Preparation method and application of bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst

Abstract

The application relates to the technical field of electrocatalysis, in particular to a preparation method and application of a bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, which comprises the following steps: S1, adding urea and ammonium chloride into water, stirring, freeze-drying, grinding, and obtaining a chelating ligand; S2, adding bismuth citrate into the chelating ligand, carrying out a solid-phase reaction, and obtaining a precursor; and S3, calcining the precursor under nitrogen protection, and obtaining the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst. The problems that reduction and reconstruction reactions are prone to occur in the process of catalyzing CO2 electrocatalytic reduction, and the difficulty in increasing the recognition and performance regulation of active sites can be solved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to a method for preparing bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst and its application. Background Technology

[0002] With modern society's increasing reliance on petrochemical resources, CO2 emissions have become more than just an environmental issue; they have risen to the level of international relations and are crucial to human survival and development. As the dual-carbon goals are advanced, numerous industries are seeking methods for capturing and utilizing carbon dioxide. Currently, CO2 conversion and utilization are mainly achieved through electrocatalysis, photocatalysis, photoelectrocatalysis, and biocatalysis. CO2 electroreduction is a highly efficient and environmentally friendly conversion method. Under a certain reduction potential, CO2 on and near the cathode surface is converted into other high-value carbon-containing compounds. Electroreduction technology converts CO2 into various carbon-containing compounds such as CO, HCOOH, ethanol, acetic acid, propanol, propane, and propionic acid. Therefore, the electrochemical reduction of CO2 into fuels and chemicals is considered an important way to store sustainable energy and solve climate problems, and an effective means to achieve carbon neutrality.

[0003] The electroreduction of CO2 is mainly affected by factors such as electrode catalyst, electrolyte type, and local electrode potential. Among these, the development of highly efficient catalysts is crucial to the technology. However, commonly used electrocatalytic materials suffer from drawbacks such as high cost, low activity, and poor stability. Bismuth metal exhibits high catalytic activity and selectivity in CO2 electroreduction. However, its current density and Faradaic efficiency still need further improvement. Currently, various methods have been developed to enhance the electrocatalytic activity of bismuth, including crystal facet exposure, morphology control, ion doping, and composite methods, which have become research hotspots in recent years.

[0004] Chinese patent CN115992365A discloses a bismuth metal-doped carbon nitride catalyst and its preparation method and application. Using urea and bismuth source as raw materials, a porous sheet-like bismuth metal-doped carbon nitride catalyst is obtained through mixing, freeze drying, calcination, acid washing and post-treatment. However, this method still has some shortcomings: (1) The prepared bismuth metal-doped carbon nitride catalyst is composed of two parts: bismuth metal and carbon nitride, with the former loaded on the latter. During the catalytic reduction of CO2, structural reconstruction phenomena such as particle size growth and active center detachment are prone to occur, which cannot guarantee the stability of its catalytic performance and increases the difficulty of identifying active sites and regulating performance. (2) During the high-temperature calcination process, the atoms inside the bismuth metal nanoparticles loaded on the surface of the carbon nitride support will diffuse and rearrange, which will cause the nanoparticles to easily agglomerate and increase in size, thus making the material synthesis more difficult. Summary of the Invention

[0005] This invention provides a method for preparing bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts and their applications, which can solve the problem that reduction and reconstruction reactions easily occur during the electrocatalytic reduction of CO2, increasing the difficulty of identifying active sites and regulating performance.

[0006] This application provides the following technical solution:

[0007] A method for preparing a bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, characterized by comprising the following steps:

[0008] S1. Add urea and ammonium chloride to water, stir evenly, and freeze dry to obtain chelated ligands;

[0009] S2. Add bismuth citrate to the chelating ligand, grind, and carry out a solid-phase reaction to obtain the precursor;

[0010] S3. Under nitrogen protection, the precursor is heated to 550℃ at a heating rate of 2~5℃ / min and held for 2~3 h. Then, it is heated to 650~800℃ at a heating rate of 2~5℃ / min and held for 2~3 h. The precursor is then naturally cooled to room temperature to obtain bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst.

