Method for preparing honeycomb-like sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst in one pot

Abstract

The application belongs to the technical field of monatomic catalysts, and relates to a method for preparing a honeycomb-shaped sulfur-nitrogen co-doped carbon loaded manganese monatomic catalyst through one-pot method, which comprises the following steps: (S1) dissolving an alkali metal salt in water to obtain a template solution; adding a manganese salt, a nitrogen-containing aromatic heterocyclic ligand and an amino acid thiol ligand into the template solution in a molar ratio of 1:(15-25):(10-20), and performing a coordination reaction at 60-80 DEG C to obtain a mixed solution; (S2) freeze-drying the mixed solution to obtain a precursor powder; (S3) carbonizing the precursor powder to obtain carbonized material; (S4) removing the alkali metal salt template from the carbonized material through water washing, and then sequentially performing acid washing, water washing and drying. The application combines the nitrogen-containing aromatic heterocyclic ligand and the amino acid thiol ligand to synergistically coordinate manganese ions, and combines the alkali metal salt template and a freeze-drying process, so that a honeycomb-shaped sulfur-nitrogen co-doped carbon loaded manganese monatomic catalyst with excellent catalytic activity and stability is prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of single-atom catalysts, and particularly relates to a method for preparing a honeycomb-shaped sulfur-nitrogen co-doped carbon loaded manganese single-atom catalyst in one pot. BACKGROUND

[0002] Catalytic oxygen reduction reaction (ORR) is the core cathode reaction process of metal-air batteries, fuel cells and other clean energy devices, which strongly depends on efficient catalysts to reduce the overpotential and improve energy conversion efficiency. Currently, noble metal platinum (Pt) based catalysts such as platinum carbon catalyst (a catalyst in which platinum is loaded on activated carbon) are still the performance benchmark for ORR, but their high cost and the scarcity of Pt in the earth's crust severely restrict their large-scale commercial application. Single-atom catalysts are a frontier direction in current catalytic science research, which have the highest atom utilization, high activity and high selectivity, and have become a research hotspot. Therefore, in recent years, transition metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) are considered as ideal materials to replace noble metal platinum (Pt) based catalysts due to their maximum atom utilization and controllable electronic structure. However, the synthesis of traditional SACs usually faces the following challenges: (1) the commonly used hard template (such as SiO2, MgO) has high cost, and the removal process needs to use strong corrosive reagents (such as hydrofluoric acid), which is not environmentally friendly and dangerous in process; (2) the metal precursor is prone to migration and agglomeration to form nanoparticles during high-temperature pyrolysis, resulting in a decrease in active site density; (3) the prepared catalyst has disordered pore structure, low mass transfer efficiency, and generally low metal loading.

[0003] CN107469855B discloses a preparation method of a nitrogen-doped graphene loaded metal single-atom catalyst. Disodium ethylenediaminetetraacetate is used as a complexing agent to form a stable complex with metal ions through an ion exchange reaction in a liquid phase. After evaporation, the complex is mixed uniformly with an alkali metal salt, and a nitrogen-doped graphene loaded metal single-atom catalyst is obtained through synchronous pyrolysis conversion. The catalyst prepared by the invention has a two-dimensional microstructure with a thickness of 0.5-2 nm and a number of graphene layers of 1-8, and a metal loading of 0.01-10 wt%. The metal single atoms are firmly riveted on the surface of the graphene, and the catalyst has high loading and good thermal stability. The invention uses an alkali metal salt as a reaction medium in a high-temperature solid phase to promote the graphitization of the carbon-containing precursor and form a two-dimensional graphene structure. However, the intrinsic activity of the prepared graphene loaded metal single-atom catalyst in the oxygen reduction reaction (ORR) cannot meet the performance requirements of metal-air batteries.

