Two-dimensional high-entropy alloy nanosheets, preparation thereof and use thereof in electrocatalytic oxygen reduction

Abstract

The present application relates to the technical field of high-entropy alloys, and particularly relates to a two-dimensional high-entropy alloy nanosheet, a preparation method thereof and application thereof in electrocatalytic oxygen reduction, which comprises Pt, Pd, Fe, Co, Ni and Mo elements, uses Pd as an active site, and forms a high-entropy alloy nanosheet by using the strong adsorption capacity of CO; the atomic percentage of each element is as follows: Pt: 5-50 at%, Pd: 5-50 at%, Fe: 5-50 at%, Co: 5-50 at%, Ni: 5-50 at%, and Mo: 5-50 at%, and the total atomic percentage of each element is 100 at%. The two-dimensional high-entropy alloy nanosheet, the preparation method thereof and the application thereof in electrocatalytic oxygen reduction can promote the occurrence of the oxygen reduction reaction with high activity, and have good stability and low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-entropy alloys, in particular to a two-dimensional high-entropy alloy nanosheet, a preparation method thereof and application thereof in electrocatalytic oxygen reduction. BACKGROUND

[0002] With the increasing energy crisis and environmental pollution caused by over-consumption of traditional fossil fuels, the development of green energy conversion technology has become an urgent need. Hydrogen energy is one of the renewable energies in industrial applications, which can be obtained through electrocatalysts, water splitting, fuel cells and metal-air batteries. Oxygen reduction as a cathode reaction of fuel cells involves complex intermediates and slow reaction kinetics, so a suitable cathode oxygen reduction electrocatalyst is needed to promote the oxygen reduction reaction process.

[0003] The widely used electrocatalyst at present is commercial Pt / C, the content of noble metal in commercial Pt / C is generally 20%-60%, which is expensive and has poor stability in harsh environments, and is difficult to use for a long time. While the catalytic performance of most non-noble metal catalysts is lower than that of noble metal-based catalysts, therefore, the electrocatalyst gradually develops towards low cost and good catalytic performance.

[0004] High-entropy alloys are usually composed of five or more elements with equal or unequal atomic ratios. Its disordered atomic structure is more attractive than that of traditional alloys. High-entropy alloys have good physical and chemical properties and mechanical properties, such as high strength, good stability and corrosion resistance, which can be used as structural materials. High-entropy alloys have five core effects: high entropy, lattice distortion, slow diffusion, cocktail effect and high stability. When having multiple near-equi-molar components, it can form a simple face-centered cubic, body-centered cubic or hexagonal closest packing phase solid solution, rather than an intermetallic compound, which is beneficial to improve the configurational entropy and stability of single-phase structure. Due to the multiple element effect of high-entropy alloys, it can replace noble metals with non-noble metals or adjust the content of metals to reduce costs.

[0005] And anisotropic two-dimensional nanostructures with high surface area to volume ratio and large catalytic active sites have attracted more and more interest in the field of catalysis. Compared with zero-dimensional and one-dimensional nanostructures, the contact area of two-dimensional nanostructures with carrier materials is increased, which enhances the electron transfer on the surface of the catalyst, promotes the combination of the catalyst and the carrier, and thus improves the catalytic activity and stability. However, the two-dimensional nanosheets used in the electrocatalytic oxygen reduction process in the prior art are mainly limited to binary or ternary alloys, which have high cost. For example, Wang's group developed a wet chemical method to synthesize wrinkled ultra-thin Pd and PdPtNi three-metal nanosheets. Xiong et al. reported a PtFeCo three-metal ternary nanostructure with enhanced hydrogen evolution reaction activity.

[0006] And the commonly used catalyst in the electrocatalytic oxygen reduction reaction is also platinum-based catalyst and palladium-based catalyst, for the platinum-based catalyst, mostly with platinum as the active site, by adding other metals to regulate the active center platinum. The (111) crystal surface of the metal palladium-based catalyst can strongly adsorb Co, preventing growth along the

[111] direction, resulting in the formation of two-dimensional nanosheet morphology. In summary, it is worth studying to construct two-dimensional multi-component high-entropy alloy nanosheet catalyst with Pd as the active site for the electrocatalytic oxygen reduction reaction. SUMMARY

[0007] The purpose of the present application is to provide two-dimensional high-entropy alloy nanosheets and their preparation and application in electrocatalytic oxygen reduction, two-dimensional high-entropy alloy nanosheets with metal palladium as the active center of the electrocatalytic oxygen reduction reaction can promote the occurrence of oxygen reduction reaction with high activity, and have good stability and low cost.

