High-entropy nanoparticle catalytic material with metal atom shell structure and preparation method of high-entropy nanoparticle catalytic material

Abstract

The invention discloses a high-entropy nanoparticle catalytic material with a metal atom shell structure and a preparation method of the high-entropy nanoparticle catalytic material, and belongs to the technical field of preparation of catalytic materials. The preparation method comprises the following steps: dispersing a metal salt and a nanofiber precursor in an organic solvent, and carrying out electrostatic spinning to obtain a nanofiber membrane; and then calcining and pre-oxidizing the nanofiber membrane, and then carbonizing and calcining to obtain the nanofiber membrane. Wherein the selection principle of the metal salt is as follows: (n-1)-(n-2) metals are selected as an alloy substrate, and the sum of the mixing enthalpy of elements of the alloy substrate is not greater than-5kJ mol <-1 >; one or two metal elements serve as a precipitated phase, and the sum of the mixing enthalpy of the metal elements of the precipitated phase and the elements of the alloy substrate is larger than 20 kJ mol <-1 >; the high-entropy nanoparticle catalytic material obtained by the method shows relatively high catalytic activity and stability, and the method has wide universality.

Description

Technical Field

[0001] The present invention specifically relates to a high-entropy nanoparticle catalytic material with a metal atom shell structure and a preparation method thereof, belonging to the technical field of catalytic material preparation. Background Art

[0002] High-entropy alloys are a new type of alloy material containing at least five metal elements. Due to their unique multi-entropy structure, high-entropy alloys exhibit unique physical and chemical properties that ordinary alloys do not have. In recent years, high-entropy alloys have been widely used in electrocatalytic reactions due to their excellent synergistic effects and electrocatalytic properties, and also show great application prospects in the field of nitrate reduction to ammonia (NO3RR).

[0003] The coexistence of multiple active sites is one of the important characteristics of HEA. The random atomic distribution in the lattice generates almost infinite atomic configurations, which leads to a nearly continuous binding energy distribution. From a statistical perspective, different configurations ensure the emergence of highly active ensembles that have a medium binding strength defined by the "Sabatier principle" for specific intermediates. However, the random element distribution in traditional high-entropy solid solutions severely limits the existence probability of the required active clusters with specific atomic arrangements.

[0004] From a kinetic perspective, especially for catalytic processes involving multiple intermediates, the rapid diffusion of reaction intermediates between multiple active sites is crucial for accelerating the overall reaction rate. Catalysts with a well-defined ordered atomic configuration encounter slow diffusion problems due to their narrow binding energy distribution. Therefore, a certain degree of disorder in the atomic configuration is required to promote intermediate diffusion, and HEA with a nearly continuous binding energy distribution is thus regarded as an ideal platform for designing high-performance catalysts.

[0005] Previous high-entropy alloys with disordered atomic arrangements ensured a nearly continuous distribution of binding energy but sacrificed the existence probability of the required active clusters. Therefore, in order to balance the requirements of "disorder" and "order", precisely manipulating the atomic arrangement in complex high-entropy systems has become an urgently concerned issue. Summary of the Invention

[0006] [Technical Problem]

[0007] Although the arrangement of disordered atoms in existing high-entropy alloys ensures a nearly continuous distribution of binding energy to a certain extent, it usually leads to the coverage of active clusters, and thus the catalytic performance is poor when the high-entropy alloy is used as a catalyst.

[0008] [Technical Solution]

[0009] Aiming at the defects and deficiencies of the existing technology, the purpose of the present invention is to provide a high-entropy nanoparticle catalytic material with a metal atomic shell structure and a preparation method thereof. This method synthesizes a high-entropy alloy / carbon nanofiber composite material as an electrocatalyst for nitrate reduction to ammonia through electrospinning technology combined with high-temperature calcination method; by introducing a variety of non-precious transition metal elements, the dosage of precious metal Pd is greatly reduced; and by evaluating the mixing enthalpy of binary alloys, a high-entropy system (FeCoNiAgPd) with controllable phase separation potential is prepared. At the same time, through programmed temperature control, the controllable dissolution of metal atomic layers on the surface of HEA is successfully realized, the precise control of the atomic arrangement on the surface of HEA is achieved, the adjustable range of HEA catalysts and their potential application scenarios are expanded; at the same time, the formed high-entropy nanoparticle catalytic material has high stability. The preparation method has low cost, is simple and easy to obtain, and the prepared electrocatalyst shows excellent NO3RR activity and stability in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3.

