Composite catalyst, its preparation method and application

Abstract

The application relates to the technical field of electrocatalytic materials, and discloses a composite catalyst as well as a preparation method and application thereof. The composite catalyst is formed by compounding a two-dimensional ultrathin high-entropy metal alkene and a three-dimensional high-entropy metal aerogel, the two-dimensional ultrathin high-entropy metal alkene is used as a carrier, the three-dimensional high-entropy metal aerogel is uniformly loaded on the surface of the two-dimensional ultrathin high-entropy metal alkene, a multi-stage composite structure is formed, and the two-dimensional ultrathin high-entropy metal alkene and the three-dimensional high-entropy metal aerogel form a synergistic catalytic system through interface strong coupling. Through an in-situ reduction loading process, the three-dimensional high-entropy metal aerogel is in-situ grown on the surface of the two-dimensional ultrathin high-entropy metal alkene and forms a stable composite structure, thereby constructing a two-dimensional + three-dimensional multi-stage structure, forming an effective electronic synergistic channel, significantly improving the electronic conduction efficiency and structural stability of the composite system, and avoiding the interface separation problem caused by physical mixing.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials technology, and in particular to a composite catalyst, its preparation method, and its application. Background Technology

[0002] Direct methanol fuel cells are considered ideal energy devices for portable electronic devices, mobile power supplies, and distributed power systems due to their advantages such as high energy density, convenient fuel storage and transportation, and environmental friendliness. The core bottleneck to their commercial application lies in the slow kinetics of the methanol oxidation reaction at the anode, the susceptibility of the catalyst to carbon monoxide poisoning, and its poor long-term stability. Therefore, developing highly active, highly resistant to poisoning, and highly stable anode catalysts is key to overcoming these bottlenecks.

[0003] Platinum-based materials are the core of traditional methanol oxidation catalysts, but they are scarce and expensive. Furthermore, single platinum-based catalysts have a high adsorption capacity for carbon monoxide, which can easily lead to blockage of active sites. Palladium-based materials, due to their relatively abundant reserves and intrinsic activity advantages in methanol oxidation, have become an important alternative to platinum-based catalysts. However, palladium-based catalysts suffer from insufficient stability and also exhibit weak resistance to carbon monoxide poisoning. To improve the performance of noble metal catalysts, researchers have introduced non-noble metals through alloying to form multi-component alloy catalysts. They utilize electronic effects to modulate the d-band centers of noble metals to optimize the adsorption / desorption behavior of reaction intermediates, while simultaneously using geometric effects to inhibit the aggregation of noble metal particles, thereby achieving a certain degree of catalytic performance improvement. However, the compositional control space of traditional binary or ternary alloy catalysts is limited, making it difficult to simultaneously achieve the high activity, resistance to poisoning, and structural stability required for methanol oxidation, thus failing to meet the practical application requirements of direct methanol fuel cells.

[0004] High-entropy alloys typically contain five or more main elements and exhibit high-entropy effects, lattice distortion effects, slow diffusion effects, and cocktail effects, providing new avenues for catalyst performance optimization. Introducing high-entropy alloy structures into direct methanol fuel cell anode catalysts allows for precise control of the catalyst's electronic structure and surface energy through the synergistic effect of multiple components, thereby improving resistance to carbon monoxide poisoning and structural stability. Furthermore, preparing high-entropy alloys into two-dimensional ultrathin high-entropy metalenes and three-dimensional high-entropy metal aerogel structures leverages structural advantages: two-dimensional ultrathin high-entropy metalenes possess a large specific surface area and abundant surface active sites, along with excellent electronic conductivity; three-dimensional high-entropy metal aerogels possess a continuous porous network structure, good mass transfer channels, and high structural stability. The combination of these two structures can construct a multi-level structure of "two-dimensional active site enrichment + three-dimensional mass transfer framework support," achieving synergistic optimization of electronic conduction, mass transport, and catalytic reactions, thus becoming a promising anode catalyst system for direct methanol fuel cells.

[0005] Currently, research on composite catalysts of two-dimensional ultrathin high-entropy metalenes and three-dimensional high-entropy metal aerogels is still in its early stages. Existing preparation processes and material designs have several problems: First, two-dimensional ultrathin high-entropy metalenes are prone to sheet aggregation and uneven thickness, and the co-reduction of multiple metals is difficult, easily leading to component segregation and making it difficult to ensure the full realization of the high-entropy effect. Second, the preparation of three-dimensional high-entropy metal aerogels often requires high-temperature heat treatment or template agent assistance. High temperatures can easily cause the porous structure to collapse, and template agent residues may obscure active sites. Furthermore, when the proportion of non-noble metals is too high, the dispersion of noble metal active sites can be poor, affecting catalytic efficiency. Third, existing composite catalysts mostly adopt simple physical mixing methods. The interfacial bonding between two-dimensional ultrathin high-entropy metalenes and three-dimensional high-entropy metal aerogels is weak, and interfacial separation is easy to occur, making it difficult to form an effective electronic synergistic effect, resulting in the composite system's performance not meeting expectations. At the same time, the process parameters such as the ratio of noble metals to non-noble metals, the total metal concentration, and the selection of reducing agents in the composite system lack systematic optimization design, making it difficult to achieve a synergistic improvement in high-entropy effect, structural formability, and catalytic performance.

[0006] Furthermore, existing preparation processes for high-entropy catalysts are mostly designed for single structures (metal olefins or aerogels), and no dedicated preparation method has yet been developed for two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite systems. In particular, achieving in-situ robust composite of two-dimensional ultrathin high-entropy metal olefins and three-dimensional high-entropy metal aerogels without high-temperature heat treatment, while ensuring the preservation of their high-entropy structure and morphology, remains a technical challenge that urgently needs to be solved.

