A porous carbon supported transition metal composite material, a preparation method and application thereof

Abstract

This invention belongs to the field of battery materials technology and discloses a porous carbon-supported transition metal composite material, its preparation method, and its application. The method involves sequentially mixing iron acetylacetone, zinc nitrate, imidazole-2-formaldehyde, 2,2-diaminodiphenyl sulfide, and melamine in an ethanol system, followed by prolonged stirring and self-assembly. After low-temperature drying, the mixture is calcined in stages under a nitrogen atmosphere to directly prepare a nitrogen- and sulfur-doped porous carbon material with a three-dimensional porous framework structure. Transition metal iron species are supported on the porous carbon matrix in the form of nanoparticles or atomic-level dispersions. Melamine can strongly interact with metal ions and construct metal-nitrogen active sites in situ. Simultaneously, it acts as both a carbon and nitrogen source in the formation of the carbon framework. High active site density and a highly conductive network structure can be achieved without the introduction of additional carbon nanotubes. The preparation process is simple, with high raw material utilization, significantly reducing the preparation cost of the composite material. The resulting material has good application prospects in the battery field.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a porous carbon-supported transition metal composite material, its preparation method and application. Background Technology

[0002] With the energy crisis and environmental pollution becoming increasingly severe, the development of new energy conversion materials that are efficient, low-cost, and environmentally friendly has become a research hotspot. Metal-air batteries, due to their advantages such as high theoretical energy density, environmental friendliness, and low cost, are considered a core technology for next-generation energy storage and conversion devices. However, the oxygen reduction reaction (ORR), as the core reaction of the cathode in metal-air batteries, suffers from slow kinetics and severe electrochemical polarization, which seriously restricts battery performance.

[0003] While commercial platinum-carbon (Pt / C) catalysts currently exhibit excellent catalytic activity, they suffer from poor stability, susceptibility to methanol poisoning, and high costs due to their scarcity, making them unsuitable for large-scale industrial applications. Transition metal-heteroatom-doped carbon-based catalysts, with their low cost, good conductivity, and tunable catalytic activity, have become ideal alternatives to Pt / C. Single-nitrogen-doped carbon-based catalysts have limited active sites and electronic structure control, while sulfur and nitrogen dual doping can regulate the electron distribution of the carbon framework through heteroatom synergy, optimizing the adsorption-desorption behavior of active sites and oxygen intermediates, and significantly improving ORR catalytic performance.

[0004] Existing processes for preparing iron-based sulfur-nitrogen co-doped carbon materials suffer from cumbersome synthesis steps, poor process stability, easy agglomeration of product particles, and low batch-to-batch consistency, limiting their industrial application. Therefore, developing a sulfur-nitrogen co-doped porous carbon-supported iron-based composite material with a simple process, high stability, and the ability to be mass-produced is of great significance for promoting the commercialization of metal-air batteries. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing porous carbon-supported transition metal composite materials; this method has low preparation cost, simple process, and the obtained composite material has excellent oxygen reduction electrocatalytic activity.

[0006] Another objective of this invention is to provide a porous carbon-supported transition metal composite material prepared by the above-mentioned preparation method, which is an iron, nitrogen, and sulfur co-doped porous carbon composite material.

[0007] Another object of the present invention is to provide the application of the above-mentioned porous carbon-supported transition metal composite material.

[0008] The objective of this invention is achieved through the following technical solution: A method for preparing a porous carbon-supported transition metal composite material includes the following steps: Iron acetylacetone, zinc nitrate, imidazole-2-formaldehyde, and 2,2-diaminodiphenyl sulfide were sequentially added and dissolved in ethanol. The mixture was stirred for 12 hours to induce coordination self-assembly. Melamine was then added and the reaction was continued for another 12 hours. After drying in an oil bath, the resulting solid was calcined in stages under a nitrogen atmosphere and then allowed to cool naturally to obtain a material with residual nanoparticles. The material with residual nanoparticles was then acid-washed with sulfuric acid and subjected to a second calcination. The temperature was increased to 950°C at a rate of 5°C / min and held for 2 hours in a tube furnace to obtain a porous carbon-supported transition metal composite material.