[0010] In order to achieve the above object, the following technical solutions are provided:

[0011] The first object of the present invention is to provide a preparation method of a high-entropy nanoparticle catalytic material with a metal atomic shell structure, and the preparation method includes the following steps:

[0012] (1) Disperse metal salts and nanofiber precursors in an organic solvent to prepare a spinning solution; then prepare a nanofiber membrane through electrospinning.

[0013] (2) Calcinate and pre-oxidize the nanofiber membrane obtained in step (1), and then raise the temperature to 800-1000 °C at a rate of 2-10 °C / min. After the temperature reaches 800-1000 °C, keep it warm for 0.5-5 hours in an inert atmosphere; after the heat preservation is over, naturally cool it to room temperature in an inert atmosphere to obtain a high-entropy nanoparticle catalytic material with a metal atomic shell structure.

[0014] In one embodiment, the selection of the metal salts in step (1) follows the principle:

[0015] (1) Select (n–1) to (n–2) metals as the alloy substrate, and it is required that the sum of the mixing enthalpies between the selected elements is not greater than -5 kJ mol –1 , where n is the number of metal element types, n is a natural number and greater than or equal to 4; for example, n can be 4, 5, 6, 7, 8, 9, 10, etc.

[0016] (2) Select 1 or 2 metal elements as the precipitation phase, and it is required that the sum of the mixing enthalpies between the selected precipitation phase metal elements and the constituent elements of the alloy substrate is greater than 20 kJ mol –1 .

[0017] In one embodiment, the nanofiber precursor in step (1) includes one or more of polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol, polystyrene, and polytetrafluoroethylene.

[0018] In one embodiment, the mass fraction of the nanofiber precursor contained in the spinning solution in step (1) is 2-20%.

[0019] In one embodiment, the organic solvent in step (1) is one or several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, and acetone; more preferably N,N-dimethylformamide.

[0020] In one embodiment, in the spinning solution of step (1), for the quinary high-entropy alloy, the molar ratio of each metal element is 5-35%; for the alloy with six or more elements, the proportion of each metal element is 100 / n ± 75 / n%, where n is the number of metal element types.

[0021] In one embodiment, the total molar concentration of each metal salt in the spinning solution in step (1) is 0.03-1 mmol / g.

[0022] In one embodiment, the parameters of the electrospinning in step (1) are: the spinning voltage is 12-25 kV, the distance from the receiving device to the spinning needle is 5-20 cm, and the solution flow rate is 0.02-1.00 mL / h.

[0023] In one embodiment, the metal salts in step (1) include any several of iron salts, cobalt salts, nickel salts, silver salts, palladium salts, copper salts, molybdenum salts, indium salts, ruthenium salts, tungsten salts, and aurichloric acid.

[0024] In one embodiment, the calcination in step (2) is to place the nanofibers in a corundum boat or a graphite clip and calcine them in the middle part of a tube furnace.

[0025] In one embodiment, the pre-oxidation calcination in step (2) is to heat up to 180-300 °C, keep the temperature for calcination for 1-6 h, and the heating rate is 2-10 °C / min.

[0026] In one embodiment, the heating rate in step (2) is preferably any one of 2 °C / min, 5 °C / min, and 10 °C / min.

[0027] In one embodiment, the temperature of the pre-oxidation calcination in step (2) is 230 °C.

[0028] In one embodiment, the pre-oxidation calcination in step (2) is carried out in an air atmosphere.

[0029] In one embodiment, after the calcination pre-oxidation in step (2), the temperature is further increased to 1000 °C at a rate of 2-10 °C / min. After the temperature reaches 1000 °C, it is kept warm for 0.5-5 hours under an inert atmosphere.

[0030] The second object of the present invention is to provide a preparation method of a highly stable high-entropy nanoparticle catalytic material with a metal atomic shell structure, and the preparation method includes the following steps:

[0031] 1) Add iron salt, cobalt salt, nickel salt, silver salt and palladium salt to N,N-dimethylformamide of polyacrylonitrile. After stirring evenly, electrospinning is carried out on this solution to obtain a FeCoNiAgPd / PAN nanofiber membrane;

[0032] 2) Calcinate the FeCoNiAgPd / PAN nanofiber membrane prepared in step 1). First, increase the temperature to 180-300 °C at a heating rate of 2-10 °C / min, and keep it warm for 1-6 hours in an air atmosphere for pre-oxidation; after the heat preservation ends, under an inert gas atmosphere, increase the temperature to 800-1200 °C at a rate of 2-10 °C / min, and keep it warm for 1-6 hours; after the heat preservation ends, naturally cool it to room temperature under an inert gas atmosphere to obtain the iron cobalt nickel silver palladium high-entropy nanoparticle catalytic material FeCoNiAgPdNPs.

