A preparation method and application of precisely placing metal particle catalyst in carbon carrier pores

Abstract

The present application relates to a preparation method and application of a metal particle catalyst precisely placed in a carbon carrier channel, comprising the following steps: mixing a metal oxide precursor with a complexing agent, heating and decomposing, adding a nanocrystalline material of a metal or a metal alloy in the decomposition process, and obtaining a metal-metal oxide core-shell nanocrystal through reaction; dispersing the metal-metal oxide core-shell nanocrystal in a solvent to form a colloidal solution, and then evaporating and drying the solvent to obtain a three-dimensional metal-metal oxide core-shell nanoparticle superlattice, or obtaining a two-dimensional metal-metal oxide core-shell nanoparticle assembly through microemulsion-based amphiphilic assembly; sequentially carbonizing, removing the metal oxide, and graphitizing the metal-metal oxide core-shell nanoparticle assembly to obtain the metal particle catalyst precisely placed in the carbon carrier channel. The present application can precisely place the nanometal inside the ordered carbon structure, and improve the stability of the nanometal.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials technology, and in particular to a method for preparing and applying a catalyst in which metal particles are precisely placed within the pores of a carbon support. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) typically use platinum as the electrode catalyst. Due to the high cost of platinum, reducing its usage is crucial for the commercialization of PEMFCs. However, the performance of existing low-platinum catalysts is often limited by localized oxygen mass transfer resistance within the catalyst layer pores and poisoning of platinum-based catalytic sites by ionomer sulfonic acid groups. Developing novel catalyst loading and encapsulation technologies, constructing catalysts with precisely placed metal particles within the pores of a carbon support, developing mesoporous carbon materials for PEMFC cathode catalysts, and controllably and precisely placing platinum particles within these materials to prepare low-platinum fuel cell catalysts have significant scientific value and practical implications for hydrogen energy utilization and fuel cell technology.

[0003] Numerous studies on improving oxygen reduction catalytic performance by influencing platinum particle distribution and ionomer coverage using carbon supports primarily focus on modifying traditional solid (e.g., Vulcan Carbon) or porous (e.g., Ketjen Black) conductive carbon black. However, these commercially available carbon supports, originally designed as conductive agents, are not specifically designed for oxygen reduction catalyst support. While commercially available carbon supports with conductive agent functions exhibit excellent conductivity, and impregnating nanoparticles onto them can fully expose catalytic active sites and achieve good catalytic performance, they cannot suppress the dissolution of platinum components and the fusion of adjacent platinum nanoparticles during long-term cycling. The structures of these commercially available carbon supports are difficult to precisely control, generally exhibiting inherent defects such as irregular morphology, non-uniform pore size, and difficulty in controlling thickness. This leads to uneven and uncontrollable spatial distribution of platinum-based catalytic sites on their surface or within the pores. Furthermore, the sulfonic acid groups in the ionomer Nafion used in commercial fuel cells, in direct contact with Pt, can cause deactivation of active sites. All of these factors contribute to a significant performance degradation of existing commercially available platinum-based catalysts during application. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the purpose of this invention is to propose a method for preparing and applying a catalyst with precisely placed metal particles within the pores of a carbon support, which enables the precise placement of nano-metals within the structure of ordered carbon, thereby improving the stability of the nano-metals.

[0005] The present invention proposes a method for preparing a catalyst by precisely placing metal particles within the pores of a carbon support, comprising the following steps:

[0006] (1) Under vacuum degassing, the metal oxide precursor and the coordinating agent are mixed in a high-boiling-point solvent and heated to 100-130°C. The mass ratio of the metal oxide precursor to the coordinating agent and the high-boiling-point solvent is 1:0.2-2:1-4. Then the protective gas is replaced and the temperature is raised to 200-280°C. The metal or metal alloy nanocrystalline material dispersed in a non-polar organic solvent is injected. Then the temperature is raised to 300-400°C and the reaction is carried out for 1-3 hours. After the reaction is completed, metal-metal oxide core-shell nanocrystals are obtained.

[0007] (2) Disperse the metal-metal oxide core-shell nanocrystals obtained in step (1) in a solvent to form a colloidal solution, then allow the solvent to evaporate and dry to obtain a three-dimensional metal-metal oxide core-shell nanoparticle superlattice, or obtain a two-dimensional metal-metal oxide core-shell nanoparticle assembly by assembling the metal-metal oxide core-shell nanocrystals obtained in step (1) based on microemulsion amphiphilicity.

[0008] (3) Carbonize, remove metal oxides and graphitize the three-dimensional metal-metal oxide core-shell nanoparticle superlattice or two-dimensional metal-metal oxide core-shell nanoparticle assembly obtained in step (2) to obtain a catalyst with metal particles precisely placed in the carbon support pores.

[0009] In this invention, the metal oxide precursor in step (1) includes any one of ferric oleate, ferric palmitate, ferric eicosene, ferric acetylacetone, or ferrous acetylacetone; the coordinating agent includes any one of oleic acid, sodium oleate, palmitate, eicosene, sodium palmitate, or sodium eicosene.

