A nitrogen and chlorine doped carbon supported cobalt monatomic catalyst and a preparation method thereof

Abstract

The application discloses a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst and a preparation method thereof. The preparation method of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst comprises the following steps: dispersing a cobalt source and a zinc source in a first solvent to obtain a metal mixed solution, adding a nitrogen organic ligand into a second solvent to obtain a nitrogen organic ligand solution, under stirring, adding the metal mixed solution at 50-70 DEG C into the nitrogen organic ligand solution at 50-70 DEG C, constant temperature stirring until suspension appears, standing to make the suspension precipitate, filtering to obtain a precipitate, washing, drying to obtain a precursor, uniformly mixing the precursor and sodium chloride, grinding, pyrolyzing under an inert atmosphere at 800-1100 DEG C, washing, drying to obtain the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst. The application adopts a molten salt assisted method to simply and accurately break the plane symmetry structure of the monatomic catalyst, so that the catalytic ORR performance of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical catalysis, and particularly relates to a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst and a preparation method thereof. BACKGROUND

[0002] Single-atom catalysts (SACs) have attracted great attention due to their completely exposed active sites, 100% atom utilization and high catalytic activity. Among them, atomically dispersed transition metal anchored nitrogen-doped carbon catalysts (M-N-C single-atom catalysts) are considered as promising catalysts for oxygen reduction reaction (ORR) to replace platinum-based catalysts (PGM). M-N-C single-atom catalysts have been widely studied, especially the catalysts with a planar symmetrical configuration of four nitrogen-coordinated metal sites (M-N4), which exhibit good catalytic performance. However, when compared with platinum-based catalysts, their ORR activity is still insufficient. This is because the planar symmetrical configuration of M-N4 leads to a symmetrical distribution of the electronic structure, which is not conducive to the adsorption or desorption of oxygen intermediates, so the M-N-C single-atom catalysts have poor catalytic activity. Moreover, due to the linear scaling relationship limit (SRL) of single active sites, that is, there are multiple steps involved in the ORR pathway (such as the adsorption of oxygen on the electrode surface), each step has its own reaction energy barrier, and the patent with publication number CN 117423840A also proposes that reducing the energy barrier of a certain step involving the active site will usually cause the potential barrier of other steps on the same site to increase.

[0003] Heteroatom (such as P, S and Cl, etc.) doping is considered as a promising way to regulate the type and coordination number of coordination elements of single-atom catalysts, which is conducive to regulating the catalytic active center, changing the catalytic selectivity and catalytic activity, and better understanding the structure-activity relationship of catalyst structure and catalytic activity. However, due to the difficulty in accurately controlling the position of heteroatoms on the carbon base, the planar symmetrical structure of M-N4 is still difficult to break, thereby limiting the further improvement of the performance of the catalyst. In addition, the introduction of heteroatoms usually requires complex experimental steps and raw materials with high prices, which will increase the production cost of the catalyst, thereby limiting its popularization in industrial applications. Moreover, some heteroatom dopants may have toxicity or environmental hazards, which may cause environmental or safety problems, and need to be strictly evaluated and regulated. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst.

[0005] Another purpose of the present application is to provide a preparation method of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst.

[0006] The application aims to achieve the above technical solutions.

[0007] A preparation method of a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst, comprising the following steps:

[0008] The cobalt source and the zinc source are dispersed in a first solvent to obtain a metal mixed solution, a nitrogen organic ligand is added to a second solvent to obtain a nitrogen organic ligand solution, under stirring, the 50-70 DEG C metal mixed solution is added to the 50-70 DEG C nitrogen organic ligand solution, constant temperature stirring is performed until suspension appears, standing is performed to make the suspension precipitate, filtration is performed to obtain a precipitate, washing is performed, drying is performed to obtain a precursor, the precursor and sodium chloride are uniformly mixed, grinding is performed, under an inert atmosphere, pyrolysis is performed at 800-1100 DEG C for 2-3 h (zinc element is discharged with tail gas, a molten salt assisted method), washing is performed, drying is performed to obtain the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst, wherein the ratio of cobalt in the cobalt source, nitrogen in the nitrogen organic ligand and chlorine in the sodium chloride is (1-2):(60-65):(65-70) in terms of the amount of substance.

