High-entropy alloy nanowire, preparation method thereof and composite catalyst

Abstract

The present application relates to a kind of high-entropy alloy nanowires and its preparation method and composite catalyst, the preparation method includes: the metal precursor mixed solution including nucleating agent, complexing agent, ammonium salt, non-noble metal salt and solvent is placed under external magnetic field, reducing agent is added to carry out reduction reaction, and high-entropy alloy nanowire is obtained;The nucleating agent includes platinum source and palladium source;The non-noble metal salt includes the combination of at least three kinds of iron salt, cobalt salt, nickel salt, copper salt or manganese salt.The present application uses platinum source, palladium source and non-noble metal salt as the reaction raw material of high-entropy alloy nanowire, and is supplemented with the addition of magnetic field, in the reduction process, the nucleation and growth process of magnetic metal particles and the self-assembly behavior of magnetic nanocrystal are controlled by magnetic force, can be prepared under room temperature and normal pressure condition, the high-entropy alloy nanowire with adjustable length-diameter ratio, structure stable and Pt dispersion uniform, after being mixed with commercial carbon powder, the composite catalyst obtained is rich in active site, and the oxygen reduction catalytic activity is excellent.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and catalysts, and particularly to a high-entropy alloy nanowire, its preparation method, and a composite catalyst. Background Technology

[0002] High-entropy alloys (HEAs) possess abundant compositional space, multiple active sites, near-continuously tunable binding energy, and stable structure, enabling their widespread application in electrocatalysis and demonstrating extremely broad prospects in catalysis and energy applications. Among them, high-entropy alloy nanowires (NWs) with one-dimensional morphology and high aspect ratio belong to one important branch of high-entropy alloy materials. Compared with traditional zero-dimensional high-entropy alloy nanoparticles, one-dimensional nanowires have unique structural and surface properties, exhibiting better conductivity and higher bonding strength with the support. In addition, the anisotropic structure of the one-dimensional morphology is more resistant to Ostwald ripening, resulting in superior stability and better catalytic performance when used in catalysts.

[0003] Fuel cells are power generation devices that convert chemical energy into electrical energy, offering advantages such as high energy conversion efficiency, mild reaction conditions, and a wide range of fuel options. The electrodes of a fuel cell are the sites of electrochemical reactions where fuel oxidation and oxidant reduction occur; the catalysts supported on the electrodes are a major limiting factor in their development. The oxygen reduction (ORR) reaction rate at the cathode is much slower than at the anode. Therefore, developing low-cost, highly active, and highly stable ORR catalysts is currently a key research focus.

[0004] Pt-based high-entropy alloy nanowires exhibit excellent ORR activity. Compared to traditional Pt nanoparticle catalysts, the lattice distortion of high-entropy alloy nanowire catalysts promotes the formation of defects and strains, resulting in a unique microstructure that provides excellent stability. Furthermore, the heterogeneous interface offers a richer pool of active sites and a moderate adsorption free energy. Moreover, compared to zero-dimensional nanoparticles, the unique structure of one-dimensional nanowires provides a larger contact area with the carbon support, enhancing the interaction and preventing catalyst detachment, thus leading to higher stability in the ORR reaction. Nanowires also possess superior electrical conductivity, providing unobstructed electron transport channels in the ORR reaction. Additionally, the uniform crystal orientation within the nanowires further modulates the adsorption and desorption of oxygen intermediates, demonstrating high catalytic activity in the ORR reaction.

[0005] Currently, methods for synthesizing high-entropy alloy nanowires include focused ion beam cutting, organic phase reduction, and aqueous phase thermal reduction. Existing technology discloses a method for preparing ultrathin nanowires by micro-doping Re into ultrathin PtNiGa nanowires to prepare a Re-PtNiGaNWs catalyst. The preparation method includes: using tungsten hexacarbonyl as a reducing agent in an oleylamine organic phase, heating at 170°C for 2 hours to reduce acetylacetone salt, centrifuging, washing repeatedly with a hexane / ethanol mixture, and then drying to obtain the product. Although this method improves the catalytic activity and stability of the catalyst compared to traditional platinum-carbon catalysts, the use of the organic phase and detergent during catalyst preparation causes significant air pollution, the carbon monoxide from the decomposition of tungsten hexacarbonyl is extremely harmful to human health, and the 2 hours of heating at 170°C requires a large energy input. Overall, these factors make it difficult to scale up production and thus meet the requirements for commercial applications.

[0006] Studies have shown that magnetic fields can influence the nucleation and growth processes of magnetic materials as well as the self-assembly behavior of magnetic nanocrystals, significantly reducing the difficulty of nanowire growth. This provides a new approach for developing a novel synthesis method for high-entropy alloy nanowires.