[0008] To achieve the above purpose, the present application provides a two-dimensional high-entropy alloy nanosheet, which comprises Pt, Pd, Fe, Co, Ni and Mo elements, uses Pd as the active site and forms a high-entropy alloy nanosheet by using the strong adsorption capacity of CO, and the atomic percentage of each element is: Pt: 5-50 at%, Pd: 5-50 at%, Fe: 5-50 at%, Co: 5-50 at%, Ni: 5-50 at%, Mo: 5-50 at%, and the total atomic percentage of each element is 100 at%.

[0009] Preferably, the high-entropy alloy nanosheet is a two-dimensional nanosheet structure, and the thickness of the two-dimensional nanosheet is 4 nm.

[0010] A preparation method of a two-dimensional high-entropy alloy nanosheet, comprising the following steps:

[0011] S1 adding platinum salt, palladium salt, iron salt, cobalt salt, nickel salt and molybdenum salt and a reducing agent into a flask with a reducing solvent in an equimolar ratio, and ultrasonic mixing until dissolution;

[0012] S2 performing co-reduction on the above dissolved solution by oil bath;

[0013] S3 after the oil bath is completed, the obtained sample is cooled to room temperature and then centrifuged and washed, and the obtained solid after washing is dried in an oven, and the dried solid is a structure-disordered high-entropy alloy nanosheet.

[0014] Preferably, in step S1, the platinum salt, palladium salt, iron salt, cobalt salt, nickel salt and molybdenum salt are respectively platinum acetylacetonate, palladium acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate and hexacarbonylmolybdenum, and the reducing agent is glucose, and the reducing solvent is oleylamine.

[0015] Preferably, in step S2, the oil bath temperature is 180 DEG C, and the oil bath time is 3 h.

[0016] Preferably, the washing agent used in step S3 is a mixed solvent of cyclohexane and ethanol, cyclohexane:ethanol = 1:9, the number of centrifugal washing is three times, the drying temperature is 80°C, and the drying time is 12h.

[0017] The application of a two-dimensional high-entropy alloy nanosheet as a catalyst in an electrocatalytic oxidation-reduction reaction.

[0018] Preferably, the catalyst is prepared by dispersing the high-entropy alloy nanosheet on an acid-treated carbon carrier, and specifically includes the following steps:

[0019] A1. The high-entropy alloy nanosheet and the acid-treated carbon carrier are dispersed in equal volumes of cyclohexane and ethanol, respectively, according to a catalyst loading of 5%, and stirred for 12h, and the two uniformly dispersed solutions are mixed;

[0020] A2. The mixed solution is subjected to suction filtration and washing, the sample obtained after suction filtration is dried, and the dried sample is placed in a tube furnace for heat treatment for 1-3h, and the product is obtained after heat treatment;

[0021] A3. 2-5mg of the product is weighed into a 1mL centrifuge tube, 950μL of isopropyl alcohol and 50μL of nafion are added to the centrifuge tube, and ultrasonic treatment is performed for 30-60min until uniform dispersion is achieved;

[0022] A4. 20μL of the uniformly dispersed slurry is uniformly transferred to a rotating ring-disk electrode as a working electrode for testing the electrocatalytic oxygen reduction performance.

[0023] Preferably, the carbon carrier is an XC-72 conductive carbon carrier.

[0024] Preferably, the heat treatment temperature in step A2 is in the range of 250-550°C.

[0025] Preferably, the diameter of the working electrode rotating ring-disk is 5mm, and the area is 0.196cm 2 , and a carbon rod is used as a counter electrode, and a mercury-mercury electrode / salt-bridge-equipped working electrode is used as a reference electrode.

