Preparation method and application of monodisperse molecular catalyst

Abstract

The invention relates to the technical field of catalysts, in particular to a preparation method and application of a monodisperse molecular catalyst, and the monodisperse molecular catalyst is particularly suitable for oxygen reduction reaction (ORR) and can be applied to new energy devices such as metal-air batteries and fuel cells. The preparation method comprises the following steps: firstly, dissolving metal precursor molecules (cobalt acetylacetonate, ferrocene, iron phthalocyanine, nickel phthalocyanine, iron phthalocyanine-nickel phthalocyanine and the like) into a solvent to obtain a uniform solution; then adding a proper amount of hollow hierarchical pore carbon spheres into the solution for mixing, and applying pressure to the hollow carbon spheres to enable the solution to be fully sucked into the hollow carbon spheres; and performing capillary condensation on the solution between carbon sheet layers through elastic extrusion, and performing photo-thermal drying on the carbon spheres sucked into the solution to obtain the monodisperse and stable oxygen reduction molecular catalyst. By simply extruding the elastic hollow hierarchical pore carbon spheres, the metal precursor active molecules are encapsulated in the carbon spheres and are uniformly dispersed, so that the electrocatalyst with excellent performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a method for preparing a monodisperse molecular catalyst and its application, which is particularly suitable for the oxygen reduction reaction (ORR) and can be applied to new energy devices such as metal-air batteries and fuel cells. Background Technology

[0002] The oxygen reduction reaction is a crucial half-reaction in both metal-air batteries and fuel cells. Particularly for hydrogen-oxygen fuel cells, the slow kinetics at the cathode limit performance, necessitating the development of highly efficient oxygen reduction catalysts. Currently, Pt-based noble metal catalysts possess excellent oxygen reduction performance and are considered the most advanced oxygen reduction catalysts in fuel cells. However, their high cost and low abundance limit their large-scale application.

[0003] To overcome the limitations of Pt-based noble metal catalysts, much research has focused on non-noble metal atomic-level catalysts. Single-atom-site catalysts, due to their higher activity density, extremely high atom utilization, and unique electronic and geometric structures, can bring superior catalytic performance to ORR. Furthermore, bimetallic and multi-metallic atomic centers can alter the oxygen reaction pathway, thereby breaking the linear relationship of oxygen intermediates, optimizing the adsorption energy and proton-electron transfer of oxygen intermediates (*OH, *O, and *OOH), and providing more favorable reaction centers to enhance oxygen reduction activity.

[0004] However, atomic-level catalysts typically require high-temperature calcination or complex heat treatment processes. For example, patent CN118341984A discloses a method for preparing manganese single-atom nanocatalysts: first, solid nanocubes of zeolite imidazole ester framework structure material (ZIF8) are prepared; then, they are etched with acid to form a hollow structure; subsequently, the etched ZIF8 HNCs adsorb manganese ions through ion exchange to obtain MnCl2-ZIF8 HNCs; finally, manganese single-atom nanomaterials are obtained through long-term high-temperature carbonization. Patent CN119447325A proposes a method for preparing a single-atom catalyst for oxygen reduction reaction: a precursor is obtained by placing a metal salt and 4,4'-bipyridine in a methanol or ethanol solution; the precursor is then calcined, followed by acid washing and filtration to obtain the target catalyst. Furthermore, methods for preparing two-site single-atom and two-atom catalysts are also discussed. For example, patent CN116037138B discloses a method for preparing a dual-site single-atom catalyst: Cu particles supported on SiO2 are added to a metal oxide solution, and then heat-treated to obtain a dual-site single-atom catalyst. Patent CN116826085A provides an iron-cobalt diatom catalyst for oxygen reduction reactions and its preparation method: utilizing the porous nature of ZIF (zinc oxide induction reactors), a cobalt-triethylenediamine complex is encapsulated within a ZIF8 cage structure, followed by Fe doping and high-temperature carbonization under nitrogen conditions to prepare an FeCo diatom catalyst, which is then applied to oxygen reduction reactions. These methods are not only complex and costly in their preparation processes, but also may result in uneven distribution of metal atoms on the support, with the possibility of local aggregation or sparse distribution. Furthermore, during the high-temperature pyrolysis process to obtain bimetallic atoms, due to the interaction forces and thermodynamic stability differences between the two metal ions, different metal atoms may migrate or agglomerate, forming nanoparticles rather than a single-atom dispersed state. These uncertainties all lead to insufficient atomic dispersion uniformity, thus affecting the activity and stability of the catalyst to varying degrees. In summary, there is still a lack of methods to prepare atomically monodisperse, highly active oxygen reduction catalysts at room temperature or low temperature. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing monodisperse molecular catalysts and their applications, solving the problems of agglomeration, complex processes, and poor stability in the preparation of traditional single-atom catalysts. The catalysts prepared by this method have the advantages of simple synthesis, high reactivity, and high stability, meeting the requirements of high-efficiency catalytic reaction applications, especially in metal-air batteries and fuel cells, to improve the kinetic reaction and mass transfer rate of the cathode and obtain excellent device performance.

