A cobalt-based catalyst, its preparation method and use

Abstract

The application provides a cobalt-based catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a boron source and a nitrogen-containing carbon source, and pyrolyzing to obtain a boron nitride-containing product; (2) mixing the boron nitride-containing product, a cobalt source, a chelating agent and an alcohol solvent, and pyrolyzing to obtain the cobalt-based catalyst. The cobalt-based catalyst is co-doped with boron and nitrogen through the boron source and the chelating agent, the boron source effectively adjusts the electronic structure of cobalt, the chelating agent can increase the nitrogen content in the carbon carrier and inhibit the agglomeration of cobalt nanoparticles, and through the synergistic effect of the boron source and the chelating agent, the cobalt nanoparticles are loaded on the boron and nitrogen co-doped carbon carrier, not only forming cobalt-nitrogen-boron active sites on the surface of the cobalt nanoparticles, but also effectively increasing the content of the active sites, so that the oxygen reduction performance of the cobalt-based catalyst is significantly improved, and a larger power density can be provided in the battery field. The preparation method has simple steps and convenient operation, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a cobalt-based catalyst, its preparation method, and its application. Background Technology

[0002] An aluminum-air battery is a metal-air battery that uses aluminum as the anode and pure oxygen or oxygen from the air as the active material for the air electrode (cathode). Metal-air batteries are one of the representatives of the new generation of green secondary batteries, possessing advantages such as low cost, non-toxicity, no pollution, high specific power, and high specific energy. They are available in abundant and renewable resources, and have a simpler structure than hydrogen fuel cells, making them a promising new energy source.

[0003] Currently, research on aluminum-air batteries mainly focuses on developing high-performance oxygen reduction catalysts. However, improving catalyst performance often relies on the use of precious metals and more complex preparation processes, which inevitably increases the cost of metal-air batteries, limiting their large-scale application to some extent. In recent years, research on aluminum-air electrode materials has mainly focused on two directions: one is the study of precious metals and alloys, such as platinum and platinum-cobalt alloys; the other is the study of non-metallic materials, such as nitrogen-doped transition metal materials and heteroatom-doped carbon-based nanomaterials.

[0004] For example, CN111490259A discloses a nitrogen-doped and defective porous carbon channel-supported cobalt cluster material for metal-air batteries and its preparation method. The material comprises nitrogen-doped and defective porous carbon and cobalt(II) clusters. This material exhibits high conductivity, which facilitates electron transport, and its porous structure increases its surface area, thereby enhancing the oxygen reduction reaction activity of the active material. CN111682224A discloses a method for preparing a single-atom cobalt-supported nitrogen-doped graphite-carbon cathode catalyst for metal-air batteries. This material, due to its unique surface structure, high conductivity, single-atom cobalt, and large specific surface area, exposes more catalytic active centers, thus enhancing the oxygen reduction reaction activity of the active material and exhibiting good performance in air batteries. CN110336049B discloses a nitrogen-cobalt doped hollow carbon nanofiber and its preparation method. The above material has good internal channels, high specific surface area and good conductivity, which can provide more active sites and shorten the electron transport path, accelerate the diffusion of oxygen and electrolyte, and disperse nitrogen and cobalt inside and on the surface of the hollow carbon nanofiber, thereby improving the electrochemical performance and cycle stability of nitrogen-cobalt doped carbon nanofiber.

[0005] However, existing cobalt-based oxygen reduction catalysts still suffer from problems such as cobalt nanoparticle aggregation and low oxygen reduction performance.

