Nitrogen-doped carbon-based monatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to the field of electrocatalytic CO2 reduction reaction catalysts, and discloses a nitrogen-doped carbon-based monatomic catalyst and a preparation method and application thereof.The preparation method comprises the steps that zinc salt is dissolved in absolute methanol, and a metal salt solution is obtained; the preparation method comprises the following steps: dissolving 2-methylimidazole in absolute methanol to obtain a ligand solution; mixing the metal salt solution and the ligand solution for liquid phase reaction to obtain a ZIF-8 precursor; a nickel source and a ZIF-8 precursor are placed on the upstream and the downstream of a tubular furnace respectively and calcined in the nitrogen atmosphere, metal particles are removed through acid pickling after cooling, and the nitrogen-doped carbon-based monatomic catalyst is obtained. Nickel atoms are confined in a ZIF-8 precursor by adopting a steam blowing and confinement method, and the nitrogen-doped carbon-based monatomic catalyst with a nickel monatomic-nitrogen coordination structure is formed after calcination, so that the size of the monatomic catalyst is optimized, a Ni-N coordination active center is introduced, and the selectivity of producing CO by reducing CO2 through electro-catalysis is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrocatalytic CO2 reduction reaction catalysts, in particular to a nitrogen-doped carbon-based single-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] Electrocatalytic CO2 reduction has attracted extensive attention in recent years, which converts CO2 into high-value-added chemicals driven by electrical energy. CO is one of the products of electrocatalytic CO2 reduction, which can be used to synthesize organic chemicals such as methanol, or further converted into liquid fuels as a component of synthesis gas, and has important industrial value. However, the reactant CO2 molecule of the electrocatalytic CO2 reduction reaction has extremely high thermodynamic stability, and there may also be a hydrogen evolution competition reaction in the electrocatalytic CO2 reduction process, which greatly reduces the activity and selectivity of the reaction. Therefore, there is great development space for developing electrocatalysts with high selectivity and activity to obtain excellent performance of electrocatalytic CO2 reduction for preparing CO.

[0003] In recent years, single-atom catalysts have shown outstanding performance in the process of electrocatalytic CO2 reduction due to their atomic dispersion characteristics and high atomic utilization. The particle size of the catalyst plays a key role in regulating the catalytic performance. By regulating the particle size of the catalyst, the specific surface area and surface defects of the catalyst can be adjusted, and then the adsorption and desorption of the reactant CO2 molecule, the reaction intermediate and the product can be adjusted, the mass transfer path can be optimized, and the activity and selectivity of the reaction can be improved. At the same time, the size of the catalyst is closely related to the structural stability of the material. A reasonably designed catalyst size has excellent structural stability, which can significantly improve the service life of the catalyst. Therefore, the development of catalyst synthesis technology with controllable size has gradually attracted widespread attention from researchers.

[0004] As disclosed in Chinese patent document CN119092724A, an aqueous ethylene glycol solution and a potassium chloroplatinate-containing ethylene glycol solution are stirred and mixed uniformly, then heated under inert gas protection, and after the reaction is completed, cooled to room temperature. After stirring uniformly, the carbon carrier material is added to the reaction solution, and then washed with water and dried to obtain a platinum-carbon catalyst. Under the action of ethylene glycol reducing agent, the water content is adjusted to achieve the effect of controlling the particle size of the metal particles. As disclosed in Chinese patent document CN119771407A, a trivalent iron salt, ethanol, water and sodium acetate are mixed in a closed container at room temperature, and then reacted, centrifuged, washed, dried and calcined to obtain a size-controllable alpha-iron oxide nanosheet catalyst.

[0005] However, the existing synthesis method is mainly to control the size of metal particles, and therefore cannot be applied to the synthesis of single-atom catalysts. Therefore, it is currently a problem to be solved to develop a size-controllable single-atom catalyst synthesis method which can accurately control the size of single-atom catalyst carriers, has high efficiency, controllable cost and is suitable for large-scale production. SUMMARY

[0006] The present application is to overcome the above-mentioned problems of the prior art CO2 reduction reaction catalyst, and provides a nitrogen-doped carbon-based single-atom catalyst and a preparation method and application thereof. The nickel element is blown in the form of steam to the surface of the precursor at high temperature by steam purging and confinement method, and is adsorbed on the carbon skeleton, so that the nickel atom is confined in the ZIF-8 precursor. After calcination, a nitrogen-doped carbon-based single-atom catalyst with nickel single-atom-nitrogen coordination structure is formed, the size of the single-atom catalyst is optimized, and the Ni-N coordination active center is introduced, thereby improving the selectivity of the electrocatalytic CO2 reduction to produce CO.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: In a first aspect, the present application provides a preparation method of a nitrogen-doped carbon-based single-atom catalyst, comprising the following steps: (1) Dissolve zinc salt in anhydrous methanol to obtain a metal salt solution; (2) Dissolve 2-methyl imidazole in anhydrous methanol to obtain a ligand solution; the molar ratio of 2-methyl imidazole to zinc ion is 5:1~3:1; (3) Mix the metal salt solution and the ligand solution to carry out liquid phase reaction to obtain a ZIF-8 precursor; (4) Place the nickel source and the ZIF-8 precursor in the upstream and downstream of a tube furnace respectively, the molar ratio of the zinc salt used in the synthesis of the nickel source and the ZIF-8 precursor is 1:20~1:5; calcine in a nitrogen atmosphere, and after cooling, remove the metal particles by acid washing to obtain the nitrogen-doped carbon-based single-atom catalyst.

