A cobalt / copper-nitrogen-carbon hollow porous nanoparticle, a preparation method and application thereof in electrocatalytic oxygen reduction

Abstract

A kind of cobalt / copper-nitrogen-carbon hollow porous nanoparticle derived from nitrogen-containing carbon polymer dot and metal organic framework, preparation method and its application in electrocatalytic oxygen reduction belong to oxygen reduction electrocatalytic material technical field.First, prepare well-dispersed approximately spherical N-CPDs and metal organic framework material precursor containing cobalt copper zinc ions with dodecahedron morphology, then react in methanol and water mixed solvent to generate MOF (Co, Zn, Cu) and N-CPDs composite nano hollow structure, finally pyrolysis under argon atmosphere, obtain cobalt / copper-nitrogen-carbon hollow porous nanoparticle.The material is used to prepare electrocatalytic working electrode, show more excellent electrocatalytic activity, better stability and higher methanol resistance than commercial 20%Pt / C catalyst.Therefore, porous hollow nanomaterial has very good application prospect as electrode material for electrocatalytic oxygen reduction.

Description

Technical Field

[0001] This invention belongs to the field of oxygen reduction electrocatalytic materials technology, specifically relating to a cobalt / copper-nitrogen-carbon hollow porous nanoparticle derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks, its preparation method, and its application in electrocatalytic oxygen reduction. Background Technology

[0002] In recent years, rechargeable devices such as fuel cells and metal-air batteries have become the focus of extensive research due to their high energy conversion efficiency and environmental friendliness. However, the slow kinetics of the cathode oxygen reduction reaction (ORR) in rechargeable devices have hindered their further development. Although platinum-based electrocatalysts (Pt / C) are currently the most efficient ORR electrocatalysts, their widespread commercialization is hampered by the low abundance of platinum on Earth, poor catalyst stability, and deactivation due to methanol poisoning. Therefore, developing low-cost, highly active ORR electrocatalysts for future rechargeable devices is imperative.

[0003] Carbonized polymer dots (CPDs) are novel zero-dimensional carbon-based materials with a unique graphite-like core / polymer shell structure, excellent electrical properties, and stability. The polymer shell on the surface of CPDs possesses abundant functional groups, providing a high density of metal binding sites, offering interfacial modification and support for transition metals, and promoting electron transfer kinetics in catalysts. Electrocatalysts constructed from CPDs and transition metals exhibit significant advantages in improving activity and stability. Metal-organic frameworks (MOFs) are periodic nanoporous materials formed by the self-assembly of organic ligands and metal ions. Their derivatives and complexes have attracted considerable attention as electrocatalysts over the past few decades, with research focusing on addressing the low conductivity and poor stability of MOFs. Therefore, establishing simple and effective preparation methods to combine CPDs and MOFs to obtain electrocatalysts with high catalytic activity and stability is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a simple process for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks, their preparation method, and their application in electrocatalytic oxygen reduction.

[0005] This invention uses a cobalt-copper-zinc metal-organic framework (MOF) (Co, Zn, Cu) as a precursor. It leverages the abundant nitrogen-containing functional groups on the polymer shell segments of nitrogen-containing carbonized polymer dots (N-CPDs) to coordinate with the cobalt, copper, and zinc in the MOF (Co, Zn, Cu). Combining this with the instability of MOF (Co, Zn, Cu) in H2O (mainly due to the etching effect of H2O), the simultaneous coordination of N-CPDs with the metal and the gradual disassembly of the MOF from the inside out is achieved. By optimizing experimental conditions, a MOF (Co, Zn, Cu) is obtained. Co,Zn,Cu) / N-CPDs composite hollow materials were further pyrolyzed at high temperatures to obtain cobalt / copper-nitrogen-carbon hollow porous nanoparticles. During the material preparation process, the polymer shell of N-CPDs was anchored to the MOF through N-metal coordination, protecting the integrity of the hollow structure of the material during H2O disassembly of the MOF. Simultaneously, this N-metal coordination effectively alleviated the aggregation of metal particles during sintering, thereby exposing more catalytic active sites. Furthermore, the graphite-like core of N-CPDs effectively improved the conductivity of the material. The MOF provided both a template for the preparation of hollow materials and abundant transition metal sources as active sites. Based on this, the nitrogen-doped carbon-based hollow porous nanomaterials loaded with transition metals, prepared by combining nitrogen-doped carbonized polymer dots and metal-organic frameworks, exhibited excellent catalytic activity and stability in the electrocatalytic oxygen reduction reaction.