[0007] A prior art method discloses a magnetic field-assisted nanowire growth preparation method. This method uses hydrazine hydrate as a reducing agent in an aqueous phase under a magnetic field generated by a bar magnet. Heating at 90°C for a period of time reduces chloride salts to obtain a black intermediate product. After repeated washing with ethanol and water and drying, the intermediate product is placed in a tube furnace and heated at 300°C for 3 hours in a hydrogen (H2) atmosphere at a flow rate of 200 mL / min to obtain FeCo nanowires. Although this method synthesizes nanowires under a magnetic field, reducing the difficulty of chemical reduction, the method relies solely on the use of a bar magnet to control the magnetic field, and the number of species that can be reduced (only Fe and Co) is limited. Heating at 300°C for 3 hours requires a large energy input, which is not conducive to industrialization and remains far from large-scale production.

[0008] Given that the above-mentioned preparation methods all suffer from severe pollution and high energy consumption, thus hindering the large-scale and commercial production of high-entropy alloy nanowires, it is urgent to solve the technical problem of how to develop a synthesis method for high-entropy alloy nanowires that can reduce pollution and energy consumption while enabling large-scale production, and at the same time, the obtained high-entropy alloy nanowires can be used as ORR catalysts that can balance certain catalytic activity and stability. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides high-entropy alloy nanowires, their preparation method, and a composite catalyst. Platinum, palladium, and non-precious metal salts are used as reaction raw materials for the high-entropy alloy nanowires, supplemented by the addition of a magnetic field. During the reduction process, the nucleation and growth of magnetic metal particles and the self-assembly behavior of magnetic nanocrystals are controlled by magnetic force. This allows for the preparation of high-entropy alloy nanowires with adjustable diameter and length, consistent growth direction, purity, high dispersion, stable structure, and uniform Pt dispersion under room temperature and atmospheric pressure conditions. The resulting composite catalyst, after mixing with commercial carbon powder, has abundant active sites and excellent oxygen reduction catalytic activity. The preparation method of this invention can be carried out at room temperature and atmospheric pressure, offering advantages such as low synthesis temperature, lower cost, less hazard, simpler equipment, higher yield, and more uniform nanowires.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing high-entropy alloy nanowires, the method comprising the following steps:

[0012] A metal precursor mixture solution was placed under an external magnetic field, and a reducing agent was added to carry out a reduction reaction to obtain high-entropy alloy nanowires.

[0013] The metal precursor mixed solution includes a nucleating agent, a complexing agent, an ammonium salt, a non-precious metal salt, and a solvent.

[0014] The nucleating agent includes a platinum source and a palladium source;

[0015] The non-precious metal salts include combinations of at least three of the following: iron salts, cobalt salts, nickel salts, copper salts, or manganese salts.

[0016] This invention utilizes the combined addition of platinum sources, palladium sources, non-precious metal salts, ammonium salts, and complexing agents to achieve synergistic effects, thereby controlling the production of high-entropy alloy nanowires with adjustable diameter and length, consistent growth direction, purity, high dispersibility, structural stability, and uniform Pt dispersion. Platinum sources, palladium sources, and non-precious metal salts are used as the reaction raw materials for the high-entropy alloy nanowires. The platinum and palladium sources also act as nucleating agents, forming a sufficient number of uniformly distributed crystal nuclei under the action of a reducing agent. This provides starting sites for the growth of non-precious metal atoms, thus lowering the nucleation barrier of metal grains and facilitating the reduction reaction. The non-precious metal salts used in this invention can be wholly or partially magnetic, allowing metal grains to align and grow along the magnetic field direction, forming an ordered nanowire structure. This enables the fabrication of nanowires with controllable aspect ratios at room temperature. High-entropy alloy nanowires with uniform dispersion and stable structure; the addition of ammonium salt can, on the one hand, act as a surfactant, increase the polarity of the reactants, and promote their dispersion and dissolution in water; on the other hand, ammonium salt can also act as a buffer solution for pH adjustment, avoiding large-scale pH changes that could affect the formation of nanowire morphology; the addition of complexing agent can form complexes with metal ions, controlling the reaction to proceed slowly, allowing the metal ions sufficient time to grow orderly under the influence of the magnetic field, and preventing the rapid reduction of metal ions from escaping the control of the magnetic field, ultimately yielding metal nanoparticles.

[0017] The method for preparing high-entropy alloy nanowires provided by this invention mainly involves the addition of a magnetic field. During the reducing process, the magnetic force provided by the magnetic field controls the nucleation and growth of magnetic metal particles along the direction of the magnetic field, as well as the self-assembly behavior of magnetic nanocrystals. This method enables the preparation of high-entropy alloy nanowires with adjustable diameter and length, consistent growth direction, purity, and high dispersion at room temperature (10-35℃) and normal pressure.

