and unique surface morphology of the network cross-linked structure are conducive to the uniform distribution of metal single atoms, enhance metal-carbon interfacial bonding, ensure efficient material and electron transfer, and help accelerate the kinetics of the electrocatalytic CO2 reduction reaction.

[0010] Preferably, the mass concentration of the urea solution in step (1) is 1-5%.

[0011] Preferably, the urea solution in step (1) is prepared by adding urea to deionized water, placing the urea in an oil bath and stirring and dissolving the urea at 60-100° C. for 5-30 min to obtain a uniform and stable urea solution.

[0012] Preferably, the soluble zinc salt in step (1) is selected from one or more of zinc nitrate, zinc sulfate and zinc chloride.

[0013] Preferably, the freeze-drying time in step (2) is 12 to 48 hours.

[0014] Preferably, the calcination temperature in step (3) is 800-1100°C, the heating rate during calcination is 2-5°C / min, and the calcination time is 1.5-2.5 h.

[0015] Preferably, the calcination in step (3) is carried out in a nitrogen atmosphere, the purity of the nitrogen atmosphere is 95-100%, and the nitrogen flow rate is 5-20 mL / min.

[0016] Preferably, the acid used in the pickling treatment in step (3) is an inorganic acid and / or an organic acid, the acid concentration is 0.5-2 mol / L, the pickling temperature is 60-80 °C, and the pickling time is 6-12 h.

[0017] In a second aspect, the present invention provides a network-crosslinked single-atom carbon-based catalyst prepared using the above-mentioned preparation method.

[0018] In a third aspect, the present invention provides a use of the aforementioned network-crosslinked carbon-based single-atom catalyst in the electrocatalytic reduction of CO to produce CO. The nitrogen-sulfur co-doped carbon-based zinc single-atom catalyst of the present invention exhibits high electrocatalytic reduction of CO to CO rates and Faradaic efficiencies in neutral and alkaline electrolytes.

[0019] Therefore, the present invention has the following beneficial effects: (1) Single zinc atoms are uniformly dispersed in the nitrogen-sulfur co-doped carbon aerogel substrate, significantly improving the atomic utilization rate and avoiding the waste of active atoms. Nitrogen-sulfur co-doping optimizes the electron transport path, enhances the charge transfer ability, improves the electrochemical reduction catalytic activity and stability, and ensures that the catalyst remains efficient and stable during long-term reactions. (2) The catalyst of the present invention has a rich porous structure, open and short diffusion channels, low resistance, significantly improving mass transport efficiency and increasing electrical conductivity; the porous structure increases the interface area, increases the number of active sites, increases the catalytic reaction rate, increases the amount of reactants processed per unit time, and enhances the reaction efficiency; (3) The preparation method is simple and easy to operate and control; the raw materials (such as carrageenan, zinc salt, urea, etc.) are widely available and inexpensive, which greatly reduces the preparation cost and provides strong support for industrial application and large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is an SEM image of the network-crosslinked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst in Example 1 of the present invention.

[0021] Figure 2This is the EDS image of the network-crosslinked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst in Example 1 of the present invention.

[0022] Figure 3 This is the XPS graph of the network-crosslinked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst in Example 1 of the present invention.

[0023] Figure 4 3 are XRD patterns of the network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalysts of Examples 1 to 3 of the present invention.

[0024] Figure 5 3 and 4. Electrochemical polarization curves of the network cross-linked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalysts in Examples 1-3 of the present invention and Comparative Examples 1-2 in a three-electrode reaction cell and 0.5 mol / L potassium bicarbonate electrolyte.

[0025] Figure 6 Graphs of the CO Faraday efficiencies of the network-crosslinked nitrogen-sulfur co-doped zinc single-atom carbon-based catalysts in Examples 1-3 of the present invention and Comparative Examples 1-2 in a three-electrode reaction cell and 0.5 mol / L potassium bicarbonate electrolyte.

[0026] Figure 7 This is a graph of the H2 Faraday efficiency of the network cross-linked structure nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst in Examples 1-3 of the present invention and Comparative Examples 1-2 in a three-electrode reaction cell and a 0.5 mol / L potassium bicarbonate electrolyte. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0029] Overall embodiment: A method for preparing a single-atom carbon-based catalyst with a network cross-linked structure comprises the following steps: (1) Add carrageenan and soluble zinc salt to the urea solution, and continue heating and stirring until a sol is formed; wherein the mass ratio of carrageenan to urea is 1:2~2:1, and the mass ratio of carrageenan to soluble zinc salt is 5:1~50:1; (2) freeze-drying the obtained sol to obtain an aerogel; (3) The obtained aerogel is calcined in an inert atmosphere, cooled, and then acid-washed to obtain the network-crosslinked structure single-atom carbon-based catalyst.