[0009] In the above technical solution, the cobalt source is cobalt acetylacetonate, the zinc source is zinc nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, and the second solvent is methanol.

[0010] In the above technical solution, the ratio of the mass fraction of the cobalt source, the mass fraction of the zinc source, the volume fraction of the first solvent and the volume fraction of the second solvent is (3-4):(11-13):150:350, the unit of the mass fraction is g, and the unit of the volume fraction is mL.

[0011] In the above technical solution, the cobalt source and the zinc source are dispersed in the 50-70 DEG C first solvent, and stirring is performed for 15-20 min to obtain the metal mixed solution.

[0012] In the above technical solution, the nitrogen organic ligand is added to the 50-70 DEG C second solvent, and stirring is performed for 10-15 min to obtain the nitrogen organic ligand solution.

[0013] In the above technical solution, the constant temperature stirring is performed for 3-5 min.

[0014] In the above technical solution, the standing is performed for 10-12 h.

[0015] In the above technical solution, the washing is performed at least 3 times with anhydrous methanol or ultrapure water.

[0016] In the above technical solution, the grinding is performed for at least 30 min.

[0017] In the above technical solution, the heating rate of the pyrolysis is 3-5 DEG C / min.

[0018] In the technical scheme, the drying temperature is 60-70 DEG C, and the drying time is 10-12h.

[0019] In the technical scheme, the inert atmosphere is argon atmosphere.

[0020] The nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared by the preparation method.

[0021] The use of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst in catalyzing ORR.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The asymmetrically coordinated nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared by the present application has a half-wave potential (E 1 / 2 ) of 0.876 V (relative to the reversible hydrogen electrode), a mass transfer limiting current density of 5.59 mA cm -2 , a kinetic current density (J k ) of 75.7 mA cm -2 at 0.85 V, and a Tafel slope of 49.8 mV dec -1 . Compared with commercial Pt / C and nitrogen doped carbon supported cobalt monatomic catalysts with planar symmetric structure, the catalytic ORR performance of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst of the present application is obviously improved.

[0024] (2) The preparation method of the present application adopts a molten salt assisted method, which simply and accurately breaks the planar symmetric structure of the monatomic catalyst, and prepares a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst with high purity and asymmetric coordination. The preparation method is simple in synthesis, low in cost, pollution-free, easy to scale up and realize industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 X-ray diffraction patterns of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, and the nitrogen doped carbon catalyst prepared in Comparative Example 2;

[0026] Figure 2 Transmission electron microscopy patterns, (a) is the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, and (b) is the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1;

[0027] Figure 3(a) is an atomic high-resolution transmission electron microscopy image of the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, (b) is an atomic high-resolution transmission electron microscopy image of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1, (c) is an energy dispersive X-ray elemental mapping image of the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, and (d) is an energy dispersive X-ray elemental mapping image of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1;

[0028] Figure 4 (a) is a Fourier transform extended X-ray absorption fine structure spectrum (FT-EXAFS) of Co element K absorption edge (Co K edge) of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, cobalt chloride, cobalt oxide, cobalt phthalocyanine and cobalt foil, (b) is a plot of the FT-EXAFS of Co element K absorption edge (Co K edge) of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, cobalt chloride, cobalt oxide, cobalt phthalocyanine and cobalt foil, and (c) is a plot of the FT-EXAFS of Co element K absorption edge (Co K edge) of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, cobalt chloride, cobalt oxide, cobalt phthalocyanine and cobalt foil. Figure 4 (a) is a plot of the FT-EXAFS of the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1 in (b) and a local structure model, (c) is a plot of the FT-EXAFS of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1 in (b) and a local structure model. Figure 4 (a) is a plot of the FT-EXAFS of the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1 in (b) and a local structure model.