[0006] The raw materials used in this invention are all commercially available substances. The reaction process and experimental operation are simple, have low risk, and are highly reproducible, allowing for mass production.

[0007] The present invention describes the preparation of cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks, comprising: (1) the preparation of approximately spherical N-CPDs with a size of 8-12 nm and good dispersibility; (2) the preparation of metal-organic framework materials MOF (Co,Zn,Cu) with a dodecahedral morphology containing cobalt, copper, and zinc ions; (3) the reaction of N-CPDs and MOF (Co,Zn,Cu) in a mixed solvent of methanol and water to generate MOF (Co,Zn,Cu) / N-CPDs composite hollow material, followed by high-temperature pyrolysis to obtain cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC); the specific steps are as follows:

[0008] (1) Synthesis of nitrogen-containing carbonized polymer dots (N-CPDs): 8-40 mg of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), 50-350 mg of NaOH, 0.5-5 mL of pyrrole (Py), and 10-50 mL of deionized water (DI water) were placed in a polytetrafluoroethylene autoclave (20-100 mL), heated in an oven at 200-250 °C for 8-12 h, and then naturally cooled to room temperature. The mixture was then transferred to a dialysis bag with a pore size of 3500 Da and dialyzed in deionized water (DI water) for 36-72 h. Finally, the dialysis solution was freeze-dried to obtain approximately spherical nitrogen-containing carbonized polymer dots (N-CPDs) with a size of 8-12 nm and good dispersibility. The N-CPDs synthesized under alkaline conditions under high pressure hydrothermal conditions have obvious graphite-like cores and nitrogen-containing polymer shells.

[0009] (2) Synthesis of MOF(Co,Zn,Cu): Zn(NO3)2·6H2O, Co(NO3)2·6H2O, and Cu(NO3)2·3H2O were dissolved in 30–150 mL of methanol, denoted as solution A. 2-methylimidazole was dissolved in 30–150 mL of methanol, denoted as solution B. The molar ratio of Zn(NO3)2·6H2O, Co(NO3)2·6H2O, Cu(NO3)2·3H2O, and 2-methylimidazole was 1:1:1:12. The concentrations of the three metal salts were all 0.5–4 mM. The concentration of imidazolium was 6–48 mM. Solutions A and B were mixed in batches (5–6 mL of solution B was added dropwise to solution A every 5–6 min), and stirred at room temperature for 12–36 h. The resulting purple suspension was centrifuged (8000–12000 rpm, 3–8 min) to obtain a purple solid product. This solid product was washed 3–5 times with methanol and dried at 50–60 °C to obtain a purple powder, which is the metal-organic framework material (MOF(Co,Zn,Cu)) containing cobalt, copper, and zinc ions. The prepared MOF(Co,Zn,Cu) exhibits metastability in water.

[0010] (3) Synthesis of CoCu-NC: 10-50 mg MOF (Co,Zn,Cu) and 20-100 mg N-CPDs were added to a mixed solution of 20-100 mL methanol and deionized water with a volume ratio of methanol to deionized water of 0.8-1.2:1. The mixture was then refluxed and stirred at 50-60 °C for 7-10 h. The resulting brown suspension was centrifuged (8000-12000 rpm, 3-8 min) to obtain a brown solid product. The product was washed with methanol 3-5 times and dried at 50-60 °C. Then, it was pyrolyzed in a tube furnace at 700-900 °C under argon conditions for 2-3 h to obtain black cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) powder. The nano-hollow structure was obtained by utilizing the metastability of MOF (Co,Zn,Cu) in water and the coordination of N with metal ions in the shell of N-CDPs. Attached Figure Description

[0011] Figure 1 High-resolution transmission electron microscope images of N-CPDs prepared in Example 1 ( Figure 1 A, where the inset is a lattice spacing image of N-CPDs) and Fourier transform infrared spectrum ( Figure 2 B), Figure 2 In B, the horizontal axis is Wavenumber (cm) -1 The y-axis represents wavenumber, and the ordinate Transmittance (%) represents light transmittance.