[0009] The oil bath heating and drying temperature is 20~100℃, preferably 80℃, and the time is 12~72h, preferably 48h.

[0010] The segmented calcination involves first heating the temperature to 300-500℃ (preferably 400℃) at a rate of 5℃ / min and holding it at that temperature for 1 hour, then heating the temperature to 900-1000℃ (preferably 950℃) at a rate of 5℃ / min and holding it at that temperature for 2 hours.

[0011] The molar ratio of acetylacetone iron, zinc nitrate, imidazole-2-carboxaldehyde, 2,2-diaminodiphenyl sulfide and melamine is (0.01~1):(0.01~5):(0.01~5):(0.01~5):(0.01~5).

[0012] A porous carbon-supported transition metal composite material prepared by the above-described method possesses a three-dimensional interconnected porous carbon-based network structure. Specifically, it is constructed by cross-linking ultrathin carbon sheets to form a continuous, interconnected multi-level pore system, exhibiting an overall hollow, sponge-like morphology. This composite material did not exhibit significant iron-based nanoparticle aggregation during high-temperature pyrolysis. Its well-developed pore structure effectively increases the specific surface area of ​​the material, fully exposing catalytic active sites; simultaneously, the interconnected carbon framework provides convenient channels for electron transport, electrolyte wetting, and reactant gas diffusion, which is beneficial for improving electrocatalytic performance.

[0013] The above-mentioned porous carbon-supported transition metal composite material is used in metal-air batteries.

[0014] A metal-air battery cathode material comprising the aforementioned porous carbon-supported transition metal composite material.

[0015] The principle of this invention: This invention employs an organic coordination-high-temperature calcination synthesis strategy, using ZIF-90, formed by the coordination of zinc nitrate and imidazole-2-formaldehyde, as a template precursor to construct a porous doped carbon material loaded with iron-based transition metal active sites. Among them, iron acetylacetone is the iron source transition metal compound, 2,2-diaminodiphenyl sulfide is the sulfur source, and melamine has the dual function of nitrogen source and carbon source, which can interact with transition metal ions to form transition metal-nitrogen-sulfur active sites, effectively inhibiting the agglomeration of transition metal-based particles and improving the dispersibility of active sites.

[0016] During the high-temperature calcination of the precursor, the organic components undergo thermal decomposition, releasing a large amount of gas and promoting the formation of a unique three-dimensional porous structure in the carbon framework. Sulfur and nitrogen atoms are uniformly doped into the carbon lattice, producing a synergistic effect with the active sites of iron-based transition metals, regulating the electronic structure and microenvironment of the carbon-based material, and optimizing the adsorption / desorption behavior between active sites and reaction intermediates during the oxygen reduction reaction. The synthesis process often encounters the problem of transition metal nanoparticles. Acid washing removes the aggregated transition metal particles, followed by a second calcination, ensuring the purity and performance stability of the product. The entire preparation process does not require the introduction of complex templates, simplifying the process steps and significantly reducing the preparation cost of the composite material.

[0017] The present invention has the following advantages and beneficial effects compared with the prior art: (1) The preparation method of this invention uses organic coordination-high temperature calcination as the synthesis strategy to prepare a unique three-dimensional porous framework sulfur-nitrogen dual-doped carbon material, with iron-based active sites highly dispersed on the porous carbon material. Since the melamine of this invention can interact with metal ions and sulfur sources to form metal-nitrogen-sulfur sites, and 2,2-diaminodiphenyl sulfide achieves uniform sulfur doping, sulfur and nitrogen synergistically regulate the electronic structure, and no additional complex template is required, the preparation method is simple and greatly reduces the preparation cost of composite materials.