[0029] Figure 5 is a plot of linear sweep voltammetry of a three-electrode system using a commercial Pt / C electrode, the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1 and the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the nitrogen-doped carbon catalyst prepared in Comparative Example 2 and the nitrogen-chlorine-doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3;

[0030] Figure 6 is a plot of half-wave potential (E 1 / 2 ) and kinetic current density (J k ) of a three-electrode system using a commercial Pt / C electrode, the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1 and the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the nitrogen-doped carbon catalyst prepared in Comparative Example 2 and the nitrogen-chlorine-doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3;

[0031] Figure 7 is a plot of Tafel slope of a three-electrode system using a commercial Pt / C electrode, the nitrogen-chlorine-doped carbon supported cobalt monatomic catalyst prepared in Example 1 and the nitrogen-doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the nitrogen-doped carbon catalyst prepared in Comparative Example 2 and the nitrogen-chlorine-doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3. DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further described in detail below in combination with the drawings and examples.

[0033] In the following examples, cobalt phthalocyanine and cobalt chloride are purchased from Aldrich, and cobalt foil is purchased from Hefei Kejing.

[0034] In the following examples, Nafion (5wt%) solution is a mixture of perfluorosulfonic acid-based polymer (Nafion), lower aliphatic alcohol and water, the concentration of perfluorosulfonic acid-based polymer (Nafion) in Nafion (5wt%) solution is 5wt%, and Nafion (5wt%) solution is purchased from Rong Reagent Co., Ltd.

[0035] In the following examples, the method for preparing the working electrode includes: weighing 10 mg of catalyst and placing it in a centrifuge tube, sequentially adding 100 μL of deionized water, 850 μL of isopropyl alcohol and 50 μL of Nafion (5wt%) solution, ultrasonic dispersion for 60 min to form a uniform solution, using a pipette to take 6 μL of the uniform solution and dropping it on a glassy carbon electrode, and naturally air-drying to obtain a working electrode, wherein the catalyst is one of commercial Pt / C, the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the nitrogen doped carbon catalyst prepared in Comparative Example 2 and the nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3.

[0036] In the following examples, the three-electrode system is composed of a working electrode, a reference electrode and a counter electrode. The catalyst in the working electrode is one of commercial Pt / C, the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the nitrogen doped carbon catalyst prepared in Comparative Example 2 and the nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3, the reference electrode is a Hg / HgO electrode, and the counter electrode is a graphite electrode.

[0037] In the following examples, the linear sweep voltammetry curve (LSV) of the three-electrode system is tested in oxygen-saturated 0.1M KOH aqueous solution using a rotating disc device and a CHI760E electrochemical workstation, and the test conditions are as follows: the linear scan rate is 5 mV·s -1 , and the scan potential range is 0.2-1.2V (vs. RHE).

[0038] Examples 1-4

[0039] A method for preparing a nitrogen and chlorine doped carbon supported cobalt monatomic catalyst includes the following steps:

[0040] The cobalt source and the zinc source are dispersed in a first solvent at 60 DEG C, mechanically stirred for 15 min to obtain a metal mixture solution, the nitrogen organic ligand is added to a second solvent at 60 DEG C, mechanically stirred for 10 min to obtain a nitrogen organic ligand solution, under stirring, the metal mixture solution at 60 DEG C is added to the nitrogen organic ligand solution at 60 DEG C, mechanically stirred at 60 DEG C for 5 min until a suspension appears, the stirring is stopped, and the suspension is allowed to settle for 12 h to precipitate, filtered to obtain a precipitate, washed with anhydrous methanol for 6 times, and dried in a vacuum drying oven at 70 DEG C for 12 h to obtain a precursor, the precursor and sodium chloride are mixed uniformly, ground for 30 min, and pyrolyzed in a tube furnace at a rate of 5 DEG C / min to T DEG C under an argon atmosphere and at T DEG C for 2 h (zinc element is discharged with tail gas), washed with ultrapure water for 3 times, and dried in a vacuum drying oven at 70 DEG C for 12 h to obtain a nitrogen-chlorine-doped carbon-supported cobalt monatomic catalyst, wherein the cobalt source is cobalt acetylacetonate, the zinc source is zinc nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, the second solvent is methanol, the ratio of cobalt in the cobalt source, nitrogen in the nitrogen organic ligand, and chlorine in the sodium chloride is 1:63:68 in terms of the amount of substance, and the ratio of the amount of cobalt source, the amount of zinc source, the volume of the first solvent, and the volume of the second solvent is 3.55:12:150:350, wherein the amount is in grams, and the volume is in milliliters.