[0026] Preferably, the electrolytic cell used for testing is a five-port electrolytic cell, and the electrolyte solution is a 0.1mol / L solution of perchloric acid and potassium hydroxide.

[0027] Preferably, the CV scan rate during electrocatalytic testing is 200mV / s, 50mV / s, the LSV scan rate is 10mV / s, and the rotation speed for polarization curve LSV testing is 625rpm, 900rpm, 1225rpm, 1600rpm, and 2025rpm, respectively.

[0028] Preferably, all tests are carried out in Ar and O2 saturated conditions, with a voltage range of 0-1.2V (vs. RHE).

[0029] The application provides a two-dimensional high-entropy alloy nanosheet taking metal palladium as an electrocatalytic oxygen reduction reaction active center, and an electrocatalytic oxygen reduction catalyst is a six-membered high-entropy alloy nanosheet composed of three transition metals FeCoNi and noble metals Pt, Pd and Mo reduced from hexacarbonylmolybdenum, and is highly dispersed on an acid-treated carbon sphere.

[0030] The application has the following beneficial effects:

[0031] (1) The preparation method is simple and low in cost, the prepared catalyst has good activity, high efficiency, good four-electron selectivity characteristics and high cycle stability in the electrocatalytic oxygen reduction process.

[0032] (2) The liquid phase reduction method is used to realize the formation of a single-phase solid solution of six metals, the liquid phase reduction method has low temperature, and the method is simple and convenient, and the multi-component (6) high-entropy alloy can be synthesized controllably at low temperature.

[0033] (3) The prepared high-entropy alloy nanosheet is dispersed on the acid-treated carbon carrier to prepare an oxygen reduction catalyst, the prepared catalyst takes Pd as the main active center of the oxygen reduction reaction, the high mixing entropy in the synthesis process promotes the stability of the catalyst, and the high activity promotes the occurrence of the oxygen reduction reaction.

[0034] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is an electron microscope image of the two-dimensional high-entropy alloy nanosheet of the embodiment 1 of the application;

[0036] Figure 2 is an electron microscope image of the catalyst of the embodiment 1 of the application;

[0037] Figure 3 is an electron microscope image of the catalyst of the embodiment 2 of the application;

[0038] Figure 4 is an electron microscope image of the catalyst of the embodiment 3 of the application;

[0039] Figure 5 is an atomic force microscope image of the two-dimensional high-entropy alloy nanosheet of the embodiment 1 of the application;

[0040] Figure 6is an electron microscope image of the catalyst of Example 4 of the present application;

[0041] Figure 7 is an electron microscope image of the catalyst of Example 5 of the present application;

[0042] Figure 8 is an electron microscope image of the catalyst of Comparative Example 1 of the present application;

[0043] Figure 9 is an electron microscope image of the catalyst of Comparative Example 2 of the present application;

[0044] Figure 10 is an electron microscope image of the catalyst of Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0045] The present application is further described below in conjunction with examples. Unless otherwise defined, technical or scientific terms used in the present application shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. The features or characteristics mentioned in the present application or the features mentioned in the specific examples can be combined in any manner, and these specific examples are only used to illustrate the present application and not to limit the scope of the present application.

[0046] Example 1

[0047] Preparation of two-dimensional high-entropy alloy nanosheets

[0048] Six metal precursor salts and a reducing agent were added into a flask with a reducing solvent in an equimolar ratio and ultrasonically dissolved. The metal precursor salts were platinum acetylacetonate, palladium acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0049] The above-mentioned solution after dissolution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3h. After the oil bath was completed, the obtained sample was cooled to room temperature and subjected to centrifugal washing three times, and the washing solvent was cyclohexane: ethanol = 1:9, so as to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h, to obtain two-dimensional high-entropy alloy nanosheets, and the dried solid was collected into a glass bottle for subsequent use.

[0050] Preparation of two-dimensional high-entropy alloy nanosheets into catalysts

[0051] The above-mentioned two-dimensional high-entropy alloy nanosheets and the acid-treated carbon spheres collected were dispersed into equal volumes of cyclohexane and ethanol, respectively, with a catalyst loading of 5%. The two solutions after uniform dispersion were mixed and stirred for 12h, so as to be uniformly mixed. The uniformly mixed solution was subjected to suction filtration and washing and collection. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, it was placed into a tube furnace and heat-treated at 350°C for 1h, to obtain a sample nanosheet catalyst PtPdFeCoNiMo-350-1h.

