A high-entropy alloy nanoflower array, a preparation method thereof and application thereof as an electrode material

Abstract

The application belongs to the technical field of high-entropy alloy catalysts, and particularly relates to a high-entropy alloy nanoflower array, a preparation method thereof and application as an electrode material. The high-entropy alloy nanoflower array comprises five metal elements of Co, Ni, Mo, Cu and Zn. The high-entropy alloy nanoflower array is composed of a plurality of two-dimensional nanosheets, and a three-dimensional (3D) porous nanostructure with a large specific surface area is constructed. The material provided by the application is simple to prepare, has high loading, does not involve noble metals, is low in cost, efficient and stable, and can be used as an electrode of a hydrogen evolution reaction, a hydrazine oxidation reaction and an OHzS (Oxidation of Hydrazine for Syngas) system. When the material is applied to the OHzS system, an industrial current density of 500 mA cm ‑2 and 1000 mA cm ‑2 can be respectively reached by using only a battery voltage of 0.260 V and 0.376 V, which shows absolute advantages of efficient and low-voltage hydrogen production, and has high practical application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-entropy alloy catalysts, and particularly relates to a high-entropy alloy nanoflower array, a preparation method thereof and application thereof as an electrode material. BACKGROUND

[0002] Hydrogen is considered as one of the most promising alternative energy sources for the next generation due to its extremely high mass energy density, zero carbon emissions and renewable advantages. Water electrolysis for hydrogen production decomposes water into hydrogen and oxygen, and is widely concerned due to high purity of the produced hydrogen and no large amount of CO2 emissions. Since water electrolysis for hydrogen production is composed of two important half-reactions of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), the OER is a relatively complex four-electron transfer process, the reaction kinetics is slow, and the theoretical potential is as high as 1.23 V, thereby leading to high power cost, and thus the large-scale application is limited. In recent years, studies have shown that the adoption of a small molecule oxidation reaction which is more favorable in thermodynamics instead of OER can greatly reduce the hydrogen production voltage and save energy, and is extremely valuable for application (Adv. Mater. 2024, 36, 2309715). The hydrazine oxidation reaction (HzOR) has a lower theoretical voltage of -0.33 V, and has been proved to be a highly promising strategy for replacing the anode OER to achieve low-voltage and high-efficiency hydrogen production. In particular, compared with the pure water electrolysis system, the hydrazine oxidation assisted hydrogen production (OHzS) system can effectively save more than half of the electrical energy, and is safer due to the byproduct being N2 instead of O2. However, the catalysts currently applied to the OHzS system have simple composition and structure and poor intrinsic activity, and it is difficult to simultaneously efficiently catalyze the cathode and anode reactions of the OHzS system. Therefore, it is still a great challenge to prepare a catalyst or electrode material capable of efficiently catalyzing the OHzS system and achieving industrial-level current density hydrogen production.

[0003] High-entropy alloy (HEA) catalysts have attracted extensive attention due to their remarkable catalytic properties. Currently, most studies have focused on powder HEA catalysts, which need to be coated on a conductive substrate for subsequent catalytic reactions. However, powder materials are prone to fall off from the conductive substrate, leading to a decrease in catalytic performance. In contrast, self-supported array electrodes formed by in-situ growth of catalysts on conductive substrates not only ensure the close contact between the catalyst and the substrate, preventing the catalyst from falling off during electrocatalysis, but also promote fast charge transfer, provide greater specific surface area and abundant active sites. In addition, porous array electrodes can also promote the diffusion of electrolyte and the rapid release of generated gas, thereby improving the overall mass transfer efficiency of the catalyst. However, due to the different physical and chemical properties of different metals, especially the different nucleation / growth kinetics of various metals in HEA, it is still a great challenge to precisely prepare high-entropy alloy nanosheet or nanoflower array materials with uniform phase structure.

[0004] To solve the above problems, the present application is proposed. SUMMARY

[0005] The present application aims to provide a high-entropy alloy nanoflower array and a preparation method thereof, and can efficiently catalyze hydrogen evolution reaction, hydrazine oxidation reaction and hydrazine oxidation assisted hydrogen production system, and has high practical application value.

[0006] The first aspect of the present application provides a high-entropy alloy nanoflower array material, which comprises: a foam cobalt substrate and a high-entropy alloy nanoflower array loaded on the foam cobalt substrate, the high-entropy alloy nanoflower array being composed of five metal elements of Co, Ni, Mo, Zn and Cu.

[0007] In the high-entropy alloy nanoflower array, the atomic percentages of Co atoms, Ni atoms, Mo atoms, Zn atoms and Cu atoms are all 0.5% to 60%.

[0008] Preferably, the high-entropy alloy nanoflower array is composed of a plurality of two-dimensional nanosheets, the plurality of two-dimensional nanosheets have different orientations, and the two-dimensional nanosheets are perpendicular to the foam cobalt substrate.

[0009] The second aspect of the present application provides a preparation method of the high-entropy alloy nanoflower array material of the first aspect, comprising the following steps:

[0010] Step a, placing a water-soluble molybdenum salt and a precipitating agent in a reaction container, adding water and dissolving to obtain a first mixed solution;

[0011] Step b, adding a water-soluble cobalt salt, a water-soluble nickel salt, a water-soluble copper salt and a water-soluble zinc salt to the first mixed solution, and mixing to obtain a second mixed solution;

[0012] Step c, placing foam cobalt into the above reaction container, closing the reaction container, and reacting the reaction container at 80-120℃ for 8-12h to obtain a foam cobalt loaded high-entropy alloy nanoflower array precursor;

[0013] Step d, placing a reducing agent and the foam cobalt loaded high-entropy alloy nanoflower array precursor obtained in step c into a reaction container, closing the reaction container, and reacting at 140-160℃ for 8-12h to obtain a foam cobalt loaded high-entropy alloy nanoflower array.

