An electrocatalyst with a transition metal single atom and transition metal cluster cooperative structure and a preparation method and application thereof

Abstract

This invention provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, its preparation method, and its application, belonging to the field of electrocatalytic materials technology. This invention first prepares metal-organic coordination polymer precursors with different spatial coordination structures by controlling the solvent environment and coordination mode. Then, in subsequent pyrolysis, metal ions at the nodes of the precursor framework aggregate to form clusters due to localized high temperatures, while metal ions anchored within the pores form single atoms, achieving controllable construction and uniform coexistence of metal single atoms and metal clusters in a carbon matrix. The electrocatalyst of this invention effectively overcomes the defects such as high hydrogen evolution overpotential and poor catalytic stability caused by the difficulty in achieving synergy between single atoms and clusters. It can simultaneously optimize the hydrogen adsorption and desorption processes, significantly improving the hydrogen evolution performance and operational stability of non-precious metal catalysts, providing a new strategy for the design of non-precious metal electrocatalysts.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and in particular to an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, its preparation method and application. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy source, plays a vital role in promoting energy structure transformation and achieving carbon neutrality. Electrolysis of water is a key technology for producing green hydrogen, but its large-scale application is limited by the development of high-performance, low-cost catalysts. While platinum-based noble metals exhibit excellent activity, their limited reserves and cost restrict their large-scale application; therefore, developing non-noble metal catalysts has become a core issue.

[0003] In the electrocatalytic hydrogen evolution reaction, catalysts need to optimize two key steps simultaneously: hydrogen atom adsorption and hydrogen desorption. Non-noble metal catalysts often face the dilemma of single-function active sites: single-atom catalysts are favorable for hydrogen adsorption due to quantum size effects, but the lack of adjacent metal sites makes hydrogen coupling and desorption difficult; while metal nanoparticles or clusters are favorable for hydrogen desorption, their continuous band structure is often unfavorable for initial hydrogen adsorption. Therefore, integrating the synergistic advantages of single atoms and clusters in a single catalyst has become the key to improving catalytic performance.

[0004] Pyrolysis of metal-organic frameworks is an effective route for preparing carbon-supported metal catalysts. However, simple pyrolysis easily leads to uncontrolled aggregation of the metal, typically forming only a single-scale form. This directly results in a single active site and a single catalytic pathway, making it difficult to simultaneously optimize hydrogen adsorption and desorption processes, and also causing poor catalytic stability. Some existing methods adjust these processes by introducing templates or post-treatments, but these are cumbersome and lack controllability. Therefore, designing precursor structures at the molecular level to precisely control the migration behavior of metal ions in the pyrolysis pathway is a fundamental strategy for achieving the synergistic construction of single atoms and clusters.

[0005] Chinese patent CN110975912A discloses the preparation and application of a cobalt-nitrogen-doped catalyst derived from bimetallic MOFs. It involves synthesizing Zn-MOFs by mixing triphenylamine tricarboxylic acid and 2-nitroterephthalic acid with zinc nitrate hexahydrate, then introducing metallic cobalt via ion exchange to synthesize bimetallic Co@Zn-MOFs materials. The bimetallic MOFs are then directly carbonized by thermal treatment to obtain the cobalt-nitrogen-doped catalyst. However, this technical solution has the following drawbacks in constructing the coexistence of metal single atoms and metal clusters in a carbon matrix: (1) In the preparation of the cobalt-nitrogen-doped catalyst, it relies on zinc volatilization during pyrolysis to create pores, resulting in a random and uncontrollable cobalt presence; (2) It cannot truly achieve the active construction and uniform coexistence of single atoms and clusters, with cobalt species mainly existing in a random doping form; (3) Regarding structural uniformity: the distribution of cobalt single atoms and clusters is uneven, relying on the residual carbon after zinc volatilization for anchoring, making it difficult to achieve uniform coexistence at the nanoscale.