[0007] Therefore, it is necessary to develop a simple process that does not require high-temperature heat treatment and can achieve homogeneous co-reduction of multiple metals to prepare a two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalyst. By controlling the ratio of noble metals to non-noble metals, the total metal concentration, and the interfacial bonding mode, a multi-level composite catalyst with high activity, high resistance to poisoning, and high stability can be constructed to promote the industrialization of anode catalysts for direct methanol fuel cells and has important practical significance and application value. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a composite catalyst, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A composite catalyst is formed by combining a two-dimensional ultrathin high-entropy metal olefin and a three-dimensional high-entropy metal aerogel. The two-dimensional ultrathin high-entropy metal olefin serves as a carrier, and the three-dimensional high-entropy metal aerogel is uniformly loaded on the surface of the two-dimensional ultrathin high-entropy metal olefin to form a multi-level composite structure. The two-dimensional ultrathin high-entropy metal olefin and the three-dimensional high-entropy metal aerogel form a synergistic catalytic system through strong interfacial coupling.

[0010] Preferably, the two-dimensional ultrathin high-entropy metalene is a high-entropy alloy ultrathin nanosheet containing Pd and composed of five or more transition metals. The transition metals are at least five of Group VIII, Group VIB, Group VIIB, and Group IB transition metals and must contain Pd. The molar ratio of Pd to other transition metals is 1:1 to 1:10, preferably 1:3 to 1:6.

[0011] Preferably, the three-dimensional high-entropy metal aerogel is a high-entropy alloy porous network structure composed of five or more transition metals, and includes at least one of Pt and Pd. The transition metals are selected from at least five transition metals of Group VIII, Group VIB, Group VIIB, and Group IB, wherein the molar ratio of Pt or Pd to other transition metals is 1:1 to 1:10, preferably 1:3 to 1:6.

[0012] The porous network structure of the three-dimensional high-entropy metal aerogel can construct efficient mass transfer channels and reduce the diffusion resistance of methanol and reaction products; its porous structure can also inhibit the aggregation of high-entropy metal olefin sheets, further improving the utilization rate of active sites.

[0013] Preferably, the mass ratio of the two-dimensional ultrathin high-entropy metalene to the three-dimensional high-entropy metal aerogel is 1:6 to 1:12, more preferably 1:8 to 1:10.

[0014] Preferably, the two-dimensional ultrathin high-entropy metalene has a two-dimensional sheet-like morphology, which is either flat or curved; the average length and / or width of a single two-dimensional ultrathin high-entropy metalene sheet is 50~500 nm; the total thickness of a single two-dimensional ultrathin high-entropy metalene sheet is 0.2~5 nm; the number of atomic layers of the two-dimensional ultrathin high-entropy metalene sheet is 1~20; and the thickness of a single layer of the two-dimensional ultrathin high-entropy metalene sheet is 0.2~1 nm.

[0015] The two-dimensional ultrathin high-entropy metal olefin has a single-phase solid solution structure with typical high-entropy effect and lattice distortion effect. Its surface has abundant defect active sites and excellent electron conduction rate, which can be used as a support substrate for high-entropy metal aerogels, while providing additional catalytic active sites.

[0016] Preferably, the diameter of individual metal particles in the three-dimensional high-entropy metal aerogel is 5-100 nm, and the specific surface area of ​​the three-dimensional high-entropy metal aerogel is 20-500 m².2 / g, the three-dimensional high-entropy metal aerogel has a chain-like morphology with interconnected particles; the porosity of the three-dimensional high-entropy metal aerogel is 50%~90%, and the pore size distribution is 2~500 nm.

[0017] The preparation method of the above-mentioned composite catalyst includes the following steps: S1: Weigh the metal salt precursor containing Pd and transition metals other than Pd according to the composition ratio of the two-dimensional ultrathin high-entropy metal olefin. Dissolve the metal salt precursor in a solvent, add the first reducing agent, stir evenly and transfer it to a reaction vessel for solvothermal reaction. After the reaction is completed, cool to room temperature, wash and dry to obtain two-dimensional ultrathin high-entropy metal olefin powder. S2: Weigh out five or more transition metal salts according to the composition ratio of the three-dimensional high-entropy metal aerogel, wherein the five or more transition metal salts contain at least one of Pt salt and Pd salt, dissolve them in deionized water, adjust the pH value of the system, and stir evenly at room temperature to form a mixed solution; then add a second reducing agent and stir initially; then add the two-dimensional ultrathin high-entropy metal ene powder obtained in step S1 according to the mass composite ratio, stir again, and let it stand for aging to obtain the two-dimensional ultrathin high-entropy metal ene / three-dimensional high-entropy metal hydrogel composite precursor; S3: The two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 is washed with deionized water and then dried to obtain the two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal aerogel composite catalyst.

[0018] Preferably, the metal salt precursors containing Pd and transition metals other than Pd mentioned in step S1 are all soluble inorganic metal salts or organic metal salts, and at least one of the metal salts is a carbonyl metal salt or a carbonyl metal complex. The solvent in step S1 is one or a combination of ethylene glycol, N,N-dimethylformamide, oleylamine, oleic acid, or octadecene; the total concentration of metal ions provided by the metal salt precursor in step S1 is 0.005~0.2 mol / L, preferably 0.01~0.1 mol / L; the first reducing agent in step S1 is one or a combination of ascorbic acid, ammonium bromide, polyvinylpyrrolidone, citric acid, tartaric acid, hydroquinone, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, sodium oleate, and polyvinyl alcohol, wherein the molar ratio of the first reducing agent to the total amount of metal ions is 0.15:1~10:1, preferably 0.5:1~3:1.

[0019] Preferably, the reaction vessel in step S1 is a polytetrafluoroethylene pressure-resistant reactor or a glass pressure-resistant tube; The reaction temperature of the solvothermal reaction in step S1 is 50~250 °C, preferably 80~150 °C; the reaction time is 1~48 h, preferably 12~24 h; the washing reagent used in step S1 is one or a combination of methanol, ethanol, isopropanol, cyclohexane and acetone.

[0020] Preferably, the drying in step S1 is freeze drying, supercritical CO2 drying, or vacuum high-temperature drying, and the drying time is 2 to 50 hours, preferably 12 to 24 hours.

[0021] Preferably, the five or more transition metal salts mentioned in step S2 are all soluble inorganic metal salts or organic metal salts; In step S2, the total concentration of metal ions provided by the five or more transition metal salts is 0.02~0.2 mol / L, preferably 0.03~0.09 mol / L; in step S2, the pH of the system is adjusted to 8~12; in step S2, the second reducing agent is one or more of sodium borohydride, potassium borohydride, hydrazine hydrate and hydrogen peroxide, and the molar ratio of the second reducing agent to the metal ions is 1:1~7.9:1.

