A 3D nitrogen-doped carbon skeleton material of a packaging alloy and a preparation method and application thereof

Abstract

The application discloses a kind of 3D nitrogen-doped carbon skeleton material of encapsulated alloy and its preparation method, which comprises the following steps: CoFe PBA is used as bimetallic source and template, HMT and DA derived polymer coating are introduced on its surface, and then 3D CoFe@NC is obtained by using dicyandiamide assisted pyrolysis, wherein CoFe alloy nanoparticles are uniformly distributed in nitrogen-doped 3D carbon skeleton and wrapped by nitrogen-doped carbon layer.Various reagents used in the application can be obtained commercially, and the raw materials are widely available and low in price.The catalyst obtained has a unique 3D porous network core-shell structure, which provides the catalyst with a hierarchical porous structure with a high specific surface area.The sample exhibits superior oxygen reduction reaction (ORR) catalytic performance compared to 40% commercial Pt / C in electrochemical tests, and also exhibits excellent discharge performance and stability as a zinc-air battery positive electrode catalyst.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell cathode catalyst design technology, specifically relating to a 3D nitrogen-doped carbon framework material for encapsulation alloy, its preparation method, and its application. Background Technology

[0002] With rapid economic and industrial development, the demand for traditional fossil fuels is increasing daily, leading to serious environmental pollution problems. Developing green and renewable energy sources such as solar, wind, and tidal power is currently considered the most effective strategy for solving the energy crisis and environmental pollution. However, these green secondary energy sources are limited by geographical conditions and have intermittent characteristics, making it impossible to provide a sustainable power source in a long-term and stable manner. Therefore, next-generation electrochemical energy storage and conversion devices such as lithium-ion batteries, fuel cells, and zinc-air batteries have been extensively studied. Among them, zinc-air batteries have attracted much attention due to their advantages such as abundant and inexpensive sources of positive and negative electrode active materials, high safety, environmental friendliness, and high theoretical energy density. Although zinc-air batteries have an early start and great potential, their development has been limited by the slow oxygen reduction kinetics of the air battery cathode and the correspondingly expensive precious metal-based air cathode catalysts. Therefore, finding non-precious metal ORR catalysts with high ORR activity and stability has become a key step in breaking the shackles on the commercial application of zinc-air batteries.

[0003] Platinum-based platinum-carbon (Pt / C) catalysts have been extensively studied for several years. However, their limited reserves, susceptibility to poisoning, and the agglomeration of Pt nanoparticles and corrosion of the carbon support during application have hindered their further commercialization. Mature theoretical knowledge and practical application experience have made Pt nanoparticle (Pt / C) catalysts distributed on carbon supports the benchmark material for evaluating the ORR activity of other non-precious metal catalysts. Transition metal-nitrogen co-doped carbon materials (MNCs) are currently a research hotspot in the field of ORR catalysts. Numerous studies have confirmed that combining the intrinsic advantages of carbon materials (high conductivity, large specific surface area) with the introduction of metals and nitrogen brings excellent ORR performance to the catalysts.

[0004] In addition, the catalyst structure is also crucial for the ORR process, as the ORR reaction occurs at the three-phase interface of oxygen, electrolyte, and catalyst. However, MNC materials obtained by traditional pyrolysis methods suffer from drawbacks such as low specific surface area, limited pore structure, and low exposure of active sites, mainly because the metal components in the precursor undergo self-aggregation to form micron-sized particles during high-temperature annealing. Therefore, preparing a three-dimensional porous network hierarchical porous structure can significantly improve the ORR performance of the catalyst.