[0052] Example 2

[0053] Preparation of two-dimensional high-entropy alloy nanosheets

[0054] Six kinds of metal precursor salts and reducing agents were added into a flask with reducing solvent in an equimolar ratio, and were ultrasonically dissolved. The metal precursor salts were platinum acetylacetone, palladium acetylacetone, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0055] The above dissolved solution was oil-bathed at a temperature of 180°C for 3h for co-reduction. After the oil-bathing was completed, the obtained sample was cooled to room temperature and then centrifugally washed three times, and the washing solvent was cyclohexane: ethanol = 1:9, so as to wash away impurities such as organic solvents. The obtained solid after washing was dried in an oven at 80°C for 12h, to obtain two-dimensional high-entropy alloy nanosheets. The dried solid was collected into a glass bottle for subsequent use.

[0056] Preparation of two-dimensional high-entropy alloy nanosheets into catalysts

[0057] The above collected two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol respectively, with a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12h to make the mixture uniform. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, the sample was placed into a tube furnace and heat-treated at 350°C for 1h to obtain a sample nanosheet catalyst PtPdFeCoNiMo-350-2h.

[0058] Example 3

[0059] Preparation of two-dimensional high-entropy alloy nanosheets

[0060] Six kinds of metal precursor salts and reducing agents were added into a flask with reducing solvent in an equimolar ratio, and were ultrasonically dissolved. The metal precursor salts were platinum acetylacetone, palladium acetylacetone, iron acetylacetone, cobalt acetylacetone, nickel acetylacetone, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0061] The above dissolved solution was oil-bathed at a temperature of 180°C for 3h for co-reduction. After the oil-bathing was completed, the obtained sample was cooled to room temperature and then centrifugally washed three times, and the washing solvent was cyclohexane: ethanol = 1:9, so as to wash away impurities such as organic solvents. The obtained solid after washing was dried in an oven at 80°C for 12h, to obtain two-dimensional high-entropy alloy nanosheets. The dried solid was collected into a glass bottle for subsequent use.

[0062] Preparation of two-dimensional high-entropy alloy nanosheets into catalysts

[0063] The two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres collected above were dispersed into equal volumes of cyclohexane and ethanol, respectively, with a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washed. The sample obtained by suction filtration was placed in an oven at 80°C and dried for 12 h. After drying was complete, the sample was placed in a tube furnace and heat-treated at 350°C for 3 h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-350-3h.

[0064] Example 4

[0065] Preparation of two-dimensional high-entropy alloy nanosheets

[0066] Six metal precursor salts and a reducing agent were added to a flask with a reducing solvent in an equimolar ratio and ultrasonicated until dissolved. The metal precursor salts were platinum acetylacetonate, palladium acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0067] The solution obtained after dissolution was co-reduced in an oil bath at a temperature of 180°C for 3 h. After oil bath, the obtained sample was cooled to room temperature and washed by centrifugation three times, with cyclohexane:ethanol = 1:9 as the washing solvent to remove organic solvent and other impurities. The solid obtained after washing was dried in an oven at 80°C for 12 h to obtain two-dimensional high-entropy alloy nanosheets. The dried solid was collected in a glass bottle for subsequent use.

[0068] Preparation of two-dimensional high-entropy alloy nanosheets into catalysts

[0069] The two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres collected above were dispersed into equal volumes of cyclohexane and ethanol, respectively, with a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washed. The sample obtained by suction filtration was placed in an oven at 80°C and dried for 12 h. After drying was complete, the sample was placed in a tube furnace and heat-treated at 450°C for 2 h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-450-2h.