[0033] In one embodiment, the iron salt in step 1) is any one of iron nitrate, iron chloride, iron acetate or iron acetylacetonate.

[0034] In one embodiment, the cobalt salt in step 1) is any one of cobalt nitrate, cobalt chloride, cobalt acetate or cobalt acetylacetonate.

[0035] In one embodiment, the nickel salt in step 1) is any one of nickel nitrate, nickel chloride, nickel acetate or nickel acetylacetonate.

[0036] In one embodiment, the silver salt in step 1) is silver nitrate.

[0037] In one embodiment, the palladium salt in step 1) is palladium chloride or palladium acetylacetonate.

[0038] The third object of the present invention is to provide a high-entropy nanoparticle catalytic material with a metal atomic shell structure obtained by the above-mentioned preparation method or a highly stable high-entropy nanoparticle catalytic material with a metal atomic shell structure FeCoNiAgPd NPs.

[0039] In one embodiment, the alloy particles in the high-entropy nanoparticle catalytic material with a metal atomic shell structure exist in the form of single-phase high-entropy alloy, high-entropy alloy with a mono- / bi-metallic skin coating on the surface, or high-entropy alloy particles with obvious precipitation phases.

[0040] In one embodiment, the structure of the high-entropy nanoparticle catalytic material with a metal atomic shell structure includes a one-dimensional carbon nanofiber network and high-entropy alloy nanoparticles uniformly dispersed on the fibers.

[0041] The fourth object of the present invention is to provide the application of the above-mentioned high-entropy nanoparticle catalytic material with a metal atomic shell structure or the high-stability high-entropy nanoparticle catalytic material FeCoNiAgPd NPs with a metal atomic shell structure in the field of electrocatalysis.

[0042] The fifth object of the present invention is to provide a method for efficiently catalyzing the nitrate reduction reaction to ammonia, and the method uses the above-mentioned high-entropy nanoparticle catalytic material with a metal atomic shell structure or the high-stability high-entropy nanoparticle catalytic material FeCoNiAgPd NPs with a metal atomic shell structure as a catalyst.

[0043] In one embodiment, the method specifically uses the above-mentioned high-entropy nanoparticle catalytic material with a metal atomic shell structure or the high-stability high-entropy nanoparticle catalytic material FeCoNiAgPd NPs as a working electrode, adopts an H-type electrolytic cell, and electrocatalyzes the nitrate reduction reaction to ammonia in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3.

[0044] Beneficial effects:

[0045] (1) By reasonably screening the elemental composition of the alloy substrate and precipitation phases through the mixing enthalpy, the present invention greatly reduces the amount of precious metal Pd by introducing a variety of non-precious transition metal elements, and synthesizes a high-entropy alloy / carbon nanofiber composite material (FeCoNiAgPd / CNFs) by using the electrospinning technique combined with the high-temperature calcination method. By reasonably controlling the calcination temperature, the present invention successfully prepares a high-entropy alloy catalyst with Ag phase precipitation on the surface. Multiple active sites in this material can simultaneously adsorb multiple key reaction intermediates and show excellent performance in the nitrate reduction reaction to ammonia.

[0046] (2) This method can be widely applied to the phase structure regulation process of various high-entropy alloy systems (FeCoNiMoIn, MoRuWPdAu, FeCoNiRuCu), indicating that this method has wide universality. Description of the drawings

[0047] Figure 1Scanning electron microscopy image of the FeCoNiAgPd / CNFs electrocatalytic material prepared in Example 1;

[0048] Figure 2 Transmission electron microscopy images of the FeCoNiAgPd / CNFs electrocatalytic material prepared in Example 1; (a) Transmission electron microscopy image of FeCoNiAgPd high-entropy alloy nanoparticles; (b) High-resolution transmission electron microscopy image of the edge region of high-resolution FeCoNiAgPd high-entropy alloy nanoparticles;

[0049] Figure 3 X-ray diffraction pattern of the FeCoNiAgPd / CNFs electrocatalytic material prepared in Example 1;

[0050] Figure 4 Testing the electrocatalytic performance of the FeCoNiAgPd / CNFs prepared in Example 1 for nitrate reduction to ammonia in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3; (a) LSV curves of FeCoNiAgPd / CNFs in 1.0 mol / L KOH and in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3; (b) Faraday efficiency and yield data graph of FeCoNiAgPd / CNFs at different voltages;

