Hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material and preparation method thereof

Abstract

The invention belongs to the technical field of preparation of inorganic nano materials, and particularly relates to a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material and a preparation method thereof. The preparation method comprises the following steps: S1, dissolving a manganese source material in N, N-diethyl formamide, and dispersing to form a uniform solution; s2, adding an organic ligand into the solution obtained in the step S1, continuously stirring to obtain a mixed solution, and transferring the mixed solution into a reaction kettle for solvothermal reaction; s3, sequentially washing and drying a product obtained by the solvothermal reaction, and uniformly grinding the product and cobalt salt to form mixture powder; and S4, performing high-temperature pyrolysis reaction on the mixture powder, and after the reaction is stopped, obtaining the hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material rich in mesopores and macropores. The transition metal / nitrogen-doped carbon electrocatalyst has a multi-element pore structure with a large specific surface area, migration and aggregation of metal particles and loss of pyrolysis intermediates in the heat treatment process are slowed down, and the electrochemical activity and stability of the transition metal / nitrogen-doped carbon electrocatalyst are improved.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanomaterial preparation technology, and particularly relates to a hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material and its preparation method. Background Technology

[0002] Currently, fossil fuels still dominate the global energy structure; however, the carbon emissions and environmental pollution resulting from fossil fuel consumption are increasingly impacting human survival and development. Therefore, developing new clean energy sources has become a common global goal. Clean energy sources such as solar and wind power are largely constrained by natural conditions, leading to problems such as unstable and discontinuous output, making them difficult to store, transport, and directly integrate into the power grid. Electrochemical energy storage systems, with their high conversion efficiency and fast response speed, are a key support for realizing the large-scale application of clean energy.

[0003] Zinc-air batteries possess advantages such as low cost, environmental friendliness, and high energy density, making them a promising next-generation energy storage device. Zinc-air batteries store and convert energy through a redox reaction between the zinc anode and the air cathode. Developing highly active oxygen electrocatalysts to drive the efficient reaction plays a crucial role in improving the overall performance of zinc-air batteries. While noble metal materials exhibit excellent catalytic performance, their high price and poor stability limit their widespread application. Therefore, developing low-cost, high-efficiency non-noble metal catalysts is currently a key research direction in the field of zinc-air batteries.

[0004] Transition metal / nitrogen-doped carbon materials are a promising type of oxygen electrocatalyst. Transition metals exhibit excellent catalytic activity, while nitrogen-doped carbon materials provide superior conductivity and tolerance. A common method for preparing transition metal / nitrogen-doped carbon materials is high-temperature pyrolysis of precursors containing carbon, nitrogen, and transition metals. These substances can be mixtures or synthesized compounds of small organic molecules, polymers, and inorganic metal salts, or naturally occurring biomass materials. Metal-organic frameworks (MOFs), a novel type of material composed of interconnected metal atoms and organic ligands, possess an ideal pyrolysis precursor for preparing transition metal / nitrogen-doped carbon materials due to their three-dimensional ordered porous structure and uniformly distributed metal sites.

[0005] However, high-temperature pyrolysis often leads to problems such as three-dimensional structural collapse and pore blockage in MOF precursors, resulting in products with a single microporous structure, which is not conducive to the diffusion of oxygen molecules and the transport of reaction intermediates during the oxygen-electrochemical reaction. On the other hand, metal atoms and carbon-containing intermediates in the material will aggregate and be lost during high-temperature processes, resulting in reduced metal utilization and insufficient conductivity of the product, ultimately affecting the electrocatalytic activity and stability of the material. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material and its preparation method. The material of this invention possesses a multi-layered porous structure, which improves the electrochemical activity and stability of transition metal / nitrogen-doped carbon electrocatalysts.

[0007] To achieve one of the above objectives, the present invention adopts the following technical solution: A method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material, characterized by the following specific steps: S1. Dissolve the manganese source material in N,N-diethylformamide and disperse it to form a uniform solution; S2. Add the organic ligand to the solution obtained in step S1 and stir continuously to obtain a mixed solution, then transfer it to a reaction vessel for solvothermal reaction; S3. The product obtained from the solvothermal reaction is washed and dried in sequence, and then the product is ground with cobalt salt to form a uniform powder mixture. S4. Transfer the mixed powder to a crucible for pyrolysis reaction. After the reaction stops, a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material rich in mesopores and macropores is obtained.