[0010] In this invention, the particle size of the metal or metal alloy nanocrystalline material described in step (1) is 1–5 nm. Small-sized metal or metal alloy nanocrystalline materials can be used as seed crystals to form the core layer of metal-metal oxide core-shell nanocrystals.

[0011] In this invention, the metal or metal alloy nanocrystalline material dispersed in a nonpolar organic solvent in step (1) includes one or more nanocrystalline materials selected from platinum, palladium, iron, cobalt, nickel, gold, or silver, preferably platinum nanocrystalline materials; the metal alloy nanocrystalline material includes nanocrystalline materials formed by alloys of any two or more metals selected from platinum, palladium, iron, cobalt, nickel, gold, or silver, preferably platinum-iron alloy nanocrystalline materials, wherein the molar ratio of platinum to iron is 1:0.3 to 3, preferably about 1:1. The nonpolar organic solvent includes one or more of n-pentane, n-hexane, n-heptane, tetradecene, hexadecene, octadecene, and eicosene. The concentration of the metal or metal alloy nanocrystalline material dispersed in the nonpolar organic solvent is 10 to 50 mg / L.

[0012] In this invention, the preparation method of the metal nanocrystalline material in step (1) specifically involves the following steps: mixing a single metal organometallic compound with a long-chain alkyl diol, a long-chain organic ligand, and a high-boiling-point solvent, and reacting to obtain the metal nanocrystalline material; the preparation method of the metal alloy nanocrystalline material specifically involves the following steps: mixing at least two different metal organometallic compounds with a long-chain alkyl diol, a long-chain organic ligand, and a high-boiling-point solvent, and reacting to obtain the metal alloy nanocrystalline material; the mass ratio of the organometallic compound, the long-chain alkyl diol, the long-chain organic ligand, and the high-boiling-point solvent is 1:0. 5~3:0.5~3:30~70; wherein: the organometallic compound includes acetylacetone salts or carbonyl metal compounds of any one of platinum, palladium, iron, cobalt, nickel, gold or silver as precursors; the long-chain alkyl diol includes one or more of 1,2-hexadecyl diol, 1,2-tetradecyl diol or 1,2-hexadecyl diol; the long-chain organic ligand includes one or more of oleic acid, 9-hexadecenoic acid, 9-eicosenoic acid, 11-eicosenoic acid, 13-eicosenoic acid or oleylamine; and the high-boiling solvent includes one or more of benzyl ether, dioctyl ether, benzylphenyl ether or phenyl ether. In this invention, the preparation method of obtaining two-dimensional metal-metal oxide core-shell nanoparticle assemblies based on microemulsion amphiphilic assembly in step (2) is as follows:

[0013] (1) Dissolving a double-ended ligand in acetic acid to obtain a clear acetic acid solution of the double-ended ligand, characterized in that the concentration of the acetic acid solution of the double-ended ligand is 0.05-0.5 g / mL;

[0014] (2) The hexane dispersion of nanoparticles is mixed with the acetic acid solution of the double-terminal ligand obtained in step (1), and ultrasonicated for 1.5-2.5 minutes to obtain a mixed solution. The hexane dispersion of nanoparticles has a concentration of 5-20 mg / mL and a volume ratio of 1:1 between the hexane dispersion of nanoparticles and the solution of the double-terminal ligand.

[0015] (3) The mixed solution obtained in step (2) is injected into the polar solvent within 1-5 seconds to make the mixed solution fully contact the polar solvent. Then, it is left to stand at room temperature for 50-70 minutes. The system gradually becomes clear and the two-dimensional material gradually precipitates to the lower layer. The characteristic is that the volume ratio of the polar solvent to the mixed solution is V(polar solvent):V(mixed solution)≥10:1.

[0016] (4) Remove the supernatant of the product obtained in step (3), wash the precipitate thoroughly with ethanol, and dry it at 55-65℃ to obtain the large-size two-dimensional material.

[0017] The application of the catalyst prepared by the method proposed in this invention, which precisely places metal particles in the pores of a carbon support, in oxygen reduction catalysis.

[0018] This invention involves adding metal or metal alloy nanocrystalline materials during the thermal decomposition of a metal oxide precursor to induce heterogeneous nucleation growth, thereby synthesizing monodisperse nanocrystals with a core-shell structure and surface-coated organic ligands. Then, through self-assembly to form an ordered superlattice during solvent evaporation or through amphiphilic assembly based on microemulsion, a two-dimensional metal-metal oxide core-shell nanoparticle assembly is obtained. Furthermore, through steps such as carbonization of surface organic ligands, removal of metal oxides, and graphitization, the nanometals can be precisely placed inside ordered mesoporous carbon, overcoming the bottleneck of the difficulty in precisely placing nanometals in pore cavities.