[0011] The bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst consists of ultrafine metallic bismuth nanoparticles embedded within nitrogen-rich graphite carbon, forming a sandwich porous structure.

[0012] Application of bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts in the electrocatalytic reduction of carbon dioxide. The application method includes the following steps:

[0013] 1) Add anhydrous ethanol and Nafion to the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, and disperse evenly by ultrasonic treatment to obtain a suspension;

[0014] 2) The suspension was evenly coated onto carbon paper and dried to obtain carbon paper loaded with bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst.

[0015] 3) Carbon paper loaded with bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst was used as the working electrode, Ag / AgCl was used as the reference electrode, platinum sheet was used as the counter electrode, KHCO3 solution was used as the electrolyte solution, and CO2 was introduced for electrocatalytic reduction.

[0016] Beneficial effects: In the preparation process, urea plays a chelating role, while ammonium chloride plays a dispersing role and forms a porous structure. Urea and ammonium chloride are freeze-dried to form a uniformly mixed, highly crystalline chelate ligand. Adding bismuth citrate to the chelate ligand and grinding it allows for full coordination and binding between bismuth citrate and the chelate ligand, improving its dispersibility. This composite structure helps stabilize bismuth ions in bismuth citrate and restricts atomic diffusion within bismuth nanoparticles during subsequent calcination, ensuring the ultrafine particle size and uniform dispersion of bismuth nanoparticles. The stepwise calcination method ensures the dispersibility and stability of the active component during carbonization, inhibiting nanoparticle aggregation and size growth, thereby obtaining ultrafine metallic bismuth nanoparticles. These nanoparticles are then embedded within nitrogen-rich graphite carbon, forming a sandwich porous structure that improves the dispersibility of the active component, increases catalytic active sites, and thus enhances the electrocatalytic reduction performance and stability of the electrode material. The bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst prepared in this application exhibits excellent selectivity and stability in the electrocatalytic reduction of carbon dioxide, and can maintain high catalytic activity for a long time, which greatly improves the catalytic efficiency compared with traditional bismuth-based catalysts.

[0017] Meanwhile, the preparation method of this technical solution is simple to operate, and the preparation process does not require the use of harmful organic solvents, reducing the risk of environmental pollution and conforming to the development concept of green chemistry. It has advantages such as strong practicality, simple process, and good universal applicability, and has promising prospects for industrial application. Moreover, the raw materials used in this technical solution are inexpensive and readily available, and the preparation process is simple and easy to implement, reducing production costs and improving economic efficiency.

[0018] Further, the mass ratio of urea, ammonium chloride, and bismuth citrate is 10:3:0.5~3. Preferably, the mass ratio of urea, ammonium chloride, and bismuth citrate is 10:3:1~2.

[0019] The above-mentioned mass ratio of urea, ammonium chloride, and bismuth citrate ensures the effective binding of the chelating ligand to the bismuth source, promoting the formation of uniformly dispersed ultrafine bismuth nanocrystals.

[0020] Furthermore, the grinding in step S2 is performed using a ball mill at a speed of 150 rpm.

[0021] Dry grinding using ball milling further reduces the particle size of bismuth citrate and chelated ligands, resulting in finer and more uniform powders. This helps to form materials with high specific surface area and good dispersibility in subsequent processing, thereby improving the performance of the final product.

[0022] Further, after cooling to room temperature in step S3, the material is ground, washed with deionized water, and vacuum dried at a temperature of 80~85℃ for 2~2.5 h.

[0023] After grinding, the catalyst is washed with deionized water to ensure effective removal of impurities without introducing new contamination, thus maintaining the catalyst's purity. During the drying process, sufficient moisture is ensured to evaporate while avoiding high temperatures that could damage the material's structure.