[0006] Therefore, there is an urgent need to develop a novel cobalt-based oxygen reduction catalyst to reduce the aggregation of cobalt nanoparticles while improving the oxygen reduction performance of the catalyst. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a cobalt-based catalyst, its preparation method, and its applications. This invention achieves boron-nitrogen co-doping of a cobalt-based catalyst through a boron source and a chelating agent. The boron source effectively modulates the electronic structure of cobalt, while the chelating agent increases the nitrogen content in the carbon support and inhibits the aggregation of cobalt nanoparticles. Through the synergistic effect of the boron source and the chelating agent, cobalt nanoparticles are loaded onto the boron-nitrogen co-doped carbon support. This not only forms cobalt-nitrogen-boron active sites on the surface of the cobalt nanoparticles but also effectively increases the content of these active sites, significantly improving the oxygen reduction performance of the cobalt-based catalyst. Applied to the battery field, this catalyst can provide a higher power density. The preparation method is simple, convenient, and has promising application prospects.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a cobalt-based catalyst, the method comprising the following steps:

[0010] (1) Mix boron source and nitrogen-containing carbon source and pyrolyze to obtain boron-containing nitride;

[0011] (2) The boron-containing nitride, cobalt source, chelating agent and alcohol solvent are mixed and pyrolyzed to obtain the cobalt-based catalyst.

[0012] This invention achieves boron-nitrogen co-doping of a cobalt-based catalyst through a boron source and a chelating agent. The boron source effectively modulates the electronic structure of cobalt, while the chelating agent increases the nitrogen content in the carbon support and inhibits the aggregation of cobalt nanoparticles. Through the synergistic effect of the boron source and chelating agent, cobalt nanoparticles are loaded onto the boron-nitrogen co-doped carbon support. This not only forms cobalt-nitrogen-boron active sites on the surface of the cobalt nanoparticles but also effectively increases the content of these active sites, significantly improving the oxygen reduction performance of the cobalt-based catalyst. Applied to the battery field, this results in a higher power density. The preparation method provided by this invention is simple, convenient, and has promising application prospects.

[0013] Preferably, the boron source in step (1) includes any one or a combination of at least two of boric acid, sodium borohydride or borax.

[0014] Preferably, the nitrogen-containing carbon source in step (1) includes any one or a combination of at least two of urea, melamine, or dicyandiamide. For example, it may be a combination of urea and dicyandiamide, a combination of urea and melamine, or a combination of dicyandiamide and melamine.

[0015] Preferably, the mass ratio of the boron source and the nitrogen-containing carbon source in step (1) is 1:(1-1000), for example, it can be 1:1, 1:5, 1:10, 1:50, 1:100, 1:200, 1:500 or 1:1000, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable, preferably 1:(100-200).

[0016] Preferably, the mixing process in step (1) is accompanied by stirring.

[0017] Preferably, the mixing method in step (1) is dry mixing.

[0018] This invention involves dry mixing boron and nitrogen-containing carbon sources in a mortar, which avoids the problem of the solids being difficult to pulverize after drying in traditional liquid-phase dispersion methods, and facilitates subsequent spreading in a ceramic boat.

[0019] Preferably, the mixing time in step (1) is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, etc.

[0020] Preferably, drying is performed before the pyrolysis in step (2).

[0021] Preferably, the pyrolysis temperature in step (1) is 350-750℃, for example, it can be 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃ or 750℃, etc.

[0022] Preferably, the pyrolysis time in step (1) is 1-2 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours.

[0023] Preferably, the atmosphere for pyrolysis in step (1) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen.

[0024] Preferably, the cobalt source in step (2) is a cobalt salt.

[0025] Preferably, the cobalt salt comprises cobalt chloride hexahydrate and / or cobalt nitrate hexahydrate.

[0026] Preferably, the chelating agent in step (2) includes any one or a combination of at least two of 1,10-phenanthroline, pyrrole, pyridine or 2-methylimidazole, preferably 1,10-phenanthroline.

[0027] Preferably, the alcohol solvent in step (2) includes methanol and / or ethanol.

[0028] Preferably, the mass ratio of the cobalt source and the boron nitride in step (2) is 1:(1-20), for example, it can be 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20, etc.

[0029] In this invention, if the mass ratio of cobalt source to boron nitride is too small, that is, if the amount of boron nitride is too large, then too many boron and nitrogen atoms will be incorporated, which will weaken the conductivity of the catalyst and thus affect the catalyst activity. If the mass ratio of cobalt source to boron nitride is too large, that is, if the amount of boron nitride is too small, then the cobalt content will increase, which will not help improve the catalyst performance.