[0019] In the catalyst prepared by this invention, metal particles are precisely placed within the pores of a carbon support. Nano-metals or nano-metal alloys are precisely placed inside an ordered mesoporous carbon framework (graphene). On the one hand, the confinement effect effectively stabilizes the internal nano-metals or nano-metal alloys to prevent melting during high-temperature calcination, and also avoids the dissolution of nano-metals or nano-metal alloys and the fusion of adjacent metal particles during long-term cycling under acidic conditions. On the other hand, when used as a fuel cell catalyst, the mesoporous carbon framework also constructs a gas-liquid mass transfer channel in the cathode catalyst layer. The reasonable pore depth can appropriately separate the catalytic sites from the ionomers, thus avoiding poisoning caused by the sulfonic acid groups of the ionomers covering the catalyst without sacrificing the proton and oxygen mass transfer rates.

[0020] This invention controls the assembly of three-dimensional ordered nanocrystals by reducing the solvent evaporation rate. A small amount (~1 wt%) of a high-boiling-point alkane solvent, such as squalane, is added to a low-boiling-point solvent like n-hexane. Due to the colligative property of dilute solutions, the boiling point of the mixed solvent will increase. The container holding the colloidal solution is covered with a glass slide, and then allowed to stand at room temperature for 3-10 hours to evaporate, resulting in a large-area three-dimensional superlattice assembly. The solvent in the colloidal solution includes low-boiling-point solvents such as n-hexane and n-heptane, and high-boiling-point solvents such as squalane. In controlling the assembly process of the three-dimensional ordered nanocrystals by reducing the solvent evaporation rate, the concentration of metal-metal oxide core-shell nanocrystals in the colloidal solution is 30-60 mg / mL, preferably about 50 mg / mL.

[0021] In this invention, the carbonization process described in step (3) involves a carbonization temperature of 350–500°C and a carbonization time of 1–2 hours. Preferably, the carbonization is carried out under a protective gas. During the carbonization process, the organic ligands on the surface of the metal-metal oxide core-shell nanoparticle assembly thermally decompose to form mesoporous ordered carbon, which can improve the electrical performance and mechanical stability of the catalyst derived from the assembly with metal particles precisely placed within the pores of the carbon support.

[0022] In this invention, the method for removing metal oxides in step (3) includes acid etching. Specifically, non-oxidizing acids, such as hydrochloric acid, phosphoric acid, hydrofluoric acid, etc., can be used. The etching temperature is 20-60℃, and the acid concentration can be set to 0.5-5 mol / L. Other concentrations of acid can also be used depending on the actual situation. During the acid etching process, the shell oxide can be selectively removed while retaining the platinum-based noble metal nanoparticles in the pores, thereby obtaining a catalyst with metal particles precisely placed in the pores of the carbon support.

[0023] In this invention, the graphitization in step (3) is carried out at a temperature of 600–1300°C for 1–4 hours, transforming the amorphous mesoporous carbon framework into a more graphitized mesoporous graphene framework film. Preferably, the graphitization is performed in a protective gas atmosphere. Graphitization further enhances the graphitization of the carbon support and the interatomic ordering of the metal or metal alloy nanocrystals.

[0024] In this invention, the protective gas in all steps refers to a non-oxidizing gas that does not react with the reactants, such as argon or nitrogen.

[0025] A second aspect of the present invention is to provide a catalyst with precisely placed metal particles within the pores of a carbon support, obtained by the above-described preparation method. The catalyst with precisely placed metal particles within the pores of the carbon support comprises a mesoporous graphene shell and metal or metal alloy nanocrystals located within the mesoporous graphene shell.

[0026] The present invention also provides an electrode comprising a substrate and a catalyst with metal particles precisely placed within the pores of a carbon support and supported on the surface of the substrate.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention is based on the synthesis of metal-oxide core-shell nanocrystals. Utilizing the heterojunction core-shell growth principle and the nanocrystal thermal injection synthesis method, metals or metal alloys are introduced as seed crystals into the oxide layer, overcoming the thermal stability problem encountered during the carbonization and calcination of superlattice ligands at the nanoscale. Through self-assembly, ligand carbonization, and acid etching, metal nanoparticles can be precisely retained within the mesoporous carbon framework left after ligand carbonization. The confinement effect of the carbon pore walls on disordered solid solution metal or alloy particles effectively protects them from sintering during secondary calcination to transform into ordered intermetallic compounds, preventing dissolution of nano-metals or nano-metal alloys and the fusion of adjacent metal particles during long-term cycling under acidic conditions.

[0029] Meanwhile, the mesoporous carbon framework also constructs the gas-liquid mass transfer channel of the cathode catalyst layer. The reasonable pore depth can appropriately separate the catalytic sites from the ionomers, so as to avoid the poisoning caused by the sulfonic acid groups of the ionomers covering the catalyst without sacrificing the proton and oxygen mass transfer rates.

