A triatomic cobalt catalyst and its preparation method and application

Abstract

The present invention is directed to the field of energy catalysis, including a kind of triatomic cobalt catalyst and its preparation method and application, the carrier used in the present invention is graphene oxide (GO), and a precursor is a synthesized cobalt cluster complex (Co3L), utilizing the electrostatic adsorption effect between Co3L and the GO surface, GO and Co3L suspension are uniformly dispersed in deionized water and then freeze-dried to prepare Co3L-GO material. Subsequently, Co3L-GO material is rapidly annealed in an inert protective atmosphere to obtain a triatomic cobalt catalyst (Co3-NG) supported by nitrogen-doped graphene. The method controllably synthesizes a catalyst with Co3ON6 active sites, effectively regulates the d band center and electronic structure of metallic cobalt, promotes the adsorption / desorption of Co3-NG and oxygen intermediates, and makes Co3-NG have good oxygen reduction performance. The method effectively suppresses the aggregation of metal atoms, synthesizes a catalyst with clear sites, improves the oxygen reduction reaction and zinc-air battery performance of the catalyst, and is expected to replace currently commercial precious metal Pt-based catalysts.

Description

Technical Field

[0001] The present invention is directed to the field of energy electrocatalysis, including a method for synthesizing nitrogen-doped graphene-supported triatomic cobalt catalysts and their application in oxygen reduction reactions and zinc-air batteries. Background Art

[0002] The development of efficient and stable oxygen reduction reaction catalysts is of great significance for advancing metal-air battery and fuel cell technologies. However, ORR is a four-electron process that exhibits slow kinetics and high energy barriers. Currently, commercial ORR catalysts are mainly based on Pt-based precious metals, but the scarcity and high cost of Pt limit its large-scale application. In recent years, multi-atom catalysts (MACs) have become a class of cutting-edge catalysts with promising applications due to their 100% atomic utilization and unique physicochemical properties. They can provide multiple adsorption sites, breaking the linear scaling relationship of single-atom catalysts and being suitable for catalytic processes involving multiple reaction steps and complex intermediates. In addition, the formation of metal-metal bonds or metal-bridge atom bonds in MACs can effectively regulate electronic configuration and geometric configuration. MACs show great potential and can serve as an ideal platform for identifying and regulating the structure of active centers to improve catalytic activity.

[0003] Triatomic catalysts have made some progress in catalyzing ORR activity. However, they still face huge problems in directional and controllable synthesis. The key issue is to suppress the agglomeration of atoms caused by high surface energy while having excellent ORR activity. Therefore, controllable synthesis of target catalysts is of paramount importance. The Chinese invention patent application with patent publication number CN116196928A discloses "a graphene-based diatomic copper-cobalt catalyst and its preparation method and application". The synthesis method is to disperse graphene nanosheets and copper salt / cobalt salt in a first dispersion to obtain a first mixed solution, followed by drying and instantaneous calcination to obtain a first mixture, and then disperse the first mixture and cobalt salt / copper salt in a second dispersion to obtain a second mixed solution, and then dry and instantaneously calcinate to obtain a graphene-based diatomic copper-cobalt catalyst. The catalyst preparation process has a certain degree of randomness. The Chinese invention patent application with patent publication number CN118538938A discloses "a nitrogen-sulfur-doped carbon-supported iron diatomic oxygen reduction catalyst, its preparation method and application". First, a sulfur-bridged iron dinuclear complex precursor is synthesized, which is then encapsulated into ZIF-8. After pyrolysis, the main carrier with the molecular framework is retained to obtain a nitrogen-sulfur-doped carbon-supported iron diatomic catalyst. However, MOF materials are difficult to synthesize and difficult to produce on a large scale. In addition, the atomic dispersion is difficult to control during the preparation process, metals in the MOF may remain after pyrolysis, and the particle size of the catalyst is large, which affects its further application. In addition, there are currently no reports on the controllable synthesis of triatomic cobalt catalysts and their application in ORR and zinc-air batteries. Summary of the Invention

[0004] To address the challenges of current synthesis techniques, we devised a rapid imprinting technique to synthesize triatomic cobalt catalysts. This technique effectively inhibits atomic migration and allows for the precise synthesis of targeted active sites. The resulting triatomic cobalt catalyst effectively catalyzes the ORR and exhibits excellent stability when used as an air electrode catalyst in zinc-air batteries.