[0024] Further, in step 2), the carbon paper loaded with bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst has a loading of 0.2~1.0 mg / cm³. 2 .

[0025] This loading not only increases the number of catalytic active sites but also avoids increasing particle size, significantly improving the selectivity and efficiency of electrocatalytic CO2 reduction while extending the catalyst's lifespan. Attached Figure Description

[0026] Figure 1 The images show the XRD patterns of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1, 2 and 3 of this invention.

[0027] Figure 2 The images show the FT-IR spectra of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1, 2 and 3 of this invention.

[0028] Figure 3 This is a SEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1 of the present invention.

[0029] Figure 4 This is a TEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1 of the present invention.

[0030] Figure 5 The image shows an HRTEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1 of this invention.

[0031] Figure 6 The images show the SEM and HRTEM images of the bismuth / carbon electrocatalyst prepared in Comparative Example 1.

[0032] Figure 7 The image shows the X-ray diffraction pattern of the electrocatalyst prepared in Comparative Example 2.

[0033] Figure 8 The Faraday efficiency of the electrocatalytic CO2 electroreduction reaction to produce formic acid in Examples 1, 2, and 3 and Comparative Examples 1 and 2 of this invention is shown. Detailed Implementation

[0034] The following detailed description illustrates the specific implementation method:

[0035] Example 1

[0036] A method for preparing a bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst includes the following steps:

[0037] Step S1: Add 10 g of urea and 3 g of ammonium chloride to 100 ml of deionized water, stir magnetically for 2 h, and then place it in a freeze dryer for freeze drying to obtain a loose powder solid. After grinding evenly, the chelated ligand is obtained.

[0038] In step S2, 0.5 g of bismuth citrate is added to the chelated ligand from step S1, and the mixture is placed in a ball mill for ball milling at a speed of 150 rpm to carry out a solid-phase reaction and obtain the precursor.

[0039] Step S3: Place the precursor obtained in step S2 into a tube furnace, use nitrogen as a protective gas, heat from room temperature to 550°C at a heating rate of 2°C / min, hold for 2 h, then heat to 800°C at a heating rate of 5°C / min, hold for 2 h, and then cool naturally to room temperature to obtain a black powder sample.

[0040] Step S4: Grind the black powder sample obtained in step S3 evenly, wash it with deionized water to remove impurities, and dry it in a vacuum drying oven at 80°C for 2 hours to obtain bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst.

[0041] Step S5, Application of bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst in electrocatalytic reduction of carbon dioxide, the application method includes the following steps:

[0042] 1) Weigh out bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst, add anhydrous ethanol and Nafion to the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst, the mass ratio of bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst, anhydrous ethanol and Nafion solution is 0.5~2:950:50, preferably 0.5:950:50, sonicate for 1 hour to obtain a uniformly dispersed suspension.

[0043] 2) The suspension was evenly coated onto carbon paper and dried in an oven at 60°C to obtain carbon paper loaded with bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst. The loading of the electrocatalyst was controlled by adjusting the amount of suspension, and the loading was 0.2 mg / cm³. 2 .

[0044] 3) An H-type electrolytic cell was used, with carbon paper loaded with bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode. The cathode and anode chambers each had a volume of 100 ml. 50 mL of 0.5 M KHCO3 solution was added to each chamber as the electrolyte solution, separated by a Nafion membrane (Nafion 117 proton exchange membrane). After setting the electrode potentials, the electrolytic cell was operated at a rate of 20 mL / min. -1CO2 is introduced into the electrolyte in the cathode chamber at a flow rate of [value missing] to start the reactor. After the reaction is complete, the liquid phase product in the electrolyte is analyzed by nuclear magnetic resonance spectroscopy, and the gas phase product is analyzed by gas chromatography.

[0045] Example 2

[0046] The difference between this embodiment and Example 1 is that the amount of bismuth citrate added in step S2 is 1 g, resulting in bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst.