[0014] Preferably, the water-soluble molybdenum salt in step a is (NH4)6Mo7O 24 4H2O, and the precipitating agent is CO(NH2)2.

[0015] Preferably, the reducing agent in step d is a glycol solution containing sodium borohydride and sodium hydroxide, wherein the concentration of sodium hydroxide in the glycol solution is 0.3-0.8 mol / L, and the concentration of sodium borohydride in the glycol solution is 0.03-0.07 mol / L.

[0016] Preferably, the mass ratio of the sodium borohydride to the high-entropy alloy nanoflower array precursor is 1:1.5.

[0017] Preferably, in the first mixed solution, the concentration of the water-soluble molybdenum salt is 0.01-0.03 mol / L, and the concentration of the precipitant is 0.25-0.45 mol / L.

[0018] Preferably, the added amounts of the water-soluble cobalt salt, the water-soluble nickel salt, the water-soluble zinc salt, and the water-soluble copper salt are 0.02-0.04 mol / L, 0.025-0.04 mol / L, 0.01-0.02 mol / L, and 0.004-0.02 mol / L, respectively, in terms of molar volume ratio to the first mixed solution.

[0019] The third aspect of the present application provides a use of the high-entropy alloy nanoflower array material of the first aspect for catalyzing a hydrogen evolution reaction.

[0020] The fourth aspect of the present application provides a use of the high-entropy alloy nanoflower array material of the first aspect for catalyzing a hydrazine oxidation reaction.

[0021] The fifth aspect of the present application provides a use of the high-entropy alloy nanoflower array material of the first aspect as a cathode and / or anode material of a hydrazine oxidation assisted hydrogen production system.

[0022] The present application has the following beneficial results:

[0023] (1) The present application first prepares a high-entropy alloy nanoflower array, and realizes the controllable synthesis of a high-entropy alloy nanoflower array with a uniform phase. Meanwhile, the preparation method of the present application is simple, and all the elements used are non-noble metal elements, thus greatly reducing the cost of preparation.

[0024] (2) The high-entropy alloy nanoflower array prepared by the present application has multiple components, realizes the construction of multiple active sites, has an adjustable electronic structure, and thus exhibits excellent hydrogen evolution reaction, hydrazine oxidation reaction, and hydrazine oxidation assisted hydrogen production system catalytic performance, as well as extremely excellent stability.

[0025] (3) The present application unexpectedly finds that, compared with other foam metal substrates, such as a foam nickel, the high-entropy alloy nanoflower array prepared by the present application has a higher loading amount on a foam cobalt substrate, thus providing a larger electrochemical active specific surface area, exposing more active sites, and having a more sufficient contact with an electrolyte.

[0026] (4) The array prepared by the present application is in close contact with the substrate, which promotes the rapid transfer of charges and can effectively prevent the catalyst from falling off during the electrocatalysis process, especially under industrial-level high current density. In addition, it has super gas-repellent properties, which can promote the diffusion of electrolyte and the rapid release of generated gas, thereby improving the overall mass transfer efficiency and having strong practical applicability.

[0027] (5) Not all random combinations of metal types can be used to form a uniformly distributed high-entropy alloy nanoflower array by the method of the present application. The present application particularly selects Co, Ni, Mo, Zn, and Cu five metals, and unexpectedly finds that they can form a high-entropy alloy nanoflower array with uniform element distribution, and unexpectedly find that they have excellent performance as hydrogen evolution reaction and hydrazine oxidation reaction catalysts. Among them: Zn and Cu metal elements are rarely used as hydrogen evolution reaction materials, but in the material of the present application, Zn and Cu can play a role in regulating the electronic structure of other metals, increasing the entropy and stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a scanning electron microscope (SEM) image of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1.

[0029] Figure 2 is a high-resolution transmission electron microscope (HRTEM) image of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1.

[0030] Figure 3 is an X-ray diffraction (XRD) pattern of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1.

[0031] Figure 4 is an atomic structure characterization diagram of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 1.

[0032] Figure 5 is an element distribution diagram (Mapping) of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 1.

[0033] Figure 6 is the result of inductively coupled plasma elemental analysis (ICP) of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1.

[0034] Figure 7 a and b are linear sweep voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, the foam cobalt substrate of Example 1, and commercial Pt / C as electrode materials for hydrogen evolution reaction and hydrazine oxidation reaction.

[0035] Figure 8 are the chronoamperometric curves (i-t) of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 and commercial Pt / C for hydrogen evolution reaction and hydrazine oxidation reaction. dl ) values

[0036] Figure 9 a and b are the Nyquist curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, the foam cobalt substrate of Example 1 and commercial Pt / C for hydrogen evolution reaction and hydrazine oxidation reaction.

[0037] Figure 10 a and b are the chronoamperometric curves (i-t) of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 and commercial Pt / C for hydrogen evolution reaction and hydrazine oxidation reaction.