[0030] Furthermore, based on existing experience with nanocrystal self-assembly methods, the obtained metal-oxide core-shell nanocrystal colloidal solution was subjected to solvent evaporation-induced self-assembly to construct a three-dimensional close-packed superlattice; alternatively, non-close-packed assemblies could be constructed using methods such as microemulsion-based amphiphilic assembly. The results show that the precise placement of metal particle catalysts within the pores of the carbon support derived from the non-close-packed assemblies at the mesoscale can avoid Ostwald ripening, agglomeration, and detachment of the metal particles, as well as electrochemical corrosion of the carbon support. The precisely placed nano-metal particles exhibit good stability. Attached Figure Description

[0031] Figure 1 A synthetic technology roadmap for precisely placing metal particle catalysts within the pores of a carbon support;

[0032] Figure 2 This is a schematic diagram of the heterogeneous nucleation and growth of metal-metal oxide core-shell nanocrystals.

[0033] Figure 3 The image is a transmission electron microscope (TEM) image of the platinum-based alloy nanocrystal PtFe obtained in step (1) of Example 1.

[0034] Figure 4 The image is a transmission electron microscope (TEM) image of the metal-metal oxide core-shell nanocrystal PtFe@Fe2O3 obtained in step (2) of Example 1.

[0035] Figure 5 Transmission electron microscope (TEM) images of Al-PtFe@MCF catalyst with metal particles precisely placed in the pores of carbon support in step (5) of Example 1; where: (a) is the overall TEM image of the sample, and (b) is a local TEM image of the sample.

[0036] Figure 6 Small-angle X-ray scattering spectra of intermediate samples PtFe@Fe2O3@OA and Al-PtFe@MCF at 500℃ and the final three-dimensional assembly L10-PtFe@MGF at 700℃ during the preparation process of Example 1;

[0037] Figure 7 The X-ray diffraction patterns of the intermediate samples PtFe@Fe2O3@OA and Al-PtFe@MCF at 500℃ and the final three-dimensional assembly L10-PtFe@MGF at 700℃ during the preparation process of Example 1 are shown. Figure 8 The data are the performance test data of L10-PtFe@MGF metal particle catalyst precisely placed in the pores of the three-dimensional ultrathin mesoporous graphitized carbon support in step (6) of Example 1, which is used as an oxygen reduction catalyst at 700℃; where: (a) is CV test data, and (b) is LSV test data;

[0038] Figure 9 The image shows a transmission electron microscope (TEM) image of the two-dimensional metal-metal oxide core-shell nanocrystal assembly PtFe@Fe2O3-Quasi-NS from step (3) of Example 2; where: (a) is the overall TEM image of the sample, and (b) is a local TEM image of the sample.

[0039] Figure 10 The image shows a transmission electron microscope (TEM) image of the PtFe@2D graphene-Quasi-NS catalyst with precisely placed metal particles in the pores of a carbon support in step (6) of Example 2; where: (a) is the overall TEM image of the sample, and (b) is a local TEM image of the sample.

[0040] Figure 11 The data are performance test data of the two-dimensional ultrathin mesoporous graphitized metal particle catalyst PtFe@2D graphene-Quasi-NS precisely placed in the pores of the carbon support in step (6) of Example 2 as an oxygen reduction catalyst; where: (a) is CV test data, (b) is LSV test data;

[0041] Figure 12 The images are transmission electron microscope (TEM) images of the PtFe@2D graphene-Quasi-NS metal particle catalyst, which was precisely placed in the pores of the carbon support and used as an oxygen reduction catalyst in step (6) of Example 2, after multiple cycles. Among them, (a) is the overall TEM image of the sample, and (b) is the local TEM image of the sample. Detailed Implementation

[0042] This invention provides a catalyst for precisely placing metal particles within the pores of a carbon support, and its synthesis route is shown in the figure below. Figure 1 As shown, alloy seed crystals grow into metal / oxide core-shell nanocrystals through heterogeneous nucleation, and then form assemblies through colloidal self-assembly and ligand carbonization. Following acid etching and secondary calcination, a catalyst containing precisely placed metal particles within the pores of a carbon support is formed, comprising ordered intermetallic compounds and ultrathin graphene. The technical solution of this invention is further illustrated below with specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all obtainable through conventional commercial channels; the processes employed, unless otherwise specified, are all conventional processes in the art.

[0043] Example 1

[0044] A three-dimensional assembly-derived catalyst with precisely placed metal particles within the pores of a carbon support, specifically a three-dimensional ultrathin mesoporous graphene with precisely placed ordered intermetallic compounds, is prepared by the following steps:

[0045] (1) Preparation of platinum-iron alloy PtFe nanocrystal seed solution:

[0046] 0.196 g of platinum acetylacetone, 0.176 g of iron acetylacetone, 0.516 g of 1,2-hexadecyldiol, 0.564 g of oleic acid, 0.534 g of oleylamine, and 20 g of benzyl ether were placed in a three-necked flask. Under vacuum degassing, the mixture was gradually heated to 100 °C and evacuated for 1 hour. The atmosphere was then replaced with nitrogen, and the reaction mixture was heated to 286 °C at a rate of 3 °C / min and reacted for 0.5 hours. Finally, the mixture was washed twice by centrifugation with ethanol and then dispersed in 5 mL of octadecene to obtain a platinum-iron alloy PtFe nanocrystal seed solution.

