Synthetic method and application of AgNPs (at) Zn-N-C catalyst

Abstract

The invention discloses a synthesis method and application of an AgNPs (at) Zn-N-C catalyst. The synthesis method comprises the following steps: preparing a ZIF-8 precursor through a reaction of a zinc salt and a nitrogen-containing organic compound; the preparation method comprises the following steps: dispersing ZIF-8 in deionized water, and adding silver salt to generate Ag / ZIF-8; and then carrying out high-temperature pyrolysis on the Ag / ZIF-8 in an inert atmosphere to obtain the AgNPs (at) Zn-N-C catalyst. In the catalyst, silver nanoparticles are uniformly dispersed on the surface of a zinc-nitrogen co-doped carbon-based carrier, and the carrier has a high specific surface area and contains Zn-N4 active sites. The AgNPs (at) Zn-N-C catalyst shows excellent catalytic performance and stability in an oxygen reduction reaction, can efficiently promote a four-electron path reaction, remarkably reduces the generation of byproducts, and keeps good stability in an acidic or alkaline medium. The synthesis method is simple to operate, low in cost and suitable for industrial production, the cost is remarkably reduced by adopting cheap raw materials, the process is pollution-free, and the green chemical requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst synthesis, and in particular to a synthesis method and application of an AgNPs@Zn-NC catalyst. Background Art

[0002] Oxygen reduction reaction (ORR) is a core reaction in new energy devices such as fuel cells (such as proton exchange membrane fuel cells, PEMFCs), metal-air batteries (such as zinc-air batteries) and microbial fuel cells, which directly affects the energy conversion efficiency and device performance. The ORR reaction pathway usually includes a four-electron pathway (generating H2O or OH - ) and two-electron pathways (producing H₂O₂), with the four-electron pathway being preferred due to its high efficiency and low byproduct formation. However, the ORR process is slow in kinetics, and high overpotentials lead to energy losses, limiting its practical application in new energy devices. Therefore, the development of efficient and stable ORR catalysts has become a research priority.

[0003] Traditionally, platinum-based catalysts (such as commercial Pt / C) have been widely used in ORR due to their high catalytic activity. Their half-wave potential can usually reach 0.90 V (vs. RHE) and they tend to favor the four-electron pathway. However, platinum-based catalysts have significant disadvantages: first, platinum resources are scarce and expensive, making it difficult to meet the needs of large-scale commercialization; second, platinum-based catalysts are prone to agglomeration or dissolution during long-term operation, resulting in activity decay, especially insufficient stability in acidic or alkaline electrolytes. These problems have prompted researchers to seek low-cost, high-performance alternative catalysts.

[0004] In recent years, non-precious metal catalysts and some precious metal catalysts have attracted widespread attention due to their cost advantages and tunable performance. Non-precious metal catalysts (such as Fe-NC, Co-NC) form active sites similar to metal-N4 through the coordination of transition metals and nitrogen, which can effectively promote the four-electron pathway of ORR. However, the activity of such catalysts is usually lower than that of Pt / C, and their stability in acidic media still needs to be improved. As a substitute for precious metals, silver (Ag) is considered to be a potential alternative to platinum due to its relatively low price and good electrocatalytic performance. Silver nanoparticles (AgNPs) show certain catalytic activity in ORR, but their stability in acidic or alkaline media is poor, and the ORR selectivity (ratio of four-electron pathway) is insufficient, which limits their practical application.

[0005] In order to improve the performance of AgNPs, researchers have tried to load them on carbon-based supports. Nitrogen-doped carbon materials (NC) are often used as catalyst supports due to their high specific surface area, good conductivity and abundant active sites. Zinc (Zn), as a transition metal, can be co-doped with nitrogen to form Zn-NC materials, which can regulate the electronic structure of carbon-based materials through Zn-N coordination (such as Zn-N4 sites) and further enhance the ORR activity. In addition, the porous structure of Zn-NC helps to increase the specific surface area of the catalyst (up to 800-1000m 2 / g), thereby exposing more active sites. However, existing methods for synthesizing AgNPs loaded on Zn-N co-doped carbon-based materials still have shortcomings: on the one hand, the preparation process is complex, making it difficult to achieve uniform dispersion of AgNPs, resulting in uneven distribution of active sites; on the other hand, the synergistic effect between AgNPs and Zn-NC has not been fully utilized, and the ORR activity and stability of the catalyst still need to be further improved.