[0070] Example 5

[0071] Preparation of two-dimensional high-entropy alloy nanosheets

[0072] Six metal precursor salts and a reducing agent were added to a flask with a reducing solvent in an equimolar ratio and ultrasonicated until dissolved. The metal precursor salts were platinum acetylacetonate, palladium acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0073] The above dissolved solution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3h. After the oil bath was completed, the obtained sample was cooled to room temperature and then subjected to centrifugal washing three times with a washing solvent of cyclohexane: ethanol = 1:9 to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h to obtain two-dimensional high-entropy alloy nanosheets, and the dried solid was collected in a glass bottle for subsequent use.

[0074] Preparation of two-dimensional high-entropy alloy nanosheets as catalysts

[0075] The above collected two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol, respectively, at a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, it was placed in a tube furnace and heat-treated at 550°C for 2h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-550-2h.

[0076] Example 6

[0077] Preparation of high-entropy alloy, wherein Pt:Pd = 1:0

[0078] Six metal precursor salts and a reducing agent were added to a flask with a reducing solvent in an equimolar ratio and ultrasonicated until dissolved. The metal precursor salts were platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0079] The above dissolved solution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3h. After the oil bath was completed, the obtained sample was cooled to room temperature and then subjected to centrifugal washing three times with a washing solvent of cyclohexane: ethanol = 1:9 to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h to obtain two-dimensional high-entropy alloy nanosheets, and the dried solid was collected in a glass bottle for subsequent use.

[0080] Preparation of two-dimensional high-entropy alloy nanoparticles as catalysts

[0081] The above collected two-dimensional high-entropy alloy nanoparticles and acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol, respectively, at a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, it was placed in a tube furnace and heat-treated at 350°C for 2h to obtain the sample nanoparticle catalyst PtFeCoNiMo-Pt:Pd(1:0).

[0082] Example 7

[0083] Preparation of two-dimensional high-entropy alloy nanosheets, wherein Pt:Pd = 1:2

[0084] Six metal precursor salts and a reducing agent were added to a flask with a reducing solvent in an equimolar ratio, and were ultrasonically dissolved. The metal precursor salts were platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine. The ratio of the metals Pt and Pd was 1:2.

[0085] The above-mentioned solution after dissolution was oil-bathed at a temperature of 180°C for 3h for co-reduction. After the oil-bathing was completed, the obtained sample was cooled to room temperature and then centrifugally washed three times, and the washing solvent was cyclohexane: ethanol = 1:9, so as to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h, and two-dimensional high-entropy alloy nanosheets were obtained. The dried solid was collected in a glass bottle for subsequent use.

[0086] Preparation of two-dimensional high-entropy alloy nanosheets, wherein Pt:Pd = 1:2

[0087] The above-mentioned two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres were dispersed in equal volumes of cyclohexane and ethanol, respectively, according to a catalyst loading of 5%. The two solutions after uniform dispersion were mixed and stirred for 12h to make the mixture uniform. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, the sample was placed in a tube furnace and heat-treated at 350°C for 2h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-Pt:Pd(1:2).

[0088] Example 8

[0089] Preparation of two-dimensional high-entropy alloy nanosheets, wherein Pt:Pd = 1:3

[0090] Six metal precursor salts and a reducing agent were added to a flask with a reducing solvent in an equimolar ratio, and were ultrasonically dissolved. The metal precursor salts were platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine. The ratio of the metals Pt and Pd was 1:3.

[0091] The above-mentioned solution after dissolution was oil-bathed at a temperature of 180°C for 3h for co-reduction. After the oil-bathing was completed, the obtained sample was cooled to room temperature and then centrifugally washed three times, and the washing solvent was cyclohexane: ethanol = 1:9, so as to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h, and two-dimensional high-entropy alloy nanosheets were obtained. The dried solid was collected in a glass bottle for subsequent use.

[0092] Preparation of two-dimensional high-entropy alloy nanosheets as catalysts

[0093] The two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres obtained above were dispersed into equal volumes of cyclohexane and ethanol, respectively, at a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12 h. After drying, the sample was placed in a tube furnace and heat-treated at 350°C for 2 h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-Pt:Pd (1:3).