[0008] Preferably, the manganese source material is manganese nitrate tetrahydrate or manganese acetate.

[0009] Preferably, the concentration of the solution formed by the manganese source material and N,N-diethylformamide in step S1 is 0.1–0.3 mol / L. -1 .

[0010] Preferably, the organic ligand is 1H-1,2,3-triazole.

[0011] Preferably, the molar ratio of the organic ligand to the manganese source material is (2-10):1.

[0012] Preferably, the washing method in step S3 is centrifugal washing, and the washing agent for centrifugal washing is methanol or N,N-dimethylformamide; the drying method in step S3 is vacuum drying, and the drying temperature is 40-70°C.

[0013] Preferably, the cobalt salt is cobalt acetate tetrahydrate, the mass ratio of the product to the cobalt salt is (10-30):1, and the grinding time is 30-60 min.

[0014] Preferably, ultrasonic dispersion is used in step S1, and the ultrasonic time is 1 to 60 min; the stirring time in step S2 is 30 min, the temperature of the solvothermal reaction is 100 to 160°C, and the reaction time of the solvothermal reaction is 16 to 36 h.

[0015] Preferably, the temperature of the pyrolysis reaction is 800–1000℃, and the heating rate is 5–10℃ / min. -1 The isothermal time is 2–4 h; the pyrolysis reaction is carried out in a nitrogen atmosphere at a flow rate of 10–40 mL / min. -1 .

[0016] To achieve the second objective mentioned above, the present invention provides a hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material, which is a hollow octahedral structure with manganese dioxide / cobalt manganate heterojunction nanoparticles as the core and porous nitrogen-doped carbon as the shell.

[0017] The advantages of this invention are: (1) The material of the present invention has a multi-dimensional porous structure with a large specific surface area, which slows down the migration and aggregation of metal particles and the loss of pyrolysis intermediates during heat treatment, and improves the electrochemical activity and stability of transition metal / nitrogen-doped carbon electrocatalyst.

[0018] (2) This invention anchors nitrogen-containing pyrolysis intermediates through the coordination between cobalt ions and nitrogen in synthesized manganese triazole (MET-2) MOFs, thus minimizing the loss of carbon and nitrogen-containing intermediates during pyrolysis, inhibiting metal ion aggregation, and improving metal atom utilization. The prepared manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material exhibits a hierarchical porous hollow structure, with mesopores and macropores accounting for as high as 97.8%. On the one hand, this significantly increases the specific surface area of ​​the material, exposing more catalytic active sites; on the other hand, it provides transport channels for oxygen molecules and reaction intermediates in the electrocatalytic process, improving mass transfer efficiency. The heterogeneous interface between manganese dioxide and cobalt manganate nanoparticles in the material induces electron redistribution, enhancing the conductivity of the material. Thanks to the unique advantages of the above composition and structure, the material has excellent bifunctional electrocatalytic activity and stability. As an air electrode catalyst, the zinc-air battery assembled with it has good energy storage performance and long-term stability, showing broad practical application prospects. Attached Figure Description

[0019] Figure 1 This is a SEM image of the MET-2 material in Example 1 of the present invention.

[0020] Figure 2 SEM image of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of this invention. Figure 1 .

[0021] Figure 3 SEM image of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of this invention. Figure 2 .

[0022] Figure 4This is a TEM image of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of the present invention.

[0023] Figure 5 The image shows the HRTEM image of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of this invention.

[0024] Figure 6 The image shows the XRD pattern of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of this invention.

[0025] Figure 7 This is a pore size distribution diagram of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of the present invention.

[0026] Figure 8 This is a TEM image of the nitrogen-doped carbon hybrid material supported on manganese dioxide, which is comparative example 1.