[0006] Against this backdrop, the present invention proposes a method for synthesizing an AgNPs@Zn-NC catalyst and its application in ORR. By optimizing the synthesis of the ZIF-8 precursor, the loading of AgNPs, and the high-temperature pyrolysis process, uniform dispersion of AgNPs on the Zn-NC support is achieved. The synergistic effects of Zn-N coordination and the carbon-based support significantly enhance the ORR activity and stability of the catalyst. This method is simple to operate, low-cost, and suitable for industrial production, providing a new technical approach for the commercial application of fuel cells and metal-air batteries. Summary of the Invention

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for synthesizing an AgNPs@Zn-NC catalyst, wherein AgNPs@Zn-NC represents silver nanoparticles AgNPs supported on a zinc-nitrogen co-doped carbon-based material ZnN-C, comprising the following steps:

[0008] (1) Preparation of ZIF-8 precursor: dissolving zinc salt and nitrogen-containing organic compound in a solvent to react to form ZIF-8;

[0009] (2) Loading AgNPs: The ZIF-8 prepared in step (1) was dispersed in deionized water and silver salt was added to generate Ag / ZIF-8;

[0010] (3) High-temperature pyrolysis: The Ag / ZIF-8 prepared in step (2) was pyrolyzed under an inert atmosphere to obtain the AgNPs@Zn-NC catalyst.

[0011] As a preferred technical solution of the present invention, in step (1), the zinc salt is Zn(NO3)2·6H2O, the nitrogen-containing organic compound is 2-methylimidazole, the solvent is methanol, and the reaction equation is: Zn(NO3)2·6H2O+2C4H6N2→Zn(C4H5N2)2+2HNO3+6H2O;

[0012] The mass of Zn(NO3)2·6H2O is 2-4 g, the mass of 2-methylimidazole is 5-8 g, the volume of methanol is 120-200 mL, and the reaction time is 12-36 hours.

[0013] As a preferred technical solution of the present invention, in step (1), after the reaction generates ZIF-8, the precipitate is collected by centrifugation, washed with methanol 2-4 times, and vacuum dried at 50-70°C for 8-16 hours to obtain ZIF-8 powder.

[0014] As a preferred technical solution of the present invention, in step (2), the silver salt is AgNO3, the amount of ZIF-8 used is 300-500 mg, and the amount of AgNO3 used is 20-30 mg.

[0015] As a preferred technical solution of the present invention, in step (2), the reduction reaction is carried out under stirring conditions, the stirring speed is 1000-1500 rpm, the reaction time is 20-40 minutes, the product Ag / ZIF-8 is centrifuged, washed with deionized water 2-4 times, and vacuum dried at 50-70°C for 8-16 hours, wherein AgNPs are initially dispersed on the surface of ZIF-8 with a particle size of 3-8 nm.

[0016] As a preferred technical solution of the present invention, in step (3), the pyrolysis conditions are: under an inert atmosphere, the temperature is raised to 800-1000°C at a heating rate of 3-7°C / min and kept warm for 1-3 hours. The reaction of pyrolysis of Ag / ZIF-8 to form AgNPs@Zn-NC is simplified to: Ag / ZIF-8→AgNPs@Zn-N-C+CO2+NH3+H2O.

[0017] As a preferred technical solution of the present invention, the inert atmosphere is argon or nitrogen.

[0018] As a preferred technical solution of the present invention, the AgNPs@Zn-NC catalyst is prepared by the synthesis method of any one of claims 1 to 7, wherein the AgNPs have a particle size of 5-10 nm and are uniformly dispersed on the surface of the Zn-NC support, and the specific surface area of the Zn-NC support is 800-1000 m 2 / g, containing Zn-N4 active sites.