[0030] As a specific implementation, the mass concentration of the urea solution in step (1) is 1-5%.

[0031] As a specific embodiment, the preparation method of the urea solution in step (1) is: adding urea to deionized water, placing it in an oil bath and stirring and dissolving it at 60-100° C. for 5-30 minutes to obtain a uniform and stable urea solution.

[0032] As a specific embodiment, the soluble zinc salt in step (1) is selected from one or more of zinc nitrate, zinc sulfate, and zinc chloride.

[0033] As a specific embodiment, the freeze-drying time in step (2) is 12 to 48 hours.

[0034] As a specific embodiment, the calcination temperature in step (3) is 800~1100°C, the heating rate during calcination is 2~5°C / min, and the calcination time is 1.5~2.5 h.

[0035] As a specific embodiment, the calcination in step (3) is carried out in a nitrogen atmosphere, the purity of the nitrogen atmosphere is 95-100%, and the nitrogen flow rate is 5-20 mL / min.

[0036] As a specific embodiment, the acid used in the pickling treatment in step (3) is an inorganic acid and / or an organic acid, the acid concentration is 0.5~2 mol / L, the pickling temperature is 60~80°C, and the pickling time is 6~12 h.

[0037] Example 1: A method for preparing a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network-like cross-linked structure, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 0.5 g of zinc nitrate hexahydrate to the urea solution and stir at 80°C until a uniform and stable mixed solution is formed. Then, add 4 g of carrageenan to the mixed solution and continue heating and stirring to form a urea-carrageenan-zinc mixed gel; Step 3: freeze-drying the urea-carrageenan-zinc mixed gel for 24 h to form an aerogel of the zinc-urea-carrageenan mixture; Step 4: Place the zinc-urea-carrageenan mixture aerogel in a porcelain boat, cover it, and place it in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, first increase the temperature to 900°C at a heating rate of 5°C / min and then hold it at 900°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is a network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst; its SEM image is shown as follows: Figure 1 As shown in Figure 1 It can be seen that the microscopic morphology of the network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst prepared by the present invention is network cross-linked; its EDS diagram is as follows Figure 2 As shown in Figure 2 It can be seen that the elements of the network cross-linked structure nitrogen and sulfur co-doped zinc single atom carbon-based catalyst prepared by the present invention are evenly distributed and do not produce agglomerated metal particles; its XPS diagram is as follows Figure 3 As shown in Figure 3 It can be seen that the network cross-linked structure nitrogen and sulfur co-doped zinc single atom carbon-based catalyst prepared by the present invention presents an S-Zn-N coordination structure, and the N content accounts for about 4.34 at.%, and the S content accounts for about 3.88 at.%; its XRD pattern is shown in FIG. Figure 4 As shown in Figure 4 It can be seen that the network cross-linked structure nitrogen-sulfur co-doped carbon-based single-atom catalyst prepared by the present invention does not contain metal nanoparticles, and the degree of crystallization of the material is low.

[0038] Example 2: A method for preparing a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network-like cross-linked structure, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 0.5 g of zinc nitrate hexahydrate to the urea solution and stir at 80°C until a uniform and stable mixed solution is formed. Then, add 4 g of carrageenan to the mixed solution and continue heating and stirring to form a urea-carrageenan-zinc mixed gel; Step 3: freeze-drying the urea-carrageenan-zinc mixed gel for 24 h to form an aerogel of the zinc-urea-carrageenan mixture; Step 4: The zinc-urea-carrageenan aerogel mixture was placed in a porcelain boat, covered, and placed in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, the temperature was first increased to 800°C at a heating rate of 5°C / min and then held at 800°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is a network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst. Its XRD pattern is as follows: Figure 4 As shown in .

[0039] Example 3: A method for preparing a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network-like cross-linked structure, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 0.5 g of zinc nitrate hexahydrate to the urea solution and stir at 80°C until a uniform and stable mixed solution is formed. Then, add 4 g of carrageenan to the mixed solution and continue heating and stirring to form a urea-carrageenan-zinc mixed gel; Step 3: freeze-drying the urea-carrageenan-zinc mixed gel for 24 h to form an aerogel of the zinc-urea-carrageenan mixture; Step 4: Place the zinc-urea-carrageenan mixture aerogel in a porcelain boat, cover it, and place it in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, first increase the temperature to 1000°C at a heating rate of 5°C / min and then hold it at 1000°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is a network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst. Its XRD pattern is as follows: Figure 4 As shown in .