[0008] The preparation principle of the nitrogen-doped carbon-based single-atom catalyst provided by the present application is as follows: under suitable environmental conditions, 2-methyl imidazole and zinc salt react in methanol, which specifically embodies that the nitrogen element in 2-methyl imidazole and the zinc element in zinc salt undergo coordination chemical reaction to generate ZIF-8 precursor, which has a rich pore structure; then, as the temperature rises during calcination, the nickel source in the upstream of the tube furnace volatilizes, is blown in the form of steam to the surface of the ZIF-8 precursor, and is adsorbed in the pore structure; after the temperature continues to rise, part of the zinc element evaporates during calcination, leaving a vacancy in the structure, and the nickel element adsorbed in the gap coordinates with the nitrogen element to fill the zinc vacancy, forming a nitrogen-doped carbon-based single-atom catalyst with nickel single-atom-nitrogen coordination structure.

[0009] The present invention controls the particle size of the product by regulating the ligand-solvent ratio, stabilizes the catalyst morphology through nitrogen protection and high-temperature calcination, and performs metal single-atom modification. This results in the preparation of a size-controllable nitrogen-doped carbon-based single-atom catalyst. The size of the single-atom catalyst is optimized, and a Ni-N coordination active center is introduced, improving the selectivity of electrocatalytic CO2 reduction to CO. Furthermore, the present invention employs a steam purge and confinement method. While zinc evaporates from the precursor ZIF-8, leaving vacancies, the evaporated nickel is simultaneously adsorbed. This allows the nickel source to be confined via the zinc vacancies during the calcination process, resulting in higher adsorption efficiency and promoting the formation of Ni-N active sites, thereby enhancing the activity of the catalytic reaction.

[0010] Preferably, in the metal salt solution in step (1), the molar ratio of anhydrous methanol to zinc salt is 100:1 to 1500:1, and the amount of anhydrous methanol in step (1) and step (2) is the same.

[0011] Preferably, the temperature of the liquid phase reaction in step (3) is 30-40°C, and the reaction time is 10-14 h.

[0012] Preferably, the volatilization temperature of the nickel source in step (4) is below 250°C.

[0013] Preferably, the calcination temperature in step (4) is 800-1000°C, and the calcination time is 1.5-2.5h.

[0014] Preferably, the heating rate during calcination in step (4) is 2-5 °C / min.

[0015] Preferably, the concentration of the nitrogen atmosphere in step (4) is 95-99.999%.

[0016] Preferably, the acid used in the pickling in step (4) is an inorganic acid, the pickling temperature is 50-90°C, and the pickling time is 5-10 h.

[0017] In a second aspect, the present invention provides a nitrogen-doped carbon-based single-atom catalyst prepared by the above method.

[0018] Preferably, the particle size of the nitrogen-doped carbon-based single-atom catalyst is 50-500 nm. Controlling the particle size of the catalyst within this range is beneficial to improving the catalytic activity.

[0019] In a third aspect, the present invention provides an application of the above-mentioned nitrogen-doped carbon-based single-atom catalyst in the electrocatalytic CO2 reduction reaction to produce CO.

[0020] Therefore, the present invention has the following beneficial effects: (1) The size of the ZIF-8 precursor was controlled by a ligand-solvent ratio control strategy, thereby controlling the catalyst particle size within the range of 50 nm to 500 nm with good structural stability; (2) During the catalyst calcination process, nitrogen is used as a protective gas to prevent oxygen in the air from entering and reacting with carbon elements, resulting in the loss of carbon elements and the collapse of the carbon skeleton. In addition, the nitrogen purge can also allow nickel elements to migrate to the surface of the ZIF-8 precursor in the form of vapor, and coordinate with nitrogen atoms to form a nickel-nitrogen coordination structure, without being oxidized to form nickel oxide particles, which affects the catalytic performance of the catalyst. Due to the high N doping amount and Ni-N coordination active sites, the catalyst of the present invention exhibits excellent electrocatalytic performance. At a current density of 350 mA cm -2 When the CO2 faradaic efficiency can be maintained above 95%; (3) Since the metal source required for single-atom modification is added during calcination and has good dispersion and controllability, the nickel content in the catalyst can be effectively adjusted; and this one-step doping method can simplify the material synthesis steps, making the material synthesis method simple and efficient, highly controllable, and reproducible, suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an SEM image of the nitrogen-doped carbon-based single-atom catalyst in Example 1 of the present invention.