[0006] The technical solution of this invention is:

[0007] A method for preparing a monodisperse molecular catalyst involves first dissolving metal precursor molecules in a dispersion solvent to obtain a metal precursor molecule solution; then mixing the solution with elastic hollow carbon spheres, and applying periodic extrusion pressure to the hollow carbon spheres to allow the solution to be fully absorbed into the pores inside the hollow carbon spheres, where capillary condensation occurs between the carbon layers due to periodic extrusion; finally, the hollow carbon spheres that have absorbed the solution are subjected to photothermal drying treatment to achieve uniform dispersion of metal precursor molecules in single-atom form on the hollow carbon sphere support, thereby obtaining a monodisperse and stable oxygen reduction molecular catalyst.

[0008] The method for preparing the monodisperse molecular catalyst described above uses a metal precursor with a molecular size of 0.5–0.9 nm and a cubic space size of 0.8–1.2 nm.

[0009] The method for preparing the monodisperse molecular catalyst wherein the metal precursor molecule is one or a mixture of two or more of the following: cobalt acetylacetonate, ferrocene, iron phthalocyanine, nickel phthalocyanine, and iron phthalocyanine-nickel phthalocyanine.

[0010] The method for preparing the monodisperse molecular catalyst uses one or more of the following as the dispersion solvent: deionized water, anhydrous ethanol, acetone, isopropanol, n-butanol, and N,N-dimethylformamide.

[0011] The method for preparing the monodisperse molecular catalyst involves preparing the metal precursor molecular solution by cell disruption and ultrasonication, water bath ultrasonication, or stirring to achieve uniform dispersion; wherein, water bath ultrasonication is performed at room temperature, with an ultrasonic frequency of 40–60 kHz and an ultrasonic treatment time of 8–12 h.

[0012] The method for preparing the monodisperse molecular catalyst involves hollow carbon spheres with an outer diameter of 10–100 nm, a cavity diameter of 2–50 nm, and a cavity wall composed of a large number of cross-linked carbon layers with a wall thickness of 4–30 nm and a distance between the carbon layers of 0.3–1 nm, which makes the hollow carbon spheres elastic.

[0013] The preparation method of the monodisperse molecular catalyst involves applying periodic extrusion pressure using a grinding method, including mechanical grinding or manual grinding, with a processing time of 5 min to 3 h.

[0014] The preparation method of the monodisperse molecular catalyst, wherein the photothermal drying method involves placing hollow carbon spheres that have absorbed the solution into a photothermal drying device, and using the thermal radiation and thermal effect of the photothermal conversion device for complete drying, with the light intensity controlled at 50–500 mW / cm². 2 The photothermal power is 100-1000W, the temperature is set at 30-80℃, and the photothermal treatment time is 0.5min-12h.

[0015] The method for preparing the monodisperse molecular catalyst described above results in a catalyst with an excellent molecular-level monodisperse structure. The metal precursor molecules are located in the surface defects and carbon layers of the hollow carbon spheres, and the mass fraction of the metal precursor molecules is 1-60% of the total mass of the monodisperse molecular catalyst.

[0016] An application of a monodisperse molecular catalyst, in which a monodisperse single-atom catalyst is prepared as an electrode and applied to a highly efficient oxygen reduction or other electrochemical catalytic reaction, is described. This catalyst exhibits excellent electrocatalytic oxygen reduction activity.