[0030] Preferably, the mass ratio of the cobalt source and the chelating agent in step (2) is 1:(1-10), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0031] In this invention, if the mass ratio of cobalt source to chelating agent is too small, that is, if too much chelating agent is used, it will result in a waste of cost; if the mass ratio of cobalt source to chelating agent is too large, that is, if too little chelating agent is used, it will not be able to effectively inhibit the aggregation of cobalt and reduce the catalyst activity.

[0032] Preferably, the mixing process in step (2) is accompanied by stirring.

[0033] Preferably, the mixing method in step (2) includes:

[0034] (a) A boron-containing nitride, a cobalt source, and a portion of an alcohol solvent are mixed to obtain a mixed suspension;

[0035] (b) Mix the mixed suspension, chelating agent and another portion of solvent.

[0036] The present invention employs the above mixing method, which allows cobalt ions to be preferentially and uniformly adsorbed onto boron-containing nitrides, and then undergo a complexation reaction with a chelating agent, thereby reducing the aggregation of cobalt.

[0037] Preferably, after the boron-containing nitride described in step (a) is mixed with the cobalt source and a portion of the alcohol solvent, it is first crushed and then stirred for 1-3 hours. The crushing method is not limited; for example, it can be ultrasonic crushing.

[0038] This invention can separate layered boron nitrides by crushing, which helps the entry and dispersion of cobalt ions.

[0039] In this invention, stirring is performed for 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0040] Preferably, the mixing process in step (b) is accompanied by stirring.

[0041] Preferably, the mixing time in step (b) is 4-8 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 7 hours, 7.5 hours or 8 hours.

[0042] Preferably, the crushing method described in step (b) includes ultrasonic crushing.

[0043] Preferably, the pyrolysis temperature in step (2) is 700-1050℃, for example, it can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or 1050℃, etc.

[0044] In this invention, if the pyrolysis temperature in step (2) is too low, the graphitization degree of the support is low, which is not conducive to electron transport and thus weakens the catalyst activity; if the pyrolysis temperature in step (2) is too high, the cobalt nanoparticles will aggregate, reducing the active sites and weakening the catalyst activity.

[0045] Preferably, the pyrolysis time in step (2) is 1-2 hours, for example, it can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours.

[0046] Preferably, the atmosphere for pyrolysis in step (2) is an inert atmosphere, and the gas in the inert atmosphere includes nitrogen.

[0047] In a second aspect, the present invention provides a cobalt-based catalyst prepared by the preparation method described in the first aspect, wherein the cobalt-based catalyst comprises a boron-nitrogen co-doped carbon support and an active component supported on the carbon support, wherein the active component is cobalt nanoparticles.

[0048] The surface of the cobalt nanoparticles is modified with cobalt-nitrogen-boron active sites, in which cobalt atoms form chemical bonds with three nitrogen atoms and one boron atom.

[0049] The cobalt-based catalyst prepared by this invention has a high content of cobalt, nitrogen, and boron active sites, exhibits high catalytic activity, and reduces cobalt nanoparticle aggregation while achieving uniform dispersion.

[0050] Preferably, the carbon support is carbon nanosheets.

[0051] Preferably, based on the mass of the boron-nitrogen co-doped carbon support, the total doping amount of boron and nitrogen in the carbon support is 1-20%, for example, it can be 1%, 3%, 5%, 9%, 13%, 18% or 20%, etc.

[0052] Preferably, the ratio of boron to nitrogen doping in the carbon support is (1-10):(1-19), wherein the range of boron doping is "1-10%", for example, 1%, 3%, 5%, 7% or 10%, and the range of nitrogen doping is "1-19%", for example, 1%, 5%, 10%, 15% or 19%, etc.

[0053] Preferably, the particle size D50 of the cobalt nanoparticles is 10-22nm, for example, it can be 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm or 22nm, etc.

[0054] Thirdly, the present invention provides an application of the cobalt-based catalyst as described in the second aspect in a metal-air battery.

