A high-loading cobalt monatomic transition metal-based composite catalyst, a preparation method thereof and oxygen reduction application

Abstract

The application belongs to the technical field of catalyst preparation, and provides a high-loading cobalt monatomic transition metal-based composite catalyst, a preparation method thereof and oxygen reduction application. ZIF material of the application is converted into nitrogen-phosphorus co-doped porous carbon through pyrolysis reaction combined with triphenylphosphine, the porous carbon is used as a carrier, and monatomic cobalt, cobalt nanoparticles, molybdenum species (MoC) and cobalt species (Co9S8) generated by pyrolysis are limited in the porous carbon. The nitrogen-phosphorus co-doped porous carbon can improve the conductivity of the catalyst, and the existence of phosphorus and nitrogen elements provides a stable environment for metal monatomic atoms, so that the catalyst has high metal loading while maintaining the monatomic structure. At the same time, Co9S8 generated by cobalt sulfide increases the metallicity of the catalyst, further provides rich catalytic active sites for the catalyst, so that the catalyst exhibits excellent performance in the oxygen reduction reaction, and the half-wave potential can reach 0.94 V, which is 90 mV higher than that of the Pt / C-based catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a high-load cobalt single-atom transition metal-based composite catalyst, its preparation method, and its application in oxygen reduction. Background Technology

[0002] The ever-increasing demand for energy has spurred in-depth research into renewable and economical energy technologies, including fuel cells and metal-air batteries. Rechargeable zinc-air batteries (ZABs) have attracted widespread attention due to their advantages such as high energy density (1086 Wh / kg), abundant zinc reserves, low cost, and high safety. However, the slow electrocatalytic reaction kinetics limit the further development of ZABs. Highly efficient and stable catalysts capable of accelerating the electrocatalytic oxygen reduction reaction (ORR) have also garnered significant interest. Although noble metal-based materials are considered promising catalysts for the ORR, their scarcity and high price are unsatisfactory.

[0003] Therefore, developing abundant and highly efficient electrocatalysts for the oxygen reduction reaction (OR) of ZABs is both necessary and extremely challenging. Atomically dispersed metal-based electrocatalysts have attracted researchers' attention due to their near-100% atom utilization and excellent catalytic performance. However, single metal atoms typically possess high surface energies, leading to a tendency for interatomic aggregation, thus making the synthesis of highly loaded and stable single-atom catalysts challenging. Currently, the methods proposed by researchers generally aim to two objectives: hindering the aggregation of isolated atoms and enhancing the interaction between isolated single atoms and their support.

[0004] Carbon materials with unique surface properties and high structural flexibility have been used to prepare advanced electrocatalysts by loading various nanoparticles or single-atom metals. Among them, metal-organic frameworks (MOFs) with their uniform channels and cage-like structures have been developed to prevent the migration of single atoms. For example, Chen et al. (Chen Y, Ji S, Wang Y, et al. Isolated singleiron atoms anchored on N-doped porous carbon as an efficient electrocatalyst for the oxygen reduction reaction[J]. Angewandte Chemie International Edition, 2017, 56(24):6937-6941.) reported that iron acetylacetone (Fe(acac)3) is a suitable Fe precursor with a pore size of cavity diameter is The zeolite imidazole ester framework-8 (ZIF-8) can form molecular-scale cages. After high-temperature treatment, ZIF-8 is transformed into nitrogen-doped porous carbon (CN), and the Fe(acac)3 in the cage is reduced to isolated single Fe atoms anchored on CN by organic linkers. However, the above catalyst has a low Fe single-atom loading, which cannot maintain a stable single-atom structure while maintaining a high loading, resulting in low catalytic activity. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a high-load cobalt single-atom transition metal-based composite catalyst, its preparation method, and its application. The high-load cobalt single-atom transition metal-based composite catalyst obtained by the preparation method provided by this invention has a high cobalt single-atom loading and high catalytic activity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a high-load cobalt single-atom transition metal-based composite catalyst, comprising the following steps:

[0008] Cobalt sulfide, molybdenum sulfide, ZIF material, and triphenylphosphine were ground and mixed, and then subjected to a pyrolysis reaction to obtain the high-load cobalt single-atom transition metal-based composite catalyst.

[0009] Preferably, the ZIF material includes one or more of ZIF-67, ZIF-9, ZIF-21 and ZIF-12.

[0010] Preferably, the total mass ratio of cobalt sulfide and molybdenum sulfide to the ZIF material is 0.2-1:1-1.2.

[0011] Preferably, the mass ratio of cobalt sulfide to molybdenum sulfide is 0.1–0.15:0.1–0.15.