[0051] Figure 5 XRD patterns of FeCoNiAgPd / CNFs-800 and FeCoNiAgPd / CNFs-1200 prepared in Example 2;

[0052] Figure 6 Testing the electrocatalytic performance of FeCoNiAgPd / CNFs-800 and FeCoNiAgPd / CNFs-1200 prepared in Example 2 for nitrate reduction to ammonia in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3; (a) LSV curves; (b) Faraday efficiency and yield data graph at -0.22 V vs. RHE;

[0053] Figure 7 X-ray diffraction pattern of the FeCoNiCuPd / CNFs electrocatalytic material prepared in Comparative Example 1;

[0054] Figure 8 Effect diagram of testing the electrocatalytic performance of FeCoNiCuPd / CNFs prepared in Comparative Example 1 for nitrate reduction to ammonia in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3;

[0055] Figure 9Electrocatalytic materials prepared in Comparative Examples 2 and 3 were tested for electrocatalytic nitrate reduction to ammonia performance (–0.22V vs. RHE) in a mixed electrolyte of 1.0mol / L KOH + 0.1mol / L KNO3, and the Faraday efficiency and yield data graphs at the ideal potential;

[0056] Figure 10 XRD pattern of the electrocatalytic material prepared in Example 3; (a) XRD patterns of FeCoNiMoIn high-entropy alloy nanoparticles at different temperatures; (b) XRD patterns of MoRuWPdAu high-entropy alloy nanoparticles at different temperatures; (c) XRD patterns of FeCoNiRuCu high-entropy alloy nanoparticles at different temperatures. Detailed implementation manners

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention. The following specific implementation manners further describe the present invention.

[0058] Example 1

[0059] A preparation method of a high-entropy nanoparticle catalytic material with a metal shell structure includes the following steps:

[0060] (1) Take 0.5 mmol of iron nitrate, 0.5 mmol of cobalt nitrate, 0.5 mmol of nickel nitrate, 0.5 mmol of silver nitrate and 0.5 mmol of palladium acetylacetonate and add them to 12 g of a DMF solution of 5 wt% polyacrylonitrile (equivalent to a total molar concentration of metal salts of 0.23 mmol / g). Stir evenly by magnetic stirring, and then electrospin the solution. Control the electrospinning voltage to be 20 kV, the distance from the receiving device roller to the electrospinning needle tip to be 12 cm, and the solution flow rate to be 0.5 mL / h to obtain a FeCoNiAgPd / PAN nanofiber membrane;

[0061] Among them, the mixing enthalpies between Fe, Co, Ni, and Pd are relatively small (ΔH FeCo = –1 kJ / mol, ΔH FeNi = –2 kJ / mol, ΔH FePd = –4 kJ / mol, ΔH CoNi = 0 kJ / mol, ΔH CoPd = –1 kJ / mol, ΔH NiPd = 0 kJ / mol), and the sum is –8 kJ / mol; the mixing enthalpies between Ag and Fe, Co, Ni, Pd are relatively large (ΔHFeAg = 28 kJ / mol, ΔH CoAg = 19 kJ / mol, ΔH NiAg = 15 kJ / mol, ΔH PdAg = –7 kJ / mol), and the sum is 55 kJ / mol;

[0062] (2) Take 0.2 g of the prepared FeCoNiAgPd / PAN nanofiber membrane and place it in a corundum boat at the middle part of a tubular furnace. First, heat it to 230 °C at a heating rate of 2 °C / min and keep it for 3 h for pre-oxidation in an argon atmosphere. After the insulation, heat it to 1000 °C at a rate of 2 °C / min in an argon atmosphere. After the temperature reaches 1000 °C, keep it for 3 hours in an inert atmosphere. After the insulation, cool it down to room temperature naturally in an argon atmosphere to obtain the FeCoNiAgPd / CNFs nanoparticle catalytic material.

[0063] Performance analysis

[0064] Take a scanning electron microscope image of the FeCoNiAgPd / CNFs nanoparticle catalytic material prepared in Example 1. Figure 1 It is the scanning electron microscope image of FeCoNiAgPd / CNFs. It can be seen that Figure 1 many alloy nanoparticles with a diameter of about 30 - 60 nm grow on the carbon nanofibers.