[0055] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) This invention achieves boron-nitrogen co-doping of cobalt-based catalysts through boron source and chelating agent. The boron source effectively regulates the electronic structure of cobalt, and the chelating agent can increase the nitrogen content in the carbon support and inhibit the aggregation of cobalt nanoparticles. Through the synergistic effect of boron source and chelating agent, cobalt nanoparticles are loaded on the boron-nitrogen co-doped carbon support. This not only forms cobalt-nitrogen-boron active sites on the surface of cobalt nanoparticles, but also effectively increases the content of active sites, thereby significantly improving the oxygen reduction performance of cobalt-based catalysts. When applied to the battery field, it can provide a larger power density.

[0058] (2) The preparation method provided by the present invention has simple steps, is easy to operate, and has good application prospects. Attached Figure Description

[0059] Figure 1 This is a TEM spectrum of the cobalt-based catalyst prepared in Example 1 of this invention at a 100 nm scale.

[0060] Figure 2 This is a particle size distribution diagram of the cobalt-based catalyst prepared in Example 1 of the present invention.

[0061] Figure 3 This is a TEM spectrum of the cobalt-based catalyst prepared in Comparative Example 1 of this invention at a 100 nm scale.

[0062] Figure 4This is a particle size distribution diagram of the cobalt-based catalyst prepared in Comparative Example 1 of the present invention.

[0063] Figure 5 This is a TEM spectrum of the cobalt-based catalyst prepared in Comparative Example 3 of this invention at a 100 nm scale.

[0064] Figure 6 This is a particle size distribution diagram of the cobalt-based catalyst prepared in Comparative Example 3 of the present invention.

[0065] Figure 7 This is a comparison of the linear voltammetric curves of the cobalt-based catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 3 of the present invention.

[0066] Figure 8 This is a comparison graph of the current density-power density curves of the cobalt-based catalysts prepared in Examples 1, 1, and 3 of this invention with those of commercial Pt / C catalysts. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0068] Example 1

[0069] This embodiment provides a method for preparing a boron-nitrogen co-doped cobalt-based catalyst, the method comprising the following steps:

[0070] (1) Grind 0.1g of boric acid and 10g of urea in a mortar for 10 minutes to obtain powder;

[0071] (2) Spread the powder evenly in a porcelain boat and pyrolyze it at 550°C for 1 hour under a nitrogen atmosphere to obtain boron-containing nitride, namely Bg-C3N4;

[0072] (3) Grind 0.8g of the boron-containing nitride, 0.2g of cobalt chloride hexahydrate and 3mL of ethanol in a mortar for 10min, then add 47mL of ethanol, then sonicate for 10min, and then stir for 2h to obtain a mixed suspension.

[0073] (4) Add 50 mL of an ethanol solution containing 0.5 g of 1,10-phenanthroline dropwise to the mixed suspension, continue stirring for 6 h, and then rotary evaporate to obtain the mixture;

[0074] (5) Spread the mixture in a ceramic boat and pyrolyze it at 950°C for 1 h under a nitrogen atmosphere to obtain a cobalt-based catalyst. The cobalt-based catalyst includes a boron-nitrogen co-doped carbon support and cobalt nanoparticles loaded on the carbon support. The surface of the cobalt nanoparticles is modified with cobalt-nitrogen-boron active sites.

[0075] Specifically, based on the mass of the boron-nitrogen co-doped carbon support, the total doping amount of boron and nitrogen in the carbon support is 11%, the doping ratio of boron to nitrogen in the carbon support is 3:8, and the particle size D50 of the cobalt nanoparticles is 14 nm.

[0076] Figure 1 The TEM spectrum of the cobalt-based catalyst prepared in this embodiment is shown at a 100 nm scale. As can be seen from the figure, this catalyst is mainly composed of carbon nanosheets and cobalt nanoparticles.

[0077] Figure 2 The particle size distribution of the cobalt-based catalyst prepared in this embodiment is shown. As can be seen from the figure, the nanoparticles of the catalyst are distributed in the range of 10-22 nm, with an average particle size of 14 nm.