[0022] Figure 2 HRTEM images of the nitrogen-doped carbon-based single-atom catalyst in Example 1 of the present invention at different magnifications.

[0023] Figure 3 This is the EDS element distribution diagram of the nitrogen-doped carbon-based single-atom catalyst in Example 1 of the present invention.

[0024] Figure 4 This is the XPS graph of the nitrogen-doped carbon-based single-atom catalyst in Example 1 of the present invention.

[0025] Figure 5 1 is the XRD pattern of the nitrogen-doped carbon-based single-atom catalyst in Examples 1 to 4 of the present invention and Comparative Example 1.

[0026] Figure 6 Graph showing the CO Faraday efficiency of the nitrogen-doped carbon-based single-atom catalysts in Examples 1-4 of the present invention and Comparative Examples 1-2 in a three-electrode reaction cell in a 1 mol / L potassium hydroxide electrolyte.

[0027] Figure 7The H2 Faraday efficiency diagram of the nitrogen-doped carbon-based monatomic catalyst in the three-electrode reaction cell, 1 mol / L potassium hydroxide electrolyte in examples 1~4 and comparative examples 1~2 of the present application. DETAILED DESCRIPTION

[0028] The present application is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] In the present application, all the equipment and raw materials can be purchased from the market or commonly used in the industry, and the methods in the following examples are conventional methods in the field unless otherwise specified.

[0030] General example: A preparation method of a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: (1) Dissolve zinc salt in anhydrous methanol to obtain a metal salt solution; (2) Dissolve 2-methylimidazole in anhydrous methanol to obtain a ligand solution; the molar ratio of 2-methylimidazole to zinc ion is 5:1~3:1; (3) Mix the metal salt solution and the ligand solution to carry out liquid phase reaction to obtain ZIF-8 precursor; (4) Place the nickel source and the ZIF-8 precursor in the upstream and downstream of the tube furnace respectively, the molar ratio of the zinc salt used when the nickel source and the ZIF-8 precursor are synthesized is 1:20~1:5; calcine in a nitrogen atmosphere, and after cooling, remove metal particles by acid washing to obtain the nitrogen-doped carbon-based monatomic catalyst.

[0031] As a specific embodiment, in the metal salt solution in step (1), the molar ratio of anhydrous methanol to zinc salt is 100:1~1500:1, and the amount of anhydrous methanol used in step (1) and step (2) is the same.

[0032] As a specific embodiment, the temperature of the liquid phase reaction in step (3) is 30~40 ℃, and the reaction time is 10~14 h.

[0033] As a specific embodiment, the volatilization temperature of the nickel source in step (4) is below 250℃.

[0034] As a specific embodiment, the temperature during calcination in step (4) is 800~1000 ℃, and the calcination time is 1.5~2.5 h.

[0035] As a specific embodiment, the heating rate during calcination in step (4) is 2~5 ℃ / min.

[0036] As a specific embodiment, the concentration of the nitrogen atmosphere in step (4) is 95~99.999%.

[0037] As a specific embodiment, the acid used in the acid washing in step (4) is an inorganic acid, the temperature of the acid washing is 50-90 ℃, and the acid washing time is 5-10 h.