[0041] The numbers and T of the nitrogen-chlorine-doped carbon-supported cobalt monatomic catalysts prepared in Examples 1-4 are shown in Table 1.

[0042] Table 1

[0043] Example No. T (unit: °C) Example 1 Co-N4Cl-C 1000 Example 2 Co-N4Cl-C-800 800 Example 3 Co-N4Cl-C-900 900 Example 4 Co-N4Cl-C-1100 1100

[0044] Comparative Example 1

[0045] A preparation method of a nitrogen-doped carbon-supported cobalt monatomic catalyst (number: Co-N4-C) includes the following steps:

[0046] The cobalt source and the zinc source are dispersed in a first solvent at 60℃, mechanically stirred for 15 min to obtain a metal mixed solution, the nitrogen organic ligand is added to a second solvent at 60℃, mechanically stirred for 10 min to obtain a nitrogen organic ligand solution, under stirring, the metal mixed solution at 60℃ is added to the nitrogen organic ligand solution at 60℃, mechanically stirred at 60℃ for 5 min until a suspension appears, stop stirring, stand for 12 h to make the suspension precipitate, filter to obtain a precipitate, wash with anhydrous methanol for 6 times, dry in a vacuum drying oven at 70℃ for 12 h to obtain a precursor, under argon atmosphere, heat to 1000℃ at a rate of 5℃ / min in a tube furnace and pyrolyze at 1000℃ for 2 h (zinc element is discharged with tail gas), wash with ultrapure water for 3 times, dry in a vacuum drying oven at 70℃ for 12 h to obtain a nitrogen-doped carbon supported cobalt monatomic catalyst, wherein the cobalt source is cobalt acetylacetonate, the zinc source is zinc nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, the second solvent is methanol, the ratio of cobalt in the cobalt source to nitrogen in the nitrogen organic ligand is 1:63 in terms of mass fraction, the ratio of the mass fraction of the cobalt source, the mass fraction of the zinc source, the volume fraction of the first solvent and the volume fraction of the second solvent is 3.55:12:150:350, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0047] Comparative Example 2

[0048] A preparation method of a nitrogen-doped carbon catalyst (No.: NC) comprises the following steps:

[0049] The zinc source is dispersed in a first solvent at 60℃, mechanically stirred for 15 min to obtain a metal solution, the nitrogen organic ligand is added to a second solvent at 60℃, mechanically stirred for 10 min to obtain a nitrogen organic ligand solution, under stirring, the metal solution at 60℃ is added to the nitrogen organic ligand solution at 60℃, mechanically stirred at 60℃ for 5 min until a suspension appears, stop stirring, stand for 12 h to make the suspension precipitate, filter to obtain a precipitate, wash with anhydrous methanol for 6 times, dry in a vacuum drying oven at 70℃ for 12 h to obtain a precursor, under argon atmosphere, heat to 1000℃ at a rate of 5℃ / min in a tube furnace and pyrolyze at 1000℃ for 2 h (zinc element is discharged with tail gas), wash with ultrapure water for 3 times, dry in a vacuum drying oven at 70℃ for 12 h to obtain a nitrogen-doped carbon catalyst, wherein the zinc source is zinc nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, the second solvent is methanol, the ratio of the mass fraction of the nitrogen organic ligand, the mass fraction of the zinc source, the volume fraction of the first solvent and the volume fraction of the second solvent is 26:12:150:350, the unit of mass fraction is mmol, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0050] Comparative Example 3

[0051] A preparation method of a nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst (No. Co-NP) comprises the following steps:

[0052] The cobalt source is dispersed in a first solvent at 60 DEG C, mechanically stirred for 15 min to obtain a metal mixed solution, the nitrogen organic ligand is added to a second solvent at 60 DEG C, mechanically stirred for 10 min to obtain a nitrogen organic ligand solution, the metal mixed solution at 60 DEG C is added to the nitrogen organic ligand solution at 60 DEG C under stirring, mechanically stirred at 60 DEG C for 5 min until the appearance of suspended matter, the stirring is stopped, and the suspended matter is allowed to settle for 12 h to obtain a precipitate, which is filtered, washed with anhydrous methanol for 6 times, and dried in a vacuum drying oven at 70 DEG C for 12 h to obtain a precursor, the precursor and sodium chloride are mixed uniformly, ground for 30 min, and pyrolyzed in a tube furnace at a rate of 5 DEG C / min to 1000 DEG C under an argon atmosphere and at 1000 DEG C for 2 h, washed with ultrapure water for 3 times, and dried in a vacuum drying oven at 70 DEG C for 12 h to obtain the nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst, wherein the cobalt source is cobalt nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, the second solvent is methanol, the ratio of cobalt in the cobalt source, nitrogen in the nitrogen organic ligand, and chlorine in the sodium chloride is 1:2.4:68 in terms of the amount of substance, and the ratio of the amount of cobalt source, the volume of the first solvent, and the volume of the second solvent is 6:200:200, wherein the unit of the amount is g, and the unit of the volume is mL.