[0006] Furthermore, the existence of the above defects directly leads to the following technical bottlenecks in the electrocatalytic hydrogen evolution reaction of the catalyst: (1) high hydrogen evolution overpotential and high energy consumption; (2) poor long-term operation stability, making it difficult to meet the life requirement of thousands of hours under industrial-scale production conditions; (3) weak anti-pollution / anti-poisoning ability and poor environmental adaptability; (4) high cell voltage and low energy conversion efficiency when assembled into an actual electrolyzer, making it difficult to replace precious metal catalysts for industrial hydrogen production. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, its preparation method, and its application. The molecular structure of the coordination polymer precursor is designed by utilizing the steric hindrance and coordination guiding effect of solvent molecules. During pyrolysis, metal ions are simultaneously induced to partially confine and anchor as single atoms and partially migrate and aggregate into clusters, thereby universally constructing a carbon-based electrocatalyst with synergistic metal single atoms and clusters. This effectively overcomes the defects of existing MOF-derived carbon-based catalysts, such as high hydrogen evolution overpotential, poor catalytic stability, weak anti-poisoning ability, and low energy conversion efficiency, which are caused by the uncontrollable existence form of metal species and the difficulty in synergistic integration of single atoms and clusters. It enables simultaneous optimization of hydrogen adsorption and desorption processes, significantly improving the hydrogen evolution performance and operational stability of non-precious metal catalysts, and meeting the demand for high-performance, low-cost catalysts in industrial water electrolysis for hydrogen production.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters includes the following steps: Step S01: After dissolving the transition metal salt and organic ligand in N,N-dimethylacetamide, the mixture is placed in a sealed container for a solvothermal reaction. The solids are then separated, collected, washed, and dried to obtain the metal-organic coordination polymer precursor. The metal element in the transition metal salt is cobalt or nickel; Step S02: Under an inert atmosphere, the metal-organic coordination polymer precursor is pyrolyzed at high temperature and then cooled to room temperature to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters.

[0009] Preferably, in step S01, the organic ligand is one of the following: terephthalic acid, 2-aminoterephthalic acid, or 2-hydroxyterephthalic acid; the transition metal salt is cobalt chloride or nickel chloride.

[0010] Preferably, in step S01, the total molar amount of the transition metal salt in N,N-dimethylacetamide is 0.05-0.1 mol / L.

[0011] Preferably, in step S01, the ratio of the total molar amount of the transition metal salt in N,N-dimethylacetamide to the total molar amount of the organic ligand is 1:0.5-1.5.

[0012] Preferably, in step S01, the temperature of the solvothermal reaction is 120-150℃, and the time of the solvothermal reaction is 12-24h.

[0013] Preferably, in step S02, the high-temperature pyrolysis temperature is 300-900℃, and the high-temperature pyrolysis time is 1-3h.

[0014] Preferably, in step S02, the heating rate of high-temperature pyrolysis is 1-5℃ / min.

[0015] Preferably, in step S02, the inert atmosphere is nitrogen or argon.

[0016] An electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters was prepared using the aforementioned method.

[0017] Application of the aforementioned electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters in alkaline hydrogen evolution reaction.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the preparation of the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters of the present invention, by controlling the solvent environment and coordination mode, metal-organic coordination polymer precursors with different spatial coordination structures are first prepared; then, in the subsequent pyrolysis process, metal ions at the nodes of the precursor skeleton aggregate to form clusters due to local high temperature, and metal ions anchored in the channels form single atoms, thereby realizing the controllable construction and uniform coexistence of metal single atoms and metal clusters in the carbon matrix. The various technical means cooperate and work together to effectively overcome the defects of high hydrogen evolution overpotential, poor catalytic stability, weak anti-poisoning ability and low energy conversion efficiency caused by the uncontrollable existence form of metal species and the difficulty in synergistic integration of single atoms and clusters in existing MOFs-derived carbon-based catalysts. It can realize the simultaneous optimization of hydrogen adsorption and hydrogen desorption processes, significantly improve the hydrogen evolution performance and operational stability of non-precious metal catalysts, and meet the demand of industrial water electrolysis for high-performance and low-cost catalysts.