[0005] For example, Chinese invention patent application CN201910567331.6 discloses a method for preparing a bifunctional oxygen evolution-oxygen reduction catalyst CoFe@NC, comprising the following steps: S1: Mixing a cobalt source, an iron source, a nitrogen-containing MOF ligand material, a dispersant, and a solvent, stirring, washing, centrifuging, and drying to obtain a precursor powder; the molar ratio of cobalt in the cobalt source to iron in the iron source is 4-19:1; the molar ratio of the total molar amount of cobalt and iron to the molar amount of the nitrogen-containing MOF ligand material is 1-1.11:8; S2: Calcining the precursor powder in a hydrogen-argon mixed atmosphere at 280-350℃ for 2-3 hours, then calcining at 600-800℃, and cooling to obtain a black powder; S3: Acid washing and drying of the powder to obtain the bifunctional oxygen evolution-oxygen reduction catalyst CoFe@NC. The metal, N, and C elements are evenly distributed, and the stability is superior to commercial Pt / C catalysts. However, its ORR electrocatalytic performance is slightly inferior to that of commercial Pt catalysts. Furthermore, the acid washing step in this preparation method may lead to the loss of the metal source, making it unsuitable for the industrial-scale production of zinc-air battery catalysts. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a 3D nitrogen-doped carbon framework material for encapsulating alloys, its preparation method, and its applications. This invention provides a method for preparing a zinc-air battery catalyst that does not require an additional template to prepare a 3D porous network structure, exhibits uniform distribution of metal, N, and C elements, good electrocatalytic oxygen reduction performance, and rate performance superior to commercial Pt / C catalysts. Simultaneously, it avoids the corrosion of the metal supported on the 3D nitrogen-doped carbon framework during acid washing. The synthesis process is simple, efficient, low-cost, versatile, and suitable for industrial production.

[0007] The technical solution of this invention is: a method for preparing a 3D nitrogen-doped carbon framework material for encapsulating alloys, comprising the following steps:

[0008] Step 1: Dissolve a certain amount of K3Fe(CN)6 in deionized water to obtain solution A;

[0009] Step 2: Dissolve a certain proportion of Co(NO3)2·6H2O and Na3C6H5O7·2H2O in deionized water to obtain solution B; add solution A to solution B and stir for a period of time, then age, wash and dry to obtain a purple powder, denoted as CoFe PBA;

[0010] Step 3: Dissolve a certain amount of the purple powder in deionized water, stir and sonicate to form a uniform dispersion, then add a certain proportion of DA and HMT, stir for a period of time to fully mix the reactants; then transfer the above mixed solution to heat to 150~170℃ and keep warm for 12h to obtain a reaction solution; after the reaction solution cools naturally, crystallize, wash and dry to obtain a brick red powder, denoted as CoFe PBA@DA-HMT;

[0011] Step 4: Mix CoFe PBA@DA-HMT with dicyandiamide in a certain proportion and grind it in a mortar. Place the resulting mixture in a tube furnace and calcine it in an inert atmosphere to obtain a 3D nitrogen-doped carbon framework material for encapsulating CoFe alloy, denoted as 3DCoFe@NC.

[0012] Preferably, the molar ratio of K3Fe(CN)6 in step one to Co(NO3)2·6H2O in step two is 1:0.5 to 1:20.

[0013] Preferably, in step two, the molar ratio of Co(NO3)2·6H2O and Na3C6H5O7·2H2O is 1:1 to 1:20, the stirring time is 5 to 20 min, and the aging time is 12 to 48 h.

[0014] Preferably, the ratio of the amount of K3Fe(CN)6 to the total amount of Co(NO3)2·6H2O and Na3C6H5O7·2H2O is 1:1 to 1:10.

[0015] Preferably, in step two, the drying temperature is 50~100℃ and the drying time is 24 h.

[0016] Preferably, in step three, the molar ratio of DA and HMT is 1:0.1 to 1:20.

[0017] Preferably, in step three, the ratio of the amount of purple powder to the total amount of DA and HMT is 1:0.1 to 1:20, and the heating time is 8 to 16 hours.

[0018] Preferably, in step four, the molar ratio of CoFe PBA@DA-HMT to dicyandiamide is 1:0.1 to 1:40. More preferably, in step four, the molar ratio of brick-red powder to dicyandiamide is 1:5 to 1:40.

[0019] Preferably, in step four, the calcination temperature is 600~1000℃, the heating rate of the tube furnace is 2~10℃ / min, and the inert atmosphere is selected from one or more of N2 and Ar; further, in step four, the calcination temperature is any temperature within 700~1000℃, the holding time is 1~5 h, and the heating rate is 2~5℃ / min.