[0018] As a preferred embodiment of the present invention, in the non-precious metal salt, the molar ratio of iron salt, cobalt salt, nickel salt, copper salt and manganese salt is 1:(0-10):(0-10):(0-5):(0-5), and the molar amounts of at least two metal salts are not 0, for example 1:0.5:0.5:0:0, 1:0.5:1:1:3, 1:0:2:0:1, 1:1:0:2:2, 1:5:0:5:0, 1:3:5:0:0, 1:0:1:2:1, 1:10:10:1:1, 1:10:10:3:4 or 1:10:10:5:5, etc.

[0019] Preferably, the non-precious metal salt includes any one or a combination of at least two of the following: chloride, nitrate, acetate, sulfate, acetylacetone, or phthalocyanine.

[0020] Preferably, the platinum source includes any one or a combination of at least two of chloroplatinic acid, potassium chloroplatinate, or sodium chloroplatinate.

[0021] Preferably, the palladium source includes any one or a combination of at least two of chloropalladium acid, palladium chloride, or potassium chloropalladiumate.

[0022] It should be noted that the present invention does not impose specific requirements or special limitations on the solvent. Any solvent commonly used by those skilled in the art is applicable to the present invention, such as deionized water, ultrapure water, or ethanol.

[0023] Preferably, the complexing agent comprises any one or a combination of at least two of sodium citrate, potassium citrate, citric acid, disodium edetate, or tartaric acid.

[0024] Preferably, the ammonium salt comprises any one or a combination of at least two of ammonium fluoride or ammonium chloride.

[0025] As a preferred technical solution of the present invention, the molar ratio of nucleating agent, complexing agent, ammonium salt and non-precious metal salt in the metal precursor mixed solution is 1:(10-500):(200-1500):(0.5-10), for example 1:10:200:0.5, 1:15:500:1, 1:50:1000:5, 1:100:1200:8, 1:300:1500:10 or 1:500:1500:1, etc.

[0026] Preferably, the concentration of the metal element in the metal precursor mixed solution is 0 mmol / L-0.5 mmol / L, and is not 0, for example, 0.05 mmol / L, 0.1 mmol / L, 0.2 mmol / L, 0.3 mmol / L, 0.4 mmol / L or 0.5 mmol / L.

[0027] Preferably, the metal precursor mixture solution further includes a pH adjuster.

[0028] It should be noted that the present invention does not impose specific requirements or special limitations on the pH adjuster. Any type commonly used by those skilled in the art is applicable to the present invention, such as sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, or sodium carbonate.

[0029] As a preferred technical solution of the present invention, the pH of the metal precursor mixed solution is 3-14, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14, preferably 8-13.

[0030] Preferably, the method for preparing the metal precursor mixed solution includes: dissolving a nucleating agent, a complexing agent, an ammonium salt, and a non-precious metal salt in a solvent and mixing them evenly, then adding a pH adjuster to obtain the metal precursor mixed solution.

[0031] As a preferred technical solution of the present invention, the field strength of the external magnetic field is 0.0001T-10T, such as 0.0001T, 0.0005T, 0.01T, 0.05T, 0.08T, 0.1T, 0.5T, 1T, 3T, 5T, 8T or 10T, etc.

[0032] The external magnetic field strength of this invention is 0.0001T-10T, which can cause non-noble metal ions to grow in a directional and orderly manner under the magnetic field, resulting in high-entropy alloy nanowires. If the strength is too high, the non-noble metal ions will adhere to the reactor wall and will be difficult to grow with noble metal nucleation sites as the starting point, thus failing to obtain high-entropy alloy nanowires with a large aspect ratio. If the strength is too low, the magnetic field will be unable to guide the directional arrangement of non-noble metals, ultimately resulting in a disordered and chaotic network structure.

[0033] It should be noted that the present invention does not impose specific requirements or special limitations on the device for generating the external magnetic field. Any type commonly used by those skilled in the art is applicable to the present invention, such as a bar magnet, a ring magnet, or an electromagnet.

[0034] It should be noted that the present invention does not impose specific requirements or limitations on the type of external magnetic field. Any type commonly used by those skilled in the art is applicable to the present invention, such as a constant magnetic field, an alternating magnetic field, or a pulsed magnetic field.

[0035] As a preferred embodiment of the present invention, the reducing agent includes sodium borohydride.

[0036] Preferably, the molar ratio of the reducing agent to the metal element is (2-100):1, such as 2:1, 5:1, 8:1, 50:1, 80:1 or 100:1.

[0037] Preferably, the reduction reaction is carried out at room temperature.

[0038] It should be noted that the reaction described in this invention is carried out under room temperature conditions, that is, without heating the reaction. Depending on the region and season, the temperature of the reduction reaction is 10-35℃, such as 10℃, 12℃, 15℃, 18℃, 20℃, 22℃, 25℃, 28℃, 30℃, 32℃ or 35℃, etc., which can produce high-entropy alloy nanowires with high aspect ratio and uniform morphology, avoiding the reaction at heating temperature and simplifying the experimental procedure.