[0004] Therefore, developing a single-atom catalyst synthesis method capable of simultaneously achieving high metal loading, excellent catalytic activity, excellent stability, and green and economical synthesis has become a key technical problem to be solved in the field. SUMMARY

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The method for preparing the honeycomb-like sulfur-nitrogen co-doped carbon loaded manganese single-atom catalyst by one-pot method comprises the following steps:

[0007] (S1) Dissolve an alkali metal salt in water to form a template solution; add a manganese salt, a nitrogen-containing aromatic heterocyclic ligand and an amino acid thiol ligand according to a molar ratio of 1:(15-25):(10-20) into the template solution, and perform a coordination reaction at 60-80 DEG C under stirring to form a mixed solution; the nitrogen-containing aromatic heterocyclic ligand is selected from at least one of 1,10-phenanthroline and 2,2'-bipyridine; the amino acid thiol ligand is selected from at least one of L-cysteine and D-penicillamine; the molar amount of the manganese salt is calculated based on Mn;

[0008] (S2) Freeze-dry the mixed solution, and obtain a precursor powder after crushing;

[0009] (S3) Place the precursor powder in a closed container, and then carbonize it under an inert atmosphere to obtain a carbonized material;

[0010] (S4) Wash the carbonized material with water to remove the alkali metal salt template, and then sequentially perform acid washing, water washing and drying to obtain the honeycomb-like sulfur-nitrogen co-doped carbon loaded manganese single-atom catalyst.

[0011] On the one hand, the core of the present application lies in the synergistic coordination of the nitrogen-containing aromatic heterocyclic ligand and the amino acid thiol ligand to the manganese ion. This process pre-constructs a stable manganese-organic complex, which lays a molecular foundation for the formation of an atomically dispersed active center. The manganese-organic complex stably anchors the manganese atom in the carbon matrix during the carbonization process, forming a high-density and stable Mn-N x active site. Most importantly, the inventors found that a certain amount of amino acid thiol ligand not only can act together with the nitrogen-containing aromatic heterocyclic ligand to form a more stable manganese-organic complex, thereby effectively inhibiting the migration and agglomeration of manganese atoms during high-temperature carbonization, but also acts as a sulfur source to achieve nitrogen-sulfur co-doping during carbonization. The sulfur atom is doped into the Mn-N xThe carbon matrix around the site co-optimizes the electronic environment of the central manganese atom, reduces the energy barrier of the oxygen reduction reaction (ORR), and thus endows the catalyst with excellent intrinsic activity and stability. In the second aspect, the "one-pot" strategy allows the alkali metal salt template to be precipitated in situ during freeze-drying, physically separates and limits the manganese-organic complex in three-dimensional space, and forms a precursor powder with a fluffy structure composed of alkali metal salt templates and manganese complexes; after carbonization treatment, the organic components in the precursor are converted into a nitrogen and sulfur co-doped carbon skeleton, and manganese is anchored in the form of a single atom in the skeleton; after water washing to remove the template, a stable three-dimensional through-honeycomb-like hierarchical pore structure is formed, which provides the catalyst with rich porosity, greatly promotes the mass transfer (such as O2 and electrolyte diffusion) and product desorption during the reaction process, and effectively improves the catalytic reaction kinetics.

[0012] Preferably, in step (S1), the molar ratio of the manganese salt, the nitrogen-containing aromatic heterocyclic ligand, and the amino acid thiol ligand is 1:(15-20):(10-15). The nitrogen-containing aromatic heterocyclic ligand also serves as a nitrogen source and a carbon source; the amino acid thiol ligand also serves as a sulfur source, an auxiliary nitrogen source, and a carbon source.

[0013] Preferably, in step (S1), the nitrogen-containing aromatic heterocyclic ligand is 1,10-phenanthroline; and the amino acid thiol ligand is L-cysteine.

[0014] Further, in step (S1), the mass ratio of the total mass of the manganese salt, the nitrogen-containing aromatic heterocyclic ligand, and the amino acid thiol ligand to the mass of the alkali metal salt in the template solution is 30-40:100.

[0015] Further, in step (S1), the alkali metal salt is sodium chloride and / or potassium chloride, the concentration of the template solution is 5-20 wt%, the manganese salt is selected from at least one of manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, and acetylacetone manganese, or a hydrate thereof; and the coordination reaction time is 1-3 h.

[0016] Further, in step (S2), the freeze-drying conditions are as follows: the mixed solution is first frozen in liquid nitrogen for 1-3 h, and then vacuum dried at -40 to -30℃ in a cold trap for 12-24 h, with a vacuum degree of 10-30 Pa; and the crushing is air-jet pulverization to a particle size of 100-200 mesh.