[0022] Preferably, the initial stirring time after adding the second reducing agent in step S2 is 5~30 min; the re-stirring time after adding the high-entropy metal olefin powder obtained in step S1 in step S2 is 5~30 min; and the standing aging time in step S2 is 2~48 h, preferably 12~24 h.

[0023] The application of the above-mentioned composite catalyst in the methanol oxidation reaction.

[0024] A membrane electrode includes a catalyst layer containing the aforementioned composite catalyst.

[0025] A fuel cell includes the membrane electrode assembly described above.

[0026] The beneficial effects of this invention are as follows: This invention addresses the technical challenges of weak interfacial bonding and easy separation in existing composite catalysts. Through an in-situ reduction loading process, a three-dimensional high-entropy metal aerogel is grown in situ on the surface of a two-dimensional ultrathin high-entropy metal olefin, forming a stable composite structure. This constructs a multi-level "two-dimensional + three-dimensional" structure, creating effective electron synergy channels, significantly improving the electronic conductivity and structural stability of the composite system, and avoiding interfacial separation problems caused by physical mixing.

[0027] This invention achieves a synergistic improvement in high activity, strong resistance to poisoning, and high stability. Utilizing the high-entropy effect and lattice distortion effect of high-entropy alloys, the CO adsorption energy barrier is lowered and the anti-poisoning performance is enhanced by controlling the metal element ratio and optimizing the catalyst's electronic structure. The ultra-large specific surface area and abundant active sites of the two-dimensional ultrathin high-entropy metal olefin are matched with the efficient mass transfer channels of the three-dimensional high-entropy metal aerogel, effectively increasing the number of three-phase interfaces, thereby significantly improving the catalytic activity and reaction kinetic rate of the methanol oxidation reaction.

[0028] Compared to simply mixing two-dimensional ultrathin high-entropy metalloenes with three-dimensional high-entropy metal aerogels, this invention constructs a dual high-entropy catalytic system with both structural complementarity and electronic synergistic effects through interfacial composite construction. In the preparation process, various transition metal salts are used as raw materials. By stepwise control of reduction conditions and interfacial composite processes, uniform anchoring of the two-dimensional ultrathin high-entropy metalloenes on the three-dimensional porous framework of the three-dimensional high-entropy metal aerogel is achieved, forming a multi-level structure of "two-dimensional ultrathin active layer + three-dimensional porous mass transfer framework". This composite structure can enhance methanol adsorption activation and intermediate product conversion, and inhibit two-dimensional sheet stacking through the three-dimensional network, improving mass transfer efficiency and structural stability; simultaneously, the interfacial electronic rearrangement significantly reduces the CO adsorption energy barrier, further enhancing anti-poisoning performance.

[0029] The composite catalyst described in this invention exhibits excellent catalytic activity, long-term cycling stability, and good resistance to CO poisoning when used in methanol oxidation. In an alkaline electrolyte system, its peak current density can reach 1.8 to 25.5 times that of commercial Pt / C catalysts, and the peak current retention rate is not less than 85% after 5000 cycles, while also demonstrating good resistance to CO poisoning. Furthermore, the preparation process of this invention is green and controllable, and easy to scale up for production.

[0030] This invention provides a new approach for the design and preparation of high-performance methanol oxidation electrocatalysts, which can be widely used in new energy devices such as direct methanol fuel cells, and has significant academic value and industrial application prospects. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of the two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalyst in Example 1 of this application; Figure 2 This is a transmission electron microscope (TEM) image of the two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalyst in Example 1 of this application; Figure 3 Cyclic voltammetry curves of the methanol oxidation reaction in alkaline methanol electrolyte are shown for the two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalyst in Example 1 of this application and the commercial Pt / C catalyst with 20% Pt metal loading in Comparative Example 1. Detailed Implementation

[0032] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention is described in detail below, but this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the methods used in this invention are conventional methods in this technical field. In this invention, materials, reagents, or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] In one embodiment, the present invention proposes a composite catalyst, which is formed by combining two-dimensional ultrathin high-entropy metalene and three-dimensional high-entropy metal aerogel. The two-dimensional ultrathin high-entropy metalene serves as a carrier, and the three-dimensional high-entropy metal aerogel is uniformly loaded on the surface of the two-dimensional ultrathin high-entropy metalene to form a multi-level composite structure. Furthermore, the two-dimensional ultrathin high-entropy metalene and the three-dimensional high-entropy metal aerogel form a synergistic catalytic system through strong interfacial coupling.

[0034] In a preferred embodiment of the present invention, the two-dimensional ultrathin high-entropy metalene is a high-entropy alloy ultrathin nanosheet containing Pd and composed of five or more transition metals. The transition metals are at least five of Group VIII, Group VIB, Group VIIB, and Group IB transition metals and must contain Pd. The molar ratio of Pd to other transition metals is 1:1 to 1:10, preferably 1:3 to 1:6.

[0035] In a preferred embodiment of the present invention, the three-dimensional high-entropy metal aerogel is a high-entropy alloy porous network structure composed of five or more transition metals, and includes at least one of Pt and Pd. The transition metals are selected from at least five transition metals of Group VIII, Group VIB, Group VIIB, and Group IB, wherein the molar ratio of Pt or Pd to other transition metals is 1:1 to 1:10, preferably 1:3 to 1:6.

[0036] The porous network structure of the three-dimensional high-entropy metal aerogel can provide mass transfer channels for the methanol oxidation reaction process, thereby reducing the diffusion resistance of methanol and reaction products in the catalyst layer.

[0037] Furthermore, the porous network structure of the three-dimensional high-entropy metal aerogel can support and disperse the two-dimensional ultrathin high-entropy metalene, reducing the possibility of aggregation of the two-dimensional ultrathin high-entropy metalene sheets, thereby improving the utilization rate of active sites.

