Bimetal nitrogen-doped carbon material as well as preparation method and application thereof

Abstract

The invention provides a bimetallic nitrogen-doped carbon material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a nitrogen carbon source, an iron salt and a cobalt salt to obtain a precursor; mixing alkali liquor with the obtained precursor to obtain a modified precursor; and pyrolyzing the obtained modified precursor. According to the preparation method, simple and effective synthesis of the bimetallic nitrogen-doped carbon material is achieved, the bulk phase of the prepared bimetallic nitrogen-doped carbon material is of a sponge structure, dense microcubes are arranged on the surface of the bimetallic nitrogen-doped carbon material, distribution is uniform, dispersion is good, the bimetallic nitrogen-doped carbon material can exert the synergistic effect among components, the microcubes serve as active sites for electrocatalytic CO2 reduction, and the carbon material can be applied to electrocatalytic CO2 reduction. The catalyst has good catalytic reduction performance and good stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials and relates to a nitrogen-doped carbon material, in particular to a bimetallic nitrogen-doped carbon material and a preparation method and application thereof. Background Art

[0002] Non-precious metal nitrogen-doped carbon materials (MN-Cs) refer to new materials produced by chemically linking or incorporating nitrogen atoms into the carbon material skeleton, such as doped graphene, porous carbon, and carbon nanofibers. MN-Cs exhibit excellent catalytic performance in the electrocatalytic reduction of CO2 to CO due to its electrical conductivity and easily modulated electronic properties. Many electrocatalysts have low stability and are easily deactivated during the catalytic reduction process, which affects their service life. Nitrogen-doped carbon materials introduce non-precious metal elements as active centers. Doping can introduce defect sites and nitrogen elements to improve the catalyst's physicochemical properties, acidity and alkalinity, and wettability, and interact with metal active species to enhance catalytic performance. Their catalytic activity is comparable to that of precious metals, but they have unique cost advantages.

[0003] CN112647095A discloses a nitrogen-doped carbon material anchored by atomically dispersed bimetallic sites, as well as its preparation and application. The nitrogen-doped carbon material is prepared by first mixing two transition metal salts with chitosan to obtain a precursor, and then subjecting it to two high-temperature carbonization steps. The resulting nitrogen-doped carbon material has atomically dispersed bimetallic sites, and the formed bimetallic nitrogen coordination structure serves as a catalytically active center, thereby improving the catalytic activity of the material and increasing the atomic utilization rate.

[0004] CN110429290A discloses a method for preparing a nitrogen-doped carbon material-loaded transition metal compound catalyst. Urea, a transition metal compound, and chitosan are mixed and ground, and then heated under a nitrogen atmosphere. This method uses grinding and pyrolysis to prepare the nitrogen-doped carbon catalyst, eliminating the need for solvents and additives. The process is simple, efficient, and rapid.

[0005] CN115679340A discloses a nitrogen-doped carbon-supported metal nickel-cobalt catalyst, its preparation method, and application. Nickel salt and cobalt salt are added to a carboxylic acid solution of chitosan to obtain a catalyst precursor, which is then pyrolyzed at 400-600°C. The resulting material has a regular flaky morphology, small metal particle size, high dispersion, and high catalytic activity and stability for hydrogen production by alkaline water electrolysis.

[0006] In the existing technology, there is a lack of preparation methods for controllable nitrogen-doped carbon material structures, and thus the understanding of their active sites is still controversial. Therefore, it is of great significance to more effectively design highly active nitrogen-doped carbon catalytic materials and to have a deep understanding of their active sites for electrocatalytic reduction of CO2. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a bimetallic nitrogen-doped carbon material and its preparation method and application, which can controllably form iron-rich microcube structures on the surface of the material as active sites to improve the catalytic activity of the material.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a bimetallic nitrogen-doped carbon material, the preparation method comprising the following steps:

[0010] (1) mixing a nitrogen and carbon source, an iron salt, and a cobalt salt to obtain a precursor;

[0011] (2) mixing the alkali solution with the precursor obtained in step (1) to obtain a modified precursor;

[0012] (3) Pyrolyzing the modified precursor obtained in step (2).