[0019] (2) The preparation method of the electrocatalyst with the synergistic structure of transition metal single atoms and transition metal clusters of the present invention effectively realizes the controllable construction and uniform coexistence of metal single atoms and metal clusters in a carbon matrix. These two types of active sites jointly optimize the electrocatalytic reaction pathway through clear electronic synergistic and spatial synergistic effects. Specifically, in the electrocatalytic hydrogen evolution reaction, single-atom sites exhibit extremely strong affinity and activation ability for water molecules due to their highly unsaturated coordination environment and quantum-sized electronic structure. The empty d orbitals of the metal on the single-atom sites can hybridize with the lone pair electrons of oxygen atoms in water molecules, effectively weakening the OH bond energy and promoting the adsorption and dissociation of water molecules, thereby efficiently generating active hydrogen intermediates. However, since the single-atom sites are spatially isolated from each other, the active hydrogen intermediates adsorbed on them are difficult to couple to form hydrogen gas through neighboring sites. At this time, the adjacent metal clusters play a key role: the continuous metal-metal bonding network composed of multiple neighboring metal atoms on the surface of the cluster provides an ideal platform for the adsorption, migration and coupling of active hydrogen intermediates. Active hydrogen can rapidly overflow from single-atom sites to the surface of the carbon matrix and transfer to the surface of the clusters, where it can be efficiently coupled and desorbed onto adjacent metal atoms to generate hydrogen gas. The prepared catalyst exhibits high activity and long-term stability over a wide pH range, especially in the electrocatalytic hydrogen evolution reaction, where the overpotential can be as low as single-digit millivolts, and it achieves stable operation for more than 2000 hours. Its performance significantly surpasses that of traditional single-site catalysts and commercial noble metal catalysts.

[0020] (3) The preparation method of the electrocatalyst with the synergistic structure of transition metal single atoms and transition metal clusters of the present invention can be widely applied to a variety of transition metals such as iron, cobalt, nickel, copper, manganese, zinc, and molybdenum. It can prepare corresponding electrocatalysts with the synergistic structure of transition metal single atoms and transition metal clusters, thereby meeting the needs of different electrocatalytic reaction conditions and providing a new strategy for the design of non-precious metal electrocatalysts.

[0021] (4) The preparation method of the electrocatalyst with the synergistic structure of transition metal single atoms and transition metal clusters of the present invention has readily available raw materials, a simple process flow, and easy control of the preparation process, and is suitable for industrial-scale promotion and application. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the single-crystal structure of the coordination polymer precursors obtained in Example 1 and Comparative Examples 1 and 2.

[0023] Figure 2 The image shows a HAADF-STEM image of the electrocatalyst of Example 1.

[0024] Figure 3 The XAFS characterization results of the electrocatalyst in Example 1 are shown in the figure. In the figure, figure a is the Co K-edge XANES spectrum and figure b is the Fourier transform EXAFS spectrum.

[0025] Figure 4 The graphs show a comparison of the electrochemical hydrogen evolution performance of the electrocatalysts of Example 1 and Comparative Examples 1 and 2 in alkaline media; in the graphs, a is the LSV curve and b is the Tafel curve.

[0026] Figure 5 The chronopotential curves show the stability of the electrocatalysts of Example 1 and Comparative Examples 1 and 2 in alkaline media. Detailed Implementation

[0027] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] In a first aspect, embodiments of the present invention provide a method for preparing an electrocatalyst having a synergistic structure of transition metal single atoms and transition metal clusters, comprising the following steps: Step S01: After dissolving the transition metal salt and organic ligand in N,N-dimethylacetamide, the mixture is placed in a sealed container for a solvothermal reaction. The solids are then separated, collected, washed, and dried to obtain the metal-organic coordination polymer precursor. The metal element in the transition metal salt is cobalt or nickel; Step S02: Under an inert atmosphere, the metal-organic coordination polymer precursor is pyrolyzed at high temperature and then cooled to room temperature to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters.

[0030] In this embodiment of the invention, by controlling the solvent environment and coordination mode, metal-organic coordination polymer precursors with different spatial coordination structures are first prepared. Then, during the subsequent pyrolysis process, metal ions at the nodes of the precursor framework aggregate to form clusters due to local high temperature, and metal ions anchored in the channels form single atoms, thereby achieving the controllable construction and uniform coexistence of metal single atoms and metal clusters in a carbon matrix. The various technical means cooperate and work synergistically to effectively overcome the defects of existing MOFs-derived carbon-based catalysts, such as high hydrogen evolution overpotential, poor catalytic stability, weak anti-poisoning ability, and low energy conversion efficiency caused by the uncontrollable existence form of metal species and the difficulty in the synergistic integration of single atoms and clusters. It can achieve simultaneous optimization of hydrogen adsorption and hydrogen desorption processes, significantly improve the hydrogen evolution performance and operational stability of non-precious metal catalysts, and meet the demand for high-performance and low-cost catalysts for industrial water electrolysis hydrogen production.

[0031] Preferably, in step S01, the organic ligand is one of the following: terephthalic acid, 2-aminoterephthalic acid, or 2-hydroxyterephthalic acid; the transition metal salt is cobalt chloride or nickel chloride.