[0078] Example 2

[0079] The difference between this embodiment and embodiment 1 is that the mass of boric acid added in step (1) is 0.2g.

[0080] The remaining preparation methods and parameters are consistent with those in Example 1.

[0081] Example 3

[0082] The difference between this embodiment and embodiment 1 is that the mass of 1,10-phenanthroline added in step (4) is 1g.

[0083] The remaining preparation methods and parameters are consistent with those in Example 1.

[0084] Example 4

[0085] The difference between this embodiment and embodiment 1 is that urea is replaced with dicyandiamide in step (1).

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Example 5

[0088] The difference between this embodiment and embodiment 1 is that urea is replaced with melamine in step (1).

[0089] The remaining preparation methods and parameters are consistent with those in Example 1.

[0090] Example 6

[0091] The difference between this embodiment and embodiment 1 is that 1,10-phenanthroline is replaced with pyrrole in step (4).

[0092] The remaining preparation methods and parameters are consistent with those in Example 1.

[0093] Example 7

[0094] This embodiment provides a method for preparing a boron-nitrogen co-doped cobalt-based catalyst, the method comprising the following steps:

[0095] (1) Grind 0.1g of boric acid and 1g of urea in a mortar for 5 minutes to obtain powder;

[0096] (2) Spread the powder evenly in a porcelain boat and pyrolyze it at 350°C for 2 hours under a nitrogen atmosphere to obtain boron-containing nitride, namely Bg-C3N4;

[0097] (3) Grind 0.4g of the boron-containing nitride, 0.2g of cobalt nitrate hexahydrate and 3mL of ethanol in a mortar for 10min, then add 47mL of ethanol, then sonicate for 10min, and then stir for 1h to obtain a mixed suspension.

[0098] (4) Add 50 mL of an ethanol solution containing 0.2 g of pyridine dropwise to the mixed suspension, continue stirring for 4 h, and then rotary evaporate to obtain the mixture;

[0099] (5) Spread the mixture in a ceramic boat and pyrolyze it at 700°C for 2 hours under a nitrogen atmosphere to obtain a cobalt-based catalyst. The cobalt-based catalyst includes a boron-nitrogen co-doped carbon support and cobalt nanoparticles loaded on the carbon support. The surface of the cobalt nanoparticles is modified with cobalt-nitrogen-boron active sites.

[0100] Specifically, based on the mass of the boron-nitrogen co-doped carbon support, the total doping amount of boron and nitrogen in the carbon support is 8%, the doping ratio of boron to nitrogen in the carbon support is 1:7, and the particle size D50 of the cobalt nanoparticles is 10 nm.

[0101] Example 8

[0102] This embodiment provides a method for preparing a boron-nitrogen co-doped cobalt-based catalyst, the method comprising the following steps:

[0103] (1) Grind 0.1g of boric acid and 50g of urea in a mortar for 15 minutes to obtain powder;

[0104] (2) Spread the powder evenly in a porcelain boat and pyrolyze it at 750°C for 1.5 h under a nitrogen atmosphere to obtain boron nitride, namely Bg-C3N4;

[0105] (3) Grind 4g of the boron-containing nitride, 0.2g of cobalt chloride hexahydrate and 3mL of methanol in a mortar for 10min, then add 47mL of methanol, then sonicate for 10min, and then stir for 3h to obtain a mixed suspension.

[0106] (4) Add 50 mL of a methanol solution containing 2 g of 1,10-phenanthroline dropwise to the mixed suspension, continue stirring for 8 h, and then rotary evaporate to obtain the mixture;

[0107] (5) Spread the mixture in a ceramic boat and pyrolyze it at 1050°C for 1.5 h under a nitrogen atmosphere to obtain a cobalt-based catalyst. The cobalt-based catalyst includes a boron-nitrogen co-doped carbon support and cobalt nanoparticles supported on the carbon support. The surface of the cobalt nanoparticles is modified with cobalt-nitrogen-boron active sites.

