Nitrogen-doped three-dimensional flower-shaped bismuth oxide electrocatalyst rich in oxygen vacancies as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped oxygen-vacancy-rich three-dimensional flower-shaped bismuth oxide electrocatalyst as well as a preparation method and application thereof, relates to the technical field of electrocatalysts, and solves the problems that a traditional bismuth oxide catalyst is insufficient in electron transfer capability and low in active site utilization rate. The preparation method comprises the following steps: dissolving bismuth nitrate, polyvinylpyrrolidone and sodium oleate in a mixed solvent of methanol and N, N-dimethylformamide, and stirring and dissolving to obtain a solution A; the preparation method comprises the following steps: dissolving 1, 3, 5-tri (4-carboxyl phenyl) benzene in a mixed solvent of methanol and N, N-dimethylformamide, and stirring and dissolving to obtain a solution B; and adding the B into the A, uniformly stirring, heating in an oil bath, reacting under magnetic stirring, cooling to room temperature, filtering, washing and drying the product to obtain white powder, calcining in a tubular furnace to obtain three-dimensional flower-shaped Bi2O3, putting in the tubular furnace, introducing argon, introducing ammonia gas, heating, and carrying out heat preservation reaction to obtain the electrocatalyst. The catalyst can be used for catalyzing nitrogen reduction synthesis ammonia reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysts, and particularly relates to a three-dimensional flower-shaped bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies, a preparation method thereof, and an application thereof. Background Art

[0002] (NH3), as an important strategic raw material in the modern industrial system, plays an irreplaceable role in fertilizer production, industrial synthesis, and clean energy fields. Currently, more than 90% of global ammonia production relies on the Haber-Bosch process, which needs to operate under high temperature (400 - 500 °C) and high pressure (15 - 30 MPa) conditions. Not only is the energy consumption intensity as high as 1 - 2% of the global total energy consumption, but it also emits approximately 1.9 tons of CO2 per ton of ammonia product, seriously restricting the realization of the carbon neutrality goal. In this context, the electrocatalytic nitrogen reduction reaction (NRR) technology has become the most promising technological innovation direction in the ammonia synthesis field due to its outstanding advantages of operating at room temperature and atmospheric pressure and being able to be coupled with renewable energy.

[0003] However, the electrocatalytic nitrogen reduction reaction technology faces dual challenges. Firstly, the high dissociation energy of N≡N leads to slow kinetics in the adsorption and activation process of nitrogen molecules, resulting in low ammonia production rate. Secondly, the existence of the competitive hydrogen evolution reaction (HER) in the aqueous solution system will reduce the selectivity of electrochemical reduction to produce ammonia. Therefore, developing efficient electrocatalysts is the key to solving this problem.

[0004] In recent years, bismuth (Bi)-based catalysts have received extensive attention due to their inertness towards the hydrogen evolution reaction and potential catalytic activity for reducing nitrogen to ammonia. Among them, bismuth oxide (Bi2O3) is considered a promising ammonia synthesis material due to its low cost, rich reserves, and environmental friendliness. However, traditional bismuth oxide catalysts have problems such as insufficient electron transfer ability and low utilization rate of active sites, which limit the further improvement of their electrocatalytic ammonia synthesis activity. To address the above defects, optimizing the structure and properties of bismuth oxide by means of doping and introducing oxygen vacancies has a significant effect on improving its catalytic performance. However, due to the complex preparation methods of traditional catalysts, it is difficult to precisely control the nitrogen doping amount and oxygen vacancy content, resulting in difficult optimization of catalytic performance. Therefore, developing a simple, efficient preparation method for bismuth oxide electrocatalysts that can precisely control the nitrogen doping amount and oxygen vacancy content is of great significance for improving its catalytic performance and promoting the practical application of electrocatalytic nitrogen reduction to synthesize ammonia. [[ID=!6]]Summary of the Invention

[0005] In order to solve the problems of insufficient electron transfer ability and low utilization rate of active sites existing in traditional bismuth oxide catalysts, the present invention proposes a three-dimensional flower-shaped bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies, a preparation method thereof, and an application thereof.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a nitrogen-doped and oxygen-vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst, comprising the following steps:

[0008] S1. Dissolve bismuth nitrate, polyvinylpyrrolidone, and sodium oleate in a mixed solvent of methanol and N,N-dimethylformamide, and stir until completely dissolved to obtain solution A;