[0013] The preparation method provided by the present invention adopts a mixed pyrolysis method to achieve a simple and effective synthesis of iron-cobalt bimetallic nitrogen-doped carbon materials. The Co element is used to controllably form an iron-rich microcubic structure and anchor it on the material surface as a catalytic active site. At the same time, the bimetallic exerts a synergistic effect, and the electrocatalytic CO2 reduction catalytic performance is good.

[0014] Preferably, the nitrogen and carbon source in step (1) comprises any one of chitosan, urea or melamine, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of chitosan and urea, a combination of urea and melamine, a combination of chitosan and melamine, or a combination of chitosan, urea and melamine.

[0015] Preferably, the amount of the nitrogen and carbon source in step (1) is 20-40% of the mass of the precursor, for example, 20%, 25%, 30%, 35% or 40%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, in the precursor of step (1), the mass ratio of iron element to cobalt element is 1:(0.6-3.0), for example, it can be 1:0.6, 1:0.8, 1:1.0, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2.0, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8 or 1:3.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the iron salt in step (1) comprises ferric nitrate.

[0018] Preferably, the cobalt salt in step (1) comprises cobalt nitrate.

[0019] Preferably, the mixing time in step (1) is 24-36 hours, for example, it can be 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours or 36 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Preferably, the mixing method in step (1) includes stirring.

[0021] Preferably, the mixing in step (1) is carried out in a solvent medium. Exemplarily, the medium includes water.

[0022] Further preferably, the amount of water is 200-300 mL, for example, 200 mL, 220 mL, 240 mL, 250 mL, 260 mL, 280 mL or 300 mL, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the reaction in step (1) is followed by washing and drying.

[0024] Preferably, the washing time is 24-48 hours, for example, it can be 24 hours, 30 hours, 36 hours, 40 hours, 42 hours or 48 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the drying temperature is 70-95°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the drying time is 12-18 hours, for example, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours or 18 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the alkali in the alkali solution in step (2) comprises potassium hydroxide.

[0028] Preferably, the concentration of the alkali solution in step (2) is 2.0-8.0 wt%, for example, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, 7.0 wt% or 8.0 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the solid-liquid ratio of the precursor to the alkali solution in step (2) is 1:(25-50) g / mL, for example, it can be 1:25 g / mL, 1:30 g / mL, 1:35 g / mL, 1:40 g / mL, 1:45 g / mL or 1:50 g / mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the mixing method in step (2) includes stirring.

[0031] Preferably, the mixing process in step (2) includes a first mixing and a second mixing performed sequentially.

[0032] Preferably, the temperature of the first mixing is 20-30°C, for example, 20°C, 22°C, 24°C, 25°C, 26°C, 28°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the first mixing time is 5-10 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] Preferably, the temperature of the second mixing is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the second mixing time is 1-4 hours, for example, 1 hour, 2 hours, 3 hours or 4 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the mixing in step (2) is followed by drying and grinding.

[0037] Preferably, the drying time is 5-10 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the heating rate of the pyrolysis in step (3) is 10-20°C / min, for example, it can be 10°C / min, 12°C / min, 14°C / min, 15°C / min, 16°C / min, 18°C / min or 20°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the pyrolysis temperature in step (3) is 600-1000°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the pyrolysis time in step (3) is 2-4 h, for example, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the pyrolysis in step (3) is followed by grinding.

[0042] In a second aspect, the present invention provides a bimetallic nitrogen-doped carbon material, which is prepared by the preparation method described in the first aspect.

[0043] The bimetallic nitrogen-doped carbon material provided by the present invention has a sponge structure in the bulk phase and dense microcubes on the surface. The microcubes are evenly distributed and well dispersed, with an average side length of 200nm. The Fe content of the microcubes is relatively high. The bimetallic can exert a synergistic effect between the components. The microcubes are used as active sites for electrocatalytic CO2 reduction, with good catalytic reduction performance and good stability. The affinity between Fe and potassium thiocyanate is used to determine that the active center of the material is Fe-N x group (where "x" represents the number of N atoms around an Fe atom).

