Monodisperse mesoporous metal-nitrogen-carbon catalyst, preparation method and application thereof

Abstract

The present application relates to the technical field of catalyst, in particular to a monodisperse mesoporous metal-nitrogen-carbon catalyst, a preparation method and application thereof, the preparation method comprises the following steps: S1, dissolving 1,3,5-trimethylbenzene and polyoxypropylene-polyoxyethylene copolymer in water, ultrasonic dispersion to obtain solution a; and dissolving melamine, formaldehyde and strong base in water, heating to obtain solution b; S2, adding the solution a and a metal source into the solution b, adding acid liquid dropwise to initiate polycondensation, and then centrifugal drying to obtain a precursor; S3, pyrolyzing the precursor to obtain a monodisperse mesoporous metal-nitrogen-carbon fuel cell oxygen reduction catalyst. The catalyst prepared by the present application has a mesoporous structure, a high nitrogen doping content, a high catalyst activity, an efficient mass transfer effect, and can be applied to a cathode catalyst of an anion exchange membrane fuel cell or a metal-air battery, and exhibits good activity and durability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a monodisperse mesoporous metal-nitrogen-carbon catalyst, a preparation method and application thereof. BACKGROUND

[0002] Fuel cells have unique advantages such as high energy, green environmental protection and the like because the oxidant is oxygen in air, and are a research hotspot in the field of energy cells. As a key component of fuel cells, the kinetics of cathode oxygen reduction reaction (ORR) is slow, which brings a large overpotential, and at present, is seriously dependent on noble metal platinum. However, the high cost, resource scarcity and poor stability of platinum greatly limit the popularization of fuel cells in commercial applications. Therefore, the development of low-cost, high-activity and long-durability alternative catalysts is crucial for promoting development.

[0003] Metal-nitrogen-carbon structures are one of the most widely studied catalyst structures, because metal sites can directly adsorb O2 molecules and destroy O-O bonds, thereby exhibiting good catalytic activity. According to different synthesis conditions and coordination environments, metal atoms have different electronic structures, which significantly affect the catalytic performance.

[0004] Although metal-carbon-based catalysts have achieved numerous results, the ORR activity of such materials is still difficult to meet the actual application requirements as a whole. The typical pore diameter of most high-surface-area porous carbon materials is less than 2 nanometers, and protons and reactants are difficult to enter, resulting in poor electrocatalytic activity. Ideal porosity helps to expose more active sites, promote mass transfer, and strengthen the interaction between active sites, electrons and reactants. At present, soft template method and hard template method are often used to prepare mesoporous materials with different structures. However, such nano-synthesis strategies are tedious, complex and time-consuming, and are not suitable for mass production. On the other hand, it is still a challenge to simply obtain uniformly doped materials with high active site density by pyrolysis method. SUMMARY

[0005] The purpose of the embodiments of the present application is to overcome the shortcomings of the prior art structure, and to provide a monodisperse mesoporous metal-nitrogen-carbon catalyst, a preparation method and application thereof, which solves the problems of the prior art, such as complicated synthesis, insufficient exposure of active sites, low utilization rate, poor catalytic activity and unsuitability for batch production.

[0006] In order to achieve the above-mentioned application purposes, the embodiments of the present application first provide a preparation method of a monodisperse mesoporous metal-nitrogen-carbon catalyst, which comprises the following steps:

[0007] S1, dissolving 1, 3, 5-trimethylbenzene and polyoxypropylene-polyoxyethylene copolymer in water, and ultrasonic dispersion to obtain solution a;

[0008] and dissolving melamine, formaldehyde and strong base in water to obtain solution b;

[0009] S2, adding the solution a and a metal source into the solution b, adding an acid solution to initiate polycondensation, and then centrifuging and drying to obtain a precursor;

[0010] S3, pyrolyzing the precursor to obtain a monodisperse mesoporous metal-nitrogen-carbon catalyst.

[0011] The purpose of adding the acid solution is to catalyze the polycondensation, reduce the pH of the system, trigger the cross-linking polycondensation of the melamine-formaldehyde prepolymer (hydroxymethyl melamine) to form a rigid resin network connected by methylene bridges, and protonate the surface of the micelles to enhance the electrostatic attraction between the positively charged MF prepolymer and the negatively charged ions, thereby promoting the uniform doping of iron.