[0005] The present invention first synthesizes a cobalt cluster precursor (Co3L) and graphene oxide, then uniformly disperses the two in an aqueous solution, obtains a Co3L-GO material by freeze-drying, and rapidly calcines it under an inert gas atmosphere to obtain a triatomic cobalt catalyst. The precursor is adsorbed on the carrier through electrostatic interaction, and the rapid calcination technology can inhibit the migration of atoms and avoid the formation of nanoparticles. The precursor Co3L has three adjacent cobalt atoms, and the triatomic cobalt is imprinted into the graphene during the calcination process. The obtained triatomic cobalt catalyst can effectively catalyze the ORR and exhibits excellent stability when assembled into a zinc-air battery as an air electrode catalyst.

[0006] The specific technical solutions are as follows:

[0007] 1) Prepare the Co3L precursor first: add 1.5g Co(CH3COO)24H2O to 15mL of glacial acetic acid and 0.5mL of pyridine, then stir and heat until all the solids are dissolved. Cool the solution and add freshly prepared peracetic acid solution (0.5mL of hydrogen peroxide solution mixed with 0.3mL of glacial acetic acid) dropwise under stirring. The color of the solution turns dark brown. Add 3mL of distilled water to it, reflux at 80°C for 1h, cool it, and add 20mL of aqueous solution dissolved in 0.5g of sodium chloride. After one week, microcrystals (Co3L) are precipitated.

[0008] 2) Weigh 5 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0009] 3) Freeze the suspension with liquid nitrogen and remove the water using a freeze-drying device to obtain black Co3L-GO powder material;

[0010] 4) The Co3L-GO material was rapidly calcined for 5s under an inert gas atmosphere to obtain Co3-NG.

[0011] The invention also discloses the application of the triatomic cobalt catalyst in oxygen reduction reaction and zinc-air battery.

[0012] The beneficial effects of the present invention are as follows: the present invention adopts a synthetic trinuclear cobalt precursor as a cobalt source, and the target catalyst is controllably synthesized to greatly improve its performance in the oxygen reduction reaction. The preparation process is simple and the prepared triatomic cobalt catalyst has a half-wave potential of E in the oxygen reduction reaction. 1 / 2 =0.878V, which is superior to commercial Pt / C catalysts. The zinc-air battery assembled with it as the air cathode showed excellent stability. This has important practical significance for the widespread application of zinc-air battery energy storage devices in practical production and life. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following drawings required for describing the embodiments or the prior art are provided;

[0014] Figure 1 is a flow chart of a method for synthesizing a tri-atom catalyst according to an embodiment of the present invention;

[0015] Figure 2 is the X-ray diffraction pattern of Comparative Example 1 and Examples 1, 2, 3, 4 and 5;

[0016] Figure 3 is a transmission electron microscope image of Example 1;

[0017] Figure 4 is a spherical aberration corrected transmission electron microscope image of Example 1;

[0018] Figure 5 1 is the linear sweep voltammetry curve of the catalysts prepared in Examples 1, 2, 3, 4 and 5;

[0019] Figure 6 The linear sweep voltammetry curves of the catalysts prepared in Example 1 and the comparative example and commercial 20 wt% Pt / C are shown;

[0020] Figure 7 is a stability comparison curve of Example 1 and commercial 20 wt% Pt / C; DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] The specific embodiments of the present invention are described below to make the objectives, technical solutions and advantages of the present invention more clearly understood. The present invention can be implemented in various forms and is not limited to the embodiments described herein.

[0023] Comparative Example 1

[0024] 1) Weigh 4.9 mg of Co(NO3)2·6H2O and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0025] 2) Freezing the suspension with liquid nitrogen and removing the water therein using a freeze-drying device to obtain a black Co-GO powder material;

[0026] 3) Weigh 20 mg of Co-GO material and place it in a porcelain boat. Under the protection of an ammonia atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain Co-NG.

[0027] Example 1

[0028] 1) Prepare the Co3L precursor first: add 1.5g Co(CH3COO)24H2O to 15mL of glacial acetic acid and 0.4mL of pyridine, then stir and heat until all the solids are dissolved. Cool the solution and add freshly prepared peracetic acid solution (0.5mL of hydrogen peroxide solution mixed with 0.3mL of glacial acetic acid) dropwise with stirring. The color of the solution turns dark brown. Add 3mL of distilled water to it, reflux at 80°C for 1h, cool it, and add 20mL of aqueous solution dissolved in 0.5g of sodium chloride. After one week, microcrystals (Co3L) are precipitated.

[0029] 2) Weigh 5 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0030] 3) Freeze the suspension with liquid nitrogen and remove the water using a freeze-drying device to obtain black Co3L-GO powder material;

[0031] 4) Weigh 20 mg of Co3L-GO material and place it in a porcelain boat. Under the protection of an inert gas atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain 1 wt% Co3-NG (simplified as Co3-NG).