[0044] In a third aspect, the present invention provides an application of the bimetallic nitrogen-doped carbon material as described in the second aspect, wherein the bimetallic nitrogen-doped carbon material is applied to an electrocatalytic CO2 reduction reaction.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The preparation method provided by the present invention realizes the simple and effective synthesis of bimetallic nitrogen-doped carbon materials. The prepared bimetallic nitrogen-doped carbon materials have a sponge structure in the bulk phase and dense microcubes on the surface, which are evenly distributed and well dispersed. The bimetallic can exert a synergistic effect between the components, using the microcubes as active sites for electrocatalytic CO2 reduction, and have good catalytic reduction performance and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a scanning electron microscope image of the bimetallic nitrogen-doped carbon material provided in Example 1.

[0048] Figure 2 This is the EDS elemental analysis diagram of the bimetallic nitrogen-doped carbon material provided in Example 1.

[0049] Figure 3 1 is the current density curve of the electrocatalytic CO2 reduction of the nitrogen-doped carbon material provided in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] Example 1

[0052] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material, the preparation method comprising the following steps:

[0053] (1) Add 250 mL of water, 2 g of chitosan, 3.6071 g of ferric nitrate nonahydrate, and 2.4692 g of cobalt nitrate hexahydrate into a beaker, where the mass ratio of Fe to Co is 1:1, and stir at room temperature for 24 h to form a precipitate. The precipitate is washed and stirred in 250 mL of water at room temperature (25°C) for 24 h, and then dried in an oven at 70°C for 12 h.

[0054] (2) A 4.0% potassium hydroxide solution was prepared and mixed with the precipitate to increase the surface area of ​​the MNC catalyst. 25 mL of potassium hydroxide solution was added to every 1 g of precipitate. In this step, the precipitate was ground using an agate mortar to better disperse it in the KOH solution. The mixture was stirred at room temperature (25°C) for 5 h, at 50°C for 1 h, and then completely dried at 100°C for 5 h before being ground into a powder.

[0055] (3) Under nitrogen atmosphere, the temperature was raised to 600 °C at a heating rate of 10 °C / min for pyrolysis for 2 h, and then naturally cooled in the furnace. Subsequently, the pyrolyzed compound was ground in an agate mortar for 20 min to obtain a black powdery FeCo-NC catalyst.

[0056] Example 2

[0057] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material, the preparation method comprising the following steps:

[0058] (1) Add 250 mL of water, 1.5 g of chitosan, 3.6071 g of ferric nitrate nonahydrate, and 2.4692 g of cobalt nitrate hexahydrate to a beaker, wherein the mass ratio of Fe to Co elements is 1:1, and stir at room temperature for 30 h to form a precipitate. The precipitate is washed and stirred in 250 mL of water at room temperature (25°C) for 36 h, and then dried in an oven at 80°C for 18 h.

[0059] (2) preparing a potassium hydroxide solution with a mass fraction of 2.0% and mixing it with the precipitate to increase the surface area of ​​the MNC catalyst, wherein 30 mL of potassium hydroxide solution was added per 1 g of precipitate. In this step, the precipitate was ground using an agate mortar to better disperse it in the KOH solution, stirred at 20°C for 10 h, stirred at 60°C for 2 h, and then completely dried at 100°C for 8 h and ground into a powder;

[0060] (3) Under nitrogen atmosphere, the temperature was raised to 700 °C at a heating rate of 15 °C / min for pyrolysis for 4 h, and then naturally cooled in the furnace. Subsequently, the pyrolyzed compound was ground in an agate mortar for 20 min to obtain a black powdery FeCo-NC catalyst.