[0017] Further, in step (S3), the closed container is an alumina crucible or a corundum boat with a cover; the inert atmosphere is nitrogen and / or argon; and the carbonization conditions are 700-900 DEG C for 2-4 h. The purpose of keeping the container closed during carbonization is to prevent the nitrogen-containing aromatic heterocyclic ligand and the amino acid thiol ligand from being prematurely volatilized and lost before reaching the carbonization temperature, thereby ensuring the full progress of the in-situ carbonization reaction and ensuring the effective formation of the sulfur-nitrogen co-doped carbon matrix and the successful anchoring of the metal manganese.

[0018] Further, in step (S4), the specific step of washing with water to remove the alkali metal salt template is stirring and washing the carbonized material at 40-60 DEG C for 20-50 min using deionized water, for a total of 2-5 times, until no white precipitate is generated in the supernatant detected by silver nitrate solution.

[0019] Further, in step (S4), the acid washing is washing with a 1-3 M hydrochloric acid aqueous solution, a sulfuric acid aqueous solution, or a nitric acid aqueous washing solution for 20-40 min; the water washing is pure water washing until the filtrate is neutral; and the drying is drying at 60-80 DEG C for 12-24 h. The acid washing aims to remove a small amount of unstable metal nanoparticles, and the subsequent water washing aims to completely remove residual acid and the alkali metal salt template.

[0020] In a second aspect, the application further provides a honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese monatomic catalyst, which is prepared by the aforementioned method.

[0021] Further, the honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese monatomic catalyst has a three-dimensional honeycomb-shaped porous structure with a pore size of 0.8-1.5 μm; and the carbon matrix is simultaneously doped with nitrogen atoms and sulfur atoms; the manganese is dispersed in the carbon matrix in the form of monatomic atoms and forms an active site core of Mn-N x .

[0022] Further, the manganese element content of the honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese monatomic catalyst is 2.8-4.0 wt%.

[0023] In a third aspect, the application further provides the use of the honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese monatomic catalyst as a cathode catalyst for a metal-air battery.

[0024] Further, the metal-air battery is a zinc-air battery.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. The present application realizes the controllable preparation of sulfur and nitrogen co-doped carbon supported manganese monatomic catalysts with high manganese loading, atomic dispersion and three-dimensional honeycomb structure by the synergistic coordination of manganese ions with nitrogen-containing aromatic heterocyclic ligands and amino acid thiol ligands, combined with alkali salt templates and freeze-drying process.

[0027] 2. The honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared by the present application has excellent catalytic activity and stability.

[0028] 3. The one-pot preparation method of the present application makes the process convenient, avoids the use of strong corrosive reagents, and is low in cost and easy to scale up. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 XRD pattern of the honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1.

[0030] Figure 2 SEM image of the honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1, wherein (a) is the SEM image at low resolution, and (b) is the SEM image at high resolution.

[0031] Figure 3 XPS image of the honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1, wherein (a) is the N 1s spectrum, and (b) is the S 2p spectrum.

[0032] Figure 4 Oxygen reduction reaction (ORR) performance test chart of the honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1, wherein (a) is the cyclic voltammetry (CV) curve, and (b) is the linear sweep voltammetry (LSV) curve.

[0033] Figure 5 Zinc-air battery performance test chart of the honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1 as a cathode, wherein (a) is the open-circuit voltage curve, (b) is the polarization curve and power density curve, (c) is the cycle rate curve, and (d) is the constant-current discharge curve. DETAILED DESCRIPTION

[0034] The present application will be further described in conjunction with specific embodiments, but the present application is not limited to the following embodiments.

[0035] In the following examples, the experimental methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0036] Pt / C catalyst, i.e. platinum-carbon catalyst, is a catalyst in which platinum is supported on activated carbon, from Suzhou Shengernuo Technology Co., Ltd., and the Pt content is 20wt%.

[0037] Example 1

[0038] (S1) 15.85 g of sodium chloride was dissolved in 150 g of deionized water to form a template solution; 0.198 g (1 mmol) of MnCl2·4H2O (equivalent to 0.126 g of MnCl2), 3.60 g (20 mmol) of 1,10-phenanthroline and 1.82 g (15 mmol) of L-cysteine (i.e. the molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:20:15, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride is 35:100) were added to the template solution, and the coordination reaction was carried out by stirring at 70°C for 2.5 h to form a uniform transparent mixed solution;

[0039] (S2) The mixed solution was poured into a culture dish, first frozen in liquid nitrogen for 2 h, and then vacuum dried at -40°C in a cold trap for 12 h, with the vacuum degree controlled at 10-20 Pa; a precursor powder with a fluffy structure separated by NaCl templates was obtained, which was airflow pulverized to 200 mesh to obtain a precursor powder;