[0032] Example 2

[0033] 1) Weigh 2.5 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0034] 2) After freezing the suspension with liquid nitrogen, the water was removed using a freeze-drying device to obtain black Co3L-GO powder material;

[0035] 3) Weigh 20 mg of Co3L-GO material and place it in a porcelain boat. Under the protection of an inert gas atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain 0.5 wt% Co3-NG.

[0036] Example 3

[0037] 1) Weigh 4 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0038] 2) After freezing the suspension with liquid nitrogen, the water was removed using a freeze-drying device to obtain black Co3L-GO powder material;

[0039] 3) Weigh 20 mg of Co3L-GO material and place it in a porcelain boat. Under the protection of an inert gas atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain 0.8 wt% Co3-NG.

[0040] Example 4

[0041] 1) Weigh 6 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0042] 2) After freezing the suspension with liquid nitrogen, the water was removed using a freeze-drying device to obtain black Co3L-GO powder material;

[0043] 3) Weigh 20 mg of Co3L-GO material and place it in a porcelain boat. Under the protection of an inert gas atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain 1.2 wt% Co3-NG.

[0044] Example 5

[0045] 1) Weigh 7.5 mg of the synthesized Co3L precursor and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 min, and ultrasonicate for 1 h to obtain a uniform suspension.

[0046] 2) After freezing the suspension with liquid nitrogen, the water was removed using a freeze-drying device to obtain black Co3L-GO powder material;

[0047] 3) Weigh 20 mg of Co3L-GO material and place it in a porcelain boat. Under the protection of an inert gas atmosphere, quickly calcine it at 2000°C for 5 seconds to obtain 1.5 wt% Co3-NG.

[0048] Structural inspection

[0049] Figure 1 The synthesis process of the triatom catalyst is described.

[0050] Figure 2 The XRD results show that there is no diffraction peak of Co nanoparticles in the samples of Comparative Example 1 and Examples 1, 2, 3, and 4, indicating that the above samples do not aggregate to form cobalt nanoparticles at high temperature.

[0051] according to Figure 3 and Figure 4 High-resolution transmission electron microscopy images and spherical aberration-corrected transmission electron microscopy images show that there are no Co nanoparticles in the sample of Example 1 synthesized by the above method, and three atoms with a triangle can be seen in the spherical aberration-corrected transmission electron microscopy image, which are considered to be three-atom sites. This shows that this method can effectively synthesize three-atom catalysts and effectively inhibit atomic agglomeration.

[0052] Performance testing

[0053] In order to evaluate the catalytic activity of the samples of Comparative Example 1 and Examples 1, 2, 3, and 4 for ORR, we conducted a performance evaluation in oxygen-saturated 0.1 M KOH. The specific steps are as follows: 2 mg of the sample was mixed with 200 uL of 0.25 wt% Nafion solution and ultrasonicated for 1 hour. The obtained ink was dropped onto a rotating ring disk electrode and naturally dried to form a film to obtain a working electrode, wherein the reference electrode was Hg / Hg2Cl2 and the counter electrode was a platinum sheet.

[0054] The ORR activity of Example 1 is better than that of Comparative Example 1, Examples 2, 3, 4 and commercial 20 wt% Pt / C, and Example 1 exhibits excellent stability.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a triatomic cobalt catalyst, characterized in that: The following steps are involved: 1) Prepare the Co3L precursor first: add 1.5 g Co(CH3COO)2·4H2O to 15 mL of glacial acetic acid and 0.5 mL of pyridine, then stir and heat until the solid is completely dissolved; cool the solution, and add a mixture of freshly prepared 0.5 mL of hydrogen peroxide solution and 0.3 mL of glacial acetic acid dropwise under stirring until the color of the solution turns dark brown; then add 3 mL of distilled water, reflux at 80 °C for 1 h, cool, and add 20 mL of aqueous solution of 0.5 g of sodium chloride. After one week, microcrystalline Co3L will precipitate; 2) Weigh 5 mg of Co3L and 100 mg of graphene oxide and add them to a 100 mL beaker with a magnet. Then add 50 mL of distilled water to the beaker, stir for 10 min, and sonicate for 1 h to obtain a uniform suspension. 3) Freeze the suspension with liquid nitrogen and remove the water using a freeze-drying device to obtain black Co3L-GO powder material; 4) The Co3L-GO material was rapidly calcined at 2000 °C for 5 s under inert gas protection to obtain Co3-NG.

2. The triatomic cobalt catalyst prepared by the method for preparing the triatomic cobalt catalyst according to claim 1.

3. Use of the triatomic cobalt catalyst as claimed in claim 2 in an electrocatalytic oxygen reduction reaction.

4. Use of the triatomic cobalt catalyst as claimed in claim 2 in a zinc-air battery.

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