[0009] S2. Dissolve 1,3,5-tris(4-carboxyphenyl)benzene in a mixed solvent of methanol and N,N-dimethylformamide, and stir until completely dissolved to obtain solution B;

[0010] S3. Add solution B to solution A and stir to mix evenly;

[0011] S4. Heat the mixed solution in an oil bath to 150 °C, and react under magnetic stirring. After the reaction is completed, naturally cool to room temperature, filter, wash, and dry the product to obtain a white powder;

[0012] S5. Place the white powder in a tube furnace, heat to the calcination temperature and then perform calcination to obtain three-dimensional flower-like Bi2O3;

[0013] S6. Place the obtained three-dimensional flower-like Bi2O3 in a tube furnace, introduce argon and then ammonia, and then heat at a heating rate of 5 °C / min to 300-400 °C and hold for 2 h, and then naturally cool to room temperature to obtain a nitrogen-doped and oxygen-vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst.

[0014] Preferably, the dosage ratio of bismuth nitrate, polyvinylpyrrolidone, sodium oleate, methanol, and N,N-dimethylformamide is 243 mg: 100 mg: 30 mg: 15 mL: 5 mL.

[0015] Preferably, the dosage ratio of 1,3,5-tris(4-carboxyphenyl)benzene, methanol, and N,N-dimethylformamide is 219 mg: 3 mL: 1 mL.

[0016] Preferably, the reaction time in step S4 is 12 h.

[0017] Preferably, the washing in step S4 is alternately with methanol and N,N-dimethylformamide.

[0018] Preferably, the drying temperature in step S4 is 60 °C and the drying time is 8 h.

[0019] Preferably, the heating rate in step S5 is 5 °C / min, the calcination temperature is 600 °C, and the calcination time is 2 h.

[0020] Preferably, the introduction time of argon in step S6 is not less than 30 min, the purity of ammonia is not less than 99.999%; the introduction time of ammonia is not less than 30 min.

[0021] The present invention also provides a nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies prepared by the above preparation method.

[0022] The present invention also provides an application of the above nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies, specifically applied to the catalytic nitrogen reduction reaction for synthesizing ammonia.

[0023] Compared with the prior art, the specific beneficial effects of the present invention are as follows:

[0024] 1. In the present invention, sodium oleate is used as a structure-confining agent and polyvinylpyrrolidone is used as a structure-directing agent to prepare a bismuth oxide precursor through a solvothermal reaction, and then a reducing gas ammonia is used for calcination in a tube furnace to introduce nitrogen doping and oxygen vacancies, obtaining a nitrogen-doped three-dimensional flower-like bismuth oxide material rich in oxygen vacancies. The catalyst provided by the present invention has a stable structure. Due to its unique morphological advantages, it can significantly increase the reaction area and the number of active sites, thereby improving the catalytic efficiency. The introduction of oxygen vacancies can adjust the electronic structure of the catalyst and enhance its adsorption capacity for nitrogen, while nitrogen doping can further optimize the electrochemical performance of the catalyst. In addition, by adjusting the reaction temperature, precise control of the nitrogen doping amount and oxygen vacancy content can be achieved. The higher the reaction temperature, the richer the oxygen vacancies and nitrogen doping amount. This regulation mechanism is based on the influence of the reaction temperature on the ammonia decomposition and nitrogen atom embedding processes, thereby realizing the optimization of the catalyst structure and performance. When applied to the electrocatalytic nitrogen reduction reaction for synthesizing ammonia, it exhibits excellent catalytic performance and stability.

[0025] 2. The preparation method of the present invention is simple to operate, has mild reaction conditions, and requires simple equipment, and has operability and repeatability. It has broad prospects in the application of electrocatalytic nitrogen reduction reaction for synthesizing ammonia. Description of the Drawings

[0026] Figure 1 SEM image of undoped three-dimensional flower-like Bi2O3 prepared in Example 1;

[0027] Figure 2 Electron paramagnetic resonance spectroscopy (EPR) images of undoped three-dimensional flower-like Bi2O3 and nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 1;

[0028] Figure 3 SEM image of nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 1;

[0029] Figure 4 Energy-dispersive X-ray spectroscopy pattern of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 1;

[0030] Figure 5 TEM image of the undoped three-dimensional flower-like Bi2O3 prepared in Example 2;