[0047] (2) Preparation of metal-metal oxide PtFe@Fe2O3 core-shell nanocrystal solution:

[0048] like Figure 2 As shown, 4.5g of ferric oleate, 1.38g of oleic acid, 0.77g of sodium oleate, and 10g of octadecene were placed in a three-necked flask to obtain an oxide precursor solution. The solution was gradually heated to 120℃ under vacuum degassing and continued to be evacuated for 1 hour, followed by replacement with nitrogen atmosphere. The reaction system was heated at a rate of 3℃ / min. When the reaction temperature reached 220℃, 1mL of the platinum-iron alloy nanocrystal seed solution from step (1) was injected using a syringe. The temperature was then further increased to 320℃ and the reaction was continued for 2 hours. Finally, the solution was centrifuged and washed twice, and then dispersed in n-hexane solution to form a metal-metal oxide core-shell nanocrystal solution with a concentration of approximately 50mg / mL. This solution was a stable colloidal solution.

[0049] (3) Preparation of three-dimensional nanoparticle superlattices:

[0050] The metal-metal oxide core-shell nanocrystal solution obtained in step (2) was placed in a ceramic boat at room temperature, and 1% squalane was added. After the n-hexane evaporated to complete dryness at room temperature, the metal-metal oxide core-shell nanoparticle superlattice was obtained through self-assembly.

[0051] (4) Preparation of three-dimensional ultrathin carbon-coated superlattice PtFe@Fe2O3@OA:

[0052] The metal-metal oxide core-shell nanoparticle superlattice obtained by self-assembly in step (3) is transferred to a tube furnace along with a ceramic boat and calcined at 500°C for 2 hours in a nitrogen or argon atmosphere.

[0053] (5) Preparation of Al-PtFe@MCF catalyst with a three-dimensional ultrathin mesoporous ordered structure, precisely placed within the pores of a carbon support at 500℃:

[0054] The ultrathin carbon-coated metal-metal oxide core-shell nanoparticle superlattice obtained in step (4) was acid-washed off the ceramic boat with 2 mol / L hydrochloric acid, and the Fe3O4 shell oxide was etched off by stirring at room temperature overnight.

[0055] (6) Preparation of three-dimensional ultrathin mesoporous graphene L10-PtFe@MGF with precisely placed ordered intermetallic compounds at 700℃:

[0056] The three-dimensional ultrathin mesoporous ordered structure of the catalyst with metal particles precisely placed in the pores of the carbon support obtained in step (5) is transferred to a tube furnace and calcined at 700°C for 2 hours in an argon or hydrogen-argon atmosphere. This yields ultrathin mesoporous graphene with precisely placed small-diameter ordered intermetallic compounds, in which the degree of alloy atomic ordering and mesoporous carbon graphitization is further increased.

[0057] Structural characterization:

[0058] The transmission electron microscope image of the platinum-based alloy nanocrystal seeds in step (1) is shown below. Figure 3 As shown. Figure 3 The results show that the platinum-based alloy nanocrystals have good dispersibility and uniformity, with the particle size mainly distributed at around 3 nm.

[0059] Transmission electron microscopy (TEM) image of the metal-metal oxide core-shell nanocrystals in step (2) is shown below. Figure 4 As shown. Figure 4 The results show that platinum-based alloy nanocrystals were successfully grown through heterogeneous nucleation to form nanocrystals with a core-shell structure. The particle size of the metal-metal oxide core-shell nanocrystals is mainly distributed between 20 and 25 nm.

[0060] Transmission electron microscopy (TEM) image of the ultrathin mesoporous catalyst with precisely placed metal particles within the pores of the carbon support obtained in step (5) is shown below. Figure 5 As shown in the figure, the ultrathin mesoporous ordered catalyst with precisely placed metal particles within the carbon support pores exhibits a carbon-coated structure, successfully placing nano-metals precisely within the carbon coating layer. Transmission electron microscopy (TEM) images of different regions of the sample, viewed at an angle, reveal a series of carbon layer pore projection structures. Measurement of the nanocrystals within the carbon layer pores shows 2–3 layers of carbon framework pores in the region shown in the figure. In some areas, even denser pores of approximately 3–5 layers of carbon framework pores are observed. This indicates that this method constructs a highly ordered and precisely placed three-dimensional mesoporous catalyst with precisely placed metal particles within the carbon support pores.

[0061] The small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) spectra of various intermediate samples PtFe@Fe2O3@OA, Al-PtFe@MCF at 500℃ and the final product L10-PtFe@MGF at 700℃ during the preparation process are shown below. Figure 6 and 7 As shown.