[0018] (2) The sulfur-nitrogen co-doped porous carbon-supported iron-based composite material prepared by the present invention has excellent oxygen reduction electrocatalytic activity. The half-wave potential in alkaline electrolyte reaches 0.89V (vs. RHE), which is similar to that of Pt / C catalyst. It also exhibits higher power density, better constant current discharge performance and step discharge performance than commercial Pt / C, and has good application prospects as a cathode catalyst for metal-air batteries. Attached Figure Description

[0019] Figure 1 The XRD patterns of Fe / S-NC, Fe-NC, S-NC, and NC obtained in Examples 1-4 of this invention are shown. Figure 2 SEM images of Fe / S-NC, Fe-NC, S-NC, and NC obtained in Examples 1-4 of this invention, respectively; Figure 3TEM of Fe / S-NC obtained in Example 1 of this invention; Figure 4 The oxygen reduction activity test graphs are shown for Fe / S-NC, Fe-NC, S-NC, NC and commercial Pt / C prepared in Examples 1 to 4 of this invention, respectively. Figure 5 The graph shows the power test results of the magnesium metal air battery provided in Embodiment 7 of the present invention. Figure 6 The 10 mA cm⁻¹ magnesium metal-air battery provided in Embodiment 7 of the present invention -2 Graph of constant current discharge test results; Figure 7 The figure shows the step discharge test results of the magnesium metal air battery provided in Embodiment 7 of the present invention.

[0020] Figure 8 The graph shows the power test results of the zinc metal air battery provided in Embodiment 8 of the present invention; Figure 9 The 10 mA cm⁻¹ zinc metal air battery provided in Embodiment 8 of the present invention -2 Graph of constant current discharge test results; Figure 10 The figure shows the step discharge test results of the zinc metal air battery provided in Embodiment 8 of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0022] Example 1 A method for preparing a porous carbon-supported transition metal composite material, specifically a method for preparing a sulfur-nitrogen co-doped porous carbon-supported iron-based composite material Fe-S-NC, is disclosed below: 0.1 mmol of acetylacetone iron, 2 mmol of zinc nitrate, 16 mmol of imidazole-2-formaldehyde, and 0.5 mmol of 2,2-diaminodiphenyl sulfide were sequentially added and dissolved in 50 mL of ethanol solution. The mixture was magnetically stirred at room temperature for 12 h to induce coordination self-assembly. Subsequently, 1 g of melamine was added, and the reaction was continued with magnetic stirring for another 12 h to obtain a mixed system of coordination compounds formed by cross-linking of ethanol, various organic ligands, and metal ions.

[0023] The mixture was transferred to an oil bath and dried at 80°C until the organic solvent was completely evaporated, yielding a solid precursor. The obtained solid precursor was placed in a tube furnace and calcined in stages under a nitrogen atmosphere. The temperature was first increased to 400°C at a rate of 5°C / min and held for 1 hour, then increased to 950°C at a rate of 5°C / min and held for 2 hours. After natural cooling, the material containing residual nanoparticles was obtained.

[0024] The material containing residual nanoparticles was acid-washed with 0.5M sulfuric acid solution for 12 hours, then filtered with deionized water until neutral, dried, and placed in a tube furnace again. Under a nitrogen atmosphere, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 2 hours for a second calcination. The final target sample, a porous carbon-supported transition metal composite material Fe / S-NC, was obtained.

[0025] Example 2 This example demonstrates the preparation of the iron-nitrogen-doped porous carbon composite material Fe-NC, a control sample. The specific preparation steps are as follows: 0.1 mmol of acetylacetone iron, 2 mmol of zinc nitrate, and 16 mmol of imidazole-2-carboxaldehyde were added sequentially and dissolved in 50 mL of ethanol solution. The mixture was magnetically stirred at room temperature for 12 h to carry out coordination self-assembly. Then, 1 g of melamine was added and the reaction was continued with magnetic stirring for another 12 h to obtain a mixed system of coordination compounds formed by cross-linking of ethanol, various organic ligands, and metal ions.

[0026] The mixture was transferred to an oil bath and dried at 80°C until the organic solvent was completely evaporated, yielding a solid precursor. The obtained solid precursor was placed in a tube furnace and calcined in stages under a nitrogen atmosphere. The temperature was first increased to 400°C at a rate of 5°C / min and held for 1 hour, then increased to 950°C at a rate of 5°C / min and held for 2 hours. After natural cooling, the material containing residual nanoparticles was obtained.

[0027] The material containing residual nanoparticles was acid-washed with 0.5M sulfuric acid solution for 12 hours, then filtered with deionized water until neutral, dried, and placed in a tube furnace again. Under a nitrogen atmosphere, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 2 hours for a second calcination, finally obtaining the target sample, the Fe-NC iron-nitrogen doped porous carbon composite material.