[0012] Figure 2 Scanning electron microscope image of the metal-organic framework (MOF) material (Co, Zn, Cu) containing cobalt, copper, and zinc ions with a dodecahedral morphology prepared in Example 1. Figure 2 A) and transmission electron microscope images ( Figure 2 B);

[0013] Figure 3 Scanning electron microscopy of cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) prepared in Example 2 Figure 3 A) Transmission electron microscope images ( Figure 3 B) and high-resolution transmission electron microscope images ( Figure 3 C, where the inset is a lattice spacing image of Co, Cu and N-CPDs;

[0014] Figure 4 X-ray diffraction patterns of CoCu-NC and N-CPDs prepared in Example 2, where the horizontal axis 2Theta (degree) represents the diffraction angle and the vertical axis Intensity (au) represents the diffraction intensity.

[0015] Figure 5 Electrocatalytic oxygen reduction performance of the cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) prepared in Example 3 and compared with a commercial 20% Pt / C catalyst; Figure 5 A is the linear voltammetric scan of electrocatalytic oxygen reduction, with the horizontal axis Potential (V vs RHE) representing the electrode potential (V, relative to the reversible hydrogen electrode) and the vertical axis j representing the current density (mA cm⁻¹). -2 ); Figure 5 B is the Tafel slope plot, with the horizontal axis being Log(|j|mA cm). -2 The vertical axis represents the logarithm of the current density, and the vertical axis Potential represents the electrode potential (V). Figure 5 C represents the linear voltammetric scan of electrocatalytic oxygen reduction at different rotational speeds. The horizontal axis, Potential (V vs RHE), represents the electrode potential (V, relative to the reversible hydrogen electrode), and the vertical axis, j, represents the current density (mA / cm²). -2 ); Figure 5 D is the AC impedance spectrum, with the horizontal axis Z′ representing the real impedance (Ω) and the vertical axis -Z″ representing the imaginary impedance (Ω).

[0016] Figure 6 A: The it curve of the electrocatalytic electrode of cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) prepared in Example 3. The horizontal axis represents time (s) and the vertical axis represents relative current (%). Figure 6 B: Methanol tolerance test graph of the electrocatalytic electrode of cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) prepared in Example 3. The horizontal axis Time represents time (s), and the vertical axis j / j0 (%) represents the relative current. The corresponding curve of commercial 20% Pt / C catalyst is attached to the graph for comparison. Detailed Implementation

[0017] The present invention will be further illustrated below with examples, but this is not intended to limit the invention.

[0018] Example 1

[0019] (1) Synthesis of nitrogen-containing carbonized polymer dots (N-CPDs): 30 mg of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), 300 mg of NaOH, 3 mL of pyrrole (Py), and 45 mL of deionized water (DI water) were transferred to a polytetrafluoroethylene autoclave (100 mL). The autoclave was heated in an oven at 200 °C for 10 h, then naturally cooled to room temperature. The solution was then transferred to a dialysis bag with a pore size of 3500 Da and continuously dialyzed in DI water for 72 h to remove unreacted small molecules and salts. The dialysis solution was freeze-dried to obtain approximately spherical N-CPDs with a size of 8–12 nm and good dispersibility, with a product mass of 20 mg. (See attached...) Figure 1 As shown, by Figure 1 Transmission electron microscopy images of A show that N-CPDs with relatively uniform size, good dispersion, and near-spherical shape were successfully obtained, with an average size of 8–12 nm. Figure 1 The inset image of N-CPDs (Figure A) shows a lattice spacing of 0.25 nm, similar to the 002 crystal plane of graphene, proving that N-CPDs possess a graphite-like lattice structure. Figure 1 The Fourier transform infrared spectrum of B shows that N-CPDs contain functional groups such as nitrogen-containing amino and amide bonds.