[0062] Small-angle X-ray scattering spectrum ( Figure 6The results show that the small-angle X-ray scattering peak shifts to a higher q value during the in-situ cross-linking carbonization, acid etching, and secondary calcination of the surface organic ligands. This indicates that the oxide acts as a hard template and plays a supporting role in the cross-linking carbonization of the surface ligands. Furthermore, the high-temperature crystallization during secondary calcination leads to a further shrinkage of the carbon framework pore volume.

[0063] X-ray diffraction pattern ( Figure 7 The results show that after in-situ carbonization of the surface ligands, acid etching selectively removes oxides while retaining atomically disordered Al-PtFe solid solution alloy particles. The superlattice diffraction peaks that appear after secondary calcination (marked with asterisks *) indicate that the disordered solid solution is transformed into an ordered intermetallic compound of L10-PtFe, and its sintering is avoided.

[0064] Performance testing:

[0065] We used a rotating disk test technique to test the ORR catalytic performance of the prepared catalyst (see attached). Figure 8 The ink slurry consisted of 1 mg L10-PtFe@MGF material at 700℃, 0.25 mg KB, 6 μL Nafion, and 250 μL GR-grade ethanol. The slurry was ultrasonicated in a high-power ultrasonic machine for at least 30 min to ensure thorough dispersion. Electrochemical tests in this application were performed at room temperature in 0.1 M HClO4 electrolyte. All materials underwent 100 cycles of cyclic voltammetry (CV) pre-activation before testing, with a voltage window of -0.05–1.1 V vs. RHE and a scan rate of 200 mV / s. Cyclic voltammetry curves were then recorded in an argon-saturated electrolyte, with a voltage window of -0.05–1.2 V vs. RHE and a scan rate of 20 mV / s. To test ORR activity, linear sweep voltammetry was performed in an oxygen-saturated electrolyte at a scan rate of 20 mV / s, with the RDE rotation speed fixed at 1600 rpm. All LSV test results in this application were compensated for iR drop.

[0066] The CV and LSV curves of L10-PtFe@MGF 700℃ material ink slurry were investigated using 10 μL, 20 μL, and 30 μL solutions, respectively. The platinum loading of the 10 μL catalyst slurry was 18.6 μg. Pt / cm 2 The platinum loading in the 20 μL catalyst slurry was 37.2 μg. Pt / cm 2 The platinum loading in the 30 μL catalyst slurry is 55.8 μg. Pt / cm 2 The loading of the precious metal platinum was determined by ICP testing and catalyst loading, and the RDE area was 0.196 cm². 2 .

[0067] CV results showed that its CV catalytic performance was only fully realized when the ink slurry loading reached 30 μL. The H content was determined using the measured cyclic voltammetric CV curves. upd The electrochemical active area (ECSA) of the catalyst Pt was calculated in the region because H upd Assuming monolayer adsorption, and that each active site on the Pt surface can only adsorb one H atom, the adsorption can be calculated using the H atom adsorption method. upd The adsorption area is used to calculate the equivalent electrochemical active area of ​​Pt in the catalyst. The calculation formula is as follows:

[0068]

[0069] H upd The H is obtained by integrating the area of ​​the adsorption or desorption region and then subtracting the double-layer capacitance of the material. upd The actual integrated charge Q in the region is the actual platinum mass loaded on the working electrode. H Unit H upd The theoretical electrical charge corresponding to the area is generally taken as 210 μC / cm². 2 S in 10 μL catalyst slurry Hups (10 μL) = 0.0061668; S of 20 μL catalyst slurry Hups (20 μL) = 0.0334832; S of 30 μL catalyst slurry Hups (30 μL) = 0.0340418. The calculated ECSA for the 20 μL volume is approximately 22 mg / L. 2 / g Pt The theoretical ECSA of 5nm Pt nanocrystals, calculated using theoretical density, should be 55.94 nm. 2 / g Pt This indicates that the catalytic activity of most nanocrystals in the L10-PtFe@MGF catalyst (700℃) derived from the three-dimensional assembly in Example 1, which precisely places metal particles within the pores of the carbon support, was not observed. Furthermore, during the LSV scan from low to high potential, a very large reduction current was initially observed, followed by a stable equilibrium region. This suggests that the mesoporous carbon pores on the electrode surface pre-contain oxygen-saturated electrolyte participating in the reaction. Subsequently, the mass transfer diffusion of the oxygen-saturated electrolyte was insufficient to satisfy the surface platinum-based catalytic reduction, indicating that the three-dimensional close-packed superlattice material is not conducive to the mass transfer diffusion of oxygen dissolved in the electrolyte.

[0070] Example 2

[0071] A two-dimensional assembly-derived catalyst with precisely placed metal particles within the pores of a carbon support, specifically a two-dimensional ultrathin mesoporous graphene with precisely ordered intermetallic compounds, is prepared by the following steps:

[0072] (1) Preparation of platinum-iron alloy PtFe nanocrystal seed solution: Same as step (1) in Example 1.

[0073] (2) Preparation of metal-metal oxide PtFe@Fe2O3 core-shell nanocrystal solution: Same as step (2) in Example 1.