[0020] This invention also provides a 3D nitrogen-doped carbon framework material for encapsulated CoFe alloys prepared according to the above-described method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys; wherein the 3D nitrogen-doped carbon framework material for encapsulated CoFe alloys has a Co content of 0.85-1%, an Fe content of 1.05-1.25%, and a N content as high as 11.85-12.05%, and a specific surface area of ​​420-440 m². 2 g -1 More specifically, the 3D nitrogen-doped carbon framework material encapsulating the CoFe alloy contains 0.92% Co, 1.18% Fe, and a high N content of 11.95%, with a specific surface area of ​​427.0402 m². 2 g -1 .

[0021] This invention also provides the application of a 3D nitrogen-doped carbon framework material of an encapsulated alloy in zinc-air battery catalytic materials.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention uses CoFe bimetal as the metal source of metal-nitrogen co-doped carbon material (MNC). The synergistic effect between Co and Fe promotes charge transfer between the catalyst and oxygen adsorbed oxygen species, exhibiting superior ORR performance compared to single metals.

[0024] 2. This invention introduces HMT and DA-derived polymer coatings onto the CoFe surface, and then uses a dicyandiamide-assisted pyrolysis method to obtain CoFe alloy nanoparticles uniformly distributed within a nitrogen-doped three-dimensional carbon framework and encapsulated by a nitrogen-doped carbon layer. The resulting 3D porous network core-shell structure, formed without the use of a template, greatly simplifies the experimental procedure and aligns with the themes of green chemistry. Furthermore, this structure is a hierarchical porous structure of micropores, mesopores, and macropores, providing ample channels for oxygen diffusion and electrolyte permeation, thereby ensuring the rapid reaction kinetics of the ORR catalyst.

[0025] 3. The 3D nitrogen-doped carbon framework material for encapsulating CoFe alloy prepared in this invention provides the catalyst with a high nitrogen content (11.95%) and a configuration dominated by pyridine nitrogen (6.36%) and graphitic nitrogen (3.39%), as well as a high degree of carbon defect (I). D : IG = 1.04), large specific surface area (427.0402 m²) 2 ·g -1 It provides conditions for rapid ORR kinetics in terms of conductivity and mass transfer, and can be used as a cathode electrocatalyst for zinc-air batteries. It also has superior ORR activity compared to commercial 40% Pt / C catalysts.

[0026] 4. The raw materials of this invention are inexpensive and the process is simple, making it suitable for large-scale production. The catalyst prepared is mainly used in fuel cells and metal-air batteries. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) characterization result of the 3D CoFe@NC (3D nitrogen-doped carbon framework material encapsulating CoFe alloy) prepared in Example 1 of this invention.

[0028] Figure 2 This is a scanning electron microscope (SEM) characterization result of the CoFe@NC material prepared in Comparative Example 1 of this invention;

[0029] Figure 3 This is a scanning electron microscope (SEM) characterization result of the CoFe / NC material prepared in Comparative Example 2 of this invention;

[0030] Figure 4 This is a transmission electron microscopy (TEM) characterization result of the 3D CoFe@NC prepared in Example 1 of this invention;

[0031] Figure 5 This is a nitrogen adsorption-desorption isotherm of the 3D CoFe@NC prepared in Example 1 of this invention;

[0032] Figure 6 The X-ray photoelectron spectrum of 3D CoFe@NC prepared in Example 1 of this invention;

[0033] Figure 7 This is a graph showing the ORR performance test results of the materials prepared in Examples 1-3 and Comparative Examples 1 and 2 of this invention compared with 40% Pt / C.

[0034] Figure 8 This is a chronocurrent curve of 3D CoFe@NC prepared in Example 1 of the present invention at half-wave potential with 40% Pt / C.