[0017] The design concept of this invention is:

[0018] Existing technologies (such as CN118341984A and CN116826085A) require high-temperature carbonization to prepare single-atom catalysts, which leads to the migration and aggregation of metal atoms due to differences in thermodynamic stability, forming nanoparticles and resulting in uneven distribution of active sites. This invention, based on traditional single-atom catalyst preparation, utilizes capillary condensation of a metal precursor molecular solution at room temperature, followed by rapid photothermal drying to remove the solvent, allowing the metal active component to exist in a monodisperse form on the support, thus improving the catalyst's activity and stability. Simultaneously, the ease with which macrocyclic molecules can enter and exit the carbon-carbon interlayer of the hollow carbon spheres further enhances the catalyst's stability. Furthermore, controlling different types of metal precursors to achieve atomic co-doping can also adjust the electronic structure of the metal active centers. This invention improves the stability and conductivity of the catalyst by utilizing the structural characteristics of hollow carbon spheres under simple process conditions, and enhances the binding force between the active metal component and the support through photothermal treatment. Under the synergistic effect of room temperature capillary condensation-photothermal drying technology, monodispersity of metal component molecules is achieved, avoiding high-temperature pyrolysis in traditional preparation processes, and obtaining a highly efficient and stable electrochemical reaction catalyst.

[0019] The advantages and beneficial effects of this invention are as follows:

[0020] 1. The catalyst support of the present invention uses hollow carbon spheres, which on the one hand capture metal precursor molecules, and on the other hand further improve the conductivity of the catalyst.

[0021] 2. The metal precursor molecules of the present invention are readily available, such as cobalt acetylacetonate, ferrocene, iron phthalocyanine, nickel phthalocyanine, etc., which are low in cost and abundant in reserves.

[0022] 3. The present invention uses photothermal technology for drying, which can not only dry quickly, but also act evenly on the sample surface and interior, avoiding local overheating or uneven drying. Photothermal treatment can increase the binding force between active molecules and the porous carbon layer of the matrix, and stabilize its catalytic activity.

[0023] 4. The monodisperse molecular oxygen reduction catalyst in this invention avoids a complex high-temperature heat treatment process in its design method, which greatly simplifies the preparation process and makes it easier to explore the oxygen reduction activity mechanism.

[0024] 5. The catalyst preparation method proposed in this invention can effectively realize monodisperse metal active component molecules, and obtain extremely high atom utilization rate and ultra-high oxygen reduction half-wave potential.

[0025] 6. In this invention, the metal precursor molecule solution is completely controllable, and co-doping (i.e., Fe, Co, Ni atoms coexist) can be achieved. Alternatively, the desired dual-active-site structure can be constructed by selecting bimetallic precursor molecules, and further, multi-metallic precursor molecules can be selected to construct multi-site structures.

[0026] 7. The method for realizing monodisperse molecular catalysts proposed in this invention has a certain degree of universality. Based on the method for preparing monodisperse molecular catalysts, it can also be used to construct a large number of monodisperse active sites in other systems in the field of electrochemistry.

[0027] 8. The method for realizing monodisperse molecular catalysts proposed in this invention is simple, reliable, easy to scale up, and has potential practical value. Attached Figure Description

[0028] Figure 1 (a) Scanning electron microscope image of the catalyst containing 10 wt.% phthalocyanine iron (FePc) prepared in Example 1 of the present invention; (b) Low-magnification transmission electron microscope image; (c) High-magnification transmission electron microscope image; (d) Corresponding aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0029] Figure 2 (a) Scanning electron microscope image of the catalyst containing 30 wt.% FePc prepared in Example 2 of the present invention; (b) Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0030] Figure 3 (a) Scanning electron microscope image of the 10 wt.% nickel phthalocyanine (NiPc) catalyst prepared in Example 4 of the present invention; (b) Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0031] Figure 4 (a) Scanning electron microscope image of the catalyst containing 10 wt.% FePc and 10 wt.% NiPc prepared in Example 5 of the present invention; (b) Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0032] Figure 5(a) Scanning electron microscope image of the catalyst containing 10 wt.% cobalt acetylacetone (Co(acac)2) prepared in Example 6 of the present invention; (b) Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0033] Figure 6 (a) Scanning electron microscope image of the 10 wt.% ferrocene (Fe(Cp)2) catalyst prepared in Example 7 of the present invention; (b) Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image.

