Preparation method and application of substrate-free high-entropy nanoflower powder used as efficient oxygen evolution catalyst

Abstract

The invention relates to a preparation method and application of substrate-free high-entropy nanoflower powder used as an efficient oxygen evolution catalyst, and the preparation method comprises the following steps: A) dispersing metal salts such as Fe, Co, Ni, Cr, Mn, Al, Zn and Cu in a solvent to obtain a uniform solution 1; b) adding a reaction condition agent and a morphology regulator into the solution 1 to obtain a turbid liquid 2; c) transferring the turbid liquid 2 into a hydrothermal reaction kettle, and firing to obtain turbid liquid 3; and D) washing and centrifuging the turbid liquid 3, and drying to obtain the substrate-free high-entropy nanoflower powder. The preparation method is simple, free of templates, environmentally friendly and suitable for large-scale production, and the lamellar thickness of the prepared substrate-free high-entropy nanoflower powder can reach the nanoscale. Meanwhile, experiments prove that the substrate-free high-entropy nanoflower powder catalyst prepared by adopting the preparation method has very high activity and stability on an anode oxygen evolution reaction of electrolyzed water.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology for the oxygen evolution reaction at the anode of water electrolysis, specifically to a method for preparing substrate-free high-entropy nanoflower powder as a highly efficient oxygen evolution catalyst and its application. Background Technology

[0002] In line with the call for a green and ecological environment, future energy development will focus on clean and environmentally friendly energy. Hydrogen energy is a pollution-free clean energy source, and its production methods are characterized by green and energy-saving features. Electrolysis of water is an effective method for hydrogen production, involving two reactions: the oxygen evolution reaction at the anode and the hydrogen evolution reaction at the cathode. The oxygen evolution reaction, due to its high energy barrier and slow reaction kinetics, limits the efficiency of hydrogen production from water electrolysis, requiring a highly efficient catalyst to promote the reaction. Commercially available catalysts are mostly precious metal catalysts; however, their abundance in the Earth's crust is low, and their cost is high. Therefore, there is a need to explore inexpensive, environmentally friendly, and highly efficient oxygen evolution catalysts.

[0003] Transition metal catalysts exhibit excellent catalytic activity under alkaline water electrolysis conditions, but they still suffer from limitations such as performance degradation under high current and stability reduction due to ion dissolution. The inherent multi-ion synergistic effect of high-entropy catalysts is expected to solve this problem. Existing technologies mainly focus on high-entropy alloys, high-entropy oxides, and high-entropy layered double hydroxide (LDH) catalysts. For example, Zhang et al. prepared NiFeCoCrW alloy catalysts using high-vacuum arc melting and electrochemical activation (Zhang T, Zhao HF, Chen ZJ, et al. High-entropy alloy enables multi-pathelectron synergism and lattice oxygen activation for enhanced oxygenevolution activity[J]. Nature Communications, 2025, 16(1):3327.). Talluri et al. prepared a high-entropy spinel oxide electrocatalyst (CoCrFeMnNi)3O4 using a soft chemical method (Talluri B, Yoo K, Kim J. High entropy spinel metal oxide (CoCrFeMnNi)3O4 nanoparticles as novel efficient electrocatalyst for methanol oxidation and oxygen evolution reactions[J]. Journal of Environmental Chemical Engineering, 2022, 10(1): 106932.). Liu et al. prepared high-entropy FeCoNiMg-LDH nanosheets on nickel foam using a hydrothermal method (Liu D, Yan X, Guo P, et al. Inert Mg incorporation to break the activity / stability relationship in high-entropy layered hydroxides for the electrocatalytic oxygen evolution reaction[J]. ACS Catalysis, 2023, 13(11): 7698-706.).However, these technologies require nickel foam or carbon paper as a substrate for growth, and the poor stability of the substrate and the non-uniformity of the growth material limit the practical application of the technology. On the other hand, the high-potential and strongly alkaline electrolysis conditions cause these catalysts to undergo severe structural reconstruction, and their stability still needs to be further improved.