[0038] Example 1: A preparation method of a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: Step one: 5.95 g of zinc nitrate hexahydrate was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes; stirring was performed for 10 minutes to completely dissolve the zinc nitrate hexahydrate; Step two: 6.57 g of solid 2-methylimidazole powder was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes; stirring was performed for 10 minutes to completely dissolve the 2-methylimidazole powder; Step three: the two solutions obtained in steps one and two were quickly mixed in a 500 mL beaker; the beaker containing the mixed solution was placed in an oven, and a constant temperature reaction was performed in the oven; specifically, the temperature of the oven was maintained at 35 ℃, and the reaction was performed for 12 h to obtain a white precipitate and a supernatant; Step four: the supernatant after the reaction was poured out, and the white precipitate obtained in the reaction was washed with anhydrous methanol; specifically, the white precipitate was dissolved in anhydrous methanol, and the suspension was subjected to centrifugal treatment, wherein the centrifugal speed was 10000 rpm, and the centrifugal time was 3 min; Step five: the supernatant was poured out after centrifugation, the precipitate was taken out, and the precipitate was placed in a vacuum oven for drying overnight; specifically, the temperature of the vacuum oven was set to 60 ℃, and the drying was performed for 12 h; Step six: the dried white powder sample was ground to be uniform in particle size; 600 mg of the powder sample was placed in a quartz boat, and the quartz boat was placed in a tube furnace; an open quartz boat containing 0.38 g of nickelocene was placed upstream of the precursor powder, and calcination treatment was performed in a nitrogen atmosphere; wherein the concentration of the nitrogen atmosphere was 99.999%; during high-temperature calcination, the temperature was raised to 1000 ℃ at a temperature raising rate of 5 ℃ / min, and the temperature was maintained for 2 h; after cooling to room temperature, the black powder sample in the quartz tube was taken out; Step seven: the obtained black powder sample was subjected to acid washing treatment with 0.5 mol / L sulfuric acid at 80 ℃ for 8 h, and the nitrogen-doped carbon-based monatomic catalyst was obtained after suction filtration and vacuum drying at 65 ℃; the SEM image of the nitrogen-doped carbon-based monatomic catalyst is shown in FIG. 1, from which it can be seen that the prepared nitrogen-doped carbon-based monatomic catalyst is of a nanoparticle shape; Figure 1 the HRTEM image of the nitrogen-doped carbon-based monatomic catalyst is shown in FIG. 2, from which it can be seen that the particle size of the prepared nitrogen-doped carbon-based monatomic catalyst is about 200 nm and no metal particles are aggregated; Figure 1 the EDS element distribution image of the nitrogen-doped carbon-based monatomic catalyst is shown in FIG. 3, from which it can be seen that the prepared nitrogen-doped carbon-based monatomic catalyst is of a nanoparticle shape; Figure 2 Figure 2 Figure 3 Figure 3 ​​​It can be seen that the carbon element, nitrogen element and nickel element in the prepared size-controllable nitrogen-doped carbon-based monatomic catalyst are uniformly dispersed, and the N content accounts for about 4.16wt.%; the XPS graph thereof is shown in Figure 4 It can be seen from Figure 4 It can be seen from x The XRD graph thereof is shown in Figure 5 It can be seen from Figure 5 It can be seen from

[0039] Example 2: A nitrogen-doped carbon-based monatomic catalyst preparation method, the steps are: Step one: 5.95 g of zinc nitrate hexahydrate is dissolved in 648 mL of methanol, ultrasonic treatment for 10 minutes, and stirring for 10 minutes to completely dissolve; Step two: 6.57 g of solid 2-methylimidazole powder is dissolved in 648 mL of methanol, ultrasonic treatment for 10 minutes, and stirring for 10 minutes to completely dissolve; Step three: the two solutions obtained in steps one and two are quickly mixed in a 500 mL beaker; the beaker containing the mixed solution is placed in an oven for constant temperature reaction; the specific operation is to maintain the oven temperature at 35 ℃ for 12 h to obtain a white precipitate and supernatant; Step four: pour off the supernatant after reaction, and wash the white precipitate obtained by reaction with anhydrous methanol; the specific operation is to dissolve the white precipitate in anhydrous methanol, and centrifuge the suspension, wherein the centrifugal speed is 10000 rpm, and the centrifugal time is 3 min; Step five: pour off the supernatant after centrifugation, take the precipitate, and place it in a vacuum oven for drying overnight; the specific operation is to set the temperature of the vacuum oven to 60 ℃, and dry for 12 h; Step six: grind the dried white powder sample to uniform particles; take 600 mg of the powder sample and place it in a quartz boat, which is placed in a tube furnace, and an open quartz boat containing 0.38 g of nickelocene is placed upstream of the precursor powder; perform calcination treatment in a nitrogen atmosphere; wherein the nitrogen atmosphere concentration is 99.999%; when high-temperature calcination, the temperature is raised to 1000 ℃ at a rate of 5 ℃ / min, and stays for 2 h; after cooling to room temperature, take out the black powder sample in the quartz tube; Step seven: the obtained black powder sample is acid washed with 0.5 mol / L sulfuric acid at 80 ℃ for 8 h, and after suction filtration and vacuum drying at 65 ℃, a nitrogen-doped carbon-based monatomic catalyst with a particle size of 50 nm is obtained.

