Method for preparing honeycomb-shaped sulfur-nitrogen co-doped carbon-loaded manganese monatomic catalyst by one-pot method

Abstract

The invention 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 by a one-pot method, which comprises the following steps: (S1) dissolving 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 according to a molar ratio of 1: (15-25): (10-20), and carrying out a coordination reaction at 60-80 DEG C to obtain a mixed solution; (S2) carrying out freeze drying on the mixed solution to obtain precursor powder; (S3) carbonizing the precursor powder to obtain a carbonized material; and (S4) washing the carbonized material with water to remove the alkali metal salt template, and then sequentially carrying out acid pickling, water washing and drying. The honeycomb-shaped sulfur-nitrogen co-doped carbon-loaded manganese monatomic catalyst with excellent catalytic activity and stability is prepared through synergistic coordination of a nitrogen-containing aromatic heterocyclic ligand and an amino acid thiol ligand to manganese ions and combination with an alkali metal salt template and a freeze-drying process.

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 sealed container is an alumina crucible or corundum boat with a lid; the inert atmosphere is nitrogen and / or argon; the carbonization conditions are: 700~900℃ for 2~4 hours. The purpose of keeping the container sealed during carbonization is to prevent premature volatilization and loss of nitrogen-containing aromatic heterocyclic ligands and amino acid-based thiols before reaching the carbonization temperature, thereby ensuring the full progress of the in-situ carbonization reaction and the effective formation of the sulfur-nitrogen co-doped carbon matrix and the successful anchoring of metallic manganese.

[0018] Further, 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 a total of 2~5 times until no white precipitate is produced in the supernatant when tested with silver nitrate solution.

[0019] Further, 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 with pure water until the filtrate is neutral; and the drying is performed at 60-80°C for 12-24 hours. The acid washing aims to remove a small amount of unstable metal nanoparticles, and the subsequent water washing aims to thoroughly remove residual acid and alkali metal salt templates.

[0020] Secondly, the present invention also provides a honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst, which is prepared by the aforementioned method.

[0021] Furthermore, the honeycomb-shaped sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst has a three-dimensional honeycomb porous structure with a pore size of 0.8~1.5μm; and nitrogen and sulfur atoms are simultaneously doped into the carbon matrix; manganese is dispersed in the carbon matrix in single-atom form, forming a Mn-N... x The core active site.

[0022] Furthermore, the manganese content of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst is 2.8~4.0 wt%.

[0023] Thirdly, the present invention also provides the application of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst as a cathode catalyst for metal-air batteries.

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

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention achieves the controllable preparation of sulfur-nitrogen co-doped carbon-supported manganese single-atom catalysts with high manganese loading, atomic-level dispersion, and three-dimensional honeycomb structure by synergistic coordination of manganese ions with nitrogen-containing aromatic heterocyclic ligands and amino acid-based thiol ligands, combined with alkali metal salt templates and freeze-drying processes.

[0027] 2. The honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared by this invention has excellent catalytic activity and stability.

[0028] 3. The "one-pot" preparation method of the present invention makes the process convenient, avoids the use of highly corrosive reagents, and is low in cost and easy to scale up for production. Attached Figure Description

[0029] Figure 1 The image shows the XRD pattern of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1.

[0030] Figure 2 The images show SEM images of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1, where (a) is a low-resolution SEM image and (b) is a high-resolution SEM image.

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

[0032] Figure 4 The graphs show the oxygen reduction reaction (ORR) performance of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1, where (a) is the cyclic voltammetry (CV) curve and (b) is the linear sweep voltammetry (LSV) curve.

[0033] Figure 5 The following are performance test diagrams of a zinc-air battery assembled with the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 as the cathode. (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 Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

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

[0036] The Pt / C catalyst, also known as the platinum-carbon catalyst, is a catalyst in which platinum is supported on activated carbon. It comes from Suzhou Shengernuo Technology Co., Ltd., and the Pt content is 20wt%.