[0004] In the aforementioned material reconstruction process, transition metal-based hydroxyl oxides are key intermediates in the oxygen evolution reaction (OER). If their structure can be stabilized by increasing entropy, directly synthesizing powdered high-entropy hydroxyl oxide catalysts will reduce application limitations and improve reproducibility. This strategy not only improves the structural stability of the catalyst but also increases the active surface area of ​​the electrocatalytic OER, exposing more active sites. Hydrothermal synthesis is a common method for synthesizing transition metal hydroxyl oxides; however, when multiple metal elements are involved, precise control of conditions such as temperature and pH during the hydrothermal reaction is necessary to ensure simultaneous and homogeneous precipitation of each element, resulting in high-entropy hydroxyl oxides with a single crystalline phase and excellent activity and stability. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for preparing substrate-free high-entropy nanoflower powder as a highly efficient oxygen evolution catalyst and its application. This invention prepares a high-entropy hydroxyl oxide nanoflower powder catalyst under substrate-free conditions, which exhibits high activity and good stability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing substrate-free high-entropy nanoflower powder for use as a highly efficient oxygen evolution catalyst includes the following steps:

[0008] A) Disperse the metal salt in a solvent to obtain a homogeneous solution 1;

[0009] The metal salts include nickel nitrate, and 4-7 of the following: manganese nitrate, cobalt nitrate, chromium nitrate, zinc chloride, copper chloride, ferric chloride, and aluminum chloride;

[0010] B) Add a reaction conditioner and a morphology modifier to the solution 1 and stir continuously to obtain suspension 2;

[0011] C) The suspension 2 is transferred to a hydrothermal reactor and calcined to obtain suspension 3;

[0012] D) The suspension 3 was washed, centrifuged, and dried to obtain substrate-free high-entropy nanoflower powder.

[0013] In the above technical solution, preferably, the molar ratio of nickel nitrate in the metal salt is 1 to 5, and the molar ratio of other metal salts is 1.

[0014] In the above technical solution, preferably, the reaction conditioner is urea, and the total molar ratio of urea to metal salt is 1:5 to 5:1.

[0015] In the above technical solution, preferably, the morphology modifier is ammonium fluoride, and the total molar ratio of ammonium fluoride to metal salt is 1:5 to 5:1.

[0016] In the above technical solution, preferably, in step A), the amount of solvent is 40-200 mL.

[0017] In the above technical solution, preferably, in step C), the hydrothermal reaction time is 6 to 15 hours and the reaction temperature is 100 to 180°C.

[0018] In the above technical solution, preferably, in step D), the centrifugation speed is 5000-8000 rpm and the time is 1-10 min; the washing reagent is one of anhydrous ethanol and water or a mixture of anhydrous ethanol and water, and the number of washings is 3-5; the drying temperature is 50-80℃ and the time is 12-24 h.

[0019] Application of substrate-free high-entropy nanoflower powder prepared by the preparation method of the present invention in the catalyst of oxygen evolution reaction at the anode of water electrolysis.

[0020] The beneficial effects of this invention are:

[0021] This invention provides a method for preparing substrate-free high-entropy nanoflower powder for use as a highly efficient oxygen evolution catalyst. The method achieves nanoscale nanosheet morphology by adjusting the proportions of metal salts and reaction conditions. Compared with existing oxygen evolution catalysts, this invention prepares a high-entropy powder catalyst with nanosheet morphology under substrate-free conditions. The amount of element introduction is controlled during the preparation of the high-entropy hydroxyl oxide powder, resulting in a composition ratio that balances catalytic activity and high active surface area. Experiments demonstrate that the catalyst prepared using this method exhibits excellent activity and stability. Furthermore, the method provided by this invention is simple to operate, template-free, environmentally friendly, suitable for large-scale production, and the sheet thickness can reach the nanometer scale. Simultaneously, experiments demonstrate that the high-entropy powder catalyst prepared using this invention exhibits high activity and stability for the oxygen evolution reaction at the anode of water electrolysis. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is an elemental mapping image under a transmission electron microscope of the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen prepared in Example 1 of this invention.

[0024] Figure 2 The image shows the morphology of the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen, prepared in Example 1 of this invention, under a scanning electron microscope.

[0025] Figure 3 The linear sweep voltammetric curve of the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen, prepared in Example 1 of this invention, in 1M potassium hydroxide solution;

[0026] Figure 4 The substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen, prepared in Example 1 of this invention, was used in a 1M potassium hydroxide solution at 10 mA / cm². -2 Timing potential curve under constant current density;

[0027] Figure 5 This is a scanning electron microscope image of the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen, prepared in Example 2 of this invention.