[0065] Take a transmission electron microscope image of the FeCoNiAgPd / CNFs nanoparticle catalytic material prepared in Example 1. Figure 2 It is the transmission electron microscope image of FeCoNiAgPd / CNFs. It can be seen that Figure 2 the outer layer of the alloy nanoparticles is the Ag phase with 2 - 3 layers of atoms, and the interplanar spacing is the inner layer of the particles is the high-entropy alloy in the fcc phase, and the interplanar spacing is

[0066] Perform X-ray diffraction on the FeCoNiAgPd / CNFs nanoparticle catalytic material prepared in Example 1. Figure 3 It is the X-ray diffraction pattern of FeCoNiAgPd / CNFs. It can be seen that Figure 3 the peaks at 38.1° and 44.4° of FeCoNiAgPd / CNFs are attributed to the (111) and (200) crystal planes of metallic Ag, and the peaks at 42.3° and 49.3° are attributed to the (111) and (200) crystal planes of HEA. The XRD results show that the fcc-phase HEA and Ag precipitation phase coexist in the prepared sample, indicating that a phase-separated high-entropy alloy nanoparticle is obtained.

[0067] The FeCoNiAgPd / CNFs nanoparticle catalytic material prepared in Example 1 was cut into a regular rectangle of 1×1 cm (with a corresponding mass of about 0.3 g). Since it has self-supporting properties, it can be directly used as a working electrode. Using a standard three-electrode system (the prepared self-supporting material as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode), the electrocatalytic performance of the material for nitrate reduction to ammonia was tested in a mixed electrolyte of 1.0 mol / L KOH and 0.1 mol / L KNO3.

[0068] Figure 4 The electrocatalytic performance of the prepared FeCoNiAgPd / CNFs for nitrate reduction to ammonia was tested in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3. Figure 4 (a) shows that after adding NO3 – , the current density is significantly increased at the same potential, indicating that the material has high catalytic activity for nitrate reduction. Figure 4 (b) shows the Faraday efficiency and yield of FeCoNiAgPd / CNFs at different voltages. The Faraday efficiency and yield are as high as 94.2% and 0.32 μmol h –1 cm –2 respectively at -0.33 V vs. RHE.

[0069] The prepared FeCoNiAgPd / CNFs has excellent stability in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3. After continuously working for 500 h at the optimal voltage (-0.33 V vs. RHE), it still maintains a high Faraday efficiency (93.6%) and yield (0.35 μmol h –1 cm –2 ), and no dissolution of metal elements can be detected in the tested electrolyte by inductively coupled plasma optical emission spectrometry (ICP-OES) (detection limit: 0.01 ppm).

[0070] Example 2: Influence of different calcination temperatures on the phase structure and electrocatalytic performance of the material

[0071] The difference from Example 1 is only that the calcination temperature in step (2) is adjusted. That is, the prepared FeCoNiAgPd / PAN nanofiber membrane is placed in a corundum boat and placed in the middle part of a tubular furnace. First, it is heated to 230 °C at a heating rate of 2 °C / min and kept at this temperature for 3 h in an argon atmosphere for pre-oxidation. After the pre-oxidation is completed; in an argon atmosphere, it is heated to 800 or 1200 °C at a speed of 2 °C / min and kept at this temperature for 3 hours; after the heat preservation is completed, it is naturally cooled to room temperature in an inert gas atmosphere to obtain FeCoNiAgPd-800 and FeCoNiAgPd-1200 respectively.

[0072] The material properties and electrocatalytic nitrate reduction to ammonia performance of FeCoNiAgPd-800 and FeCoNiAgPd-1200 were tested according to the above test method, and the results are as Figure 5 and Figure 6 shown:

[0073] Figure 5 are the XRD patterns of FeCoNiAgPd-800 and FeCoNiAgPd-1200. There is a HEA with an fcc phase in both. Among them, FeCoNiAgPd-800 shows a strong diffraction peak of the Ag phase, indicating that in addition to the high-entropy phase, there is an unmerged Ag phase in this material. However, there is no appearance of the Ag diffraction peak in FeCoNiAgPd-1200. This indicates that the Ag phase only appears at a lower temperature and gradually merges with the HEA phase as the temperature increases.

[0074] Figure 6 The electrocatalytic nitrate reduction to ammonia performance of FeCoNiAgPd / CNFs-800 and FeCoNiAgPd / CNFs-1200 was tested in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3. The LSV graph shows that FeCoNiAgPd / CNFs-800 (Faraday efficiency and yield are 76.4%, 0.16 μmol h –1 cm –2 ) and FeCoNiAgPd / CNFs-1200 (Faraday efficiency and yield are 87.7%, 0.13 μmol h –1 cm –2 ) have current densities lower than those of the samples in Example 1, and both the Faraday efficiency and yield are poor, indicating that the phase structure change caused by reasonably regulating the calcination temperature can significantly affect the electrocatalytic nitrate reduction to ammonia performance of the material.