[0040] Example 3: A preparation method of a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: Step one: 5.95 g of zinc nitrate hexahydrate was dissolved in 324 mL of methanol, and ultrasonic treatment was performed for 10 minutes, and then stirring was performed for 10 minutes to completely dissolve the zinc nitrate hexahydrate; Step two: 6.57 g of solid 2-methylimidazole powder was dissolved in 324 mL of methanol, and ultrasonic treatment was performed for 10 minutes, and then stirring was performed for 10 minutes to completely dissolve the 2-methylimidazole powder; Step three: the two solutions obtained in steps one and two were quickly mixed in a 500 mL beaker; the beaker containing the mixed solution was placed in an oven, and a constant temperature reaction was performed in the oven; specifically, the temperature of the oven was maintained at 35 ℃, and the reaction was performed for 12 hours to obtain a white precipitate and a supernatant; Step four: the supernatant after the reaction was poured out, and the white precipitate obtained in the reaction was washed with anhydrous methanol; specifically, the white precipitate was dissolved in anhydrous methanol, and the suspension was subjected to centrifugal treatment, wherein the centrifugal speed was 10000 rpm, and the centrifugal time was 3 minutes; Step five: the supernatant was poured out after centrifugation, the precipitate was taken out, and the precipitate was placed in a vacuum oven for drying overnight; specifically, the temperature of the vacuum oven was set to 60 ℃, and the drying was performed for 12 hours; Step six: the dried white powder sample was ground to be uniform in particle size; 600 mg of the powder sample was placed in a quartz boat, and the quartz boat was placed in a tube furnace; an open quartz boat containing 0.38 g of nickelocene was placed upstream of the precursor powder, and calcination treatment was performed in a nitrogen atmosphere; wherein the concentration of the nitrogen atmosphere was 99.999%; during high-temperature calcination, the temperature was increased to 1000 ℃ at a temperature increasing rate of 5 ℃ / min, and the temperature was maintained for 2 hours; after cooling to room temperature, the black powder sample in the quartz tube was taken out; Step seven: the obtained black powder sample was subjected to acid washing treatment at 80 ℃ for 8 hours using 0.5 mol / L sulfuric acid, and then vacuum drying was performed at 65 ℃ to obtain a nitrogen-doped carbon-based monatomic catalyst with a particle size of 100 nm.

[0041] Example 4: A preparation method of a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: Step one: 5.95 g of zinc nitrate hexahydrate was dissolved in 81 mL of methanol, and ultrasonic treatment was performed for 10 minutes, and then stirring was performed for 10 minutes to completely dissolve the zinc nitrate hexahydrate; Step two: 6.57 g of solid 2-methylimidazole powder was dissolved in 81 mL of methanol, and ultrasonic treatment was performed for 10 minutes, and then stirring was performed for 10 minutes to completely dissolve the 2-methylimidazole powder; Step three: quickly mix the two solutions obtained in step one and step two in a 500 mL beaker; place the beaker containing the mixed solution into an oven for constant temperature reaction; the specific operation is to maintain the oven temperature at 35 °C for 12 h, and white precipitate and supernatant are obtained; Step four: pour away the supernatant after reaction, and wash the white precipitate obtained by reaction with anhydrous methanol; the specific operation is to dissolve the white precipitate in anhydrous methanol, and centrifuge the suspension, wherein the centrifugal speed is 10000 rpm and the centrifugal time is 3 min; Step five: pour away the supernatant after centrifugation, take the precipitate, and place it in a vacuum oven for drying overnight; the specific operation is to set the temperature of the vacuum oven to 60 °C and dry for 12 h; Step six: grind the dried white powder sample to uniform particles; take 600 mg of the powder sample and place it in a quartz boat, place it into a tube furnace, and place an open quartz boat containing 0.38 g of nickelocene upstream of the precursor powder for calcination treatment in a nitrogen atmosphere; wherein the nitrogen atmosphere concentration is 99.999%; during high-temperature calcination, heat to 1000 °C at a heating rate of 5 °C / min, and stay for 2 h; after cooling to room temperature, take out the black powder sample in the quartz tube; Step seven: the obtained black powder sample is treated with 0.5 mol / L sulfuric acid at 80 °C for 8 h, and after suction filtration and vacuum drying at 65 °C, a nitrogen-doped carbon-based monatomic catalyst with a particle size of 500 nm is obtained.

[0042] Example 5: A method for preparing a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: Step one: dissolve 5.95 g of zinc nitrate hexahydrate in 162 mL of methanol, ultrasonic for 10 minutes, and stir for 10 minutes to completely dissolve; Step two: dissolve 6.57 g of solid 2-methylimidazole powder in 162 mL of methanol, ultrasonic for 10 minutes, and stir for 10 minutes to completely dissolve; Step three: quickly mix the two solutions obtained in step one and step two in a 500 mL beaker; place the beaker containing the mixed solution into an oven for constant temperature reaction; the specific operation is to maintain the oven temperature at 35 °C for 12 h, and white precipitate and supernatant are obtained; Step four: pour away the supernatant after reaction, and wash the white precipitate obtained by reaction with anhydrous methanol; the specific operation is to dissolve the white precipitate in anhydrous methanol, and centrifuge the suspension, wherein the centrifugal speed is 10000 rpm and the centrifugal time is 3 min; Step five: after centrifugation, pour off the supernatant, take the precipitate, and place it in a vacuum oven for drying overnight; the specific operation is to set the temperature of the vacuum oven to 60 ℃, and dry for 12 h; Step six: grind the dried white powder sample to uniform particles; take 600 mg of the powder sample and place it in a quartz boat, place it in a tube furnace, and place an open quartz boat containing 0.38 g of nickelocene upstream of the precursor powder, and perform calcination treatment in a nitrogen atmosphere; the nitrogen atmosphere concentration is 99.999%; during high-temperature calcination, the temperature is raised to 800 ℃ at a rate of 5 ℃ / min, and stays for 2 h; after cooling to room temperature, take out the black powder sample in the quartz tube; Step seven: the obtained black powder sample is acid washed with 0.5 mol / L sulfuric acid at 80 ℃ for 8 h, and after suction filtration and vacuum drying at 65 ℃, the nitrogen-doped carbon-based monatomic catalyst is obtained.