[0094] Example 9

[0095] Preparation of two-dimensional high-entropy alloy nanosheets with Pt:Pd = 1:4

[0096] Six metal precursor salts and a reducing agent were added to a flask containing a reducing solvent in an equimolar ratio and ultrasonicated until dissolved. The metal precursor salts were platinum acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine. The ratio of the metals Pt and Pd was 1:4.

[0097] The solution obtained above was co-reduced in an oil bath at a temperature of 180°C for 3 h. After oil bath, the obtained sample was cooled to room temperature and washed by centrifugation three times, with cyclohexane:ethanol = 1:9 as the washing solvent to remove organic solvent and other impurities. The solid obtained after washing was dried in an oven at 80°C for 12 h to obtain two-dimensional high-entropy alloy nanosheets. The dried solid was collected in a glass bottle for subsequent use.

[0098] Preparation of two-dimensional high-entropy alloy nanosheets as catalysts

[0099] The two-dimensional high-entropy alloy nanosheets and acid-treated carbon spheres obtained above were dispersed into equal volumes of cyclohexane and ethanol, respectively, at a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washing. The sample obtained by suction filtration was dried in an oven at 80°C for 12 h. After drying, the sample was placed in a tube furnace and heat-treated at 350°C for 2 h to obtain the sample nanosheet catalyst PtPdFeCoNiMo-Pt:Pd (1:4).

[0100] Comparative Example 1

[0101] Preparation of high-entropy alloy

[0102] Metal precursor salt and reducing agent were added into a flask with reducing solvent in an equimolar ratio, and ultrasonic was applied until dissolution. The metal precursor salt was acetylacetone platinum, acetylacetone iron, acetylacetone cobalt, acetylacetone nickel, and hexacarbonylmolybdenum. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0103] The above-mentioned solution after dissolution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3h. After the oil bath was completed, the obtained sample was cooled to room temperature and then subjected to centrifugal washing three times, with cyclohexane: ethanol = 1:9 as the washing solvent, so as to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h, and PtFeCoNiMo nanoparticles were obtained. The dried solid was collected into a glass bottle for subsequent use.

[0104] Preparation of high-entropy alloy as a catalyst

[0105] The above-mentioned PtFeCoNiMo nanoparticles and the acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol respectively according to a catalyst loading of 5%. The two solutions after uniform dispersion were mixed and stirred for 12h, so as to be uniformly mixed. The uniformly mixed solution was subjected to suction filtration and washing and collection. The sample obtained by suction filtration was dried in an oven at 80°C for 12h. After drying was completed, the sample was placed into a tube furnace and heat-treated at 350°C for 2h, and a sample nanoparticle catalyst PtFeCoNiMo-350-2h was obtained.

[0106] Comparative example 2

[0107] Preparation of high-entropy alloy

[0108] Metal precursor salt and reducing agent were added into a flask with reducing solvent in an equimolar ratio, and ultrasonic was applied until dissolution. The metal precursor salt was acetylacetone platinum, acetylacetone iron, acetylacetone cobalt, acetylacetone nickel, and hexacarbonylmolybdenum. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0109] The above-mentioned solution after dissolution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3h. After the oil bath was completed, the obtained sample was cooled to room temperature and then subjected to centrifugal washing three times, with cyclohexane: ethanol = 1:9 as the washing solvent, so as to wash away impurities such as organic solvents. The solid obtained after washing was dried in an oven at 80°C for 12h, and PtFeCoNiMo nanoparticles were obtained. The dried solid was collected into a glass bottle for subsequent use.

[0110] Preparation of high-entropy alloy as a catalyst

[0111] The PdFeCoNiMo nanosheets collected above and the acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol, respectively, with a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washed. The sample obtained by suction filtration was dried in an oven at 80°C for 12 h. After drying, the sample was placed in a tube furnace and heat-treated at 350°C for 2 h to obtain the sample nanosheet catalyst PdFeCoNiMo-350-2h.

[0112] Comparative Example 3

[0113] Preparation of high-entropy alloy

[0114] The metal precursor salt and the reducing agent were added into a flask with a reducing solvent in an equimolar ratio and ultrasonicated until dissolved. The metal precursor salt was iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl. The reducing agent was glucose, and the reducing solvent was oleylamine.