[0040] (S3) The precursor powder was placed in an alumina crucible with a cover, the cover was covered, and then placed in a tube furnace, and heated to 800°C at 8°C / min under an inert atmosphere, and kept for 3 h, and then cooled to room temperature to obtain a carbonized material;

[0041] (S4) The carbonized material was placed in deionized water and stirred at 50°C for 30 min to remove the sodium chloride template, and a total of 3 times of washing was performed until no white precipitate was generated in the supernatant detected by silver nitrate solution; the obtained solid was filtered, and then the solid was sequentially washed with 2M hydrochloric acid aqueous solution for 30 min, washed with pure water until the filtrate was neutral, and dried at 70°C for 24 h, and then cooled to room temperature to obtain a honeycomb-like sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst.

[0042] Example 2

[0043] The rest is the same as example 1, the difference is that the molar ratio of sodium chloride, 1,10-phenanthroline, L-cysteine in step (S1) is different; The specific amount of each material is: 11.53g of sodium chloride, 0.198g (1mmol) of MnCl2·4H2O, 2.70g (15mmol) of 1,10-phenanthroline and 1.21g (10mmol) of L-cysteine. The molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:15:10, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride is 35:100.

[0044] Example 3

[0045] The rest is the same as example 1, the difference is that the molar ratio of sodium chloride, 1,10-phenanthroline, L-cysteine in step (S1) is different; The specific amount of each material is: 18.42g of sodium chloride, 0.198g (1mmol) of MnCl2·4H2O, 4.50g (25mmol) of 1,10-phenanthroline and 1.82g (15mmol) of L-cysteine. The molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:25:15, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride is 35:100.

[0046] Example 4

[0047] The rest is the same as example 1, the difference is that the molar ratio of sodium chloride, 1,10-phenanthroline, L-cysteine in step (S1) is different; The specific amount of each material is: 20.13g of sodium chloride, 0.198g (1mmol) of MnCl2·4H2O, 4.50g (25mmol) of 1,10-phenanthroline and 2.42g (20mmol) of L-cysteine. The molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:25:20, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride is 35:100.

[0048] Example 5

[0049] The rest is the same as example 1, the difference is that the amount of sodium chloride in step (S1) and the coordination reaction conditions are different, which are as follows:

[0050] (S1) 18.49 g of sodium chloride was dissolved in 150 g of deionized water to form a template solution; 0.198 g (1 mmol) of MnCl2·4H2O, 3.60 g (20 mmol) of 1,10-phenanthroline and 1.82 g (15 mmol) of L-cysteine (i.e. the molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine was 1:20:15, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride was 30:100) were added to the template solution, and a homogeneous transparent mixed solution was formed after stirring at 60°C for 2 h for coordination reaction;

[0051] (S2) The same as Example 1;

[0052] (S3) The same as Example 1;

[0053] (S4) The same as Example 1.

[0054] Example 6

[0055] The rest was the same as Example 1, except that the amount of sodium chloride in step (S1) and the coordination reaction conditions were different, and specifically:

[0056] (S1) 13.87 g of sodium chloride was dissolved in 150 g of deionized water to form a template solution; 0.198 g (1 mmol) of MnCl2·4H2O, 3.60 g (20 mmol) of 1,10-phenanthroline and 1.82 g (15 mmol) of L-cysteine (i.e. the molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine was 1:20:15, and the mass ratio of the total mass of MnCl2, 1,10-phenanthroline and L-cysteine to the mass of sodium chloride was 40:100) were added to the template solution, and a homogeneous transparent mixed solution was formed after stirring at 60°C for 2 h for coordination reaction;

[0057] (S2) The same as Example 1;

[0058] (S3) The same as Example 1;

[0059] (S4) The same as Example 1.

[0060] Example 7

[0061] The rest is the same as example 1, the difference is that: in step (S1) using potassium chloride instead of sodium chloride, using 2,2'-dipyridyl instead of 1,10-phenanthroline, using D-penicillamine instead of L-cysteine; the specific amount of each material is: 15.67 g of potassium chloride, 0.198 g (1 mmol) of MnCl2·4H2O, 3.12 g (20 mmol) of 2,2'-dipyridyl and 2.24 g (15 mmol) of D-penicillamine. That is, the amount of each material described above is to ensure that the molar ratio of manganese salt, nitrogen-containing aromatic heterocyclic ligand and amino acid thiol ligand, and the mass ratio of the total mass of manganese salt, nitrogen-containing aromatic heterocyclic ligand, amino acid thiol ligand and alkali metal salt is the same as example 1.