[0020] (2) Synthesis of MOF(Co,Zn,Cu): Zn(NO3)2·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O were dissolved in 120 mL of methanol and labeled as solution A. The concentrations of Zn(NO3)2·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O were all 3 mM. 2-Methylimidazole was dissolved in 120 mL of methanol and labeled as solution B. The concentration of 2-methylimidazole was 36 mM. Solutions A and B were mixed in batches (i.e., 5 mL of solution B was added dropwise to solution A every 5 min) and stirred at room temperature for 24 h. The resulting purple suspension was centrifuged (10000 rpm, 5 min). The resulting purple solid product was washed three times with methanol and dried at 60 °C to obtain a metal-organic framework material MOF(Co,Zn,Cu) with a dodecahedral morphology containing cobalt, copper and zinc ions. The product mass was 70 mg. As attached Figure 2 A and Figure 2 As shown in Figure B, MOF(Co,Zn,Cu) is a well-dispersed dodecahedral nanocrystal with an average size of 200–280 nm.

[0021] (3) Synthesis of CoCu-NC: 45 mg MOF (Co, Zn, Cu) and 90 mg N-CPDs were mixed with 90 mL of methanol and deionized water (volume ratio = 1:1) and then refluxed at 60 °C for 7 h. The resulting brown suspension was centrifuged (10000 rpm, 5 min). The resulting brown solid product was washed three times with methanol and dried at 60 °C. The product mass was 80 mg. The product was then placed in a tube furnace and pyrolyzed at 800 °C for 2 h under argon atmosphere to obtain cobalt / copper-nitrogen-carbon hollow porous nanoparticles CoCu-NC. The product mass was 40 mg.

[0022] Example 2

[0023] (1) Synthesis of nitrogen-containing carbonized polymer dots (N-CPDs): 10 mg of perylene 3,4,9,10-tetracarboxylic dianhydride (PTCDA), 100 mg of NaOH, 1 mL of pyrrole (Py), and 15 mL of deionized water (DI water) were transferred to a polytetrafluoroethylene autoclave (25 mL). The autoclave was heated in an oven at 200 °C for 10 h and then naturally cooled to room temperature. The solution was then transferred to a dialysis bag with a pore size of 3500 Da and dialyzed in DI water for 72 h. The dialysis solution was freeze-dried to obtain approximately spherical N-CPDs with a size of 10 nm and good dispersibility. The product mass was 8 mg.

[0024] (2) Synthesis of MOF(Co,Zn,Cu): Zn(NO3)2·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O were dissolved in 40 mL of methanol and recorded as solution A. The concentrations of Zn(NO3)2·6H2O, Co(NO3)2·6H2O and Cu(NO3)2·3H2O were all 1 mM. 2-Methylimidazole was dissolved in 40 mL of methanol and recorded as solution B. The concentration of 2-methylimidazole was 12 mM. Solution A and solution B were mixed in batches (i.e., 5 mL of solution B was added dropwise to solution A every 5 min) and stirred at room temperature for 24 h. The resulting purple suspension was centrifuged (10000 rpm, 5 min). The resulting purple solid was washed three times with methanol and dried at 60 °C. It was a metal-organic framework material MOF(Co,Zn,Cu) with a dodecahedral morphology containing cobalt, copper and zinc ions. The mass of the product was 30 mg.

[0025] (3) Synthesis of CoCu-NC: 15 mg MOF (Co, Zn, Cu) and 30 mg N-CPDs were mixed with 30 mL of methanol and deionized water (volume ratio = 1:1) and then refluxed at 60 °C for 7 h. The obtained brown suspension was centrifuged (10000 rpm, 5 min). The obtained brown solid was washed three times with methanol and dried at 60 °C. The product mass was 35 mg. The product was then placed in a tube furnace and pyrolyzed at 800 °C for 2 h under argon atmosphere to obtain cobalt / copper-nitrogen-carbon hollow porous nanoparticles CoCu-NC. The product mass was 18 mg.