[0039] Preferably, the reduction reaction time is 0.01-24h, for example 0.01h, 0.05h, 0.1h, 0.5h, 0.8h, 1h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 22h or 24h.

[0040] As a preferred embodiment of the present invention, the reduction reaction is followed by solid-liquid separation, washing, and drying.

[0041] Preferably, the solid-liquid separation method includes using a magnet for separation.

[0042] In this invention, the product and solution can be quickly separated by magnetic separation, and this separation method is simple and efficient.

[0043] Preferably, the washing solution comprises any one or a combination of at least two of deionized water, ultrapure water, ethanol, or cyclohexane.

[0044] Preferably, the drying includes any one or a combination of at least two of the following: forced-air drying, vacuum drying, or freeze drying.

[0045] Preferably, the drying includes a combination of freeze drying and vacuum drying, or a combination of freeze drying and forced-air drying.

[0046] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0047] Nucleating agent, complexing agent, ammonium salt and non-noble metal salt are dissolved in solvent and mixed evenly. pH adjuster is added to obtain a mixed solution of metal precursors with pH of 8-13. The solution is placed under an external magnetic field with a field strength of 0.0001-10T and a reducing agent is added to carry out a reduction reaction. After reduction at room temperature for 0.01-24h, the reaction product is separated by a magnet. After washing and drying, high-entropy alloy nanowires are obtained.

[0048] The nucleating agent comprises a platinum source and a palladium source; the non-precious metal salt comprises a combination of at least three of iron, cobalt, nickel, copper, or manganese salts; the molar ratio of iron, cobalt, nickel, copper, and manganese salts in the non-precious metal salt is 1:(0-10):(0-10):(0-5):(0-5), and the molar amount of at least two metal salts is not 0; in the metal precursor mixed solution, the molar ratio of nucleating agent, complexing agent, ammonium salt, and non-precious metal salt is 1:(10-500):(200-1500):(0.5-10); the concentration of the metal element in the metal precursor mixed solution is 0 mmol / L-0.5 mmol / L, and is not 0; the reducing agent comprises sodium borohydride; the molar ratio of the reducing agent to the metal element is (2-100):1.

[0049] In a second aspect, the present invention also provides a high-entropy alloy nanowire prepared according to the preparation method described in the first aspect, wherein the high-entropy alloy nanowire has a diameter of 100nm-300nm, such as 100nm, 150nm, 200nm, 250nm or 300nm; and a length of 5μm-80μm, such as 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm or 80μm.

[0050] Thirdly, the present invention also provides a composite catalyst, the composite catalyst comprising high-entropy alloy nanowires prepared by the preparation method described in the first aspect, or high-entropy alloy nanowires as described in the second aspect.

[0051] In this invention, since the nucleating agent includes a platinum source, a certain amount of Pt is dispersed in the composite catalyst, providing active sites for oxygen reduction catalysis. At the same time, the structure of Pt-based high-entropy alloy nanowires has a large number of heterogeneous interfaces, providing more active sites and moderate adsorption free energy. The nanowire structure has better conductivity and has unobstructed electron transport channels in the ORR reaction, thus exhibiting high catalytic activity in the ORR reaction.

[0052] Compared with the prior art, the present invention has at least the following beneficial effects:

[0053] 1) By leveraging the synergistic effect and content relationship between raw materials, combined with pH control, the addition of an external magnetic field, and the reduction of a reducing agent, this invention prepares high-entropy alloy nanowires with superior morphology, high aspect ratio, and no branching at room temperature.

[0054] 2) The high-entropy alloy nanowires prepared by this invention have stable structures and uniform Pt dispersion. The composite catalyst obtained after mixing with commercial carbon powder has a large number of high-entropy alloy crystal structures and nanowire morphology orientations, abundant active sites, and excellent oxygen reduction catalytic activity. The initial mass activity at 0.9V is 135 mA / mg and above, and the highest can reach 336 mA / mg.

[0055] 3) The preparation method of this invention is simple and universal, and the reaction process can be carried out at room temperature and normal pressure. It is safe and pollution-free and suitable for mass production. Attached Figure Description

[0056] Figure 1 This is a SEM image of the high-entropy alloy nanowires prepared in Example 1 of this invention.

[0057] Figure 2 This is the EDS image of the high-entropy alloy nanowires prepared in Example 1 of this invention.

[0058] Figure 3This is a SEM image of the high-entropy alloy prepared in Comparative Example 1 of this invention.

[0059] Figure 4 This is a SEM image of the alloy prepared in Comparative Example 3 of this invention. Detailed Implementation

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0061] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0062] The commercial Pt / C catalyst used in Comparative Application Example 4 of this invention has a Pt loading of 20 wt% and was purchased from Shanghai Sanshe Industrial Co., Ltd.