[0028] Example 3 This example demonstrates the preparation of the sulfur-nitrogen-doped porous carbon composite material S-NC, a control sample. The specific preparation steps are as follows: 2 mmol zinc nitrate, 16 mmol imidazole-2-formaldehyde, and 0.5 mmol 2,2-diaminodiphenyl sulfide were sequentially added and dissolved in 50 mL of ethanol solution. The mixture was magnetically stirred at room temperature for 12 h to induce coordination self-assembly. Subsequently, 1 g melamine was added, and the reaction was continued with magnetic stirring for another 12 h to obtain a mixed system of coordination compounds formed by cross-linking of ethanol, various organic ligands, and metal ions.

[0029] The mixture was transferred to an oil bath and dried at 80°C until the organic solvent was completely evaporated, yielding a solid precursor. The obtained solid precursor was placed in a tube furnace and calcined in stages under a nitrogen atmosphere. The temperature was first increased to 400°C at a rate of 5°C / min and held for 1 hour, then increased to 950°C at a rate of 5°C / min and held for 2 hours. After natural cooling, the material containing residual nanoparticles was obtained.

[0030] The material containing residual nanoparticles was acid-washed with 0.5M sulfuric acid solution for 12 hours, then filtered with deionized water until neutral, dried, and placed in a tube furnace again. Under a nitrogen atmosphere, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 2 hours for a second calcination, finally obtaining the target sample, sulfur-nitrogen doped porous carbon composite material S-NC.

[0031] Example 4 This example demonstrates the preparation of the nitrogen-doped porous carbon composite material (NC) as a control sample. The specific preparation steps are as follows: 2 mmol zinc nitrate and 16 mmol imidazole-2-carboxaldehyde were added sequentially and dissolved in 50 mL ethanol solution. The mixture was magnetically stirred at room temperature for 12 h to carry out coordination self-assembly. Then 1 g melamine was added and the reaction was continued to be magnetically stirred for 12 h to obtain a mixed system of coordination compounds formed by cross-linking of ethanol, various organic ligands and metal ions.

[0032] The mixture was transferred to an oil bath and dried at 80°C until the organic solvent was completely evaporated, yielding a solid precursor. The obtained solid precursor was placed in a tube furnace and calcined in stages under a nitrogen atmosphere. The temperature was first increased to 400°C at a rate of 5°C / min and held for 1 hour, then increased to 950°C at a rate of 5°C / min and held for 2 hours. After natural cooling, the material containing residual nanoparticles was obtained.

[0033] The material containing residual nanoparticles was acid-washed with 0.5M sulfuric acid solution for 12 hours, then filtered with deionized water until neutral, dried, and placed in a tube furnace again. Under a nitrogen atmosphere, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 2 hours for a second calcination, finally obtaining the target sample nitrogen-doped porous carbon composite material NC.

[0034] Example 5 The Fe / S-NC, Fe-NC, S-NC, and NC samples obtained in Examples 1-4 were characterized by XRD, and the results are as follows: Figure 1 As shown, Fe / S-NC, Fe-NC, S-NC, and NC were successfully prepared in Examples 1-4. The main phase of Fe / S-NC is carbon, with no obvious characteristic peaks of iron-based particles, indicating that the iron-based active sites are highly dispersed; the main phase of Fe-NC is carbon with a small amount of iron and nitrogen phases; the main phase of S-NC is carbon; and NC is pure carbon.

[0035] The Fe / S-NC prepared in Example 1 was characterized by SEM and TEM, and the results are as follows: Figure 2 and Figure 3 As shown, the Fe / S-NC material has a large number of three-dimensional pores uniformly distributed on the surface, with no obvious particle agglomeration. Sulfur, nitrogen and iron elements are uniformly distributed in the carbon skeleton, and it has a high specific surface area, which can provide sufficient active sites and mass transfer channels for oxygen reduction reaction.

[0036] The Fe-NC prepared in Example 2 and the S-NC prepared in Example 3 were characterized by SEM, and the results are as follows: Figure 2 The results show that both Fe-NC and S-NC surfaces have porous structures, but the uniformity of the pores is lower than that of Fe / S-NC, and a small number of iron-based particles are aggregated on the Fe-NC surface.