[0038] Figure 11 a and b are the LSV performance comparison of the OhzS and OWS systems with the electrodes constructed, the electrolytes used are 1.0 molar potassium hydroxide solution containing 0.2 molar hydrazine hydrate (N2H4) and 1.0 molar potassium hydroxide solution, respectively.

[0039] Figure 12 are the chronoamperometric curves (i-t) of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 for OhzS system.

[0040] Figure 13 are the high resolution transmission electron microscope (HRTEM) images of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2.

[0041] Figure 14 are the element mapping (Mapping) images of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 2.

[0042] Figure 15 are the results of inductively coupled plasma elemental analysis (ICP) of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2.

[0043] Figure 16 a and 16b are the linear sweep voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2 as electrode material for hydrogen evolution reaction and hydrazine oxidation reaction.

[0044] Figure 17 are the scanning electron microscope (SEM) images of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 3.

[0045] Figure 18 a and 18b are linear voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array as an electrode material for hydrogen evolution reaction and hydrazine oxidation reaction obtained in Example 3.

[0046] Figure 19 is a scanning electron microscope (SEM) image of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 4.

[0047] Figure 20 a and 20b are linear voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array as an electrode material for hydrogen evolution reaction and hydrazine oxidation reaction obtained in Example 4.

[0048] Figure 21 is a linear voltammetry (LSV) test curve of the catalytic material obtained in Comparative Example 1 and the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 for hydrogen evolution reaction.

[0049] Figure 22 is a scanning electron microscope (SEM) image of the catalytic material obtained in Comparative Example 2.

[0050] Figure 23 is a linear voltammetry (LSV) test curve of the catalytic material obtained in Comparative Example 3 and the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 for hydrogen evolution reaction. DETAILED DESCRIPTION

[0051] The present application is further described in conjunction with the specific examples. These specific examples are intended to be illustrative only and not limiting of the scope of the present application.

[0052] Example 1

[0053] The high-entropy alloy nanoflower array material was prepared by the following steps:

[0054] Step a, (NH4)6Mo7O 24 ·4H2O and CO(NH2)2 were placed in a 100 mL reaction kettle, 40 mL of deionized water was added and ultrasonic dissolution was performed to obtain a first mixed solution so that the concentration of (NH4)6Mo7O 24 ·4H2O in the first mixed solution was 0.03 moles / liter and the concentration of CO(NH2)2 was 0.45 moles / liter.

[0055] Step b, adding Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, Cu(NO3)2·3H2O into the first mixed solution, ultrasonic mixing to obtain a second mixed solution; the adding amount of the water-soluble cobalt salt, the water-soluble nickel salt, the water-soluble copper salt, the water-soluble zinc salt is 0.04 mol / L, 0.04 mol / L, 0.02 mol / L, 0.02 mol / L respectively, and the molar volume ratio of the adding amount to the first mixed solution is 0.04 mol / L, 0.04 mol / L, 0.02 mol / L, 0.02 mol / L respectively.

[0056] Step c, placing the 2cm*4cm size foam cobalt into 40mL of 6mol / L HCl solution, ultrasonic treatment for 3min, then using deionized water and ethanol to ultrasonic cleaning the foam cobalt for three times respectively, then blowing dry the foam cobalt, and putting it into the above-mentioned 100mL reactor, making it fully immersed in the solution, closing the reactor, and moving the reactor into the air oven, reacting at 120℃ for 12h. After the reaction is completed, the foam cobalt with sample is taken out, and deionized water and ethanol are used to ultrasonic clean it for three times respectively, and after cleaning, it is put into the air oven and dried at 80℃ for 8h to obtain foam cobalt loaded 0.15g NiCoMoZnCu high-entropy alloy nanoflower array precursor;

[0057] Step d, pouring 36mL of ethylene glycol solution containing 0.07mol / L of sodium borohydride and 0.8mol / L of sodium hydroxide into a 50mL reactor, then putting the foam cobalt loaded 0.15g high-entropy alloy nanoflower array precursor obtained in step c into the reactor (the mass ratio of sodium borohydride to high-entropy alloy nanoflower array precursor is 1:1.5), making it fully immersed in the solution, closing the reactor, and moving the reactor into the air oven, reacting at 160℃ for 12h. After the reaction is completed, the reduced sample is taken out, and deionized water and ethanol are used to ultrasonic clean it for three times respectively, and after cleaning, it is put into the vacuum drying oven and dried at 60℃ for 2h to obtain foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array, and it is stored under the condition of oxygen isolation for standby use.

[0058] Figure 1 is the scanning electron microscope (SEM) image of the foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, it can be seen that the NiCoMoZnCu high-entropy alloy nanoflower array is composed of multiple two-dimensional nanosheets, the two-dimensional nanosheets have different orientations, and the two-dimensional nanosheets are perpendicular to the foam cobalt substrate, constructing a stable nanoflower array structure. It is worth noting that the obtained foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array is collected after sufficient ultrasonic treatment, so the dense nanoflower array indicates that the foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array is tightly combined with the foam cobalt substrate.

[0059] Figure 2 is the high-resolution transmission electron microscopy (HRTEM) image of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, further confirming that each nanoflower is composed of multiple two-dimensional nanosheets, constructing a three-dimensional (3D) porous nanostructure with a large specific surface area.