[0027] Figure 9 The image shows the HRTEM image of the nitrogen-doped carbon hybrid material supported on manganese dioxide, as shown in Comparative Example 1.

[0028] Figure 10 The image shows the XRD pattern of the nitrogen-doped carbon hybrid material supported on manganese dioxide, as shown in Comparative Example 1.

[0029] Figure 11 The pore size distribution of the nitrogen-doped carbon hybrid material supported on manganese dioxide, as shown in Comparative Example 1, is shown in the diagram.

[0030] Figure 12 This is the oxygen reduction (ORR) polarization curve of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of the present invention.

[0031] Figure 13 This is an oxygen evolution (OER) polarization curve of the nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of the present invention.

[0032] Figure 14 The graph shows the charge-discharge polarization curves and power density curves of the zinc-air battery driven by the hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material in Example 1 of this invention.

[0033] Figure 15 The graph shows the charge-discharge cycle stability of a zinc-air battery driven by a nitrogen-doped carbon hybrid material supported on hollow manganese dioxide / cobalt manganate in Example 1 of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] Example 1 S1. Weigh 0.5 g of manganese nitrate tetrahydrate and add it to 10 mL of N,N-diethylformamide. Disperse the mixture by ultrasonication for 30 min. S2. Add 5 mmol of 1H-1,2,3-triazole to the solution obtained in step S1 and stir continuously for 30 min to obtain a mixed solution. Then transfer it to a 25 mL polytetrafluoroethylene liner and place it in a high-pressure reactor for a solvothermal reaction at a reaction temperature of 120 °C for 24 h. S3. After the reaction is complete and the reactor has cooled to room temperature, the product is washed three times with methanol by centrifugation. Finally, the washed product is dried in a vacuum drying oven at 60°C for 12 hours to obtain a white powdery MET-2 material. Figure 1 As shown; S4. Weigh 100 mg of the prepared MET-2 material and 5 mg of cobalt acetate tetrahydrate, pour them into an agate mortar, and grind for 20 min to ensure thorough and uniform mixing. Then, pour the mixture into a ceramic crucible and transfer it to a tube furnace for high-temperature pyrolysis. The pyrolysis process is carried out in a nitrogen atmosphere with a flow rate of 40 mL / min. The pyrolysis process is completed by programmed temperature control, with an initial temperature of 25 °C, a heating rate of 5 °C / min, and a target temperature of 850 °C. After reaching the target temperature, the temperature is held constant for 2 h. Finally, after the furnace temperature drops to room temperature, black hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material is obtained.

[0036] Comparative Example 1 S1. Weigh 0.5 g of manganese nitrate tetrahydrate and add it to 10 mL of N,N-diethylformamide. Disperse the mixture by ultrasonication for 30 min. S2. Add 5 mmol of 1H-1,2,3-triazole to the solution obtained in step S1 and stir continuously for 30 min to obtain a mixed solution. Then transfer it to a 25 mL polytetrafluoroethylene liner and place it in a high-pressure reactor for a solvothermal reaction at a reaction temperature of 120 °C for 24 h. S3. After the reaction is complete and the reactor is cooled to room temperature, the product is washed three times by centrifugation with methanol. Finally, the washed product is placed in a vacuum drying oven at 60°C and dried for 12 hours to obtain a white powdery MET-2 material. S4. Weigh 100 mg of the prepared MET-2 material, pour it into a ceramic crucible, and transfer it to a tube furnace for high-temperature pyrolysis. The pyrolysis process is carried out in a nitrogen atmosphere with a flow rate of 40 mL / min. The pyrolysis process is completed by programmed temperature control, with an initial temperature of 25 °C, a heating rate of 5 °C / min, and a target temperature of 850 °C. After reaching the target temperature, the temperature is held constant for 2 hours. Finally, after the furnace temperature drops to room temperature, a black manganese dioxide-supported nitrogen-doped carbon hybrid material is obtained.