[0037] Example 1

[0038] (S1) Dissolve 15.85g of sodium chloride in 150g of deionized water to form a template solution; add 0.198g (1mmol) of MnCl2·4H2O (equivalent to 0.126g of MnCl2), 3.60g (20mmol) of 1,10-phenanthroline and 1.82g (15mmol) 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) to the template solution, stir at 70℃ for 2.5h to carry out the coordination reaction, and form a homogeneous and transparent mixed solution;

[0039] (S2) Pour the mixed solution into a petri dish, freeze it in liquid nitrogen for 2 hours, and then vacuum dry it in a cold trap at -40°C for 12 hours with the vacuum degree controlled at 10~20 Pa; obtain a precursor powder with a fluffy structure separated by NaCl template, and then air-jet pulverize it to 200 mesh to obtain the precursor powder.

[0040] (S3) Place the precursor powder in a covered alumina crucible, cover it, and then place it in a tube furnace. Under an inert atmosphere, heat the furnace to 800℃ at 8℃ / min and hold for 3 hours. Cool the furnace to room temperature to obtain the carbonized material.

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

[0042] Example 2

[0043] The rest is the same as in Example 1, except that the molar ratio of sodium chloride, 1,10-phenanthroline, and L-cysteine ​​is different in step (S1). Specifically, the amounts of each material are: 11.53 g sodium chloride, 0.198 g (1 mmol) MnCl2·4H2O, 2.70 g (15 mmol) 1,10-phenanthroline, and 1.21 g (10 mmol) L-cysteine. That is, 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 in Example 1, except that the molar ratio of sodium chloride, 1,10-phenanthroline, and L-cysteine ​​is different in step (S1). Specifically, the amounts of each material are: 18.42 g sodium chloride, 0.198 g (1 mmol) MnCl2·4H2O, 4.50 g (25 mmol) 1,10-phenanthroline, and 1.82 g (15 mmol) L-cysteine. That is, 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 in Example 1, except that the molar ratio of sodium chloride, 1,10-phenanthroline, and L-cysteine ​​is different in step (S1). Specifically, the amounts of each material are: 20.13 g sodium chloride, 0.198 g (1 mmol) MnCl2·4H2O, 4.50 g (25 mmol) 1,10-phenanthroline, and 2.42 g (20 mmol) L-cysteine. That is, 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 in Example 1, except that the amount of sodium chloride and the coordination reaction conditions in step (S1) are different, specifically:

[0050] (S1) Dissolve 18.49 g of sodium chloride in 150 g of deionized water to form a template solution; add 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 ​​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 30:100) to the template solution, stir at 60 °C for 2 h to carry out the coordination reaction, and form a homogeneous and transparent mixed solution;

[0051] (S2) Same as Example 1;

[0052] (S3) Same as Example 1;

[0053] (S4) Same as Example 1.

[0054] Example 6

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

[0056] (S1) Dissolve 13.87 g of sodium chloride in 150 g of deionized water to form a template solution; add 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 ​​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 40:100) to the template solution, stir at 60 °C for 2 h to carry out the coordination reaction, and form a homogeneous and transparent mixed solution;

[0057] (S2) Same as Example 1;

[0058] (S3) Same as Example 1;

[0059] (S4) Same as Example 1.

[0060] Example 7

[0061] The remainder is the same as in Example 1, except that in step (S1), potassium chloride is used in place of sodium chloride by an equal mass, 2,2'-bipyridine is used in place of 1,10-phenanthroline by an equal molar amount, and D-penicillamine is used in place of L-cysteine ​​by an equal molar amount. Specifically, the amounts of each material are: 15.67 g potassium chloride, 0.198 g (1 mmol) MnCl2·4H2O, 3.12 g (20 mmol) 2,2'-bipyridine, and 2.24 g (15 mmol) D-penicillamine. This ensures that the molar ratio of manganese salt, nitrogen-containing aromatic heterocyclic ligand, and amino acid thiol ligand, as well as the total mass of manganese salt, nitrogen-containing aromatic heterocyclic ligand, and amino acid thiol ligand to the mass ratio of alkali metal salt, are the same as in Example 1.