[0063] Example 1

[0064] This embodiment provides a method for preparing high-entropy alloy nanowires, the method comprising the following steps:

[0065] Weigh 0.05 mmol H₂PtCl₆, 0.01 mmol PdCl₂, 1 mmol sodium citrate, 50 mmol ammonium fluoride, 0.04 mmol FeSO₄, 0.01 mmol CoSO₄, and 0.01 mmol NiSO₄ into a reaction vessel. The molar ratio of nucleating agents (H₂PtCl₆ and PdCl₂): sodium citrate: ammonium fluoride: non-precious metal salt is 1:16.7:833.3:1, and the molar ratio of FeSO₄:CoSO₄:NiSO₄ is 1:0.25:0.25. Add 400 mL of deionized water and stir until homogeneous. Then add solid sodium hydroxide and continue stirring until the pH is adjusted to 12, yielding a metal element concentration of 0.3 mmol. A mixed solution of metal precursors of / L was obtained and transferred to a constant magnetic field of 0.2T generated by an electromagnet. 1 mmol of sodium borohydride (molar ratio of sodium borohydride to metal element was 8.33:1) was added, and the reaction was allowed to stand for 12 h. The product was separated by a magnet, washed three times with deionized water and then three times with ethanol. It was then dispersed in tert-butanol and freeze-dried using a freeze dryer to obtain high-entropy alloy nanowires PtPdFeCoNi-NWs.

[0066] Figure 1 The SEM image of the high-entropy alloy nanowires prepared in this embodiment is shown. As can be seen from the figure, the high-entropy alloy nanowires have a uniform morphology, are relatively dispersed, have no branches, and have a consistent growth orientation.

[0067] Figure 2 The EDS diagram of the high-entropy alloy nanowires prepared in this embodiment is shown. As can be seen from the figure, the Pt content is relatively high, which can be used as a catalyst.

[0068] Example 2

[0069] This embodiment provides a method for preparing high-entropy alloy nanowires, the method comprising the following steps:

[0070] Weigh out 0.05 mmol H₂PtCl₆, 0.01 mmol PdCl₂, 0.6 mmol sodium citrate, 15 mmol ammonium fluoride, 0.015 mmol FeSO₄, 0.0075 mmol CoSO₄, and 0.0075 mmol... In a reaction vessel, NiSO4 was prepared with nucleating agents (H2PtCl6 and PdCl2): sodium citrate: ammonium fluoride: non-precious metal salt in a molar ratio of 1:10:250:0.5, and FeSO4:CoSO4:NiSO4 in a molar ratio of 1:0.5:0.5. 180 mL of deionized water was added, and the mixture was stirred until homogeneous. Solid sodium hydroxide was then added, and the mixture was stirred continuously until the pH was adjusted to 10, resulting in a mixed solution of metal precursors with a metal element concentration of 0.5 mmol / L. This mixed solution was then transferred to a constant magnetic field of 5 T generated by an electromagnet, and 1.8 mmol of sodium borohydride (molar ratio of sodium borohydride to metal element was 20:1) was added. The mixture was allowed to stand for 18 h. The reaction product was separated using a magnet, washed three times with deionized water, then three times with ethanol, and subsequently dispersed in tert-butanol. The product was then freeze-dried using a freeze dryer to obtain high-entropy alloy nanowires PtPdFeCoNi-NWs.

[0071] Example 3

[0072] This embodiment provides a method for preparing high-entropy alloy nanowires, the method comprising the following steps:

[0073] Weigh 0.05 mmol H₂PtCl₆, 0.01 mmol PdCl₂, 30 mmol sodium citrate, 60 mmol ammonium fluoride, 0.06 mmol FeSO₄, 0.024 mmol CoSO₄, 0.024 mmol NiSO₄, and 0.012 mmol MnSO₄ into a reaction vessel. The molar ratio of nucleating agent (H₂PtCl₆ and PdCl₂): sodium citrate: ammonium fluoride: non-precious metal salt is 1:500:1000:2, and the molar ratio of FeSO₄:CoSO₄:NiSO₄:MnSO₄ is 1:0.4:0.4:0.2. Add 450 mL of deionized water and stir well. Then add solid sodium hydroxide and continue stirring until the pH is adjusted to 9, yielding a metal element concentration of 0.4 mg / mL. A mol / L mixed solution of metal precursors was prepared and transferred to a constant magnetic field of 10T generated by an electromagnet. 0.36 mmol of sodium borohydride (molar ratio of sodium borohydride to metal element was 2:1) was added, and the reaction was allowed to stand for 0.5 h. The reaction product was separated by a magnet, washed three times with deionized water and then three times with ethanol. It was then dispersed in tert-butanol and freeze-dried using a freeze dryer to obtain high-entropy alloy nanowires PtPdFeCoNi-NWs.