[0037] The properties of the materials prepared in Example 1 and Comparative Example 1 were characterized, and the results are as follows: Figure 1-15 As shown: Depend on Figure 1 It can be seen that the synthesized MET-2 precursor is a smooth octahedron. After grinding with cobalt salt and pyrolysis at high temperature, the product exhibits a hollow octahedral structure with manganese dioxide / cobalt manganate heterojunction nanoparticles as the core and porous nitrogen-doped carbon as the shell. Figure 2-5 ). Figure 6 The characteristic peaks at 34.9°, 40.6°, and 36.1° in the XRD pattern are attributed to the (111) and (200) crystal planes of manganese dioxide and the (211) crystal plane of cobalt manganate, respectively. From... Figure 7 It can be seen that the surface material has a hierarchical porous structure. Mesopores mainly originate from the porous nitrogen-doped carbon nanosheet shell, while macropores mainly come from the hollow structure of the material. The sum of mesopores and macropores reaches 97.8%. Conversely, [the following text appears to be incomplete and requires further context: "by..."] Figure 8-11 It can be seen that the manganese dioxide-supported nitrogen-doped carbon hybrid material has a solid structure dominated by micropores, with micropores accounting for 95.1%, and significant aggregation of metal particles. The abundant mesopores and macropores not only facilitate the full exposure of catalytic active sites in the material, but also provide transport channels for oxygen molecules and reaction intermediates in the electrocatalytic process, thereby improving mass transfer efficiency.

[0038] Depend on Figure 12-15 It can be seen that the prepared hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material exhibits excellent bifunctional oxygen electrocatalytic activity and practical application performance. Specifically, the oxygen reduction (ORR) half-wave potential is 0.85 V in 0.1 M KOH solution, and the current density is 10 mA / cm² in 1 M KOH solution. 2 The corresponding oxygen evolution overpotential (OER) is 1.556 V. A zinc-air battery driven by this material as an air electrode catalyst exhibits a 168.6 mW / cm² voltage. -2 Peak power density and over 600 charge-discharge cycle stability.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material, characterized in that, The specific steps are as follows: S1. Dissolve the manganese source material in N,N-diethylformamide and disperse it to form a uniform solution; S2. Add the organic ligand to the solution obtained in step S1 and stir continuously to obtain a mixed solution, then transfer it to a reaction vessel for solvothermal reaction; S3. The product obtained from the solvothermal reaction is washed and dried in sequence, and then the product is ground with cobalt salt to form a uniform powder mixture. S4. The mixture powder is subjected to a pyrolysis reaction. After the reaction stops, a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material rich in mesopores and macropores is obtained.

2. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The manganese source material is manganese nitrate tetrahydrate or manganese acetate.

3. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: In step S1, the concentration of the solution formed by the manganese source material and N,N-diethylformamide is 0.1–0.3 mol / L. -1 .

4. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The organic ligand is 1H-1,2,3-triazole.

5. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The molar ratio of the organic ligand to the manganese source material is (2-10):

1.

6. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The washing method in step S3 is centrifugal washing, and the washing agent for centrifugal washing is methanol or N,N-dimethylformamide; the drying method in step S3 is vacuum drying, and the drying temperature is 40-70℃.

7. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The cobalt salt is cobalt acetate tetrahydrate, and the mass ratio of the product to the cobalt salt is (10-30):

1. The grinding time is 30-60 min.

8. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: In step S1, ultrasonic dispersion is used for 1–60 min; in step S2, the stirring time is 30 min, the temperature of the solvothermal reaction is 100–160 °C, and the reaction time of the solvothermal reaction is 16–36 h.

9. The method for preparing a hollow manganese dioxide / cobalt manganate-supported nitrogen-doped carbon hybrid material according to claim 1, characterized in that: The pyrolysis reaction is carried out at a temperature of 800–1000℃, with a heating rate of 5–10℃ / min. -1 The isothermal time is 2–4 h; the pyrolysis reaction is carried out in a nitrogen atmosphere at a flow rate of 10–40 mL / min. -1 .

10. A material prepared by the method for preparing hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material as described in any one of claims 1-9, characterized in that: The material is a hollow octahedral structure with manganese dioxide / cobalt manganate heterojunction nanoparticles as the core and porous nitrogen-doped carbon as the shell.

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