[0034] Figure 7 The ORR polarization curves of the catalyst containing 30 wt.% FePc and 20 wt.% commercial Pt / C prepared in Example 2 of this invention are shown. In the figure, the horizontal axis represents the electrode potential (V vs. RHE), and the vertical axis represents the current density (mA cm⁻¹). -2 ).

[0035] Figure 8 This is a Tafel slope plot of the catalyst containing 30 wt.% FePc and 20 wt.% commercial Pt / C prepared in Example 2 of this invention. In the figure, the horizontal axis Log|j| represents the logarithm of the absolute value of the current density (j) (mA cm⁻¹). -2 The vertical axis, Potential, represents the electrode potential (V vs. RHE).

[0036] Figure 9 This is a graph showing the number of transferred electrons and hydrogen peroxide yield of the catalyst containing 30 wt.% FePc and 20 wt.% commercial Pt / C prepared in Example 2 of this invention. In the graph, the horizontal axis represents the electrode potential (V vs. RHE), and the left vertical axis represents H2O. - Yield represents the hydrogen peroxide yield (%), and the right-hand vertical axis represents the number of transferred electrons (n).

[0037] Figure 10 The ORR polarization curves of the 30 wt.% FePc catalyst prepared in Example 2 of this invention before and after 5000 cycles are shown. In the figure, the horizontal axis represents the electrode potential (V vs. RHE), and the vertical axis represents the current density (mA cm⁻¹). -2 ). Detailed Implementation

[0038] In its specific implementation, this invention proposes a method for preparing a monodisperse molecular catalyst. A solution containing metal precursor molecules is selected, and through periodic extrusion, the metal precursor molecule solution undergoes capillary condensation within hollow carbon spheres. After the solution is completely absorbed, it is subjected to photothermal drying, thereby achieving uniform dispersion of the metal precursor molecules in single-atom form on the carbon sphere support. The specific steps are as follows:

[0039] (1) Dissolve the metal precursor molecules in a suitable solvent to form a homogeneous solution containing the metal precursor molecules.

[0040] The selected metal precursor molecules include macrocyclic molecules such as cobalt acetylacetonate, ferrocene, iron phthalocyanine, and nickel phthalocyanine. Furthermore, they are not limited to monocyclic compounds; one, two, or more of cobalt acetylacetonate, ferrocene, iron phthalocyanine, and nickel phthalocyanine can be used. The selected solvent is generally one or two of deionized water, ethanol, acetone, isopropanol, n-butanol, and N,N dimethylformamide. In the preparation of a homogeneous solution containing the metal precursor molecules, a certain mass of solute (metal precursor molecules) is mixed with a certain volume of solvent to form a dispersion solution with a concentration of 5 mg / mL to 75 mg / mL. The solute and solvent are placed in a slightly larger centrifuge tube / sample vial and subjected to ultrasonic treatment in a room temperature water bath at a frequency of 40–60 kHz for 8–12 hours.

[0041] (2) Place an appropriate amount of elastic hollow carbon spheres into the above solution, and use a grinding method to apply periodic extrusion pressure to the hollow carbon spheres so that the metal dispersion enters the interior of the hollow carbon spheres. The processing time is 10 min to 3 h.

[0042] Hollow carbon spheres possess a certain degree of elasticity, with an outer diameter of 10–100 nm and a cavity diameter of 2–50 nm. The cavity walls are composed of numerous cross-linked carbon layers with a wall thickness of 2–20 nm, and the distance between the carbon layers is between 0.3–1 nm. Before dispersion, based on the absorption limit of the elastic hollow carbon spheres, a certain mass of hollow carbon spheres and a corresponding volume of solution containing metal precursor molecules are added sequentially to a mortar. The solution containing the metal precursor is slowly injected into the container containing the hollow carbon spheres, and periodic pressure is applied to the hollow carbon spheres until the solution almost disappears (capillary coagulation occurs between the carbon layers through elastic compression). Grinding is stopped when the carbon spheres are completely saturated.

[0043] (3) Place the carbon balls that have absorbed the solution into a photothermal drying device for complete drying. The light intensity should be controlled between 50 and 500 mW / cm². 2 The light exposure time ranges from 0.5 min to 12 h.