[0012] Further preferably, the metal source is selected from an iron source, a cobalt source and a nickel source; the iron source is selected from one of potassium ferricyanide, ferric chloride, ferric nitrate and ferric sulfate; the cobalt source is selected from one of potassium cobalticyanide, cobalt chloride, cobalt nitrate and cobalt sulfate; the nickel source is selected from one of potassium tetracyanoniickelate, nickel chloride, nickel sulfate and nickel nitrate; and the strong base is selected from one of sodium hydroxide and potassium hydroxide or a combination of both.

[0013] Further preferably, the mass ratio of the 1,3,5-trimethylbenzene to the polyoxypropylene-polyoxyethylene copolymer is (0.5-3.0 g):(0.5-1.0 g).

[0014] Further preferably, the mass ratio of the melamine, formaldehyde and strong base is (0.1-1 g):(0.08-0.2 g):(0.0001-0.001 g).

[0015] Further preferably, the specific method of step S3 is to heat to 700-800℃ at 1-2℃ / min under an inert atmosphere, and the pyrolysis duration is 3h.

[0016] Further preferably, the acid solution is a hydrochloric acid solution with a concentration of 37 wt%, and the dropwise addition amount is 50-200μL.

[0017] In addition, the present application also provides a monodisperse mesoporous metal-nitrogen-carbon catalyst prepared by the above method, wherein:

[0018] The monodisperse microspheres have a particle size of 100-250nm and a mesopore size of 10-30nm.

[0019] The specific surface area is ≥750m 2 / g, and the mesopore volume is ≥1.20cm 3 / g.

[0020] The metal is dispersed in the nitrogen-doped carbon matrix at an atomic level.

[0021] Further preferably, the metal is at least one of Fe, Co and Ni.

[0022] In addition, the application also provides an application of the catalyst in the oxygen reduction reaction in the cathode of a fuel cell.

[0023] In addition, the application also provides an application of the catalyst in the cathode catalytic layer of a zinc-air battery.

[0024] In addition, the application also provides a zinc-air battery, wherein the cathode comprises the catalyst.

[0025] By using the technical scheme, the monodisperse mesoporous metal-nitrogen-carbon fuel cell oxygen reduction catalyst prepared by the application is synthesized by template-free self-assembly, in-situ doping-limited pyrolysis, the interaction between the metal and the carrier is enhanced, the interface charge transfer is promoted, the specific surface area of the material is increased by the mesopores, a large number of anchoring sites are provided, the metal aggregation is inhibited, the active sites are fully exposed, the mass transfer efficiency is improved, the efficient dispersion of the metal active sites and the precise regulation of the mesoporous structure are realized, the raw material cost is low, the operation is safe, the synthesis strategy is simple, the synthesis strategy is easy to repeat, and the scale production can be realized by the equal proportion quantization. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above features and advantages of the application will become more apparent and easily understood from the following description of exemplary embodiments thereof in conjunction with the accompanying drawings.

[0027] Figure 1 TEM image of the monodisperse mesoporous metal-nitrogen-carbon material of Example 1 before carbonization;

[0028] Figure 2 TEM image of the monodisperse mesoporous metal-nitrogen-carbon material of Example 2 before carbonization;

[0029] Figure 3 TEM image of the monodisperse mesoporous metal-nitrogen-carbon material of Example 3 before carbonization;

[0030] Figure 4 Nitrogen adsorption-desorption capacity curve of the monodisperse mesoporous metal-nitrogen-carbon material prepared in Examples 1 to 3 after carbonization at the same carbonization temperature;

[0031] Figure 5 TEM image of the monodisperse mesoporous iron-nitrogen-carbon material of Example 1;

[0032] Figure 6 TEM image of the monodisperse mesoporous cobalt-nitrogen-carbon material prepared in Example 6;

[0033] Figure 7 X-ray diffraction patterns of oxygen reduction catalysts prepared for Examples 4 to 6;

[0034] Figure 8 Nls high resolution spectra of oxygen reduction catalysts prepared for Examples 7 to 9;

[0035] Figure 9 Graph showing oxygen reduction catalytic activity of oxygen reduction catalysts prepared for Examples 1 to 3 and a commercial Pt / C catalyst in alkaline medium;

[0036] Figure 10 LSV curves at different rotation speeds and K-L plots at different potentials of an oxygen reduction catalyst prepared for Example 4 (inset);