[0108] Specifically, based on the mass of the boron-nitrogen co-doped carbon support, the total doping amount of boron and nitrogen in the carbon support is 16%, the doping ratio of boron to nitrogen in the carbon support is 4:12, and the particle size D50 of the cobalt nanoparticles is 22 nm.

[0109] Example 9

[0110] The difference between this embodiment and embodiment 1 is that the mass of the boron-containing nitride in step (3) is 0.15g, that is, the mass ratio of cobalt chloride hexahydrate to boron-containing nitride is 1:0.75.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 10

[0113] The difference between this embodiment and embodiment 1 is that the mass of the boron-containing nitride in step (3) is 5g, that is, the mass ratio of cobalt chloride hexahydrate to boron-containing nitride is 1:25.

[0114] The remaining preparation methods and parameters are consistent with those in Example 1.

[0115] Example 11

[0116] The difference between this embodiment and embodiment 1 is that the mass of 1,10-phenanthroline in step (4) is 0.15g, that is, the mass ratio of cobalt chloride hexahydrate to 1,10-phenanthroline is 1:0.75.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 12

[0119] The difference between this embodiment and embodiment 1 is that the mass of 1,10-phenanthroline in step (4) is 3g, that is, the mass ratio of cobalt chloride hexahydrate to 1,10-phenanthroline is 1:15.

[0120] The remaining preparation methods and parameters are consistent with those in Example 1.

[0121] Example 13

[0122] The difference between this embodiment and embodiment 1 is that the pyrolysis temperature in step (5) is 600℃.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 14

[0125] The difference between this embodiment and embodiment 1 is that the pyrolysis temperature in step (5) is 1150℃.

[0126] The remaining preparation methods and parameters are consistent with those in Example 1.

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 1 is that boric acid is not added in step (1).

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Figure 3 The TEM spectrum of the cobalt-based catalyst prepared in this comparative example is shown at a 100 nm scale. As can be seen from the figure, this catalyst is mainly composed of carbon nanosheets and nanoparticles.

[0131] Figure 4 The particle size distribution of the cobalt-based catalyst prepared in this comparative example is shown. As can be seen from the figure, the nanoparticles are distributed in the range of 8-28 nm, with an average particle size of 15.6 nm.

[0132] Comparative Example 2

[0133] The difference between this comparative example and Example 1 is that 1,10-phenanthroline is not added in step (4).

[0134] The remaining preparation methods and parameters are consistent with those in Example 1.

[0135] Comparative Example 3

[0136] The difference between this comparative example and Example 1 is that boric acid is not added in step (1) and 1,10-phenanthroline is not added in step (4).

[0137] The remaining preparation methods and parameters are consistent with those in Example 1.

[0138] Figure 5 The TEM spectrum of the cobalt-based catalyst prepared in this comparative example is shown at a 100 nm scale. As can be seen from the figure, the catalyst is mainly composed of carbon nanotubes and nanoparticles.

[0139] Figure 6The particle size distribution of the cobalt-based catalyst prepared in this comparative example is shown. As can be seen from the figure, the nanoparticles are distributed in the range of 5-45 nm, with an average particle size of 19.4 nm.

[0140] Performance testing

[0141] 5 mg of the cobalt-based catalysts provided in Examples 1-14 and Comparative Examples 1-3 were weighed and added to a mixed solution containing 485 μL of anhydrous ethanol, 500 μL of deionized water, and 15 μL of 5% Nafion solution, respectively. The mixture was sonicated for 30 minutes to obtain a homogeneous suspension. Then, 7 μL of the homogeneous solution was drop-coated onto a rotating disk electrode with a diameter of 3 mm and allowed to air dry. The catalyst loading was 510 μg / cm³. -2 It was used as the working electrode, in conjunction with a saturated calomel electrode (reference electrode) and a platinum sheet (1 cm). 2 A three-electrode system consisting of (counter electrode) was used to perform linear sweep voltammetry in a 0.1M potassium hydroxide solution saturated with O2.