[0043] Example 6: A method for preparing a nitrogen-doped carbon-based monatomic catalyst, the steps are: Step one: dissolve 5.95 g of zinc nitrate hexahydrate in 162 mL of methanol, ultrasonic for 10 minutes, and stir for 10 minutes to completely dissolve; Step two: dissolve 6.57 g of solid 2-methylimidazole powder in 162 mL of methanol, ultrasonic for 10 minutes, and stir for 10 minutes to completely dissolve; Step three: quickly mix the two solutions obtained in steps one and two in a 500 mL beaker; place the beaker containing the mixed solution in an oven for constant temperature reaction; the specific operation is to maintain the oven temperature at 35 ℃ for 12 h to obtain a white precipitate and a supernatant; Step four: pour off the supernatant after the reaction, and wash the white precipitate obtained in the reaction with anhydrous methanol; the specific operation is to dissolve the white precipitate in anhydrous methanol, and centrifuge the suspension; the centrifugal speed is 10000 rpm, and the centrifugal time is 3 min; Step five: after centrifugation, pour off the supernatant, take the precipitate, and place it in a vacuum oven for drying overnight; the specific operation is to set the temperature of the vacuum oven to 60 ℃, and dry for 12 h; Step six: grind the dried white powder sample to uniform particles; take 600 mg of the powder sample and place it in a quartz boat, place it in a tube furnace, and place an open quartz boat containing 0.38 g of nickelocene upstream of the precursor powder, and perform calcination treatment in a nitrogen atmosphere; the nitrogen atmosphere concentration is 99.999%; during high-temperature calcination, the temperature is raised to 800 ℃ at a rate of 5 ℃ / min, and stays for 2 h; after cooling to room temperature, take out the black powder sample in the quartz tube; Step seven, the obtained black powder sample was treated with 0.5 mol / L sulfuric acid at 80 ℃ for 8 h, and after suction filtration and vacuum drying at 65 ℃, the nitrogen-doped carbon-based monatomic catalyst was obtained.

[0044] Comparative example 1 (without nickel doping): A method for preparing a nitrogen-doped carbon-based catalyst, comprising the following steps: Step one: 5.95 g of zinc nitrate hexahydrate was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes. The solution was completely dissolved after stirring for 10 minutes. Step two: 6.57 g of solid 2-methylimidazole powder was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes. The solution was completely dissolved after stirring for 10 minutes. Step three: The two solutions obtained in steps one and two were quickly mixed in a 500 mL beaker. The beaker containing the mixed solution was placed in an oven for constant temperature reaction. The specific operation was to maintain the temperature of the oven at 35 ℃ for 12 h to obtain white precipitate and supernatant. Step four: The supernatant after reaction was poured off, and the white precipitate obtained by reaction was washed with anhydrous methanol. The specific operation was to dissolve the white precipitate in anhydrous methanol, and the suspension was centrifuged at a speed of 10000 rpm for 3 min. Step five: After centrifugation, the supernatant was poured off, and the precipitate was taken out and dried in a vacuum oven overnight. The specific operation was to set the temperature of the vacuum oven to 60 ℃, and dry for 12 h. Step six: The dried white powder sample was ground to uniform particles. 600 mg of the powder sample was placed in a quartz tube with an open end, and was placed in a tube furnace for calcination treatment in a nitrogen atmosphere. The nitrogen atmosphere concentration was 99.999%. During high-temperature calcination, the temperature was raised to 1000 ℃ at a rate of 5 ℃ / min, and was kept for 2 h. After cooling to room temperature, the nitrogen-doped carbon-based catalyst was obtained.