[0035] Figure 9 This is a power-current density diagram of 3D CoFe@NC and 40%Pt / C prepared in Example 1 of this invention;

[0036] Figure 10This is the potential-time diagram of the 3D CoFe@NC prepared in Example 1 of this invention. Detailed Implementation

[0037] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0038] Example 1

[0039] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 6 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0040] 0.1517 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 0.74 g of DA and 0.28 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0041] CoFe PBA@DA-HMT and dicyandiamide were ground in a mortar at a ratio of 1:20 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The heating rate was increased from room temperature to 700 °C and held for 3 h, then cooled to room temperature. The final product carbonized at 700 °C was denoted as 3D CoFe@NC (3D nitrogen-doped carbon skeleton material encapsulating CoFe alloy).

[0042] Example 2

[0043] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 6 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0044] 0.1517 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 0.74 g of DA and 0.28 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0045] CoFe PBA@DA-HMT and dicyandiamide were ground in a mortar at a ratio of 1:20 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased from room temperature to 800 °C and held for 3 h, then cooled to room temperature. The final product carbonized at 800 °C was denoted as 3D CoFe@NC-700.

[0046] Example 3

[0047] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 6 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0048] 0.1517 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 0.74 g of DA and 0.28 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0049] CoFe PBA@DA-HMT and dicyandiamide were ground in a mortar at a ratio of 1:20 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased from room temperature to 900 °C and held for 3 h, then cooled to room temperature. The final product carbonized at 900 °C was denoted as 3D CoFe@NC-900.

[0050] Example 4

[0051] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 12 mmol of Co(NO3)2·6H2O and 20 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0052] 0.3034 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 2.22 g of DA and 0.84 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0053] CoFe PBA@DA-HMT and dicyandiamide were ground in a mortar at a ratio of 1:30 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1The temperature was increased from room temperature to 800 °C and held for 3 h, then cooled to room temperature. The final product carbonized at 800 °C was denoted as 3D CoFe@NC-700.

[0054] Example 5

[0055] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 40 mmol of Co(NO3)2·6H2O and 40 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0056] 0.4551 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 3.7 g of DA and 1.4 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0057] CoFe PBA@DA-HMT and dicyandiamide were ground in a mortar at a ratio of 1:20 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The temperature was increased from room temperature to 800 °C and held for 3 h, then cooled to room temperature. The final product carbonized at 800 °C was denoted as 3D CoFe@NC-700.

[0058] Comparative Example 1

[0059] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 6 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0060] 0.1517 g of CoFe PBA was dispersed in 240 mL of water, sonicated for 20 min, and then stirred for 20 min to form a homogeneous dispersion. Then, 0.74 g of DA and 0.28 g of HMT were added, and the mixture was stirred for 30 min to ensure thorough mixing. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene hydrothermal reactor and incubated at 160 °C for 12 h. After naturally cooling to room temperature, the solution was washed several times with deionized water and then vacuum dried at 60 °C for 24 h to obtain a brick-red powder, designated CoFe PBA@DA-HMT.

[0061] Take an appropriate amount of CoFe PBA@DA-HMT and place it in a tube furnace. Under a N2 atmosphere, incubate at 5 °C·min. -1 The temperature was increased from room temperature to 800℃, held for 3 h, and then cooled to room temperature. The final product was denoted as CoFe@NC.

[0062] Comparative Example 2

[0063] Dissolve 4 mmol of K3Fe(CN)6 in 200 mL of water and stir for 10 min to form a clear solution A. Separately, dissolve 6 mmol of Co(NO3)2·6H2O and 9 mmol of Na3C6H5O7·2H2O in 200 mL of water and stir for 5 min to form a clear solution B. Pour solution A into solution B, stir for 15 min, and then age at room temperature for 24 h. Wash the aged brown suspension several times with deionized water and vacuum dry at 60 °C for 24 h to obtain a purple powder, denoted as CoFe PBA.

[0064] CoFePBA and dicyandiamide were ground in a mortar at a ratio of 1:20 for 20 min. The resulting mixture was then placed in a tube furnace and heated at 5 °C / min under a N2 atmosphere. -1 The heating rate was increased from room temperature to 800 °C and held for 3 h, then cooled to room temperature. The final product was denoted as CoFe / NC.