[0037] The NC obtained in Example 4 was characterized by SEM, and the results are as follows: Figure 2 The results show that the NC surface has a sparse porous structure, a small specific surface area, and no heteroatoms or metal active sites.

[0038] Example 6 The oxygen reduction activity of Fe / S-NC, Fe-NC, S-NC, and NC prepared in Examples 1-4, and commercial Pt / C were tested. The specific preparation steps are as follows: Weigh 8 mg of the samples prepared in Examples 1-4 into sample vials, add 1 mL of ethanol, 1 mL of deionized water, and 80 μL of Nafion, and sonicate for 30 minutes. After sonication, use a pipette to drop 12.5 μL of the sonicated solution onto a glassy carbon electrode, and dry the water and alcohol with an infrared lamp (catalyst loading: 0.4 mg / cm³). 2 Using a glassy carbon electrode as the working electrode, graphite and Ag / AgCl as the counter and reference electrodes, respectively, and 0.1 M KOH solution as the electrolyte, linear voltammetry was performed at a rotation speed of 1600 rpm, with a scan range of 0.2–1.0 V (vs. RHE). The test results are as follows. Figure 4 As shown.

[0039] like Figure 4As shown, the oxygen reduction activities of Fe / S-NC, Fe-NC, S-NC and NC catalysts are similar to those of Pt / C catalysts, but the best performance is that of Fe / S-NC catalyst, with a half-wave potential of 0.89V (vs. RHE).

[0040] Example 7 The metal-air battery was assembled as follows: 8 mg of Pt / C or Fe / S-NC prepared in Example 1 was weighed into a sample vial, and 1 mL of ethanol, 1 mL of deionized water, and 80 μL of Nafion were added. The mixture was then sonicated for 30 minutes to obtain a Pt / C solution or a Fe / S-NC solution. A 6.5 × 2 cm piece of hydrophilic / hydrophobic carbon cloth was cut, and 562.5 μL of the above Pt / C solution or Fe / S-NC solution was evenly added dropwise to a 1.5 × 1.5 cm area on the hydrophilic side (carbon cloth catalyst loading: 1 mg / cm²). 2 After drying, carbon cloth coated with Pt / C or Fe / S-NC is obtained, which is used as the positive electrode material for subsequent air batteries. The air battery is assembled using a specific mold, with a magnesium sheet as the negative electrode, the carbon cloth coated with Pt / C or Fe / S-NC as the positive electrode, and an appropriate amount of 6M KOH added as the electrolyte.

[0041] The air batteries assembled using the above method were used to perform power tests on Fe / S-NC and Pt / C batteries. The test results are as follows: Figure 5 As shown, the maximum power density of Fe / S-NC is 44.71 mW / cm². -2 36.80 mW cm⁻¹ higher than Pt / C -2 This further demonstrates that Fe / S-NC possesses excellent oxygen reduction performance.

[0042] The air battery assembled according to the above method was used to test Fe / S-NC and Pt / C at a current density of 10 mA cm⁻¹. -2 Constant current discharge test. The test results are as follows: Figure 6 As shown, the specific capacity of Fe / S-NC is 1169.7 mAh g. -1 Compared to the 1144.7mAh g of commercial Pt / C -1 high.

[0043] The batteries assembled according to the above method were subjected to step discharge tests on Fe / S-NC and Pt / C batteries. The test results are as follows: Figure 7 As shown, Fe / S-NC exhibits performance at open circuit, 2, 5, and 10 mA cm⁻¹. -2 The voltage values ​​below are all higher than Pt / C.

[0044] Example 8 The metal-air battery was assembled as follows: 8 mg of Pt / C or Fe / S-NC prepared in Example 1 was weighed into a sample vial, and 1 mL of ethanol, 1 mL of deionized water, and 80 μL of Nafion were added. The mixture was then sonicated for 30 minutes to obtain a Pt / C solution or a Fe / S-NC solution. A 6.5 × 2 cm piece of hydrophilic / hydrophobic carbon cloth was cut, and 562.5 μL of the above Pt / C solution or Fe / S-NC solution was evenly added dropwise to a 1.5 × 1.5 cm area on the hydrophilic side (carbon cloth catalyst loading: 1 mg / cm²). 2 After drying, carbon cloth coated with Pt / C or Fe / S-NC is obtained and used as the positive electrode material in subsequent air batteries. Air batteries are assembled using specific molds, with zinc sheets as the negative electrode, coated with 1 mg / cm³ of Pt / C or Fe / S-NC. 2 Fe / S-NC and Pt / C carbon cloth are used as positive electrodes, and an appropriate amount of 3.5wt% NaCl is added as the electrolyte.