[0060] Figure 3 is the X-ray diffraction (XRD) pattern of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, no obvious diffraction peaks of other impurities are observed, and compared with the characterization diffraction peaks of pure Co, Ni, Mo, Zn and Cu, the diffraction peaks of the catalytic material obtained in Example 1 are obviously shifted, indicating that the NiCoMoZnCu high-entropy alloy nanoflower array with single-phase structure is successfully synthesized.

[0061] Figure 4 is the atomic structure characterization image of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 1, it can be clearly seen that the five atoms of Co, Ni, Mo, Zn and Cu are uniformly dispersed in the bright sublattice, which further indicates that the NiCoMoZnCu high-entropy alloy nanoflower with single-phase structure is successfully synthesized.

[0062] Figure 5 is the element distribution map (Mapping) of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 1, clearly showing that the five elements of Co, Ni, Mo, Zn and Cu are uniformly distributed in the high-entropy alloy nanoflower, without phase separation.

[0063] Figure 6 is the result of inductively coupled plasma elemental analysis (ICP) of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, it can be seen that the atomic percentage of the five metal atoms is Co:Ni:Mo:Zn:Cu = 59%:27%:7%:5%:2%. The sum of the atomic percentages of the five metal atoms is 100%.

[0064] Figure 7 a and 7b are the linear sweep voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, the foam cobalt substrate of Example 1 and commercial Pt / C as electrode materials for hydrogen evolution reaction and hydrazine oxidation reaction. The electrolyte used for hydrogen evolution reaction is 1.0 mol / L potassium hydroxide solution. The electrolyte used for hydrazine oxidation reaction is 1.0 mol / L potassium hydroxide solution containing 0.3 mol / L hydrazine hydrate (N2H4). In Figure 7As can be seen in Example 1, the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array exhibits superior catalytic performance compared to a simple cobalt-supported foam substrate and commercial Pt / C. For the hydrogen evolution reaction, it requires only relatively low overpotentials of 242.9 mV and 307.5 mV, respectively, to reach 500 mA cm⁻¹. -2 and 1000mA cm -2 The current density is superior to that of cobalt foam substrates (635.2 mV and 684.9 mV) and commercial Pt / C (365.5 mV and 437.5 mV). For the hydrazine oxidation reaction, it requires only lower operating potentials of -18.6 mV and 16.9 mV, respectively, to reach 500 mA cm⁻¹. -2 and 1000mA cm -2 The current density is significantly higher than that of cobalt foam substrates and commercial Pt / C, which require higher operating potentials of 162.5 mV and 103.2 mV, respectively, to reach 500 mA cm⁻¹. -2 The current density is [value missing]. This demonstrates that the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array of the present invention exhibits excellent catalytic performance for the hydrogen evolution reaction and hydrazine oxidation reaction.

[0065] Figure 8 The bilayer capacitance (C0) of the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 and commercial Pt / C as the electrode material at different scan rates is shown. dl ) value. C dl The values ​​can be obtained using cyclic voltammetry (CV), and the electrochemical active area (ECSA) was then evaluated. Figure 8 As can be seen, the C of the NiCoMoZnCu high-entropy alloy nanoflower array supported by cobalt foam... dl The value is as high as 268.8mF cm -2 This significantly exceeds that of commercial Pt / C electrodes. This indicates that the NiCoMoZnCu high-entropy alloy nanoflower array supported on cobalt foam possesses an ultra-high effective electrochemical area. The main reason for this is that the loading of the NiCoMoZnCu high-entropy alloy nanoflower array grown on the cobalt foam substrate can reach 5.8 mg.

[0066] Figure 9 a and 9b are Nyquist curves for the hydrogen evolution reaction and hydrazine oxidation reaction, respectively, of the cobalt-foam-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1, the cobalt-foam substrate of Example 1, and commercial Pt / C. In comparison, the cobalt-foam-supported NiCoMoZnCu high-entropy alloy nanoflower array exhibits a lower charge transfer resistance (Ro). ctThis further confirms that the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array exhibits faster hydrogen evolution reaction and hydrazine oxidation reaction kinetics at the electrolyte / catalyst interface.

[0067] Figure 10 a and 10b are the chronoamperometry (IT) curves of the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 and commercial Pt / C for the hydrogen evolution reaction and hydrazine oxidation reaction. It can be seen that for the hydrogen evolution reaction, at 100 mA cm⁻¹... -2 At a current density of 50 mA cm⁻¹, the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 can operate stably for 55 hours, maintaining 98.2% of the initial current density. In contrast, the commercial Pt / C electrode can only maintain 73.4% of the initial current density after 15 hours of operation. For the hydrazine oxidation reaction, at 50 mA cm⁻¹... -2 At the specified current density, the cobalt-fed NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 maintained 96.8% of its initial current density after 50 hours of continuous testing, while the commercial Pt / C electrode could only maintain 65.6% of its initial current density after 7 hours of testing. The above results indicate that the cobalt-fed NiCoMoZnCu high-entropy alloy nanoflower array obtained in this invention has superior stability against hydrogen evolution reaction and hydrazine oxidation reaction.

[0068] Figure 11 a and 11b are comparisons of the LSV performance of hydrazine oxidation-assisted hydrogen production (OHzS) and water electrolysis (OWS) systems composed of various electrodes.

[0069] in, Figure 11 a is a comparison of the LSV performance of the OHzS system constructed from the foamed cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 and commercial Pt / C as the cathode and anode catalysts.