[0075] Example 3

[0076] The difference from Example 1 is only that in step (1), 0.5 mmol of each of iron nitrate, cobalt nitrate, nickel nitrate, silver nitrate, and vanadyl acetylacetonate was added to a DMF solution of 12 g of polyacrylonitrile with a mass fraction of 5 wt% (equivalent to a total molar concentration of metal salts of 0.23 mmol / g), and it was stirred evenly by magnetic stirring. Then, electrospinning was used to spin the solution, controlling the electrospinning voltage to be 20 kV, the distance from the receiving device roller to the electrospinning needle tip to be 12 cm, and the solution flow rate to be 0.5 mL / h to obtain a FeCoNiVAg / PAN nanofiber membrane; other parameters and conditions are the same as those in Example 1.

[0077] Among them, the mixing enthalpy between Fe, Co, Ni, and V is small (ΔHFeCo = -1 kJ / mol, ΔH FeNi = -2 kJ / mol, ΔH FeV = -7 kJ / mol, ΔH CoNi = 0 kJ / mol, ΔH CoV = -14 kJ / mol, ΔH NiV = -18 kJ / mol), and the sum is -42 kJ / mol; the mixing enthalpies between Ag and Fe, Co, Ni, V are relatively large (ΔH FeAg = 28 kJ / mol, ΔH CoAg = 19 kJ / mol, ΔH NiAg = 15 kJ / mol, ΔH VAg = 17 kJ / mol), and the sum is 79 kJ / mol.

[0078] The stability of the material was tested in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO₃. After cumulative working for 500 h at -0.33 V vs. RHE, the electrolyte after the test was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and obvious dissolution of metal elements was detected (Fe: 0.023 ppm, V: 0.017 ppm).

[0079] Comparative Example 1

[0080] The difference from Example 1 is only that silver nitrate in step (1) is replaced with copper nitrate; other parameters and conditions are the same as those in Example 1; among them, the mixing enthalpies between Fe, Co, Ni, Pd are relatively small; the mixing enthalpies between Cu and Fe, Co, Ni, Pd are also relatively small (ΔH FeCu = 13 kJ / mol, ΔH CoCu = 6 kJ / mol, ΔH NiCu = 4 kJ / mol, ΔH PdCu = -14 kJ / mol), and the sum is 9 kJ / mol.

[0081] X-ray diffraction was performed on the FeCoNiCuPd / CNFs nanoparticle catalytic material prepared in Comparative Example 1, Figure 7 which is the X-ray diffraction pattern of FeCoNiCuPd / CNFs. It can be seen from Figure 7 that the peaks at 43.3° and 50.5° of FeCoNiCuPd / CNFs are attributed to the (111) crystal plane and (200) crystal plane of HEA. The XRD results show that only homogeneous fcc-HEA exists in this material, indicating that a single-phase high-entropy alloy nanoparticle is obtained.

[0082] Figure 8The electrocatalytic ammonia production performance of the prepared FeCoNiCuPd / CNFs was tested in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3. The current density of FeCoNiCuPd / CNFs was significantly lower than that of FeCoNiAgPd / CNFs, and after adding NO3 – the current density did not increase significantly at the same potential (after adding NO3 – the current density only increased from 14 mA / cm 2 to 19 mA / cm 2 ).

[0083] Comparative Example 2

[0084] The difference from Example 1 is only that in step (1), 0.5 mmol of each of iron nitrate, cobalt nitrate, nickel nitrate, and palladium acetylacetonate was added to 12 g of a DMF solution of 5 wt% polyacrylonitrile (equivalent to a total molar concentration of metal salts of 0.23 mmol / g), and the mixture was stirred evenly by magnetic stirring. Then, the solution was electrospun, controlling the electrospinning voltage at 20 kV, the distance from the receiving device roller to the electrospinning needle tip at 12 cm, and the solution flow rate at 0.5 mL / h to obtain a FeCoNiPd / PAN nanofiber membrane; other parameters and conditions were the same as those in Example 1.

[0085] Comparative Example 3

[0086] The difference from Example 1 is only that in step (1), 0.5 mmol of each of iron nitrate, cobalt nitrate, nickel nitrate, and silver nitrate was added to 12 g of a DMF solution of 5 wt% polyacrylonitrile (equivalent to a total molar concentration of metal salts of 0.23 mmol / g), and the mixture was stirred evenly by magnetic stirring. Then, the solution was electrospun, controlling the electrospinning voltage at 20 kV, the distance from the receiving device roller to the electrospinning needle tip at 12 cm, and the solution flow rate at 0.5 mL / h to obtain a FeCoNiAg / PAN nanofiber membrane; other parameters and conditions were the same as those in Example 1.