[0044] The drying conditions are as follows: Hollow carbon spheres containing a saturated condensed solution are placed in a drying device equipped with a photothermal conversion unit. This device is equipped with a near-infrared light source (wavelength between 780 and 2526 nm) and includes temperature and light intensity sensors. Photothermal parameters are set according to the material, size, and characteristics of the loaded metal precursor molecules of the hollow carbon spheres. The light intensity is controlled between 50 and 500 mW / cm². 2 The temperature was set between 30 and 80°C, and the illumination time was adjusted from 0.5 min to 12 h depending on the amount of solution and the carbon ball load.

[0045] To provide a clearer and more detailed description of the present invention, further explanation is given below with reference to the accompanying drawings and examples. Furthermore, the embodiments of the present invention described below are typical, not limiting, embodiments, and not all embodiments, and are not intended to limit the scope of the invention.

[0046] In the following embodiments, all raw materials used are conventional chemicals purchased from the market.

[0047] Example 1

[0048] Take a clean 200mL sample bottle, add 1g of iron phthalocyanine (FePc) and 50mL of deionized water, seal it, and place it in an ultrasonic cleaner for ultrasonic dispersion. After 10 hours, a homogeneous FePc solution A with a concentration of 20mg / mL is formed. Take 10g of hollow carbon spheres with an outer diameter of 30nm, an inner diameter of 20nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.4-0.9nm. Slowly add the above homogeneous solution A, and then mechanically grind for 1 hour to mix until the solution is completely absorbed into the hollow carbon spheres. Finally, place it in a photothermal drying device at 30℃ and 100mW cm⁻¹. -2 The catalyst was dried in a light source with a photothermal power of 300W for 1 hour to obtain a monodisperse FePc molecular catalyst containing 10 wt.%.

[0049] Example 2

[0050] The preparation method is basically the same as in Example 1, except that: 3g of iron phthalocyanine (FePc) is dissolved in 60mL of deionized water to form a homogeneous FePc solution A with a concentration of 50mg / mL. This solution is then mixed with 10g of hollow carbon spheres with an outer diameter of 20nm, an inner diameter of 10nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.3-0.8nm. The mixture is then mechanically ground for 1 hour until the solution is completely absorbed into the hollow carbon spheres. Finally, the solution is placed in a photothermal drying apparatus and dried at 50℃ and 120mW cm⁻¹. -2 After drying with a light intensity of 500W for 1 hour, a monodisperse FePc molecular catalyst containing 30wt.% was obtained.

[0051] Example 3

[0052] The preparation method is basically the same as in Example 1, except that: 6g of iron phthalocyanine (FePc) is dissolved in 80mL of deionized water to form a homogeneous FePc solution A with a concentration of 75mg / mL. This solution is then mixed with 10g of hollow carbon spheres with an outer diameter of 50nm, an inner diameter of 30nm, a carbon layer wall thickness of 10nm, and a distance between carbon layers of 0.5-1nm. The mixture is then mechanically ground for 2 hours until the solution is completely absorbed into the hollow carbon spheres. Finally, the solution is placed in a photothermal drying apparatus and dried at 70℃ and 150mW cm⁻¹. -2 After drying with a light intensity of 800W for 30 minutes, a monodisperse FePc molecular catalyst containing 60wt.% was obtained.

[0053] Example 4

[0054] The preparation method is basically the same as in Example 1, except that: 1g of nickel phthalocyanine (NiPc) is dissolved in 50mL of deionized water to form a homogeneous NiPc solution A with a concentration of 20mg / mL. Similarly, 10g of hollow carbon spheres with an outer diameter of 30nm, an inner diameter of 20nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.4-0.9nm are mixed and then mechanically ground for 0.5h until the solution is completely absorbed into the hollow carbon spheres. Finally, the mixture is placed in a photothermal drying device and dried at 30℃ with 100mW cm⁻¹. -2 After drying with a light intensity of 400W for 1 hour, a monodisperse NiPc molecular catalyst containing 10wt.% was obtained.