[0012] Preferably, the mass ratio of the ZIF material to triphenylphosphine is 1-1.2:0.5-0.6.

[0013] Preferably, the grinding and mixing time is 15 to 30 minutes.

[0014] Preferably, the temperature of the pyrolysis reaction is 700–900°C, the time is 100–150 min, and the rate of heating to the temperature of the pyrolysis reaction is 5–7°C / min.

[0015] The present invention also provides a high-load cobalt single-atom transition metal-based composite catalyst prepared by the preparation method described above, wherein the high-load cobalt single-atom transition metal-based composite catalyst comprises nitrogen and phosphorus co-doped porous carbon, and Co, Co9S8 and MoC dispersed on the nitrogen and phosphorus co-doped porous carbon.

[0016] The present invention also provides the application of the high-load cobalt single-atom transition metal-based composite catalyst described in the above technical solution in the electrocatalytic oxygen reduction reaction (ORR).

[0017] This invention provides a method for preparing a high-load cobalt single-atom transition metal-based composite catalyst, comprising the following steps: grinding and mixing cobalt sulfide, molybdenum sulfide, ZIF material and triphenylphosphine, and carrying out a pyrolysis reaction to obtain the high-load cobalt single-atom transition metal-based composite catalyst.

[0018] The ZIF material of this invention is converted into nitrogen-phosphorus co-doped porous carbon via pyrolysis of triphenylphosphine. This porous carbon serves as a support, confining single-atom cobalt, cobalt nanoparticles, molybdenum species (MoC), and cobalt species (Co9S8). Simultaneously, the nitrogen-phosphorus co-doped porous carbon further stabilizes the isolated single-atom cobalt and cobalt nanoparticles, restricting the aggregation of cobalt metal (single-atom cobalt and cobalt nanoparticles) and improving catalyst stability. The nitrogen-phosphorus co-doped porous carbon enables high cobalt metal loading while still forming a single-atom cobalt structure, providing numerous catalytically active sites and resulting in excellent catalyst performance in the electrocatalytic oxygen reduction reaction (ORR). Furthermore, the carbon nanocages formed after the pyrolysis of the ZIF of this invention confine the aggregation of single-atom Co atoms. The addition of sulfides (cobalt sulfide and molybdenum sulfide) causes the single-atom Co-N bonds to compete with the Co-S bonds, ultimately leading to the formation of Co-N3 or even Co-N2 bonds, which are more conducive to the oxygen reduction reaction. The high-load cobalt single-atom transition metal-based composite catalyst provided by this invention has a half-wave potential of 0.94V, which is 80mV higher than that of the Pt / C-based catalyst. Attached Figure Description

[0019] Figure 1 The XRD and SEM spectra of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 1 are shown below.

[0020] Figure 2 The TEM spectrum of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 1 is shown below.

[0021] Figure 3 Aberration-corrected electron microscopy image of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 1;

[0022] Figure 4 The XRD and SEM spectra of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 2 are shown below.

[0023] Figure 5 The XRD and SEM spectra of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 3 are shown below.

[0024] Figure 6 The graph shows a comparison of the LSV performance of the high-load cobalt single-atom transition metal-based composite catalysts obtained in Examples 1, 2, and 3 with that of commercial platinum-carbon catalysts in ORR. Detailed Implementation

[0025] This invention provides a method for preparing a high-load cobalt single-atom transition metal-based composite catalyst, comprising the following steps:

[0026] Cobalt sulfide, molybdenum sulfide, ZIF material, and triphenylphosphine were ground and mixed, and then subjected to a pyrolysis reaction to obtain the high-load cobalt single-atom transition metal-based composite catalyst.

[0027] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0028] In this invention, the ZIF material preferably includes one or more of ZIF-67, ZIF-9, ZIF-21, and ZIF-12, and more preferably ZIF-67. In this invention, the carbon nanocages formed after the pyrolysis of the ZIF material can confine the aggregation of single Co atoms. The addition of sulfides (cobalt sulfide and molybdenum sulfide) causes the single-atom Co-N bonds to compete with the Co-S bonds, ultimately causing the original single-atom Co-N4 bonds to form Co-N3 or even Co-N2, which are more conducive to oxygen reduction reactions.