[0065] To verify the performance of the 3D nitrogen-doped carbon framework material for encapsulating CoFe alloy prepared in this invention, the inventors conducted the following experiments on Examples 1-3 and Comparative Examples 1-2:

[0066] The morphology of 3D CoFe@NC, CoFe@NC, and CoFe / NC materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 was characterized using a Hitachi S4700 scanning electron microscope (Hitachi, Japan). The microstructure of the 3D nitrogen-doped carbon framework materials was studied, and the results are as follows: Figures 1-3 As shown. From Figure 1The prepared 3D CoFe@NC exhibits a 3D porous network structure, which solves the shortcomings of traditional pyrolysis-based MNC materials, such as low specific surface area, limited pore structure, and low exposure rate of active sites.

[0067] exist Figure 2 As can be seen in Comparative Example 1, the CoFe@NC prepared exhibits a spherical shape. Figure 3 As can be seen in Comparative Example 2, the CoFe / NC prepared exhibits carbon nanotubes of varying sizes and diameters that are intertwined. This may be because the exposed metal particles induce the decomposition of dicyandiamide during the high-temperature process, resulting in the formation of carbon nanotubes from g-C3N4 nanosheets. The tightly intertwined and disordered carbon nanotubes and the aggregated metal particles can bury the active sites, thereby causing a sharp decrease in its ORR catalytic activity.

[0068] The morphology of the 3D CoFe@NC prepared in Example 1 was characterized using a Tecnai G2 F30 S-Twin transmission electron microscope from Philips-FEI (Netherlands). The results are as follows: Figure 4 As shown. From Figure 4 It can be clearly seen that metal particles of about 20 nm are wrapped by carbon layers of about 3 nm, and are uniformly distributed on the graphene nanosheets. The wrapped carbon layers are derived from the polymer coating.

[0069] The apparent density, specific surface area, and pore volume of the 3D CoFe@NC prepared in Example 1 were analyzed using an ASAP 2460 surface area and pore size analyzer manufactured by Micromeritics, USA. Specific surface area was measured using the gas adsorption method, obtaining adsorption isotherms by adsorbing N2 through the material's pores at 77 K. Figure 5 As shown in the figure, the amount of N2 adsorbed by the material was calculated, and the measured value was then fitted using the Brunauer-Emmet-Teller (BET) model to calculate the surface area. The specific surface area of ​​Example 1 of the invention was measured to be 427.0402 m². 2 g -1 The pore size distribution of the catalyst was then evaluated using the BJH computational model. Figure 5 In the illustration, 3D CoFe@NC exhibits a hierarchical porous structure of micropores, mesopores, and macropores, providing ample channels for oxygen diffusion and electrolyte permeation, thereby ensuring the rapid reaction kinetics of the catalyst ORR.

[0070] This paper uses a Thermo Scientific K-Alpha X-ray photoelectron spectroscopy system from Thermo Fisher Scientific, USA, to characterize the surface chemical composition and elemental state of the 3D CoFe@NC prepared in Example 1. The characterization results are as follows: Figure 6 As shown, the 3D nitrogen-doped carbon framework material encapsulating the CoFe alloy has a Co content of 0.92%, an Fe content of 1.18%, and a N content as high as 11.95%.

[0071] Using a Hg / HgO electrode as the reference electrode and a graphite electrode as the counter electrode, the ORR performance of all prepared catalysts and the 40% Pt / C catalyst was tested using a rotating disk electrode in 0.1 MKOH. The ORR activity of all prepared catalysts and the 40% Pt / C catalyst was evaluated using LSV curves. The onset potential was set at 0.1 mA·cm⁻². The ORR performance of 3D CoFe@NC, 3D CoFe@NC-700, 3D CoFe@NC-900, CoFe / NC, and CoFe@NC prepared in Examples 1-3 and Comparative Examples 1 and 2 was also tested. Figure 7 The 3D CoFe@NC shown has an onset potential of 1.011 V and a limiting current density of 6.02 mA·cm⁻¹. -2 The 3D CoFe@NC catalyst showed superior performance compared to 40% Pt / C (0.955 V, 5.23 mA·cm⁻²). 40% Pt / C is currently the most representative ORR catalyst for air electrodes, indicating significant application value of 3D CoFe@NC in zinc-air batteries. The stability of 3D CoFe@NC in alkaline solution was then tested using a chronoamperometry method. Figure 8 As shown, with the half-wave potential (the potential corresponding to 1 / 2 limiting current density) as the constant potential, the response current decreased by only 8.94% after 2 hours, while that of 40% Pt / C decreased by 48.17%, indicating that 3D CoFe@NC has better stability in alkaline solution than 40% Pt / C.