[0070] Figure 11 b is a comparison of the LSV performance of the OHzS and OWS systems constructed using the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array from Example 1 as both cathode and anode catalysts.

[0071] The electrolyte used in the OHzS system is a 1.0 mol / L potassium hydroxide solution containing 0.2 mol / L hydrazine hydrate (N₂H₄). All electrolytes in the OWS system are 1.0 mol / L potassium hydroxide solutions. Figure 10It can be seen in a that the OhzS system composed of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 as cathode and anode catalysts only needs a cell voltage of 0.081, 0.260 and 0.376 V to achieve a current density of 100, 500 and 1000 mA cm -2 , and can also achieve a high current density of 2000 mA cm -2 at a lower cell voltage of 0.646 V, while the OhzS system composed of commercial Pt / C as cathode and anode catalysts can only achieve a current density of 622.5 mA cm -2 at the same voltage. This shows that the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 has extremely high intrinsic activity for the OhzS system. Meanwhile, in Figure 10 It can be seen in b that for the OWS system composed of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 as cathode and anode catalysts, it needs a higher cell voltage of 1.729, 1.885 and 1.975 V to achieve a current density of 100, 500 and 1000 mA cm -2 . This shows that the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array material of Example 1 has an absolute advantage in efficient hydrogen production in the OhzS system compared to the OWS system.

[0072] Figure 12 is the chronoamperogram (i-t) of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array of Example 1 for the OhzS system. It can be seen that the OhzS system composed of the NiCoMoZnCu high-entropy alloy nanoflower array can be stably operated at a current density of 500 mA cm -2 for 300 h, showing super-strong stability.

[0073] Example 2

[0074] The high-entropy alloy nanoflower array is prepared by the following steps

[0075] Step a, (NH4)6Mo7O 24 ·4H2O and CO(NH2)2 are placed in a 100 mL reaction kettle, 40 mL of deionized water is added and ultrasonic dissolution is performed to obtain a first mixed solution such that the concentration of (NH4)6Mo7O 24 ·4H2O in the first mixed solution is 0.03 moles / liter and the concentration of CO(NH2)2 is 0.38 moles / liter.

[0076] Step b, Co(NO3)2.6H2O, Ni(NO3)2.6H2O, Zn(NO3)2.6H2O, Cu(NO3)2.3H2O were added into the first mixed solution, ultrasonic mixing to obtain a second mixed solution; the water-soluble cobalt salt, water-soluble nickel salt, water-soluble copper salt, water-soluble zinc salt were added in the molar volume ratio of 0.04 mol / L, 0.04 mol / L, 0.02 mol / L, 0.01 mol / L, respectively, to the first mixed solution.

[0077] Step c, the 2cm x 4cm size of the foam cobalt was placed in 40mL of 6mol / L HCl solution, ultrasonic treatment for 3min, then the foam cobalt was ultrasonic cleaned with deionized water and ethanol for three times respectively, then the foam cobalt was blown dry, put into the above-mentioned 100mL reaction kettle, make it completely immersed in the solution, close the reaction kettle, move the reaction kettle into the air oven, react at 120℃ for 8h. After the reaction was completed, the foam cobalt with sample was taken out, ultrasonic cleaned with deionized water and ethanol for three times respectively, after cleaning, it was put into the air oven and dried at 80℃ for 8h, to obtain 0.12g of foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array precursor;

[0078] Step d, 36mL of ethylene glycol solution containing 0.06mol / L of sodium borohydride and 0.7mol / L of sodium hydroxide was poured into a 50mL reaction kettle, then 0.12g of high-entropy alloy nanoflower array precursor obtained in step c was put into the reaction kettle (the mass ratio of sodium borohydride to high-entropy alloy nanoflower array precursor was 1:1.5), make it completely immersed in the solution, close the reaction kettle, move the reaction kettle into the air oven, react at 160℃ for 12h. After the reaction was completed, the reduced sample was taken out, ultrasonic cleaned with deionized water and ethanol for three times respectively, after cleaning, it was put into the vacuum drying oven and dried at 60℃ for 2h, to obtain foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array, and stored under the condition of oxygen isolation for standby use.

[0079] Figure 13 is the high-resolution transmission electron microscope (HRTEM) of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2, it can be seen that each nanoflower is composed of multiple two-dimensional nanosheets, which constructs a three-dimensional (3D) porous nanostructure with large surface area.

[0080] Figure 14 is the element distribution map (Mapping) of the NiCoMoZnCu high-entropy alloy nanoflower obtained in Example 2, which clearly shows that the five elements of Co, Ni, Mo, Zn and Cu are uniformly distributed in the high-entropy alloy nanoflower, and no phase separation occurs.

[0081] Figure 15 The results of inductively coupled plasma elemental analysis (ICP) of the NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2 show that the atomic percentages of the five metals are: Co:Ni:Mo:Zn:Cu = 56.6%:29.8%:6.9%:6.0%:0.7%. The highest percentage of any metal is close to 60%, while the lowest is close to 0.5%. This demonstrates that the content of each element in the high-entropy alloy nanoflower array can be controlled by adjusting the amount of metal salt added; the atomic percentages of Co, Ni, Mo, Zn, and Cu atoms are all between 0.5% and 60%.