[0087] Figure 9 The electrocatalytic ammonia production performance, Faraday efficiency, and yield at the ideal potential of the prepared FeCoNiPd / CNFs and FeCoNiAg / CNFs in Comparative Example 2 and Comparative Example 3 were tested in a mixed electrolyte of 1.0 mol / L KOH + 0.1 mol / L KNO3. The results showed that the Faraday efficiency and yield of FeCoNiPd / CNFs and FeCoNiAg / CNFs were significantly lower than those of FeCoNiAgPd / CNFs in Example 1; it was shown that the high-entropy alloy with an Ag shell exhibited higher activity in the electrocatalytic reduction of nitrate to ammonia.

[0088] Example 4

[0089] A preparation method of a high-entropy nanoparticle catalytic material with a metal shell structure, including the following steps:

[0090] Step (1): Prepare precursor solutions of FeCoNiMoIn, MoRuWPdAu, and FeCoNiRuCu; add 0.5 mmol of each corresponding metal salt (iron nitrate, cobalt nitrate, nickel nitrate, molybdenum acetylacetonate, indium nitrate, ruthenium chloride, tungsten chloride, palladium acetylacetonate, chloroauric acid, copper nitrate) to 12 g of a DMF solution of 5 wt% polyacrylonitrile (equivalent to a total molar concentration of metal salts of 0.23 mmol / g), stir evenly by magnetic stirring, and the electrospinning process is the same as in Example 1;

[0091] Among them, in FeCoNiMoIn, the mixing enthalpies between Fe, Co, Ni, and Mo are relatively small (ΔH FeCo = -1 kJ / mol, ΔH FeNi = -2 kJ / mol, ΔH FeMo = -2 kJ / mol, ΔH CoNi = 0 kJ / mol, ΔH CoPd = -5 kJ / mol, ΔH NiMo = -7 kJ / mol), and the sum is -17 kJ / mol; the mixing enthalpies between In and Fe, Co, Ni, and Mo are relatively large (ΔH FeIn = 19 kJ / mol, ΔH CoIn = 7 kJ / mol, ΔH NiIn = 2 kJ / mol, ΔH MoIn = 33 kJ / mol), and the sum is 61 kJ / mol;

[0092] Among MoRuWPdAu, the mixing enthalpies between Mo, Ru, W, Pd, and Au are all relatively small (ΔH MoRu = -14 kJ / mol,

[0093] ΔH MoW = 0 kJ / mol, ΔH MoPd = -15 kJ / mol, ΔH RuW = -10 kJ / mol, ΔH RuPd = 6 kJ / mol, ΔH WPd

[0094] = -6 kJ / mol), and the sum is -39 kJ / mol. The mixing enthalpies between Au and Mo, Ru, W, and Pd are generally relatively large (ΔH MoAu = 3 kJ / mol, ΔH RuAu= 15 kJ / mol, ΔH WAu = 12 kJ / mol, ΔH PdAu = 0 kJ / mol), and the sum is –1 kJ / mol;

[0095] In FeCoNiRuCu, the mixing enthalpy between Fe, Co, Ni, and Ru is relatively small (ΔH FeCo = 30 kJ / mol, ΔH FeNi = –2 kJ / mol, ΔH FeRu = –5 kJ / mol, ΔH CoNi = 0 kJ / mol, ΔH CoRu = –1 kJ / mol, ΔH NiRu = 0 kJ / mol), and the sum is –9 kJ / mol; the mixing enthalpy between Cu and Fe, Co, Ni, Ru is relatively large (ΔH FeCu = 13 kJ / mol, ΔH CoCu = 6 kJ / mol, ΔH NiCu = 4 kJ / mol, ΔH RuCu = 7 kJ / mol), and the sum is 30 kJ / mol.

[0096] Step (2): Put 0.2 g of the prepared FeCoNiMoIn / PAN, MoRuWPdAu / PAN, and FeCoNiRuCu / PAN nanofiber membranes into a corundum boat and place it in the middle of a tube furnace. First, heat it at a heating rate of 2 °C / min to 230 °C and keep it for 3 h for pre-oxidation in an argon atmosphere; after the heat preservation ends, in an argon atmosphere, heat it to 800, 900, 1000, 1200 °C at a rate of 2 °C / min, keep it for 3 hours in an argon atmosphere, and after the heat preservation ends, naturally cool it to room temperature in an inert gas atmosphere to obtain the required samples.