[0062] Comparative Example 1

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

[0064] Comparative Example 2

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

[0066] Comparative Example 3

[0067] The rest is the same as in Example 1, except that L-cysteine ​​is not used in step (S1), and the specific amounts of each material are: 10.65g sodium chloride, 0.198 g (1mmol) MnCl2·4H2O, and 3.60g (20mmol) 1,10-phenanthroline.

[0068] Analysis and Testing

[0069] 1) Structural characterization and manganese loading

[0070] The XRD pattern of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 is shown below. Figure 1 As shown, from Figure 1As 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] Table 1 shows that the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalysts prepared in the examples have a high manganese content, ranging from 2.5% to 4.0 wt%. Although Comparative Example 1 (insufficient ligands) has a high manganese content, subsequent application tests showed that the open-circuit voltage and peak power density of the assembled zinc-air battery were low (as shown in Table 2). This indicates that insufficient ligands cannot effectively anchor all manganese atoms during carbonization, leading to the migration and aggregation of some manganese into inactive particles, thus reducing catalytic activity. Comparative Example 2 (excessive ligands) has a low manganese content, and its corresponding battery performance is also poor. This may be because excessive ligands reduce the effective Mn-N content in the carbon matrix. x The density of active sites decreased. Comparative Example 3 (without amino acid thiol ligands) had a higher manganese content, but subsequent applications showed that the open-circuit voltage and peak power density of the zinc-air battery assembled with it were significantly lower. This indicates that without the synergistic effect of sulfur-containing ligands, manganese cannot be well anchored in the carbon matrix in single-atom form to form effective active sites, thereby reducing catalytic activity.

[0077] 2) Performance testing of catalytic oxygen reduction reaction (ORR)

[0078] Electrochemical ORR performance testing was conducted using an electrochemical workstation (CHI 760E, Shanghai Chenhua, China), a rotating disk electrode apparatus, and a standard three-electrode system. The electrolyte was 0.1 M KOH saturated with O2 or N2. The working electrode was a catalyst-coated rotating disk electrode (RDE, 5 mm diameter). The reference and counter electrodes were a Hg / HgO electrode and a graphite rod, respectively. 4 mg of catalyst was weighed into a 5 mL glass bottle, and 1 mL of a mixed solution (H2O:isopropanol:5% Nafion = 16:3:1, where 5% Nafion was a 5% perfluorosulfonic acid resin solution) was added. The solution was sonicated at room temperature for 1 h until a catalyst slurry was formed. Then, 10 μL of the catalyst slurry was spin-coated twice onto the pretreated RDE and allowed to air dry until a dry and uniform catalyst film was formed. The ORR performance test results of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 are shown in the figure. Figure 4As shown, (a) is the cyclic voltammetry (CV) curve, and (b) is the linear sweep voltammetry (LSV) curve. The CV curve shows a significant reduction peak under an O2 atmosphere, indicating that the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 has certain ORR catalytic activity. Meanwhile, the LSV curve shows that the half-wave potential of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 is 0.89 V, which is higher than the 0.83 V of the commercial Pt / C catalyst, verifying its excellent ORR catalytic activity. The ORR performance test curves of the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalysts prepared in the other examples are shown below. Figure 4 similar.