[0032] Preferably, in step S01, the total molar amount of the transition metal salt in N,N-dimethylacetamide is 0.05-0.1 mol / L.

[0033] Preferably, in step S01, the ratio of the total molar amount of the transition metal salt in N,N-dimethylacetamide to the total molar amount of the organic ligand is 1:0.5-1.5.

[0034] Preferably, in step S01, the temperature of the solvothermal reaction is 80-200℃ and the time of the solvothermal reaction is 6-72h; more preferably, the temperature of the solvothermal reaction is 120-150℃ and the time of the solvothermal reaction is 12-24h.

[0035] Preferably, in step S02, the inert atmosphere is nitrogen or argon.

[0036] Preferably, in step S02, the high-temperature pyrolysis temperature is 300-1100℃ and the high-temperature pyrolysis time is 0.5-12h; more preferably, the high-temperature pyrolysis temperature is 300-900℃ and the high-temperature pyrolysis time is 1-3h.

[0037] Preferably, in step S02, the heating rate of high-temperature pyrolysis is 1-20℃ / min; more preferably, the heating rate of high-temperature pyrolysis is 1-5℃ / min.

[0038] Secondly, embodiments of the present invention also provide an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method.

[0039] Thirdly, embodiments of the present invention also provide the application of the electrocatalyst having a synergistic structure of transition metal single atoms and transition metal clusters in the alkaline hydrogen evolution reaction.

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with some specific embodiments.

[0041] Example 1 This embodiment provides a method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters. The specific steps are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 4.0 mmol CoCl2·6H2O (purity 99.99 wt%) and 4.0 mmol terephthalic acid (purity 99 wt%), dissolve them in 40 mL of N,N-dimethylacetamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat it to 120 °C in a forced-air drying oven and keep it at that temperature for 12 h. After cooling to room temperature with the furnace, wash it three times with anhydrous methanol and anhydrous ethanol, respectively, by centrifugation, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0042] (2) Preparation of catalyst: The precursor is spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 800°C at a rate of 5°C / min and kept at the temperature for 2 hours. Then, it is naturally cooled to room temperature under the protection of nitrogen flow to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, denoted as Co1 / C-NC.

[0043] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system; specifically, the working electrode was the electrode prepared by coating the catalyst of this embodiment onto a conductive substrate (taking Co1 / C-NC as an example: 5 mg of catalyst was weighed and dispersed in a dispersant, ultrasonically dispersed evenly, and the catalyst dispersion was dropped onto a 1×1 cm substrate). 2On a nickel foam substrate, it was naturally dried, with the catalyst loading controlled at 5 mg / cm³. 2 The counter electrode was a carbon rod; the reference electrode was a saturated calomel electrode; and electrochemical tests were performed using a Chenhua 760E electrochemical workstation.

[0044] Tests showed that the hydrogen evolution overpotential of Co1 / C-NC in 1.0M KOH electrolyte was only 8.5mV@10mA·cm. -2 The Tafel slope is 155 mV·dec -1 ; capable of 10mA·cm -2 It can operate continuously and stably under constant current for more than 2000 hours.

[0045] This embodiment also provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method; from Figure 2 As can be seen, the HAADF-STEM image reveals a large number of isolated cobalt single-atom bright spots and tiny cobalt clusters composed of several atoms coexisting uniformly on the carbon matrix. Figure 3 The XAFS characterization results showed that the coordination number of Co-C was 2.1 and the coordination number of Co-Co was 5.1.

[0046] Example 2 This embodiment provides a method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters. The specific steps are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 1.0 mmol NiCl2·6H2O (purity 99.99 wt%) and 1.0 mmol terephthalic acid (purity 99 wt%), dissolve them in 15 mL of N,N-dimethylacetamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat it to 150 °C in a forced-air drying oven and keep it at that temperature for 12 h. After cooling to room temperature with the oven, wash it three times with anhydrous methanol and anhydrous ethanol, respectively, by centrifugation, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0047] (2) Preparation of catalyst: The precursor is spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 350°C at a rate of 2°C / min. After pyrolysis for 2 hours, it is naturally cooled to room temperature under nitrogen protection to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, denoted as Ni / C-NC.