[0047] Example 3

[0048] The difference between this embodiment and Example 1 is that the amount of bismuth citrate added in step S2 is 2 g, resulting in bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that no chelating ligand is added. Bismuth citrate is ball-milled, calcined under nitrogen protection, and cooled to obtain a bismuth / carbon electrocatalyst.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 1 is that: during the calcination process, under nitrogen protection, the temperature was raised from room temperature to the pyrolysis temperature at a rate of 2℃ / min, and then raised from room temperature to 550℃, held for 2 h, and naturally cooled to room temperature to obtain the electrocatalyst.

[0053] The electrocatalysts prepared in Examples 1-3 and Comparative Examples 1 and 2 were measured, and the results are as follows:

[0054] 1. Figure 1 The images show the XRD patterns of the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1-3. Figure 1 It can be seen that the main diffraction peaks of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1-3 match the diffraction peaks of orthorhombic bismuth metal, and no obvious diffraction peaks of bismuth oxide were observed, confirming that bismuth exists in the form of metallic bismuth and has good crystallinity. Obvious graphite carbon diffraction peaks also appeared. No other impurity peaks were found, indicating that the sample has high purity. Therefore, it can be determined that the electrocatalysts prepared in Examples 1-3 are mainly composed of metallic bismuth and graphite carbon.

[0055] 2. Figure 2 The images show the FT-IR spectra of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1-3. Figure 2 It can be seen that the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts prepared in Examples 1-3 contain a large number of carbon-containing groups.

[0056] 3. Figure 3This is a SEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1. From... Figure 3 It can be seen that the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1 is composed of ultrathin nanosheets with obvious wrinkles. The thickness of the sheets is very thin, significantly less than 10 nanometers, and no obvious particles were found, indicating that the bismuth metal is highly dispersed in the ultrathin nanosheets.

[0057] 4. Figure 4 This is a TEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1. From... Figure 4 It can be seen that the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1 exhibits an ultrathin sheet structure and has no obvious bismuth metal particles.

[0058] 5. Figure 5 This is an HRTEM image of the bismuth metal / nitrogen-rich graphite carbon electrocatalyst prepared in Example 1. From... Figure 5 Further observation revealed that the surface of the bismuth / nitrogen-rich graphite carbon electrocatalyst exhibited a certain degree of lattice fringes, confirming the formation of graphite carbon. Furthermore, no obvious bismuth particles were observed. Therefore, it can be concluded that the formed bismuth is highly embedded within the nitrogen-rich graphite carbon, constituting a sandwich-type porous structure.

[0059] 6. Figure 6 SEM image of the bismuth / carbon electrocatalyst prepared in Comparative Example 1 ( Figure 6 (a) and HRTEM diagram ( Figure 6 (b)). From Figure 6 As shown in (a), the bismuth / carbon electrocatalyst prepared in Comparative Example 1 consists of thin, stacked sheets with numerous pore structures and a large number of metallic bismuth nanoparticles. Figure 6 As shown in (b), the bismuth / carbon electrocatalyst prepared in Comparative Example 1 is composed of a large number of metallic bismuth nanoparticles. Therefore, it can be concluded that without the introduction of a chelating agent, the resulting sample consists of metallic bismuth nanoparticles supported on the surface of a carbon material, and the resulting metallic bismuth particles have a relatively large particle size.

[0060] 7. Figure 7 The image shows the X-ray diffraction pattern of the electrocatalyst prepared in Comparative Example 2. Figure 7 As can be seen from the data, the electrocatalyst prepared in Comparative Example 2 exhibits good performance at values ​​of 27.2, 37.9, 39.6, and 48.7. 0 Strong diffraction peaks appeared, corresponding to the (0 1 2), (0 1 4), (1 1 0), and (2 0 2) crystal planes of orthorhombic bismuth. Additionally, strong diffraction peaks were observed at 30.1 and 32.6. 0The diffraction peaks of the sample matched those of Bi₂O₃ at (2 22) and (3 2 1). This indicates that the electrocatalyst prepared in Comparative Example 2 was a mixture of metallic bismuth and Bi₂O₃. This demonstrates that the calcination process has a significant impact on the structure of the prepared electrocatalyst.