[0142] Test conditions: potential window of -0.685-0.315V vs Hg / HgO, scan rate of 5mV / s, and electrode rotation rate of 1600rpm.

[0143] Test results are as follows Figure 7 , Figure 8 As shown in Table 1.

[0144] Figure 7 A comparison of linear voltammetric curves for the cobalt-based catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 3 is shown. As can be seen from the figure, the half-wave potentials of Comparative Example 1, Comparative Example 3, and Example 1 are 0.789, 0.795, and 0.828 V vs RHE, respectively. This indicates that the introduction of the boron source and chelating agent can improve the oxygen reduction performance of the catalyst. Example 1 exhibits the best oxygen reduction performance and is superior to commercial Pt / C (0.805 V vs RHE).

[0145] Figure 8 The current-power curves of the cobalt-based catalysts prepared in Examples 1, 1, and 3, and the commercial Pt / C catalyst are shown in the figure. As can be seen from the figure, Example 1 has the highest power density of 24.9 mW / cm². -2 It is about 20% higher than commercial Pt / C.

[0146] Table 1

[0147]

[0148]

[0149] analyze:

[0150] As shown in the table above, the preparation method provided by the present invention can effectively increase the content of active sites in cobalt-based catalysts, thereby significantly improving the oxygen reduction performance of cobalt-based catalysts and providing a larger power density when applied in the battery field.

[0151] A comparison of the data results from Examples 1 and 9-10 shows that if the mass ratio of cobalt source to boron-containing compound is too small, the boron-nitrogen content will be too high, the conductivity of the catalyst will decrease, resulting in a decrease in oxygen reduction performance; if the mass ratio of cobalt source to boron-containing compound is too large, there will be too much metallic cobalt, which will not have an obvious effect on promoting the reaction, thus leading to a decrease in performance.

[0152] A comparison of the data results from Examples 1 and 11-12 shows that if the mass ratio of cobalt source to chelating agent is too high, metallic cobalt will aggregate, resulting in a decrease in catalyst performance; if the mass ratio of cobalt source to chelating agent is too low, the excessive chelating agent will decompose into carbon and nitrogen materials after pyrolysis, which will not have an obvious effect on promoting the reaction. Although the performance will not be significantly reduced, the cost will be significantly increased.

[0153] Comparison of the data results of Example 1 and Examples 13-14 shows that if the pyrolysis temperature in step (5) is too low, the degree of graphitization will be too low, which is not conducive to electron transport and thus leads to a decrease in performance; if the pyrolysis temperature in step (5) is too high, the cobalt nanoparticles will aggregate and thus lead to a decrease in catalyst performance.

[0154] A comparison of the data results from Example 1 and Comparative Example 1 shows that if no boron source is added, a cobalt-nitrogen active site is obtained, but its catalytic performance is lower than that of the cobalt-nitrogen-boron active site, resulting in a decrease in catalyst performance.

[0155] A comparison of the data results from Example 1 and Comparative Example 2 shows that if no chelating agent is added, a cobalt-boron active site is obtained, but its catalytic performance is lower than that of the cobalt-nitrogen-boron active site. At the same time, larger nanoparticles will appear, leading to a decrease in catalyst performance.

[0156] A comparison of the data results from Example 1 and Comparative Example 3 shows that if no boron source and chelating agent are added, the catalyst contains low levels of active sites and large-sized nanoparticles, resulting in a decrease in catalyst performance.

[0157] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a cobalt-based catalyst, characterized in that, The preparation method includes the following steps: (1) A boron source and a nitrogen-containing carbon source are mixed and pyrolyzed to obtain boron-containing nitrides; (2) The boron-containing nitride, cobalt source, chelating agent and alcohol solvent are mixed and pyrolyzed to obtain the cobalt-based catalyst; The chelating agent in step (2) includes any one or a combination of at least two of 1,10-phenanthroline, pyrrole, pyridine, or 2-methylimidazole; The atmosphere for pyrolysis in step (1) is an inert atmosphere; The atmosphere for pyrolysis in step (2) is an inert atmosphere; The cobalt-based catalyst comprises a boron-nitrogen co-doped carbon support and an active component supported on the carbon support, wherein the active component is cobalt nanoparticles.

