Nitrogen-doped porous carbon supported single-atom catalyst and preparation method and application thereof

Abstract

The application discloses a nitrogen-doped porous carbon loaded monatomic catalyst and a preparation method and application thereof, wherein dimethyl imidazole and zinc nitrate hexahydrate are used as solutes, anhydrous methanol is used as a solvent, and ZIF 8 is formed by stirring at normal temperature; phen (phenanthroline), dopamine (DA), a transition metal source (M) and trimethylolamine are added into the ZIF 8 to form a precursor ZIF8@MPhenPDA; the ZIF-8@M-PhenPDA precursor is subjected to gradient temperature control pyrolysis in a protective gas atmosphere, and the monatomic catalyst is obtained after cooling. The raw material cost is low, the preparation process is simple, the monatomic catalyst can be prepared in a large amount, is suitable for large-scale synthesis of the monatomic catalyst, has universal applicability, and solves the problems of complexity in the prior art and difficulty in large-scale preparation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalysts, and particularly relates to a nitrogen-doped porous carbon supported single-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] To help achieve the goal of global carbon dioxide emissions reaching a peak, it is urgent to develop green renewable energy storage and conversion technologies, which cannot be separated from the core energy unit-battery. Compared with other energy conversion devices, metal-air batteries have unique advantages such as high theoretical specific energy density, low cost, and environmental friendliness, and are therefore considered as one of the most effective green energy conversion technologies. The oxygen reduction reaction (ORR) is a key reaction that determines the metal-air battery, and the slow kinetics of the cathode ORR seriously limits the industrial application of metal-air batteries. The noble metal Pt-based electrocatalyst is considered to be the most effective and commercially viable electrocatalyst for ORR, but its high cost, scarcity and poor stability limit its wide application.

[0003] Single-atom catalysts (SACs) have isolated sites, high dispersity, maximum atomic utilization efficiency, and diverse coordination environments, making them widely concerned in the fields of fuel cells, metal-air batteries, etc. Compared with noble metal catalysts, non-noble metal single-atom catalysts are low in price and have good ORR electrocatalytic performance, and therefore have become one of the most promising candidates to replace noble metal catalysts.

[0004] Although single-atom catalysts have excellent activity, there are still many problems in the preparation process, such as high price of precursors, complex preparation method, easy agglomeration, difficulty in large-scale preparation, environmental pollution, and easy deactivation of active sites of non-noble metal single-atom catalysts, etc. Moreover, the preparation method is often only effective for one kind of metal, and there is a lack of a universal strategy for preparing single-atom catalysts for multiple metals.

[0005] Therefore, it is an important measure to develop a universal preparation strategy for single-atom catalysts with simple and efficient synthesis method, low cost and high activity for the development of energy systems such as metal-air batteries. SUMMARY

[0006] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the present application aims at overcoming the deficiencies in the prior art and providing a nitrogen-doped porous carbon supported monatomic catalyst.

[0009] To solve the above technical problems, the present application provides the following technical solutions: comprising a nitrogen-doped porous carbon composite carrier and a monatomic active component supported on the carrier.

[0010] The composite carrier is obtained by coating ZIF nanomaterials with phenanthroline and dopamine polymers, and the monatomic active component comprises one of Fe, Co, Ni and Mn.

[0011] As a preferred scheme of the nitrogen-doped porous carbon supported monatomic catalyst, the monatomic active component is derived from one of Fe(II), Co(II), Ni(II) and Mn(II) metal salts, and the molar ratio of the metal salt to dopamine is 1:0.25-1.

[0012] Another object of the present application is to overcome the deficiencies in the prior art and provide a preparation method of a nitrogen-doped porous carbon supported monatomic catalyst.

[0013] To solve the above technical problems, the present application provides the following technical solutions: comprising,

[0014] Phenanthroline (Phen), dopamine (DA) and a transition metal source (M) are dissolved in deionized water, ultrasonic dispersion is performed to obtain solution I;

[0015] ZIF8 and trimethylamine are dissolved in ethanol, ultrasonic dispersion is performed to obtain solution II, solution I is poured into solution II, stirring is performed to form a precursor ZIF8@MPhenPDA, centrifugation, washing and drying are performed to obtain a ZIF8@MPhenPDA powder sample;

[0016] The ZIF8@MPhenPDA powder is gradient temperature pyrolyzed, and the nitrogen-doped porous carbon supported monatomic catalyst is obtained after cooling.