[0038] In a preferred embodiment of the present invention, the mass ratio of the two-dimensional ultrathin high-entropy metalene to the three-dimensional high-entropy metal aerogel is 1:6 to 1:12, preferably 1:8 to 1:10.

[0039] In a preferred embodiment of the present invention, the two-dimensional ultrathin high-entropy metalene has a two-dimensional sheet-like morphology, which is either flat or curved; the average length and / or width of a single two-dimensional ultrathin high-entropy metalene sheet is 50~500 nm; the total thickness of a single two-dimensional ultrathin high-entropy metalene sheet is 0.2~5 nm; the number of atomic layers of the two-dimensional ultrathin high-entropy metalene sheet is 1~20; and the thickness of a single layer of the two-dimensional ultrathin high-entropy metalene sheet is 0.2~1 nm.

[0040] The two-dimensional ultrathin high-entropy metalene is a Pd-containing high-entropy alloy ultrathin nanosheet composed of five or more transition metals. The two-dimensional ultrathin high-entropy metalene has a single-phase solid solution structure, exhibits typical high-entropy effects and lattice distortion effects, has defective active sites on its surface, and has excellent electronic conductivity.

[0041] In the composite catalyst, the two-dimensional ultrathin high-entropy metal olefin serves as a support for loading the three-dimensional high-entropy metal aerogel. At the same time, the two-dimensional ultrathin high-entropy metal olefin itself can also provide catalytic active sites, thus forming a synergistic catalytic system together with the three-dimensional high-entropy metal aerogel.

[0042] In a preferred embodiment of the present invention, the diameter of individual metal particles in the three-dimensional high-entropy metal aerogel is 5-100 nm, and the specific surface area of ​​the three-dimensional high-entropy metal aerogel is 20-500 m². 2 / g, the three-dimensional high-entropy metal aerogel has a chain-like morphology with interconnected particles; the porosity of the three-dimensional high-entropy metal aerogel is 50%~90%, and the pore size distribution is 2~500 nm.

[0043] The preparation method of the above-mentioned composite catalyst includes the following steps: S1: Weigh the metal salt precursor containing Pd and transition metals other than Pd according to the composition ratio of the two-dimensional ultrathin high-entropy metal olefin. Dissolve the metal salt precursor in a solvent, add the first reducing agent, stir evenly and transfer it to a reaction vessel for solvothermal reaction. After the reaction is completed, cool to room temperature, wash and dry to obtain two-dimensional ultrathin high-entropy metal olefin powder. S2: Weigh out five or more transition metal salts according to the composition ratio of the three-dimensional high-entropy metal aerogel, wherein the five or more transition metal salts contain at least one of Pt salt and Pd salt, dissolve them in deionized water, adjust the pH value of the system, and stir evenly at room temperature to form a mixed solution; then add a second reducing agent and stir initially; then add the two-dimensional ultrathin high-entropy metal ene powder obtained in step S1 according to the mass composite ratio, stir again, and let it stand for aging to obtain the two-dimensional ultrathin high-entropy metal ene / three-dimensional high-entropy metal hydrogel composite precursor; S3: The two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 is washed with deionized water and then dried to obtain the two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal aerogel composite catalyst.

[0044] In a preferred embodiment of the present invention, the metal salt precursors containing Pd and transition metals other than Pd in ​​step S1 are all soluble inorganic metal salts or organic metal salts, and at least one of the metal salts is a carbonyl metal salt or a carbonyl metal complex. The solvent in step S1 is one or a combination of ethylene glycol, N,N-dimethylformamide, oleylamine, oleic acid, or octadecene; the total concentration of metal ions provided by the metal salt precursor in step S1 is 0.005~0.2 mol / L, preferably 0.01~0.1 mol / L; the first reducing agent in step S1 is one or a combination of ascorbic acid, ammonium bromide, polyvinylpyrrolidone, citric acid, tartaric acid, hydroquinone, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, sodium oleate, and polyvinyl alcohol, wherein the molar ratio of the first reducing agent to the total amount of metal ions is 0.15:1~10:1, preferably 0.5:1~3:1.

[0045] In a preferred embodiment of the present invention, the reaction vessel in step S1 is a polytetrafluoroethylene pressure-resistant reactor or a glass pressure-resistant tube. The reaction temperature of the solvothermal reaction in step S1 is 50~250 °C, preferably 80~150 °C; the reaction time is 1~48 h, preferably 12~24 h; the washing reagent used in step S1 is one or a combination of methanol, ethanol, isopropanol, cyclohexane and acetone.

[0046] In a preferred embodiment of the present invention, the drying in step S1 is freeze drying, supercritical CO2 drying or vacuum high-temperature drying, and the drying time is 2 to 50 h, preferably 12 to 24 h.

[0047] In a preferred embodiment of the present invention, the five or more transition metal salts mentioned in step S2 are all soluble inorganic metal salts or organic metal salts. In step S2, the total concentration of metal ions provided by the five or more transition metal salts is 0.02~0.2 mol / L, preferably 0.03~0.09 mol / L; in step S2, the pH of the system is adjusted to 8~12; in step S2, the second reducing agent is one or more of sodium borohydride, potassium borohydride, hydrazine hydrate and hydrogen peroxide, and the molar ratio of the second reducing agent to the metal ions is 1:1~7.9:1.

[0048] In a preferred embodiment of the present invention, the initial stirring time after adding the second reducing agent in step S2 is 5-30 min; the re-stirring time after adding the high-entropy metal olefin powder obtained in step S1 in step S2 is 5-30 min; and the standing aging time in step S2 is 2-48 h, preferably 12-24 h.

[0049] In one embodiment, the present invention also proposes the application of the above-described composite catalyst in the methanol oxidation reaction.

[0050] In one embodiment, the present invention also provides a membrane electrode comprising a catalyst layer containing the aforementioned composite catalyst.

[0051] In one embodiment, the present invention also provides a fuel cell including the membrane electrode described above.