[0072] The assembled zinc-air battery was tested for discharge curves using a German Zahner instrument, with a voltage range of 0.4~1.5V. Figure 9 The figure shows the corresponding power density curve of the zinc-air battery. The 3D CoFe@NC-based zinc-air battery also exhibits a larger maximum power density of 216.3 mW·cm⁻¹. -2 It outperforms PBA-NC, PBA@NC and Pt / C (158.1 mW·cm⁻¹). -2The more significant discharge performance of 3DCoFe@NC is attributed to its hierarchical porous structure resulting from its 3D network structure, which facilitates matter and charge transfer. Figure 10 The current density can be seen to be 20 mA·cm. -2 Under the given conditions, it can be seen from the figure that the response potential remained at 95.03% after 100 h of constant current discharge. The excellent stability is due to the stable 3D network skeleton, in which the CoFe alloy is wrapped in a graphitized carbon layer and does not come into contact with high concentration of alkaline solution, thus avoiding the dissolution and aggregation of metal particles and ensuring excellent ORR performance.

Claims

1. A method for preparing an encapsulated alloy 3D nitrogen-doped carbon skeleton material, comprising the following steps: Step 1: a certain amount of K3Fe(CN)6 is dissolved in deionized water to obtain solution A; Step 2: a certain proportion of Co(NO3)2·6H2O and Na3C6H5O7·2H2O is dissolved in deionized water to obtain solution B; solution A is added to solution B and stirred for a period of time, and then aged, washed and dried to obtain a purple powder; Step 3: a certain amount of the purple powder is dissolved in deionized water, stirred and ultrasonically treated to form a uniform dispersion, then a certain proportion of DA and HMT is added, and the reactants are fully mixed after stirring for a period of time; then the mixed solution is transferred and heated to 150-170℃ and kept for 12 hours to obtain a reaction solution; After the reaction solution is naturally cooled, it is crystallized, washed and dried to obtain a brick red powder; Step 4: the brick red powder is mixed with dicyandiamide in a mortar and ground, and the obtained mixture is calcined in a tube furnace in an inert atmosphere to obtain an encapsulated CoFe alloy 3D nitrogen-doped carbon skeleton material.

2. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, The molar ratio of K3Fe(CN)6 in step 1 to Co(NO3)2·6H2O in step 2 is 1:0.5-1:

20.

3. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, In step 2, the molar ratio of Co(NO3)2·6H2O to Na3C6H5O7·2H2O is 1:1-1:20, the stirring time is 5-20 min, and the aging time is 12-48 h.

4. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, In step 3, the molar ratio of DA to HMT is 1:0.1-1:

20.

5. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, In step 3, the molar ratio of the purple powder to DA and HMT is 1:0.1-1:

20.

6. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, In step 4, the molar ratio of the brick red powder to dicyandiamide is 1:5-1:

40.

7. The method for preparing a 3D nitrogen-doped carbon framework material for encapsulated alloys according to claim 1, characterized in that, In step 4, the calcination temperature is 600-1000℃, the temperature rising rate of the tube furnace is 2-10℃ / min, and the inert atmosphere is selected from one or more of N2 and Ar.

8. A 3D nitrogen-doped carbon framework material encapsulating an alloy, characterized in that, An encapsulated alloy 3D nitrogen-doped carbon skeleton material prepared by the method of any one of claims 1-7. 9.The use of an encapsulated alloy 3D nitrogen-doped carbon skeleton material as claimed in claim 8 in a zinc-air battery catalytic material.

Images