[0019] As a preferred technical solution of the present invention, Zn and N in the catalyst form a Zn-N4 coordination structure, Ag exists in a zero-valent state, the catalyst has an oxygen reduction reaction half-wave potential of 0.88V in 0.1MKOH solution, a mass activity of 4.5A / mg_Ag, and an activity decay of less than 5% after 50,000 cycle tests.

[0020] As a preferred technical solution of the present invention, applied to proton exchange membrane fuel cells PEMFCs, zinc-air batteries or microbial fuel cells, the ORR reaction mainly follows a four-electron pathway:

[0021] O2+4H + +4e - →2H2O (acidic medium) or O2+2H2O+4e - →4OH - (alkaline medium);

[0022] Among them, the H2O2 yield is less than 2%. In zinc-air batteries, AgNPs@Zn-NC is used as an air electrode catalyst, and the battery open circuit voltage is 1.45V and the peak power density is 200mW / cm 2 .

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The beneficial effects of the present invention can be summarized from three aspects: catalyst performance, preparation process and application prospects.

[0025] First, the AgNPs@Zn-NC catalyst demonstrated excellent catalytic performance and stability in the oxygen reduction reaction, effectively promoting the four-electron pathway reaction, significantly reducing byproduct formation, and improving energy conversion efficiency. Furthermore, the catalyst exhibited excellent stability in both acidic and alkaline media, addressing the vulnerability of traditional silver-based catalysts to failure and extending their service life.

[0026] Secondly, the synthesis method of the present invention is simple to operate, low-cost, and suitable for industrial production. By optimizing the precursor synthesis, uniform loading of silver nanoparticles, and high-temperature pyrolysis process, uniform dispersion of silver nanoparticles on a zinc-nitrogen co-doped carbon-based support is achieved, and catalytic performance is enhanced through coordination and support synergy. Compared with traditional platinum-based catalysts, the use of inexpensive raw materials significantly reduces costs, and the preparation process is non-toxic and pollution-free, meeting the requirements of green chemistry.

[0027] Finally, the AgNPs@Zn-NC catalyst has broad application prospects in new energy devices. As an air electrode catalyst in zinc-air batteries, it can improve battery performance and cycling stability. Furthermore, the catalyst is also suitable for use in proton exchange membrane fuel cells and microbial fuel cells, helping to improve the battery's power density, cycle life, and energy output, providing a new technological path for the commercial application of fuel cells and metal-air batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Attachment Figure 1 : SEM and TEM images of AgNPs@Zn-NC;

[0029] Attachment Figure 2 : XPS spectrum of AgNPs@Zn-NC;

[0030] Attachment Figure 3 : Comparison of ORR polarization curves of AgNPs@Zn-NC and commercial Pt / C. DETAILED DESCRIPTION

[0031] To further illustrate the synthesis method of the AgNPs@Zn-NC catalyst of the present invention, the following detailed implementation method is described. These examples are intended only to illustrate the technical solution of the present invention and do not limit the scope of protection. Equivalent substitutions or modifications made by those skilled in the art without departing from the technical solution of the present invention are also within the scope of protection of the present invention.

[0032] This invention provides a method for synthesizing an AgNPs@Zn-NC catalyst. AgNPs@Zn-NC refers to silver nanoparticles (AgNPs) supported on a zinc-nitrogen co-doped carbon-based material (Zn-NC). This catalyst can be used for the oxygen reduction reaction (ORR) and is suitable for use in new energy devices such as proton exchange membrane fuel cells (PEMFCs), zinc-air batteries, and microbial fuel cells. The following detailed description of the catalyst's preparation process, structural features, performance, and applications is provided through specific examples to fully demonstrate the technical content of this invention.

[0033] First, prepare the ZIF-8 precursor by dissolving 2-4g of Zn(NO₃)₂·6H₂O (typically 3g) in 80mL of methanol and stirring to obtain Solution A. Dissolve 5-8g of 2-methylimidazole (typically 6.5g) in 80mL of methanol and stir to obtain Solution B. This solution is slowly added to Solution A and stirred for 1 hour. After mixing thoroughly, the mixture is allowed to stand for 12-36 hours (typically 24 hours) to allow the ZIF-8 crystals to fully precipitate. The reaction equation is: Zn(NO₃)₂·6H₂O + 2C₄H₆N₂ → Zn(C₄H₅N₂)₂ + 2HNO₃ + 6H₂O. The white precipitate is collected by centrifugation, washed 2-4 times (typically 3 times) with methanol, and dried in vacuo at 50-70°C (typically 60°C) for 8-16 hours (typically 12 hours) to obtain ZIF-8 powder.