[0074] (3) Preparation of two-dimensional metal-metal oxide core-shell nanocrystal assembly PtFe@Fe2O3 Quasi-NS: 1.8 g of 12-aminododecanoic acid was dissolved in 20 mL of acetic acid to obtain a clear solution. 20 mL of a 10 mg / mL hexane solution of the metal-metal oxide core-shell nanocrystals obtained in step (2) was taken, and the double-ended ligand solution was mixed with the particle solution and sonicated for 2 minutes. Then, the mixed solution was quickly injected into 500 mL of a mixed polar solvent of methanol and N,N-dimethylformamide in a volume ratio of 1:1. After vigorous shaking, it was allowed to stand for 1 h. The supernatant was removed, and the precipitated two-dimensional material was washed three times with 50 mL of ethanol, centrifuged, and dried at 60 °C to obtain a two-dimensional material composed of metal-metal oxide core-shell nanocrystals with a size greater than 10 μm and a thickness less than 30 nm.

[0075] (4) Preparation of two-dimensional ultrathin carbon-coated metal-metal oxide core-shell nanocrystal assembly PtFe@Fe2O3@carbon-Quasi-NS: Same as step (4) in Example 1.

[0076] (5) Preparation of Al-PtFe@2D-carbon-Quasi-NS catalyst with metal particles precisely placed in the pores of carbon support derived from two-dimensional assembly: same as step (5) in Example 1.

[0077] (6) Preparation of L10-PtFe@2D graphene-Quasi-NS catalyst with metal particles precisely placed in the pores of a graphitic carbon support derived from two-dimensional assembly: same as step (6) in Example 1.

[0078] Structural characterization:

[0079] The transmission electron microscope image of the two-dimensional metal-metal oxide core-shell nanocrystal assembly obtained in step (3) is shown below. Figure 9 As shown, the yield of two-dimensional assemblies is high and the size is above 10μm.

[0080] Transmission electron microscopy (TEM) image of the L10-PtFe@2D graphene-Quasi-NS catalyst with precisely placed metal particles within the pores of the two-dimensional ultrathin mesoporous graphene carbon support prepared in step (6) is shown below. Figure 10 As shown, compared to the three-dimensional ultrathin mesoporous graphitized carbon support in Example 1, the metal particle catalyst L10-PtFe@MGF was precisely placed within the pores at 700℃. Figure 5 Regarding the three-dimensional close-packed structure, the precise placement of metal particle catalysts within the pores of the two-dimensional ultrathin mesoporous graphitized carbon support obtained in Example 2 can effectively improve the limitation of mass transfer in traditional three-dimensional close-packed structures. Furthermore, high-resolution structural observation reveals that the surface of the ordered interphase metal compound nanoparticles contains approximately 2-3 layers of dense graphene.

[0081] Transmission electron microscopy (TEM) image of the L10-PtFe@2D graphene-Quasi-NS catalyst, precisely placed within the pores of the two-dimensional ultrathin mesoporous graphitized carbon support prepared in step (6), after participating in high-potential cycling. Figure 11 As shown, multiple groups of activated catalysts were ultrasonically washed off the electrode, and their morphological changes were observed. The results showed that the graphite carbon layer on the surface of the catalyst almost disappeared, and there was significant nanocrystal aggregation at the edge, while most of the metal nanocrystals confined by the mesoporous carbon layer still maintained monodisperse small particle size.

[0082] Performance testing:

[0083] The performance testing method in Example 2 is the same as in Example 1, with the addition of an accelerated aging durability test for the oxygen reduction catalyst. The low-potential durability test involves a CV scan of 0.6-0.95V at 50mV / s; the high-potential durability test involves a CV scan of 1.0-1.5V at 500mV / s. The catalytic performance test data are as follows: Figure 11 As shown, the oxygen reduction catalytic performance was initially poor during the oxygen reduction catalytic cycle. Only after multiple accelerated cycles of aging did the catalyst performance gradually become apparent, with no decrease in catalytic performance. This indicates that the present invention can precisely place nano-metals within the structure of ordered carbon, and this type of catalyst design improves the stability of the nano-metal particles.

[0084] Combination Figure 10 Transmission electron microscopy (TEM) characterization revealed that the L10-PtFe@2D graphene-Quasi-NS metal particles contained approximately 2–3 layers of dense graphene on their surface. This dense graphene, acting like an "armor," hindered normal contact between the platinum-based alloy and the substrate, potentially explaining its low first-efficiency catalytic performance. This indicates that the presence of a fully or partially reformed carbon coating on the nanocrystal surface negatively impacts oxygen reduction catalysis.

[0085] Combination Figure 12 Transmission electron microscopy (TEM) characterization revealed that after participating in multiple catalytic cycles, the original dense graphene on the surface of the L10-PtFe@2D graphene-Quasi-NS particles completely disappeared, and significant aggregation of the metal particles at the edges occurred. This indicates that the two-dimensional porous structure can prevent Ostwald ripening, agglomeration, and detachment of metal particles, as well as electrochemical corrosion of the carbon support.