[0055] Example 5

[0056] The preparation method is basically the same as in Example 1, except that: 1g of bimetallic precursor molecules of iron phthalocyanine (FePc) and 1g of nickel phthalocyanine (NiPc) are dissolved in 50mL of deionized water to form a mixed solution A with a concentration of 20mg / mL iron phthalocyanine and 20mg / mL nickel phthalocyanine. This solution is then mixed with 10g of hollow carbon spheres with an outer diameter of 20nm, an inner diameter of 10nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.3-0.8nm. The mixture is then mechanically ground for 1.5h until the solution is completely absorbed into the hollow carbon spheres. Finally, the mixture is placed in a photothermal drying device and dried at 60℃ and 180mW cm⁻¹. -2 After drying with a photothermal power of 900W for 20 minutes, a monodisperse bimolecular catalyst containing 10 wt.% FePc and 10 wt.% NiPc was obtained.

[0057] Example 6

[0058] The preparation method is basically the same as in Example 1, except that: 1g of cobalt acetylacetonate (Co(acac)2) is dissolved in 50mL of deionized water to form a Co(acac)2 solution A with a concentration of 20mg / mL. This solution is then mixed with 10g of hollow carbon spheres with an outer diameter of 30nm, an inner diameter of 20nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.4-0.9nm. The mixture is then mechanically ground for 1 hour until the solution is completely absorbed into the hollow carbon spheres. Finally, the mixture is placed in a photothermal drying device and dried at 30℃ with 100mW cm⁻¹. -2 After drying with a light intensity of 200W for 1 hour, a monodisperse Co(acac)2 molecular catalyst containing 10wt.% was obtained.

[0059] Example 7

[0060] The preparation method is basically the same as in Example 1, except that: 0.25g of ferrocene (Fe(Cp)2) is dissolved in 50mL of deionized water to form Fe(Cp)2 solution A with a concentration of 5mg / mL. This solution is then mixed with 10g of hollow carbon spheres with an outer diameter of 30nm, an inner diameter of 20nm, a carbon layer wall thickness of 5nm, and a distance between carbon layers of 0.4-0.9nm. The mixture is then mechanically ground for 0.5h until the solution is completely absorbed into the hollow carbon spheres. Finally, the mixture is placed in a photothermal drying device and dried at 30℃ and 100mW cm⁻¹. -2 After drying with a light intensity of 600W for 1 hour, a monodisperse Fe(Cp)2 molecular catalyst containing 1 wt.% was obtained.

[0061] Performance testing

[0062] The hollow carbon sphere-supported catalyst containing 10 wt.% FePc molecules prepared in Example 1 was characterized by electron microscopy, and its morphology is as follows: Figure 1 As shown, the top left image (a) is a scanning electron microscope (SEM) image, revealing a large number of carbon spheres. The top right image (b) is a low-magnification transmission electron microscope (TEM) image, similarly showing a large number of entangled carbon spheres. The bottom left image (c) is a high-magnification TEM image, showing thin layers of carbon stacked on the carbon spheres. Single dispersion of FePc molecules can be seen in the gaps and pores between the carbon layers, without the appearance of lattice fringes. The bottom right image (d) is a spherical aberration electron microscope (SEM) image, showing multiple bright spots corresponding to the presence of FePc molecules, proving that Fe is distributed on the carbon support in the form of dispersed single atoms. Similarly, Examples 2, 4, 5, 6, and 7 correspond to... Figure 2 , 3The corresponding added metal precursor molecules can be seen in samples 4, 5, and 6. In particular, for the bimetallic precursor molecule solution (10 wt.% FePc and 10 wt.% NiPc), the presence of the two metal molecules can still be seen in the carbon layer-carbon layer gap under a spherical aberration corrected high-angle annular dark-field scanning transmission electron microscope, which proves the successful preparation of this monodisperse molecular catalyst and its universality.

[0063] Electrochemical RDE and RRDE tests were performed on Example 2 and a commercial 20 wt.% Pt / C catalyst. Figure 7 As shown, the monodisperse molecular catalyst exhibits higher oxygen reduction reaction activity than commercial Pt / C catalysts, with a half-wave potential (E0) of [missing value]. 1 / 2 It increased by 60mV. (For example...) Figure 8 As shown, the Tafel slope of the monodisperse molecular catalyst is much smaller than that of the commercial platinum-carbon catalyst, indicating that it improves the kinetic reaction rate compared to platinum-carbon. Figure 9 As shown, monodisperse molecular catalysts exhibit lower hydrogen peroxide yields and a greater tendency for electron transfer (4-electron transfer) during the oxygen reduction reaction, indicating that they are more conducive to the oxygen reduction reaction. Figure 10 As shown, the performance of the monodisperse molecular catalyst did not decline after 5000 cycles but increased by 20mV, indicating its good oxygen reduction stability.