[0017] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon supported monatomic catalyst, the preparation method of the ZIF8 comprises,

[0018] 2-methylimidazole and zinc nitrate are respectively dissolved in anhydrous methanol, ultrasonic dispersion is performed, and then stirring is performed to form ZIF8, wherein the molar ratio of zinc nitrate to dimethyl imidazole is 1:(4-10).

[0019] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon supported monatomic catalyst, the transition metal source (M) comprises one of Fe(II), Co(II), Ni(II) and Mn(II) metal salts.

[0020] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon loaded monatomic catalyst according to the application, wherein: the transition metal source (M) comprises one of C4H6FeO4, C4H6CoO4, C4H6NiO4 and C4H6MnO4.

[0021] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon loaded monatomic catalyst according to the application, wherein: in the precursor ZIF8@MPhenPDA, the molar ratio of phenanthroline, transition metal source, dopamine and trimethylolamine is 1:1:(0.25-1):8.

[0022] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon loaded monatomic catalyst according to the application, wherein: the gradient temperature control pyrolysis is first heated to 500-550 DEG C, and kept for 1-3 h, and then heated to 900-1000 DEG C, and kept for 2-3 h.

[0023] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon loaded monatomic catalyst according to the application, wherein: in the gradient temperature control pyrolysis, the heating rate is 2-5 DEG C / min, and the cooling rate is 3-8 DEG C / min.

[0024] As a preferred scheme of the preparation method of the nitrogen-doped porous carbon loaded monatomic catalyst according to the application, wherein: the catalyst prepared by the method has a three-dimensional hierarchical porous structure.

[0025] Another object of the application is to provide an application of the nitrogen-doped porous carbon loaded monatomic catalyst as an electrocatalyst in an oxidation-reduction reaction.

[0026] The application has the following beneficial effects:

[0027] (1) The application provides a universal synthesis method of monatomic catalysts, which is effective for Fe, Co, Ni, Mn and other metals, solves the defect that other methods are only effective for one kind of metal, and is simple and effective, and can be used for large-scale synthesis of monatomic catalysts.

[0028] (2) The catalyst prepared by the method has a three-dimensional hierarchical porous structure with a hollow structure, which can improve the mass transfer rate, expose more active sites, promote the mass transfer process, and thus make the catalyst material have extremely high catalytic activity, and the Fe-N4 coordination structure acts as an active site for oxygen reduction reaction, and adsorbs and reduces oxygen and desorbs products. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to make the technical solutions of the embodiments of the present application clearer, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings. Among them:

[0030] Figure 1 The spherical aberration electron microscope image of the Fe-based single-atom catalyst prepared in Embodiment 1 of the present application.

[0031] Figure 2 The performance comparison chart of the catalysts prepared in Embodiments 1-4 of the present application and the commercial catalyst of Comparative Example 1.

[0032] Figure 3 The LSV curve chart of the catalysts prepared in Embodiment 1 and Comparative Example 2 of the present application.

[0033] Figure 4 The LSV curve chart of the catalysts prepared in Embodiment 1 and Comparative Example 3 of the present application.

[0034] Figure 5 The spherical aberration electron microscope image of the catalyst prepared in Comparative Example 3 of the present application.

[0035] Figure 6 The ORR performance chart of the catalyst prepared in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the present application more apparent and comprehensible, the specific embodiments of the present application will be described in detail in the following with reference to the description of the embodiments.

[0037] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in other manners different from those described herein, and those skilled in the art can make similar generalizations without departing from the scope of the present application, so the present application is not limited to the specific embodiments disclosed below.

[0038] Secondly, the "one embodiment" or "embodiment" referred to herein can include specific features, structures or characteristics included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an independent or alternative embodiment that excludes other embodiments.

[0039] The catalyst performance detection method in the present application is as follows:

[0040] Weigh 3 mg of the prepared catalyst powder, and mix with 240 μL of water, 240 μL of anhydrous ethanol, and 20 μL of a 0.05% Nafion solution, respectively, and ultrasonic dispersion until uniform to prepare a test solution. Take 10 μL of the test solution and deposit on a polished working electrode, and dry at room temperature to form a uniform black film. Then test the ORR performance in 0.1 M KOH, and the LSV curve scanning is 5 mV / s. The greater the half-wave potential and the kinetic current density at the same potential represent the better catalytic activity.