[0062] Comparative example 1

[0063] The rest is the same as example 1, the difference is that: in step (S1) the molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:10:5; the specific amount of each material is: 7.25 g of sodium chloride, 0.198 g (1 mmol) of MnCl2·4H2O, 1.80 g (10 mmol) of 1,10-phenanthroline and 0.61 g (5 mmol) of L-cysteine.

[0064] Comparative example 2

[0065] The rest is the same as example 1, the difference is that: in step (S1) the molar ratio of MnCl2, 1,10-phenanthroline and L-cysteine is 1:30:25; the specific amount of each material is: 24.47 g of sodium chloride, 0.198 g (1 mmol) of MnCl2·4H2O, 5.41 g (30 mmol) of 1,10-phenanthroline and 3.03 g (25 mmol) of L-cysteine.

[0066] Comparative example 3

[0067] The rest is the same as example 1, the difference is that: in step (S1) there is no L-cysteine, the specific amount of each material is: 10.65 g of sodium chloride, 0.198 g (1 mmol) of MnCl2·4H2O, 3.60 g (20 mmol) of 1,10-phenanthroline.

[0068] Analysis and test

[0069] 1) Structure characterization and manganese loading

[0070] The XRD pattern of the honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in example 1 is shown in Figure 1 Figure 1 ​As can be seen, only broad, diffuse peaks belonging to graphitic carbon were observed around 25° and 43°, and no crystalline peaks of manganese metal or its oxides were found, indicating that manganese is highly dispersed in the carbon support in an atomic-level form.

[0071] SEM image of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 is shown below. Figure 2 As shown, (a) is a low-resolution SEM image, and (b) is a high-resolution SEM image. Figure 2 The study clearly showed that the material has a rich three-dimensional honeycomb porous structure with pore sizes ranging from 0.8 to 1.5 μm, and no nanoparticles or nanoclusters were observed.

[0072] XPS image of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst (MnSA-SCN) prepared in Example 1 is shown below. Figure 3 As shown, (a) is the N 1s spectrum and (b) is the S 2p spectrum. Figure 3 (a) Visible pyridine N (398.2 eV), Mn-N x Characteristic peaks of N (399.1 eV), pyrrole N (400.8 eV), graphite N (402.2 eV) and N oxide (403.4 eV). Figure 3 In (b), the characteristic peaks of thiophene S (164.2 eV and 165.4 eV) are mainly visible. The formation of thiophene S may be related to the interaction between C and S near pyridine N and Mn-N. Meanwhile, Figure 3 As shown in (a), the MnSA-SCN prepared in Example 1 has a higher Mn-N content compared to the carbon-supported manganese catalyst (MnSA-CN, sulfur-free) prepared in Comparative Example 3. x The content of Mn-N decreased, while the content of pyridine N decreased accordingly, indicating that the introduction of amino acid thiol ligands facilitated the formation of a higher density of Mn-N. x Active sites. We hypothesize that successful sulfur doping plays a crucial role. Due to the large radius of S atoms, their incorporation into the carbon lattice causes lattice distortion and defects, which themselves can serve as ORR active sites. Furthermore, they can stabilize metallic Mn atoms and prevent their migration and aggregation, thereby indirectly increasing the Mn-N ratio. x The number and stability of sites.

[0073] The manganese (Mn) element in the carbon-supported manganese catalysts prepared in the examples and comparative examples was determined by ICP-MS. The specific results of Mn element and specific surface area are shown in Table 1.