[0048] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The results showed that the hydrogen evolution overpotential of Ni / C-NC in 1.0 M KOH electrolyte was only 53 mV @ 10 mA·cm.-2 The Tafel slope is 61mV·dec -1 .

[0049] This embodiment also provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method.

[0050] Example 3 This embodiment provides a method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters. The specific steps are as follows: (1) Precursor synthesis: Weigh 0.5 mmol NiCl2·6H2O (purity 99.99 wt%), 0.5 mmol FeCl3·6H2O (purity 99.99 wt%) and 1.0 mmol terephthalic acid (purity 99 wt%), dissolve them in 15 mL of N,N-dimethylacetamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat it to 150 °C in a forced-air drying oven and keep it at that temperature for 12 h. After cooling to room temperature with the furnace, wash it three times with anhydrous methanol and anhydrous ethanol, respectively, by centrifugation, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0051] (2) Preparation of catalyst: The precursor is spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 600℃ at a rate of 2℃ / min and kept at the temperature for 2h for pyrolysis. Then, it is naturally cooled to room temperature under the protection of nitrogen flow to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, denoted as NiFe / C-NC.

[0052] (3) Performance Testing: The catalyst in this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The results showed that the hydrogen evolution overpotential of NiFe / C-NC in 1.0M KOH electrolyte was only 36mV@10mA·cm. -2 The Tafel slope is 78 mV·dec -1 .

[0053] This embodiment also provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method.

[0054] Example 4 This embodiment provides a method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters. The specific steps are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 1.0 mmol CoCl2·6H2O (purity 99.99 wt%) and 1.0 mmol 2-aminoterephthalic acid (purity 99 wt%), dissolve them in 15 mL of N,N-dimethylacetamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat it to 150 °C in a forced-air drying oven and keep it at that temperature for 12 h. After cooling to room temperature with the oven, wash it three times with anhydrous methanol and anhydrous ethanol, respectively, by centrifugation, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0055] (2) Preparation of catalyst: The precursor is spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 800℃ at a rate of 2℃ / min. After pyrolysis for 2 hours, it is naturally cooled to room temperature under nitrogen protection to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, denoted as Co4 / C-NC.

[0056] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The results showed that the hydrogen evolution overpotential of Co4 / C-NC in 1.0M KOH electrolyte was only 35mV@10mA·cm. -2 The Tafel slope is 71mV·dec -1 .

[0057] This embodiment also provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method.

[0058] Example 5 This embodiment provides a method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters. The specific steps are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 1.0 mmol CoCl2·6H2O (purity 99.99 wt%) and 1.0 mmol 2-hydroxyterephthalic acid (purity 99 wt%), dissolve them in 15 mL of N,N-dimethylacetamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat the reactor to 120 °C in a forced-air drying oven and hold the temperature for 12 h. After cooling to room temperature in the oven, wash the reactor three times with anhydrous methanol and anhydrous ethanol, respectively, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0059] (2) Preparation of catalyst: The precursor was spread on a ceramic boat and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 800°C at a rate of 2°C / min. After pyrolysis for 2 hours, the catalyst was naturally cooled to room temperature under the protection of argon flow to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, denoted as Co5 / C-NC.

[0060] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The results showed that the hydrogen evolution overpotential of Co5 / C-NC in 1.0 M KOH electrolyte was only 46 mV @ 10 mA·cm⁻¹. -2 The Tafel slope is 90 mV·dec -1 .

[0061] This embodiment also provides an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters prepared by the aforementioned method.

[0062] Comparative Example 1 Comparative Example 1 used a commercially available precious metal-based 20wt% Pt / C catalyst; a three-electrode system was used for testing, and the specific testing method was the same as in Example 1. The hydrogen evolution overpotential of this catalyst in 1.0M KOH electrolyte was measured to be approximately 30 mV @ 10 m·Acm. -2 The Tafel slope is 120 mV·dec -1 The catalytic performance significantly decreased after 200 hours of constant current operation.