[0045] Comparative example 2 (low nickel content): A method for preparing a nitrogen-doped carbon-based monatomic catalyst, comprising the following steps: Step one: 5.95 g of zinc nitrate hexahydrate was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes. The solution was completely dissolved after stirring for 10 minutes. Step two: 6.57 g of solid 2-methylimidazole powder was dissolved in 162 mL of methanol, and ultrasonic treatment was performed for 10 minutes. The solution was completely dissolved after stirring for 10 minutes. Step three: The two solutions obtained in steps one and two were quickly mixed in a 500 mL beaker. The beaker containing the mixed solution was placed in an oven for constant temperature reaction. The specific operation was to maintain the temperature of the oven at 35 ℃ for 12 h to obtain white precipitate and supernatant. Step four: pour off the supernatant after the reaction, and wash the white precipitate obtained in the reaction with anhydrous methanol; the specific operation is to dissolve the white precipitate in anhydrous methanol, and centrifuge the suspension, with a centrifugal speed of 10000 rpm and a centrifugal time of 3 min; Step five: pour off the supernatant after centrifugation, take the precipitate, and place it in a vacuum oven for drying overnight; the specific operation is to set the temperature of the vacuum oven to 60 ℃, and dry for 12 h; Step six: grind the dried white powder sample to uniform particles; take 600 mg of the powder sample and place it in a quartz boat, and place it in a tube furnace; place an open quartz boat containing 0.19 g of nickelocene upstream of the precursor powder, and perform calcination treatment in a nitrogen atmosphere; the nitrogen atmosphere concentration is 99.999%; during high-temperature calcination, heat to 1000 ℃ at a heating rate of 5 ℃ / min, and stay for 2 h; after cooling to room temperature, take out the black powder sample in the quartz tube; Step seven: the obtained black powder sample is acid washed with 0.5 mol / L sulfuric acid at 80 ℃ for 8 h, and after suction filtration and vacuum drying at 65 ℃, the nitrogen-doped carbon-based monatomic catalyst is obtained.

[0046] Comparative Example 3 (using an adsorption method to load nickel): A method for preparing a nitrogen-doped carbon-based monatomic catalyst, the steps are: Step one: respectively dissolve 0.558 g of zinc nitrate hexahydrate in 15 mL of methanol, and dissolve 0.616 g of solid 2-methylimidazole powder in 15 mL of methanol; Step two: under ultrasonic, add the methanol solution containing zinc nitrate hexahydrate to the methanol solution containing 2-methylimidazole; then the mixed solution is reacted for 12 h under static state, and the reaction temperature is maintained at 35 ℃; Step three: wash the precipitate after the reaction with methanol for 3 times, and dry in a vacuum drying oven at 65 ℃ overnight to obtain a ZIF-8 precursor; Step four: ultrasonically disperse 100 mg of the obtained ZIF-8 precursor powder in 10 mL of N-hexane to form a uniform solution, and then slowly inject 50 μL of zinc nitrate aqueous solution (100 mg mL -1 ) into the mixed solution for 2 min; stir the mixed solution vigorously at room temperature for 3 h to completely absorb the nickel nitrate salt solution; Step five: centrifuge the sample in the solution, and dry in a vacuum at 65 ℃ for 6 h; place the obtained sample in a tube furnace for calcination treatment at 1000 ℃ in an argon atmosphere (10 mL / min) (heating rate is 5 ℃ / min); after cooling to room temperature, the nitrogen-doped carbon-based monatomic catalyst is obtained.

[0047] Application Example: The catalyst prepared in the above examples and comparative examples was applied to the electrocatalytic CO2 reduction reaction to prepare CO as a cathode material, and its catalytic performance was tested. The specific method was as follows: Step one: 10 mg of the catalyst prepared in the examples and comparative examples was weighed by an analytical balance, 1950 μL of anhydrous ethanol and 50 μL of a 5 wt.% Nafion solution were taken, and the three were uniformly mixed and then placed in a sample bottle for ultrasonic treatment for 2 h and magnetic stirring for 12 h; Step two: a hydrophobic carbon fiber paper with a size of 1.5 × 1.5 cm 2 was cut out, and 675 μL of the catalyst solution prepared in step one was uniformly sprayed onto the cut carbon paper, which was then dried at room temperature or under infrared light as a working electrode; Step three: Ag / AgCl was used as a reference electrode, a foam nickel sheet was used as a counter electrode, and a three-electrode system was formed with the working electrode and placed in a flow-type electrolytic cell. 1 mol / L potassium hydroxide was used as an electrolyte solution, CO2 gas was introduced into the gas chamber, and the test was carried out at different potentials. The production of CO and H2 was analyzed by a gas chromatograph, and the results are shown in Table 1 and Figure 6 and Figure 7 .