[0074] Table 1 Mn element content

[0075]

[0076] The data in Table 1 shows that the manganese element content of the honeycomb-shaped sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst prepared in the examples is relatively high, in the range of 2.5-4.0 wt%. The manganese content of Comparative Example 1 (insufficient ligand) is relatively high, but the open-circuit voltage and peak power density of the zinc-air battery assembled therefrom are relatively low in the subsequent application test (as shown in Table 2), which indicates that when the amount of ligand is insufficient, all manganese atoms cannot be effectively anchored during the carbonization process, resulting in the migration and agglomeration of part of the manganese to form particles without catalytic activity, thereby reducing the catalytic activity. The manganese content of Comparative Example 2 (excessive ligand) is relatively low, and the battery performance corresponding thereto is also poor, which may be due to the excessive amount of ligand, which reduces the effective Mn-N x active site density in the carbon matrix. The manganese content of Comparative Example 3 (without amino acid thiol ligand) is relatively high, but the open-circuit voltage and peak power density of the zinc-air battery assembled therefrom are significantly lower in the subsequent application, which indicates that without the synergistic effect of the sulfur-containing ligand, manganese cannot be well anchored in the carbon matrix in the form of monatomic atoms to form effective active sites, thereby reducing the catalytic activity.

[0077] 2) Catalytic oxygen reduction reaction (ORR) performance test

[0078] The electrochemical ORR performance test was carried out by an electrochemical workstation (CHI 760E, Shanghai Chenhua), a rotating ring-disk electrode instrument and a standard three-electrode system, in which 0.1 M KOH saturated with O2 or N2 was used as the electrolyte, and the rotating disk electrode (RDE, disk diameter 5 mm) coated with the catalyst was used as the working electrode, the reference electrode and the counter electrode were Hg / HgO electrode and graphite rod, respectively. 4 mg of catalyst was weighed into a 5 mL glass bottle, and 1 mL of mixed solution (H2O: isopropanol: 5% Nafion = 16:3:1, 5% Nafion is a 5% mass fraction of perfluorosulfonic acid resin solution) was added, and ultrasonic was carried out at room temperature for 1 h until the catalyst slurry was formed; 10 μL of the catalyst slurry was spin-coated on the pretreated RDE in two times and naturally air-dried until a dry and uniform catalyst film was formed. The oxygen reduction reaction (ORR) performance test of the honeycomb-shaped sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1 is shown in FIG. 2. Figure 4are shown, wherein (a) is cyclic voltammetry (CV) curve, (b) is linear sweep voltammetry (LSV) curve. The CV curve shows that there is an obvious reduction peak under O2 atmosphere, indicating that the honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1 has certain ORR catalytic activity; at the same time, the LSV curve shows that the half-wave potential of the honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1 is 0.89 V, which is higher than that of the commercial Pt / C catalyst (0.83 V), verifying that it has excellent ORR catalytic activity. The ORR performance test graphs of the honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalysts prepared in the other examples are similar to Figure 4 .

[0079] 3) Application test

[0080] The carbon supported manganese catalysts prepared in the examples and comparative examples were used in zinc-air batteries for performance test, specifically, the carbon supported manganese catalysts prepared in the examples and comparative examples were used as cathode, zinc foil was used as anode, 0.2M Zn (Ac)2+ 6M KOH was used as electrolyte, and zinc-air batteries were assembled. At the same time, the commercial Pt / C catalyst was used as reference for the same test. The performance test graph of the zinc-air battery assembled with the honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst prepared in Example 1 as cathode is shown in Figure 5 , wherein (a) is open circuit voltage curve, (b) is polarization curve and power density curve, (c) is cycle rate curve, and (d) is constant current discharge curve. As can be seen from (a) of Figure 5 , the open circuit voltage of the battery reaches 1.58 V, which is higher than that of the commercial Pt / C based reference battery (1.51 V). As can be seen from (b) of Figure 5 , the peak power density of the battery reaches 264.5 mW / cm 2 . As can be seen from (c) of Figure 5 , under different current densities, the constant current discharge curve of the battery is stable and higher than that of the commercial Pt / C based reference battery, and after one full current discharge, the voltage of the battery can still return to the voltage value under the initial current density, indicating that it has high rate capacity and excellent stability; the cycle rate curves of the zinc-air batteries corresponding to the other examples are similar to (c) of Figure 5 . As can be seen from (d) of Figure 5 , the specific capacity of the battery is 714.3 mA·h / g Zn , which is 1.35 times of the specific capacity (529.8 mA·h / g Zn ) of the commercial Pt / C based reference battery, and is 1.35 times of the theoretical capacity (820 mA·h / g Zn(Theoretically, 2 mol of electrons will be released to the external circuit for every 1 mol of zinc atom consumed, i.e. 53611 mA·h of electricity is generated, and the capacity provided by unit mass of zinc is 820 mA·h / g Zn ) are not much different.