[0037] Figure 11 Power density curves of a zinc-air battery assembled with an oxygen reduction catalyst prepared for Example 4;

[0038] Figure 12 Graph showing the results of a 250 h stability electrochemical test of a zinc-air battery assembled with an oxygen reduction catalyst prepared for Example 7 at a constant current density (10 mA / cm 2 ). DETAILED DESCRIPTION

[0039] The present application will be described in detail below with specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0040] The terms such as "front", "back", "left", "right", "inner", "outer" and the like cited in the specification are only for the convenience of clear description, and are not intended to limit the scope of the present application. The change or adjustment of the relative relationship without substantial change of the technical content is also considered as the scope of the present application.

[0041] In the description of the following examples, unless otherwise explicitly specified and limited, the term "connection" and the like should be understood broadly, for example, "connection" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or indirect connection through intermediate medium, can be internal communication of two elements or interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] Example 1

[0043] The preparation steps of this example are:

[0044] (1) 0.6 g of polyoxypropylene polyoxyethylene copolymer was dissolved in 2 g of 1,3,5-trimethylbenzene, and magnetically stirred for 2 h;

[0045] (2) 0.3 g of melamine was dissolved in 50 ml of water, heated to dissolve, 0.02 g of formaldehyde, 0.0002 g of sodium hydroxide were added, and stirred for 1 hour;

[0046] (3) The two solutions were mixed, 0.1 g of potassium ferricyanide was added, stirred for 10 minutes, 50 μL of 37 wt% hydrochloric acid was added dropwise, stirred for 3 h to complete the reaction, and washed with water and ethanol for 3 times by centrifugation to obtain a light yellow powder;

[0047] (4) The light yellow powder was placed in an inert gas, carbonized at a temperature of 800℃ with a heating rate of 1℃ / min for 3 hours to obtain the monodisperse mesoporous iron-nitrogen-carbon M-Fe / N / C.

[0048] It can be understood that the above-mentioned selected hydrochloric acid solution is only an example, and other acidic solutions can be selected by those skilled in the art to replace it according to the metal precursor doped, and the acid concentration, dropwise rate, washing procedure and other process parameters are selected accordingly, as long as the following conditions are met:

[0049] Non-weak acid to ensure rapid triggering of polycondensation; for example, acetic acid, pKa is 4.75;

[0050] No strong oxidizing / reducing property to avoid destroying the structure of the metal precursor or prepolymer; for example, oxalic acid reduces potassium ferricyanide;

[0051] The anion should not cause side reactions such as precipitation and complexation after being added; for example, sulfuric acid, its SO4 2- may form a slightly soluble substance with Fe 3+ ;

[0052] Safe operation; for example, hydrofluoric acid is highly toxic and corrosive to instruments.

[0053] Since the chemical properties of acids are well known in the art, the acidic solutions meeting the process requirements of the present application are not listed one by one in the examples.

[0054] Example 2

[0055] Compared with Example 1, the amount of 1,3,5-trimethylbenzene in step (1) of this example is adjusted to 1.5 g, and 0.1 g of ferric chloride is used instead of potassium ferricyanide in step (3), and the others are the same as Example 1.

[0056] Example 3

[0057] The amount of 1,3,5-trimethylbenzene in step (1) is adjusted to 0.8 g, and the potassium ferricyanide in step (3) is replaced with 0.1 g of ferric sulfate in this example compared with Example 1, and the others are the same as Example 1.

[0058] Figure 1 TEM image of monodisperse mesoporous iron-nitrogen-carbon microspheres before carbonization of Example 1.

[0059] wherein, Figure 2 and Figure 3 TEM images of monodisperse mesoporous iron-nitrogen-carbon microspheres before carbonization of Example 2 and Example 3, indicating the monodispersity and mesoporous characteristics of the microspheres, Figure 5 Comparison of TEM images of monodisperse mesoporous iron-nitrogen-carbon Figure 1 It is found that the microsphere structure is well preserved before and after carbonization, with rich internal pores, a flower-like structure, and clear pore network, and uniform distribution of mesopores or macropores can be observed, with some pores penetrating through.