[0031] Figure 6 EPR patterns of the undoped three-dimensional flower-like Bi2O3 and the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 2;

[0032] Figure 7 TEM image of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 2;

[0033] Figure 8 EDX pattern of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies prepared in Example 2;

[0034] Figure 9 UV spectra of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies at different test voltages in the Effect Example;

[0035] Figure 10 Ammonia production rate and Faraday efficiency diagrams of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies at different test voltages in the Effect Example;

[0036] Figure 11 SEM image of the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies after the catalytic reaction in the Effect Example;

[0037] Figure 12 EPR comparison diagrams of the undoped three-dimensional flower-like Bi2O3 and the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies (300 °C and 400 °C) in the Effect Example;

[0038] Figure 13 Ammonia production rate diagrams of the undoped three-dimensional flower-like Bi2O3 and the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies (300 °C and 400 °C) at different test potentials in the Effect Example;

[0039] Figure 14 is Faraday efficiency diagrams of the undoped three-dimensional flower-like Bi2O3 and the nitrogen-doped three-dimensional flower-like Bi2O3 rich in oxygen vacancies (300 °C and 400 °C) at different test potentials in the Effect Example. Detailed implementation manners

[0040] To make the technical solution of the present invention clearer, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be construed as a limitation of the present invention.

[0041] Example 1.

[0042] In this example, a three-dimensional flower-like bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies was prepared. The specific operation process is as follows:

[0043] Preparation of three-dimensional flower-like bismuth oxide:

[0044] Dissolve 243 mg of bismuth nitrate (Bi(NO3)3·5H2O), 100 mg of polyvinylpyrrolidone (PVP), and 30 mg of sodium oleate in a mixed solvent of 15 mL of methanol and 5 mL of N,N-dimethylformamide (DMF), and stir at room temperature until completely dissolved to form solution A. Subsequently, dissolve 219 mg of 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB) in a mixed solvent of 3 mL of methanol and 1 mL of DMF, and stir until completely dissolved to form solution B. Slowly add solution B to solution A and continue to stir for 30 min to ensure uniform mixing. Place the mixed solution in an oil bath and heat it to 150 °C, and keep it for 12 h under magnetic stirring. After the reaction is completed, the mixture is naturally cooled to room temperature, and the product is separated by filtration. Wash the product alternately with methanol and DMF to remove residual impurities. The washed product is dried at 60 °C for 8 h to obtain a white powder. Finally, place the powder in a tubular furnace and heat it to 600 °C in air at a heating rate of 5 °C / min, and calcine it for 2 h to obtain three-dimensional flower-like Bi2O3.

[0045] Observe the SEM image and EPR image of the three-dimensional flower-like Bi2O3, as shown in Figure 1 and Figure 2 respectively. The SEM image shows that the product presents a three-dimensional flower-like stacked structure, and no obvious electron-hole characteristic peak appears in the EPR image, indicating that the product does not contain oxygen vacancies.

[0046] Introduction of nitrogen doping and oxygen vacancies:

[0047] Place the prepared three-dimensional flower-like Bi2O3 in the quartz tube of the tubular furnace, introduce high-purity argon (purity ≥ 99.999%) for 30 min, and the argon flow rate is 60 mL / min. Subsequently, continuously introduce high-purity ammonia (purity ≥ 99.999%), the ammonia flow rate is 200 mL / min, and the introduction time is 30 min. Then, heat it to 400 °C at a heating rate of 5 °C / min and keep the reaction at this temperature for 2 h. After the reaction is completed, it is naturally cooled to room temperature to obtain a three-dimensional flower-like bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies.

[0048] Observe its EPR diagram, SEM diagram and EDX diagram, as shown respectively in Figure 2 , Figure 3 and Figure 4 shown. The SEM diagram shows that the product presents a three-dimensional flower-like structure, and symmetric electron-hole characteristic peaks appear in the EPR diagram, indicating that the product is rich in oxygen vacancies. The EDX diagram shows that the doping amount of nitrogen element is 4.53%.

[0049] Example 2.