[0063] Comparative Example 2 Comparative Example 2 uses the technical solution of Example 1, except that the solvent used is replaced with N,N-dimethylformamide and N,N-dimethylacetamide in a volume ratio of 1:1. Everything else is the same as in Example 1. The specific steps of Comparative Example 2 are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 4.0 mmol CoCl2·6H2O (purity 99.99%) and 4.0 mmol terephthalic acid (purity 99%), dissolve them in 40 mL of solvent (N,N-dimethylformamide and N,N-dimethylacetamide in a 1:1 ratio), and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat the reactor to 120 °C in a forced-air drying oven and hold the temperature for 12 h. After cooling to room temperature with the furnace, wash the reactor three times with anhydrous methanol and anhydrous ethanol, respectively, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0064] (2) Preparation of catalyst: The precursor was spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and kept at the temperature for 2 hours for pyrolysis. Then, it was naturally cooled to room temperature under the protection of nitrogen flow to obtain the electrocatalyst of Comparative Example 2, denoted as Co2 / C-NC.

[0065] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The hydrogen evolution overpotential of Co2 / C-NC in 1.0M KOH electrolyte was measured to be 79 mV@10 mA·cm⁻¹. -2 Tafel slope 190mV·dec -1 ; at 10mA·cm -2 The continuous stable operation time under constant current is approximately 200 hours.

[0066] Comparative Example 3 Comparative Example 3 uses the same technical solution as Example 1, except that the solvent used is entirely replaced with N,N-dimethylformamide. Everything else is the same as in Example 1. The specific steps of Comparative Example 3 are as follows: (1) Preparation of metal-organic coordination polymer precursor: Weigh 4.0 mmol CoCl2·6H2O (purity 99.99%) and 4.0 mmol terephthalic acid (purity 99%), dissolve them in 40 mL of N,N-dimethylformamide solvent, and stir at room temperature for 30 min until completely dissolved. Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and seal it. Heat the reactor to 120 °C in a forced-air drying oven and hold the temperature for 12 h. After cooling to room temperature with the furnace, wash the reactor three times with anhydrous methanol and anhydrous ethanol, respectively, and dry it under vacuum at 60 °C for 12 h to obtain the precursor.

[0067] (2) Preparation of catalyst: The precursor was spread on a ceramic boat and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was raised to 800°C at a rate of 5°C / min and kept at the temperature for 2 hours for pyrolysis. Then, it was naturally cooled to room temperature under the protection of nitrogen flow to obtain the electrocatalyst of Comparative Example 3, denoted as Co3 / C-NC.

[0068] (3) Performance testing: The catalyst of this embodiment was tested using a three-electrode system, and the specific testing method was the same as in Example 1. The results showed that the hydrogen evolution overpotential of Co3 / C-NC in 1.0 M KOH electrolyte was only 160 mV @ 10 mA·cm. -2 Tafel slope 266mV·dec -1 At 10 mA·cm -2 The continuous stable operation time under constant current is approximately 200 hours.

[0069] The comprehensive performance comparison data of Examples 1-5 and Comparative Examples 1-3 are summarized in the table below:

[0070] As shown in the table above, the single-atom and cluster synergistic structure constructed by controlling the precursor solvent coordination environment enabled Example 1 to exhibit excellent electrocatalytic hydrogen evolution activity and ultralong-term stability. The overpotential of the catalyst in Example 1 was only 8.5 mV, and the Tafel slope was 155 mV·dec. -1 And it can be used at 10mA·cm -2 The catalyst operated stably under constant current for 2000 hours with almost no potential decay. In contrast, the overpotential of the commercial noble metal Pt / C catalyst in Comparative Example 1 was 30 mV, and the Tafel slope was 120 mV·dec. -1 Its catalytic performance significantly decreased after 200 hours of constant current operation, and its long-term catalytic stability was significantly different from that of Example 1. These results indicate that the single-atom and cluster synergistic structure constructed in this invention can effectively integrate the advantages of both types of active sites, significantly reducing the hydrogen evolution overpotential while greatly improving operational stability, providing an effective solution for the design of non-noble metal electrocatalysts.

[0071] Figure 1 This is a schematic diagram of the single-crystal structure of the coordination polymer precursors obtained in Example 1 and Comparative Examples 2 and 3. Figure 1 The results show that the obtained precursors are periodically arranged along the c-axis, with cobalt ions in Example 1 being orderly anchored on the inner walls of the pores and at the framework nodes. This pore structure, with a uniform distribution of approximately 5 Å, provides the structural basis for the form in which cobalt exists during subsequent pyrolysis. In contrast, Comparative Examples 2 and 3 lack the presence of pores anchoring single-atom phases, and the arrangement in Comparative Example 2 is relatively disordered.