[0074] Example 4

[0075] This embodiment provides a method for preparing high-entropy alloy nanowires, the method comprising the following steps:

[0076] Weigh out 0.05 mmol H₂PtCl₆, 0.01 mmol PdCl₂, 18 mmol sodium citrate, 90 mmol ammonium fluoride, 0.12 mmol FeSO₄, 0.30 mmol CoSO₄, and 0.18 mmol... CuSO4 was placed in a reaction vessel, with the molar ratio of nucleating agents (H2PtCl6 and PdCl2): sodium citrate: ammonium fluoride: non-noble metal salt being 1:300:1500:10, and the molar ratio of FeSO4:CoSO4:CuSO4 being 1:2.5:1.5. 1320 mL of deionized water was added, and the mixture was stirred until homogeneous. Solid sodium hydroxide was then added, and the mixture was stirred continuously until the pH was adjusted to 13, resulting in a mixed solution of metal precursors with a metal element concentration of 0.5 mmol / L. This mixed solution was then transferred to a constant magnetic field of 0.2 T generated by an electromagnet, and 66 mmol of sodium borohydride (molar ratio of sodium borohydride to metal element being 100:1) was added. The mixture was allowed to stand for 24 h. The reaction product was separated using a magnet, washed three times with deionized water, then three times with ethanol, and subsequently dispersed in tert-butanol. The product was then freeze-dried using a freeze dryer to obtain high-entropy alloy nanowires PtPdFeCoNi-NWs.

[0077] Example 5

[0078] This embodiment provides a method for preparing high-entropy alloy nanowires. The difference between this method and Example 1 is that the molar ratio of nucleating agent: sodium citrate: ammonium fluoride: non-precious metal salt is 1:16.7:833.3:0.25. The remaining preparation methods and parameters are consistent with those of Example 1.

[0079] Example 6

[0080] This embodiment provides a method for preparing high-entropy alloy nanowires. The difference between this method and that of Example 1 is that the molar ratio of nucleating agent: sodium citrate: ammonium fluoride: non-precious metal salt is 1:16.7:833.3:12, while the rest of the preparation method and parameters remain the same as in Example 1.

[0081] Example 7

[0082] This embodiment provides a method for preparing high-entropy alloy nanowires. The difference between this method and that of Embodiment 1 is that the constant magnetic field generated by the electromagnet is 13T, while the rest of the preparation method and parameters remain the same as those of Embodiment 1.

[0083] Example 8

[0084] This embodiment provides a method for preparing high-entropy alloy nanowires. The difference between this method and Example 1 is that 13.2 mmol of sodium borohydride is added during the reduction process (the molar ratio of sodium borohydride to the metal element is 110:1). The rest of the preparation method and parameters are the same as in Example 1.

[0085] Example 9

[0086] This embodiment provides a method for preparing high-entropy alloy nanowires. The difference between this method and Example 1 is that 0.12 mmol of sodium borohydride is added during the reduction process (the molar ratio of sodium borohydride to the metal element is 1:1). The rest of the preparation method and parameters are the same as in Example 1.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing a high-entropy alloy. The difference between this method and Example 1 is that the auxiliary external magnetic field is omitted, while the rest of the preparation method and parameters remain the same as in Example 1.

[0089] Figure 3 The SEM image of the high-entropy alloy prepared in this comparative example is shown. As can be seen from the figure, the high-entropy alloy has a non-nanowire morphology and is an aggregated aerogel structure.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing an alloy. The difference between this method and Example 1 is that the nucleating agents H2PtCl6 and PdCl2 are omitted, while the rest of the preparation method and parameters remain the same as in Example 1.

[0092] Because the nucleating agents H2PtCl6 and PdCl2 were omitted, no product was generated in the solution after reduction in this comparative example.

[0093] Comparative Example 3

[0094] This comparative example provides a method for preparing an alloy. The difference between this method and Example 1 is that the addition of FeSO4, CoSO4 and NiSO4 is omitted, that is, the addition of non-precious metal salts is omitted. The rest of the preparation method and parameters are the same as in Example 1.

[0095] Figure 4 The SEM image of the alloy prepared in this comparative example is shown. As can be seen from the figure, the alloy has a non-nanowire morphology and a loose aerogel structure.

[0096] The diameter and length of the high-entropy alloy nanowires prepared in Examples 1-9 were measured using the linear distance measurement method of scanning electron microscopy, and the average value was taken. The specific test data are shown in Table 1.

[0097] Table 1

[0098] Example 1 50 200 250:1 Example 2 30 130 231:1 Example 3 18 110 164:1 Example 4 70 280 250:1 Example 5 10 70 143:1 Example 6 70 350 200:1 Example 7 10 1000 10:1 Example 8 15 80 187:1 Example 9 3 100 30:1 Comparative Example 1 / / / Comparative Example 2 / / / Comparative Example 3 / / /

[0099] Note: " / " indicates that no nanowire morphology was generated, and the average length and average diameter could not be tested.