[0050] In this example, a three-dimensional flower-like bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies is prepared. The specific operation process is as follows:

[0051] Preparation of three-dimensional flower-like bismuth oxide:

[0052] Dissolve 243 mg of bismuth nitrate (Bi(NO3)3·5H2O), 100 mg of polyvinylpyrrolidone (PVP) and 30 mg of sodium oleate in a mixed solvent of 15 mL of methanol and 5 mL of N,N-dimethylformamide (DMF), and stir at room temperature until completely dissolved to form solution A. Subsequently, dissolve 219 mg of 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB) in a mixed solvent of 3 mL of methanol and 1 mL of DMF, and stir until completely dissolved to form solution B. Slowly add solution B to solution A and continue to stir for 30 min to ensure uniform mixing. Place the mixed solution in an oil bath and heat it to 150 °C, and keep it for 12 h under magnetic stirring. After the reaction is completed, the mixture is naturally cooled to room temperature, and the product is separated by filtration. Wash the product alternately with methanol and DMF to remove residual impurities. The washed product is dried at 60 °C for 8 h to obtain a white powder. Finally, place the powder in a tubular furnace and heat it to 600 °C in air at a heating rate of 5 °C / min and calcine for 2 h to obtain three-dimensional flower-like Bi2O3.

[0053] Respectively observe its TEM diagram and EPR diagram, as shown respectively in Figure 5 and Figure 6 shown. The TEM diagram shows that the product presents a three-dimensional flower-like stacked structure, and no obvious electron-hole characteristic peaks appear in the EPR diagram, indicating that the product does not contain oxygen vacancies.

[0054] Nitrogen doping and oxygen vacancy introduction:

[0055] The three-dimensional flower-like Bi2O3 prepared in Step 1 was placed in a quartz tube of a tubular furnace, and high-purity argon gas (purity ≥ 99.999%) was introduced for 30 min at an argon gas flow rate of 60 mL / min. Subsequently, high-purity ammonia gas (purity ≥ 99.999%) was continuously introduced at an ammonia gas flow rate of 200 mL / min for 30 min. Then, the temperature was raised to 300 °C at a heating rate of 5 °C / min and maintained at this temperature for a reaction of 2 h. After the reaction, it was naturally cooled to room temperature to obtain a nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst.

[0056] Observing its EPR diagram, TEM diagram, and EDX diagram, as Figure 6 , Figure 7 and Figure 8 shown, the TEM diagram shows that the product presents a three-dimensional flower-like structure, and a symmetric electron-hole characteristic peak appears in the EPR diagram, indicating that the product is rich in oxygen vacancies. The EDX diagram shows that the doping amount of nitrogen element is 3.46%.

[0057] Effect example.

[0058] The nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like bismuth oxide electrocatalysts prepared in Examples 1 and 2 were applied to the electrocatalytic nitrogen reduction reaction for ammonia synthesis, and their performance was tested. The specific operations are as follows:

[0059] (1) Catalyst performance test:

[0060] Take 3 mg of the nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like Bi2O3 electrocatalyst prepared in Example 1, disperse it in 0.8 mL of deionized water, add 200 μL of 5% Nafion solution, and ultrasonicate for 30 min. Drop 10 μL of the dispersion on a glassy carbon electrode with a diameter of 5 mm, and after drying, perform chronoamperometry testing with an electrochemical workstation. The test uses a three-electrode system. Nitrogen gas is continuously introduced before and during the test, and the test electrolyte is 0.1 M potassium hydroxide solution. Ultraviolet spectrophotometry testing and ammonia production rate calculation are carried out at different test voltages.

[0061] The test results show that at a potential of -0.5 V vs. RHE, the catalyst has the highest ammonia production rate (102.3 μg h - 1 mg cat -1 ) and Faraday efficiency (14.7%), as Figure 9 and Figure 10 shown.

[0062] The above results stem from the synergistic mechanism of nitrogen doping, oxygen vacancy formation, and the three-dimensional flower-like structure. After nitrogen atoms replace some lattice oxygen, the d-band center of Bi moves upward, enhancing the electron injection ability of Bi active sites and effectively weakening the strength of the N≡N bond. Oxygen vacancies, as electron defect centers, can generate a local electric field to promote the polarized adsorption of N2 molecules. The three-dimensional flower-like structure significantly increases the three-phase reaction interface, improving the utilization rate of active sites.