[0053] The nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3 is ZIF-67, and according to the literature (Zeolitic imidazolate framework-67 and its derivatives for photocatalytic applications, Coordination Chemistry Reviews 502 (2024) 215612), the nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst prepared in Comparative Example 3 is a tetrahedral skeleton periodic network structure.

[0054] Comparative Example 4

[0055] A preparation method of a nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst comprises the following steps:

[0056] The cobalt source was dispersed in the first solvent at 60℃, mechanically stirred for 15 min to obtain a metal mixed solution, the nitrogen organic ligand was added to the second solvent at 60℃, mechanically stirred for 10 min to obtain a nitrogen organic ligand solution, under stirring, the metal mixed solution at 60℃ was added to the nitrogen organic ligand solution at 60℃, and mechanical stirring at 60℃ for 5 min did not produce suspended matter, that is, the preparation method of Comparative Example 4 did not obtain a nitrogen and chlorine doped carbon supported cobalt nanoparticle catalyst, wherein the cobalt source is cobalt acetylacetone, the nitrogen organic ligand is dimethyl imidazole, the first solvent is methanol, the second solvent is methanol, the ratio of cobalt in the cobalt source to nitrogen in the nitrogen organic ligand is 1:63 by mass fraction, the ratio of the mass fraction of the cobalt source, the volume fraction of the first solvent and the volume fraction of the second solvent is 3.55:150:350, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0057] The nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1 and the nitrogen doped carbon catalyst prepared in Comparative Example 2 were subjected to X-ray diffraction (XRD) test, and the results are shown in Figure 1 The XRD patterns of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1, the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1 and the nitrogen doped carbon catalyst prepared in Comparative Example 2 have two obvious characteristic peaks at 25.9° and 42.9°, which correspond to the (002) crystal face and the (100) crystal face of graphite carbon, respectively. In addition, no other obvious characteristic peaks were detected in the XRD pattern, which means that the Co atoms may exist in the form of amorphous phase, atomic form or embedded in the N-C framework.

[0058] The nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1 and the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1 were subjected to transmission electron microscopy (TEM) test, and the results are shown in Figure 2 As shown in (a) of Figure 2 , the amorphous carbon appearance of the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1 is a similar polyhedral structure, and the size of the polyhedral structure is similar and the size distribution is uniform, as shown in (b) of Figure 2 , the amorphous carbon appearance of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1 is a similar spherical structure, and the size of the spherical structure is similar and the size distribution is uniform. Compared with the nitrogen doped carbon supported cobalt monatomic catalyst prepared in Comparative Example 1, the surface of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared in Example 1 is etched and peeled off by fused salt (NaCl), thereby exposing more active sites, and Figure 2 No obvious black shadow aggregation was observed in (a) and (b) of

[0059] The nitrogen-chlorine doped carbon-supported cobalt single atom catalyst prepared in Example 1 and the nitrogen-doped carbon-supported cobalt single atom catalyst prepared in Comparative Example 1 were tested by atomic high-resolution transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray elemental mapping (EDS). Figure 3 As shown by Figure 3 As shown in (a) and (b), the HAADF-STEM images of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 and the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 have dense and isolated spot-like bright spots (bright spots are marked by circles), indicating that the atomically dispersed Co atoms are anchored on the carbon substrate. Figure 3 It can be seen from (c) and (d) that C, N and Co are uniformly dispersed on the surface of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 and the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1, and no bright aggregation points are observed, proving that no metal clusters are formed during the Co doping process. Figure 3 (d) also shows that Cl is uniformly dispersed on the surface of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1, proving the successful introduction of Cl.