[0079] 3) Application Testing

[0080] The carbon-supported manganese catalysts prepared in the examples and comparative examples were used in zinc-air batteries for performance testing. Specifically, zinc-air batteries were assembled using the carbon-supported manganese catalysts prepared in the examples and comparative examples as cathodes, zinc foil as anodes, and 0.2 M Zn(Ac)2+ 6 M KOH as electrolytes. Simultaneously, a commercial Pt / C catalyst was used as a reference for the same testing. The performance test results of the zinc-air battery assembled using the honeycomb sulfur-nitrogen co-doped carbon-supported manganese single-atom catalyst prepared in Example 1 as the cathode are shown in the figure below. Figure 5 As shown, (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. From Figure 5 As can be seen from (a), the open-circuit voltage of this battery reaches 1.58V, which is higher than the 1.51V of the commercial Pt / C-based reference battery. From Figure 5 (b) shows that the battery has a peak power density of up to 264.5 mW / cm³. 2 .from Figure 5 As can be seen from (c), under different current densities, the constant current discharge curve plateau of this battery is stable and higher than that of the commercial Pt / C-based reference battery. Furthermore, after one full current discharge, the battery voltage can still return to the voltage value at the initial current density, indicating that it has high rate capacity and excellent stability. The zinc-air batteries corresponding to the other embodiments have similar characteristics. Figure 5 The cycle ratio curve of (c). From Figure 5 As can be seen from (d), the specific capacity of this battery is 714.3 mA·h / g. Zn This is the specific capacity of a commercially available Pt / C-based reference cell (529.8 mA·h / g). Zn It is 1.35 times that of the theoretical capacity of 820 mA·h / g. Zn(Theoretically, for every 1 mol of zinc atoms consumed, 2 mol of electrons are released into the external circuit, which generates 53611 mA·h of electricity. Therefore, the capacity provided by a unit mass of zinc is 820 mA·h / g) Zn The difference is not significant.

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

[0082] Table 2 Application Performance Test

[0083]

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

[0085] In summary, the embodiments of the present invention have prepared a manganese single-atom catalyst with high metal loading, atomic-level dispersion characteristics, and a three-dimensional honeycomb structure, which exhibits excellent catalytic activity and stability.

Claims

1. A method for one-pot preparation of honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst, characterized in that, The method comprises the following steps: (S1) dissolving an alkali metal salt in water to form a template solution; adding a manganese salt, a nitrogen-containing aromatic heterocyclic ligand and an amino acid thiol ligand in a molar ratio of 1:(15-25):(10-20) into the template solution, and performing 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; (S2) freeze-drying the mixed solution, and obtaining a precursor powder after crushing; (S3) placing the precursor powder in a closed container, and then carbonizing under an inert atmosphere to obtain carbonized material; (S4) washing the carbonized material with water to remove the alkali metal salt template, and then sequentially performing acid washing, water washing and drying to obtain a honeycomb-shaped sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst.

2. The method of claim 1, wherein, 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 of claim 1, wherein, In step (S1), the nitrogen-containing aromatic heterocyclic ligand is 1,10-phenanthroline; and the amino acid thiol ligand is L-cysteine.

4. The method of claim 1, wherein, 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.

5. The method of claim 1, wherein, 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 manganese acetylacetonate or a hydrate thereof, and the coordination reaction is performed for 1-3 h.

6. The method of claim 1, wherein, In step (S2), the freeze-drying is performed in the following manner: the mixed solution is first frozen in liquid nitrogen for 1-3 h, and then vacuum dried at-40--30 DEG C in a cold trap for 12-24 h, with a vacuum degree of 10-30 Pa; and the crushing is performed by airflow crushing to a particle size of 100-200 mesh.

7. The method of claim 1, wherein, 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 is performed in the following manner: 700-900 DEG C for 2-4 h.

8. The method of claim 1, wherein, In step (S4), the specific steps for washing the carbonized material with water to remove the alkali metal salt template are as follows: stirring and washing the carbonized material with deionized water at 40-60 DEG C for 20-50 min, a total of 2-5 times, until no white precipitate is generated in the supernatant when detected by silver nitrate solution; and / or, In step (S4), the acid washing is performed using a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution or a nitric acid aqueous washing solution with a concentration of 1-3 M for 20-40 min; the water washing is performed with pure water until the filtrate is neutral; and the drying is performed at 60-80 DEG C for 12-24 h.

9. A honeycomb-like sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst, characterized in that, The honeycomb-shaped sulfur-nitrogen co-doped carbon supported manganese monatomic catalyst is prepared by the method of any one of claims 1-8.

10. The honeycomb sulfur and nitrogen co-doped carbon supported manganese monatomic catalyst of claim 9, wherein, It has a three-dimensional honeycomb porous structure with a pore size of 0.8-1.5 μm; and nitrogen atoms and sulfur atoms are doped in the carbon matrix at the same time; manganese is dispersed in the carbon matrix in the form of single atoms, and forms a Mn-N x active site with manganese as the core; the content of manganese element is 2.8-4.0 wt%.

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