[0034] Next, AgNPs were loaded by dispersing 300-500 mg (typically 400 mg) of the ZIF-8 powder prepared above in 30 mL of deionized water and sonicating for 30 minutes to obtain a uniform suspension. 20-30 mg (typically 25 mg) of AgNO₃ was then added to the suspension and stirred to dissolve.

[0035] Under stirring conditions (rotation speed of 10,000-15,000 rpm, typically 12,000 rpm), after the reaction is completed, the product is collected by centrifugation, washed with deionized water 2-4 times (typically 3 times), and vacuum dried at 50-70°C (typically 60°C) for 8-16 hours (typically 12 hours) to obtain an Ag / ZIF-8 intermediate. At this point, AgNPs are initially dispersed on the ZIF-8 surface with a particle size of 3-8 nm.

[0036] Subsequently, a high-temperature pyrolysis reaction is performed. The Ag / ZIF-8 prepared above is placed in a tube furnace and heated at a rate of 3-7°C / min (typically 5°C / min) to 800-1000°C (typically 900°C) under an inert atmosphere (argon or nitrogen, typically argon). The temperature is then maintained for 1-3 hours (typically 2 hours). During the pyrolysis process, the Ag / ZIF-8 decomposes to form AgNPs@Zn-NC. The reaction is simplified to: Ag / ZIF-8 → AgNPs@Zn-N-C + CO2 + NH3 + H2O. After cooling to room temperature, the final product, the AgNPs@Zn-NC catalyst, is obtained.

[0037] The AgNPs@Zn-NC catalyst prepared by the above method has the following structural characteristics: the AgNPs particle size is 5-10 nm and is uniformly dispersed on the surface of the Zn-NC support; the specific surface area of the Zn-NC support is 800-1000 m 2 / g, containing Zn-N4 active sites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis further confirmed the uniform dispersion of AgNPs (see Appendix Figure 1 : SEM and TEM images of AgNPs@Zn-NC, showing that AgNPs are uniformly dispersed). X-ray photoelectron spectroscopy (XPS) analysis shows that Zn and N form a Zn-N4 coordination structure, and Ag is in a zero-valent state (Ag 0 ) exists (see Appendix Figure 2 :XPS spectrum of AgNPs@Zn-NC, confirming that Zn-N4 and Ag 0 existence).

[0038] The electrochemical performance of the AgNPs@Zn-NC catalyst was tested. In 0.1M KOH solution, a rotating disk electrode (RDE) was used to test its oxygen reduction reaction (ORR) performance. The results showed that the half-wave potential of the catalyst reached 0.88V (vs. RHE) and the mass activity was 4.5Amg -1 Ag, ORR reaction mainly follows the four-electron pathway: O2+2H2O+4e - →4OH - (alkaline medium), the H2O2 yield was less than 2%. Compared with the commercial Pt / C catalyst, AgNPs@Zn-NC showed similar performance (see Appendix Figure 3 Comparison of ORR polarization curves of AgNPs@Zn-NC and commercial Pt / C. Furthermore, after 50,000 cycles, the catalyst activity decayed by less than 5%, demonstrating excellent stability.

[0039] The AgNPs@Zn-NC catalyst was applied to zinc-air batteries as an air electrode catalyst. The assembled zinc-air battery achieved an open-circuit voltage of 1.45V, a peak power density of 200mWcm⁻², and a performance retention rate of 95% after 120 hours of cyclic charge and discharge. Furthermore, the catalyst can also be applied to proton exchange membrane fuel cells (PEMFCs) and microbial fuel cells. In PEMFCs, the catalyst acts as a cathode catalyst, improving the battery's power density and cycle life; in microbial fuel cells, the catalyst can enhance the ORR efficiency and increase the battery's energy output.