[0115] The above solution after dissolution was subjected to co-reduction in an oil bath at a temperature of 180°C for 3 h. After oil bath, the obtained sample was cooled to room temperature and washed by centrifugation three times, with cyclohexane:ethanol = 1:9 as the washing solvent to remove organic solvent and other impurities. The solid obtained after washing was dried in an oven at 80°C for 12 h to obtain FeCoNiMo nanoparticles. The dried solid was collected in a glass bottle for subsequent use.

[0116] Preparation of high-entropy alloy as a catalyst

[0117] The FeCoNiMo nanoparticles collected above and the acid-treated carbon spheres were dispersed into equal volumes of cyclohexane and ethanol, respectively, with a catalyst loading of 5%. The two uniformly dispersed solutions were mixed and stirred for 12 h to ensure uniform mixing. The uniformly mixed solution was collected by suction filtration and washed. The sample obtained by suction filtration was dried in an oven at 80°C for 12 h. After drying, the sample was placed in a tube furnace and heat-treated at 350°C for 2 h to obtain the sample nanoparticle catalyst FeCoNiMo-350-2h.

[0118] Figure 1 is an electron microscope image of the two-dimensional high-entropy alloy nanosheet of Example 1 of the present application, Figure 2 is an electron microscope image of the catalyst of Example 1 of the present application, Figure 3 is an electron microscope image of the catalyst of Example 2 of the present application, Figure 4 is an electron microscope image of the catalyst of Example 3 of the present application, Figure 5 is an atomic force microscope image of the two-dimensional high-entropy alloy nanosheet of Example 1 of the present application, Figure 6 is an electron microscope image of the catalyst of Example 4 of the present application, Figure 7 is an electron microscope image of the catalyst of Example 5 of the present application,Figures 1 to 7 It can be seen that the catalysts prepared in Examples 1-5 are all in a sheet structure. Figure 8 is an electron microscope image of the catalyst of the present application Comparative Example 1, Figure 9 is an electron microscope image of the catalyst of the present application Comparative Example 2, Figure 10 is an electron microscope image of the catalyst of the present application Comparative Example 3, and Figures 8 to 10 It can be seen that the catalysts prepared in Comparative Examples 1 and 3 are all in a nanoparticle structure, and the catalyst prepared in Comparative Example 2 is in a nanosheet structure.

[0119] The catalysts prepared in Examples 1-5 and Comparative Examples 1-3 were applied to the electrocatalytic oxygen reduction performance test. Specifically as follows:

[0120] 5 mg of the sample was weighed into a 1 mL centrifuge tube. 950 μL of isopropanol and 50 μL of nafion were added to the centrifuge tube. Ultrasonic dispersion was performed for 60 min until uniform dispersion was achieved. The uniformly dispersed slurry was uniformly transferred to a platinum carbon electrode, and cyclic voltammetry test and polarization curve test were performed under Ar and O2 atmosphere, respectively, to obtain the half-wave potential and limiting diffusion current density under acidic conditions, and the half-wave potential and limiting diffusion current density under alkaline conditions. The results are shown in Table 1.

[0121] Table 1 Results of the catalysts prepared in Examples 1-9 and Comparative Examples 1-3 applied to the electrocatalytic oxygen reduction performance test

[0122]

[0123]

[0124] As can be seen from Table 1, by comparing Examples 1-5 with Comparative Examples 1-3, it is found that when preparing a high-entropy alloy, without adding molybdenum hexacarbonyl or metal element Pd, two-dimensional nanosheets cannot be produced, and nanoparticles are obtained. Only when molybdenum hexacarbonyl and metal element Pd are added, two-dimensional nanosheets can be produced. It can be found that the presence of Pd plays a decisive role in the formation of nanosheets. The CO produced by the decomposition of molybdenum hexacarbonyl is adsorbed on the 111 crystal plane of Pd, which inhibits the growth of the metal on the 111 crystal plane and promotes the formation of two-dimensional nanosheet morphology.