[0100] The test results show that:

[0101] (1) As can be seen from Examples 1 to 4, the high-entropy alloy nanowires prepared by the preparation method of the present invention all meet the requirements of having a diameter of 100nm-300nm, a length of 5μm-80μm, a high aspect ratio, a superior morphology, and no branches. When further applied to composite catalysts, they can expose a certain amount of active sites, ensuring that the catalyst has a certain activity. Moreover, the preparation method of the present invention is simple, universal, and the reaction process can be carried out at room temperature and normal pressure, which is safe and pollution-free, and suitable for mass production.

[0102] Furthermore, when the content of non-precious metal salts is too high or too low, the constant magnetic field is too high or too low, or the content of sodium borohydride is too high or too low, the morphology and size of the high-entropy alloy nanowires prepared will be affected, thereby affecting the degree of Pt dispersion on the nanowire surface, resulting in a reduction in the number of active sites. When further applied to composite catalysts, the performance of the catalyst will be reduced.

[0103] (2) As can be seen from Comparative Examples 1-3, if the external magnetic field is omitted, or the nucleating agents H2PtCl6 and PdCl2 are omitted, or the non-noble metal salt is omitted, the high-entropy alloy nanowire morphology cannot be obtained. In Comparative Example 2, no product is generated because the nucleating agent is omitted, which shows that the nucleating agent as a whole lowers the nucleation barrier of metal grains, making the reduction reaction easier to proceed.

[0104] Application Examples 1-9

[0105] The high-entropy alloy nanowires prepared in Examples 1-9 were mixed with commercial carbon powder at a mass ratio of 1:2.4 to obtain composite catalysts, which correspond to Application Examples 1-9 respectively.

[0106] Comparative Application Example 1

[0107] The alloy prepared in Comparative Example 1 was mixed with commercial carbon powder at a mass ratio of 1:2.4 to obtain a composite catalyst.

[0108] Comparative Application Example 2

[0109] Comparative Example 2: No product was formed.

[0110] Comparative Application Example 3

[0111] The alloy prepared in Comparative Example 3 was mixed with commercial carbon powder at a mass ratio of 1:2.4 to obtain a composite catalyst.

[0112] Comparative Application Example 4

[0113] This comparative application example uses a commercial Pt / C catalyst.

[0114] The composite catalysts prepared in Application Examples 1-9 and Comparative Application Examples 1-3, as well as the commercial Pt / C catalyst provided in Comparative Application Example 4, were subjected to linear sweep voltammetry (LSV) testing. The test parameters were as follows: scan voltage 0.05-1.05 V, scan rate 5 mV / s, rotation speed 1600 rpm. Under oxygen-flushing conditions, 0.02 mg of the composite catalyst was dropped onto a glassy carbon electrode tip with an area of ​​0.196 cm². 2 The initial mass activity value of 0.9V was calculated, and the specific test data are shown in Table 2.

[0115] Table 2

[0116] Application Example 1 336 Application Example 2 311 Application Example 3 279 Application Example 4 177 Application Example 5 156 Application Example 6 135 Application Example 7 221 Application Example 8 206 Application Example 9 143 Comparative Application Example 1 133 Comparative Application Example 2 / Comparative Application Example 3 123 Comparative Application Example 4 104

[0117] Note: " / " indicates that no product was generated and activity testing could not be performed.

[0118] The test results show that:

[0119] (1) As can be seen from Application Examples 1 to 9, when the loading of Pt in the composite catalyst is relatively high, it is dispersed in the catalyst and provides more active sites for oxygen reduction catalysis, showing a higher initial mass activity of 0.9V.

[0120] Furthermore, when the molar ratio of nucleating agent, complexing agent, ammonium salt and non-noble metal salt is limited to 1:(10-500):(200-1500):(0.5-10), the appropriate atomic ratio of Pt to non-noble metal can regulate the electronic properties of Pt to a certain extent. That is, the transition metal may act as an electron donor or acceptor, adjust the electron density on the Pt surface, affect the adsorption and reaction of oxygen molecules, and thus optimize the kinetics of oxygen reduction reaction. At the same time, the addition of an appropriate amount of transition metal may change the atomic arrangement on the platinum surface and provide more active sites.

[0121] (2) By comparing Application Example 1 and Application Example 3, it can be seen that when a high-entropy alloy with a non-nanowire morphology is prepared, the inconsistent crystal orientation at various locations affects the adsorption and desorption of oxygen intermediate species, while reducing conductivity and hindering the smooth transport of electrons in the ORR reaction, thereby reducing the activity of the composite catalyst.