[0040] The above examples show that the method provided by the present invention can prepare highly active and stable AgNPs@Zn-NC catalysts. The preparation process is simple, low-cost, and suitable for industrial production, providing a new approach for the commercial application of fuel cells and metal-air batteries.

[0041] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing a catalyst, wherein Silver nanoparticles AgNPs are loaded on zinc-nitrogen co-doped carbon-based materials ZnN-C, characterized in that: The following steps are involved: (1) Preparation of ZIF-8 precursor: dissolving zinc salt and nitrogen-containing organic compound in a solvent to react and generate ZIF-8; (2) Loading AgNPs: The ZIF-8 prepared in step (1) was dispersed in deionized water and silver salt was added to generate Ag / ZIF-8; (3) High-temperature pyrolysis: The Ag / ZIF-8 prepared in step (2) was pyrolyzed under an inert atmosphere to obtain catalyst.

2. according to claim 1 A method for synthesizing a catalyst, characterized in that: In step (1), the zinc salt is Zn(NO3)2·6H2O, the nitrogen-containing organic compound is 2-methylimidazole, the solvent is methanol, and the reaction equation is: Zn(NO3)2·6H2O+2C4H6N2→Zn(C4H5N2)2+2HNO3+6H2O; The mass of Zn(NO3)2·6H2O is 2-4 g, the mass of 2-methylimidazole is 5-8 g, the volume of methanol is 120-200 mL, and the reaction time is 12-36 hours.

3. according to claim 1 A method for synthesizing a catalyst, characterized in that: In step (1), after the reaction generates ZIF-8, the precipitate is collected by centrifugation, washed with methanol 2-4 times, and vacuum-dried at 50-70° C. for 8-16 hours to obtain ZIF-8 powder.

4. according to claim 1 A method for synthesizing a catalyst, characterized in that: In step (2), the silver salt is AgNO3, and the amount of ZIF-8 used is 300-500 mg.

5. according to claim 1 A method for synthesizing a catalyst, characterized in that: In step (2), the reduction reaction is carried out under stirring conditions at a stirring speed of 1000-1500 rpm and a reaction time of 20-40 minutes. The product Ag / ZIF-8 is centrifuged, washed with deionized water 2-4 times, and vacuum-dried at 50-70°C for 8-16 hours, wherein AgNPs are initially dispersed on the surface of ZIF-8 with a particle size of 3-8 nm.

6. according to claim 1 A method for synthesizing a catalyst, characterized in that: In step (3), the pyrolysis conditions are: in an inert atmosphere, the temperature is raised to 800-1000°C at a heating rate of 3-7°C / min, and the temperature is kept for 1-3 hours. Ag / ZIF-8 is pyrolyzed to form The reaction is simplified to:

7. according to claim 1 A method for synthesizing a catalyst, characterized in that: The inert atmosphere is argon or nitrogen.

8. A A catalyst characterized in that By any one of claims 1 to 7 The catalyst was prepared by the synthesis method. The AgNPs had a particle size of 5-10 nm and were evenly dispersed on the surface of the Zn-NC support. The specific surface area of the Zn-NC support was 800-1000 m 2 / g, containing Zn-N4 active sites.

9. according to claim 8 A catalyst characterized in that Zn and N in the catalyst form a Zn-N4 coordination structure, and Ag exists in a zero-valent state. The catalyst has an oxygen reduction reaction half-wave potential of 0.88V in 0.1MKOH solution, and a mass activity of 4.5A / mg_Ag. After 50,000 cycle tests, the activity decay is less than 5%.

10. The method according to claim 8 The use of a catalyst in an oxygen reduction reaction is characterized in that Applied to proton exchange membrane fuel cells (PEMFCs), zinc-air batteries, or microbial fuel cells, the ORR reaction mainly follows a four-electron pathway: O2+4H + +4e - →2H2O (acidic medium) or O2+2H2O+4e - →4OH - (alkaline medium); Among them, the H2O2 production rate is less than 2%. In zinc-air batteries, As an air electrode catalyst, the cell open circuit voltage is 1.45V and the peak power density is 200mW / cm 2 .

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