[0041] The raw materials used in the present application are commercially available in the art without special instructions.

[0042] Example 1

[0043] The present embodiment provides a preparation method of a nitrogen-doped porous carbon supported Fe monatomic catalyst, specifically comprising:

[0044] 1) Preparation of ZIF8:

[0045] Weigh 5.2 g of 2-methylimidazole and 4.5 g of Zn(NO3)2·6H2O, respectively, and dissolve in 100 mL of anhydrous methanol, ultrasonic dispersion for 20 min, and then pour the solution containing Zn(NO3)2·6H2O into the 2-methylimidazole solution, and mix and stir at 25°C for 12 h to form ZIF8.

[0046] 2) Synthesis of ZIF8@FePhenPDA:

[0047] 22.5 mg of phenanthroline (Phen), 21.8 mg of C4H6FeO4, and 20 mg of dopamine (DA) are dissolved in 100 mL of deionized water, ultrasonic dispersion for 20 min to obtain solution I;

[0048] 250 mg of ZIF8 and 120 mg of trimethylolamine are dissolved in 100 mL of ethanol, ultrasonic dispersion for 20 min to obtain solution II;

[0049] Pour solution I into solution II, stir at 25°C for 18 h to form the precursor ZIF8@FePhenPDA, centrifuge and wash with methanol three times, and dry in a drying oven at 70°C overnight to obtain ZIF8@FePhenPDA powder sample.

[0050] 3) Gradient temperature pyrolysis:

[0051] The ZIF8@FePhenPDA powder is placed in a quartz boat and heated to 550°C at a heating rate of 2°C / min in a nitrogen environment, and kept for 2 h;

[0052] Continuing to increase the temperature at a rate of 5℃ / min to 950℃, and keeping the temperature for 2h, then cooling to room temperature to obtain a black powder. The obtained solid is ground into fine powder to obtain N-doped porous carbon loaded Fe single-atom catalyst, denoted as ZIF8@FePhenPDA-950.

[0053] Figure 1 The spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the Fe-based single-atom catalyst prepared in Example 1 is shown in the HAADF mode, in which the brightness of an atom is proportional to the 1.8th power of the atomic number, so the metal on the carbon-nitrogen carrier will be particularly bright. The results show that a large number of bright spots are distributed in the carbon matrix, indicating that Fe is anchored in the carbon material in the form of single atoms.

[0054] Example 2

[0055] The present embodiment provides a preparation method of a nitrogen-doped porous carbon loaded Co single-atom catalyst. The difference from Example 1 is that the precursor ZIF8@FePhenPDA in step 2) is adjusted to ZIF8@CoPhenPDA, specifically as follows:

[0056] 2) Synthesis of ZIF8@CoPhenPDA:

[0057] 22.5mg phenanthroline (Phen), 21.8mg C4H6CoO4, 20mg dopamine (DA) are dissolved in 100ml deionized water, and ultrasonic dispersion is performed for 20min to obtain solution I;

[0058] 250mg ZIF8, 120mg trimethylolmethane are dissolved in 100ml ethanol, and ultrasonic dispersion is performed for 20min to obtain solution II;

[0059] Solution I is poured into solution II, and stirring is performed at 25℃ for 18h to form the precursor ZIF8@CoPhenPDA. Centrifugation is performed and methanol is used for cleaning three times. The sample is placed in a drying box at 70℃ for drying overnight to obtain a ZIF8@CoPhenPDA powder sample.

[0060] The remaining steps are the same as those in Example 1, and a nitrogen-doped porous carbon loaded Co single-atom catalyst is prepared, denoted as ZIF8@CoPhenPDA-950.

[0061] Example 3

[0062] The present embodiment provides a preparation method of a nitrogen-doped porous carbon loaded Ni single-atom catalyst. The difference from Example 1 is that the precursor ZIF8@FePhenPDA in step 2) is adjusted to ZIF8@NiPhenPDA, specifically as follows:

[0063] 2) Synthesis of ZIF8@NiPhenPDA:

[0064] 22.5 mg Phenanthroline (Phen), 31.5 mg C4H6NiO4, 20 mg Dopamine (DA) were dissolved in 100 ml deionized water and ultrasonically dispersed for 20 min to obtain solution I;

[0065] 250 mg ZIF8, 120 mg Tris(hydroxymethyl)methylamine were dissolved in 100 ml ethanol and ultrasonically dispersed for 20 min to obtain solution II;

[0066] Solution I was poured into solution II, stirred at 25°C for 18 h to form the precursor ZIF8@NiPhenPDA, centrifuged and washed with methanol three times, and dried in a drying oven at 70°C overnight to obtain a ZIF8@NiPhenPDA powder sample.