[0082] Figure 16 Figures a and 16b show the linear voltammetry (LSV) curves of the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 2 as electrode materials for the hydrogen evolution reaction and hydrazine oxidation reaction. The electrolyte used for the hydrogen evolution reaction was a 1.0 mol / L potassium hydroxide solution. The electrolyte used for the hydrazine oxidation reaction was a 1.0 mol / L potassium hydroxide solution containing 0.1 mol / L hydrazine hydrate (N₂H₄). Figure 16 As can be seen in section a, for the hydrogen evolution reaction, only relatively low overpotentials of 65.6 and 151.3 mV are required to reach 10 and 100 mA cm⁻¹, respectively. -2 The current density. Figure 16 As shown in b, for the hydrazine oxidation reaction, only relatively low operating potentials of -61.8 and -9.1 mV are required to reach 10 and 100 mA cm⁻¹, respectively. -2 The current density.

[0083] Example 3

[0084] High-entropy alloy nanoflower arrays were prepared using the following steps.

[0085] Step a, (NH4)6Mo7O 24 ·4H2O and CO(NH2)2 were placed in a 100mL reactor, 40mL of deionized water was added and the mixture was dissolved by sonication to obtain a first mixed solution. In this first mixed solution, (NH4)6Mo7O 24 The concentration of ·4H2O is 0.03 mol / L, and the concentration of CO(NH2)2 is 0.45 mol / L.

[0086] Step b, adding Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, Cu(NO3)2·3H2O into the first mixed solution, ultrasonic mixing to obtain a second mixed solution; the adding amount of the water-soluble cobalt salt, the water-soluble nickel salt, the water-soluble copper salt, and the water-soluble zinc salt is 0.02 mol / L, 0.04 mol / L, 0.01 mol / L, and 0.004 mol / L, respectively, in terms of molar volume ratio with the first mixed solution.

[0087] Step c, placing the 2 cm x 4 cm size foam cobalt into 40 mL of 6 mol / L HCl solution, ultrasonic treatment for 3 min, then ultrasonic cleaning the foam cobalt with deionized water and ethanol for three times respectively, then blowing dry the foam cobalt, and putting it into the above-mentioned 100 mL reactor, making it completely immersed in the solution, closing the reactor, and moving the reactor into the air oven, and reacting at 120°C for 8 h. After the reaction is completed, the foam cobalt with the sample is taken out, and ultrasonic cleaning is performed with deionized water and ethanol for three times respectively, and after cleaning, it is placed in the air oven and dried at 80°C for 8 h to obtain a foam cobalt loaded 0.08 g NiCoMoZnCu high-entropy alloy nanoflower array precursor;

[0088] Step d, pouring 36 mL of ethylene glycol solution containing 0.04 mol / L sodium borohydride and 0.3 mol / L sodium hydroxide into a 50 mL reactor (the mass ratio of the sodium borohydride to the high-entropy alloy nanoflower array precursor is 1:1.5), and then putting the high-entropy alloy nanoflower array precursor obtained in step c into the reactor, making it completely immersed in the solution, closing the reactor, and moving the reactor into the air oven, and reacting at 140°C for 12 h. After the reaction is completed, the reduced sample is taken out, and ultrasonic cleaning is performed with deionized water and ethanol for three times respectively, and after cleaning, it is placed in a vacuum drying oven and dried at 60°C for 2 h to obtain a foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array, and it is stored under the condition of oxygen isolation for standby use.

[0089] Figure 17 is a scanning electron microscope (SEM) image of the foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 3, and it can be seen that after adjusting the adding amount of the metal salt, the morphology structure is still a nanoflower array structure.

[0090] Figure 18a and 18b are linear sweep voltammetry (LSV) test curves of the foam cobalt supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 3 as electrode material for hydrogen evolution reaction and hydrazine oxidation reaction. The electrolyte used for hydrogen evolution reaction is 1.0 mol / L potassium hydroxide solution. The electrolyte used for hydrazine oxidation reaction is 1.0 mol / L potassium hydroxide solution containing 0.1 mol / L hydrazine hydrate (N2H4). In Figure 18 a, it can be seen that for hydrogen evolution reaction, only a lower overpotential of 66.2 and 140.8 mV respectively is needed to reach a current density of 10 and 100 mA cm -2 -2, respectively. In Figure 18 b, it can be seen that for hydrazine oxidation reaction, only a lower working potential of -60.5 and -14.1 mV respectively is needed to reach a current density of 10 and 100 mA cm -2 -2, respectively.

[0091] Example 4

[0092] The high-entropy alloy nanoflower array is prepared by the following steps

[0093] Step a, (NH4)6Mo7O 24 ·4H2O and CO(NH2)2 are placed in a 100 mL reaction kettle, 40 mL of deionized water is added and ultrasonic dissolution is performed to obtain a first mixed solution, so that in the first mixed solution, the concentration of (NH4)6Mo7O 24 ·4H2O is 0.01 mol / L, and the concentration of CO(NH2)2 is 0.25 mol / L.

[0094] Step b, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O and Cu(NO3)2·3H2O are added to the first mixed solution, and ultrasonic mixing is performed to obtain a second mixed solution; the added amounts of the water-soluble cobalt salt, the water-soluble nickel salt, the water-soluble copper salt and the water-soluble zinc salt are 0.04 mol / L, 0.025 mol / L, 0.01 mol / L and 0.004 mol / L, respectively, in terms of molar volume ratio with the first mixed solution.