[0052] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0053] Example 1: S1, according to the molar ratio of Pd:Fe:Co:Mo:Rh=45:15:15:15:10, 8.2 mg of palladium acetylacetone, 5.5 μL of iron pentacarbonyl, 6.8 mg of cobalt acetylacetone, 6.6 mg of molybdenum hexacarbonyl, and 2.7 mg of rhodium acetylacetone were weighed and added to a 25 mL pressure-resistant glass tube. 10 mL of oleylamine was added as a solvent, and 40 mg of ascorbic acid was added as the first reducing agent. The pressure-resistant glass tube was placed in an oil bath, stirred, and heated to 80 °C for 15 h. After the reaction was completed, it was cooled to room temperature and washed three times alternately with methanol and ethanol. The solid was then collected by centrifugation and freeze-dried for 8 h to obtain PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin powder.

[0054] S2, according to the molar ratio of Pt:Pd:Fe:Co:Cu=20:20:20:20:20, 115.7 mg of platinum acetylacetonate, 49.6 mg of palladium chloride, 159.4 mg of ferric chloride hexahydrate, 140.5 mg of cobalt chloride hexahydrate, and 83.9 mg of copper chloride dihydrate were weighed and dissolved in 50 mL of deionized water. The pH of the system was adjusted to 8.5 with ammonia. 35 mL of 0.2 mol / L sodium borohydride solution was added as a second reducing agent and stirred for 15 min. Then, 25 mg of the PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin powder prepared in step S1 was added, stirred for 20 min, and allowed to stand for aging for 24 h to obtain the PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin / PtPdFeCoCu three-dimensional high-entropy metal hydrogel composite precursor.

[0055] S3, the PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin / PtPdFeCoCu three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 was washed five times with a large amount of deionized water to remove residual impurities, and then freeze-dried at -55 ℃ for 20 h to obtain the PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin / PtPdFeCoCu three-dimensional high-entropy metal aerogel composite catalyst.

[0056] Example 2: S1, according to the molar ratio of Pd:Ru:Fe:Co:Ni=43:12:15:15:15, 8.1 mg of palladium acetylacetonate, 3.4 mg of ruthenium acetylacetonate, 5.6 μL of iron pentacarbonyl, 7.2 mg of cobalt acetylacetonate, and 6.1 mg of nickel acetylacetonate were weighed and added to a 25 mL pressure-resistant glass tube. 10 mL of oleylamine was added as a solvent, and 38.5 mg of ascorbic acid was added as the first reducing agent. The pressure-resistant glass tube was placed in an oil bath, stirred, and heated to 100 °C and kept at that temperature for 12 h. After the reaction was completed, the mixture was cooled to room temperature and washed three times alternately with methanol and ethanol. The solid was then collected by centrifugation and freeze-dried for 8 h to obtain PdRuFeCoNi two-dimensional ultrathin high-entropy metal olefin powder.

[0057] S2, according to the molar ratio of Pt:Ni:Cu:Fe:Ag=22:20:20:18:20, weigh 253 mg of platinum acetylacetonate, 104.6 mg of nickel chloride hexahydrate, 187.6 mg of copper chloride dihydrate, 302.4 mg of ferric chloride hexahydrate, and 91.4 mg of silver nitrate, dissolve them in 50 mL of deionized water, and adjust the pH of the system to 9 with sodium hydroxide; add 36.5 mL of 0.4 mol / L potassium borohydride aqueous solution as a second reducing agent, and stir for 15 min; then add 25 mg of PdRuFeCoNi two-dimensional ultrathin high-entropy metal olefin powder prepared in step S1, stir for 20 min, and let stand for 20 h to age, to obtain the PdRuFeCoNi two-dimensional ultrathin high-entropy metal olefin / PtNiCuFeAg three-dimensional high-entropy metal hydrogel composite precursor.

[0058] S3, the PdRuFeCoNi two-dimensional ultrathin high-entropy metal olefin / PtNiCuFeAg three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 was washed five times with a large amount of deionized water to remove residual impurities, and then freeze-dried at -65 ℃ for 12 h to obtain the PdRuFeCoNi two-dimensional ultrathin high-entropy metal olefin / PtNiCuFeAg three-dimensional high-entropy metal aerogel composite catalyst.

[0059] Example 3: S1, according to the molar ratio of Pd:Mo:Ru:W:Ir=43:12:15:15:15, 8.2 mg of palladium acetylacetone, 7.5 mg of molybdenum hexacarbonyl, 3.5 mg of ruthenium acetylacetone, 7.8 mg of tungsten hexacarbonyl, and 5.2 mg of iridium acetylacetone were weighed and added to a 25 mL pressure-resistant glass tube. 10 mL of oleylamine was added as a solvent, and 920 mg of polyvinylpyrrolidone (average molecular weight 10000) was added as the first reducing agent. The pressure-resistant glass tube was placed in an oil bath, stirred, and heated to 150 °C and kept at that temperature for 12 h. After the reaction was completed, the mixture was cooled to room temperature and washed 5 times alternately with isopropanol and acetone. The solid was then collected by centrifugation and freeze-dried for 12 h to obtain PdMoRuWIr two-dimensional ultrathin high-entropy metal olefin powder.

[0060] S2, according to the molar ratio of Pt:Rh:Cu:Ni:Mn=22:20:20:18:20, 127.0 mg of platinum acetylacetonate, 53.5 mg of rhodium trichloride trihydrate, 94.0 mg of copper chloride dihydrate, 51.8 mg of nickel chloride hexahydrate, and 49.2 mg of manganese chloride tetrahydrate were weighed and dissolved in 50 mL of deionized water. The pH of the system was adjusted to 9.5 with sodium hydroxide. 18.0 mL of 0.5 mol / L hydrazine hydrate aqueous solution was added as a second reducing agent and stirred for 15 min. Then, 25 mg of PdMoRuWIr two-dimensional ultrathin high-entropy metal ene powder prepared in step S1 was added, stirred for 20 min, and allowed to stand for aging for 20 h to obtain the PdMoRuWIr two-dimensional ultrathin high-entropy metal ene / PtRhCuNiMn three-dimensional high-entropy metal hydrogel composite precursor.

[0061] S3, the PdMoRuWIr two-dimensional ultrathin high-entropy metal olefin / PtRhCuNiMn three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 was washed five times with a large amount of deionized water to remove residual impurities, and then freeze-dried at -60 ℃ for 24 h to obtain the PdMoRuWIr two-dimensional ultrathin high-entropy metal olefin / PtRhCuNiMn three-dimensional high-entropy metal aerogel composite catalyst.