[0028] Figure 6 The linear sweep voltammetric curve of the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen, prepared in Example 2 of this invention, in 1M potassium hydroxide solution. Detailed Implementation

[0029] This invention provides a method for preparing substrate-free high-entropy nanoflower powder for use as a highly efficient oxygen evolution catalyst, comprising the following steps:

[0030] A) Disperse the metal salt in a solvent to obtain a homogeneous solution 1;

[0031] B) Add a reaction conditioner and a morphology modifier to the solution 1 and stir continuously to obtain suspension 2;

[0032] C) The suspension 2 is transferred to a hydrothermal reactor and calcined to obtain suspension 3;

[0033] D) After washing, centrifuging and separating the suspension 3, the suspension is dried to obtain substrate-free high-entropy nanoflower powder, which is a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0034] Preferably, the metal salt is selected from nickel nitrate, manganese nitrate, cobalt nitrate, chromium nitrate, zinc chloride, copper chloride, ferric chloride, and aluminum chloride, etc., and the metal salt is 5 to 8 of the above metal salts, of which nickel nitrate is mandatory and its molar ratio is 1 to 5, and the molar ratio of the other metal salts is 1.

[0035] Preferably, the reaction conditioner is selected from urea, and the total molar ratio of urea to metal salt is 1:5 to 5:1.

[0036] Preferably, the morphology modifier is ammonium fluoride, and the total molar ratio of ammonium fluoride to metal salt is 1:5 to 5:1.

[0037] Preferably, in step A), the amount of solvent is 40 to 200 mL.

[0038] Preferably, in step C), the hydrothermal reaction time is 6 to 15 hours and the reaction temperature is 100 to 180°C.

[0039] Preferably, in step D), the centrifugation speed is 5000-8000 rpm and the time is 1-10 min; the washing reagent is one of anhydrous ethanol and water or a mixture of anhydrous ethanol and water, and the number of washings is 3-5; the drying temperature is 50-80℃ and the time is 12-24 h.

[0040] This application also provides the application of the substrate-free high-entropy nanoflower powder prepared by the above preparation method in the catalyst of the oxygen evolution reaction at the anode of water electrolysis.

[0041] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0042] All raw materials used in the following examples are commercially available analytical grade chemicals and have not undergone any further processing.

[0043] Example 1

[0044] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0045] High-angle annular dark-field imaging and elemental mapping were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 1. The results are as follows: Figure 1 As shown, all elements in the obtained catalyst are uniformly dispersed in the catalyst without agglomeration.

[0046] Scanning electron microscopy analysis was performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 1. The results are as follows: Figure 2 As shown, the catalyst exhibits a uniform sheet morphology, and the sheet thickness is relatively thin, reaching the nanometer scale.

[0047] The substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 1 was subjected to linear sweep voltammetry in 1M potassium hydroxide solution. The results are as follows: Figure 3 As shown, the obtained catalyst exhibits excellent alkaline oxygen evolution activity, which is superior to substrate-free single-element Fe, Co, Ni hydroxy oxide powder catalysts and high-entropy catalysts based on nickel foam substrates prepared under the same conditions.

[0048] The substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 1 was tested in a 1M potassium hydroxide solution at a constant 10 mA cm⁻¹. -2 Chronopotential testing was performed at current density, and the results are as follows: Figure 4 As shown, the obtained catalyst exhibits excellent stability.

[0049] Example 2

[0050] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and aluminum chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. Under stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 1:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0051] Scanning electron microscopy analysis was performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 2. The results are as follows: Figure 5 As shown, the catalyst exhibits a uniform sheet morphology, and the sheet thickness is relatively thin, reaching the nanometer scale.

[0052] The substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 2 was subjected to linear sweep voltammetry in 1M potassium hydroxide solution, and the results are as follows: Figure 6 As shown, the obtained catalyst exhibits excellent alkaline oxygen evolution activity.

[0053] Example 3

[0054] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. Under stirring, 6 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 1:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0055] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 3. The results were similar to those in Example 1.

[0056] Example 4

[0057] At room temperature, 2 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 10 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with water as the solvent, and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0058] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 4. The results were similar to those in Example 1.

[0059] Example 5

[0060] At room temperature, 3 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 150 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with ethanol as solvent, and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0061] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 5. The results were similar to those in Example 1.

[0062] Example 6

[0063] At room temperature, 2.8 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 6 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0064] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 6. The results were similar to those in Example 1.

[0065] Example 7

[0066] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and aluminum chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 8000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis to produce hydrogen.