[0095] Step c: Place a 2cm × 4cm cobalt foam in 40mL of 6 mol / L HCl solution and sonicate for 3 min. Then, sonicate the cobalt foam three times with deionized water and ethanol respectively. After drying the cobalt foam, place it in the 100mL reaction vessel to completely immerse it in the solution. Seal the reaction vessel and transfer it to a forced-air drying oven. React at 80℃ for 12 h. After the reaction is complete, remove the cobalt foam with the sample and sonicate it three times with deionized water and ethanol respectively. After cleaning, place it in a forced-air drying oven and dry at 80℃ for 8 h to obtain 0.06g of NiCoMoZnCu high-entropy alloy nanoflower array precursor loaded with cobalt foam.

[0096] Step d: Pour 36 mL of ethylene glycol solution containing 0.03 mol / L sodium borohydride and 0.4 mol / L sodium hydroxide into a 50 mL reaction vessel. Then, place the high-entropy alloy nanoflower array precursor obtained in step c into the reaction vessel (the mass ratio of sodium borohydride to the high-entropy alloy nanoflower array precursor is 1:1.5), ensuring it is completely immersed in the solution. Seal the reaction vessel and transfer it to a forced-air drying oven, reacting at 140 °C for 8 h. After the reaction is complete, remove the reduced sample and ultrasonically clean it three times with deionized water and ethanol, respectively. After cleaning, place it in a vacuum drying oven and dry it at 60 °C for 2 h to obtain a cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array, which is then stored under oxygen-free conditions for later use.

[0097] Figure 19 This is a scanning electron microscope (SEM) image of the cobalt foam-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 4. It can be seen that even after adjusting the amount of metal salt added and the composition of the reducing agent, its morphology and structure remain a nanoflower array structure.

[0098] Figure 20 Figures a and 20b show the linear voltammetry (LSV) curves of the cobalt-supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 4 as electrode materials for the hydrogen evolution reaction and hydrazine oxidation reaction. The electrolyte used for the hydrogen evolution reaction was a 1.0 mol / L potassium hydroxide solution. The electrolyte used for the hydrazine oxidation reaction was a 1.0 mol / L potassium hydroxide solution containing 0.1 mol / L hydrazine hydrate (N₂H₄). Figure 20 As can be seen in section a, for the hydrogen evolution reaction, only relatively low overpotentials of 75.3 and 167.2 mV are required to reach 10 and 100 mA cm⁻¹, respectively. -2 The current density. Figure 20 As shown in b, for the hydrazine oxidation reaction, only relatively low operating potentials of -43.3 and 14.9 mV are required to reach 10 and 100 mA cm⁻¹, respectively. -2current density. The experimental data shown in the figures fully demonstrate the excellent performance of the NiCoMoZnCu high-entropy alloy nanoflower array catalyst of the present application, many of whose physical and chemical properties have greatly exceeded the current commercial Pt / C catalyst, and it is a major breakthrough in the field of high-entropy alloy catalyst materials, and has considerable prospects in practical applications.

[0099] Comparative Example 1

[0100] Referring to the method in Example 1, the cobalt foam substrate is replaced by a nickel foam substrate, and the other steps remain unchanged to obtain a nickel foam supported high-entropy alloy nanoflower array. The loading of the high-entropy alloy nanoflower array grown on the nickel foam substrate is 1 mg.

[0101] Figure 21 are linear voltammetry (LSV) test curves of the catalytic material obtained in Comparative Example 1 and the cobalt foam supported NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 for hydrogen evolution reaction. The electrolyte used is 1.0 mol / L potassium hydroxide solution. In Figure 21 It can be seen in that for hydrogen evolution reaction, the NiCoMoZnCu high-entropy alloy nanoflower array grown on the cobalt foam substrate in Example 1 only needs a lower overpotential of 63.1 and 139.6 mV to reach a current density of 10 and 100 mAcm -2 , which is better than the material obtained in Comparative Example 1 (79.8 mV) and 167.6 mV). The main reason is that the loading of the nickel foam substrate (1 mg) is much lower than the loading of the cobalt foam substrate (5.8 mg), which makes it have a lower electrochemical specific surface area, thereby leading to a decrease in catalytic activity. This shows that the selection of cobalt foam as the substrate in the present application has an unexpected technical effect.

[0102] Comparative Example 2

[0103] Referring to the method in Example 1, the concentration of sodium borohydride in the ethylene glycol solution is changed to 0.35 mol / L.

[0104] Figure 22 is a scanning electron microscope (SEM) image of the catalytic material obtained in Comparative Example 2. It can be seen that when the concentration of sodium borohydride is increased, the high-entropy alloy nanoflower array structure will collapse, and the overall morphology is granular.

[0105] Comparative Example 3

[0106] Referring to the method in Example 1, (NH4)6Mo7O 24 ·4H2O is no longer dissolved alone, but is ultrasonically dissolved together with other metal salts.