[0062] Example 4: S1, according to the molar ratio of Pd:V:Mn:Ru:Os=43:12:15:15:15, 8.3 mg of palladium acetylacetone, 4.1 mg of vanadium nitrate, 5.8 mg of manganese nitrate tetrahydrate, 3.2 mg of ruthenium tricarbonyl, and 6.5 mg of osmium nitrate were weighed and added to a 25 mL pressure-resistant glass tube; 5 mL of oleic acid and 5 mL of oleylamine were added as solvents, and 48.0 mg of citric acid was added as the first reducing agent. The pressure-resistant glass tube was placed in an oil bath, stirred, and heated to 105 °C and kept at that temperature for 15 h. After the reaction was completed, the mixture was cooled to room temperature, washed 5 times alternately with ethanol and acetone, and then the solid was collected by centrifugation and subjected to supercritical CO2 drying for 12 h to obtain PdVMnRuOs two-dimensional ultrathin high-entropy metal olefin powder.

[0063] S2, according to the molar ratio of Pt:Cu:Zn:Mo:Nb=25:19:18:18:20, 143.2 mg of chloroplatinic acid, 107.1 mg of copper nitrate trihydrate, 99.8 mg of zinc nitrate hexahydrate, 60.8 mg of ammonium molybdate, and 59.3 mg of niobium nitrate were weighed and dissolved in 50 mL of deionized water. The pH of the system was adjusted to 8 with sodium hydroxide. 22.5 mL of 0.5 mol / L hydrogen peroxide aqueous solution was added as a second reducing agent and stirred for 15 min. Then, 55 mg of the PdVMnRuOs two-dimensional ultrathin high-entropy metal olefin powder prepared in step S1 was added, stirred for 10 min, and allowed to stand for aging for 18 h to obtain the PdVMnRuOs two-dimensional ultrathin high-entropy metal olefin / PtCuZnMoNb three-dimensional high-entropy metal hydrogel composite precursor.

[0064] S3, the PdVMnRuOs two-dimensional ultrathin high-entropy metal olefin / PtCuZnMoNb three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 was washed 5 times with a large amount of deionized water to remove residual impurities, and then subjected to supercritical CO2 drying for 12 h to obtain the PdVMnRuOs two-dimensional ultrathin high-entropy metal olefin / PtCuZnMoNb three-dimensional high-entropy metal aerogel composite catalyst.

[0065] Example 5: S1, according to the molar ratio of Pd:Rh:Fe:Ir:Cu=40:13:17:15:15, 8.1 mg of palladium acetylacetonate, 4.2 mg of rhodium trichloride trihydrate, 5.9 μL of iron pentacarbonyl, 5.3 mg of iridium acetylacetonate, and 4.8 mg of copper nitrate trihydrate were weighed and added to a 25 mL pressure-resistant reactor; 10 mL of octadecene was added as a solvent, and 50.0 mg of citric acid was added as the first reducing agent. The pressure-resistant reactor was placed in an oil bath, stirred, and heated to 95 °C and kept at that temperature for 25 h. After the reaction was completed, the mixture was cooled to room temperature, washed 5 times with ethanol, and then the solid was collected by centrifugation and dried under vacuum at 65 °C for 12 h to obtain PdRhFeIrCu two-dimensional ultrathin high-entropy metal olefin powder.

[0066] S2, according to the molar ratio of Pd:Cu:Zn:Ir:W=23:21:19:17:20, weigh 9.8 mg palladium chloride, 102.3 mg copper nitrate trihydrate, 87.6 mg zinc nitrate hexahydrate, 59.8 mg iridium trichloride, and 61.5 mg tungsten hexachloride, dissolve them in 50 mL deionized water, and adjust the pH of the system to 12 with sodium hydroxide; add 24.0 mL of 0.5 mol / L sodium borohydride aqueous solution as a second reducing agent, and stir for 15 min; then add 55 mg of PdRhFeIrCu two-dimensional ultrathin high-entropy metal ene powder prepared in step S1, stir for 30 min, and let stand for 24 h to age, to obtain the PdRhFeIrCu two-dimensional ultrathin high-entropy metal ene / PdCuZnIrW three-dimensional high-entropy metal hydrogel composite precursor.

[0067] S3, the PdRhFeIrCu two-dimensional ultrathin high-entropy metal olefin / PdCuZnIrW three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 was washed 10 times with a large amount of deionized water to remove residual impurities, and then freeze-dried at -70 ℃ for 24 h to obtain the PdRhFeIrCu two-dimensional ultrathin high-entropy metal olefin / PdCuZnIrW three-dimensional high-entropy metal aerogel composite catalyst.

[0068] Comparative Example 1: This comparative example provides a commercial Pt / C catalyst with a Pt metal loading of 20%.

[0069] Comparative Example 2: The difference between this comparative example and Example 1 is that only step S1 of Example 1 is followed to prepare two-dimensional ultrathin high-entropy metal olefin powder, without performing steps S2 and S3 to obtain a three-dimensional high-entropy metal aerogel composite structure.

[0070] Comparative Example 3: The difference between this comparative example and Example 1 is that the three-dimensional high-entropy metal aerogel is prepared only according to the process of steps S2 and S3 of Example 1, and the operation of adding two-dimensional ultrathin high-entropy metal olefin powder is omitted in step S2.

[0071] Comparative Example 4: The difference between this comparative example and Example 1 is that in step S1, the metal salt precursor was changed to 9.1 mg palladium acetylacetonate and 7.4 mg molybdenum hexacarbonyl, and the amount of the first reducing agent ascorbic acid was changed to 30 mg. The other parameters remained unchanged, and PdMo two-dimensional ultrathin metal olefin powder was obtained. Steps S2 and S3 remained unchanged, and finally PdMo two-dimensional ultrathin metal olefin / PtPdFeCoCu three-dimensional high-entropy metal aerogel composite catalyst was obtained.