[0060] Examples 1 to 3 adjust the amount of 1,3,5-trimethylbenzene to adjust the pore channels of the iron-nitrogen-doped monodisperse mesoporous microspheres. The microspheres with a 0.8 g dosage show a porous surface; the microspheres with a 1.5 g dosage have further increased pore size, making the microspheres exhibit a honeycomb-like structure with more regular pores, and the overall morphology still maintains a good spherical shape; the microspheres with a 2 g dosage have slightly increased pore size, uniform mesopore size, and more obvious openings on the surface of some microspheres, maintaining a highly developed pore network. It can be seen that the larger the amount of 1,3,5-trimethylbenzene, the more abundant the pore channels of the prepared microspheres.

[0061] Characteristics analysis of the pore size of the monodisperse mesoporous iron-nitrogen-carbon prepared in Examples 1 to 3 at different amounts of 1,3,5-trimethylbenzene, and the test data are shown in Table 1.

[0062]

[0063] As can be seen from Table 1, the internal pore size characteristics of the mesoporous carbon microspheres carbonized at different amounts of 1,3,5-trimethylbenzene are different, and the specific surface area increases from low to high as the amount increases. This is mainly because the multi-level pore carbonization of Example 1 causes the internal micropores to collapse and convert into mesopores; the microporous structure of Example 3 is relatively low and stays on the surface, which is not conducive to the distribution of the internal multi-level gradient pore structure. Example 1 exhibits a higher specific surface area of 766.06 m 2 g -1 , a higher mesopore volume of 1.24 cm 3 g -1The micropore volume is small. Therefore, the pore size of the mesoporous carbon microspheres can be adjusted by adjusting the amount of 1,3,5-trimethylbenzene.

[0064] Through comparative analysis Figure 4 The nitrogen adsorption-desorption isotherms of the three different embodiments show that: in the low-pressure range (P / P0 = 0-0.1), the adsorption capacity of Example 1 is slightly higher than that of Examples 2 and 3, indicating that Example 1 may have more microporous structures. The presence of micropores is crucial for improving the specific surface area and adsorption performance of the material. In the medium-pressure range (P / P0 = 0.1-0.9), the adsorption capacity of the three embodiments shows a similar trend, but the adsorption capacity of Example 1 is consistently slightly higher than that of the other two embodiments. This indicates that in the medium-pressure range, all three embodiments have a certain amount of mesoporous structures, and the mesoporous structure of Example 1 may be more abundant, which has a positive impact on the adsorption performance and catalytic activity of the material. In the high-pressure range (P / P0 = 0.9-1.0), the adsorption capacity of Example 1 is significantly higher than that of Examples 2 and 3, indicating that Example 1 may have more macroporous structures. The presence of macropores helps to improve the diffusion performance and adsorption rate of the material. Figure 4 This fully illustrates the differences in the internal pore size characteristics of the material under different embodiments. By adjusting the preparation conditions, precise control of the material's pore structure can be achieved, thereby optimizing the material's performance.

[0065] Example 4

[0066] The preparation steps in this embodiment are as follows:

[0067] 1) Dissolve 0.6g of polyoxypropylene-polyoxyethylene copolymer in 1.5g of 1,3,5-trimethylbenzene and stir magnetically for 2 hours;

[0068] (2) Take 0.5g of melamine, dissolve it in 50ml of water, heat to dissolve, add 0.15g of formaldehyde and 0.001g of potassium hydroxide, and stir for 1 hour;

[0069] (3) Mix the two solutions, add 0.3g cobalt nitrate, stir for 30 minutes, add 100μL of 37wt% hydrochloric acid dropwise, stir for 3h until the reaction is complete, centrifuge and wash three times with water and ethanol to obtain a light purple powder;

[0070] (4) The light purple powder was placed in an inert gas and carbonized at 700°C for 3 hours at a heating rate of 1°C / min to obtain the monodisperse mesoporous cobalt nitrogen carbon M-Co / N / C.

[0071] Example 5

[0072] Compared with Example 4, in this embodiment, cobalt nitrate in step (3) is replaced with 0.3g of cobalt chloride, and the carbonization temperature in step (4) is adjusted to 600℃. All other aspects are the same as in Example 4.

[0073] Example 6

[0074] Compared with Example 4, in this embodiment, cobalt nitrate in step (3) is replaced with 0.3g of cobalt sulfate, and the carbonization temperature in step (4) is adjusted to 900℃. All other aspects are the same as in Example 4.

[0075] The pore size characteristics of monodisperse mesoporous cobalt-nitrogen-carbon M-Co / N / C samples prepared at different carbonization temperatures in Examples 4 to 6 were analyzed, and the test data are shown in Table 2.