[0029] In this invention, the mass ratio of cobalt sulfide to molybdenum sulfide is preferably 0.1–0.15:0.1–0.15. In this invention, the cobalt sulfide and molybdenum sulfide are preferably used in the form of a mixture of cobalt sulfide and molybdenum sulfide. The preparation method of the cobalt sulfide and molybdenum sulfide mixture preferably includes the following steps: mixing a sulfur source, a molybdenum salt, a cobalt salt, and water, and carrying out a hydrothermal reaction to obtain the cobalt sulfide and molybdenum sulfide mixture. In this invention, the sulfur source preferably includes thioacetamide and / or thiourea, more preferably thioacetamide. In this invention, the molybdenum salt preferably includes one or more of molybdenum pentachloride, molybdenum sulfate, ammonium molybdate, and sodium molybdate, more preferably sodium molybdate. In this invention, the cobalt salt preferably includes one or more of cobalt chloride, cobalt sulfate, cobalt carbonate, and cobalt nitrate, more preferably cobalt nitrate. In this invention, the molar ratio of the sulfur source to the molybdenum salt is preferably 0.02928:0.00619962. In this invention, the molar ratio of the molybdenum salt to the cobalt salt is preferably 0.00619962:0.005154. In this invention, the hydrothermal reaction temperature is preferably 200°C, and the reaction time is preferably 1440 min. After the hydrothermal reaction, this invention preferably further includes: filtering the obtained hydrothermal reaction solution and drying the resulting solid.

[0030] In this invention, the mass ratio of the total mass of cobalt sulfide and molybdenum sulfide to the mass of ZIF material is preferably 0.2 to 1:1 to 1.2, and more preferably 0.2:1.

[0031] In this invention, the mass ratio of the ZIF material to triphenylphosphine is preferably 1–1.2:0.5–0.6, more preferably 2:1. In this invention, triphenylphosphine serves only as a phosphorus source in the final electrocatalyst to form phosphorus-doped carbon, without forming additional metal compound species.

[0032] In this invention, the grinding and mixing time is preferably 15 to 30 minutes. In this invention, the grinding and mixing is preferably carried out in a mortar.

[0033] In this invention, the preferred temperature for the pyrolysis reaction is 700–900°C, more preferably 800°C; the preferred time is 100–150 min, more preferably 120 min; and the preferred rate of heating to the pyrolysis reaction temperature is 5–7°C / min. In this invention, the preferred atmosphere for the pyrolysis reaction is nitrogen. In this invention, the preferred equipment for the pyrolysis reaction is a Hefei Kejing OTF-1200X vacuum tube furnace.

[0034] Following the pyrolysis reaction, the present invention preferably further includes furnace cooling.

[0035] In this invention, during the pyrolysis reaction, ZIF material and triphenylphosphine can be converted into nitrogen-phosphorus co-doped porous carbon. This nitrogen-phosphorus co-doped porous carbon serves as a support for single-atom cobalt, cobalt nanoparticles, molybdenum species (MoC), and cobalt species (Co9S8), confining these elements within its structure. Simultaneously, the nitrogen-phosphorus co-doped porous carbon further stabilizes the isolated single-atom cobalt and cobalt nanoparticles, restricting the aggregation of cobalt metal (single-atom cobalt and cobalt nanoparticles) and improving catalyst stability. The nitrogen-phosphorus co-doped porous carbon enables high cobalt metal loading while still maintaining a single-atom cobalt structure, providing numerous catalytically active sites and resulting in excellent catalyst performance in the electrocatalytic oxygen reduction reaction (ORR).

[0036] This invention also provides a high-load cobalt single-atom transition metal-based composite catalyst prepared by the preparation method described above. The high-load cobalt single-atom transition metal-based composite catalyst comprises nitrogen-phosphorus co-doped porous carbon, and Co, Co9S8, and MoC dispersed on the nitrogen-phosphorus co-doped porous carbon. In this invention, the Co preferably comprises single-atom cobalt and cobalt nanoparticles.

[0037] The ZIF material of this invention is combined with triphenylphosphine and converted into nitrogen-phosphorus co-doped porous carbon via pyrolysis. This porous carbon serves as a support, confining the pyrolysis-generated single-atom cobalt, cobalt nanoparticles, molybdenum species (MoC), and cobalt species (Co9S8) within it. The nitrogen-phosphorus co-doped porous carbon improves the conductivity of the catalyst, and the presence of phosphorus and nitrogen provides a stable environment for the metal single atoms, allowing the catalyst to maintain its single-atom structure while exhibiting a high metal loading. Simultaneously, the Co9S8 generated from cobalt sulfide increases the metallicity of the catalyst, providing abundant catalytic active sites and resulting in excellent performance of the catalyst in the oxygen reduction reaction.

[0038] The present invention also provides the application of the high-load cobalt single-atom transition metal-based composite catalyst described in the above technical solution in the electrocatalytic oxygen reduction reaction (ORR).

[0039] The present invention does not impose specific limitations on the application of the high-load cobalt single-atom transition metal-based composite catalyst; any operation known to those skilled in the art can be used.