[0061] Example 3

[0062] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material, the preparation method comprising the following steps:

[0063] (1) Add 250 mL of water, 4 g of chitosan, 3.6071 g of ferric nitrate nonahydrate, and 2.4692 g of cobalt nitrate hexahydrate to a beaker, where the mass ratio of Fe to Co is 1:1, and stir at room temperature for 36 h to form a precipitate. The precipitate is washed and stirred in 250 mL of water at room temperature (25°C) for 48 h, and then dried in an oven at 95°C for 15 h.

[0064] (2) preparing a potassium hydroxide solution with a mass fraction of 8.0% and mixing it with the precipitate to increase the surface area of ​​the MNC catalyst, wherein 50 mL of potassium hydroxide solution was added to every 1 g of precipitate. In this step, the precipitate was ground using an agate mortar to better disperse it in the KOH solution, stirred at 30°C for 8 h, stirred at 40°C for 4 h, and then completely dried at 100°C for 10 h and ground into a powder;

[0065] (3) Under nitrogen atmosphere, the temperature was raised to 1000 °C at a heating rate of 20 °C / min for pyrolysis for 3 h, and then naturally cooled in the furnace. Subsequently, the pyrolyzed compound was ground in an agate mortar for 20 min to obtain a black powdery FeCo-NC catalyst.

[0066] Example 4

[0067] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the mass ratio of Fe to Co in step (1) is controlled to be 0.6:1, and the rest is the same as Example 1.

[0068] Example 5

[0069] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the mass ratio of Fe to Co in step (1) is controlled to be 3.0:1, and the rest is the same as Example 1.

[0070] Example 6

[0071] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the mass fraction of potassium hydroxide in step (2) is controlled to be 1.0%, and the rest is the same as Example 1.

[0072] Example 7

[0073] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the mass fraction of potassium hydroxide in step (2) is controlled to be 9.0%, and the rest is the same as Example 1.

[0074] Example 8

[0075] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, in step (2), the stirring process is controlled to be stirred at 25° C. for 5 h, and the rest is the same as Example 1.

[0076] Example 9

[0077] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the pyrolysis temperature in step (3) is controlled to be 500° C., and the rest is the same as Example 1.

[0078] Example 10

[0079] This embodiment provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, the pyrolysis temperature in step (3) is controlled to be 1100° C., and the rest is the same as Example 1.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing a nitrogen-doped carbon material, which comprises the following steps: compared with Example 1, no metal salt is added in step (1), the mass of chitosan is 8 g, and the rest are the same as Example 1.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a metal nitrogen-doped carbon material. Compared with Example 1, the metal salt added in step (1) is 6 g of ferric nitrate, and no cobalt nitrate is added. The rest is the same as Example 1.

[0084] Comparative Example 3

[0085] This comparative example provides a method for preparing a metal nitrogen-doped carbon material. Compared with Example 1, the metal salt added in step (1) is 5 g of cobalt nitrate, and no iron nitrate is added. The rest is the same as Example 1.

[0086] Comparative Example 4

[0087] This comparative example provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, in step (1), cobalt nitrate nonahydrate is replaced with copper nitrate according to equal masses of cobalt and copper, and the rest is the same as Example 1.

[0088] Comparative Example 5

[0089] This comparative example provides a method for preparing a bimetallic nitrogen-doped carbon material. Compared with Example 1, step (2) is not performed, and the rest is the same as Example 1.

[0090] Performance Characterization

[0091] The catalytic performance of the materials provided in the examples and comparative examples was tested using the following method:

[0092] The electrocatalytic CO2 reduction performance of the prepared materials was tested using linear sweep voltammetry (LSV) using an electrochemical workstation (CH Instrument 760E) and a rotating disk electrode (WaveVortex 10). The electrolyte used was 0.1M KHCO3 (CO2-saturated), and the scan rate was 5 mV / s. During the experiment, CO2 gas was kept flowing at the top of the solution to maintain a saturated atmosphere in the electrolyte. The catalytic activity was evaluated by measuring the onset potential (calculated as the potential at which the current density increases by one order of magnitude compared to the capacitive current) and the current density at a constant potential (-0.9 V vs. RHE). The results are listed in Table 1.