[0040] Example 4: A method for preparing a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network-like cross-linked structure, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 0.2 g of zinc nitrate hexahydrate to the urea solution and stir at 80°C until a uniform and stable mixed solution is formed. Then, add 4 g of carrageenan to the mixed solution and continue heating and stirring to form a urea-carrageenan-zinc mixed gel; Step 3: freeze-drying the urea-carrageenan-zinc mixed gel for 24 h to form an aerogel of the zinc-urea-carrageenan mixture; Step 4: The zinc-urea-carrageenan aerogel mixture was placed in a porcelain boat, covered, and placed in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, the temperature was first increased to 900°C at a heating rate of 5°C / min and then held at 900°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is a network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst.

[0041] Example 5: A method for preparing a nitrogen-sulfur co-doped zinc single-atom carbon-based catalyst with a network-like cross-linked structure, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 0.8 g of zinc nitrate hexahydrate to the urea solution and stir at 80°C until a uniform and stable mixed solution is formed. Then, add 4 g of carrageenan to the mixed solution and continue heating and stirring to form a urea-carrageenan-zinc mixed gel; Step 3: freeze-drying the urea-carrageenan-zinc mixed gel for 24 h to form an aerogel of the zinc-urea-carrageenan mixture; Step 4: The zinc-urea-carrageenan aerogel mixture was placed in a porcelain boat, covered, and placed in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, the temperature was first increased to 900°C at a heating rate of 5°C / min and then held at 900°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is a network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst.

[0042] Comparative Example 1 (without adding urea): A method for preparing a sulfur-doped zinc single-atom carbon-based catalyst, comprising the following steps: Step 1: Dissolve 0.5 g of zinc nitrate hexahydrate in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath at 80°C. Stir and dissolve for 10 minutes to obtain a uniform and stable zinc nitrate solution. Step 2: Add 4 g of carrageenan to the zinc nitrate solution and continue heating and stirring to form a carrageenan-zinc mixed gel; Step 3: freeze-drying the carrageenan-zinc mixed gel for 24 h to form a carrageenan-zinc mixture aerogel; Step 4: Place the carrageenan-zinc mixture aerogel in a porcelain boat, cover it, and place it in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, first increase the temperature to 900°C at a heating rate of 5°C / min and then hold at 900°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is the sulfur-doped zinc single-atom carbon-based catalyst.

[0043] Comparative Example 2 (without adding zinc nitrate hexahydrate): A method for preparing a nitrogen-sulfur co-doped carbon-based catalyst, comprising the following steps: Step 1: Dissolve 4 g of solid urea powder in 200 mL of deionized water. Place the solution in a 500 mL beaker and place the beaker in an oil bath. Maintain the oil bath at 80°C and stir for 10 minutes to obtain a uniform and stable urea solution. Step 2: Add 4 g of carrageenan to the urea solution and continue heating and stirring to form a urea-carrageenan mixed gel; Step 3: freeze-drying the urea-carrageenan mixed gel for 24 h to form an aerogel of the urea-carrageenan mixture; Step 4: Place the urea-carrageenan mixture aerogel in a porcelain boat, cover it, and place it in a tube furnace for calcination in a nitrogen atmosphere with a purity of 99.999%. During high-temperature calcination, first increase the temperature to 900°C at a heating rate of 5°C / min and then hold at 900°C for 2 hours. Step 5: After the tube furnace cools to room temperature, remove the sample from the porcelain boat, grind it to uniform particles, and then pickle it. The acid used for pickling is 1 mol / L sulfuric acid, the pickling temperature is 80 ° C, and the pickling time is 8 h. Step 6: The sample after acid washing is vacuum filtered and vacuum dried to obtain a black powder which is the nitrogen-sulfur co-doped carbon-based catalyst.

[0044] Application examples: The catalysts prepared in the above examples and comparative examples were used as cathode materials in the electrocatalytic CO2 reduction reaction to produce CO, and their catalytic performance was tested. The specific method is as follows: Step 1: Using an analytical balance, 5 mg of the catalysts prepared in the examples and comparative examples were weighed, and 450 μL of anhydrous ethanol and 50 μL of a 0.5 wt.% Nafion solution were uniformly mixed. The mixture was then placed in a sample bottle and ultrasonicated for 2 h and magnetically stirred for 12 h. Step 2: Cut out 1×3 cm 2 Weigh 100 μL of the catalyst solution prepared in step 1 and add it dropwise to the 1×1 cm 2 The carbon paper in the region is dried at room temperature or under infrared light to serve as the working electrode; Step 3: Use Ag / AgCl as the reference electrode, platinum wire as the counter electrode, and the working electrode to form a three-electrode system and place it in a sealed H-type electrolytic cell. Use 0.5 mol / L potassium bicarbonate as the electrolyte solution. Test at different potentials and analyze the production of CO and H2 by gas chromatography. The results are as follows: Figures 5 to 7 As shown in .