[0040] The following detailed description, in conjunction with embodiments, illustrates the high-load cobalt single-atom transition metal-based composite catalyst, its preparation method, and its applications provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1

[0042] 2.2 g of thioacetamide (0.02928 mol), 1.5 g of sodium molybdate (0.00619962 mol), and 1.5 g of cobalt nitrate (0.005154 mol) were dissolved in 40 mL of water and reacted hydrothermally at 200 °C for 1440 min. The resulting system was filtered, and the solid was dried to produce a mixed precursor of 0.1 g of cobalt sulfide and 0.1 g of molybdenum sulfide.

[0043] Mix 0.2g of precursor (cobalt sulfide and molybdenum sulfide in a mass ratio of 1:1) with 1g of ZIF-67 and 0.5g of triphenylphosphine (0.0019mol), and grind in a grinding mortar for 15min.

[0044] The mixture was pyrolyzed at 800℃ for 120 min under a nitrogen atmosphere with a heating rate of 5℃ / min, and then cooled to room temperature in the furnace to form a high-load cobalt single-atom transition metal-based composite catalyst.

[0045] Figure 1 The images show the XRD and SEM spectra of the obtained high-load cobalt single-atom transition metal-based composite catalyst. The left image is the XRD spectrum, and the right image is the SEM spectrum. Figure 1It can be seen that the catalyst contains Co, Co9S8 and MoC, and the catalyst retains the structure of ZIF-67 carbon nanocages during high-temperature sintering.

[0046] Figure 2 The TEM spectrum of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 1 is shown below. Figure 2 The measured lattice spacing further confirms that the catalyst contains Co, Co9S8, and MoC species.

[0047] Figure 3 This is a spherical aberration electron microscope image of the high-load cobalt single-atom transition metal-based composite catalyst obtained in Example 1. Figure 3 In the diagram, small white circles represent cobalt single-atom structures, and large black circles represent cobalt nanoparticles. Therefore, it can be seen that the catalyst of this invention contains cobalt single-atom structures.

[0048] Example 2

[0049] 2.2 g of thioacetamide (0.02928 mol), 1.5 g of sodium molybdate (0.00619962 mol), and 1.5 g of cobalt nitrate (0.005154 mol) were dissolved in 40 mL of water and reacted hydrothermally at 200 °C for 1440 min. The resulting system was filtered, and the solid was dried to produce a mixed precursor of 0.1 g of cobalt sulfide and 0.1 g of molybdenum sulfide.

[0050] Mix 0.2g of precursor (cobalt sulfide and molybdenum sulfide in a mass ratio of 1:1) with 1g of ZIF-67 and 0.5g of triphenylphosphine (0.0019mol), and grind in a grinding mortar for 15min.

[0051] The mixture was pyrolyzed at 700℃ for 120 min under a nitrogen atmosphere with a heating rate of 5℃ / min, and then cooled to room temperature in the furnace to form a high-load cobalt single-atom transition metal-based composite catalyst.

[0052] Figure 4 The images show the XRD and SEM spectra of the obtained high-load cobalt single-atom transition metal-based composite catalyst. The left image is the XRD spectrum, and the right image is the SEM spectrum. Figure 4 It can be seen that a small amount of metallic cobalt is present, and the catalyst retains the structure of ZIF-67 carbon nanocages.

[0053] Example 3

[0054] 2.2 g of thioacetamide (0.02928 mol), 1.5 g of sodium molybdate (0.00619962 mol), and 1.5 g of cobalt nitrate (0.005154 mol) were dissolved in 40 mL of water and reacted hydrothermally at 200 °C for 1440 min. The resulting system was filtered, and the solid was dried to produce a mixed precursor of 0.1 g of cobalt sulfide and 0.1 g of molybdenum sulfide.

[0055] Mix 0.2g of precursor (cobalt sulfide and molybdenum sulfide in a mass ratio of 1:1) with 1g of ZIF-67 and 0.5g of triphenylphosphine (0.0019mol), and grind in a grinding mortar for 15min.

[0056] The mixture was pyrolyzed at 900℃ for 120 min under a nitrogen atmosphere with a heating rate of 5℃ / min, and then cooled to room temperature in the furnace to form a high-load cobalt single-atom transition metal-based composite catalyst.

[0057] Figure 5 The images show the XRD and SEM spectra of the obtained high-load cobalt single-atom transition metal-based composite catalyst. The left image is the XRD spectrum, and the right image is the SEM spectrum. Figure 5 It can be seen that at 900℃, cobalt metal is excessively reduced, making the peaks of other species less obvious, and the catalyst retains the structure of ZIF-67 carbon nanocages.