[0122] (3) As can be seen from Application Example 1 and Comparative Application Example 4, in the composite catalyst of Application Example 1 of the present invention, the Pt loading is about 13 wt%, and the initial mass activity at 0.9V is 336 mA / mg. In contrast, in Comparative Application Example 4, the Pt loading is 20 wt%, which is significantly higher than that of Application Example 1, but the initial mass activity at 0.9V is only 104 mA / mg. This further indicates that the composite catalyst provided by the present invention still has relatively high activity even with a lower Pt loading, more than three times higher than that of commercial Pt / C catalysts.

[0123] In summary, this invention provides a high-entropy alloy nanowire, its preparation method, and a composite catalyst. Platinum source, palladium source, and non-precious metal salts are used as reaction raw materials for the high-entropy alloy nanowire, supplemented by the addition of a magnetic field. During the reduction process, the nucleation and growth process of magnetic metal particles and the self-assembly behavior of magnetic nanocrystals are controlled by magnetic force. This enables the preparation of high-entropy alloy nanowires with adjustable diameter and length, consistent growth direction, high purity, high dispersibility, stable structure, and uniform Pt dispersion under room temperature and atmospheric pressure conditions. The resulting composite catalyst, after mixing with commercial carbon powder, has abundant active sites and exhibits excellent oxygen reduction catalytic activity.

[0124] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing high-entropy alloy nanowires, characterized in that, The preparation method includes the following steps: A metal precursor mixture solution was placed under an external magnetic field, and a reducing agent was added to carry out a reduction reaction at 10-35℃ to obtain high-entropy alloy nanowires. The metal precursor mixed solution comprises a nucleating agent, a complexing agent, an ammonium salt, a non-precious metal salt, and a solvent; the molar ratio of the nucleating agent, complexing agent, ammonium salt, and non-precious metal salt is 1:(10-500):(200-1500):(0.5-10); the nucleating agent comprises a platinum source and a palladium source, and the ammonium salt comprises ammonium fluoride and / or ammonium chloride; The non-precious metal salts include combinations of at least three of the following: iron salts, cobalt salts, nickel salts, copper salts, or manganese salts. In the metal precursor mixed solution, the concentration of the metal element is 0 mmol / L-0.5 mmol / L, and is not 0; the molar ratio of the reducing agent to the metal element is (2-100):

1.

2. The preparation method according to claim 1, characterized in that, In the non-precious metal salt, the molar ratio of iron salt, cobalt salt, nickel salt, copper salt and manganese salt is 1:(0-10):(0-10):(0-5):(0-5), and the molar amount of at least two metal salts is not 0.

3. The preparation method according to claim 1, characterized in that, The metal precursor mixture also includes a pH adjuster.

4. The preparation method according to claim 1, characterized in that, The pH of the metal precursor mixture solution is 3-14.

5. The preparation method according to claim 4, characterized in that, The pH of the metal precursor mixture solution is 8-13.

6. The preparation method according to claim 1, characterized in that, The field strength of the external magnetic field is 0.0001T-10T.

7. The preparation method according to claim 1, characterized in that, The reducing agent includes sodium borohydride.

8. The preparation method according to claim 1, wherein the reduction reaction time is 0.01 h to 24 h.

9. The preparation method according to claim 1, characterized in that, The reduction reaction is followed by solid-liquid separation, washing, and drying.

10. The preparation method according to claim 9, characterized in that, The solid-liquid separation method includes using magnets for separation.

11. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: Nucleating agent, complexing agent, ammonium salt and non-noble metal salt are dissolved in solvent and mixed evenly. pH adjuster is added to obtain a mixed solution of metal precursors with pH of 8-13. The solution is placed under an external magnetic field with a field strength of 0.0001T-10T and a reducing agent is added to carry out a reduction reaction. After reduction at room temperature for 0.01h-24h, the reaction product is separated by a magnet. After washing and drying, high-entropy alloy nanowires are obtained. The nucleating agent comprises a platinum source and a palladium source; the non-precious metal salt comprises a combination of at least three of iron, cobalt, nickel, copper, or manganese salts; the molar ratio of iron, cobalt, nickel, copper, and manganese salts in the non-precious metal salt is 1:(0-10):(0-10):(0-5):(0-5), and the molar amount of at least two metal salts is not 0; the molar ratio of nucleating agent, complexing agent, ammonium salt, and non-precious metal salt in the metal precursor mixed solution is 1:(10-500):(200-1500):(0.5-10); the concentration of the metal element in the metal precursor mixed solution is 0 mmol / L-0.5 mmol / L, and is not 0; the reducing agent comprises sodium borohydride; the molar ratio of the reducing agent to the metal element is (2-100):

1.

12. A high-entropy alloy nanowire prepared by the preparation method according to any one of claims 1-11, characterized in that, The high-entropy alloy nanowires have a diameter of 100nm-300nm and a length of 5μm-80μm.

13. A composite catalyst, characterized in that, The composite catalyst includes high-entropy alloy nanowires prepared by the preparation method according to any one of claims 1-11, or high-entropy alloy nanowires according to claim 12.

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