[0067] The remaining steps were the same as in Example 1 to obtain an N-doped porous carbon loaded Ni monatomic catalyst, denoted as ZIF8@NiPhenPDA-950.

[0068] Example 4

[0069] The present example provides a method for preparing a nitrogen-doped porous carbon loaded Mn monatomic catalyst, which differs from Example 1 in that step 2) synthesis of the precursor ZIF8@FePhenPDA is adjusted to ZIF8@MnPhenPDA, specifically:

[0070] 2) Synthesis of ZIF8@MnPhenPDA:

[0071] 22.5 mg Phenanthroline (Phen), 31.5 mg C4H6NiO4, 20 mg Dopamine (DA) were dissolved in 100 ml deionized water and ultrasonically dispersed for 20 min to obtain solution I;

[0072] 250 mg ZIF8, 120 mg Tris(hydroxymethyl)methylamine were dissolved in 100 ml ethanol and ultrasonically dispersed for 20 min to obtain solution II;

[0073] Solution I was poured into solution II, stirred at 25°C for 18 h to form the precursor ZIF8@NiPhenPDA, centrifuged and washed with methanol three times, and dried in a drying oven at 70°C overnight to obtain a ZIF8@NiPhenPDA powder sample.

[0074] The remaining steps were the same as in Example 1 to obtain an N-doped porous carbon loaded Mn monatomic catalyst, denoted as ZIF8@MnPhenPDA-950.

[0075] Comparative Example 1

[0076] The comparative example uses an ORR commercial benchmark Pt / C catalyst as a control.

[0077] Figure 2 The performance comparison diagram of the catalysts prepared in Examples 1-4 and the ORR commercial benchmark Pt / C catalyst shows that the half-wave potential and kinetic current density of the Fe single-atom catalyst are higher than those of the Pt / C catalyst at a potential of 0.85 V, indicating that the Fe single-atom catalyst has better ORR performance. The ORR performance of the Co, Ni, and Mn-based single-atom catalysts is also very close to that of the Pt / C catalyst, indicating that the preparation method of the single-atom catalyst provided by the application is suitable for Fe, Co, Ni, and Mn metals and has universality.

[0078] Comparative Example 2

[0079] The difference between the comparative example and Example 1 is that the gradient temperature pyrolysis in step 3) is adjusted to one-step pyrolysis, specifically:

[0080] The ZIF8@FePhenPDA powder is placed in a quartz boat and heated to 950℃ at a heating rate of 5℃ / min in a nitrogen environment, and then cooled to room temperature to obtain a black powder. The obtained solid is ground into a fine powder to obtain an N-doped porous carbon supported Fe single-atom catalyst, which is denoted as ZIF 8@FePhenPDA-950.

[0081] From Figure 3 It can be seen that the material obtained by step-by-step pyrolysis has better performance. This is because under the condition of a trimethylolamine alkaline buffer solution, ZIF8 nanomaterials, a transition metal source (M), phenanthroline, and dopamine are used as raw materials, anhydrous ethanol is used as a solvent, MPhenPDA polymers are formed by stirring at room temperature to wrap ZIF-8 nanomaterials (MPhenPDA@ZIF8); gradient pyrolysis is carried out under the protection of nitrogen or inert gas to obtain N-doped carbon wrapped ZIF8 derived porous carbon composites; at a high temperature of 900-1000℃, the metal atoms are further coordinated with the nitrogen on the N-doped carbon and ZIF8 derived porous carbon composites through chemical bonds, thereby overcoming the huge surface free energy of a single metal atom, and finally obtaining a transition metal single-atom catalyst with atomically dispersed M-N4 active sites (MPhenPDA@ZIF8-950).