[0060] The K absorption edge of Co element (Co K edge) in the nitrogen-chlorine-doped carbon-supported cobalt single atom catalyst prepared in Example 1, the nitrogen-doped carbon-supported cobalt single atom catalyst prepared in Comparative Example 1, cobalt chloride, cobalt oxide, cobalt phthalocyanine and cobalt foil was tested by Fourier transform extended X-ray absorption fine structure spectroscopy (FT-EXAFS). The FT-EXAFS of cobalt oxide is as follows: Figure 4 (a) "CoO * 0.6”, the FT-EXAFS of cobalt phthalocyanine is as shown in Figure 4 (a) "Co-Pc * 0.7”, the FT-EXAFS of cobalt foil is as follows Figure 4 (a) "Co foil * 0.5”, shown by Figure 4 (a) shows that compared with cobalt phthalocyanine, the FT-EXAFS spectrum of the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 is located at The main peak at can be attributed to the Co-N bond; compared with cobalt chloride, the main peak of the Co-N bond of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 is located at ~ It happened The positive shift is because the introduction of highly electronegative Cl atoms lengthens the bond length of the Co-N bond; no Co-Co scattering peak appears in the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 and the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1, which verifies the atomic dispersion of Co in the carbon substrate; according to the FT-EXAFS of the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 and the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1, a fitting curve is obtained (as shown in the figure "fitting"), and the local structure model of the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 and the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 is further obtained, as shown in FIG. Figure 4 As shown in (b) and (c), Figure 4 From (c), it can be seen that the local structure model of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 is composed of asymmetrically coordinated Co-N4Cl.

[0061] The catalytic oxygen reduction reaction (ORR) performance of the nitrogen-chlorine-doped carbon-supported cobalt single atom catalyst prepared in Example 1, the nitrogen-doped carbon-supported cobalt single atom catalyst prepared in Comparative Example 1, the nitrogen-doped carbon catalyst prepared in Comparative Example 2, and the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 were investigated respectively. A three-electrode system was constructed for testing. The test results are as follows Figure 5 As shown, for comparison, commercial Pt / C was also tested under the same conditions.

[0062] Depend on Figure 5 The half-wave potential (E 1 / 2 ) is 0.876V (relative to the reversible hydrogen electrode), which is better than the 0.832V of the commercial Pt / C electrode (relative to the reversible hydrogen electrode), the 0.804V of the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 (relative to the reversible hydrogen electrode), the 0.738V of the nitrogen-doped carbon catalyst prepared in Comparative Example 2 (relative to the reversible hydrogen electrode), and the 0.795V of the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 (relative to the reversible hydrogen electrode), showing good catalytic ORR activity. In addition, the mass transfer limiting current density of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 reached 5.59 mA cm -2 , exceeding the 5.45 mA cm of commercial Pt / C electrode. -2 The nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 has a peak of 4.74 mA cm -2 The nitrogen-doped carbon catalyst prepared in Comparative Example 2 had a peak of 3.44 mA cm -2 The 3.70 mA cm-1 of the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 was -2This higher limiting current density appears to be due to the rapid desorption of the product (oxygen-containing intermediates produced during the test) on the working electrode containing the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1. Furthermore, the superior ORR activity of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1 compared to the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 is also related to the participation of zinc in establishing the asymmetric coordinated Co-N4Cl structure of the catalyst.

[0063] in accordance with Figure 5 The current density shown is calculated using the KL equation to obtain the kinetic current density (J k ), the half-wave potential (E) of the three-electrode system using the commercial Pt / C electrode, the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst prepared in Example 1, the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1, the nitrogen-doped carbon catalyst prepared in Comparative Example 2, and the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 was calculated. 1 / 2 ) and kinetic current density (J k ) are integrated into a bar chart, such as Figure 6 As shown by Figure 6 It can be seen that the nitrogen-chlorine doped carbon-supported cobalt single atom catalyst prepared in Example 1 has a higher kinetic current density (J k ), up to 75.7 mA cm at 0.85 V -2 , is a commercial Pt / C electrode (25.2 mA cm -2 ). In contrast, the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 showed poor ORR activity, J k Reduced to 4.95 mA cm -2 , E 1 / 2 Smaller (0.804V).

