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

Abstract

The application belongs to the technical field of inorganic nanometer material preparation, and particularly relates to a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material and a preparation method thereof. The steps of the application are as follows: S1, dispersing manganese source material in N,N-dimethylformamide to form a uniform solution; S2, adding an organic ligand to the solution obtained in step S1 and continuously stirring to obtain a mixed solution, and then transferring the mixed solution to a reaction kettle for a solvothermal reaction; S3, sequentially washing and drying the product obtained through the solvothermal reaction, and then grinding the product and a cobalt salt to form a mixture powder; and S4, performing a high-temperature pyrolysis reaction on the mixture powder, and obtaining the hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material rich in mesopores and macropores after the reaction stops. The application has a large specific surface area and a multi-pore structure, slows down the migration and aggregation of metal particles and the loss of pyrolysis intermediates in the heat treatment process, and improves the electrochemical activity and stability of the transition metal / nitrogen-doped carbon electrocatalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic nanomaterials, and particularly relates to a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material and a preparation method thereof. BACKGROUND

[0002] Currently, fossil energy still occupies a dominant position in the global energy structure, but carbon emissions and environmental pollution caused by the consumption of fossil energy are increasingly affecting human survival and development. Therefore, developing new clean energy has become a global goal. Clean energy such as solar energy and wind energy is largely constrained by natural conditions, resulting in problems such as unstable and discontinuous output, and is difficult to store, transport and directly integrate into the power grid. Electrochemical energy storage systems have high conversion efficiency and fast response speed, and are a key support for the large-scale application of clean energy.

[0003] Zinc-air batteries have the advantages of low cost, environmental friendliness and high energy density, and are expected to become a new generation of energy storage devices. Zinc-air batteries store and convert energy through the redox reaction between the anode metal zinc and the air cathode. Developing oxygen electrocatalysts with high activity to drive the reaction efficiently plays a key role in the overall improvement of the performance of zinc-air batteries. Although noble metal materials have excellent catalytic performance, their high price and poor stability limit their widespread application. Therefore, developing low-cost and 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 kind of oxygen electrocatalysts with great application potential. Among them, transition metals have excellent catalytic activity, and nitrogen-doped carbon materials provide excellent electrical conductivity and resistance. The 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 synthetic substances of organic small molecules, polymers, inorganic metal salts, etc., or natural biomass materials. Among them, metal-organic frameworks (MOFs) are a new type of material formed by the mutual connection of metal atoms and organic ligands. Their three-dimensional ordered pore structure and uniformly distributed metal sites make them ideal pyrolysis precursors for preparing transition metal / nitrogen-doped carbon materials.

[0005] However, the high-temperature pyrolysis process often causes problems such as collapse of the three-dimensional structure and blockage of the pores of the MOF precursor. The resulting product often has a single microporous structure, which is not conducive to the diffusion of oxygen molecules and the transmission of reaction intermediates during the oxygen electrochemical reaction. On the other hand, metal atoms and carbon-containing intermediates in the material will respectively aggregate and flow away during the high-temperature process, resulting in low metal utilization rate of the product, insufficient electrical conductivity, and ultimately affecting the electrocatalytic activity and stability of the material. SUMMARY

[0006] In order to overcome the defects in the prior art, the hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material and a preparation method thereof are provided.

[0007] To achieve one of the above purposes, the application adopts the following technical solutions:

[0008] A preparation method of a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material, characterized by the following specific steps:

[0009] S1, dispersing a manganese source material in N,N-dimethylformamide to form a uniform solution;

[0010] S2, adding an organic ligand to the solution obtained in step S1 and continuously stirring to obtain a mixed solution, and then transferring the mixed solution to a reaction kettle for a solvothermal reaction;

[0011] S3, sequentially washing and drying the product obtained by the solvothermal reaction, and then uniformly grinding the product with a cobalt salt to form a mixture powder;

[0012] S4, transferring the mixture powder to a crucible for a pyrolysis reaction, and obtaining a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material rich in mesopores and macropores after the reaction stops.

[0013] Preferably, the manganese source material is manganese nitrate tetrahydrate or manganese acetate.

[0014] Preferably, the concentration of the solution formed by the manganese source material and N,N-dimethylformamide in step S1 is 0.1-0.3 mol / L. -1 .

[0015] Preferably, the organic ligand is 1H-1,2,3-triazole.

[0016] Preferably, the molar ratio of the organic ligand to the manganese source material is (2-10):1.

[0017] Preferably, the washing method in step S3 is centrifugal washing, and the washing agent for centrifugal washing is methanol or N,N-dimethylformamide; and the drying method in step S3 is vacuum drying, and the drying temperature is 40-70°C.

[0018] 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.

[0019] 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.

[0020] 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 .

[0021] 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.

[0022] The advantages of this invention are:

[0023] (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.

[0024] (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

[0025] Figure 1 This is a SEM image of the MET-2 material in Example 1 of the present invention.

[0026] 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 .

[0027] Figure 3 SEM of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention Figure 2 .