[0076]

[0077] As shown in Table 2, the specific surface area increases from 600℃ to 700℃, but decreases when the temperature reaches 900℃. This is mainly because the carbonization temperature in Example 6 was too high, leading to structural collapse, while the carbonization temperature in Example 5 was relatively too low, which was not conducive to the distribution of the multi-level gradient internal pore structure. Figure 6 The collapse of the material structure and the aggregation of metal particles can be clearly seen.

[0078] X-ray diffraction patterns of the oxygen reduction catalysts prepared in Examples 4, 5, and 6 Figure 7 As shown. Figure 7 As shown, the prepared oxygen reduction catalyst mainly contains four elements: C, N, O, and Co. Through the samples of Examples 4, 5, and 6, it can be seen that the N content is highest after carbonization at 700℃, and the nitrogen doping efficiency reaches its optimal state, effectively regulating the electronic structure of the catalyst and increasing the number and activity of its surface active sites.

[0079] Example 7

[0080] The preparation steps in this embodiment are as follows:

[0081] 1) Dissolve 0.6g of polyoxypropylene-polyoxyethylene copolymer in 2.5g of 1,3,5-trimethylbenzene and stir magnetically for 2 hours;

[0082] (2) Take 1.0g of melamine, dissolve it in 50ml of water, heat to dissolve, add 0.05g of formaldehyde and 0.001g of potassium hydroxide, and stir for 30 minutes;

[0083] (3) The two solutions were mixed, 0.5 g of nickel chloride was added, stirred for 30 minutes, 100 μL of 37 wt% hydrochloric acid was added dropwise, stirred for 3 h until the reaction was complete, washed with water and ethanol 3 times by centrifugation, and a light green powder was obtained;

[0084] (4) The light green powder was carbonized in inert gas at a temperature of 800℃ with a heating rate of 1℃ / min for 3 hours to obtain the monodisperse mesoporous nickel-nitrogen-carbon M-Ni / N / C.

[0085] Example 8

[0086] Compared with Example 7, the heating rate in step (4) of this example was adjusted to 2℃ / min, and the other steps were the same as those in Example 7.

[0087] Example 9

[0088] Compared with Example 8, the heating rate in step (4) of this example was adjusted to 5℃ / min, and the other steps were the same as those in Example 7.

[0089] The pore size of the monodisperse mesoporous nickel-nitrogen-carbon M-Ni / N / C prepared in Examples 7-9 at different carbonization temperatures was analyzed, and the test data are shown in Table 3.

[0090]

[0091] The formulations and process parameters of each example were statistically analyzed, as shown in Table 4.

[0092] Table 4

[0093]

[0094] As can be seen from Table 3, the pore size characteristics of the mesoporous carbon microspheres obtained by carbonization at different heating rates are significantly different. With the increase of the heating rate, the specific surface area shows a downward trend, which indicates that a slower heating rate is beneficial to form a larger specific surface area. Specifically, the specific surface area of Example 7 (1℃ / min) is the highest, reaching 752.43 m 2 / g, while the specific surface area of Example 9 (5℃ / min) is the lowest, reaching 301.56 m 2 / g. In addition, the average pore diameter also decreases with the increase of the heating rate, which may be due to the rapid closure of the pore structure during carbonization at a faster heating rate. The mesopore volume and micropore volume show similar trends as the specific surface area, i.e., they decrease with the increase of the heating rate. The mesopore volume of Example 7 is 1.20 cm 3 / g, and the micropore volume is 0.0645 cm 3 / g, while the mesopore volume and micropore volume of Example 9 decrease to 0.3 cm 3 / g and 0.0231 cm 3 / g. By adjusting the heating rate, the pore size and distribution of the mesoporous carbon microspheres can be effectively regulated, thereby optimizing their performance.