[0107] The specific method is as follows:

[0108] A high-entropy alloy nanoflower array material is prepared by the following steps:

[0109] Step a, 1.07 mmol of (NH4)6Mo7O 24 4H2O, 1.5 mmol of Co(NO3)2·6H2O, 1.5 mmol of Ni(NO3)2·6H2O, 0.9 mmol of Zn(NO3)2·6H2O, 0.75 mmol of Cu(NO3)2·3H2O, and 18 mmol of CO(NH2)2are placed in a 100 mL reaction kettle, 40 mL of deionized water is added and ultrasonic dissolution is performed to obtain a mixed solution;

[0110] Step b, a 2 cm x 4 cm size of cobalt foam is placed in 40 mL of 6M HCl solution, ultrasonic treatment is performed for 3 min, then the cobalt foam is ultrasonically cleaned with deionized water and ethanol for three times respectively, then the cobalt foam is blown dry and placed in the above-mentioned 100 mL reaction kettle, so that it is completely immersed in the solution, the reaction kettle is closed, and the reaction kettle is moved into a blast oven, and reaction is performed at 120°C for 12 h. After the reaction is completed, the cobalt foam with the sample is taken out, ultrasonic cleaning is performed with deionized water and ethanol for three times respectively, and then the cobalt foam is placed in a blast oven and dried at 80°C for 8 h to obtain a foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array precursor;

[0111] Step c, 36 mL of ethylene glycol solution containing 0.07 M sodium borohydride and 0.8 M sodium hydroxide is poured into a 50 mL reaction kettle, and the high-entropy alloy nanoflower array precursor obtained in step c is placed in the reaction kettle, so that it is completely immersed in the solution, the reaction kettle is closed, and the reaction kettle is moved into a blast oven and reacted at 160°C for 12 h. After the reaction is completed, the reduced sample is taken out, ultrasonic cleaning is performed with deionized water and ethanol for three times respectively, and then the sample is placed in a vacuum drying box and dried at 60°C for 2 h to obtain a catalytic material, which is stored under the condition of oxygen isolation for standby use.

[0112] Figure 23 are the linear voltammetry (LSV) test curves of the catalytic material obtained in Comparative Example 3 and the foam cobalt loaded NiCoMoZnCu high-entropy alloy nanoflower array obtained in Example 1 for the hydrogen evolution reaction. The electrolyte used is 1.0 mol / L potassium hydroxide solution. It can be seen that when (NH4)6Mo7O 24 4H2O is dissolved together with other metal salts, the performance of the obtained catalytic material is poor, and a lower overpotential of 201.5 and 304.7 mV respectively is needed to reach 10 and 100 mA cm -2current density. The NiCoMoZnCu high-entropy alloy nanoflower array grown on the Co foam substrate of Example 1 only needs a lower overpotential of 63.1 and 139.6 mV to achieve a current density of 10 and 100 mA cm -2 , respectively. The main reason is that (NH4)6Mo7O 24 ·4H2O produces insoluble precipitates when it is dissolved together with other metal salts, which affects the growth of the high-entropy alloy nanoflower array on the Co foam substrate and further leads to the deterioration of its catalytic performance.

Claims

1. A high-entropy alloy nanoflower array material, characterized in that, The high-entropy alloy nanoflower array material comprises: a cobalt foam substrate and a high-entropy alloy nanoflower array loaded on the cobalt foam substrate, wherein the high-entropy alloy nanoflower array is composed of five metallic elements: Co, Ni, Mo, Zn, and Cu. In the high-entropy alloy nanoflower array, the atomic percentages of Co atoms, Ni atoms, Mo atoms, Zn atoms, and Cu atoms are all 0.5% to 60%.

2. A method for preparing the high-entropy alloy nanoflower array material according to claim 1, comprising the following steps: Step a: Place the water-soluble molybdenum salt and precipitant in a reaction vessel, add water and dissolve to obtain the first mixed solution; Step b: Add water-soluble cobalt salt, water-soluble nickel salt, water-soluble copper salt, and water-soluble zinc salt to the first mixed solution, mix, and obtain a second mixed solution; Step c: Place the cobalt foam into the above reaction vessel, seal the reaction vessel, and react the reaction vessel at 80-120 ℃ for 8-12 h to obtain the cobalt foam-supported high-entropy alloy nanoflower array precursor. Step d: Place the reducing agent and the foam cobalt-supported high-entropy alloy nanoflower array precursor obtained in step c into a reaction vessel, seal the reaction vessel, and react at 140-160℃ for 8-12 h to obtain the foam cobalt-supported high-entropy alloy nanoflower array. The water-soluble molybdenum salt in step a is (NH4)6Mo7O 24 ·4H2O, the precipitant is CO(NH2)2; In step d, the reducing agent is an ethylene glycol solution containing sodium borohydride and sodium hydroxide, wherein the concentration of sodium hydroxide in the ethylene glycol solution is 0.3-0.8 mol / L, and the concentration of sodium borohydride in the ethylene glycol solution is 0.03-0.07 mol / L. In the first mixed solution, the concentration of water-soluble molybdenum salt is 0.01-0.03 mol / L, and the concentration of precipitant is 0.25-0.45 mol / L; The amounts of water-soluble cobalt salt, water-soluble nickel salt, water-soluble zinc salt, and water-soluble copper salt added are such that the concentrations of the water-soluble cobalt salt, water-soluble nickel salt, water-soluble zinc salt, and water-soluble copper salt in the second mixed solution are, in order: 0.02-0.04 mol / L, 0.025-0.04 mol / L, 0.01-0.02 mol / L, and 0.004-0.02 mol / L.

3. The use of the high-entropy alloy nanoflower array material of claim 1 for catalyzing the hydrogen evolution reaction.

4. The use of the high-entropy alloy nanoflower array material of claim 1 for catalyzing the oxidation reaction of hydrazine.

5. The use of the high-entropy alloy nanoflower array material of claim 1 as a cathode and / or anode material in a hydrazine oxidation-assisted hydrogen production system.

Images