[0082] Comparative Example 3

[0083] The difference between the comparative example and Example 1 is that dopamine is not added during the synthesis of the precursor ZIF8@FePhenPDA in step 2), specifically:

[0084] 3) Synthesis of ZIF8@FePhen:

[0085] 22.5 mg Phen, 21.8 mg C4H6FeO4 were dissolved in 100 ml deionized water, and ultrasonic dispersion was performed for 20 min to obtain solution I;

[0086] 250 mg ZIF8 was dissolved in 100 ml ethanol, and ultrasonic dispersion was performed for 20 min to obtain solution II;

[0087] Solution I was poured into solution II, and stirring was performed at 25°C for 18 h to form a precursor ZIF8@FePhen. Centrifugation was performed and washing was performed three times with methanol. Drying was performed in a drying box at 70°C overnight to obtain a ZIF8@FePhen powder sample.

[0088] The remaining steps were the same as those in Example 1, and a N-doped porous carbon supported Fe monatomic catalyst was prepared to obtain ZIF8@FePhen-950.

[0089] Figure 4 The performance of the catalyst prepared in this comparative example was compared with that in Example 1, Figure 5 The spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the Fe catalyst prepared in this comparative example showed that metal Fe atoms formed clusters and metal nanoparticles in the HAADF mode, and therefore the Fe monatomic catalyst was not successfully synthesized. This is because the lack of polydopamine material to inhibit thermal migration led to easy aggregation of Fe atoms during pyrolysis, forming metal iron nanoparticles.

[0090] Comparative Example 4

[0091] This comparative example was different from Example 1 in that the added ZIF8 in step 2) was adjusted to be pyrolyzed ZIF8 (NC). Specifically:

[0092] The ZIF-8 white powder in step 1 was first placed in a quartz boat and heated to 950°C at a heating rate of 5°C / min in a nitrogen environment, and then heat preservation was performed for 2 h. Cooling to room temperature obtained a black powder, which was recorded as NC. 2) Synthesis of NC@FePhenPDA:

[0093] 22.5 mg Phen, 21.8 mg C4H6FeO4 were dissolved in 100 ml deionized water, and ultrasonic dispersion was performed for 20 min to obtain solution I;

[0094] 250 mg black powder NC, 120 mg tris-hydroxymethyl methylamine were dissolved in 100 ml ethanol, and ultrasonic dispersion was performed for 20 min to obtain solution II;

[0095] Solution I was poured into solution II, stirred at 25℃ for 18h to form precursor NC@FePhenPDA, centrifuged and washed with methanol for three times, and dried in a drying oven at 70℃ overnight to obtain a NC@FePhenPDA powder sample.

[0096] 3) Gradient temperature control pyrolysis:

[0097] The NC@FePhenPDA powder was placed in a quartz boat and heated to 550℃ at a heating rate of 2℃ / min in a nitrogen environment, and kept for 2h;

[0098] Then the heating rate was continued to 950℃ at 5℃ / min, and after keeping for 2h, it was cooled to room temperature to obtain a black powder. The obtained solid was ground into a fine powder to obtain an N-doped porous carbon loaded Fe monatomic catalyst, denoted as NC@FePhenPDA-950.

[0099] Figure 6 The ORR performance graph of the catalyst prepared for this comparative example was obtained. From the graph, it can be seen that the half-wave potential of the catalyst is less than that of Example 1.

[0100] Example 5

[0101] The difference between this comparative example and Example 1 is that the molar ratio of metal salt to dopamine in the process of synthesizing the precursor ZIF8@FePhenPDA in step 2) is adjusted to 1:0.25, 1:0.5, 1:1, 1:2 and 1:3, respectively, to explore the influence of different ratios of metal salt and dopamine on the performance of the catalyst material, and the results are shown in Table 1.

[0102] Table 1 Influence of different ratios of metal salt and dopamine on the performance of the material

[0103]

[0104] As can be seen from Table 1, the introduction of polydopamine material can not only inhibit the thermal migration of metal atoms and prevent the generation of metal nanoparticles or clusters, but also dopamine can act as a reducing agent, which helps to uniformly disperse metal ions on the carrier by complexing with metal ions, thereby enhancing the dispersion performance of the catalyst.

[0105] Dopamine can also increase the surface area of metal nanoparticles and the nitrogen content to anchor more metal atoms, form a synergistic effect with metal ions, change the electronic state of metal ions, thereby exposing more active sites, and form a hierarchical porous carbon structure with micro-pores, mesopores and macropores coexisting, wherein the micro-pores are beneficial to the increase of specific surface area and the exposure of catalytically active sites, and the macropores / mesopores promote the transport of substances and improve the accessibility of catalytically active sites. The complex pore structure is beneficial to improving the mass transfer efficiency, thereby improving the ORR electrocatalytic activity of the catalyst.