[0095] As can be seen from Table 3, under the premise of only serving as a metal source and not participating in pore formation, different heating rates still exhibit significant regulation effects on the pore size characteristics of the prepared monodisperse mesoporous nickel-nitrogen-carbon microspheres: as the heating rate increases from 1 ℃ / min to 5 ℃ / min, the specific surface area decreases significantly from 752.43 m 2 / g to 301.56 m 2 / g, the average pore size rapidly decreases from 27.89 nm to 3.23 nm, and the mesopore volume and micropore volume also decrease synchronously. This result again confirms that the formation and evolution of the mesoporous structure are mainly controlled by pyrolysis kinetics, and are not directly related to the types of metal sources and anion ligands. In theory, as long as the total amount of metal elements and the atomic dispersion state are consistent, each of the soluble salts (nitrate, chloride, sulfate, cyanide complex, etc.) of iron, cobalt, and nickel listed in the present application will be decomposed into corresponding atomic metal species and anchored by the nitrogen-doped carbon framework in a high-temperature inert atmosphere, and the anions will be completely volatilized or converted into harmless gases, without introducing additional template effects or affecting the pore size distribution. Therefore, the above-mentioned metal salts can be replaced with each other without substantially changing the support structure and the final catalytic performance, which is conducive to process simplification and intellectual property protection.

[0096] From the peak separation analysis of the N1s high-resolution spectrum of Figure 8 It can be known from the peak separation analysis of the N1s high-resolution spectrum of the catalyst that the types of N elements in the catalyst mainly include pyridine-type N, pyrrole-type N (Ni-N species), graphite-type N, and nitrogen oxides, wherein the peak positions of the pyrrole-type N and the Ni-N species are close and difficult to distinguish. It can be known from the comparison that Example 7 exhibits the optimal contents of pyrrole nitrogen and pyridine nitrogen, which is related to its specific carbonization condition. Specifically, Example 7 adopts a heating rate of 1 ℃ / min, and the XPS spectrum shows that the contents of pyrrole nitrogen and pyridine nitrogen are relatively high, and the content of graphite nitrogen is relatively low. This result shows that a slower heating rate can be more conducive to the formation of pyrrole and pyridine structures by nitrogen atoms in the carbonization process. The formation of such structures can be related to the fact that a slower heating rate gives nitrogen atoms more time for structural reorganization and optimization, thereby promoting the formation of pyrrole nitrogen and pyridine nitrogen. As the heating rate increases, the contents of pyrrole nitrogen and pyridine nitrogen further decrease, and the content of graphite nitrogen further increases, and a faster heating rate leads to the graphite structure being more easily formed by nitrogen atoms in the carbonization process.

[0097] Examples 1 to 9 above demonstrate that by adjusting the amount of pore-forming agent, the calcination and carbonization temperature, and the heating rate, the distribution of the multi-level channels, the level of nitrogen content, and their existing forms can be adjusted from the outside to the inside, thereby promoting the effective transport of water and gas, achieving efficient mass transfer at the three-phase interface during the catalytic process, and obtaining a highly efficient oxygen reduction catalyst.

[0098] Test case

[0099] Weigh 2.5 mg each of the electrocatalyst material from Examples 1-3 and 40 wt% Pt / C, and add 80 μL of water, 400 μL of ethanol and 20 μL of Nafion in sequence. Sonicate until homogeneous, and then drop onto a disk electrode for oxygen reduction electrochemical performance testing.

[0100] Linear sweep voltammetry (LSV) test, such as Figure 9 As shown, the oxygen reduction half-wave potential of the sample in Example 1 reached 0.889 V vs RHE, which is 57 mV higher than the half-wave potential (0.832 V) of the sample in Example 3 with incomplete pore exposure, and 32 mV higher than the commercial Pt / C catalyst (0.857 V), demonstrating good oxygen reduction electrocatalytic activity. This is mainly due to the increased specific surface area activated by the rich hierarchical pore structure, which promotes mass transfer and thus improves the utilization rate of active sites.

[0101] Depend on Figure 10 It can be seen that the hydrogen peroxide yield was tested using the rotating disk electrode technique. The oxygen reduction catalyst prepared in Example 4 was calculated to have an average electron transfer number of 4.04 using the KL equation, indicating that it has a 4-electron reaction selectivity and excellent ORR catalytic selectivity.

[0102] The catalyst was uniformly drop-coated onto hydrophobic HCP120 carbon paper as an air cathode, and loaded with 1 mg·cm⁻¹. -2 A water-based zinc-air battery was assembled using a polished zinc sheet (0.20 mm thick) as the anode and a 6 M KOH solution containing 0.2 M Zn(Ac)2·2H2O as the electrolyte.