[0045] from Figure 5 It can be seen that compared with the comparative example, the catalytic reaction current density in Example 1 is the highest, indicating that the network cross-linked structure nitrogen-sulfur co-doped zinc single atom carbon-based catalyst prepared by the method of the present invention in Example 1 has better conductivity and catalytic activity.

[0046] from Figure 6As can be seen in the examples, the network-crosslinked nitrogen-sulfur co-doped zinc single-atom carbon-based catalysts prepared using the method of the present invention exhibit high CO Faradaic efficiencies. The highest CO Faradaic efficiency in Example 1 was approximately 99.6%. In Example 2, calcined at a lower temperature (800°C), the material exhibited a relatively weak conductivity at 800°C, resulting in a decrease in CO Faradaic efficiency compared to Example 1, with a maximum CO Faradaic efficiency of approximately 70.9%. In Example 3, calcined at a higher temperature, the highest CO Faradaic efficiency was approximately 96.5%. In Example 4, the zinc content in the catalyst was reduced, resulting in a decrease in CO Faradaic efficiency compared to Example 1, with a maximum CO Faradaic efficiency of approximately 80.5%. In Example 5, the zinc content was increased, but the CO Faradaic efficiency also decreased compared to Example 1, with a maximum CO Faradaic efficiency of approximately 87.6%, due to the potential disruption of the carbon sp² network continuity by excessive metal intercalation, which increases the support's resistance and hinders electron transport from the support to the active sites. The catalyst in Comparative Example 1 is not doped with nitrogen, making it difficult to stabilize a high density of single-atom sites. Even if successfully loaded, the electronic structure of the metal-carbon center is generally not ideal for adsorption of reaction intermediates, resulting in reduced catalytic performance. The CO Faradaic efficiency is lower than that of Example 1, with the highest CO Faradaic efficiency being approximately 82.2%. The catalyst in Comparative Example 2 is not doped with Zn. Due to the lack of highly active metal single-atom sites, the CO Faradaic efficiency is also lower than that of Example 1, with the highest CO Faradaic efficiency being approximately 72.3%.

[0047] from Figure 7 It can be seen that the H2 Faraday efficiency of Example 1 is significantly lower than that of the comparative example, indicating that the catalyst prepared by the method of the present invention in Example 1 is less affected by the hydrogen evolution side reaction and has a better performance in the electrocatalytic reduction of CO2 to produce CO. This trend is also consistent with Figure 6 The same as shown.

[0048] It should be noted that the specific implementation method described above provides a detailed description of the technical solutions and application results of the present invention. The above embodiments are only the most preferred embodiments and are not intended to limit the present invention. Modifications or equivalent replacements made by relevant technical personnel within the core theoretical scope of the present invention should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a network cross-linked single-atom carbon-based catalyst, characterized in that: The steps include: (1) Add carrageenan and soluble zinc salt to the urea solution, and continue heating and stirring until a sol is formed; wherein the mass ratio of carrageenan to urea is 1:2~2:1, and the mass ratio of carrageenan to soluble zinc salt is 5:1~50:1; (2) freeze-drying the obtained sol to obtain an aerogel; (3) The obtained aerogel is calcined in an inert atmosphere, cooled, and then acid-washed to obtain the network-crosslinked structure single-atom carbon-based catalyst.

2. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1, wherein: The mass concentration of the urea solution in step (1) is 1-5%.

3. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1 or 2, characterized in that: The preparation method of the urea solution in step (1) is as follows: urea is added to deionized water, placed in an oil bath and stirred and dissolved at 60-100°C for 5-30 minutes to obtain a uniform and stable urea solution.

4. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1, wherein: The soluble zinc salt described in step (1) is selected from one or more of zinc nitrate, zinc sulfate and zinc chloride.

5. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1, wherein: The freeze-drying time in step (2) is 12 to 48 hours.

6. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1, wherein: The calcination temperature in step (3) is 800~1100°C, the heating rate during calcination is 2~5°C / min, and the calcination time is 1.5~2.5h.

7. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1 or 6, characterized in that: In step (3), calcination is carried out in a nitrogen atmosphere with a purity of 95-100% and a nitrogen flow rate of 5-20 mL / min.

8. The method for preparing a network cross-linked single-atom carbon-based catalyst according to claim 1, wherein: The acid used in the pickling treatment in step (3) is an inorganic acid and / or an organic acid, the acid concentration is 0.5~2 mol / L, the pickling temperature is 60~80℃, and the pickling time is 6~12 h.

9. A network cross-linked single-atom carbon-based catalyst, characterized in that: It is prepared using the preparation method according to any one of claims 1 to 8.

10. An application of the network cross-linked single-atom carbon-based catalyst according to claim 9, characterized in that: Applied to the electrocatalytic reduction of CO2 to produce CO reaction.

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