[0067] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 7. The results were similar to those in Example 1.

[0068] Example 8

[0069] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 2.5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 3 min, then washed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0070] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 8. The results were similar to those in Example 1.

[0071] Example 9

[0072] At room temperature, 2.8 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and ferric chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 7.5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then washed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 24 h to obtain a substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0073] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 9. The results were similar to those in Example 1.

[0074] Example 10

[0075] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and aluminum chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 120 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then rinsed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a 50 °C drying oven for 12 h to obtain a substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0076] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 10. The results were similar to those in Example 1.

[0077] Example 11

[0078] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, and copper chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 32.5 mmol of ammonium fluoride and 6.5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then rinsed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a 60 °C drying oven for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0079] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 11. The results were similar to those in Example 1.

[0080] Example 12

[0081] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, zinc chloride, and copper chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then rinsed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0082] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 12. The results were similar to those in Example 1.

[0083] Example 13

[0084] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, ferric chloride, zinc chloride, and aluminum chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 6.5 mmol of ammonium fluoride and 32.5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then rinsed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0085] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 13. The results were similar to those in Example 1.

[0086] Example 14

[0087] At room temperature, 2.5 mmol of nickel nitrate and 1 mmol each of cobalt nitrate, chromium nitrate, manganese nitrate, zinc chloride, copper chloride, ferric chloride, and aluminum chloride were added to 40 mL of ultrapure water and stirred thoroughly to obtain a homogeneous solution 1. While stirring, 12.5 mmol of ammonium fluoride and 5 mmol of urea were added to solution 1 and reacted for 1 h to obtain suspension 2. Suspension 2 was transferred to a hydrothermal reactor and reacted at 180 °C for 12 h to obtain suspension 3. After suspension 3 was cooled to room temperature, it was centrifuged at 6000 rpm for 5 min, then rinsed three times with a solvent of water and ethanol in a 2:1 (volume ratio), and finally dried in a drying oven at 60 °C for 12 h to obtain a substrate-free nanosheet structured high-entropy hydroxyl oxide powder anode catalyst for water electrolysis hydrogen production.

[0088] Scanning electron microscopy and linear scanning voltammetry were performed on the substrate-free nanosheet structure high-entropy hydroxyl oxide powder anode catalyst for water electrolysis in Example 14. The results were similar to those in Example 1.

[0089] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0090] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing substrate-free high-entropy nanoflower powder for use as a highly efficient oxygen evolution catalyst, characterized in that, Includes the following steps: A) Disperse the metal salt in a solvent to obtain a homogeneous solution 1; The metal salts include nickel nitrate, and 4-7 of the following: manganese nitrate, cobalt nitrate, chromium nitrate, zinc chloride, copper chloride, ferric chloride, and aluminum chloride; B) Add a reaction conditioner and a morphology modifier to the solution 1 and stir continuously to obtain suspension 2; C) The suspension 2 is transferred to a hydrothermal reactor and calcined to obtain suspension 3; D) The suspension 3 was washed, centrifuged, and dried to obtain substrate-free high-entropy nanoflower powder.

2. The preparation method according to claim 1, characterized in that, The molar ratio of nickel nitrate in the metal salt is 1 to 5, and the molar ratio of other metal salts is 1.

3. The preparation method according to claim 1, characterized in that, The reaction conditioner is urea, and the total molar ratio of urea to metal salt is 1:5 to 5:

1.

4. The preparation method according to claim 1, characterized in that, The morphology modifier is ammonium fluoride, and the total molar ratio of ammonium fluoride to metal salt is 1:5 to 5:

1.

5. The preparation method according to claim 1, characterized in that, In step A), the amount of solvent is 40 to 200 mL.

6. The preparation method according to claim 1, characterized in that, In step C), the hydrothermal reaction takes 6 to 15 hours and the reaction temperature is 100 to 180°C.

7. The preparation method according to claim 1, characterized in that, In step D), the centrifugation speed is 5000-8000 rpm and the time is 1-10 min; the washing reagent is one of anhydrous ethanol and water or a mixture of anhydrous ethanol and water, and the washing is performed 3-5 times; the drying temperature is 50-80℃ and the time is 12-24 h.

8. The application of substrate-free high-entropy nanoflower powder prepared by the preparation method according to any one of claims 1-7 in the catalyst of oxygen evolution reaction at the anode of water electrolysis.

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