[0093] The current density curves of the nitrogen-doped carbon materials for electrocatalytic CO2 reduction provided by Example 1 (denoted as FeCo-NC), Comparative Example 1 (denoted as metal-free-NC), Comparative Example 2 (denoted as Fe-NC) and Comparative Example 3 (denoted as Co-NC) are shown in FIG. Figure 3 shown.

[0094] Table 1

[0095]

[0096]

[0097] As can be seen from Table 1:

[0098] The bimetallic but doped carbon material provided by the present invention exhibits a more positive reaction onset potential and a higher reduction peak current density compared to metal-free or monometallic doping. The iron-rich microcube structure acts as the active center, and the iron-cobalt bimetallic synergistic effect produces a good catalytic reduction effect. The preparation method provided by the present invention is simple and efficient, and under the preferred preparation conditions of the present invention, the material can achieve optimal catalytic activity. Compared with Example 1, Comparative Example 4 uses iron and copper metals, but the lack of cobalt makes it difficult to form a microcube structure, resulting in a significant decrease in catalytic performance. In Comparative Example 5, the absence of a base reduces the number of active sites in the material, resulting in a decrease in catalytic performance.

[0099] In summary, the preparation method provided by the present invention realizes the simple and effective synthesis of bimetallic nitrogen-doped carbon materials. The prepared bimetallic nitrogen-doped carbon material has a sponge structure in the bulk phase and dense microcubes on the surface, which are evenly distributed and well dispersed. The bimetallic can exert a synergistic effect between the components, and the microcubes are used as active sites for electrocatalytic CO2 reduction, with good catalytic reduction performance and good stability.

[0100] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a bimetallic nitrogen-doped carbon material, characterized in that: The preparation method comprises the following steps: (1) mixing a nitrogen and carbon source, an iron salt, and a cobalt salt to obtain a precursor; (2) mixing the alkali solution with the precursor obtained in step (1) to obtain a modified precursor; (3) Pyrolyzing the modified precursor obtained in step (2).

2. The preparation method according to claim 1, characterized in that The nitrogen and carbon sources in step (1) include any one of chitosan, urea or melamine, or a combination of at least two thereof; Preferably, the amount of the nitrogen and carbon source in step (1) is 20-40% of the mass of the precursor.

3. The preparation method according to claim 1 or 2, characterized in that In the precursor of step (1), the mass ratio of iron element to cobalt element is 1:(0.6-3.0); Preferably, the iron salt in step (1) comprises ferric nitrate; Preferably, the cobalt salt in step (1) comprises cobalt nitrate.

4. The preparation method according to any one of claims 1 to 3, characterized in that The mixing time in step (1) is 24-36 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that The alkali in the alkali solution of step (2) comprises potassium hydroxide; Preferably, the concentration of the alkali solution in step (2) is 2.0-8.0 wt%.

6. The preparation method according to any one of claims 1 to 5, characterized in that The solid-to-liquid ratio of the precursor to the alkali solution in step (2) is 1:(25-50) g / mL.

7. The preparation method according to any one of claims 1 to 6, characterized in that The mixing process in step (2) includes a first mixing and a second mixing performed sequentially; Preferably, the temperature of the first mixing is 20-30°C; Preferably, the first mixing time is 5-10h; Preferably, the temperature of the second mixing is 40-60°C; Preferably, the second mixing time is 1-4 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that The heating rate of the pyrolysis in step (3) is 10-20°C / min; Preferably, the pyrolysis temperature in step (3) is 600-1000°C; Preferably, the pyrolysis time in step (3) is 2-4 hours.

9. A bimetallic nitrogen-doped carbon material, characterized in that: The bimetallic nitrogen-doped carbon material is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the bimetallic nitrogen-doped carbon material according to claim 9, characterized in that: The bimetallic nitrogen-doped carbon material is applied to electrocatalytic CO2 reduction reaction.

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