[0061] 8. Figure 8 The Faraday efficiency of the electrocatalytic CO2 electroreduction reaction to formic acid production in Examples 1-3 and Comparative Examples 1 and 2 is given. Figure 8 As can be seen, under the same reaction conditions, the Faradaic efficiency of the formate produced in Example 1 was 83.7%, the Faradaic efficiency of the formate produced in Example 2 was 89.6%, and the Faradaic efficiency of the formate produced in Example 3 was 95.2%. In contrast, the Faradaic efficiency of the formate produced in Comparative Example 1 was 61.2%, and the Faradaic efficiency of the formate produced in Comparative Example 2 was 26.5%. Therefore, the catalytic performance of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalysts in Examples 1-3 is significantly higher than that in Comparative Examples 1 and 2. This confirms that the excellent catalytic performance of the bismuth nanocrystals / nitrogen-rich graphite carbon electrocatalyst of the present invention is due to the encapsulation of ultrafine metallic bismuth nanoparticles within ultrathin nitrogen-rich graphite carbon nanosheets, forming a sandwich structure that effectively improves the dispersibility of the active component and increases the number of catalytic active sites.

[0062] The above are merely embodiments of the present invention, and the invention is not limited to the fields covered by these embodiments. Commonly known structures and characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, characterized in that, The preparation method comprises the following steps: S1, adding urea and ammonium chloride into water, stirring uniformly, and performing freeze-drying to obtain a chelating ligand; S2, adding bismuth citrate into the chelating ligand, grinding, and performing solid-phase reaction to obtain a precursor; S3, heating the precursor to 550℃ at a heating rate of 2-5℃ / min under nitrogen protection, and then heating to 650-800℃ at a heating rate of 2-5℃ / min, and naturally cooling to room temperature, to obtain the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst; the mass ratio of the urea, the ammonium chloride and the bismuth citrate is 10:3:0.5-3.

2. The method of claim 1, wherein: The mass ratio of the urea, the ammonium chloride and the bismuth citrate is 10:3:1-2.

3. The method of claim 1, wherein: The grinding in step S2 adopts ball milling, and the rotating speed is 150 r / min.

4. The method of claim 1, wherein: After cooling to room temperature in step S3, grinding is performed, and the product is cleaned with deionized water, vacuum dried, the drying temperature is 80-85℃, and the drying time is 2-2.5 h.

5. The bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst prepared by the preparation method in any one of claims 1-4.

6. The bismuth nanocrystal / nitrogen-rich graphitic carbon electrocatalyst of claim 5, wherein, The superfine metal bismuth nanoparticles are embedded in the nitrogen-rich graphite carbon, and a sandwich type porous structure is formed.

7. The bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst in claim 6 is applied to electrocatalytic reduction of carbon dioxide.

8. Use according to claim 7, characterized in that: The application method comprises the following steps: 1) adding anhydrous ethanol and Nafion into the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, and uniformly dispersing by ultrasonic treatment to obtain a suspension; 2) uniformly coating the suspension on carbon paper, and drying to obtain carbon paper loaded with the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst; 3) taking the carbon paper loaded with the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst as a working electrode, taking Ag / AgCl as a reference electrode, taking a platinum sheet as a counter electrode, taking KHCO3 solution as an electrolyte solution, and introducing CO2 to perform electrocatalytic reduction.

9. Use according to claim 8, characterized in that: Step 2) the carbon paper loaded with the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst, the loading amount of the bismuth nanocrystal / nitrogen-rich graphite carbon electrocatalyst being 0.2-1.0 mg / cm 2 .

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