[0097] Figure 10 is the XRD pattern of the sample obtained in Example 3. The results show that there are controllable phase transformation processes in FeCoNiMoIn / CNFs, MoRuWPdAu / CNFs, and FeCoNiRuCu / CNFs, and InNi, Au, and Cu phases precipitate at relatively low temperatures respectively, indicating the universality of this method in the controllable phase transformation of high-entropy alloys.

[0098] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit their execution order. Obvious improvements made by those skilled in the art to the present invention in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A preparation method of a high-entropy nanoparticle catalytic material with a metal atomic shell structure, characterized in that, The preparation method includes the following steps: (1)Disperse metal salts and nanofiber precursors in an organic solvent to prepare a spinning solution; then prepare a nanofiber membrane by electrospinning; (2)Calcine and pre-oxidize the nanofiber membrane obtained in step (1), and then raise the temperature to 800-1000 °C at a rate of 2-10 °C / min. After the temperature reaches 800-1000 °C, keep it warm for 0.5-5 hours in an inert atmosphere; after the heat preservation ends, naturally cool it to room temperature in an inert atmosphere to obtain a high-entropy nanoparticle catalytic material with a metal atomic shell structure; The principle followed for the selection of the metal salts in step (1) is: (1) Select (n–1) to (n–2) metals as the alloy substrate, and require that the sum of the mixing enthalpies between the selected elements is not greater than –5 kJ mol –1 , where n is the number of metal element types, and n is a natural number greater than or equal to 4; (2) Select one or two metal elements as the precipitated phase, and it is required that the sum of the mixing enthalpies between the selected precipitated phase metal elements and the constituent elements of the alloy substrate is greater than 20 kJ / mol. –1 .

2. The method according to claim 1, wherein The nanofiber precursors in step (1) include one or more of polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol, polystyrene, and polytetrafluoroethylene.

3. The method according to claim 1, characterized in that, The organic solvents in step (1) are one or several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, and acetone.

4. The method according to claim 1, wherein In the spinning solution of step (1), for a quinary high-entropy alloy, the molar proportion of each metal element is 5-35%; for an alloy with six or more elements, the proportion of each metal element is 100 / n ± 75 / n%, where n is the number of metal element types.

5. The method according to claim 1, wherein The metal salts in step (1) include any several of iron salts, cobalt salts, nickel salts, silver salts, palladium salts, copper salts, molybdenum salts, indium salts, ruthenium salts, tungsten salts, and chloroauric acid.

6. The method according to claim 1, wherein After the calcination and pre-oxidation in step (2), then raise the temperature to 1000 °C at a rate of 2-10 °C / min. After the temperature reaches 1000 °C, keep it warm for 0.5-5 hours in an inert atmosphere.

7. A preparation method of a highly stable high-entropy nanoparticle catalytic material with a metal atomic shell structure, characterized in that, The preparation method includes the following steps: 1) Add iron salts, cobalt salts, nickel salts, silver salts, and palladium salts to the N,N-dimethylformamide of polyacrylonitrile, stir evenly, and then spin the solution by electrospinning to obtain a FeCoNiAgPd / PAN nanofiber membrane; 2) Calcinate the FeCoNiAgPd / PAN nanofiber membrane prepared in step 1). First, raise the temperature to 180-300 °C at a heating rate of 2-10 °C / min and keep it warm for 1-6 hours in an air atmosphere for pre-oxidation; after the heat preservation ends, in an inert gas atmosphere, raise the temperature to 800-1200 °C at a rate of 2-10 °C / min and keep it warm for 1-6 hours; after the heat preservation ends, naturally cool it to room temperature in an inert gas atmosphere to obtain a highly stable high-entropy nanoparticle catalytic material FeCoNiAgPd NPs.

8. A high-entropy nanoparticle catalytic material with a metal atomic shell structure obtained by the preparation method according to any one of claims 1-6 or a highly stable high-entropy nanoparticle catalytic material FeCoNiAgPd NPs obtained by the preparation method according to claim 7.

9. Application of the high-entropy nanoparticle catalytic material with a metal atomic shell structure or the highly stable high-entropy nanoparticle catalytic material FeCoNiAgPd NPs according to claim 8 in the field of electrocatalysis.

10. A method for efficiently catalyzing the nitrate reduction reaction to ammonia, characterized in that, The method uses the high-entropy nanoparticle catalytic material with a metal atomic shell structure described in claim 8 or the highly stable high-entropy nanoparticle catalytic material FeCoNiAgPd NPs as a catalyst.

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