[0125] Meanwhile, when the heat treatment temperature of the catalyst is changed, it is found that the catalyst has a morphology of nanosheet when the heat treatment temperature is 350 DEG C. When the temperature is raised to 450 DEG C, the morphology of nanosheet is destroyed, and the state of coexistence of nanosheet and nanoparticle is formed. When the temperature is continuously raised, the nanosheet no longer exists, and the morphology of nanoband is formed, and the state of coexistence of nanoparticle and nanoband is formed. Further, when the heat treatment time is changed, it is found that the morphology does not change with the change of the heat treatment time. According to the performance comparison, the two-dimensional nanosheet is more beneficial to the occurrence of the ORR reaction than the nanoparticle, and the hexa-high-entropy-alloy nanosheet has the optimal ORR performance.

[0126] According to examples 6-9, it is proved that Pd is the active center of the ORR reaction by adjusting Pt:Pd to be 0-0.5.

[0127] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application rather than limiting them, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A two-dimensional high-entropy alloy nanosheet, characterized in that: It is composed of Pt, Pd, Fe, Co, Ni and Mo elements, with the atomic percentages of each element as follows: Pt: 5-50 at%, Pd: 5-50 at%, Fe: 5-50 at%, Co: 5-50 at%, Ni: 5-50 at%, Mo: 5-50 at%, and the total atomic percentage of each element is 100 at%. The high-entropy alloy nanosheets are two-dimensional nanosheet structures with a thickness of 4 nm. The above-mentioned two-dimensional high-entropy alloy nanosheets are prepared by liquid-phase reduction method, including the following steps: S1: Platinum salt, palladium salt, iron salt, cobalt salt, nickel salt, molybdenum salt, and reducing agent are added to a flask containing a reducing solvent in an equimolar ratio and mixed, then sonicated until dissolved; the reducing agent is glucose, and the reducing solvent is oleylamine. S2 will perform co-reduction of the dissolved solution in an oil bath; After the S3 oil bath was completed, the obtained sample was cooled to room temperature and then centrifuged and washed. The solid obtained after washing was dried in an oven. The dried solid was a high-entropy alloy nanosheet with disordered structure.

2. The two-dimensional high-entropy alloy nanosheet according to claim 1, characterized in that: In step S1, the platinum salt, palladium salt, iron salt, cobalt salt, nickel salt, and molybdenum salt are platinum acetylacetonate, palladium acetylacetonate, iron acetylacetonate, cobalt acetylacetonate, nickel acetylacetonate, and molybdenum hexacarbonyl, respectively.

3. The two-dimensional high-entropy alloy nanosheet according to claim 1, characterized in that: In step S2, the oil bath temperature is 180℃ and the oil bath time is 3 hours.

4. The two-dimensional high-entropy alloy nanosheet according to claim 1, characterized in that: In step S3, the detergent used for centrifugal washing is a mixed solvent of cyclohexane and ethanol, with a cyclohexane:ethanol ratio of 1:

9. The centrifugal washing is performed three times, the drying temperature is 80°C, and the drying time is 12 hours.

5. An application of a two-dimensional high-entropy alloy nanosheet as described in any one of claims 1-4, characterized in that: It is used as a catalyst in electrocatalytic redox reactions.

6. The application of the two-dimensional high-entropy alloy nanosheet according to claim 5, characterized in that: The catalyst is prepared by dispersing high-entropy alloy nanosheets on an acidified carbon support, specifically including the following steps: A1 dispersed high-entropy alloy nanosheets and acid-treated carbon support into equal volumes of cyclohexane and ethanol, respectively, and then mixed the two solutions after they were evenly dispersed. A2 The mixed solution is filtered and washed, the sample obtained after filtration is dried, and the dried sample is placed in a tube furnace for heat treatment. After the heat treatment is completed, the product is obtained. A3 Weigh 2-5 mg of the product into a 1 mL centrifuge tube, add 950 μL of isopropanol and 50 μL of nafion to the centrifuge tube, and sonicate for 30-60 min until evenly dispersed. A4 20 μL of uniformly dispersed slurry was evenly transferred onto a rotating ring electrode as the working electrode for testing the electrocatalytic oxygen reduction performance.

7. The application of the two-dimensional high-entropy alloy nanosheet according to claim 6, characterized in that: The temperature range for heat treatment in step A2 is 250-550℃.

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