[0063] (2) Catalyst stability test:

[0064] The electrode after the electrochemical test was ultrasonically treated, and the SEM image of the catalyst sample shed off was tested, as Figure 11 shown. Comparing before and after the catalytic test, the morphology of the catalyst basically did not change, indicating that the catalyst prepared by the present invention has excellent stability. The three-dimensional cross-linked framework synthesized by the PVP template guidance resists the shear force of the electrolyte through the Bi-O-Bi bond network; the N-Bi covalent bond formed by nitrogen doping inhibits the irreversible annihilation of oxygen vacancies at the reduction potential.

[0065] (3) Comparative experiment:

[0066] EPR comparative tests were carried out on the nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like Bi2O3 prepared in Example 1 and Example 2 and the undoped three-dimensional flower-like Bi2O3, as Figure 12 shown. The EPR signal intensities of the nitrogen-doped and oxygen vacancy-rich Bi2O3 prepared at different reaction temperatures are different, indicating that catalysts with different oxygen vacancy contents can be prepared by adjusting the reaction temperature. The higher the reaction temperature, the richer the oxygen vacancies and nitrogen doping amount. This regulation mechanism is based on the influence of the reaction temperature on the ammonia decomposition and nitrogen atom embedding processes, thereby realizing the optimization of the catalyst structure and performance. In addition, at a potential of -0.5 V vs. RHE, the ammonia production rate and Faraday efficiency of the nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like Bi2O3 are better than those of the undoped Bi2O3, as Figure 13 and as shown in Figure 14 shown.

[0067] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of a nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies, characterized in that, It includes the following steps: S1. Dissolve bismuth nitrate, polyvinylpyrrolidone and sodium oleate in a mixed solvent of methanol and N,N-dimethylformamide, and stir until completely dissolved to obtain solution A; S2. Dissolve 1,3,5-tris(4-carboxyphenyl)benzene in a mixed solvent of methanol and N,N-dimethylformamide, and stir until completely dissolved to obtain solution B; S3. Add solution B to solution A and stir to mix evenly; S4. Heat the mixed solution in an oil bath to 150 °C, and react under magnetic stirring. After the reaction is completed, naturally cool to room temperature, filter, wash and dry the product to obtain a white powder; S5. Place the white powder in a tubular furnace, heat it to the calcination temperature and then carry out calcination to obtain three-dimensional flower-like Bi2O3; S6. Place the obtained three-dimensional flower-like Bi2O3 in a tubular furnace, introduce argon and then ammonia gas, then heat it to 300-400 °C at a heating rate of 5 °C / min and keep it warm for reaction for 2 h, and then naturally cool to room temperature to obtain a nitrogen-doped and oxygen-vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst.

2. The preparation method of the nitrogen-doped and oxygen-vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst according to claim 1, characterized in that, The dosage ratio of bismuth nitrate, polyvinylpyrrolidone, sodium oleate, methanol and N,N-dimethylformamide is 243 mg: 100 mg: 30 mg: 15 mL: 5 mL.

3. The preparation method of the nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies according to claim 1, characterized in that, The dosage ratio of 1,3,5-tris(4-carboxyphenyl)benzene, methanol and N,N-dimethylformamide is 219 mg: 3 mL: 1 mL.

4. The preparation method of the nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst according to claim 1, characterized in that, The reaction time in step S4 is 12 h.

5. The preparation method of the nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies according to claim 1, characterized in that, The washing in step S4 is carried out alternately with methanol and N,N-dimethylformamide.

6. The preparation method of the nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst according to claim 1, characterized in that, The drying temperature in step S4 is 60 °C and the drying time is 8 h.

7. The preparation method of the nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies according to claim 1, characterized in that, The heating rate in step S5 is 5 °C / min, the calcination temperature is 600 °C, and the calcination time is 2 h.

8. The preparation method of the nitrogen-doped three-dimensional flower-like bismuth oxide electrocatalyst rich in oxygen vacancies according to claim 1, characterized in that, The argon introduction time in step S6 is not less than 30 min, the purity of the ammonia gas is not less than 99.999%; the ammonia gas introduction time is not less than 30 min.

9. A three-dimensional flower-like bismuth oxide electrocatalyst doped with nitrogen and rich in oxygen vacancies, characterized in that, It is prepared by using the preparation method described in any one of claims 1 to 8.

10. Application of a nitrogen-doped and oxygen vacancy-rich three-dimensional flower-like bismuth oxide electrocatalyst as described in claim 9, characterized in that, It is applied to the catalytic nitrogen reduction reaction for synthesizing ammonia.

Images