[0064] Based on the above tests and analyses, it has been demonstrated that the monodisperse molecular catalyst exhibits high activity and high stability in the oxygen reduction reaction. The monodisperse single-atom catalyst prepared above can be used as an electrode for efficient oxygen reduction and other electrochemical catalytic reactions, and has great potential for commercial applications.

[0065] The results show that this invention, through simple extrusion of elastic hollow layered porous carbon spheres, encapsulates metal precursor active molecules within the carbon spheres, achieving uniform dispersion and yielding a high-performance electrocatalyst. The preparation method is simple, highly stable, and shows promising prospects for large-scale application. Furthermore, by selecting different types and ratios of metal precursors, the electronic structure and active sites of the catalyst can be flexibly controlled to meet the needs of various electrochemical reactions.

Claims

1. A method for preparing a monodisperse molecular catalyst, characterized in that, First, metal precursor molecules are dissolved in a dispersion solvent to obtain a metal precursor molecule solution. Then, elastic hollow carbon spheres are mixed with the above solution. By applying periodic extrusion pressure to the hollow carbon spheres, the solution is fully absorbed into the pores inside the hollow carbon spheres. The solution undergoes capillary coagulation between the carbon layers through periodic extrusion. Finally, the hollow carbon spheres that have absorbed the solution are subjected to photothermal drying treatment to achieve uniform dispersion of metal precursor molecules in the form of single atoms on the hollow carbon sphere support, thereby obtaining a monodisperse and stable oxygen reduction molecular catalyst.

2. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The molecular size of the metal precursor is 0.5–0.9 nm, and its size in cubic space is 0.8–1.2 nm.

3. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The metal precursor molecule is one or a mixture of two or more of the following: cobalt acetylacetonate, ferrocene, iron phthalocyanine, nickel phthalocyanine, and iron phthalocyanine-nickel phthalocyanine.

4. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The dispersion solvent is one or a mixture of two or more of the following: deionized water, anhydrous ethanol, acetone, isopropanol, n-butanol, and N,N-dimethylformamide.

5. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The preparation method of the metal precursor molecule solution is to achieve uniform dispersion by cell disruption and sonication, water bath sonication, or stirring; wherein, water bath sonication is carried out at room temperature, the ultrasonic frequency is 40-60 kHz, and the ultrasonic treatment time is 8-12 h.

6. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The hollow carbon spheres have an outer diameter of 10–100 nm, a cavity diameter of 2–50 nm, and a cavity wall composed of a large number of cross-linked carbon layers with a wall thickness of 4–30 nm. The distance between the carbon layers is between 0.3 and 1 nm, which makes the hollow carbon spheres elastic.

7. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, Periodic extrusion pressure is applied using grinding methods, including mechanical or manual grinding, with a processing time of 5 minutes to 3 hours.

8. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The photothermal drying method involves placing hollow carbon spheres that have absorbed the solution into a photothermal drying device, where they are completely dried using the thermal radiation and thermal effect of the photothermal conversion device. The light intensity is controlled between 50 and 500 mW / cm². 2 The photothermal power is 100-1000W, the temperature is set at 30-80℃, and the photothermal treatment time is 0.5min-12h.

9. The method for preparing the monodisperse molecular catalyst according to claim 1, characterized in that, The catalyst has an excellent molecular-level monodisperse structure, with metal precursor molecules located in the surface defects and carbon layers of hollow carbon spheres. The mass fraction of metal precursor molecules is 1-60% of the total mass of the monodisperse molecular catalyst.

10. The application of a monodisperse molecular catalyst prepared by the method according to any one of claims 1 to 9, characterized in that, Monodisperse single-atom catalysts are prepared into electrodes and applied to efficient oxygen reduction or other electrochemical catalytic reactions. These catalysts exhibit excellent electrocatalytic oxygen reduction activity.

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