[0026] The prepared cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) have a size of approximately 20–100 nm, such as Figure 3 A and Figure 3 As shown in B, its morphology is a hollow structure, as can be seen from the scanning electron microscope and transmission electron microscope images; Figure 3 The high-resolution transmission electron microscope image of C shows the lattice structures corresponding to Co, Cu, and N-CPDs; the XRD patterns of CoCu-NC and N-CPDs are shown below. Figure 4 As shown, both N-CPDs and CoCu-NC exhibit a broad peak at 22° (belonging to the (002 plane) interlayer peak of graphitic carbon), indicating that N-CPDs enhance the graphite-like structure of the material. Furthermore, CoCu-NC shows six characteristic diffraction peaks at 43.4° / 50.5° / 74.2° and 44.5° / 51.7° / 76.3°, which can be attributed to face-centered cubic Cu atoms (PDF#04-0836 111, 200, and 220 planes) and Co atoms (PDF#15-0806 111, 200, and 220 planes). No characteristic crystal peaks of other metal oxides were found, suggesting that N-CPDs facilitate the transformation of metal ions in MOFs (Co,Zn,Cu) into well-dispersed metal particles, rather than metal oxides or aggregates. This demonstrates that N-CPDs play a crucial role in the formation of CoCu-NC and the improvement of ORR performance.

[0027] Example 3

[0028] (1) Preparation of electrocatalytic working electrodes: 2 mg of cobalt / copper-nitrogen-carbon hollow porous nanoparticles (CoCu-NC) prepared in Example 2 were dispersed in 480 μL of methanol and 20 μL of 5 wt% Nafion solution. After continuous ultrasonic treatment, 1 mL of the solution was uniformly dropped onto a rotating ring electrode (RRDE) and a rotating disk electrode (RDE), respectively. After drying under ambient conditions, two types of electrocatalytic working electrodes were obtained. In the electrochemical test, a carbon rod electrode was used as the counter electrode, a newly prepared Ag / AgCl 3MKCl electrode was used as the reference electrode, and O2-saturated 0.1 M KOH aqueous solution was used as the ORR electrolyte.

[0029] (2) Linear Voltammetry Test: The voltage range for linear voltammetry is 1.2–1.6 V, the scan rate is 2 mV per second, the electrolyte is 0.1 M potassium hydroxide solution, and a rotating disk electrode (RDE) is used for testing. Figure 5 As shown in Figure A, the initial potential (E0) of this material is 0.94V, and the half-wave potential (E... 1 / 2 The voltage is 0.92V, exceeding commercial use by 20% for Pt / C (E0 = 0.93V, E...). 1 / 2 =0.85V); Figure 5 B is calculated based on the Tafel slope formula. Figure 5 The Tafel slope plot obtained from the linear voltammetry curve in A shows that the Tafel slope of this material is 69.98 mV dec. -1 Also exceeding commercial use by 20% Pt / C (155.52mV dec) -1 ).

[0030] (3) Cyclic voltammetry test: First, a cyclic voltammetry scan was performed with a voltage range of 0–0.5 V, a scan rate of 100 mV per second, and 5000 scan cycles using a rotating disk electrode (RDE). Then, the linear voltammetry scan in step (2) was performed, and the results were compared with those in step (2). After 5000 cycles, the electrocatalytic performance decayed relatively little, indicating that the material has good working stability. Linear voltammetry test of electrocatalytic oxygen reduction at different rotation speeds: In O2-saturated 0.1 M KOH electrolyte, at a rotation speed of 400–2025 rpm, the voltage range of the linear voltammetry test was 1.2–1.6 V, the scan rate was 2 mV per second, the electrolyte used was 0.1 M potassium hydroxide solution, and the test was performed using a rotating ring disk electrode (RRDE). The ORR polarization curves at different rotation speeds (ω) were discussed. Figure 5 C). Limiting current density (j) of all catalysts LThe values ​​of both increase with increasing rotational speed and conform to the first-order kinetic equation. Furthermore, calculations using the Kouteckey-Levitich (KL) equation confirm that CoCu-NC exhibits approximately 4 electron transfers (n = 3.94) in the potential range of 0.30–0.70 V, demonstrating ORR catalytic activity.

[0031] (4) Electrochemical impedance spectroscopy test: initial voltage 0.5 eV, high frequency 10 5 Hz, with a low frequency of 0.01Hz, measured using a rotating disk electrode (RDE). For example... Figure 5 As shown in Figure D, the electrochemical impedance of this material is smaller than that of commercial 20% Pt / C material, indicating that this material has a more efficient electron transport rate.