[0064] in accordance with Figure 5 The current density shown is obtained by applying the Tafel formula and linear fitting to obtain the linear fitting slope (i.e., Tafel slope). The results are as follows Figure 7 As shown, the Tafel slope of the three-electrode system using the nitrogen-doped carbon-supported cobalt single-atom catalyst prepared in Comparative Example 1 is 59.2 mV dec. -1 The Tafel slope of the three-electrode system using the nitrogen-doped carbon catalyst prepared in Comparative Example 2 was 83.3 mV dec. -1 The Tafel slope of the three-electrode system using the nitrogen-chlorine-doped carbon-supported cobalt nanoparticle catalyst prepared in Comparative Example 3 was 66.4 mV dec. -1 The Tafel slope of the commercial Pt / C three-electrode system is 57.6 mV dec. -1The Tafel slope of the three-electrode system of the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared by using the preparation method of Example 1 is the smallest, which is 49.8 mV dec -1 , which reflects that the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared by using the preparation method of Example 1 has high catalytic activity.

[0065] The nitrogen and chlorine doped carbon supported cobalt monatomic catalysts prepared by using the preparation methods of Examples 2-4 can obtain the same technical effects as the nitrogen and chlorine doped carbon supported cobalt monatomic catalyst prepared by using the preparation method of Example 1.

[0066] The above has made an exemplary description of the present application, it should be explained that, without departing from the core of the present application, any simple modification, change or other equivalent replacement which can not cost the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A method for preparing a nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst, characterized in that: The following steps are involved: A cobalt source and a zinc source are dispersed in a first solvent to obtain a metal mixture, a nitrogen organic ligand is added to a second solvent to obtain a nitrogen organic ligand solution, the metal mixture at 50-70°C is added to the nitrogen organic ligand solution at 50-70°C under stirring, the mixture is stirred at a constant temperature until a suspended matter appears, the mixture is allowed to stand to allow the suspended matter to settle, the precipitate is filtered to obtain a precursor, the precipitate is washed, and the precursor is dried to obtain a precursor, the precursor and sodium chloride are mixed uniformly, ground, and pyrolyzed at 800-1100°C for 2-3 hours under an inert atmosphere, the zinc element is discharged with the tail gas, and the catalyst is washed and dried to obtain a nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst, wherein, based on the amount of substance, the ratio of cobalt in the cobalt source, nitrogen in the nitrogen organic ligand, and chlorine in the sodium chloride is (1-2):(60-65):(65-70).

2. The preparation method according to claim 1, characterized in that The cobalt source is cobalt acetylacetonate, the zinc source is zinc nitrate hexahydrate, the nitrogen organic ligand is dimethylimidazole, the first solvent is methanol, and the second solvent is methanol.

3. The preparation method according to claim 1, characterized in that The ratio of the mass fraction of the cobalt source, the mass fraction of the zinc source, the volume fraction of the first solvent and the volume fraction of the second solvent is (3-4): (11-13): 150: 350, the unit of the mass fraction is g, and the volume fraction is mL.

4. The preparation method according to claim 1, characterized in that The cobalt source and the zinc source are dispersed in a first solvent at 50-70° C. and stirred for 15-20 minutes to obtain a metal mixed solution.

5. The preparation method according to claim 1, characterized in that The nitrogen organic ligand is added to the second solvent at 50-70° C. and stirred for 10-15 minutes to obtain a nitrogen organic ligand solution.

6. The preparation method according to claim 1, characterized in that The constant temperature stirring time is 3 to 5 minutes; the standing time is 10 to 12 hours.

7. The preparation method according to claim 1, characterized in that Wash at least 3 times with anhydrous methanol or ultrapure water.

8. The preparation method according to claim 1, characterized in that The grinding is performed for at least 30 minutes; the heating rate of the pyrolysis is 3 to 5° C. / min; the drying temperature is 60 to 70° C., and the drying time is 10 to 12 hours; and the inert atmosphere is an argon atmosphere.

9. The nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the nitrogen-chlorine-doped carbon-supported cobalt single-atom catalyst as claimed in claim 9 in catalyzing ORR.

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