[0048] Table 1: Performance comparison of catalysts in examples 1 and comparative examples in a three-electrode reaction cell

[0049] As can be seen from Table 1 and Figure 6 , the nitrogen-doped carbon-based single-atom catalyst prepared by the method of the present application in the examples has a high CO Faraday efficiency. When the current density is 300 mA cm -2 , the highest CO Faraday efficiency of example 1 is about 97.5%. In examples 2-4, the particle size of the catalyst was controlled by adjusting the amount of solvent. As can be seen from the results, if the particle size of the catalyst is too large or too small, the catalytic performance will decrease. In examples 5 and 6, the temperature during calcination was adjusted. Since the graphitization degree of the carbon material decreases at a relatively low calcination temperature, the electrical conductivity of the material decreases. In addition, the zinc element in the material cannot evaporate to form vacancies at a relatively low calcination temperature, and the specific surface area of the material decreases, hindering the adsorption and desorption of reactants and intermediates, resulting in a decrease in catalytic performance compared with example 1. In comparative example 1, no nickel was added to the catalyst, and the catalytic activity of the catalyst was significantly lower than that of example 1 when the current density was 100 mA cm -2The highest Faraday efficiency of electrocatalytic reduction of CO2 to CO was about 80.5%. In Comparative Example 2, the amount of nickel added was too small, and the catalytic performance also decreased, and the current density was 300 mA cm -2 The highest Faraday efficiency of electrocatalytic reduction of CO2 to CO was about 94.6%. In Comparative Example 3, a double-solvent method was used to adsorb nickel salt, and the highest Faraday efficiency of electrocatalytic reduction of CO2 to CO obtained by the catalyst was only 71.9%, and the current density was only 10.48 mA cm -2 ; This is because, unlike the steam blowing and confinement method used in Example 1, in the double-solvent adsorption method, the adsorption of nickel salt is carried out in a liquid phase system, while the steam blowing and confinement method adsorbs nickel in a gas phase process, so it has higher adsorption efficiency, is more conducive to the metal ligand exchange process in the high-temperature calcination process, promotes the generation of active sites Ni-N, and thus improves the activity of the catalytic reaction.

[0050] The H2 Faraday efficiency of Example 1 was significantly lower than that of the comparative examples, indicating that the catalyst prepared by the method of the present application in Example 1 was less affected by the hydrogen evolution side reaction, and had superior performance in the electrocatalytic reduction of CO2 to prepare CO, which was consistent with the trend shown in Figure 6 .

[0051] It should be noted that the specific implementation methods described above have detailed the technical solutions and application results of the present application. The above examples are only the most preferred examples and are not intended to limit the present application. Modifications or equivalent replacements made by relevant technical personnel within the core theoretical range of the present application should be within the protection scope of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon-based single-atom catalyst, characterized in that it comprises The steps are as follows: (1) Dissolving zinc salt in anhydrous methanol to obtain a metal salt solution; (2) dissolving 2-methylimidazole in anhydrous methanol to obtain a ligand solution; the molar ratio of 2-methylimidazole to zinc ion is 5:1 to 3:1; (3) Mixing the metal salt solution and the ligand solution for liquid phase reaction to obtain a ZIF-8 precursor; (4) Placing a nickel source and a ZIF-8 precursor at the upstream and downstream of a tube furnace, respectively, wherein the molar ratio of the zinc salt used in the synthesis of the nickel source and the ZIF-8 precursor is 1:20 to 1:5; calcining in a nitrogen atmosphere, and acid washing to remove metal particles after cooling to obtain the nitrogen-doped carbon-based single-atom catalyst.

2. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1, wherein: In the metal salt solution in step (1), the molar ratio of anhydrous methanol to zinc salt is 100:1 to 1500:1; the amount of anhydrous methanol in step (1) and step (2) is the same.

3. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1, wherein: The temperature of the liquid phase reaction in step (3) is 30-40°C, and the reaction time is 10-14 h.

4. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1, wherein: The volatilization temperature of the nickel source described in step (4) is below 250°C.

5. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1 or 4, characterized in that: The calcination temperature in step (4) is 800-1000°C, the calcination time is 1.5-2.5h, and the heating rate during calcination is 2-5°C / min.

6. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1 or 4, characterized in that: The concentration of the nitrogen atmosphere in step (4) is 95-99.999%.

7. The method for preparing the nitrogen-doped carbon-based single-atom catalyst according to claim 1, wherein: The acid used in the pickling in step (4) is an inorganic acid, the pickling temperature is 50~90℃, and the pickling time is 5~10 hours.

8. A nitrogen-doped carbon-based single-atom catalyst, characterized in that: It is prepared using the preparation method according to any one of claims 1 to 7.

9. The nitrogen-doped carbon-based single-atom catalyst according to claim 8, characterized in that: The particle size is 50~500 nm.

10. Use of the nitrogen-doped carbon-based single-atom catalyst according to claim 8 or 9, characterized in that: Applied to the electrocatalytic reduction of CO2 to produce CO reaction.

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