[0032] (5) Potential-time test: The potential change is measured under constant current conditions using a rotating disk electrode (RDE) test, such as... Figure 6 As shown in Figure A, when the current is 20mA cm -2 Under these conditions, the material exhibits better working stability than commercially available 20% Pt / C material, lasting for 32,500 seconds.

[0033] (6) Methanol tolerance test: Potential change is tested under constant current conditions using a rotating disk electrode (RDE). Figure 6 As shown in Figure B, at a current of 20mA cm -2 Under the conditions of continuous operation for 2500s, 1M methanol was added to the electrolyte at a test time of 300s. It was found that the current density of commercial 20% Pt / C decreased significantly, while the material maintained a relatively stable current response, indicating that the material has better methanol tolerance in alkaline solution than commercial 20% Pt / C.

[0034] This material achieves highly efficient compositing of N-CPDs with a metal-organic framework. The results demonstrate that this material possesses excellent catalytic activity, good stability, and good methanol tolerance. This invention is simple to operate and has broad application prospects in high-performance electrocatalysis and energy storage devices.

Claims

1. A method for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks, comprising the following steps: (1) Synthesis of nitrogen-containing carbonized polymer dots: 8-40 mg of perylene-3,4,9,10-tetracarboxylic acid dianhydride, 50-350 mg of NaOH, 0.5-5 mL of pyrrole and 10-50 mL of deionized water were placed in a polytetrafluoroethylene autoclave and heated in an oven at 200-250 °C for 8-12 h. After cooling to room temperature, the mixture was transferred to a dialysis bag with a pore size of 3500 Da and dialyzed in deionized water for 36-72 h. Finally, the dialysis solution was freeze-dried to obtain nitrogen-containing carbonized polymer dots with a size of 8-12 nm and approximately spherical shape. (2) Synthesis of metal-organic framework materials containing cobalt, copper, and zinc ions: Zn(NO3)2∙6H2O, Co(NO3)2∙6H2O, and Cu(NO3)2∙3H2O were dissolved in 30-150 mL of methanol and labeled as solution A. 2-methylimidazole was dissolved in 30-150 mL of methanol and labeled as solution B. The molar ratio of Zn(NO3)2∙6H2O, Co(NO3)2∙6H2O, Cu(NO3)2∙3H2O, and 2-methylimidazole was 1:1:1:

12. Solutions A and B were mixed in batches and stirred at room temperature for 12-36 h. The resulting purple suspension was centrifuged to obtain a purple solid product, which was washed with methanol 3-5 times and dried at 50-60 °C to obtain a purple powder, which is the metal-organic framework material containing cobalt, copper, and zinc ions. (3) Synthesis of cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks: 10-50 mg of metal-organic framework material containing cobalt, copper and zinc ions and 20-100 mg of nitrogen-containing carbonized polymer dots were added to a mixed solution of 20-100 mL of methanol and deionized water, and then refluxed and stirred at 50-60 °C for 7-10 h; the resulting brown suspension was centrifuged to obtain a brown solid product, which was washed with methanol 3-5 times and dried at 50-60 °C, and then pyrolyzed at 700-900 °C for 2-3 h under argon conditions to obtain black cobalt / copper-nitrogen-carbon hollow porous nanoparticle powder derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks.

2. The method for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks as described in claim 1, characterized in that: In step (2), the concentrations of the three metal salts are 0.5~4 mM and the concentration of 2-methylimidazole is 6~48 mM.

3. The method for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks as described in claim 1, characterized in that: In step (2), mixing solution A and solution B in batches involves adding 5-6 mL of solution B to solution A every 5-6 minutes.

4. The method for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks as described in claim 1, characterized in that: In step (3), the volume ratio of methanol to deionized water is 0.8~1.2:

1.

5. The method for preparing cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks as described in claim 1, characterized in that: In steps (2) and (3), centrifugation is performed at 8000~12000 rpm for 3~8 min.

6. A cobalt / copper-nitrogen-carbon hollow porous nanoparticle derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

7. The application of cobalt / copper-nitrogen-carbon hollow porous nanoparticles derived from nitrogen-containing carbonized polymer dots and metal-organic frameworks as described in claim 6 in electrocatalytic oxygen reduction reactions.

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