[0072] Comparative Example 5: The difference between this comparative example and Example 1 is that step S1 remains unchanged; step S2 is changed to: weighing 433.8 mg of platinum acetylacetonate and 111.6 mg of palladium chloride according to the molar ratio of Pt:Pd=50:50, dissolving in 50 mL of deionized water, adjusting the pH of the system to 8.5 with ammonia; adding 20 mL of 0.5 mol / L sodium borohydride aqueous solution as a reducing agent, stirring for 15 min, adding 67.5 mg of PdFeCoMoRh two-dimensional ultrathin high-entropy metal ene powder prepared according to step S1, continuing to stir for 20 min, and then allowing to stand for aging for 24 h to obtain the PdFeCoMoRh two-dimensional ultrathin high-entropy metal ene / PtPd metal hydrogel composite precursor; step S3 remains unchanged, and finally the PdFeCoMoRh two-dimensional ultrathin high-entropy metal ene / PtPd metal aerogel composite catalyst is obtained.

[0073] The two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalysts provided in Examples 1-5 were analyzed by scanning electron microscopy (SEM). The SEM image of the composite catalyst provided in Example 1 is shown below. Figure 1 As shown. By Figure 1 As can be seen, the composite catalyst exhibits a continuous, cross-linked nanoscale porous framework, which conforms to the three-dimensional porous structure of the three-dimensional high-entropy metal aerogel prepared in step S3. Numerous ultrathin, wrinkled two-dimensional nanosheet structures are visible on the surface of this porous framework. These two-dimensional nanosheet structures are uniformly dispersed and anchored on the network of the three-dimensional high-entropy metal aerogel, thus forming a multi-level composite structure of two-dimensional ultrathin high-entropy metal olefins and three-dimensional high-entropy metal aerogel. This interwoven porous structure and the two-dimensional sheet structure together endow the composite catalyst with a high specific surface area, providing abundant active sites for electrocatalytic reactions.

[0074] The two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalysts provided in Examples 1-5 were analyzed by transmission electron microscopy (TEM). The TEM image of the composite catalyst provided in Example 1 is shown below. Figure 2 As shown. By Figure 2 As can be seen, the three-dimensional high-entropy metal aerogel is formed by the cross-linking of metal particles to form a continuous one-dimensional chain structure, which in turn forms a three-dimensional network structure through the cross-linking of multiple chain structures. The diameter of a single metal particle is approximately 10-20 nm. The presence of two-dimensional ultrathin high-entropy metal olefins can be observed through contrast changes. These two-dimensional ultrathin high-entropy metal olefins exhibit an ultrathin, flat two-dimensional nanosheet morphology, with an average length and / or width of approximately 300-500 nm for a single sheet. The two-dimensional sheet structure of the two-dimensional ultrathin high-entropy metal olefins provides stable support for the three-dimensional high-entropy metal aerogel particles, which helps reduce aggregation and shedding. At the same time, the two-dimensional ultrathin high-entropy metal olefins and the porous network of the three-dimensional high-entropy metal aerogel are interconnected, which helps accelerate the diffusion of substances during the reaction, thereby improving the catalytic reaction kinetic rate.

[0075] Electrochemical testing employed a standard three-electrode system, using a carbon rod as the counter electrode, a reversible hydrogen electrode as the reference electrode, and a working electrode with an area of ​​0.19625 cm². 2 Glassy carbon electrodes were prepared by preparing slurries from the materials provided in Examples 1-5 and Comparative Examples 1-5, respectively. A certain amount of each slurry was then drop-coated onto the surface of the glassy carbon electrode. After the slurries were fully dried, working electrodes containing active substances were obtained for electrochemical testing.

[0076] The test solution was a mixture of 0.1 mol / L potassium hydroxide and 1 mol / L methanol; the electrochemical window was 0~1.1V; and the scan rate was 50 mV / s.

[0077] Table 1 shows the comparison of the electrocatalytic performance of the two-dimensional ultrathin high-entropy metal olefin / three-dimensional high-entropy metal aerogel composite catalysts provided in Examples 1-5 and the catalysts provided in Comparative Examples 1-5 in the methanol oxidation reaction in an alkaline methanol system: Table 1

[0078] From Table 1 and Figure 3 As can be seen, the embodiments of this application significantly increase the number of three-phase interfaces and improve mass transfer efficiency by combining two-dimensional ultrathin high-entropy metal olefins with three-dimensional high-entropy metal aerogels, thereby greatly improving the catalytic activity, stability and CO poisoning resistance of the catalyst in the methanol oxidation reaction.

[0079] The PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin / PtPdFeCoCu three-dimensional high-entropy metal aerogel composite catalyst provided in Example 1 of this application exhibited a peak current density of 19.09 A / mg(Pt+Pd) in the catalytic reaction of a 0.1 mol / L potassium hydroxide and 1 mol / L methanol electrolyte solution. This is 11.2 times that of the commercial Pt / C catalyst with 20% Pt metal loading in Comparative Example 1 (1.71 A / mg(Pt)), demonstrating excellent catalytic performance for methanol oxidation. After 5000 cycles of cyclic voltammetry testing, its peak current retention rate was 91.3%, far superior to the commercial Pt / C catalyst with 20% Pt metal loading (46.6%), showing good stability.

[0080] Meanwhile, in the carbon monoxide oxidation experiment, the peak potential of the PdFeCoMoRh two-dimensional ultrathin high-entropy metal olefin / PtPdFeCoCu three-dimensional high-entropy metal aerogel composite catalyst was negatively shifted by 65 mV compared to the commercial Pt / C catalyst with 20% Pt metal loading, indicating a significant improvement in its resistance to CO poisoning. This is mainly attributed to the lattice distortion effect and electronic hybridization effect generated by the two-dimensional ultrathin high-entropy metal olefin and the three-dimensional high-entropy metal aerogel composite material: on the one hand, the transition metal optimizes the d-band centers of Pt and Pd, reducing the adsorption capacity of methanol oxidation intermediates (CO*) on the active sites, accelerating the desorption of CO* into CO2, and inhibiting poisoning from the source; on the other hand, strong electronic interactions are formed at the interface of the composite material, increasing the interfacial electron conduction rate, accelerating the electron transfer step in the methanol oxidation reaction, thereby improving the reaction kinetic efficiency.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite catalyst, characterized in that, The composite catalyst is formed by combining two-dimensional ultrathin high-entropy metalene and three-dimensional high-entropy metal aerogel. The two-dimensional ultrathin high-entropy metalene serves as a carrier, and the three-dimensional high-entropy metal aerogel is uniformly loaded on the surface of the two-dimensional ultrathin high-entropy metalene to form a multi-level composite structure. Furthermore, the two-dimensional ultrathin high-entropy metalene and the three-dimensional high-entropy metal aerogel form a synergistic catalytic system through strong interfacial coupling.

