Triatomic cobalt catalyst and preparation method and application thereof

Abstract

Aiming at the field of energy catalysis, the invention provides a triatomic cobalt catalyst and a preparation method and application thereof, a carrier used in the invention is graphene oxide (GO), a precursor is a synthesized cobalt cluster complex (Co3L), and a Co3L-GO material is prepared by uniformly dispersing a suspension of GO and Co3L in deionized water by utilizing an electrostatic adsorption effect between the Co3L and the surface of GO and then freeze-drying. Then, the Co3L-GO material is rapidly annealed in an inert protective atmosphere, and the nitrogen-doped graphene loaded triatomic cobalt catalyst (Co3-NG) is obtained. The method controllably synthesizes the catalyst with Co3ON6 active sites, effectively adjusts the d-band center and electronic structure of metal cobalt, promotes adsorption / desorption of Co3-NG and an oxygen intermediate, and enables Co3-NG to have good oxygen reduction performance. The method effectively inhibits the aggregation of metal atoms, synthesizes the catalyst with definite sites, improves the oxygen reduction reaction and zinc-air battery performance of the catalyst, and is expected to replace the current commercial noble metal Pt-based catalyst.

Description

Technical Field

[0001] The present invention is directed to the field of energy electrocatalysis, including a method for synthesizing a nitrogen-doped graphene-supported triatomic cobalt catalyst and its 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 technology. 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, which can provide multiple adsorption sites, break the linear proportional relationship of single-atom catalysts, and are 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 configurations and geometric configurations. MACs show great potential 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 catalytic ORR activity. However, they still face huge problems in directional controllable synthesis. The key problem is to suppress atomic agglomeration 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 calcine 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 and 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 of 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 mass produce. 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 applications in ORR and zinc-air batteries. Summary of the invention

[0004] Based on the problems faced by current synthesis technology, we designed a rapid imprinting technology to synthesize triatomic cobalt catalysts, which can effectively inhibit atomic migration and accurately synthesize target active sites. The obtained triatomic cobalt catalyst can effectively catalyze ORR, and it is assembled into zinc-air batteries as air electrode catalysts, showing excellent stability.

[0005] The present invention first synthesizes a cobalt cluster precursor (Co3L) and graphene oxide, then evenly disperses the two in an aqueous solution, obtains a Co3L-GO material by freeze drying, and rapidly calcines it in an inert gas atmosphere to obtain a triatomic cobalt catalyst. The precursor is adsorbed on the carrier by electrostatic action, 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 ORR, and it is assembled into a zinc-air battery as an air electrode catalyst to show excellent stability.

[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, add the freshly prepared peracetic acid solution (0.5mL of hydrogen peroxide solution mixed with 0.3mL of glacial acetic acid) dropwise under stirring, and the color of the solution turns dark brown. Add 3mL of distilled water to it, reflux at 80℃ for 1h, cool it, add 20mL of aqueous solution dissolved in 0.5g of sodium chloride, and microcrystals (Co3L) will precipitate after one week.

[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 min, and ultrasonicate for 1 h to obtain a uniform suspension;

[0009] 3) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment to obtain black Co3L-GO powder material;

[0010] 4) The Co3L-GO material was rapidly calcined for 5 seconds in 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, controllably synthesizes the target catalyst, greatly improves 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 better than commercial Pt / C catalyst, and the zinc-air battery assembled with it as air cathode shows excellent stability. This has important practical significance for the widespread application of zinc-air battery energy storage devices in actual production and life. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0014] Figure 1 is a flow chart of a method for synthesizing a tri-atom catalyst in 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 the spherical aberration corrected transmission electron microscope image of Example 1;

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

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

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

[0021] In order to make the purpose, technical solution 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 used to limit the present invention.

[0022] The specific implementation modes of the present invention are described below so as 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 Co(NO3)2·6H2O and 100 mg graphene oxide and add them into a 100 mL beaker with a magnet. Then add 50 mL of distilled water into the beaker, stir for 10 minutes, and ultrasonicate for 1 hour to obtain a uniform suspension.

[0025] 2) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment to obtain 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, add the freshly prepared peracetic acid solution (0.5mL of hydrogen peroxide solution mixed with 0.3mL of glacial acetic acid) dropwise under stirring, and the color of the solution turns dark brown. Add 3mL of distilled water to it, reflux at 80℃ for 1h, cool it, add 20mL of aqueous solution dissolved in 0.5g of sodium chloride, and microcrystals (Co3L) will precipitate after one week.

[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 min, and ultrasonicate for 1 h to obtain a uniform suspension;

[0030] 3) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment 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 into a 100 mL beaker with a magnet. Then add 50 mL of distilled water into the beaker, stir for 10 min, and ultrasonicate for 1 h to obtain a uniform suspension.

[0034] 2) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment 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 into a 100 mL beaker with a magnet. Then add 50 mL of distilled water into the beaker, stir for 10 min, and ultrasonicate for 1 h to obtain a uniform suspension.

[0038] 2) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment 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 into a 100 mL beaker with a magnet. Then add 50 mL of distilled water into the beaker, stir for 10 min, and ultrasonicate for 1 h to obtain a uniform suspension.

[0042] 2) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment 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 into a 100 mL beaker with a magnet. Then add 50 mL of distilled water into 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 therein is removed by freeze drying equipment 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 three-atom catalyst is described.

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

[0051] according to Figure 3 and Figure 4 It can be seen from the high-resolution transmission electron microscope image and the spherical aberration corrected transmission electron microscope image 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 microscope 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 embodiments 1, 2, 3, and 4 for ORR, we conducted a performance evaluation in 0.1M KOH saturated with oxygen. 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 principle of the present invention should be included in the protection scope 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 1.5g 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, add freshly prepared peracetic acid solution (0.5mL of hydrogen peroxide solution mixed with 0.3mL of glacial acetic acid) dropwise under stirring, and the color of the solution turns dark brown; then add 3mL of distilled water, reflux at 80°C for 1h, cool, add 0.5g of sodium chloride dissolved in 20mL of aqueous solution, and microcrystals (Co3L) are precipitated after one week; 2) Weigh 5 mg Co3L and 100 mg 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; 3) After freezing the suspension with liquid nitrogen, the water therein is removed by freeze drying equipment to obtain black Co3L-GO powder material; 4) The Co3L-GO material was rapidly calcined at 2000°C for 5s under inert gas protection to obtain Co3-NG.

2. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 1), ensure the synthesis of Co3L precursor.

3. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 2), the Co3L precursor and graphene oxide are uniformly dispersed in 50 mL of distilled water.

4. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 2), 5 mg of Co3L precursor and 100 mg of graphene oxide were weighed to achieve precise control of the mass fraction of Co species, and the mass of the added Co3L precursor was 1 mg, 5 mg, 10 mg or 15 mg, respectively.

5. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 3), the moisture is completely removed using a freeze-drying device to obtain a black Co3L-GO powder material.

6. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 4), the black Co3L-GO powder material needs to be calcined under an inert gas atmosphere.

7. The method for preparing a triatomic cobalt catalyst according to claim 1, characterized in that: In step 4), the black Co3L-GO powder material is kept at 2000°C for 5s and then rapidly cooled to room temperature.

8. The triatomic cobalt catalyst prepared by the method for preparing the triatomic cobalt catalyst according to any one of claims 1 to 7 is used in electrocatalytic oxygen reduction reaction and zinc-air battery.

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