[0106] However, with the increase of dopamine content, the half-wave potential is continuously decreased, and the kinetic current density also shows a downward trend. This is because when a small amount of dopamine is added, the polydopamine layer formed cannot completely cover the surface of the ZIF8 material, which will cause a small part of the metal atoms to migrate; when an excess of dopamine is added, the polydopamine layer formed will be thicker, so that more active sites cannot be exposed, resulting in the decrease of the ORR activity of the catalyst.

[0107] To sum up, the application provides a universal synthesis method of single-atom catalyst, which is effective for Fe, Co, Ni, Mn and other metals, solves the defect that other methods are only effective for one kind of metal, and is simple and effective, and can be used for large-scale synthesis of single-atom catalyst.

[0108] The catalyst prepared by the method has a three-dimensional hierarchical porous structure with a hollow structure, which can improve the mass transfer rate and expose more active sites to promote the mass transfer process, so that the catalyst material has extremely high catalytic activity. The Fe-N4 coordination structure acts as an active site for the oxygen reduction reaction, and the adsorption and reduction of oxygen and the desorption of products occur.

[0109] It should be noted that the above examples are only used to illustrate the technical solutions of the application and are not limiting. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the application, and all should be covered in the scope of the claims of the application.

Claims

1. A method for preparing a nitrogen-doped porous carbon supported single-atom catalyst, characterized in that: The application relates to a single-atom catalyst and a preparation method thereof. Phen, dopamine (DA) and a transition metal source (M) are dissolved in deionized water, ultrasonic dispersion is carried out, and solution I is obtained; ZIF8 and trimethylamine are dissolved in ethanol, ultrasonic dispersion is carried out, and solution II is obtained; solution I is poured into solution II, stirring is carried out, a precursor ZIF8@MPhenPDA is formed, centrifugal separation, washing and drying are carried out, and a ZIF8@MPhenPDA powder sample is obtained; The ZIF8@MPhenPDA powder is gradient temperature control pyrolyzed; the gradient temperature control pyrolysis is that the temperature is first increased to 500-550 DEG C, and the temperature is kept for 1-3 hours; then the temperature is continuously increased to 900-1000 DEG C, and the temperature is kept for 2-3 hours; wherein, the temperature increasing rate is 2-5 DEG C / min, and the temperature decreasing rate is 3-8 DEG C / min; and after cooling, a nitrogen-doped porous carbon loaded single-atom catalyst is obtained; The nitrogen-doped porous carbon loaded single-atom catalyst is composed of a nitrogen-doped porous carbon composite carrier and a single-atom active component loaded on the carrier; The composite carrier is obtained by coating ZIF nanomaterials with phenanthroline and dopamine polymers, and the single-atom active component includes one of Fe, Co, Ni and Mn; The single-atom active component is from one of Fe (II), Co (II), Ni (II) and Mn (II) metal salts, and the molar ratio of the metal salt to dopamine is 1:0.25-1.

2. The method for preparing a nitrogen-doped porous carbon supported single-atom catalyst according to claim 1, characterized in that: The preparation method of the ZIF8 comprises the following steps: 2-methyl imidazole and zinc nitrate are respectively dissolved in anhydrous methanol, ultrasonic dispersion is carried out, and then stirring is carried out, so that ZIF8 is formed; wherein, the molar ratio of zinc nitrate to dimethyl imidazole is 1:(4-10).

3. The method of claim 1, wherein the method is characterized by: The transition metal source (M) includes one of Fe (II), Co (II), Ni (II) and Mn (II) metal salts.

4. The method for preparing a nitrogen-doped porous carbon supported single-atom catalyst according to claim 3, characterized in that: The transition metal source (M) includes one of C4H6FeO4, C4H6CoO4, C4H6NiO4 and C4H6MnO4.

5. The method for preparing the nitrogen-doped porous carbon-supported single-atom catalyst as described in claim 1, characterized in that: In the precursor ZIF8@MPhenPDA, the molar ratio of phenanthroline, the transition metal source, dopamine and trimethylamine is 1:1:(0.25-1):

8.

6. The nitrogen-doped porous carbon supported single-atom catalyst prepared by the method according to claim 1, and application of the nitrogen-doped porous carbon supported single-atom catalyst. The single-atom catalyst is used as an electrocatalyst in an oxidation-reduction reaction.

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