[0045] The zinc-air batteries assembled according to the above method were used to perform power tests on Fe / S-NC and Pt / C batteries. The test results are as follows: Figure 8 As shown, the maximum power density of Fe / S-NC is 133.11 mW / cm². -2 58.4 mW cm⁻¹ higher than Pt / C -2 This further demonstrates the excellent oxygen reduction performance of Fe / S-NC.

[0046] The zinc-air battery assembled according to the above method was used to test Fe / S-NC and Pt / C at a current density of 10 mA / cm². -2 Constant current discharge test. The test results are as follows: Figure 9 As shown, the specific capacity of Fe / S-NC is 784.9 mAh g. -1 Compared to the 696.5mAh g of commercial Pt / C -1 high.

[0047] The batteries assembled according to the above method were subjected to step discharge tests on Fe / S-NC and Pt / C batteries. The test results are as follows: Figure 10 As shown, Fe / S-NC exhibits performance at open circuit, 2, 5, 10, 15, and 20 mA cm⁻¹. -2 The voltage values ​​below are all higher than Pt / C.

[0048] The above embodiments are preferred and important implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon-supported transition metal composite material, characterized in that... Includes the following steps: Iron acetylacetone, zinc nitrate, imidazole-2-carboxaldehyde and 2,2-diaminodiphenyl sulfide were added sequentially and dissolved in ethanol. The mixture was stirred for 12 hours to carry out coordination self-assembly. Then, melamine was added and the mixture was stirred for another 12 hours to carry out the reaction. After drying by heating in an oil bath, the resulting solid was calcined in stages under a nitrogen atmosphere and then cooled naturally to obtain a material with residual nanoparticles. The material containing residual nanoparticles was acid-washed with sulfuric acid and then calcined a second time. The temperature was increased to 950°C at a rate of 5°C / min and held for 2 hours in a tube furnace to obtain a porous carbon-supported transition metal composite material.

2. The method for preparing a porous carbon-supported transition metal composite material according to claim 1, characterized in that: The oil bath heating and drying temperature is 20~100℃, and the time is 12~72h.

3. The method for preparing a porous carbon-supported transition metal composite material according to claim 1, characterized in that: The oil bath heating and drying temperature is 80℃, and the time is 48h.

4. The method for preparing a porous carbon-supported transition metal composite material according to claim 1, characterized in that: The segmented calcination involves first heating to 300-500℃ at a rate of 5℃ / min and holding for 1 hour, then heating to 900-1000℃ at a rate of 5℃ / min and holding for 2 hours.

5. The method for preparing a porous carbon-supported transition metal composite material according to claim 1, characterized in that: The segmented calcination involves first heating to 400℃ at a rate of 5℃ / min and holding for 1 hour, then heating to 950℃ at a rate of 5℃ / min and holding for 2 hours.

6. The method for preparing a porous carbon-supported transition metal composite material according to claim 1, characterized in that: The molar ratio of acetylacetone iron, zinc nitrate, imidazole-2-carboxaldehyde, 2,2-diaminodiphenyl sulfide and melamine is (0.01~1):(0.01~5):(0.01~5):(0.01~5):(0.01~5).

7. A porous carbon-supported transition metal composite material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The porous carbon-loaded transition metal composite material has a three-dimensional interconnected porous carbon-based network structure, specifically constructed by the cross-linking of ultrathin carbon sheets to form a continuous and interconnected multi-level pore system, presenting an overall hollow sponge-like morphology.

8. The application of the porous carbon-supported transition metal composite material according to claim 7 in metal-air batteries.

9. A metal-air battery cathode material comprising the porous carbon-supported transition metal composite material of claim 7.

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