[0028] Figure 4 TEM image of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0029] Figure 5 HRTEM image of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0030] Figure 6 XRD pattern of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0031] Figure 7 Pore size distribution of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0032] Figure 8 TEM image of manganese dioxide supported nitrogen-doped carbon hybrid material of Comparative Example 1.

[0033] Figure 9 HRTEM image of manganese dioxide supported nitrogen-doped carbon hybrid material of Comparative Example 1.

[0034] Figure 10 XRD pattern of manganese dioxide supported nitrogen-doped carbon hybrid material of Comparative Example 1.

[0035] Figure 11 Pore size distribution of manganese dioxide supported nitrogen-doped carbon hybrid material of Comparative Example 1.

[0036] Figure 12 Oxygen reduction (ORR) polarization curve of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0037] Figure 13 Oxygen evolution (OER) polarization curve of hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0038] Figure 14 Charge-discharge polarization curve and power density curve of zinc-air battery driven by hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention.

[0039] Figure 15 Charge-discharge cycle stability curve of zinc-air battery driven by hollow manganese dioxide / cobalt manganate supported nitrogen-doped carbon hybrid material of Example 1 of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. All other examples obtained by those skilled in the art without creative labor based on the examples in the present application belong to the protection scope of the present application.

[0041] Example 1

[0042] S1, 0.5 grams of manganese nitrate tetrahydrate was weighed into 10 milliliters of N,N-dimethylformamide and ultrasonically dispersed into a uniform solution, the ultrasonic time was 30 min;

[0043] S2, 5 mmol of 1H-1,2,3-triazole was added to the solution obtained in step S1 and continuously stirred for 30 min to obtain a mixed solution, which was then transferred to a 25 milliliter polytetrafluoroethylene liner and placed in a high-pressure reaction kettle for solvothermal reaction, the reaction temperature was 120℃, and the reaction lasted for 24 h;

[0044] S3, after the reaction was completed and the reaction kettle was cooled to room temperature, the product was washed by centrifugation with methanol three times, and finally the washed product was placed in a vacuum drying oven at 60℃ for drying for 12 h, to obtain a white powder MET-2 material, as shown in Figure 1

[0045] S4, 100 milligrams of prepared MET-2 material and 5 milligrams of cobalt acetate tetrahydrate were weighed into an agate mortar and ground for 20 min to mix uniformly, then the mixture was poured into a ceramic crucible and transferred to a tube furnace for high-temperature pyrolysis, the pyrolysis process was carried out in a nitrogen atmosphere with a flow rate of 40 milliliters / minute. The pyrolysis process was completed by programmed temperature control, the starting temperature was 25℃, the heating rate was 5℃ / minute, the target temperature was 850℃, and after the temperature reached the target temperature, it was kept constant for 2 h, and finally the black hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material was obtained after the furnace temperature dropped to room temperature.

[0046] Comparative Example 1

[0047] S1, 0.5 grams of manganese nitrate tetrahydrate was weighed into 10 milliliters of N,N-dimethylformamide and ultrasonically dispersed into a uniform solution, the ultrasonic time was 30 min;

[0048] S2, 5 mmol of 1H-1,2,3-triazole was added to the solution obtained in step S1 and continuously stirred for 30 min to obtain a mixed solution, which was then transferred to a 25 milliliter polytetrafluoroethylene liner and placed in a high-pressure reaction kettle for solvothermal reaction, the reaction temperature was 120℃, and the reaction lasted for 24 h;

[0049] ​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.

[0050] 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.

[0051] The properties of the materials prepared in Example 1 and Comparative Example 1 were characterized, and the results are as follows: Figures 1-15 As shown:

[0052] 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. Figures 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..."] Figures 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.

[0053] Depend on Figures 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. -2The peak power density and the charge-discharge cycle stability of more than 600 cycles.

[0054] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

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, dispersing a manganese source material in N,N-dimethylformamide to form a uniform solution; S2, adding an organic ligand to the solution obtained in step S1 and continuously stirring to obtain a mixed solution, and then transferring the mixed solution to a reaction kettle for a solvothermal reaction; S3, sequentially washing and drying the product obtained in the solvothermal reaction, and then uniformly grinding the product with a cobalt salt to form a mixture powder; S4, pyrolyzing the mixture powder to obtain a hollow manganese dioxide / cobalt manganate loaded nitrogen-doped carbon hybrid material rich in mesopores and macropores; The organic ligand is 1H-1,2,3-triazole.

2. The method for preparing hollow manganese dioxide / cobalt manganate loaded 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: The concentration of the solution formed by the manganese source material and N,N-diethylformamide in step S1 is 0.1 to 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 molar ratio of the organic ligand to the manganese source material is (2-10):

1.

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 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℃.

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 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.

7. 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, and the ultrasonic time is 1-60 min; in step S2, the stirring time is 30 min, the temperature of the solvothermal reaction is 100-160℃, and the reaction time of the solvothermal reaction is 16-36 h.

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

9. A material prepared according to the method of any one of claims 1 to 8, 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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