2. The preparation method according to claim 1, characterized in that, The boron source in step (1) includes any one or a combination of at least two of boric acid, sodium borohydride or borax.

3. The preparation method according to claim 1, characterized in that, The nitrogen-containing carbon source in step (1) includes any one or a combination of at least two of urea, melamine or dicyandiamide.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the boron source and the nitrogen-containing carbon source in step (1) is 1:(1-1000).

5. The preparation method according to claim 4, characterized in that, The mass ratio of the boron source and the nitrogen-containing carbon source in step (1) is 1:(100-200).

6. The preparation method according to claim 1, characterized in that, The mixing process described in step (1) is accompanied by stirring.

7. The preparation method according to claim 1, characterized in that, The mixing time in step (1) is 5-15 minutes.

8. The preparation method according to claim 1, characterized in that, The pyrolysis temperature in step (1) is 350-750℃.

9. The preparation method according to claim 1, characterized in that, The pyrolysis time in step (1) is 1-2 hours.

10. The preparation method according to claim 1, characterized in that, The gas in the inert atmosphere in step (1) includes nitrogen.

11. The preparation method according to claim 1, characterized in that, The cobalt source in step (2) is a cobalt salt.

12. The preparation method according to claim 11, characterized in that, The cobalt salts include cobalt chloride hexahydrate and / or cobalt nitrate hexahydrate.

13. The preparation method according to claim 1, characterized in that, The chelating agent in step (2) is 1,10-phenanthroline.

14. The preparation method according to claim 1, characterized in that, The alcohol solvents mentioned in step (2) include methanol and / or ethanol.

15. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the cobalt source to the boron nitride is 1:(1-20).

16. The preparation method according to claim 1, characterized in that, The mass ratio of the cobalt source and the chelating agent in step (2) is 1:(1-10).

17. The preparation method according to claim 1, characterized in that, The mixing method described in step (2) includes: (a) A mixed suspension is obtained by mixing a boron-containing nitride, a cobalt source, and a portion of an alcohol solvent; (b) Mix the mixed suspension, chelating agent and another portion of alcohol solvent.

18. The preparation method according to claim 17, characterized in that, After the boron-containing nitride described in step (a) is mixed with a cobalt source and a portion of an alcohol solvent, it is first crushed and then stirred for 1-3 hours.

19. The preparation method according to claim 17, characterized in that, The mixing process described in step (b) is accompanied by stirring.

20. The preparation method according to claim 17, characterized in that, The mixing time in step (b) is 4-8 hours.

21. The preparation method according to claim 18, characterized in that, The fragmentation method includes ultrasonic fragmentation.

22. The preparation method according to claim 1, characterized in that, Drying is performed before pyrolysis in step (2).

23. The preparation method according to claim 1, characterized in that, The pyrolysis temperature in step (2) is 700-1050℃.

24. The preparation method according to claim 1, characterized in that, The pyrolysis time in step (2) is 1-2 hours.

25. The preparation method according to claim 1, characterized in that, The gas in the inert atmosphere in step (2) includes nitrogen.

26. A cobalt-based catalyst prepared by the method according to any one of claims 1-25, characterized in that, The cobalt-based catalyst comprises a boron-nitrogen co-doped carbon support and an active component supported on the carbon support, wherein the active component is cobalt nanoparticles.

27. The cobalt-based catalyst according to claim 26, characterized in that, Based on the mass of the boron-nitrogen co-doped carbon support, the total doping amount of boron and nitrogen in the carbon support is 1-20%.

28. The cobalt-based catalyst according to claim 27, characterized in that, The ratio of boron to nitrogen doping in the carbon support is (1-10):(1-19).

29. The cobalt-based catalyst according to claim 26, characterized in that, The cobalt nanoparticles have a particle size D50 of 10-22 nm.

30. The application of a cobalt-based catalyst as described in any one of claims 26-29 in a metal-air battery.

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