[0086] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a catalyst by precisely placing metal particles within the pores of a carbon support, characterized in that: Includes the following steps: (1) Under vacuum degassing, the metal oxide precursor and the coordinating agent are mixed in a high-boiling-point solvent and heated to 100-130°C. The mass ratio of the metal oxide precursor to the coordinating agent and the high-boiling-point solvent is 1:0.2-2:1-4. Then, the protective gas is replaced, and the temperature is raised to 200-280°C. Then, the metal or metal alloy nanocrystalline material dispersed in a non-polar organic solvent is injected. Then, the temperature is raised to 300-400°C and the reaction is carried out for 1-3 days. h, the reaction is complete, yielding metal-metal oxide core-shell nanocrystals; the metal oxide precursor includes any one of ferric oleate, ferric palmitate, ferric eicosene, ferric acetylacetone, or ferrous acetylacetone; the coordinating agent includes any one of oleic acid, sodium oleate, palmitate, eicosene, sodium palmitate, or sodium eicosene; the high-boiling solvent includes one or more of tetradecene, hexadecene, octadecene, and eicosene; the nanocrystal material of the metal or metal alloy dispersed in a nonpolar organic solvent has a particle size of 1–5 nm, the nonpolar organic solvent includes one or more of n-pentane, n-hexane, n-heptane, tetradecene, hexadecene, octadecene, or eicosene, and the mass concentration of the nanocrystal material of the metal or metal alloy dispersed in the nonpolar organic solvent is 10–50. mg / L; The nanocrystalline material of the metal includes one or more nanocrystalline materials selected from platinum, palladium, iron, cobalt, nickel, gold or silver; The nanocrystalline material of the metal alloy includes nanocrystalline materials formed by alloys of any two or more metals selected from platinum, palladium, iron, cobalt, nickel, gold or silver. (2) Disperse the metal-metal oxide core-shell nanocrystals obtained in step (1) in a solvent to form a colloidal solution, then allow the solvent to evaporate and dry to obtain a three-dimensional metal-metal oxide core-shell nanoparticle superlattice, or obtain a two-dimensional metal-metal oxide core-shell nanoparticle assembly by assembling the metal-metal oxide core-shell nanocrystals obtained in step (1) based on microemulsion amphiphilicity. (3) Carbonize, remove metal oxides and graphitize the three-dimensional metal-metal oxide core-shell nanoparticle superlattice or two-dimensional metal-metal oxide core-shell nanoparticle assembly obtained in step (2) to obtain a catalyst with metal particles precisely placed in the carbon support pores.

2. The preparation method according to claim 1, characterized in that: The preparation method of the metal nanocrystalline material in step (1) specifically involves the following steps: mixing a single metal organometallic compound with a long-chain alkyl diol, a long-chain organic ligand, and a high-boiling-point solvent to react and obtain the metal nanocrystalline material; the preparation method of the metal alloy nanocrystalline material specifically involves the following steps: mixing at least two different metal organometallic compounds with a long-chain alkyl diol, a long-chain organic ligand, and a high-boiling-point solvent to react and obtain the metal alloy nanocrystalline material; the organometallic compound, long-chain alkyl diol, long-chain organic ligand, and high-boiling-point solvent... The mass ratio of boiling point solvents is 1:0.5-3:0.5-3:30-70; wherein: the organometallic compound includes acetylacetone salts or carbonyl metal compounds of any one of platinum, palladium, iron, cobalt, nickel, gold or silver as precursors; the long-chain alkyl diol is 1,2-hexadecyl diol; the long-chain organic ligand includes one or more of oleic acid, 9-hexadecenoic acid, 9-eicosenoic acid, 11-eicosenoic acid, 13-eicosenoic acid or oleylamine; and the high-boiling point solvent includes one or more of benzyl ether, dioctyl ether, benzylphenyl ether or phenyl ether.

3. The preparation method according to claim 1, characterized in that: The preparation method for obtaining two-dimensional metal-metal oxide core-shell nanoparticle assemblies based on microemulsion amphiphilic assembly described in step (2) is as follows: (1) Dissolve the double-terminal ligand in acetic acid to obtain a clear acetic acid solution of the double-terminal ligand; (2) Mix the hexane dispersion of nanoparticles with the acetic acid solution of the double-terminal ligand obtained in step (1), and sonicate for 1.5-2.5 minutes to obtain a mixed solution; (3) Inject the mixed solution obtained in step (2) into the polar solvent within 1-5 seconds to make the mixed solution fully contact the polar solvent, and then let it stand at room temperature for 50-70 minutes. The system gradually becomes clear and the two-dimensional material gradually precipitates to the lower layer. (4) Remove the supernatant of the product obtained in step (3), wash the precipitate thoroughly with ethanol, and dry it at 55-65℃ to obtain large-size two-dimensional material.

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