[0072] Figure 2 The image shows a HAADF-STEM image of the electrocatalyst Co1 / C-NC from Example 1. As can be seen, numerous isolated cobalt single-atom bright spots and tiny cobalt clusters composed of several atoms coexist uniformly on the carbon matrix at the nanoscale. This result directly confirms that the controllable construction of single atoms and clusters can be achieved by modulating the precursor solvent coordination environment.

[0073] Figure 3 The XAFS characterization results of the electrocatalyst Co1 / C-NC in Example 1 are shown in Figure a. Figure a shows the Co K-edge XANES spectrum, which indicates that the absorption edge position of the electrocatalyst in Example 1 is between that of the Co foil and CoO, indicating the presence of both metallic and ionic cobalt. Figure b shows the Fourier transform EXAFS spectrum, which simultaneously exhibits a Co-C coordination peak at approximately 1.53 Å and a Co-Co coordination peak at approximately 2.2 Å. Quantitative fitting yielded a Co-C coordination number of 2.1 and a Co-Co coordination number of 5.1, confirming the coexistence and proportional relationship of cobalt single atoms and cobalt clusters at the atomic scale.

[0074] Figure 4 The graphs show a comparison of the electrochemical hydrogen evolution performance of the electrocatalysts of Example 1 and Comparative Examples 2 and 3 in alkaline media; in the graphs, a is the LSV curve and b is the Tafel curve. The LSV curve in graph a shows that the catalyst of Example 1 exhibits better performance at 10 mA·cm⁻¹. -2 The overpotential was only 8.5 mV, and the Tafel curve showed that the Tafel slope of Example 1 was 155 mV·dec. - ¹ This reflects that the synergistic structure of single atoms and clusters effectively improves the reaction kinetics of the Volmer step. The hydrogen evolution overpotential of Co2 / C-NC is only 79 mV @ 10 mA·cm. -2 Tafel slope 190mV·dec -1 ; at 10mA·cm -2 It operated continuously for 200 hours under constant current. The hydrogen evolution overpotential of Co3 / C-NC was only 160 mV @ 10 mA·cm. -2 Tafel slope 266mV·dec -1 ; at 10mA·cm -2 It can run continuously for 200 hours under constant current.

[0075] Figure 5 The figures show the chronopotential curves of the electrocatalysts of Example 1 and Comparative Examples 2 and 3 in alkaline media. It can be seen that Example 1 effectively suppressed the migration and aggregation of the active form during electrochemical cycling, exhibiting an exceptionally long operating stability of 2000 hours. In contrast, Comparative Examples 2 and 3 degraded after only 200 hours. The performance of Example 1 benefits from the stable local coordination environment formed by chemical bonding between single atoms and clusters, resulting in outstanding stability in practical applications.

[0076] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0077] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters, characterized in that, Includes the following steps: Step S01: After dissolving the transition metal salt and organic ligand in N,N-dimethylacetamide, the mixture is placed in a sealed container for a solvothermal reaction. The solids are then separated, collected, washed, and dried to obtain the metal-organic coordination polymer precursor. The metal element in the transition metal salt is cobalt or nickel; Step S02: Under an inert atmosphere, the metal-organic coordination polymer precursor is pyrolyzed at high temperature and then cooled to room temperature to obtain an electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters.

2. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S01, the organic ligand is one of the following: terephthalic acid, 2-aminoterephthalic acid, or 2-hydroxyterephthalic acid; The transition metal salts are cobalt chloride or nickel chloride.

3. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S01, the total molar amount of the transition metal salt in N,N-dimethylacetamide is 0.05-0.1 mol / L.

4. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S01, the ratio of the total molar amount of the transition metal salt to the total molar amount of the organic ligand in N,N-dimethylacetamide is 1:0.5-1.

5.

5. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S01, the temperature of the solvothermal reaction is 120-150℃, and the reaction time is 12-24h.

6. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S02, the temperature of high-temperature pyrolysis is 300-900℃, and the time of high-temperature pyrolysis is 1-3h.

7. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S02, the heating rate of high-temperature pyrolysis is 1-5℃ / min.

8. The method for preparing the electrocatalyst with a synergistic structure of transition metal single atoms and transition metal clusters according to claim 1, characterized in that, In step S02, the inert atmosphere is nitrogen or argon.

9. An electrocatalyst having a synergistic structure of transition metal single atoms and transition metal clusters, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of an electrocatalyst having a synergistic structure of transition metal single atoms and transition metal clusters as described in claim 9 in an alkaline hydrogen evolution reaction.

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