2. The composite catalyst according to claim 1, characterized in that, The two-dimensional ultrathin high-entropy metalene is a high-entropy alloy ultrathin nanosheet containing Pd and composed of five or more transition metals. The transition metals are at least five of the transition metals from Group VIII, Group VIB, Group VIIB, and Group IB and must contain Pd, wherein the molar ratio of Pd to other transition metals is 1:1 to 1:

10. The three-dimensional high-entropy metal aerogel is a high-entropy alloy porous network structure composed of five or more transition metals, and contains at least one of Pt and Pd. The transition metals are selected from at least five transition metals of Group VIII, Group VIB, Group VIIB and Group IB, wherein the molar ratio of Pt or Pd to other transition metals is 1:1 to 1:

10. The mass ratio of the two-dimensional ultrathin high-entropy metalene to the three-dimensional high-entropy metal aerogel is 1:6 to 1:

12.

3. The composite catalyst according to claim 1, characterized in that, The two-dimensional ultrathin high-entropy metalene has a two-dimensional sheet-like morphology, which is either flat or curved. The average length and / or width of a single two-dimensional ultrathin high-entropy metalene sheet is 50~500 nm. The total thickness of a single two-dimensional ultrathin high-entropy metalene sheet is 0.2~5 nm. The number of atomic layers of the two-dimensional ultrathin high-entropy metalene sheet is 1~20, and the thickness of a single layer of the two-dimensional ultrathin high-entropy metalene sheet is 0.2~1 nm. The individual metal particles of the three-dimensional high-entropy metal aerogel have a diameter of 5-100 nm, and the specific surface area of ​​the three-dimensional high-entropy metal aerogel is 20-500 m². 2 / g, the three-dimensional high-entropy metal aerogel has a chain-like morphology with interconnected particles; the porosity of the three-dimensional high-entropy metal aerogel is 50%~90%, and the pore size distribution is 2~500 nm.

4. A method for preparing a composite catalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Weigh the metal salt precursor containing Pd and transition metals other than Pd according to the composition ratio of the two-dimensional ultrathin high-entropy metal olefin. Dissolve the metal salt precursor in a solvent, add the first reducing agent, stir evenly and transfer it to a reaction vessel for solvothermal reaction. After the reaction is completed, cool to room temperature, wash and dry to obtain two-dimensional ultrathin high-entropy metal olefin powder. S2: Weigh out five or more transition metal salts according to the composition ratio of the three-dimensional high-entropy metal aerogel, wherein the five or more transition metal salts contain at least one of Pt salt and Pd salt, dissolve them in deionized water, adjust the pH value of the system, and stir evenly at room temperature to form a mixed solution; then add a second reducing agent and stir initially; then add the two-dimensional ultrathin high-entropy metal ene powder obtained in step S1 according to the mass composite ratio, stir again, and let it stand for aging to obtain the two-dimensional ultrathin high-entropy metal ene / three-dimensional high-entropy metal hydrogel composite precursor; S3: The two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal hydrogel composite precursor obtained in step S2 is washed with deionized water and then dried to obtain the two-dimensional ultrathin high-entropy metalene / three-dimensional high-entropy metal aerogel composite catalyst.

5. The method for preparing a composite catalyst according to claim 4, characterized in that, The metal salt precursors containing Pd and transition metals other than Pd mentioned in step S1 are all soluble inorganic metal salts or organic metal salts, and at least one of the metal salts is a carbonyl metal salt or a carbonyl metal complex. The solvent in step S1 is one or a combination of ethylene glycol, N,N-dimethylformamide, oleylamine, oleic acid, or octadecene; the total concentration of metal ions provided by the metal salt precursor in step S1 is 0.005~0.2 mol / L; the first reducing agent in step S1 is one or a combination of ascorbic acid, ammonium bromide, polyvinylpyrrolidone, citric acid, tartaric acid, hydroquinone, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, sodium oleate, and polyvinyl alcohol, wherein the molar ratio of the first reducing agent to the total amount of metal ions is 0.15:1~10:

1.

6. The method for preparing a composite catalyst according to claim 4, characterized in that, The reaction vessel mentioned in step S1 is a polytetrafluoroethylene pressure-resistant reactor or a glass pressure-resistant tube; The reaction temperature of the solvothermal reaction in step S1 is 50~250 ℃, and the reaction time is 1~48 h; the washing reagent used in step S1 is one or a combination of methanol, ethanol, isopropanol, cyclohexane and acetone.

7. The method for preparing a composite catalyst according to claim 4, characterized in that, The drying process described in step S1 is freeze drying, supercritical CO2 drying, or vacuum high-temperature drying, with a drying time of 2 to 50 hours.

8. The method for preparing a composite catalyst according to claim 4, characterized in that, The five or more transition metal salts mentioned in step S2 are all soluble inorganic or organic metal salts; In step S2, the total concentration of metal ions provided by the five or more transition metal salts is 0.02~0.2 mol / L; in step S2, the pH of the system is adjusted to 8~12; in step S2, the second reducing agent is one or more of sodium borohydride, potassium borohydride, hydrazine hydrate and hydrogen peroxide, and the molar ratio of the second reducing agent to the metal ions is 1:1~7.9:

1.

9. The method for preparing a composite catalyst according to claim 4, characterized in that, The initial stirring time after adding the second reducing agent in step S2 is 5~30 min; the stirring time after adding the two-dimensional ultrathin high-entropy metal olefin powder obtained in step S1 in step S2 is 5~30 min; the standing aging time in step S2 is 2~48 h.

10. The application of the composite catalyst as described in any one of claims 1-3 in the methanol oxidation reaction.

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