[0103] Figure 11 The discharge and power density curves of the liquid battery assembled in Example 4 are shown. The maximum power density of the battery was calculated to be 147.2 mW·cm. -2 This is significantly higher than that of Pt / C-based zinc-air batteries (91.4 mW·cm⁻¹). -2 This demonstrates the significant advantages of the electrode material structure design, accelerating the internal reaction rate and ion transport efficiency. Compared to traditional Pt / C-based zinc-air batteries, it exhibits superior energy conversion and output capabilities.

[0104] The liquid cell assembled with the sample prepared in Example 7 was tested at 10 mA cm 2 The cycle charge-discharge was carried out at constant current density, and the cell could be cycled stably for more than 250 h Figure 12 ), and the discharge voltage was stable without obvious decay within 250 hours, which indicated that the cell had superior reversibility and lower energy loss. Thus, it can be concluded that the cell with the air cathode prepared in Example 7 had excellent performance.

[0105] The above embodiments are only one of the preferred embodiments of the present application, and for the sake of brevity, all the embodiments cannot be listed one by one, and any embodiment that can embody the technical solutions of the claims of the present application is within the protection scope of the present application.

[0106] It should be noted that the above is a further detailed description of the present application in combination with specific embodiments, and the specific embodiments of the present application are not limited to the above. Under the guidance of the above embodiments, those skilled in the art can make various improvements and modifications on the basis of the above embodiments, and these improvements or modifications are within the protection scope of the present application.

Claims

1. A method for preparing a monodisperse mesoporous metal-nitrogen-carbon catalyst, characterized by, The method comprises the following steps: S1, dissolving 1, 3, 5-trimethylbenzene and polyoxypropylene polyoxyethylene copolymer in water, ultrasonic dispersion to obtain solution a; and dissolving melamine, formaldehyde and strong base in water, heating to obtain solution b; S2, adding the solution a and a metal source to the solution b, adding acid liquid to initiate polycondensation, and then centrifugal drying to obtain a precursor; S3, pyrolyzing the precursor to obtain a monodisperse mesoporous metal-nitrogen-carbon catalyst.

2. The method for preparing a monodisperse mesoporous metal nitrogen-carbon catalyst as described in claim 1, characterized in that: The metal source is selected from iron source, cobalt source and nickel source; the iron source is selected from one of potassium ferricyanide, ferric chloride, ferric nitrate and ferric sulfate; the cobalt source is selected from one of potassium cobalticyanide, cobalt chloride, cobalt nitrate and cobalt sulfate; the nickel source is selected from one of potassium tetracyanoniickelate, nickel chloride, nickel sulfate and nickel nitrate; the strong base is selected from one of sodium hydroxide, potassium hydroxide or a combination of the two; and the acid liquid is hydrochloric acid.

3. The method for preparing a monodisperse mesoporous metal nitrogen-carbon catalyst as described in claim 1, characterized in that: The mass ratio of 1, 3, 5-trimethylbenzene to polyoxypropylene polyoxyethylene copolymer is (0.5-3.0 g) : (0.5-1.0 g).

4. The method for preparing a monodisperse mesoporous metal nitrogen-carbon catalyst as described in claim 1, characterized in that: The mass ratio of melamine, formaldehyde and strong base is (0.1-1 g) : (0.08-0.2 g) : (0.0001-0.001 g).

5. The method for preparing a monodisperse mesoporous metal nitrogen-carbon catalyst as described in claim 1, characterized in that, The specific method of step S3 is: under inert atmosphere, heating to 700-800℃ at 1-2℃ / min, and pyrolysis for 3h.

6. A monodisperse mesoporous metal-nitrogen-carbon catalyst prepared by the method of any one of claims 1-5, characterized in that: The monodisperse microspheres have a particle size of 100-250 nm and a mesopore size of 10-30 nm; Specific surface area ≥ 750 m 2 / g, mesopore volume ≥ 1.20 cm 3 / g; The metal is dispersed in the nitrogen-doped carbon matrix at an atomic level.

7. The monodisperse mesoporous metal-nitrogen-carbon catalyst of claim 6, wherein: The metal is at least one of Fe, Co and Ni.

8. Use of the catalyst of claim 6 or 7 in the oxygen reduction reaction of a fuel cell cathode.

9. Use of the catalyst of claim 6 or 7 in the cathode catalytic layer of a zinc-air battery.

10. A zinc-air battery, characterized by, The cathode comprises the catalyst of claim 6 or 7.

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