[0081] The open-circuit voltage and peak power density test results of the zinc-air batteries assembled by the carbon-supported manganese catalysts prepared in each embodiment and the comparative examples are shown in Table 2.

[0082] Table 2 Application performance test

[0083]

[0084] As can be seen from Table 2, when the honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese monatomic catalyst prepared in the embodiments of the present application is used as a cathode catalyst of a zinc-air battery, the zinc-air battery has a higher open-circuit voltage and peak power density.

[0085] In summary, the manganese monatomic catalyst prepared in the embodiments of the present application has high metal loading, atomic dispersion characteristics and a three-dimensional honeycomb structure, and has excellent catalytic activity and stability.

Claims

1. A method for one-pot preparation of honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese single-atom catalysts, characterized in that, Includes the following steps: (S1) Dissolve the alkali metal salt in water to form a template solution; add the manganese salt, nitrogen-containing aromatic heterocyclic ligand, and amino acid thiol ligand to the template solution in a molar ratio of 1:(15~25):(10~20), and carry out a coordination reaction at 60~80℃ under stirring to form a mixed solution; the nitrogen-containing aromatic heterocyclic ligand is selected from at least one of 1,10-phenanthroline and 2,2'-bipyridine; the amino acid thiol ligand is selected from at least one of L-cysteine ​​and D-penicillamine; the molar amount of manganese salt is calculated as Mn; (S2) The mixed solution is freeze-dried and crushed to obtain precursor powder; (S3) Place the precursor powder in a closed container and then carbonize it under an inert atmosphere to obtain carbonized material; (S4) The carbonized material is washed with water to remove the alkali metal salt template, and then subjected to acid washing, water washing and drying in sequence to obtain a honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst.

2. The method according to claim 1, characterized in that, In step (S1), the molar ratio of the manganese salt, the nitrogen-containing aromatic heterocyclic ligand, and the amino acid thiol ligand is 1:(15~20):(10~15).

3. The method according to claim 1, characterized in that, In step (S1), the nitrogen-containing aromatic heterocyclic ligand is 1,10-phenanthroline; the amino acid thiol ligand is L-cysteine.

4. The method according to claim 1, characterized in that, In step (S1), the total mass ratio of the manganese salt, nitrogen-containing aromatic heterocyclic ligand, and amino acid thiol ligand to the alkali metal salt in the template solution is 30~40:

100.

5. The method according to claim 1, characterized in that, In step (S1), the alkali metal salt is sodium chloride and / or potassium chloride, the concentration of the template solution is 5-20 wt%, the manganese salt is selected from at least one of manganese chloride, manganese nitrate, manganese sulfate, manganese acetate, manganese acetylacetone or their hydrates, and the coordination reaction time is 1-3 h.

6. The method according to claim 1, characterized in that, In step (S2), the freeze-drying conditions are as follows: the mixed solution is first frozen in liquid nitrogen for 1-3 hours, and then vacuum dried in a cold trap at -40 to -30°C for 12-24 hours with a vacuum degree of 10-30 Pa; the crushing is performed by air jet pulverization to a particle size of 100-200 mesh.

7. The method according to claim 1, characterized in that, In step (S3), the sealed container is an alumina crucible or corundum boat with a lid; the inert atmosphere is nitrogen and / or argon; and the carbonization conditions are: 700~900℃ for 2~4 hours.

8. The method according to claim 1, characterized in that, In step (S4), the specific steps for washing away the alkali metal salt template are as follows: the carbonized material is stirred and washed with deionized water at 40~60℃ for 20~50 minutes, and washed 2~5 times in total, until no white precipitate is produced in the supernatant when tested with silver nitrate solution; And / or, In step (S4), the acid washing is performed using a 1-3M hydrochloric acid aqueous solution, sulfuric acid aqueous solution, or nitric acid aqueous solution for 20-40 minutes; the water washing is performed using pure water until the filtrate is neutral; and the drying is performed at 60-80℃ for 12-24 hours.

9. A honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst according to claim 9, characterized in that, It has a three-dimensional honeycomb porous structure with pore sizes ranging from 0.8 to 1.5 μm; and both nitrogen and sulfur atoms are doped into the carbon matrix; manganese is dispersed in the carbon matrix in the form of single atoms, forming a Mn-N complex. x The core active site is manganese, with a content of 2.8~4.0 wt%.

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