[0058] ORR electrochemical testing was performed on a Shanghai Chenhua CHI 760E electrochemical workstation. The reference electrode was a saturated Ag / AgCl electrode, and the counter electrode was a platinum sheet, forming a three-electrode configuration with the working electrode. In this patent, the measured potentials (vs Ag / AgCl) were all converted to reversible hydrogen electrode potentials (RHE) and analyzed according to the Nernst equation (E... RHE =E Ag / AgCl The pH was corrected to +0.197 +0.059. The working electrode was prepared as follows: 3 mg of catalyst and 3 mg of carbon powder were dispersed and sonicated in 8 mL of petroleum ether for 4 h. After centrifugation and drying, the mixture was ground for 10 min. 6 mg of this catalyst was then dispersed and sonicated in 1470 μL of N,N-Dimethylformamide (DMF) solution. 30 μL of Nafion was added and sonicated for 8 h. Then, 7 μL of catalyst was dropped onto a rotating disk working electrode (RRDE) (loading capacity of 0.2 mg / cm³). -2 The catalyst was dried at room temperature. For further comparison, a commercially available Pt / C catalyst was used as a reference catalyst. All ORR performance was tested in 0.1M KOH solution, and the results are as follows: Figure 6 As shown.

[0059] Figure 6This is a comparison of the LSV performance in ORR between the high-load cobalt single-atom transition metal-based composite catalysts obtained in Examples 1, 2, and 3 and a commercial platinum-carbon catalyst. MoC / Co9S8-Co@NPC-1 corresponds to the catalyst in Example 2, MoC / Co9S8-Co@NPC-2 corresponds to the catalyst in Example 1, and MoC / Co9S8-Co@NPC-3 corresponds to the catalyst in Example 3. Figure 6 It can be seen that the half-wave potential of the LSV curve of the catalyst obtained in Example 1 reaches 0.94V, which is higher than that of platinum carbon (0.85V).

[0060] The catalyst obtained in Example 1 was subjected to ICP testing, and the results are shown in Table 1.

[0061] Table 1. ICP test results of the catalyst obtained in Example 1

[0062] Serial Number Example 1 <![CDATA[Sample mass m0 (g)]]> 0.0190 <![CDATA[Constant volume V0 (mL)]]> 25 test element Co <![CDATA[Element concentration C0 (mg / L) of the test solution]]> 2.629 Dilution factor 100 <![CDATA[Element concentration C1 (mg / L) of the original digestion solution]]> 262.891125 <![CDATA[Element content of the sample C x (mg / kg)]]> 345909.4 Sample elemental content w (%) 34.59％

[0063] As can be seen from Table 1, the catalyst has a cobalt metal loading of over 30%, combined with... Figure 3 This demonstrates that the catalyst of the present invention maintains a single-atom structure while maintaining a high cobalt metal loading.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-load cobalt single-atom transition metal-based composite catalyst, characterized in that, Includes the following steps: Cobalt sulfide, molybdenum sulfide, ZIF material, and triphenylphosphine were ground and mixed, and then subjected to a pyrolysis reaction to obtain the high-load cobalt single-atom transition metal-based composite catalyst.

2. The preparation method according to claim 1, characterized in that, The ZIF material includes one or more of ZIF-67, ZIF-9, ZIF-21, and ZIF-12.

3. The preparation method according to claim 1, characterized in that, The total mass ratio of cobalt sulfide and molybdenum sulfide to the ZIF material is 0.2–1:1–1.

2.

4. The preparation method according to claim 1 or 3, characterized in that, The mass ratio of cobalt sulfide to molybdenum sulfide is 0.1–0.15:0.1–0.

15.

5. The preparation method according to claim 1, characterized in that, The mass ratio of ZIF material to triphenylphosphine is 1–1.2:0.5–0.

6.

6. The preparation method according to claim 1, characterized in that, The grinding and mixing time is 15 to 30 minutes.

7. The preparation method according to claim 1, characterized in that, The pyrolysis reaction temperature is 700–900℃, the holding time is 100–150 min, and the rate of heating to the pyrolysis reaction temperature is 5–7℃ / min.

8. The high-load cobalt single-atom transition metal-based composite catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The high-load cobalt single-atom transition metal-based composite catalyst comprises nitrogen-phosphorus co-doped porous carbon, and Co, Co9S8 and MoC dispersed on the nitrogen-phosphorus co-doped porous carbon.

9. The application of the high-load cobalt single-atom transition metal-based composite catalyst according to claim 8 in electrocatalytic oxygen reduction reaction.

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